August 1982 

Design Approaches for 

Solar Industrial Process 

Heat Systems 

Nontracking and Line-Focus 

Collector Technologies 

Charles F. Kutscher 

Roger L. Davenport 

Douglarr A. Dougherty 

Randy C. Gee 

P. Michael Masterson 

E. Kenneth May 
Printed in the United States of America 

Available from: 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

Price: 

Microfiche $3.00 

Printed Copy $14.50 

NOTICE 

This report was prepared as an account of work sponsored by the United States 

Government. Neither the United States nor the United States Department of Energy, 

nor any of their employees, nor any of their contractors, subcontractors, or their 

employees, makes any warranty, express or implied, or assumes any legal liability 

or responsibility for the accuracy, completeness or usefulness of any information, 

apparatus, product or process disclosed, or represents that its use would not 

infringe privately owned rights. 
SERl/lR-253-1356 

UC Category: 62 

Design Approaches for Solar 

Industrial Process Heat 

Systems 

Nontracking and Line-Focus 

Collector Technologies 

Charles F. Kutscher 

Roger L. Davenport 

Douglas A. Dougherty 

Randy C. Gee 

P. Michael Masterson 

E. Kenneth May 

August 1982 

Prepared Under Task No. 1007.99 

WPA NO. 279-81 

. Solar Energy Research Institute 

A Division of Midwest Research Institute 

1617 Cole Boulevard 

Golden, Colorado 80401 

Prepared for the 

U.S. Department of Energy 

Contract No. EG-77-C-01-4042 
sin TR-1356 

The authors would like to thank everyone who took the time to review and 

comment on the draft of this document. Reviewers include Gerald Nix, Robert 

Copeland, L. M. Murphy, Larry Flowers, Shirley Stadjuhar, and Allan 

Lewandowski of SERI:; William Marlat t and Robert Baisley of Rockwell 

International; Kenneth Brown of Science Applications, Inc.; Jefferson 

Shingleton of Mueller Associates; Walter Carey of Nestle; Ed Carnegie of 

California Polytechnic State Univ.; Tetsw Noguchi of the Solar Research 

Laboratory, Nagoya, Japan ; Danny Def f enbaugh of Southwest Research Institute ; 

David Kaplan of The Lummus Company; Michael Rast of Pacific Sun, Inc.; David 

Allen of Foster Wheeler; William Engel of Owens-Illinois; Nick Kaplan and 

Harold Wilkening of AAI Corp.; Karl Wally of Sandia National Laboratories, 

Livermore; Harry Gaul (formerly of SERI); and Ari Rabl of Princeton 

University. 

Special thanks go to John Wright of SERI for his considerable contribution to 

the section on controls, to James Leach of North Carolina State University for 

writing the unfired boiler subroutine of SOLIPE in conjunction with a summer 

research project at SERI, and to Rob Partington of SERI for his help in making 

the numerous SOLIPH computer runs. The authors are also very grateful to 

David Rearney for his extensive review of the document, in both early and 

final draft stages, and for supporting this undertaking at its outset while he 

was manager of the Solar Thermal, Ocean, and Wind Division at SERI. Finally, 

the authors are deeply indebted to William her and Jerry Greyerbiehl of the 

U.S. Department of Energy, who secured the funding for this work. 
Since 1976, the U.S. government has funded over a dozen projects that apply 

solar thermal energy to industrial processes. We can draw two major 

conclusions from experiences gained in designing, constructing, and operating 

these projects: design and installation errors need to be avoided, and costs 

must be reduced. Thfs design handbook was prepared with both points in 

mind. Designers are given a design procedure that has been formulated to help 

them avoid problems that have occurred in past systems. At the same time, the 

design tools contained in the text are intended to shorten the time required 

for conceptual and preliminary design, which should, in turn, reduce total 

design costs. (In the past, design costs have been as much as 45% of 

construction costs. ) In addition, emphasis on cost-effective optimization of 

sys terns and components is intended to lower construction, operating, and 

maintenance costs. 

Thfs handbook is not without precedent. In March 1981, the Solar Energy 

Research Institute published a forerunner document entitled "Design 

Considerations for. Solar Industrial Process Heat Systems-" That report, which 

drew upon the experiences of a number of IPH system designers and Department 

of Energy technical advisors, contained qualitative lists of items that should 

be considered in the design of a solar IPEi system. This document is intended 

to provide the quantitative information needed to complete a step-by-step 

design. 

The contents of this handbook have been arranged td guide the user through a 

system design. The first part, "Objectives and Fundamentals, " provides an 

introduction to the uses of solar thermal energy in industry. It is intended 

for those who do not have experience in the solar IPH field, but it could also 

serve as a useful review. The second part, "Conceptual Design," describes how 

to choose the proper application and system configuration and how to estimate 

the amount of energy the solar system can be expected to supply. The 

conceptual design should supply enough information to allow the user to make 

an informed decision about whether to proceed with the project, and it will 

also provide a firm foundation for further design work. The third part, 

"Preliminary Design," describes how to select and optimize system 

components. This section also explains how to determine the delivered energy 

more accurately. A chapter on installation and start-up is included, because 

they have caused problems in the past. Items of special interest are covered 

in the appendices, and a glossary is provided for those new to the solar 

energy field. Although SI units are used throughout, a detailed conversion 

table is provided in Appendix I for those who are more comfortable with 

English units. 

The final, detailed design is left to the reader. Actual selection of 

hardware by brand name and model number, mechanical and electrical drawings, 

construction specifications, etc., are all highly specific to the system, and 

require the reader to draw upon his professional experience. 

The reader will note that, although computer techniques are discussed in this 

report, the emphasis is on simplified design tools. These were generated by 

thousands of runs of an hour-by-hour computer program (SOLIPB) specifically 
written to model solar industrial process heat systems. These design tools 

are simple to use and require no computer programming knowledge. They are 

intended to supply values within a few percentage points of the detailed 

computer program and apply to both large and small installations. Considering 

current uncertainties about degradation of pipe insulation and collectors and 

the large variations in annual solar radiation at any given site, using simple 

design tools is a pragmatic approach. It frees the designer to concentrate on 

the hardware and installation problems which in the past have lowered energy 

collection values well below those predicted by sophisticated but idealistic 

computer models. 

Because the field of solar thermal energy as it is applied in industry is 

still young, design questions cannot all be answered in this handbook. We 

hope, however, that it contains the best information currently available. The 

types of industrial processes and corresponding solar system configuration 

alternatives are manifold. Thus, system designers will find a considerable 

number of opportunities to deviate from the generic design procedures 

contained here, and they should feel free to do so. Readers are encouraged to 

contact the authors with any ideas or experiences they have had that could 

augment or improve this handbook. 

Charles F. Rutschee Task Leader 

Thermal Systems and Engineering 

Branch 

Approved for 

SOLAR ENERGY RESEARCH INSTITUTE 

p4. (1RX ohn P. Thornton, Chief 

Thermal Systems and Engineering Branch 

Barry Bfler , -Manager 

solaflermal and katerials Research 

Division 
2 area (m ) 

A, collector aperture area 

Ag ground area covered by collector array 

% heat exchanger surface area 

factor in Eq. 7-31 

incident-angle modifier coefficient 

constant-pressure specific heat (J kg-' JC-l) 

diameter (m) 

Di insulation diameter 

Dp pipe diameter 

specific diameter of a pump impeller 

solar fraction (portion of total load supplied by solar system) 

friction factor 

collector heat removal efficiency factor 

Fg based on collector inlet temperature 

Fm based on mean collector temperature 

F, based on collector outlet temperature 

dewinter heat exchanger factor 

heat transfer film coefficient (W m-* K-I) 

h, convective heat transfer coefficient 

hi heat transfer coefficient on inside of a pipe 

ho heat transfer coefficient on outside of a pipe 

h, radiative heat transfer coefficient 

latent heat of evaporation (J kg-') 

head of a pump (Pa) 

irradiance (W m2) 

I, irradiance available to a collector 

Ib beam irradiance 

Id diffuse irradiance 

Ig global irradiance 

Ih global irradiance on a horizontal surface 
~CLATURE (Continued) 

- 

Ib long-term average beam irradiance during daylight hours 

- 

Ig long-term average global irradiance during daylight 

hours 

thermal conductivity (W m-' K-l) 

ka thermal conductivity of air 

kf thermal conductivity of a fluid 

ki thermal conductivity of insulation 

kp thermal conductivity of a pipe wall 

ko thermal conductivity on shell side of a heat exchanger 

Kh clearness index 

%T incident-angle modifier (flat plate) 

Kp a= incident-angle modifier correction factor (evacuated tube and 

, parabolic trough) 

- 

L length (m) 

Lend spillage end loss factor for prabolic troughs 

mc collector mass flow rate per unit collector area (kg s-I m-') 

M total mass (kg) 

k total mass flow rate (kg s-l) 

hc collector mass flow rate '. 

Mg load mass flow rate 

hs mass flow rate through storage 

N 

Ns 

NPSH 

number of rows of tubes across the diameter of the shell of a 

heat exchanger 

rotational speed (rev min-' ) 

specific speed 

Net Positive Suction Head (Pa) 

NPSHA NPSH available 

NPSHR NPSH required 

pressure (Pa, absolute unless otherwise noted) 

vapor pressure (Pa, absolute) 

pumping power (W) 

energy per unit collector area (J m2) (for subscripts, see Q) 
HOHENCU4TURE (Continued) 

energy rate per unit collector area (W Q~) 

energ collection rate for a solar system with infinite storage 

(W *-TI 

energy (J) 

Q, energy collected 

Qd energy delivered to the process from the solar system 

Qg energy lost 

Qr energy required by the process 

Q, energy stored 

energy rate (W) 

volumetric flow rate (m3 s-I) 

thermal resistance per unit thickness (m K W-I) 

2 thermal resistance (m K W-l) 

Rf thermal resistance due to fouling 

Ri thermal resistance on inside of pipe or tube 

Ro thermal resistance on outside of pipe or tube 

% total thermal resistance 

thermal resistance at wall of pipe or tube 

spacing (4 

'baf baffle spacing in heat exchanger 

Smin minimum tube spacing in heat exchanger 

time (s) 

thickness of insulation (m) 

temperature (K or OC) 

Ta .ambient temperature 

T, collector temperature 

Tf fluid temperature 

Ti insulation temperature 

Te load temperature 

Tp plate temperature in f lat-plate collector 

T, effective radiative temperature of surroundings (K only) 
NOMENCLBTDBE (Continued) 

Ts storage temperature 

Tg,r load return temperature ("C) 

U thermal conductance (W m-2 K-l) 

u~ overall collector heat loss coefficient (W m-2 K-' ) 

V speed (m s-l) 

W heat capacity flow rate (W K-l) 

Wc collector heat capacity flow rate 

Ws storage loop heat capacity flow rate 

Y parameter in Eq. 7-70 

Secondary Subscripts 

daytime 

fluid 

inlet, inside 

mean 

outlet, outside 

start-up 

Nondimensional Numbers 

Nu Nusselt Number (= h D K-l) 

Pr Prandtl Number (= u cp K-I) 

Re Reynolds Number (= p V D u-l) 

Greek Symbols 

a altitude of sun (0 to +90°) 

as absorptance for solar radiation 

B surface tilt (0 to +90°; toward equator is positive) 

Y azimuth of a surface (0 to 360"; clockwise from North) 

A declination (0 to '23.45O; North is positive) 

E heat exchanger effectiveness 
~CLA!l!URE (Concluded) 

infrared emittance of a surface 

efficiency 

nC collector efficiency 

n sys tern thermal efficiency 

no collector optical efficiency 

incident angle (0 to +90°; measured from perpendicular) 

zenith angle (0 to +90°) 

dynamic viscosity (Pa s) 

2 -1 kinematic viscosity (: v/p ) (m s ) 

density (kg m3) 

reflectance for solar radiation 

Stefan-Boltzmann constant (5.67 x lo-* W 6' K-~) 

transmittance-absorptance product of a collector 

latitude (0 to +90°; North is positive) 

hour angle of sun (0 to 360'; noon is 0°, afternoon is positive) 
LIST OF ECONWIC TKRns 

CRF 

d 

DEP 

cumulative present worth of depreciation tax credits per dollar 

invested 

B~~ with declining balance depreciation 

B~~ with straight-line depreciation 

BSOn with sum-of-years-digits depreciation 

collector cost per unit area ($ m-2) 

piping insulation cost per unit length of pipe ($ m-l) 

piping insulation jacketing cost per unit length of pipe ($ m-l) 

cost of labor to install pipe insulation, per unit length of 

pipe ($ m-5 

annual base cost of maintenance of pipe insulation, per unit 

length of pipe ($ m-' yr-l) 

total annual cost of pipe insulation per unit length ($ m-' 

yr-l) 

heat exchanger cost per unit area ($ m-2) 

storage tank insulation cost per unit area ($ m2) 

storage tank insulation cost per unit volume ($ m-3) 

total collector cost ($) 

total insulation cost ($) 

cost function defined by Eq. 7-10 

levelized (annualized) required revenue in current dollars to 

purchase solar energy 

levelized required revenue in constant zero-year dollars to 

purchase solar energy 

total system cost of heat exchangers and collectors (= A, cc 

+ 4, ex) ($1 

cost to minimize, defined in Eq. 7-9 

capital recovery factor R [= 1 - (1 + R)-~ I

annual discount rate 

present value of depreciation charges as a fraction of initial 

investment 
LIST OF ECOBOMIC TERMS (Continued) 

DP depreciation period 

Ec economic parameter for levelizing collector costs 

E~ economic parameter for levelizing storage tank insulation costs 

Es annual solar energy provided by solar system at the point of use 

E1'E2 economic coefficients for piping insulation costs 

f fraction of total initial system investment financed by loan 

F annual usage factor 0 < F ( 1 for an insulated component 

assumed general inflation rate over the life of a system 

assumed overall escalation rate (includes general inflation) of 

conventional fuel used in backup system 

fuel inflation rate in year t 

annual insurance cost as a fraction of the initial system cost 

annual interest rate on mortgage 

total initial solar system investment in zero-year dollars 

n 

levelizing factor [= CRF(R,N) (1 + gt) !/(I + R)~] , t =l 

loan period (always to be taken as equal to or less than system 

life) 

the "M-factor" = C,/I; levelized required revenue per total 

investment dollar 

major component replacement cost in year t = tc as a fraction of 

total initial investment; this cost is expressed in terms of 

zero-year dollars 

system life; also the period over which system costs are 

measured in a lif e-cycle cost calculation 

levelized cost in current dollars fox operation, maintenance, 

property tax, and insurance, as a fraction of total initial 

investment 

average cost of above items, expressed in zero-year dollars, as 

a fraction of total initial investment 

annual property tax rate 

economic factor used in evaluating piping insulation 
LIST OF ZoJNOMIC TKRMS (Concluded) 

Pf levelized price of fuel ($/MBtu, $/kwh, $/GJ) 

Pfo price of fuel in zero-year 

Ps levelizecl price of solar energy = Cs/Es ($/MB~u, $/kwh, $/GJ) 

R after-tax, market rate of return on investment 

R* internal, after-tax, market rate of return on solar investment 

% compound, after-tax, market interest rate at which solar 

investment dollars grow, evaluated at the end of solar system 

life 

r market interest rate on loan 

r ' real interest rate on loan 

S net salvage value of solar system, expressed in zero-year 

dollars, as a fraction af total initial investment 

SOYD sum-of-years digits method of accelerated depreciation 

year of system operation under consideration; system constructed 

in year zero and begins operation on first day of year one 

tc year in which a major component replacement is made 

TC total investment tax credit rate 

UA* annualized heat loss coefficient per unit length for piping heat 

loss (= 3.154 x 10' x A) (GJ m-' yr-l K-~) 

Greek Symbols 

fraction of system first cost that was paid as a downpayment 

(= 1 - f) 

investment tax credit 

declining balance multiplier 

solar effectiveness factor (= fuel energy saved by a solar 

energy system divided by the solar energy delivered) 

T marginal composite income tax rate [= rs + (1 - T,) T*] 

Tf marginal federal income tax rate 

=s marginal state income tax rate 
. 

Page 

PART I: Objectives and Fundamentals 

1.0 Objectives and Design Methodology ................................... 1 

1.1 Introduction ................................................... 1 

1.2 Design &thodology ............................................. 2 

1.3 Additional Sources of Information .............................. 5 

2.0 Solar Energy in Industry: An Overview .............................. 7 

2.1 Introduction ................................................... 7 

2.2 Solar Applications in IPH ...................................... 12 

2.2.1 Hot Water ............................................... 12 

2.2.2 Drying and &hydration .................................. 13 

2.2.3 Stem ................................................... 15 

2.3 Industrial Process Heat Field Tests ............................ 16 

2.4 References ..................................................... 22 

PART 11: Conceptual Design 

3.0 Solar IPH Suitability Analysis ..................................... 25 

3.1 Environmental Factors ........................................ 25 

3.2 Process Factors ................................................ 28 

3.3 Economic factor^........................^.....^..^.... 32 

3.4 Company Factors ............................................ 33 

3 -5 Examples of Favorable Solar Thermal Applications .. .. ........... 33 

3.6 References ..................................................... 34 

4.0 IPH System Configuration ............................................ 35 

4.1 Hot Air Systems ................................................ 35 

4.2 Hot Water Systems 36 

4.3 Steam Systems ................................................ . 38 

4.3.1 Flash Steam Systems ..................................... 40 

4.3.2 Unfired-Boiler Systems .................................. 42 

4.3.3 Direct Steam Generation .............................. 43 

4.4 Storage Configurations ......................................... 43 

4.4.1 Hot Water Storage ....................................... 43 

4.4.2 Storage for Steam Systems ............................... 47 

4.5 ~rocess/Solar System Interface ................................. 50 

4.6 References ..................................................... 51 
TABLE OF COIUTENTS (Continued) 

. 

Page 

5.0 Solar Collectors .................................................... 53 

5.1 Types of Co1lector.s ............................................ 5.1.1 Flat-Plate Collectors ................................... 5.1.1.1 Components ..................................... 5.1.1.2 Improvements ................................... 5.1.2 Evacuated-Tube Collectors ............................... 5.1.2.1 Components ..................................... 5.1.2.2 Improvements ................................... 5.1.3 Parabolic Trough Collectors ............................. 5.1.3.1 Components ..................................... 5.1.3.2 Improvements ................................... 5.1.4 Other Types of Collectors ............................... 5.1.4.1 Solar Ponds .................................... 5.1.4.2 Compound Parabolic Concentrators ............... 5.1.4.3 Presnel Lens Collectors ........................ 5.1.4.4 Multiple-Reflector Collectors .................. 5.1.4.5 Parabolic Dish Collectors ...................... 5.1.4.6 Central Receivers .............................. 5.2 Instantaneous Performance of Collectors ........................ 5.2.1 Analysis ................................................. 5.2.2 Testing ................................................. 5.3 Collector Selection Procedure .................................. 5.3.1 A Preliminary Comparison of Collector Performance ....... 5.3.2 Other Considerations in Selecting an Appropriate 

Collector ............................................. 5.4 References ..................................................... PART 111: Preliminary Design 

6.0 Annual Performance of a Solar Energy System ......................... 83 

6.1 Annual Energy Collection for Several IW 

System Configurations ........................................ 83 

6.1.1 Hot Air and Hot Water Systems ........................... 86 

6.1.1.1 No-Storage IPH System .......................... 89 

6.1.1.2 Mixed-Tank. Recirculation IPH System ........... 93 

6.1.1.3 Variable-Volume Storage System ................. 107 

6.1.2 Steam Systems ........................................... 111 

6.1.2.1 Unfired-Boiler Steam System .................... 111 

6.1.2.2 Flash Steam System ............................. 113 

6.2 Incident-Angle Effects ........................................ 114 

6.2.1 Incident-Angle Modifiers ................................ 115 

6.2.2 End Losses .............................................. 118 

6.3 Row-to-Row Shading Losses .................................. 119 

6.4 Annual Thermal Losses of Collector Field Piping and Storage .... 122 

6.4.1 Steady-State Losses .................................... 126 

6.4.2 Overnight Losses ....................................... 127 

6.4.3 Freeze-Protection Heat Losses ........................... 129 
TAB= OF CONTENTS (Continued) 

Page 

6.5 Utilization and Availability ................................... 132 

6.6 Step-by-step Procedure ......................................... 135 

6.7 References ..................................................... 138 

7.0 The Energy Transport System ....................................... 139 

7.1 Piping and Insulation .......................................... 139 

7.1.1 Collector Field Piping Configurations ................... 139 

7.1.2 Optimm Array Flow Rate and Collector Configuration ..... 141 

7.1.3 Pipes and Sizing technique^...............^..^...^...... 143 

7.1.4 Insulation and Heat Losses .............................. 144 

7.2 Heat Transfer Fluids ............................................ 164 

7.2.1 Types of Fluids ......................................... 165 

7.2.1.1 Water .......................................... 165 

7.2.1.2 Water-Glycol Mixtures .......................... 165 

7.2.1.3 Aliphatic Hydrocarbons ......................... 165 

7.2.1.4 Aromatic hydrocarbon^..............^........... 165 

7.2.1.5 silicone^.......................^.............. 166 

7.2.2 Temperature-Dependent Thermal Properties ................ 166 

7.2.3 Other Thermal Properties ............................... 170 

7.3 Pumps.. .......................... 170 

7.3.1 Sizing a Single-Speed Centrifugal Pump O................. 171 

7.3.2 Multispeed Centrifugal Pumps ............................ 175 

7.3.3 Positive Displacement Pumps ............................. 176 

7.4 Valves ........................................................ 179 

7.4.1 Characteristics of Solar Systems ~...~~.~~~~~~~

179 

7.4.2 Types of Valves ......................................... 180 

7.4.3 Guidelines for Selecting Valves ......................... 181 

7.5 Heat Exchangers ................................................ 182 

7.5.1 Heat Transfer Relations ................................. 182 

7.5.2 Overall Heat Transfer Coefficient ....................... 184 

7.5.3 Heat Exchanger Factor for Solar System Performance ...... 187 

7.5.4 Economical Reat Exchanger Area .......................... 189 

7.5 . 5 Practical Considerations in Selecting a Heat 

Exchanger ............................................ 190 

7.5.6 Plate Heat Exchangers ................................... 192 

7.6 Storage ........................................................ 193 

7.6.1 Storage Media ........................................... 194 

7.6.1.1 Sensible Heat Storage .......................... 194 

7.6.1.2 Latent Heat Storage ............................ 195 

7.6.2 Storage Vessels ........................................ 197 

7.6.3 Storage Tank Insulation ................................ 199 

7.6.4 Storage Location ........................................ 202 

7.6.4.1 Interior Storage ............................... 202 

7.6.4.2 Exterior Storage ............................... 203 

7.7 References, ..................................................... 203 

8.0 Controls and Instrumentation ........................................ 207 

xvii 
TABLE OF aONTBNTS (Continued) 

Page 

8.1 Fundamentals of Controls ................................. 207 

8.1.1 Controllers ............................................. 207 

8.1.2 Conuuon Control Loops ................................... 208 

8.1.3 Measurement Dynamics .................................... 209 

8.1.4 Noise ................................................... 210 

8.1.5 Valves .................................................. 210 

8.1.6 Miscellaneous Considerations .......................... 212 

8.1.7 Multivariable Control Loops ............................. 212 

8.1.7.1 Cascade ....................................... 212 

8.1.7.2 Feed-Forward ................................... 212 

8.1.7.3 Split-Range Control ............................ 213 

8.1.7.4 Overrides ..................................... 213 

8.1.8 Computers ............................................... 213 

8.2 Control Design ................................................. 214 

8.2.1 Normal Operating Modes .................................. 214 

8.2.2 Start-Up/Shutdown ....................................... 227 

8.2.3 Freezinglstagnation ................................... 229 

8.2.4 Emergency Conditions ................................ 229 

8.2.5 Operator TrainingIDisplay ............................. 230 

8.2.6 Control System Checkout ................................. 230 

8.3 Instrumentation and Data Acquisition .......................... 231 

8.3.1 Flow Measurement .................................. 231 

8.3.2 Level Measurement .................................. 233 

8.3.3 Pressure Measurement ............................. 233 

8.3.4 Temperature Measurement ................................ 233 

8.3.5 Irradiation Measurement ............................. . 235 

8.3.6 Converters .............................................. 235 

8.3.7 Data Acquisition ........................................ 236 

8.4 References ..................................................... 237 

9.0 Installation and Start-up ........................................... 239 

9.1 Installation and Checkout ................................... 239 

9.1.1 Scheduling .............................................. 239 

9.1.2 Installing the Collectors .............................. 239 

9.1.2.1 1nstalling.Flat-Plate Collectors ............... 239 

9.1.2.2 Installing Evacuated-Tube Collectors ........... 240 

9.1.2.3 Installing Line-Focus Collectors ............... 241 

9.1.2.4 Piping. Fittings. and Insulation ............... 242 

9.1.3 Installing Heat Exchangers ............................. 246 

9.1.4 Installing Pumps ...................................... 246 

9.1.5 Installing Pressure Vessels and Storage Tanks ........... 247 

9.1.6 Installing Controls. Electrical Lines. and 

Instrumentation .................................... 248 

9.1.7 Personnel and Environmental Safety Precautions .......... 248 

9.2 Start-up ....................................................... 249 

9.2.1 Line Flushing ........................................... 249 

9.2.2 Pressure Testing ........................................ 250 

9.2.3 Fluid Loading ........................................... 251 

9.2.4 Commissioning of Solar System ........................... 252 

9.2.5 Perforuance Testing .................................... 252 

xviii 
TaB'ILE OP COH!DZMTS (Continued) 

Page 

9.3 Summary ......................................................... 253 

9.4 References .................................................... 253 

10.0 Solar System Economics ............................................. 257 

10.1 Methods of System Cost Estimation ............................. 257 

- 10.1.1 Historical IPH System and Subsystem Costs ............. 257 

10.1.1.1 Historical System Costs ..................... 258 

10.1.1.2 Historical Subsystem Costs .................. 260 

10.1.1.3 Estimating Construction Costs Using the 

Mueller Data .............................. 261 

10.1.2 Modular Cost Estimating ............................... 269 

10.2 Life-Cycle Cost Analysis ...................................... 270 

10.3 Methods of Financing Solar Systems ............................ 281 

10.3.1 Conventional Financing ................................ 281 

10.3.2 Conventional Lease Arrangements ....................... 281 

10.3.3 Solar Management Company/Limited Partnership .......... 281 

10.4 References .................................................... 283 

11.0 Safety and Environmental issue^.........................^.......... 285 

11.1 Safety Concerns in IPH Systems ................................ 285 

11.1.1 Fire Safety ........................................... 285 

11.1.1.1 Mterials ................................... 285 

11.1.1.2 Equipment and Procedures .................... 286 

11.1.2 Physical Hazards ................................... 288 

11.1.3 Fluid Toxicity Considerations ......................... 289 

11.1.4 Protection from Overtemperature and Overpressure ...... 289 

11.1.5 Product Contamination ................................. 290 

11.1.6 Noise ................................................. 291 

11.1.7 Applicable Regulations and Agencies ................... 291 

11.2 Environmental Aspects of Solar IPH Systems .................... 292 

11.2.1 Environmental Impacts of Solar IPH Systems ............ 292 

11.2.2 National Environmental Protection Laws and 

Organizations ....................................... 293 

11.2.2.1 Air-Pollution Control ....................... 293 

11.2.2.2 Water-Pollution Control ..................... 293 

11.2.2.3 Waste Disposal .............................. 295 

11.2.2.4 Noise ....................................... 295 

11.2.2.5 Land Use .................................... 295 

11.2.3 State Environmental Regulations ....................... 295 

11.3 Bibliography .................................................. 295 

11.4 References .................................................... 296 

Appendix A Effects of Solar Systems on the Efficiency of Hot Water 

Boilers .................................................... 305 

Appendix B Properties of Heat-Transfer Fluids ........................... 317 

Appendix C The SOLIPH Computer Program .................................. 351 

Appendix D Derivation of Annual-Performance Empirical Correlations ...... 371 

xix 
TR- 1 3 56 s=?I 

TABLJl OF COLPTENTS (Concluded) 

Page 

Appendix E Derivation of Annual Performance Modifiers ................... 383 

Appendix F Ambient Temperature Data for 72 U.S. Cities .................. 393 

Appendix G Sources of Information ...................................... 395 

Appendix H Glossary ..................................................... 397 

Appendix I Conversion Tables ............................................ 407 

Index .................................................................... 419 
TR-1356 sin +I 

LIST OF FIGURES 

Page 

Solar IW System Design Process ..................................... 3 

U.S. Energy Demand by Sector ........................................ 7 

Solar Attractiveness Index for Parabolic Trough Collectors .......... 9 

Energy Use by bjor Industrial Groups ............................... 11 

Distribution of IPH Requirements by Temperature ..................... 11 

Operating Temperatures for Various Types of Collectors .............. 12 

Pork Building Products Solar Hot Water System .. .............. ....... 13 

Lamanuzzi and Pantaleo Foods Solar Air System ....................... 14 

2-8 LaCour Lumber Kiln Solar Rot-Water-to-Air System .................... 14 

2-9 Solar Steam Production Using an Unfired Boiler ...................... 15 

2-10 Solar Steam Production Using a Flash Tank ........................... 16 

3-1 Average Daily Global Solar Radiation on a Horizontal Surface 

2 (kJ/m ) ........................................................... 26 

'2 3-2 Average Daily Direct Normal Solar Radiation (kJ/m ) ................. 27 

3-3 Normal Daily Average Temperature (OF) in January ..................... 29 

3-4 Normal Daily Average Temperature (OF) in July ....................... 30 

3-5 Mean Annual Number of Freezing Days id the United States ............ 31 

3-6 Real Costs of Conventional Fuels .................................... 33 

4-1 Direct Hot Air Solar System ......................................... 35 

4-2 Water-to-Air Solar System .......................................... 36 

4-3 A Direct Solar Hot Water System .......................+............. 37 

4-4 An Indirect Solar Hot Water System .................................. 37 

4-5 Direct Hot Water System with Drain-Out Freeze Protection ........... 39 

4-6 Indirect Hot Water System with Drain-Back (to Tank) Freeze 

Protectionand Nonpressurized Tank ............................... 39 

xxi 
LIST FIGURES (Continued) . 

Page 

4-7 Indirect Hot Water System with Drain-Back to Holding Tank and 

Pressurized Storage Tank .......................................... 40 

4-8 Flash-Steam Solar System ............................................ 41 

4-9 Unfired-Boiler Steam-Generating System .............................. 42 

4-10 Four-Pipe Storage Configuration ..................................... 43 

4-11 Two-Pipe Storage Configuration ................................... 44 

4-12 Multiple-Tank Storage Configuration for Achieving Stratification .... 44 

4-13 Variable-Volume Storage Configuration ............................... 45 

4-14 Thermocline or Mixed Tank Configuration with Unfired-Boiler 

Steam System .................................................... 48 

4-15 Variable-Volume Storage Tank Configuration for Unfired Boiler Steam 

System ............................................................ 48 

4-16 Annual Energy Delivery as a Function of Collector Area. Storage 

Type. and Size for an Unfired-Boiler System ....................... 49 

5-1 Cross Section of Typical Flat-Plate Collector ....................... 54 

5-2 Concentric Glass Evacuated-Tube Collector ........................... 57 

5-3 Evacuated-Tube Collector Utilizing Metal Flow Passage ............... 58 

5-4 Typical Parabolic Trough Collector .................................. 59 

5-5 System Performance Increases vs . Absorber Temperature for Various 

Component Improvements of Horizontal Parabolic Troughs ............ 62 

5-6 A CPC Collector Module ............................................ 64 

5-7 Concentration With a Fresnel Lens ................................... 64 

5-8 Typical Instantaneous Efficiency Curves for Collectors Used in 

IPH Applications .............................................. 68 

5-9 Typical Incident-Angle Modifiers for Collectors Used in 

IPH Applications ................................................ 70 

5-10 Average Global Solar Irradiance During Daylight Hours 2 on a Horizontal Surface (W/m ) .................................... 76 

xxii 
LIST OF FIGUBES (Continued) 

- Page 

5-11 Average Dire t Normal Solar Irradiance During Daylight 

Hours (W/m 4 )............m.m.............~.~~~~~.......~.77 

5-12 Graphi a1 Determination of Yearly Average Energy Collection Rate 5 (W/m ) During Daylight Hours for Unshaded Flat Plates, Evacuated 

Tubes, and Parabolic Troughs as a Function of Intensity Ratio..... 78 

6-1 Graphical Determination of Yearly Average Energy Collection Rate 

(w/rn2) During Daylight Hours for Unshaded Flat Plates, Evacuated 

Tubes, and Parabolic Troughs as a Function of Intensity Ratio..... 87 

6-2 An Indirect Solar Hot Air or Hot Water System.. . . . . . . . . . . . . . . . . . . ... 88 

6-3 Mixed-Tank Recirculation System.............................*....... 94 

6-4 Annual Recirculation System Storage-Load Modifier for Flat 

Plates (24 h/day load)..................^^^^^^^^^^^^.^^^^^ 97 

6-5 Annual Recirculation System Storage-Load Modifiers for Evacuated 

Tubes (24 h/day load^..............................^.......... 98 

Annual RecPrculation System Storage-Load Modifiers for East-West 

Parabolic Troughs (24 h/day load)........... ...................... 99 

Annual Recirculation System Storage-Load Modifiers for North-South 

Parabolic Troughs (24 h/day load) ................................. 100 

Annual Recirculation Sys tern Storage-Load Modifiers for Flat 

Plates (8 h/day load)............................................. 101 

Annual Recirculation System Storage-Load Modifiers for Evacuated 

Tubes (8 h/day load) .............................................. 102 

Annual Recirculation System Storage-Load Modifiers for East-West 

Parabolic Troughs (8 h/day -load).................................. 103 

Annual Recirculation System Storage-Load Modifiers for North-South 

Parabolic Troughs (8 h/day load) .................................. 104 

Variable-Volume Storage Configuration.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 

Annual Incident-Angle Modifier Correct ion Factors for Flat-Plate 

Collectors.............................~......................... 117 

Annual Optical Efficiency Incident-Angle Weighting Factors for a 

North-South Trough .............................................. 118 

Row-to-Row Shading Geometries....................................... 121 

xxiii 
LIST tX FIGURES (Continued) 

Page 

6-16 Annual Row-to-Row Shading-Loss Modifier for Flat Plates and 

Evacuated Tubes Tilted at Latitude ................................ 123 

6-17 Annual Row-to-Row Shading-Loss Modifier for East-West Parabolic 

Troughs ............................................................ 124 

6-18 Annual Row-to-Row Shading-Loss Modifier for North-South Parabolic 

Troughs ........................................................... 125 

6-19 Hours of Freezing Temperatures per Year as a Function of Freezing 

Days per Year .................................................. 131 

6-20 Average Below-Freezing Temperatures as a Function of Average 

January Daytime Temperature ....................................... 132 

7-1 Solar System Collector Field Layouts ................................ 140 

7-2 Effect of Insulation Thickness on Delivered Energy Cost ............. 144 

7-3 Insulated Pipe Model ............................................. 145 

7-4 Thermal Conductivity of Rigid Insulating Materials .................. 158 

7-5 Sensitivity of UA/L Values to Changes in Parameters--Outdoors ....... 159 

Sensitivity of UA/L Values to Changes in Parameters.. Indoors ........ Heat Transfer Efficiency Factors for Twenty Fluids .................. Summary of Types of Pumps ........................................... Typical Head-Flow Curves for a Centrifugal Pump ..................... Selection Curves for a Centrifugal Pump ............................. Net Positive Suction Head Required by Pump .......................... Pumping Power Reiquired by Different Pump Configurations ............. Capacity vs . NPSB- for Variable-Speed Pumps ........................ Head-Flow Curves for Two Centrifugal Pumps in Parallel .............. Example Heat Exchanger System ....................................... 

Floating Tubesheet Shell-and-Tube Heat Exchanger .................... 
LIST OF FIGURES (Concluded) 

Page 

Storage Capacity per Unit Volume as a Function of Temperature 

for Selected Latent-Heat Storage Materials ........................ 198 

Constant Flow-Rate Control .......................................... 215 

Constant Flow-Rate Control Using Three-Way Valve .................... 216 

Outlet Temperature Control by Flow-Rate Manipulation ................ 216 

Turndown Ratio as a Function of Equivalent Lag and Capacitance 

Ratio (p) for Proportional Control .................................. 218 

Turndown Ratio as a Function of Equivalent Lag and Capacitance 

Ratio (p) for Proportional-Integral Control ....................... 218 

Dimensionless Controller Gain as a Function of Equfvalent Lag and' 

Capacitance Ratio (p) for froportlonal-Only Control ............... 219 

Dimensionless Controller Gain as a Function of Equivalent Lag and 

Capacitance Ratio (p) for Proportional-Integral Control ........... 220 

Dimensionless Integral Time as a Function of Equivalent Lag and 

Capacitance Ratio (p) for Proportional-Integral Control ........... 221 

Solar System Response with Proportional-Only Control ................ 225 

Solar System Response with Proportional-Integral Control ............ 226 

Typical Control Loop Tracking Control ............................... 228 

Hose Deployment for Use With Either Rotatable or Nonrotatable 

Receivers ......................................................... 243 

Examples of Insulation Techniques for Pipe Supports and Hangers ..... 245 

Design for Rgducing Overnight Heat Losses in Drainback Systems ...... 248 

Economies-of-Scale Factor ....................bb.....~............... 265 

Modular Cost-Estimating Procedure Used by ECONMAT ................... 271 

Graphical Solution of Eq . 10-10 for Different Loan Fractions and 

Fuel Escalation Rates ............................................. 282 
. LIST 4'E TbBlXS 

Page 

U.S. Industrial Energy Consumption by State ......................... 10 

Fuel Use by Industrial Sector (1980) ................................ 10 

Solar Industrial Process Beat Projects in the United States ......... 17 

Problems Encountered in DOE-Funded Field Tests .....................a 20 

Factors Favoring the Use of Solar ZPH Systems ....................... 25 

Typical Ebnges of Liquid Collector. Performance 

Characteristics ................................................... 75 

Maximum Daily Irradiation Available for Several Collector Types ..... 109 

All-Day Average of End-Loss Factors ................................. 119 

Economic Fluid Velocities for Schedule 40 Steel Pipes. Obtained 

Using the Perry and Chilton Method ................................ 143 

7-2 Typical Thicknesses of Calcium Silicate Pipe Insulation ............ 146 

7-3 Average Values of Independent Variables Used in Calculation of 

UA/L .............................................................. 149 

7-4 Outdoor Pipe UA/L Values (W/K-m of len th) for Insulation 

k = 0.0288 W/m-K (0.20 Btu-in./hr-ftq-OF) ........................ 150 

7-5 Outdoor Pipe UA/L Values (W/K-m of len th) for Insulation 

k = 0.0577 W/rK (0.40 Btu-in./hr-ftf-OF) ......................... 151 

7-6 Outdoor Pipe UA/L Values (W/K-m of len th) for Insulation 

k = 0.0865 W/m-R (0.60 Bt~.in./hr.ft'.~P) ......................... 152 

7-7 Outdoor Pipe UA/L Value (W/K-m of length) for Insulation 

k = 0.1154 W/m-K (0.80 ~tu-in./hr-ft~-'~) ......em...............O.. 153 

7-8 Indoor Pipe UA/L Values (W/K-m of leng h) for Insulation 

k = 0.0288 W1m-K (0.20 Btu-in./hr-ftg-OF) ......................... 154 

7-9 Indoor Pipe UA/L Values (W/K-~ of length) for Insulation 

k = 0.0577 W/m-K (0.40 ~tu-in./hr-ft~-~~) ......................... 155 

7-10 Indoor Pipe UA/L Values (W/K- of leng h) for Insulation 

k - 0.0865 W/m-K (0.60 Btu.in./hr.ft'~F). ...e...e................ 156 

7-11 Indoor Pipe UA/L Values (W/K-m .of leng h) for Insulation 

k = 0.1154 W/rK (0.80 Btu-in./hs-ft5-OF) ......................... 157 

xxvii 
LIST OF TABLES (Concluded) 

Page 

7-12 Typical Overall Heat Transfer Coefficient Values for Tubular 

Beat Exchangers ................................................... 184 

7-13 Typical Fouling Resistances ......................................... 185 

7-14 Storage Size Comparison of Different Media Based on 1 GJ Storage 

and 30 K Temperature Swing ........................................ 196 

9-1 Installation Checklist .............................................. 254 

10-1 Modified Solar IPH Subsystem Costs .................................. 259 

10-2 Conceptual Phase Cost Estimating Guide ............................... 263 

10-3 Design Cost Factors .......................................... 264 

10-4 Cost Estimating Guide ................................................ 267 

10-5 Factor Definitions for Modular cost Estimating ...................... 272 

.1 0-6a Recommended Values for Modular Factors .............................. 272 

10-6b Recommended Values for Modular Factors .............................. 273 

10-7 Values of Capital Recovery Factor ................................... 274 

10-8 Values of Levelizing Factor LF to Convert a Zero-Year Fuel Price 

to a Levelized Price Over N Years ................................. 276 

10-9a Values of M-Factor (R = 0.10) ....................................... 278 

10-9b Values of M-Factor (R = 0.15) ................................... 279 

10-9c Values of M-Factor (R = 0.20) ...................................... 280 

11-1 Fire-Resistance Properties of Various Insulating Materials .......... 287 

11-2 Safety Regulations and Agencies ................................ 291 

11-3 Summary of Environmental Agencies and Regulations ................... 294 

11-4 State Environmental Impact Statement Requirements ................... 297 

xxviii 

SECTIOH 1.0 

OBJECTIVES m D3SICB ~ODOLOGY 

In an effort to expedite the commercialization of solar energy, the U.S. 

Department of Energy has funded a number of field tests- These include over 

100 projects that demonstrate solar heating and cooling (SHAC) of buildings 

and about a dozen projects to date in which solar collectors supply industrial 

process heat (IPH). Results from these projects generally showed lower than 

predicted energy deliveries due to a variety of system design, plumbing, and 

hardware problems, most of which can be expected in a new technology. Various 

handbooks were writ ten to help designers avoid problems already encountered ; 

later projects showed marked improvementsApplication of solar energy to industrial processes began later than the SHAC 

program, but similar problems have occurred in the IPH projects. Differences - 

in types - - of collectors, environment, and loads created some new problems as 

well. There was obviously a need to make contractors for new projects aware 

of mistakes made in the past. A great deal had been learned from the operation of the hot airlhot water IPH-projects; from those experiences, a set of 

guidelines was prepared to help design engineers with future solar industrial 

process heat systems. A questionnaire was mailed to previous contractors and 

DOE technical advisors, and a draft document was prepared from the results. 

Following a final review meeting at SERI, Design Considerations for Solar 

Industrial Process Beat Systems (Kutscher 1981) was published in March. 

The purpose of this handbook is to provide specific design information. 

Choosing appropriate components such as collectors, storage, piping, insulation, pumps, valves, heat exchangers, and heat transfer fluids is covered in 

detail. System integration, controls, economics, start-up procedures and 

safety and environmental issues are also addressed, and a new, simple method 

for predicting energy delivery is included. 

A considerable amount of time and money is often spent performing detailed 

computer simulations of a solar energy system. The authors belfeve, however, 

that if solar IPH applications are to become economically viable, they must be 

designed in ways that are typically used in the heating, ventilating, and air 

conditioning (HVAC) industry. Although the sensitivity of solar energy systems to variable solar input and thermal losses dictates more sophisticated 

"rules of thumb" than those used to size a building air conditioning system, 

simple graphs and tables can supply design values that are completely sufficient for system design. To save designers both extra steps and considerable expense, we have replaced the computer simulation step with some 

simple rules. 

Design tools can be generated either from actual performance measurements 

taken in the field or from large numbers of computer simulations- Because 

actual field data are still very limited, the bulk of design tool development 

in this handbook has incorporated data from computer simulations. Therefore, 

before this handbook was written, a study was done comparing the capabilities 

of various solar simulation codes for IPH applications. The two most likely 
candidates were TRNSYS, developed by the University of Wisconsin, and SOLTES, 

developed by Sandia Laboratories (see Sec. 6.0). For a variety of reasons, 

each code would have required considerable modification; thus, a new in-house 

code specifically geared for solar IPH design tool development was created. 

The result, SOLIPH, is not highly user-oriented like TRNSYS or SOLTES but is 

very easy to modify, inexpensive to run, and well suited to the purposes of 

this handbook. To verify the accuracy of the design tools generated by 

SOLIPH, the SOLIPH program was tested against other well-respected computer 

programs (see Appendix C). 

This handbook was designed to be used by readers with experience in basic 

mechanical engineering. Knowledge of computer programming is not necessary, 

however, and previous solar energy experience, although advantageous, is not 

required. Because of its simplicity of approach, the handbook should be 

useful to an industrial firm contemplating solar energy and interested in 

having an in-house engineering staff manage conceptual and preliminary 

designs. It is recommended that the design engineer read the chapters in 

order. Results of conceptual design calculations will indicate whether the 

designer should proceed to the preliminary design. The iteration needed in 

completing a design is discussed in the next section. 

Because this 'field : is . constantly changing aiid new , information continues to 

come in from industry tests, this handbook is clearly not the last word in IPH 

design. As funding permits, efforts will be made to update the handbook when 

new information becomes available. Users of the handbook are encouraged to 

supply the authors with feedback, and we are particularly interested in how 

easy users find the design procedurg. 

1.2 DESIGN ~ODOLOGY 

As we mentioned earlier, a design process involves a considerable amount of 

iteration. The material in this handbook is arranged so that conceptual 

design is treated first, followed by more detailed aspects of the process; but 

it is also important to see how the different design elements interact. 

Figure 1-1 is intended to inject some order into the variety of items the 

designer must address. The figure shows the design process progressing from 

left to right. The same process covers both conceptual and preliminary 

designs. Conceptual design does not go into as much detail as preliminary 

design, nor does it go quite so far. All preliminary design items are denoted 

by an asterisk. 

The overall process is subdivided into four basic design problems: Application Selection, System Specification, System Analysis, and System 

Optimization/Design Completion. Application Selection requires a suitability 

analysis. Plant location, competing alternative energy sources, conservation 

opportunities, and process loads are all assessed using methods described in 

Sec. 3.0. This analysis results in information that can be used in two major 

design decisions. The load schedule, load interface, and freeze protection 

requirements help the designer choose the system configuration. The total 

load, load temperature, available space, and solar radiation data aid in the 

selection of a collector. 

The System Configuration segment of conceptual design includes selecting a 

basic configuration (e-g., open or closed loop, type of freeze protection) 

(Sec. 4.0); deciding whether or not to use storage (Sec. 6.0); and defining a 

basic control system (Sec. 8.0). Detailed design involves actually sizing 

storage and subsystem components (Sec. 7.0) and writing specifications for a 

control system (Sec. 8.0). 

Selecting a collector, done along with selecting a system configuration, 

involves choosing a collector type, an array location, and an approximate collector area for conceptual design (Sec. 5.0). The optimum area, specific collector parameters, mounting details, and ground cover ratio are determined in 

preliminary design (Sec. 6.0). As we will discuss later, the system configuration and collector segments provide most of the options that require 

iteration (basic configuration, storage size, and collector area). 

The next step, System Analysis, is to analyze system performance and overall 

system costs. System performance analysis involves a simple calculation of 

collected energy and a rough estimate of system losses (Sec. 6.0). Next, 

detailed system losses are determined (Sec. 6.0). The costs segment involves 

an estimate of total system cost (based largely on collector area), in conceptual design (Sec. 5.0); and a system cost that takes into account all the 

components of the actual system, in preliminary design (Sec. 10.0). 

In the last segment, System Optimization/Design Completion, outputs from the 

system analysis provide system energy cost for the conceptual design. The 

results of a complete life-cycle cost analysis are available during preliminary design. If cost is the major criterion in sizing a system, a 

decision is made here. The designer reworks the System Specification segment 

and tries different combinations: type of collector, basic configuration, 

collector area, etc., in conceptual design; collector parameters, row-to-row 

spacing, storage, pipe and heat exchanger sizes, and collector area in preliminary design. 

At the end of the conceptual design phase, it may be decided not to continue 

to develop a preliminary design. Before making such a negative decision, however, the designer could go all the way back to the beginning and try a different plant process with a different temperature and load profile. Moreover, 

a plant owner may be concerned more with fuel curtailment than economics and 

decide to use solar energy as a hedge against that possibility. Or, the plant 

owner may want to experiment with a system that has future potential. In such 

cases, an arbitrary solar fraction may be chosen, or collector area may be 

fixed by the size of a roof or by land space set aside for it. Once the 

iterations in conceptual design are complete and certain criteria are met, the 

designer moves on to the preliminary design phase. When those iterations are 

in turn complete, the designer then addresses items in the design completion 

section of Fig. 1-1. Piping and instrumentation are diagrammed, equipment 

specifications are listed, and final system and energy costs are determined. 

Obviously, it would be too time-consuming to go through the design process 

with every possible permutation of system parameters. The experienced 

designer, and particularly the experienced solar IPH system engineer, will be 

able to recognize what combinations offer the best chance of success. Suggestions are given throughout the text to help expedite the process. 
1.3 ADDITIONAL SOURCES OP 'INPO~TZOI 

This handbook is based on experience with the IPH field test program; thus, it 

covers a specific technology area. Line-focus, flat-plate, and evacuated-tube 

collectors are included in temperature ranges from ambient to about 290°C 

(550°~). Although air collector systems are covered generally, design tools 

in this edition apply specifically only to liquid and steam systems. Solar 

ponds, point-focus collectors, and central receivers are not addressed here in 

great detail. 

In addition, certain sources of solar thermal energy information were not 

enlarged upon, such as SOLMET and TMY weather data, product specifications, 

computer programs, etc. The reader is referred to Appendix G for additional 

sources of information on these subjects and on other solar thermal 

technologies. 

SECTION 2.0 

SOLAR RmcwY IN mDUSTRY: Alf WERVLEW 

The industrial sector is the largest energy user in the U.S. economy, consuming 39% of total demand (see Fig. 2-1). Of that 39X, approximately 45% 

(about 18% of the overall energy usage) involves direct thermal energy use and 

represents a significant potential market for solar energy applications. 

There are several possible advantages to using solar energy for industrial 

process heat (IPH) rather than for residential or commercial heating and 

cooling applications: 

Industrial loads are usually more constant throughout the year. 

Industrial plants usually already have crews who could attend to the 

maintenance of solar energy systems, thus ensuring operation of the system at peak efficiency. 

The total impact on the nation's energy use would be greater for solar 

IPR systems than for SHAC. 

Compared with alternative industrial fuels, solar energy offers the additional 

advantages of being nonpolluting and independent of interruptions in supply 

caused by political or economic conditions. Solar energy systems can also be 

A 1. Commercial 

15% 

Figure 2-1. U.S. Bnergy Demand by Sector 

7 
constructed in reasonably short periods of time. Of course, certain impediments to using solar energy in IPH also exist: 

Land availability: Existing roofs often are not large or strong enough 

to support collector arrays. Either additional supports must be built or 

other areas or lands must be used. (Commercial land in urban areas can 

be scarce.) 

Industrial effluents: An industrial environment creates greater possibilities for contamination of solar collectors than does a commercial or 

residential one. Concentrating collectors that require high specular 

reflectivity are particularly susceptible to degradation. 

Nonconstant energy source: The plant must be able to utilize a variable 

solar energy delivery. 

Availability of conservation alternatives: Many plants can employ 

simple, inexpensive energy conservation techniques which should precede 

any commitment to solar energy. These include using waste heat from 

high-temperature processes to supply low-temperature processes (such as 

boiler feedwater preheat). 

Economics: Industry often requires payback periods of less than 

5 years. In general, solar energy systems currently are too expensive 

and conventional fuels are too cheap to provide such paybacks. 

The suitability of solar energy in a particular application depends on a 

number of factors, such as climate, economics, process temperature, and 

available space. A market suitability study sponsored by SERI used computergenerated maps to identify regions of high solar favorability. The primary 

criteria were collector performance, air-quality constraints on competitive 

fuels, state solar tax incentives, fuel costs, and degree of coal usage. 

Figure 2-2 shows the resulting solar attractiveness map for parabolic trough 

collectors. As one might expect, the Southwest is a highly favorable 

region. The State of California is particularly noteworthy because of its 

excellent tax incentive, favorable climate, and stringent air-quality standards. Areas where coal is heavily used show up as least favorable. 

Table 2-1 shows that current industrial energy consumption is highly regional; 

ten states account for 61% of the total. Also, whether solar energy is 

economical depends to a great extent on what fuel it must be measured 

against. Table 2-2 shows the percentages of each type of fuel (less feedstocks) used by the industrial sector in 1980. Oil and natural gas, which can 

be expected to become less stable in price, accounted for 67.2% of total 

energy use. Coal can be expected to remain fairly inexpensive (although cost 

and extent of use will depend greatly on pollution requirements and transportation costs). Electricity is likely to remain expensive, but it is usually 

used for applications other than process heat. Figure 2-3 shows that more 

than 80% of the total industrial process heat energy is used by six major 

industries. 

Table 2-1. U.S. Industrial 

Energy Consumption 

by State (1977) 

(61% of total in 10 

States) 

State % of U.S. Total 

Texas 

Louisiana 

Ohio 

Pennsylvania 

Illinois 

California 

Michigan 

Indiana 

New York 

Alabama 

The temperature at which energy is used is also important in assessing the 

solar option. At higher temperatures, solar collectors lose more of their 

collected heat to the environment; thus, their efficiency is reduced. But as 

shown in Fig. 2-4, 49% of the energy consumed by industry is at temperatures 

below 260 OC (500 OF)--a conservative limit for collectors currently in production. The process temperature largely dictates which type of collector is 

most appropriate. This handbook concentrates on those that have already been 

used commercially: flat-plate, line-focus, and evacuated-tube collectors. 

Typical operating temperature ranges for these as well as for three other 

types of collectors being developed are shown in Fig. 2-5. All of these collectors are described in more detail in Sec. 5.0. 

Table 2-2. Fuel .Use by 

Industrial 

Sector (1980) 

Fuel X 

Coal 7.9 

Oil 24.3 

Natural gas 42.9 

Electricity 15.8 

Other 9.0 
Quads (10'~ Btu/yr) 

1 .O 2.0 3.0 

I 8 4 I 

Chemicals and Allied Products 11 2-48 

Primary Metals 11 *+* 

Petroleum and Coal Products 1-1 1.20 

Paper and Allied Products 1-1 1-16 

Stone, Clay and Glass Products -1 1.15 

Food and Kindred Products 1-10.82 4 

~~~~~~~

I 80% of Total 

Figme 2-3. Energy Use by Major Industrial Groups 

-I (Cumulative Percentages are Shown in Parentheses) 

SOURCE: F. Krawiec et al.. July 1981. 

Figure 2-4. Distribution of IPH Requirements by Temperature 

40 - 

30 - 

t-------- 

I 

Range of 

I (1 00) 

Production I 34.0 

Collectors I 

(27.2 j 

20.3 I 

20 - b 

(44.1 ) I 

I > loooO F 

16.9 

I 

I (58.8) (65.8) 

6.8 7.1 

(48.9) 1 (52.0) 

4.8 (50.4) 3 

1.3 1.6 
Type of Collector: 

Central Receiver 

Point Focus 

(Parabolic Dish and 

Fresnel Lens) 

Line Focus 

(Parabolic Trough and 

Fresnel Lens, also 

Multiple Reflector) 

Evacuated Tube 

Flat-Plate 

Solar Pond 

Operating Temperature 

NOTE: Line-focus, evacuated-tube, and flat-plate collectors are commercially 

available: central receivers, point-focus collectors, and solar ponds are still 

being developed. 

Figure 2-5. Operating Temperatures for Various Types of Collectors 

2- 2 SOLAR BPPLICATIONS IW 

The three main areas of solar thermal application in industry are 

Process hot water 

Drying/dehydration 

Process steam. 

2.2.1 Hot Water 

Heated water is used in large amounts at temperatures between 50' and 100~~ 

(120~-212~~) for cooking, washing, bleaching, and anodi3ing and represents 

about 2% of the IPH demand, or 0.2 quad (1 quad = 10 Btu). Preheating 

boiler feedwater accounts for another 3 quads; often this could be supplied by 

associated higher-temperature waste heat. Water can be heated either directly 

in a collector loop or by means of a separate heat transfer fluid used in conjunction with a heat exchanger. The latter approach can reduce freezing and 

corrosion problems, but it also results in somewhat higher collector temperatures and, thus, reduced efficiency. 
An example of an IPR hot water system is shown in Fig. 2-6. This particular 

system su plies 454 ~/min (120 gallmin) of hot water in the range of 55' to 8 83'~ (130 to 180~~) to the York Building Products concrete bl ck curing plant 

in Harrisburg, Pa. The collector array consists of 829 my (9216 ft ) of 

multiple-reflector linear concentrators. A shell-and-tube heat exchanger is 

used to transfer heat from the water-and-ethylene-glycol collector loop to the 

process water. A unique feature of this application is that the large, under- 3 ground, concrete curing area, or rotoclave, contains about 190 m (50,000 gal) 

of water and serves as built-in storage. 

2.2-2 Drying and Dehydration 

The United States uses about 1.4 quads of solar-heated air at temperatures 

below 177'~ (350~~1, mostly for crop drying. The two most common ways to 

supply solar-heated air are (I) to heat the air directly in the collectors and 

(2) to heat a liquid in the collectors and then use a liquid-to-air heat 

exchanger. An example of the first type of system is shown in Fig. 2-7. 

2 2 In that particular system, 1890 m (21,000 ft ) of air collectors supply 60°c 

(140'~) air to a prune- and raisin-drying tunnel at the Laaanuz i and Pantaleo 

(L and P) Foods plant in Fresno, Calif. A 420-m3 (14,000-ft 5 ) rock bin is 

used for storage. A unique aspect of this plant is a heat recovery wheel that 

transfers heat frm the tunnel exhaust to the collector array inlet. Although 

this raises the collector array's temperature, thereby lowering the array's 

sf ficiency, the heat recovered more than makes up for the loss in efficiency. The heat recovery wheel has a payback period of less than 1 year, and 

its success demonstrates the importance of implementing conservation alternatives before proceeding to solar applications. 

d 

m2 (9216 ft2) Solar Array r Boiler E 

York's Auxiliary 

Boiler/Rotoclave 

Shell-and-Tu be 

Heat Exchanger 

AAl's Solar Array/ 

Rotoclave Piping Circuit 

York's Make-Up 

Water Circuit 

Figure 2-6- York Building Products Solar kt Water System 
I 

at Recovery Unit 

Inlet Guide Vane Control 

Figure 2-7. Iamnuzzi and Pantaleo Foods Solar Air System 

An example of heating water to ultimately supply hot air is shown in Fig. 2-8, 

which illustrates the system in use at the J. A. LaCour lumber-drying kiln in 

2 2 Canton, Miss. At this plant, 225 m (2500 ft ) of flat-plate collectors heat 

water to 60'~ (140°Z'), which then supplies -hot air to two hardwood lumber 

kilns via finned-tube heat exchangers. Although this system results in higher 

collector temperatures than does a direct-air approach, pumping power needed 

for the liquid loop is generally less than fan po er for 1 9 air loop. To 

increase collected energy at the LaCour plant, 216 m (2400 ft ) of reflectors 

are included in the colikctor array. 

Figure 2-8- LaConr hmber Kiln Solar Hot-Water-to-Air System 

14 
A third way of using solar heat for drying should be mentioned. Rather than 

using collectors at all, drying houses can be constructed so that sunlight 

directly strikes the product. This method entails relatively low temperatures 

and long drying times and generally requires that the product be spread out 

over a large area. However, it can be cost-effective. 

2.2.3 Steam 

About 6 quads of energy are consumed in the United States for process steam, 

80% at temperatures below 177'~ (350'~). Steam can be supplied with solar 

collectors in these three ways: 

Using a high-temperature fluid in the collectors and transferring the 

heat to an unfired boiler 

Circulating pressurized water in the collectors and flashing it to steam 

in a flash tank 

Boiling water in collectors. 

The first type of system is shown in Fig. 2-9. In this exanyle, Thermin 1 55 4 is heated to 246O~ (475'~) in an array consisting of 900 m (10,000 it ) of 

parabolic-trough collectors. The hot Therminol then boils water in an unfired 

boiler, supplying steam at 0.96 MPa (125 psig). The system shown was built 

for the Lone Star Brewery in San Antonio, Tex. The flash system shown in 

Fig. 2-10 was an alternative design for the brewery. In that system, water is 

heated directly to 247O~ (477'~) and 4 MPa (600 psi) in the collector loop and 

then flashed to steam. This procedure eliminates the need for an expensive 

Line-Focus 

Existing 

Solar-Fired Steam Boiler 1 Condensate 

Pump 

Figure 2-9. Solar Steam Production Using an Wired Boiler 
- 

Existing 

Flash Tank check Equipment 

Line-Focus 

Collector Fluid Loop 

of Pressurized Water 

circulating Pump 

Figure 2-10. Solar Steam Production Using a Flash Tank 

unfired boiler and can provide more collected energy because it eliminates the 

temperature difference across the heat exchanger. On the other hand, freeze 

protection is required, and considerable pumping power must be provided to 

supply the pressure difference across the flash valve. A flash system similar 

in principle to the one shown was built at the Ore-Ida Foods, Inc., frenchfried potato plant in Ontario, Ore. The third alternative, boiling water in 

the collectors, has not yet been attempted. A recent study conducted at SERI 

concludes that it is a promising concept, however, and merits further investigation (Murphy and May 1982) (see Sec. 4.2). 

Although steam.is used widely in industry to transport heat, it is probably 

better to combine solar energy with hot water. If hot water supplies heat to 

a process, solar collectors can be used without unfired boilers and without 

the disadvantages of flash systems. Thus, if solar energy is being considered 

for a new plant, some consideration should also be given to using pressurized 

hot water in place of steam. 

2.3 IlODUSTBIBt PROCESS EEAT FIELD !U3STS 

In an effort to advance the state of the art in solar industrial process heat, 

the U.S. Department of Energy (DOE) funded a number of field tests throughout 

the United States. These were funded in cycles, and each new cycle tested a 

different area for solar application: hot water [<lOoOc (212'~)~; hot air; 

low-temperature steam [100~-177~~ (212°-3500~)]; and intermediate-temperature 

steam [177'-275'~ (350'-550' ) . In ad ition, two cycles were funded for 

5 

9 lar e-collector-area [4500 '(50,000 ft )I projects both above and below 

100 C (212'~) in order to investigate economies of scale. A list of these 

projects, along with privately funded efforts, is given in Table 2-3. 
Table 2-3. Solar Industrial Process Heat Projects in the United States 

----- - - - 

Process Temperat,rre Collector Collector Stze of Array Company 1.oca t ion Process Application Type Man~tfacturer ( f t2) Status QundLng 

(OF) I 

HOT WATER SYSTEMS 

I Sweet Sue Kitchens Inc. Athena, Ala. Preheat botlct Feedwater 130 Po11 

2 Amertcan Linen Supply Co. El Centro, Callf. Preheat hotler feedwater, wash water 200 PT r 

3 Aratex Service Inc. Prenno, Calif. Heat process water 220-160 P 1 

4 IrCs Xmagea Mill Valley ,Calif. Film proceueing 75-100 P1 

5 Stauffer Chemical Co. . Oxrrard, Calif. Chemical processing 125 Pla 

16,560 IDS Cov 

12,150 CDc Go91 

6,720 Opr. 9/77 Cov 

6/10 Opr.8177 Cov 

38,000 f~r; G/P 

6 Jhirmack Rnterprlses I nc. Redding, Calif. Preheat baller Feedwater 

7 Campbell Soup Co. Sacr~mento, Calif. can washing 

8 Caterpillar Tractor Co. Snn Leandro, Calif. Heat wnsh water 

9 Salz teatlters Inc. Santa Cruz, Calif. Tanning and ffntshtng 

10 Aarkley N~at Co. S. Lake Tahoe, Calif. Santtation 

160-200 P 1 NAv 6,750 Opr.7/80 PPf 

180-195 PTr, PL ACX, SC 7,335 Dpr. 11/77 Gov 

235 PTr SK 50,400 XDs C/P 

85-160 PI NAv 75,200 IDS G/P 

LOO P 1 NAv 2,500 Opr. PFI 

11 Anlrerrser-nusch Inc . Jacksonville, Fla. Beer paeteurtsatton 

12 Dana Corp. Spicer Clutch Dtv. Auburn, Ind, Parts waehing 

13 Oecar Meyar Corp. Perry, Iowa Meat proceeoing 

14 Sohto Petroleum Co. Grnrrts, NM Uranium-ore processing 

15 Genera1 Extrusion Inc. Youngstown, Oltio Solrtt tan heat tng 

140 ETtl 01 4,600 Opr. 2/78 PFt 

130 P L REV 936 Opr. 5/77 PPL 

155 NAv NAv 40,320 IDS C/P 

140 Pon NAv 6,780 Tst Cov 

160-180 Tu CSC 4,400 Opt. 9/77 PFI 

lG York nulldtng Products Inc. Harrfeburg, Pa. Concrete-block curtng 

17 Nestle Enterprises Inc. S~nta Isabel, PR Juice paaterrrisatton 

18 Rtegel Textile Corp. LaFrance, SC Iteat dye-heck water 

19 Coca-Cola RottlLng Co. Jackson, Tenn. Bottle washing 

20 Tyson Foods Inc. Shelhyville, Tenn. Poultry processing 

135 HRe AA 1 9,216 Opr. 9/78 Gov 

210 ETa GE 50,000 IDS c/e rsn ETU GE 6,680 opr. 6/78 cov 

NAv ETu 01 9,480 Opr. 9/79 PFi 

129-140 ETu 0 I 53,430 LDs CIP 

21 Mnry Kay Co~mettca Ilic. Dal. las , Tex. 

22 M & M Mare Corp. WRCO, Tex. 

23 Easco Photo Rtchmond, Va. 

S~tllttztng 

lleat water for cafetertah 

Ft Lm processlrlg 

ser 

NAv 

SUN 

1,000 

NAv 

NAv 

PFi 

NAv 

PTi 

tlOT-AIR DRYING SYSTEMS 

24 Gold Kist Inc. Decntur, ALa. Prelieat dryer air 180 

3.5 I.nmnnuxzi & Pantnleo 

Foods Inc. Fresno, Calif. nrytng 143 

26 Ci lroy Foods Inc. Gilroy, Calif. Preheat dryrr atc. holler feedwater 194 

27 Western Alfalfa Corp. Lawrence, Uan. Prelreat dryer ~tr 400 

28 LaCour Kf ln Servtcee Inc. Canton, Miss. Lumber drytrrg 180 

3.9 U.S. Cypsum Co. Sweo twa ter , Tex. Board drying 900 

Cov 

P 1 

P,Tu 

PTr, P1 

elR 

llc 1. 

TRW 

GE 

IIX 

CMC 

ROE 

Opr. 8/78 

Opr. 9/79 

r n9 

Opr. 11/77 

I Ds 

Cov 

Cov 

Gov 

Cov 

G/P 

'~tth reflectors. 

h~xDansfrln For process use rlnder way. 
Table 2-3. Solar Industrial Process Heat Projects in the United States (Concl.uded) 

Compnny Location Procenn Appl lca t i on 

Proresn Collector Collector Size of Array - 

(OF) Type Manufactljrrr (ft2) F'ln'l'nE 

-- I -. -- - - . -- - - -- - - - - -- - --- -. -- -- -- - .- -- - - - . .-- --- - -- - - - 

TIIERJ4AI.-LIQIJID HEATING SYSTEMS/DIRECT-FIRED PROCESS IIEATING I 

30 Ergoli Inc. Mohile, A1a. lleat Ll~ermal liquid 130-190 PTr ACX 2O.lh0 10s Gov 

31 Atlanttc Richfield Oil 6 

Gas Co. RakersFleld, Callf. llent thermal Ilquid 5 60 llel NOR 181,120 IDS G/P 

32 Valley Nitrogen Producers Inc. El Centro, Cell€. nlrect procens heatlne 1600 llel EIU 633,360 10s G/Y 

STEAM SYSTEMS 

33 West Point-Pepperell Inc. Fairfax, Ala. Pabrtc drying 

34 Provident Energy Co. Mobile, Arlz. Produce ref lnery steam 

35 Exxon Corp. Rakersfleld, Calif. 011 recovery 

36 Exxon Corp. nakersfleld, Calif. Oil recovery 

37 Petro Lewis Corp. Rakerefield, Calif. 011 recovery 

320 PT r ll 7,512 Opr. 9/78 Gov 

7 00 Ilel MD 712,352 IDS G/P 

500 PT r NAv 254,208 10s G/P 

567 He 1 MFIC 432,000 IDS G/P 

500 Li F OAC 340,800 iUs G/P 

38 llome Laundry Pasadena, Calif. Produce steam, preheat was11 water 360 PTr JD 6,496 ICn Gov 

39 NI. Industries Lac. Newberry Springs, Calif. Hectortte drylng 372 PT r JU 10,240 IDS Gov 

40 Troptcat~a Products Inc. Bradenton, Pln. Tce-block thawing 300 ETu GE 10,000 Opr. 12/80 Gov 

41 Dow Chemical Co. Dalton, Ga. 1,ate~ manufacturing 366 PT r STC IIX 9,930 ICn Gov 

P 42 Bl-eyle of America Inc. Slienandonh, Ga. Produce s team, Iient water 7 50 PTr GI? 49,382 ICn Cov 

03 

43 Hilo Coast Processlng Co. Pepeeko, lkwall 

44 Stauffer Cliemlcal Co. Ilenderson, Nev. 

45 Southern Union Co. Ilobbs, NM 

46 G11lf Mlneral Reaoilrcen Co. San Mateo, MI 

47 U.S. Steel Ghemlcnla Co. llnverhlll, Ohio 

Sugar-cane procesalng 400 PTr SK 50,400 IDS G/P 

Chemtcal stripping 368 PTr STC IIX 10,592 10s Gov 

Produce refinery maln steam 375 PTr SK 10,080 ICn Gov 

Uranium-ore processLng 366 Ilel MU 232,1139 IDS CIP 

Polyptyrene processtng 373 PTr SK 50,000 10s GIP 

48 We-Ida Foods Co. Ontarlo, Ore. Produce steam 417 PTr STC IIX 9,520 ICn Gov 

49 Raten Contniner Inc. Qt. Worth, Tex. Produce nteam 370 PTr SK 34,720 IDS G/P 

50 Lone Star Rrewtng Co. San Antonio, Tex. Produce ateam 353 PTr SK 9,450 ICn Gov 

51 Johnson 6 Johtison Sherman, Tex. Produce process stenm 345 PTr AC X 11,520 Opr. 1/80 Cov -- - - - - - - -- - - -- -- - -- - - - - -- -- - - - . - - - - - - - - - - . - - . - -- - -- - - -- .. - -- - - - - -. - . - - 

Source: Kenneth Brown. 1981 (Nov.). +r Magazine. Vol. 125 (No. 11). 

legend to Table 2-3 

ETtl - Evacuated tube PFL - Privately flnnnced 

G/P - Shared government and PI - Flat plate 

prlvate Financing Pon - Shallow pond 

Gov - Governmelit financed Plr - Paralrol LC trough 

He1 - Helloatat Tst - Test only 

ICn - In constructton Ti1 - 'lube 

10s - In doaten 

I.iF - Line focus 

FIR@ - Multiple reflector 

NAv - Not avatlahle 

Opr - Operattonal 

AA1 - AAl Curp. 

ACX - Aclirex Corp. 

ROE - Uoeine. Engllieerlng 6 

Constrllctlo~i Co. 

CMC - Cl~amherlain Mallufacturing Co. 

GAC - General Atomic Co. 

CF. -- Ceticr:~l F.l.ectrLc Co. 

CSC - Cetieral Solar Corp. 

ll - lloneyuell Inc. 

IK - llexccl Corp. 

JD - Jacohs Del. Corp. 

Fm - FIcDonnnl 1 -Douglas Corp. 

EiMC - FIartln Marietta Corp. 

NOR - Nortl~rup Inr.. 

01 - Owens-Tlltnoln Inc. 

REV - Kevere Copper L Brass Inc. 

SEI - Solnr Enterprises Inc. 

SG - SolareenLcs Inc. 

SK - Solnr Kl~isticn Corp. 

SR - Solaron Corp. 

s'rc - sllntec Corp. 

SUN - Entho~ic 1111:. Sunworkr Dfv. 

TRW - TRI4 Lnc. 
Much has already been learned from the existing field tests. Seven DOE projects operating for a year or longer that were the subjects of a SERI report 

(Kutscher and Davenport 1981) showed efficiencies ranging from 8% to 33% 

during their first year of operation. As corrective actions continue to be 

taken to solve problems, these percentages should increase considerably. As 

newly designed projects benefit from past experiences with these field tests, 

reliability and performance can be expected to increase as well. 

Although seven projects represent only a limited statistical basis on which to 

make generalizations, some basic conclusions can be drawn that should prove 

useful .in future projects : 

Solar collector arrays have generally shown high availability. However, 

industrial processes of ten have not sufficiently utilized that available 

energy. 

The durability of collectors could prove to be a major problem in a field 

application of solar projects. Degradation of absorber surfaces and 

glazings is still relatively common. 

Problems similar to those encountered in the SWC buildings program also 

occur in IPH applications. Better education in system design is needed 

to prevent thermal shocking of evacuated tube collectors, heat exchanger 

freezing due to thermosyphon heat loss, and other problems. 

Parasitic power has proved to be a major contributor to low performance 

in systems employing air collectors. 

Both operational and overnight piping losses can be significant in solar 

IPH applications. 

Data acquisition systems have generally been unreliable. 

Solar IPH is not yet cost-effective, considering the typical payback 

periods required by industrial owners. Some industrial managers are concerned with fuel supply curtailments, however; to a certain extent, this 

can offset the economic shortcomings associated with solar IPH. 

A considerable investment in maintenance has been necessary to approach 

predicted performance in first-generation projects. 

Environmental contaminants can seriously impede the performance of solar 

collectors. 

Certain adjustments in plant operation schedules, hardware, and control 

logic are often needed to make optimum use of a solar energy system. 

Opportunities for energy conservation are abundant in industry, and many 

of them provide more rapid payback periods than do solar energy systems. Just as in the SHAC buildings program, energy conservation should 

precede solar implementation. 

In some applications, solar energy may improve the quality of a final 

product in addition to saving fossil fuel. 

A summary of the problems encountered in the seven projects studied is given 

in Table 2-4. Problems related to the data acquisition equipment in these 

systems are marked with asterisks. These problems caused loss of data but 

typically did not affect the operation of the system. For more information on 
Table 2-4. Problems Encountered in DOE-Funded Field Tests 

Project Problems Corrective Action 

Campbell Soup *Data logger failure 

*Magnetic tape recorder 

failure 

*Nonoperative flowmeters 

Broken glass cover tubes 

Wind damage 

Shutdown of can line 

while changing soup type 

Leakage of f lat-plate 

glazings 

Silt accumulation 

Failure of tracker motor 

Degradation of black 

chrome selective surfaces 

Riegel Textile Contamination of reflectors 

by boiler stack effluents 

Excessive night losses 

Thed shock tube breakage 

Low flow rate through 

collector 

Poor insulation in collector headers 

Deterioration of copper fins 

in collectors 

Pork Building Failure of black chrome 

Products coating 

Thermosyphon freeze-up 

Mirror breakage (thermal) 

Insufficient wire size for 

motors 

Drive motor grease too 

thick 

*Data logger not compatible 

with tape drive 

Mirror desilvering 

*Dust problems with data 

logger 

Exhaust fan installed 

Replaced, but interfacing 

problems are still unsolved 

Replaced with Kates control 

valve, calibrated monthly 

Removed glass tubes 

Repaired damage 

None 

None 

Installed Cyclone separator 

(Nov. 1980) 

Replaced (Dec. 1980) 

Painted absorber tubes flat 

black 

Reflectors polished (April 1980) 

None 

Installed over-temperature 

indicator; circuit box made 

less accessible 

Larger pump impeller installed; 

fittings made larger 

(April 1980) 

Headers reinsulated (April 1980) 

Under study 

Painted with flat black paint 

(completed May 1980) 

Installed check valves in collector loop piping; replaced 

heat exchanger tube bundle 

(Feb.. 1979) 

Mirrors replaced (Nov. 1979 and 

Au~. 1980) 

Replaced wires with heavier 

gauge (Oct. 1978) 

Replaced grease with lowtemperature grease (Dec. 1978) 

Replaced data logger with 

different brand (Feb. 1979) 

New mirrors have protective 

coating 

Relocated to building lobby 

(Jan. 1979) 
sm :al TR-1356 

Table 2-4. Problems Encountered in DOE-Funded Field Tests (Continued) 

Project Proble~ms Corrective Action 

Gilroy Foods 

Gold Kist 

LaCour Kiln 

Lamanuzzi and 

f antaleo 

Low flow rate from rotoclave 

P'J="P 

*Lightning damage to DAS 

Leakage f ram bellows-type 

expansion joints 

Ultraviolet deterioration 

of flexible insulation 

Sagging support structure 

*Voltage spikes causing 

cassette to shut off 

Inadequate heat sf& for 

energy produced in offseason 

Collector contamination by 

soybean chaff and oil 

Poor performance of automatic sprinkler system 

*Data logger failure due to 

low temperature 

Water seepage into insulat ion 

Plant operation schedule 

calling for maintenance 

during daytime 

CPVC pipe failure due to 

overheating during nonload conditions 

Gravel in collector loop 

piping 

*Flood damage to data 

acquisition system 

*Dust in disk drive 

*Erratic water flowmeters 

Poor turndown ratio on 

conventional heaters 

Inadequate collector pipe 

slope to ensure draindown 

Rain leakage into damper 

housings 

Nonuniform rock storage bed 

Rerouted pipes to reduce head 

(June 1980) 

Repaired (July 1980) 

Replaced with expansion loops . 

(Feb. 1980) 

Painted to stop deterioration 

Several members replaced 

(Oct. 1981) 

Insolation transformer added 

to DAS system 

None; reconnnendations have been 

made for providing additional 

heat sinks 

Developed automatic sprinkler 

system 

Collectors washed manually on a 

monthly basis 

Defective card replaced; heater. 

repaired 

None 

Changed operation schedule to 

use solar equipment more 

efficiently 

Replaced all CPVC with steel 

pipe ; installed hightemperature cutoff; installed 

larger pressure relief valve 

Replaced flowmeters; installed 

screens 

None 

Placed computer in £1 lterequipped, air-conditioned room 

Replaced f lowme t ers ; added 

turbine f lowmeters 

None 

Wooden supports added to prop up 

pipe 

Repaired damper motors 

None 
Table 2-4. Problems Encountered in DOE-Funded Field Tests (Concluded) 

Project Problems Corrective Action 

*Timeclock failures in data Isolated clockwith capacitors 

acquisition system 

Lexan stress failure and Collectors reglazed (July 1980) 

yellowing 

Vandalism None 

Failure of solar system Repaired (July 1980) 

microprocessor-based 

controller 

*Problems related to data acquisition equipment. 

the low-temperature field tests, including total costs, the reader is referred 

to Kutscher and Davenport (1981). 

'J%e future of solar energy in industrial process heat depends on a number of 

factors. Higher-cost fossil fuels certainly make solar energy more attractive. Interruption or curtailment of fossil-fuel supplies will have an even 

greater impact, and mass producing collectors could reduce solar energy costs 

substantially. Improvements in both the efficiency and reliability of collectors will also accelerate solar energy's implementation. It is hoped that 

continued research will lead to substantially lower collector and balance-ofsystem costs in the future. Cost studies have shown that tax incentives play a 

large part in bringing solar costs in line with what industry is willing to 

pay. And new financing schemes that involve leasing a collector array can 

increase the economic attractiveness of a solar system. 

Battelle Columbus Laboratories. 1977. Survey of the Applications of SolarThermal Energy Systems to Industrial Process Heat. Columbus, OH: 3 Vols. 

Dickinson, W. C.; Brown, K. 1981 (Aug.). Economic Analysis of Solar Industrial Process Heat Systems: A Methodology to Determine Annual Required 

Revenue and Internal Rate of Return. UCRL-52814. Rev. 1. Livermore, 

Fraser, M. D. 1977. Analysis of the Economic Potential of Solar Thermal 

Enerev w- to Provide Industrial Process Heat. C00/2829. 3 Vols. Warrenton, 

VA: InterTechnology Corporation. 

Krawiec, F.; et al. 1981. Energy End-Use Requirements in Manufacturing. 

SERIITR-733-790~. Golden, CO: Solar Energy Research Institute. 

Kutscher, C. F.; Davenport, R. 1981 (June). Preliminary Results of the 

Operational Industrial Process Heat Field Tests. SERIITR-632-385R. 

Golden, CO: Solar Energy Research Institute. 
Murphy, L. M; May, E. R. 1982 (April). Steam Generation in Line-Focus Solar 

Collectors- SERI/TR-632-1311. Golden, CO: Solar Enerev Research 

Institute. 

Turner, A. R.; Weber, J. C.; DeAngelis, M. 1981. A Geographic Market Suitability Analysis for Low- and Intermediate-Temperature Solar IPH Systems. 

SERI/TR-733-1194. Golden, CO: Solar Energy Research Institute. 

PART 11 

CON~PTUAL ZIESIGRJ 
SBCTIOH 3-0 

SOLAR IPE SUITABILITY ~YSIS 

In designing a solar energy system, the objective is to minimize delivered 

energy costs. To meet this objective, it is important first,to select the 

most favorable solar application. Some guidelines for selecting a favorable 

solar application are listed in Table 3-1 and discussed below. In the sections that follow, these factors will be quantified as part of a complete 

solar system design . 

Table 3-1. Factors Favoring the Use of Solar 

IPE Systems 

1. Environmental Factors 

High insolation 

High ambient temperatures 

Low pollution levels 

2. Process Factors 

Low-temperature processes 

Operations 7 days per week 

Heat demand peak during the day and in 

summer 

Built-in process storage 

3. Economic Factors 

High fuel costs 

Uncertain fuel supplies 

Available land or strong roof 

Available capital 

Federal, state, and local tax incentives 

Energy-intensive operations 

Conservation measures complete 

New plants 

4. Company Factors 

Management commitment 

Skilled plant maintenance 

Company engineering staff 

3- 1 ElWIRONMKKCAL FACTORS 

The intensity of solar radiation is an obvious factor in the delivered cost of 

solar energy. Figure 3-1 3hows average evels of global insolation on a hori- 5 zontal plane (10,000 kJ/m = 881 ~tu/ft ). This diagram is useful in an 

initial comparison of the heat output of horizontally mounted, nontracking 

collectors and solar ponds in various locations. Figure 3-2 shows average 

levels of direct-beam radiation in a plane facing the sun. The energy output 

of tracking collectors can be correlated to the values on this map. (More 


accurate methods of predicting the energy outputs of collectors are described 

in Sec. 6.0.) Note that collectors located in the Southwest will intercept 

about twice as much energy as the same collectors located in either the Northeast or the Northwest. 

Ambient temperature affects the performance of a solar energy system in two 

ways. First, high ambient temperatures reduce the thermal losses that can be 

associated with solar collectors and related equipment both during operation 

and overnight. Second, high ambient temperatures in winter permit the use of 

water as a heat-transfer fluid in the collectors without the need for a 

freeze-protection mechanism. As will be discussed in Sec. 7.2, water is the 

preferred energy transport fluid if freezing problems can be overcome. 

Figures 3-3 and 3-4 show average ambient temperatures; and Fig. 3-5, the 

number of days per year that minimum temperatures reach OOC. 

High concentrations of atmospheric pollutants can affect the life and performance of solar systems. For example, near seacoasts, chlorides can corrode 

aluminum surfaces. Chemicals emitted from cooling towers can form hard-toremove precipitates on collector surfaces. Smog can reduce the intensity of 

radiation. The effect of atmospheric pollutants on solar collectors can be so 

severe that a materials test program is strongly recommended. This test program would involve placing representative samples of collector materials in 

the vicinity of the collector field for at least six months before proceeding 

with construction of the entire system. Determining the effects of washing 

procedures should be an integral part of the exposure test, as well. 

The test program need not be elaborate or expensive. Reports by Morris (1982) 

and DSET (1981) describe formal test programs conducted in conjunction with 

the DOE industrial field test program. While short-term testing does not 

guarantee the long-term durability of collector components, poor test results 

can prompt further investigations to determine the cause of the problem. As 

more and more solar projects come on line and operational experience 

increases, the need for material test programs will decline. 

Pollution regulations that limit the use of conventional fuels could provide 

an impetus for exploring the feasibility of solar applications. This would 

apply only where the pollution does not affect solar system components 

adversely, however. 

3.2 PROCESS FACTOBS 

The efficiency of a solar system decreases, and its installed cost tends to 

increase, as operating temperature increases. Thermal storage, which can 

greatly increase the contribution of solar energy to a process, is also more 

economical at lower temperatures. These are good reasons to adapt the industrial process to accept heat from a solar system operating as close as possible to a required process temperature. Heating washwater and preheating 

boiler make-up water are examples of particularly favorable solar applications. Steam is used almost universally in industry to provide indirect 

heating. A solar system can be designed to produce steam, if doing so would 

cost less than retrofitting the industrial process to accept solar heat 

directly (as pressurized hot water, for instance). 



Knowing the schedule of an industrial process is important in determining the 

volume of thermal storage that will be required to expand the fraction of process heat beyond that supplied directly from the solar system. (Some industrial processes provide built-in heat storage.) A seven-days-per-week 

schedule minimizes the need for storage capacity, as do heating requirements 

that peak during daylight hours and summer months. Storing solar heat as hot 

water at temperatures up to 121'~ (250'~) appears to be cost-effective. At 

higher temperatures, a low-vapor-pressure oil/rock system can be used, but it 

is more costly. 

Difficulties have been encountered in fully utilizing available solar energy 

in some IPH projects. In selecting a process, control modifications required 

to maximize solar energy usage must be considered. For example, a boiler or 

furnace may have to be modified so that it operates at a lower firing rate. 

Also, it is best to make the connection between the solar system and the 

industrial process as flexible as possible. For example, dedicating a solar 

system to one of several parallel process lines would result in poor utilization if that one line were shut down. To minimize piping costs and thermal 

losses, a process close to the collector field site is preferable. An interface location that permits most of the piping to be run indoors minimizes heat 

losses and weather degradation problems: 

Sufficient vacant land for siting the collectors, or a strong roof, is a major 

requirement. Moreover, planning a solar system for a new plant is easier than 

retrofitting a system to an existing plant, in terms of locating the collectors and integrating collectors with the structures and the process. 

3.3 ECONOMIC FACTORS 

The dependability of the fuel supply and the stability of the cost of solar 

heat are attractive features. Figure 3-6 illustrates the dramatic increases 

that have occurred in the costs of conventional fuels in recent years. In 

early 1981, distillate fuel oil cost about $l.lO/gal ($7.50165). Even if cost 

increases exceed the rate of inflation by only 3% per year, the real cost 

would almost double in 20 years. After deregulation, natural gas prices can 

be expected to climb even higher. 

Solar energy systems are capital-intensive. A company must have sufficient 

financial resources to fund even the most favorable solar project. Federal, 

state, and local tax incentives, however, can defray some of these up-front 

costs. Currently, industrial solar system purchasers are entitled to a 25% 

federal tax credit. California is one state that offers an additional 25% 

state tax credit. Innovative financing schemes by which a holding company 

owns and operates the solar system and sells solar heat are becoming available 

and can help overcome problems encountered in obtaining capital (see 

Sec. 10.0). 
sin TR-1356 

t' 

Coal / ,.' Natural Gas 

Industries for which energy represents a large fraction of their processing 

costs are the ones most likely to consider alternative energy sources. Such 

energy-intensive industries are also likely to first exhaust economical energy 

conservation measures before converting to other fuels. 

000. 

A solar energy system can be quite complicated compared with a typical package 

boiler, and it will require maintenance. However, designing and managing a 

solar system is often within the capability of the engineering work force in 

residence at many medium-sized plants and certainly within the capabilitiesof 

a corporate engineering staff. On-site maintenance helps to ensure the 

reliability of the solar system, a& in-house system design can reduce design 

and installation costs significantly. Material presented in this handbook 

will acquaint engineers with aspects of solar system design that they might 

not have encountered in previous work and provide them with many of the tools 

they will need to design, build, and operate a solar system. 

I 1 1 I I 

3.5 EXAMPLES OF FAVORABTJ3 SOW TEEWKL APPLICATIONS 

1960 1965 1970 1975 1980 

Year 

Figure 3-6. Real Costs of Conventional Fuels 

(Constant 1978 dollars) 

DeAngelis (1980) summarizes numerous surveys and techniques that have been 

used to determine which industrial markets have the greatest near-term 

potential for economical solar thermal applications. Industries identified 

include food processors; meat packers (including poultry); manufacturers of 

concrete blocks, bricks, and paving mixtures; wood finishing and paper plants; 
and fabric producers. However, as the Case Study Program at SERI has illustrated (Hooker et al. 1980; May et al. 1982), many suitable applications are 

lost after they are classified under broad industrial categories. Plants that 

dewater crude petroleum or produce specialty chemicals, aluminum cans, or 

metal castings are good prospects for solar applications. Plant engineers 

should therefore use all available information to evaluate their plants to 

determine the applicability of a solar IPH system. 

3-6 REFERENCES 

DeAngelis, M. 1980 (Dec.). "Market Surveys: Potential for Solar IPH 

Applications." Presented at the Solar Industrial Process Heat Conference, 

Houston, Texas. 

DSET Laboratories, Inc. 1981. Final Report: Industrial Process Heat 

Environmental Exposure Program. Prepared for the Solar Energy Research 

Institute under Subcontract XH-0-9087-1. 

Hooker, D. W.; May, E. K.; West, R. E. 1980 (May). Industrial Process Heat 

Case Studies. SERIITR-733-323. Golden, CO: Solar Energy Research 

Institute. 

May, E. K.; Green, H. J.; Schlepp, D. R. 1982. Solar Industrial Process Heat 

Case Studies. SERI/TR-733-1024. Golden, CO: Solar Energy Research 

Institute. 

Morris, V. L. 1982 (Jan.). Final Report on Solar Collector Materials 

Exposure at IPH Site Environments. Vol. 11. SAND 81-7028111. 

Albuquerque, NM: Sandia National Laboratories. 
SECTION 4.0 

IPB SPsTm CO~IGUBBTION 

For the most part, the form in which the energy is to be used determines the 

nature and configuration of the components that will make up an IPH solar system. Since industrial process energy requirements are primarily met by hot 

air, hot water, and steam systems, representative configurations of these 

three groups are presented in this section. Each system description should be 

general enough to permit the system designer to identify major components and 

their functions easily. Simple schematics of the systems are provided to 

facilitate this understanding. 

4.1 HOT AIR SYSTEMS 

Industrial processes that require hot air can be configured to utilize solar 

energy as shown in Figs. 4-1 and 4-2. Figure 4-1 illustrates a typical direct 

hot-air system. Ambient air or process return air is circulated through solar 

collectors that in turn provide heated air to the process. The hot air can be 

used at the temperature supplied by the collectors or can be further heated by 

an auxiliary heater before it goes to the process load. This is a direct hot 

air system because the air provided to the process is the same as that heated 

by the solar collectors. 

Hot Air 

5 TO o 0 

Process 

Ambient I A - 

Air 

Pigure 4-1. Direct Hot Air Solar System 
Hot Air * To 

Process 

WaterTo-Air 

Heat 

Exchanger 

Ambient - d 

Air 

Figure 4-2. Water-To-Air Solar System 

A rock-filled storage tank can be plumbed along with the solar collectors, and 

heated air from the collectors can be routed through the rock bin when energy 

is not needed by the process. Heating the rock bin when there is no load permits discharge of this stored energy later, when the process requires heat but 

the solar collectors are not operating. An alternative to the direct hot air 

system is to use liquid collectors and a liquid-to-air heat exchanger, as 

shown in Fig. 4-2. Thermal storage can be provided by a water-filled tank. 

This system reduces parasitic power requirements, but the freeze protection 

problem must still be addressed. 

4.2 HOT UATER SYSTEMS 

Solar systems to service industrial processes that require hot water can be 

configured as shown in Figs. 4-3 and 4-4. A direct hot water system is shown 

in the first figure, and an indirect system is shown in the second. In the 

direct system, process water is the working fluid in the solar collectors. 

The indirect system has two separate fluid loops and usually employs an antifreeze solution or a heat transfer oil in the collector loop. 

When water is the heat transfer fluid, freeze protection is afforded by 

draining the water (either through a drain or back to the solar tank) or, in 

mild climates, by circulating warm water periodically during the night when 

the system temperature approaches freezing. Electrical heat tracing is not 

recommended because a power failure on a cold night could significantly damage 

the system. 

Figures 4-5 through 4-7 show typical freeze protection configurations for 

domestic hot water systems using water in the collector loop. These can also 

be used for some IPH applications. 

Figure 4-5 illustrates a direct hot water system with drain-out freeze protection. Because the collector loop operates at city water pressure, solenoid 

' valves are needed to isolate the piping from that pressure when the system has 

to be drained. Figures 4-6 and 4-7 present drain-back systems. In one case, 

the solar tank is unpressurized, and the collector water drains back into that 

tank. In the other design, a pressurized tank (at line pressure) is isolated 

from the solar loop, and a small holding tank is required to contain extra 

collector fluid. Neither system requires a solenoid valve and will drain 

whenever the pump stops. An excellent discussion of the advantages and disIndirect systems can diminish collector freezing problems because they employ 

a fluid with a lower freezing point than water. For process loads above 

10oOc, indirect systems allow the collector loop to operate at lower pressures. A direct hot water system requires pressurization of the entire collector field to prevent boiling. An indirect system can employ a fluid with a 

lower vapor pressure in the collector loop; pressurization is not required. 

Corrosion problems can also be minimized with an indirect system employing a 

heat transfer fluid with a corrosion inhibitor. Because the indirect system 

requires an additional heat exchanger and a heat exchanger fluid, it is recommended only if freeze protection, corrosion, or loop pressurization concerns 

preclude the use of a direct hot water system. Commonly used heat transfer 

fluids are glycol solutions, hydrocarbon-based fluids such as Caloriam and 

Therminolm, and silicones (see Sec. 7.2.). 

Liquid collectors are designed to use water in direct systems; generally, 

liquid collectors are also used in indirect hot water systems. Theoretically, 

air collectors could be used in conjunction with an air-to-water heat 

exchanger, but the poor heat transfer and the increased power needed to transport the air make this option a poor choice. Liquid-based flat-plate collectors, evacuated-tube collectors, and parabolic troughs are all more 

appropriate. 

A check valve is needed in the collector loop for indirect and drain-back 

direct systems to prevent thermosiphoning (reverse flow caused by natural convection) when the pump is not operating. An expansion tank must also be 

attached to the collector loop in indirect systems to allow the working fluid 

to expand as it is heated. Isolation valves, drains, and filters must be 

installed as in other piping systems. 

4.3 STEAM SYS~ 

Steam is industry's most common heat transport medium for low-temperature 

(generally less than 200°c), indirect process heat. Industries have gained a 

great deal of operating experience in using steam, and package steam boilers 

Figure 4-7. Indirect Hot Flater System with Drain-Back to Bolding Tank and 

Pressurized Storage Tank 

have proven to be extremely reliable. Generating steam by means of a solar 

system involves a fairly simple plant interface that feeds directly into a 

plant's steam distribution system without necessitating changes in existing 

processing practices. 

Flash-steam and unfired-boiler solar energy systems utilizing line-focus concentrating collectors have already been constructed to supply industrial process steam. A third and promising option that involves generating steam 

directly in line-focus collector tubes is under investigation at SERI (Murphy 

and May 1982). 

4.3.1 Flash-Steam System 

A'schematic of a flash-steam system is shown in Fig. 4-8. Water at a pressure 

high enough to prevent boiling is circulated through the collector field and 

flashed to steam across a throttling valve into a separator. This constatlt 

enthalpy process converts the sensible heat of the water into the latent heat 

of a two-phase mixture at the conditions prevailing in the separator. Steam 

qualities (the fraction of total flow that is vapor) are usually less than 

10%. The steam is fed into the plant utility system and the liquid is 

recirculated. Boiler feed water make-up is injected into the pump suction to 

maintain the liquid level in the separator. 
Using water as a heat transfer fluid simplifies the construction of a flashsteam system, since it is an open-loop process. However, although water is an 

excellent heat transport medium, freezing problems can occur. Therefore, the 

freeze protection mechanism must be carefully designed and controlled to 

ensure that a minimum amount of heat ' is supplied to the water to prevent 

freezing . 

The disadvantages of the flash-steam system are associated with the steamgeneration mechanism. Collector temperatures must be considerably higher than 

the steam delivery temperature to obtain reasonable steam qualities downstream 

of the throttling valve and to limit the water recirculation rate (the ratio 

of collector flow rate to steam production rate or the reciprocal of steam 

quality). But higher temperatures reduce the collectors' efficiency. In 

addition, the pressure drop across the flash valve, which can be considerable, 

must be overcome by the circulating pump. Various control schemes have been 

suggested to reduce pumping power requirements by modulating the flash 

valve; these are described in Sec. 8.0. 

Moreover, the ra id rise in the vapor pressure of water at temperatures above g about 177'~ (350 F) limits the steam pressures that can be generated by this 

method to approximately 2 MFa (305 psig) at acceptable levels of required 

electrical power. 

Steam * To 

Process 

- 

Flash Tank 

Valve 

Reci rculated 

Water 

1' 

1 1 - - Feedwater 

Figure 4-8. Flash-Steam Solar System 
4.3.2 Wired-Boiler System 

A schematic of an unfired-boiler steam system is presented in Fig. 4-9. A 

heat transfer fluid is circulated through the collector field and steam is 

generated in an unfired boiler. A variation of the system shown incorporates 

a preheater in the water make-up line, which increases system cost but also 

reduces the inlet temperature to the collectors. Water could be circulated in 

the collector loop, but the fluid generally selected is a low-vapor-pressure, 

nonfreezing hydrocarbon or silicone oil. Using such an oil overcomes the disadvantages associated with water (high vapor pressure and freezing) and accommodates energy storage, but certain characteristics of these oils cause other 

problems (see Sec. 7.2). Generally, precautions must be taken to prevent the 

oil from leaking out of the system, which could result in a fire. In addition, the oils are expensive and have poorer heat transport properties than 

water. They are extremely viscous when cold, and a positive displacement pump 

is sometimes needed to start the system after it has cooled down. 

The unfired boiler itself is an expensive item requiring alloy tubes for corrosion protection, and it is an additional resistance to heat flow. As in the 

flash-steam system, the collectors must operate at a temperature considerably 

above the steam delivery temperature. Because the process steam must be 

maintained at a certain temperature, the solar-produced steam is delivered at 

a variable flow rate. The collector outlet temperature can be held constant 

by varying the flow rate through the collectors (see Sec. 8.2.1) . 

Existing N 

m Parabolic Trough Equipment 2 0 Solar System 1 Check r---- - L I 

t - . I 0 I 

Steam Boiler 

Heat Transfer 

Fluid Loop 

Expansion Tank 

n I

Circulating 

Pump 

I plant I 

Figure 4-9. Unfired-Boiler Steam-erating System 
4.3.3 Direct Steae Generation 

Direct steam generation in the receiver tubes of a line-focus collector is an 

attractive concept because the average collector operating temperature would 

be near the steam delivery temperature and because the phase change reduces 

the required water flow rate through the circulating pump. The system 

schematic would be similar to that of the flash-steam system but without a 

flash valve. The disadvantages of the concept are associated with an 

incomplete understanding of the boiling mechanism and possible operating 

instabilities. Investigations by Murphy and May (1982) and Pederson and May 

(1982) validated the attractiveness of the concept. An experimental program 

has been proposed to test the system and to validate analytical predictions of 

performance. 

When solar energy supplies only a small fraction of the process load, storage 

is generally not warranted unless the collectors might otherwise be idle for 

significant periods of time (e.g., during weekend plant shutdowns or at 

night). Also, if a large solar fraction is desired or a considerable load 

occu<s at night, a storage system will be needed. 

4.4.1 Bot Water Storage 

' Four possible configurations for hot water storage are shown in Figs. 4-10, 

. 4-11, 4-12, and 4-13. All four figures illustrate direct systems that 

incorporate process water passing through the collector array. (Freeze protection occurs by means of drain-back or recirculation). In any of them, however, a heat exchanger could be placed between the collectors and the storage 

tank, creating a separate collector loop containing a nonfreezing fluid. 

Load 

Supply 

I Mixed 1 

Load 

Return 

Figure 4-10. Four-Pipe Storage Configuration 

Variable 

~-l"o,"me I 

Load Supply 

-1 

I I 

I I 

Load Return 

1 I 

I I I Variable Volume 

Cold Tank 

(Not Needed for 

Open Load Loops) 

Figuxe 4-13. Variable-Volume Storage Configuration 

Figure 4-10, a four-pipe storage system, is the most comon configuration and 

is usually found in solar space heating/domestic hot water systems. The tank 

has two inlets and two outlets, one pair each for the collector loop and the 

load loop. The two loops operate independently of each other. The collectors 

can supply heat to storage whether or not the load is extracting heat from 

it. Conversely, heat from storage can be supplied to the load with or without 

available solar energy. In applications where the difference between load 

supply and return temperatures (AT) is small (e.g., space heating systems) or 

where the load is on only a small percentage of the time the collectors are 

operating (e.g., domestic hot water), a four-pipe system is appropriate. However, if the load AT is large and the load is fairly constant during the day, 

the collector inlet temperature will be higher than it needs to be. This 

occurs because the collector inlet water comes from the mixed storage tank at 

a temperature close to that of the load supply. Using a thermocline storage 

tank would solve the problem, but such a thermocline can be difficult to 

achieve in water tanks because the high collector flow rate disrupts stratificationThe configuration of Fig. 4-11, a two-pipe storage system, resolves this 

difficulty by allowing cold load return fluid to be fed directly to the collectors. Since many IPH applications are open loop (e.g., clean-up water), 

this temperature will be the same as city make-up water-considerably below 

the load supply temperature. If the load operates during a good portion of 

the day, using make-up water in the collectors will 'increase their efficiency. At the same time, the top bypass of the tank allows the hottest water 

to be supplied directly to the load without mixing it with the cooler water in 

storage. The collector and load loop do not operate quite as independently in 

this arrangement as they do in the four-pipe system. Storage can be charged 
ssn (a(b TR-1356 

without a load, or storage can be discharged if the collector loop is not 

operating exactly as in the four-pipe system. However, energy cannot be 

directly supplied from storage at the same time the collectors deliver energy 

to the load unless the collector flow rate is less than the load flow rate. 

In some cases, this could result in higher storage temperatures than 

necessary. Adding an extra pump and valve would permit dual delivery to the 

load by lowering the collector flow rate, but this would somewhat reduce the 

efficiency of the collector. An increase in collector efficiency occurs only 

when the load is operating during periods of collection. 

The performance of the two-pipe system configuration could be improved significantly if the tank could maintain a perfect thermocline. As we mentioned 

earlier, however, this is very difficult. A way to achieve some stratification is shown in the multiple-tank system of Fig. 4-12. Using multiple tanks 

(in this case, two), the collector inlet temperature can be kept below the 

load supply temperature during no-load conditions. Unlike the variable-volume 

tank system, these simple, mixed storage tanks require no level control. As 

more tanks are used, performance comes closer to a perfect thermocline. However, multiple tanks increase system cost and exacerbate heat-loss problems. 

If the process load profile indicates that the collectors will be operating 

for substantial amounts of time during which there is no load (e.g., load only 

from 12: 00 noon to 8:00 PM, or the plant is shut down on weekends), collector 

performance can be most effectively increased by means of the variable-volume 

system shown in Fig. 4-13. This is a step up in complexity from the two-pipe 

system that increases collector efficiency even if the load is not operating. 

Essentially, variable-volume storage tanks permit a load to be run all day as 

far as the collector loop is concerned. For closed-loop load applications, 

two variable-volume tanks would be used-one cold and one hot. If the load is 

not on during the day, water is pumped from the cold tank through the collectors to the hot tank. If load is needed when the collectors are shut down, 

the hot water is taken out of the hot tank, and if the load loop is open, the 

cold tank is not needed. Make-up water can be circulated through the collectors during the day to charge the hot tank. In any case, the collector 

array is always supplied with the coldest possible water whenever it is 

operating, regardless of whether the load is on or off. A load-loop bypass 

line permits closed-loop flow between the collectors and the hot tank to 

charge the tank at temperatures above those of the load supply during long, 

no-load periods when the hot tank becomes full. 

Which configuration to choose depends on the application. The four-pipe 

storage system is simple to control in any application and will perform very 

well at a low-load AT. A two-pipe storage system performs better, but the 

problem remains of how best to control the collector flow when it is necessary 

to supply load from the collectors and storage simultaneously. The variablevolume tank configuration has the highest performance potential, but since the 

total amount of water supplied to the tank should equal the required amount of 

load water, different collector flow rates are needed at different times of 

the year (a result of variations in lengths of day and in collector operating 

times). System performance would be less than ideal on partly cloudy days 

because a preset flow rate would be lower than optimum for those days. 
4.4.2 Storage for Steam Sgsteas 

The hot-water storage systems shown would also be appropriate for steam systems using unfired boilers, except that the collector fluid would be oil and 

the load supply and return would connect to the unfired boiler. Oil storage 

is used because of the high pressures that would be encountered with water 

storage. To maximize performance, a thermocline tank can be included that 

incorporates a mixture of oil and rocks (Fig. 4-14), or a system with two 

variable tanks can be used (Fig. 4-15). 

In an oil system, a large AT can exist on the load side between the make-up 

water and steam supply temperatures. Because most of the energy delivered to 

the load is in the form of latent heat from boiling water, the make-up water 

flow rate in a steam system is relatively small. As a result, the temperature 

of the oil exiting the unfired boiler does not come very close to the make-up 

water temperature, and the temperature gradient that can be achieved in a 

thermocline tank or between two variable-volume tanks is not as great as would 

be expected. Moreover, the relatively flat efficiency curve of a parabolictrough collector, which would be used in a steam system, diminishes the 

advantage of temperature stratification. 

A recent, unpublished study conducted by James Leach at SERI provided some 

interesting results. The study compared various storage schemes for large 

(25-Wt), unfired-boiler IPH systems using projected, parabolic trough efficiency curves. Leach used the SOLTPH computer program to compare configurations on the basis of annual energy delivery. Figure 4-16 presents performance data for two-tank (variable-volume) systems (which performed like a 

thermocline tank) compared with that of a mixed-tank system. Below solar 

fractions of about 40%, there is no difference in performance between the systems or between them and a system with no storage. Above 40X, the energy 

delivered by a two-tank system exceeds that of a mixed-tank system by only 

about 5%. This graph was done for a daytime (6 : 00 AM to 6: 00 PM) load. But 

even for a 24-hour load, the performance increase resulting from the thermocline was relatively small. 

Dual-medium rock/oil is the most common method of thermocline storage in an 

oil system. However, it is still in the development phase (see Sec. 7.0). 

Using two variable-volume tanks is certainly not beyond the state of the art, 

but could be more expensive than the single thermocline tank. Because of the 

cost and uncertainties involved in achieving a storage-temperature gradient 

and only a minimal increase in performance, however, a simple mixed-storage 

tank is probably sufficient for present-day, unf ired-boiler applications. 

In connection with the storage system study, note in Fig. 4-16 that the plot 

of energy delivery versus collector area is linear until, when excess energy 

begins to be collected, the curve deviates abruptly. This is characteristic 

of a steam system. Because the steam is supplied at a constant temperature, 

the storage tank or collector outlet must be kept to that temperature to 

deliver energy to the load. Preheating is not a significant fraction of the 

load. Increasing collector area and solar fraction results in greater water 

flow rate and steam production and does not appreciably affect the inlet or 

outlet temperatures of the collector. Thus, array efficiency stays constant 


and energy delivery rises linearly as collector area increases until a point 

is reached at which excess energy is collected. After that point, efficiency 

drops as more and more energy is discarded. 

In hot water systems, the most efficient way to use the collectors is to preheat all of the load water. Thus, the load flow rate is constant; as collector area increases, the solar water temperature delivered rises as well as 

collector outlet and storage tank temperatures. This, however, reduces the 

efficiency of the collector. As a result, the plot of energy delivery versus 

collector area diverges from a straight line at relatively low solar fractions. For a given load temperature, however, the hot water system will perform better than the steam - 

system using the same collectors, because it can -- deliver energy more efficiently ,at lower collector outlet temperatures and it 

also displays lower inlet temperatures. 

Flash-steam systems are ordinarily considered to be nonstorage systems, 

because of the cost of storing pressurized water. (It should be noted, however, that any high-temperature storage system degrades the performance and 

economics of a solar steam system.) Using an intermediate steam/oil/water 

loop for thermal storage in an open-loop steam system greatly increases system 

complexity and cost. 

A solar system may interface with the process to which it supplies heat either 

in series or parallel with an existing or auxiliary boiler or heater. In a 

series configuration, heat from the solar system is used to preheat the process working fluid, which then goes to the auxiliary heat source. If the 

solar system cannot heat the process fluid to the required temperature, the 

auxiliary heat source supplies the final boost to the load temperature. If 

the energy from the solar system is available at a higher temperature than 

that required by the load, a tempering valve mixes cool, incoming process 

fluid with solar-heated fluid to achieve the desired load temperature. A 

series configuratxon is used in direct systems and 'is preferred for indirect 

hot water and hot air systems because it provides a lower average collector 

temperature than does a parallel configuration, prompting higher collector 

efficiency. Series configurations cannot be used in steam systems except for 

preheating the feedwater, a small part of the load. In a series configuration, the backup heater must modulate to accommodate varying solar power 

input. Although boiler efficiency can decline in combination with low firing 

rates, overall fuel savings increase when the backup hot water heater is 

modulated over as large a range of firing rates as possible, in order to 

increase collector efficiency (see Appendix A). 

In a parallel configuration, the solar system must produce the desired load 

temperature before it can deliver energy to the process. Because heat cannot 

be delivered to the process at a temperature lower than that of the load, the 

storage tank temperature remains at or above load temperature at all times; in 

open-loop applications, the collector inlet temperature usually is higher than 

it would be in a comparable series system. Parallel systems can be used in 

closed-loop applications where the return temperature can vary (for example, a 

space heating system), because under those circumstances a series arrangement 

could heat storage with auxiliary heat, thereby lowering collector efficiency. 
A series configuration with storage bypass capability is possible, however. 

Parallel systems are also used in saturated steam production, where the solar 

system supplies steam directly to a plant's steam main. Because most of the 

heat transfer in a steam system takes place at the steam temperature, parallel 

systems are ideal for such applications; the penalty associated with parallel 

systems in lower- temperature applications is not a factor here. 

In any solar system/process interface, the designer should take care to provide for complete isolation of the solar system. In this way, any solarrelated problems that might arise will not interfere with plant process operations. 

Argonne National Laboratory. 1980 (Sept.). Interim Reliability and Materials 

Design Guidelines for Solar Domestic Hot Water Systems. SOLAR/0907-80/70. 

Argonne, IL: Argonne National Laboratory. 

Murphy, L. M. ; May, E. K. 1982 (Apr .). Steam Generation in Line Focus Solar 

Collectors: A Comparative Assessment of Thermal Performance, Operating 

Stability, and Cost Issues. SERI:/TR-632-1311. Golden, CO: Solar Energy 

Research Institute . 

Pederson, R. J.; May, E. K. 1982 (Mar.). Flow Instability During Direct 

Steam Generation in a Line-Focus Solar Collector System. 

SERI/TR-632-1354. Golden, CO: Solar Energy Research Institute. 

SECTION 5.0 

Basically, solar collectors are heat exchangers that transfer the radiant 

energy of incident solar radiation to the sensible heat of a working fluid-- 

liquid or air. Many different types of solar collectors can supply energy to 

IPH systems. In this section, we describe several of these types of collectors, define the significance of a collectorts instantaneous performance and 

how it is measured, and provide a method of selecting an appropriate collector 

for a particular IPH system. 

5.1 TYPES OF COLLECTORS 

A substantial number of different kinds of solar collectors have been proposed 

for solar industrial process heat systems, partly because of the wide range of 

process temperatures found in industry. However, the major types of collectors used thus far in industrial process heat field tests are flat plates, 

evacuated tubes, and parabolic troughs. These three kinds of collectors, 

their components, and potential or suggested improvements are described in the 

following subsections. We also describe in more general terms other types of 

collectors that may be utilized in IPH systems in the future. 

5.1.1 Flat-Plate Collectors 

Flat plates are the most commonly used solar collectors. They can supply hot 

air or hot water at temperatures ug to about 90'~ (200°~), although operating 

temperatures above about 70'~ (160 F) diminish the relative efficiency of the 

system. The advantages of these collectors include the lack of moving parts, 

durability, and capability of collecting both direct and diffuse radiation. 

Flat-plate collectors can be installed as a large, flat array atop a sloping 

roof or mounted in a sawtooth fashion on the ground. In the latter case, collector spacing mst be sufficient to minimize row-to-row shading losses (see 

Sec. 6.3). Although it is possible to mount collectors flat on the ground, 

the savings in support costs would be outweighed by the losses in available 

irradiation at U.S. latitudes. The array should be oriented to face within 

30' of south to maximize incident irradiation. 

5.1.1.1 Components 

The flat-plate collector consists of the following basic components (shown in 

cross-section in Fig. 5-1) : 

Absorber plate--usually copper, steel, aluminum, or plastic; surface covered with flat black paint or a selective coating to maximize absorption 

and minimize reradiation. 
Fluid 

Figure 5-1. Cross Section of Typical Flat-Plate Collector 

Flow passages--liquids usually flow through tubes that are attached to, 

or an integral part of, the absorber plate. Air flows above or below the 

plate, and heat transfer surface area is maximized by means of fins, 

slots, or metal screening. 

Cover plate(s)--one, two, or three transparent covers, made of glass or 

various plastic materials, reduce convective and radiative heat losses to 

the outside air. 

Insulation--to reduce heat losses from the back and sides of the collector, typically fiberglass or isocyanurate. 

Enclosure--a box to hold collector components together and protect them 

from the weather. 

In a typical liquid collector employing a metallic absorber, tubes are spaced 

several inches apart with the absorber surface between them acting as "fins" 

that absorb the heat and conduct it to the tubes. Copper, aluminum, and steel 

are all used for absorber plates. Copper has the highest conductivity, and 

although it is expensive, it is the most corrosion-resistant material. If a 

low thermal-conductivity material such as plastic is used for the absorber 

plate, the flow passages must be designed to maximize wetted surface area. 

Copper tubes are often welded, soldered, or clamped to copper plates or 

clamped to aluminum plates The thermal conductance of the bond is critical _ 

and can vary from 5700 W/m i K (1000 ~tu/hr-ft~~~) for a well-soldered tube to 

2 less than 30 W/m K (5 ~tu/hr-ft~~~) for a poorly clamped one. A better technique is to incorporate a tube pattern into the plate during manufacture. 
Tubes can be routed through the collector in parallel paths from an inlet to 

an outlet header, or a single tube can be routed in a serpentine fashion. The 

latter technique eliminates the possibility of header leaks and ensures uniform flow, it but also increases pressure drop. If a drain-down freeze protection system is used, the flow passages must be easy to drain. 

Air collector absorber plates need not have high thermal conductivity because 

the air comes in contact with the entire surface. Flow can be above or below 

the plate, but the latter tends to result in less thermal loss through the 

glazing. An air system eliminates freezing and boiling problems, and leaks 

are not as troublesome as they are in a liquid system. However, fan power is 

significant, large ducts are required, and greater storage volume is needed, 

The type of coating on the collector absorber plate determines the fraction of 

incident solar energy absorbed. Flat black paint is the most commonly used 

coating. It has an absorptance, a, of between 0.92 and 0.96; that is, it 

absorbs between 92% and 96% of the incident short-wave solar radiation. It is 

also quite durable. However, a hot absorber plate will radiate long-wave 

energy to the cooler environment to an extent that depends on its emittance, 

E- Flat black paint has a high a, but its E is also high--on the order of 

0.88- So-called selective surfaces have a high short-wave a but a low longwave &; thus, they retain heat better. .Black chrome, the most popular selective surface, has an a of from 0.92 to 0.98 and an E of about 0.1. Selective 

surfaces improve the performance of the collector but increase the cost, and 

their long-term durability is still questionable, especially at higher temperatures. An important characteristic of any absorptive coating is that it 

adheres well and does not peel or otherwise deteriorate during high-temperature stagnation (no-flow) conditions. 

The most commonly used cover material is glass. A 3.2- (1/8-in.) sheet of 

window glass (0.12% iron content) has a transmittance to solar radiation (at 

normal incidence) of 85% (? = 0.85) Water white glass (0.01% iron) has a 

T of 0.92. Glass has the added advantage of being practically opaque to any 

long-wave radiation given off by the absorber plate. If it is tempered, it is 

also highly durable. Deterioration is negligible, even over very long periods 

of exposure to intense ultraviolet radiation. Various plastic materials are 

also used for collector glazings and are cheaper and lighter than glass. 

Because they come in thin sheets, they often also have a higher transmittance, 

However, they often do not trap thermal radiation as well as glass and are 

generally not as durable. Degradation from ultraviolet radiation or high temperatures can be severe. Tedlarm, for example, should not be used as an inner 

glazing in a two-cover collector because of its susceptibility to thermal 

degradation. The number of glazings depends on the application and on a costversus-performance trade-off. A single-glazed collector with a selective 

coating will often outperform a double-glazed one with a nonselective coating. 

Generally speaking, more covers are needed as the difference between the temperature of the collector plate and the ambient temperature increases. 

The collector enclosure is ordinarily made of steel, aluminum, or fiberglass 

and supports the absorber plate and covers. Ideally, it would expand and contract along with the components as temperatures change, although adequate 

clearance (around a glass cover, for example) and proper gaskets must be provided for differential expansion. The frame should be designed to cast almost 
no shadow on the absorber plate, and the aperture area should be at least 85% 

of the gross area. Sealing compounds and gaskets should be capable of withstanding stagnation temperatures without outgassing, and they also must be 

capable of withstanding thermal cycling. Various types of insulation can be 

used in collectors to prevent heat losses from the back and sides. The insulation should not outgas under stagnation conditions, because such gases could 

coat the inside of the glazing and greatly reduce transmittance. More information on flat-plate collector designs and on properties of the materials used 

in the collectors can be found in Franta et al. (1981). 

One recent improvement to the basic flat-plate collector involves treating the 

glass cover to reduce reflection; this method can increase performance by as 

much as 4%. Coatings on the inner glass surface to reflect the long-wave 

radiation (which would otherwise heat the glass) have also been used, although 

these can reduce transmittance as well. A honeycomb between the inner cover 

and the absorber plate can reduce both convective and radiative heat losses, 

but it usually also decreases optical efficiency at off-normal incident ., angles. Planar reflectors placed in front of a row of flat-plate collectors 

can increase annual energy collection by over 25%. However, many rows of 

solar collectors are usually needed for IPH applications, and the resulting 

shading of reflectors by adjacent rows greatly reduces the effectiveness of 

planar reflectors. 

5-1-2 Evacuated-Tube Collectors 

One way to reduce convective heat losses is with a vacuum between the glazing 

and the absorber surface. However, because a vacuum would cause a typical 

flat-plate collector to collapse, this techni ue is used in conjunction with a 

tubular design. Vacuums on the order of lo-' torr eliminate both convection 

and conduction losses. Because evacuated-tube collectors lose less heat to 

the environment than flat-plate collectors do, they can operate at higher temperatures-up to about 175'~ (350'~). Like flat plates, they can collect both 

direct and diffuse solar radiation and do not require tracking. However, 

because evacuated tubes can operate at lower insolation levels than flat 

plates, they can collect more energy on cloudy days. And because of the vacuum, the evacuated tube is much less susceptible to wind-induced losses than 

other types of collectors. Another advantage is that the selective surface is 

contained in a vacuum, which ensures greater stability and a longer life for 

the coating. 

The field layout of evacuated-tube collectors is similar to that of flat 

plates; either roof- or ground-mounting is acceptable. Insulated leaders are 

usually supplied with these collectors. Because of the fragile nature of the 

tubes, care should be taken to protect the array from vandalism. 

5.1.2.1 Components 

There are various types of evacuated tube collectors on the market. One 

design, shown in Fig. 5-2, employs three concentric glass tubes. Fluid flows 
Fluid-Out Fluid In 

Figure 5-2. Concentric Glass Evacuated-Tube Collector 

into the annular space between the inner and the second tubes and back out the 

inner tube. The annulus between the second and third (outer) tube is evacuated, and the outside of the second tube contains a selective coating. 

Another design (Fig. 5-3) employs only two concentric glass tubes; the space 

between them is evacuated, and the outer surface of the inner tube contains 

the absorptive coating. A metal fin conforms to the inside surface of the 

inner tube; attached to this fin is a metal U-tube, which carries the fluid. 

The U-tube readily acconnnodates thermal expansion, and glass breakage 

will not result in a leak. However, cases of copper oxidation caused by stagnation temperatures have been reported. Although the fin thickness is not 

highly critical to the performance of the collector, it is recommended that 

stagnation temperatures be avoided. A V-reflector is shown in Fig. 5-3. 

Reflectors in other shapes (such as CPC) can be used behind evacuated tubes 

and provide a small amount of concentration. 

The performance of evacuated-tube collectors can be substantially different 

from that of flat-plates at off-normal incident angles. As the sun angle gets 

lower, the effective gap between the tubes shrinks, thereby increasing the 

efficiency of panels without specular reflectors. The type of reflectors used 

has a large effect on offnormal performance, and although it is not evident 

from a solar noon efficiency curve, the effects of incident angle can give an 

evacuated tube an advantage in day-long performance, compared with flat 

plates. 
Heat Transfer 

Coated inner 

Glass Tube 

(Absorber) Serpentine Finned 

Tube 

Figure 5-3. Evacuated-Tube Collector Utilizing Metal Flm Passage 

Whereas flat-plate collectors typically are limited to operating temperatures 

under about 70'~ (160°F), evacuated-tube collectors can perform at temperatures over 120'~ (250'~). Evacuated-tube collectors are more fragile, however, and glass breakage has been a problem. In some cases, "shocking" a 

stagnating collector array with cold water has caused the breakage; in other 

instances, local thermal gradients during wet stagnation have been the cause. 

Therefore, evacuated-tube collectors should not be filled when they are hot 

and should not be allowed to stagnate when they are filled. The latter consideration dictates the need for a heat rejector for nondrainable evacuatedtube collectors. Field experience has shown that borosilicate glass is more 

durable than soda-lime glass in these applications. 

5.1.2.2 Improvements 

To improve the performance of evacuated-tube collectors, work is under way to 

increase their optical efficiencies. Higher-absorptance selective coatings 

are being developed for application to the glass surface. Higher-reflectance 

materials are also being investigated for the reflectors beneath the evacuated 

tubes. Manufacturers are also attempting to reduce costs by making longer 

tubes and developing tube/header arrangements that will also lessen installation costs. 
5.1.3 Parabolic Trounh Collectors 

Parabolic troughs are the best-developed line-focus concentrating collectors 

and have been used in several IPH field tests, Parabolic troughs can operate 

at temperatures up to about 300'~ (57o0I?), as the result of optical concentration effected .by the parabolic-shaped concentrator. Optical concentration 

reduces the absorber surface area relative to the collector aperture area and 

thereby significantly reduces thermal losses. However, this optical concentration requires the collector to rotate to follow the apparent motion of the 

sun, And because only direct solar radiation is concentrated by a parabolic 

concentrator, the diffuse component is lost. That loss can be made up by a 

tracking collector, however, as it intercepts extra direct solar radiation. 

One noteworthy advantage of parabolic trough collectors is the low pressure 

drop associated with these systems as fluid passes through a single, straight 

absorber tube. Also, overnight thermal losses are minimal because of the 

small amount of fluid in the parabolic trough's receiver (see Fig. 5-4). 

Parabolic troughs can be mounted on the ground or on a roof; the receiver 

tubes are horizontal. Because of 'the large point and wind loads associated 

with parabolic trough collectors and the necessity of a rigid support for 

accurate tracking, roof mounting can require expensive structural modifications. Flammable heat-transfer oils in high-temperature trough applications 

can also pose a fire hazard to the building. For these reasons, parabolic 

troughs are usually better suited for ground mounting. 

Figure 5-4. Typical Parabolic Trough Collector 
5.1.3.1 Components 

The parabolic concentrator reflects direct solar radiation to an absorber tube 

located at the focus of the parabola. As the absorber tube is heated by solar 

radiation, a fluid passes within the tube and withdraws the heat. The 

absorber - tube typically has a selective surface. To further reduce thermal 

losses and protect the surface, the absorber tube is usually surrounded by a 

cylindrical glass tube that reduces convective heat losses from the absorber 

tube. The receiver comprises the glass/absorber tube assembly. The parabolic 

concentrator is covered with a reflective material having a high specular 

reflectance. Three major types of reflectors have been used: polished aluminum sheets, aluminized plastics, and silvered glass. Polished aluminum has a 

specular reflectance of 0.75 to 0.80 when new, but it suffers from gradual 

reflectance loss as the aluminum weathers. Aluminized plastic films currently 

are the most widely used. The specular reflectance of these films is usually 

from 0.80 to 0.86 when new. The principal durability problem with aluminized 

films is the damage that results from scratching of the surface by airborne 

particles which, in turn, results in loss of specularity. 

To maintain the flux concentration along the receiver, the collector must 

track the sun in one axis. A drive assembly is required for this rotation. 

One drive assembly is usually sufficient for several collector modules driven 

together in one row. A drive string is typically 24 to 36 m (80 to 120 ft) in 

length. The drive assembly varies among the different parabolic troughs; some 

manufacturers use an electric motor and gearbox combination to provide for 

rotation, and others use hydraulic drive systems. 

Typically, several drive strings are connected in series up to about 150 m in 

length to comprise a AT string. To permit linear expansion of the receiver, 

flexible hoses are used to join the drive strings. These flexible hoses also 

allow for the movement of the absorber tube as the collector tracks during the 

day, and they are used to join the receivers to the headers at both ends of 

each row as well. Correct installation of flexible hoses is illustrated in 

Sec. 9.0, and header size and field plumbing are discussed in more detail in 

Sec. 7.0. 

The rotation of a parabolic trough is directed by a sun tracker. The sun 

tracker instructs the drive assembly when and in which direction to rotate the 

collector. Typically, one sun tracker is used on each drive string. Two main 

types of sun trackers are utilized--shadow-band (aperture-based) trackers and 

flux-line trackers. Shadow-band sun trackers are mounted on the concentrator 

and face the sun as they are tracking. Two sensors, one on each side of a 

separating shadow band, detect the position of the sun. When the collector is 

correctly pointed, the shadow band shades both sensors equally, and both sensor output signals balance. Flux-line sun trackers are mounted on the 

receiver. Sensors are also placed on each side of the receiver to detect the 

concentrated flux of the receiver. The collector is correctly pointed when 

both sensors are illuminated equally. When installed correctly, both types of 

sun trackers have been shown to exhibit excellent tracking accuracies 

(Gee 1982). 

Parabolic troughs are usually installed so that their axes of rotation are 

oriented either north-south or east-west. However, any orientation is suitable. The directional orientation of the troughs usually corresponds to the 
orientation of the land areas or rooftops on which the troughs are installed. 

The orientation has an impact on the sun's incident angle upon the tracking 

collector which, in turn, affects collector performance. Seasonal variations 

in collector output for north-south oriented troughs can be quite large. 

Three to four times more energy is delivered daily during average summer 

months than during average winter months, depending on the latitude and site 

weather patterns. Seasonal variations in energy delivery are much smaller for 

an east-west orientation, typically less than 50%, and are caused primarily by 

seasonal variations in the amount of available insolation. See Sec. 6.0 for 

more on the impact of seasonal output variations on the annual performance of 

parabolic troughs. 

A number of improvements to parabolic troughs are under development. Three of 

the most promisfng are silvered-glass reflectors, evacuated receivers, and 

antireflection-coated receivers. Figure 5-5 shows the annual performance benefit that is expected from these improvements as a function of the operating 

temperature of the trough. The performance shown (Normalized System Performance) is the ratio of the annual performance of an improved trough to the 

annual performance of an unimproved one (Gee et al. 1980). 

Silvered-glass reflectors perform significantly better over all operating temperatures, and they are expected to replace polished aluminum and aluminized 

acrylic reflectors. Evacuated-tube receivers also enhance performance significantly, especially at higher operating temperatures. Some manufacturers of 

parabolic troughs are now developing these receivers. Antireflection-coated 

receivers can also enhance annual performance considerably. Sandia National 

Laboratories in Albuquerque, N0M.B has investigated such coatings for parabolic trough receivers. 

5-1.4 Other !l'ypes of Collectors 

While flat plates, evacuated tubes, and parabolic troughs have been the most 

widely used collectors in IPH systems, several other types of collectors have 

also enjoyed some limited IPH field experience. With certain modifications, 

they could soon be suitable for IPH applications. A brief description of each 

f ollaws . 

514.1 Solar Ponds 

Salt-gradient solar ponds and shallow solar ponds, the two basic types, are 

among the least expensive kinds of solar collectors. 

A salt-gradient solar pond employs a salt concentration gradient to suppress 

natural convection. Water heated by solar radiation holds more dissolved salt 

than cooler water. The salty, heated water is also heavier; thus, it remains 

at the bottom of the solar pond. Sunlight penetrating though the top layers 

of the pond is absorbed at the bottom and trapped by the nonconvecting gradient layer which acts as an effective thermal insulator against conduction. In 

practice, a salt-gradient solar pond consists of three layers, or zones: 

san :al TR-1356 

(1) a surface convecting zone of low-salinity water, typically 20 to 

40 cm thick; 

(2) a nonconvecting or salinity-gradient zone beneath the surface zone, 

in which salt concentration increases with depth, typically 1 to 

1.5 m thick; and 

(3) a storage zone at the bottom of the pond of uniformly high salt concentration that stores heat and is typically 1 to 3 m thick, depending on the system application. 

A salt-gradient solar pond can provide heat at temperatures in excess of 90°c 

(194~~). Such a pond provides built-in thermal storage of such volume that 

heat can be collected in summer and stored for use during winter. Pioneering 

work in this field has been done in Israel (Tabor 1981). Edesess et al. 

(1981) describe a simple procedure for designing salt-gradient solar ponds, 

and SERI has compiled a selected bibliography on the subject (1981). The bibliography also contains a list of references on shallow solar ponds, and a 

design guide is provided by Casamajor and Parsons (1979). 

Shallow solar pond collectors consist of inflatable bags of water supported by 

insulated footings. When insolation- conditions are favorable, water is pumped 

from an underground storage tank into collectors. The water inside the collectors absorbs solar radiation and can attain temperatures up to 60'~ 

(140~~). The heated water can be used directly in an industrial process or 

can be drained to a storage tank for later use. At night or during unfavorable insolation conditions, the water in the collectors is drained back to the 

underground tank. 

5.1.4.2 Compound Parabolic Concentrators 

A compound parabolic concentrator (CPC) design, shown in Fig. 5-6, consists of 

two half-parabolic reflectors with an absorber located at the bottom of each. 

Some designs also utilize a cover plate above the reflectors to keep off dirt 

and dust. The CPC is a nonimaging concentrator and essentially "funnels" the 

radiation rather than focuses it. If oriented east-west, a trough with a low 

concentration ratio requires only seasonal adjustment and collects a considerable amount of diffuse as well as direct radiation. Unlike other concentrators, its reflective surface does not need to be highly specular; thus, it can 

more readily tolerate dust and degradation. Developed by Roland Winston 

(1974) of Argonne National Laboratory, this design offers the advantage of a 

wide acceptance angle-at low concentration ratios. A disadvantage is the relatively large amount of reflector area it requires. A comparison of CPC performance with other types of collectors is given by Rabl (1976). 

5*1.4,3 Fresnel Lens Collectors 

A variety of collectors that utilize a Fresnel lens have been developed. Some 

track in one axis to form a line focus; others track in two axes to form a 

point focus. A line-focus Fresnel lens is shown in Fig. 5-7. Direct solar 

radiation is refracted by the Fresnel lens (consisting of many small refractive surfaces) onto an absorber tube. Although this refractive concentration 

can be done with a convex lens, a Fresnel lens is utilized because it is 

cheaper, lighter, and absorbs less radiant energy. Line-focus Fresnel lens 

collectors can operate to about 290'~ (550~~). Point-focus Fresnel lens collectors can operate at temperatures in excess of 600'~ (1100~~). 

5m1m4m4 Multiple-Reflector Collectors 

Multiple-reflector collectors are usually associated with line-focus optics. 

Some designs incorporate several long, narrow reflectors that rotate to the 

correct position to reflect sunlight to a stationary receiver. Other designs 

employ movable absorbers and stationary reflectors. An advantage of the movable reflector/stationary receiver designs is that the reflectors can be 

rotated away from the sky (stowed) when they are not collecting energy. This 

protects them from dirt and dust accumulation as well as from hail damage. 

All multiple-reflector collectors suffer somewhat in efficiency as lost sunlight falls between reflectors. Also, because of the number of reflectors, 

the drive mechanism tends to be more complex than that of a parabolic trough. 

5.1.4.5 Parabolic Dish Collectors 

The concentrators for parabolic dish collectors are shaped in paraboloids of 

revolution (dish-shaped). This permits a high concentration of direct solar 

radiation to a point at the focus of the parabola. Good thermal efficiency at 

high temperatures can be achieved because of the small receiver area, compared 

with the aperture area, of the concentrator. Temperatures of up to 1100~~ 

(2000~~) can be supplied. A disadvantage of these collectors is that they 

require two-axis tracking (azimuth and elevation) of the sun. Also, they do 

not use land space as efficiently as other kinds of collectors, and the field 

piping layouts necessary can cause relatively larger thermal losses. 

SmlmSm6 Central Ikceivers 

By mounting a receiver on a tower surrounded by a field of carefully aimed 

individual reflectors (heliostats), very high energy concentrations and, thus, 

high temperatures can be achieved. Because all of the energy is transmitted 

to one central receiver in the form of light, piping losses associated with 

distributed receivers are eliminated. Drawbacks include tower support costs, 

two-axis tracking requirements, highly accurate (and costly) heliostat optics, 

and exclusive use of direct insolation. Central receivers are still under 

development, and most of the development to date has been applied to electric 

power plants. 

5.2 INSTiWWNEOUS PERFO~CE OF COLLECTORS 

The instantaneous performance of a collector is normally expressed in terms of 

its efficiency. Instantaneous efficiency is important because it defines how 

much of the solar energy available to a collector is actually converted to 

useful thermal energy. However, as a measure of performance it is limited in 

its usefulness. For example, it cannot be used, by itself, to measure the 

annual performance of the collector and, therefore, should not be used as a 
means of quantitatively comparing the performance of different collectors. A 

method for using the instantaneous performance parameters of a collector along 

with site and process load characteristics to predict annual performance is 

described in Sec. 5.3.1. This section develops the equation that defines a 

collector's instantaneous efficiency and describes how collectors are tested 

for efficiency . 

5-2-1 Analysis 

An analysis of collector performance begins with a simple steady-state instantaneous energy balance of a solar collector: 

energy collected = energy absorbed - energy lost to surroundings, or 

where 

. 2 qc = energy collection rate per unit collector aperture area (W/m ) 

2 I, = available irradiance on collector plane (~/m ) 

no = optical efficiency of collector (~a for a flat plate) 

2 -1 UL = overall collector heat loss coefficient (W/m K ) 

Tp = average absorber plate surface temperature (OC) 

Ta = outside ambient air temperature (OC). 

Usually, however, the average absorber surface temperature is not known. To 

express energy collection in terms of the more readily measured collector 

inlet fluid temperature, the collector heat removal efficiency factor FR is 

introduced as 

energy collected FR = energy collected if entire plate were at inlet fluid temperature 

Assuming that UL is a constant, FR can be expressed as follows (Duffie and 

Beckman 1974) : 

where 

F' = heat transfer resistance from absorber to ambient air 

heat transfer resistance from fluid to ambient air 

ic = collector field flow rate per unit collector area (kg s-' m-2 
Now, the collector energy balance can be expressed as 

where T = inlet fluid temperature (OC). f,i 

A collector's instantaneous efficiency is defined as 

SO, we have 

energy collected nc = qc =- available irradiation I, ' 

All the equations above apply to all types of collectors. However, the quantity used for I, varies among them. For flat-plate and evacuated-tube collectors, the global irradiance on the colle'ctor plane, as measured by a pyranow 

eter, should be used, This includes both direct and diffuse components of 

solar radiation. Parabolic troughs are largely insensitive to diffuse irradiance because of their higher concentration ratios, so the available radiation 

is the direct irradiance incident upon the collector plane. 

Thfs first-order form of the efficiency equation is quite accurate for most 

types of collectors. However, for collectors that can operate at higher temperatures, such as parabolic troughs, the variation of UL with temperature can 

become significant , and a second-order efficiency equation is sometimes used, 

The correct form of such an efficiency fit (Tabor 1980) is 

To plot a parabolic trough's efficiency on the same graph as a flat plate 

(i.e., versus AT/I), theequation is often given as 

2 thus giving us (AT/I) , the second-order term. This is accurate only for one 

value of I. 

Figure 5-8 presents typical solar-noon instantaneous efficiency curves for 

collectors used in IPH applications. Two flat-plate curves are shown: one 

with a flat black absorber and one glazing, and the other with a black chrome 

selective surface and two glazings. Note that for large values of the parameter (Tf - Ta)/Ia (corresponding to the collector supplying a heated fluid 

at a sig&if icantly higher temperature than ambient), the two-cover collector 

has a higher efficiency than the single-cover collector. This is because the 
sea + TR- 1 3 56 

1 Flat Plate - 1 glazing, flat black 

2 Flat Plate - 2 glazings, selective - 

3 Evacuated Tube 

- 4 High Performance Parabolic 

Trough - glass reflector 8 

- (at 1000 W/m2 direct) 

Figure 5-8. Typical Instantaneous Efficiency Curves for 

Collectors Used in IPH Applications 

second cover and selective surface reduce heat loss, resulting in a smaller UL 

and a flatter slope of the curve. At small values of (TfSi - Ta)/Ia, however, 

a single-cover collector outperforms a two-cover model, because the singlecover collector has a higher transmittance and thus a higher optical efficiency, which is, in turn, reflected in a higher intercept. 

Evacuated-tube efficiency exceeds flat-plate efficiencies at higher values of 

(T - Ta)Ia This is because of the reduced heat losses from evacuated 

tub& compared with flat plates. Because the absorber area per unit aperture 

area is smaller, and convective heat transfer between the absorber and the 

glass envelope is eliminated, the UL value is significantly reduced. For this 

reason, evacuated-tube collectors are used for applications where higher 

temperatures are involved--generally between 80'~ and 150'~. Parabolic 

troughs usually exhibit even smaller heat losses because of their increased 

concentration and the resulting decrease in absorber area per unit aperture 

area. In fact, the trough's efficiency is higher than that of other types of 

collectors at all temperatures. Of course, trough efficiency is based only on 

direct radiation; the trough cannot collect the diffuse radiation available to 

flat plates and evacuated tubes. 

Variations in optical efficiency should also be accounted for to predict collector performance closely. Optical efficiency can vary with the angle of 

incidence of solar radiation on the collector's aperture plane. Correction 

factors (incident-angle modifiers) account for this variation and are generated with standard collector performance tests. Examples of incident-angle 
modifers for flat-plate, evacuated-tube, and parabolic-trough collectors are 

shown in Fig. 5-9. For most flat-plate collectors, the incident-angle modif ier can be plotted as a straight line. agaias t the quantity [ (cos e)-l - 11 . The equation of such a line is 

where 

bo = a constant dependent on the collector's optical properties 

8 = angle of incidence of direct solar irradiation. 

5.2.2 Testing 

The generally accepted method of testing the efficiency of a solar collector 

employs an open system in which the temperature rise across the collector is 

measured under steady-state conditions. Along with the inlet and outlet collector fluid temperatures, the fluid mass flow rate and instantaneous irradiance are measured as well. Collector efficiency is then defined as 

useful energy collected - nc = - Mcp(~f,e - Tf,i) available irradiation on collector Wa , (5-8) 

where 

M = mass flow rate of collector fluid 

c = heat capacity of fluid P 

Tf,e = fluid exit temperature 

Tf,i = fluid inlet temperature 

A, = gross collector area 

I, = available irradiation on collector. 

Based on a procedure developed by the National Bureau of Standards, the 

American Society of Heating, Refrigerating, and Air Conditioning Engineers 

(ASARAE) adopted Standard 93-77, "Methods of Testing to Determine the Thermal 

Performance of Solar Collectors." It is most applicable to nontracking collectors like flat plates and evacuated tubes. Three basic tests are called 

for, and these determine the following: 

time constant of collector 

instantaneous collector efficiency 

incident-angle modifier of collector. 

The collector tine constant T, is the time required for the difference between 

fluid inlet and outlet temperatures to drop to 36.8% of initial value after a 

step decrease in insolation or inlet fluid temperature. In a typical test, 

the incident solar flux is abruptly reduced from a steady-state value of at 

least 790 w/m2. (250 ~tu/h-ft2) to zero. At time t = rc after such a step 

change, with inlet collector temperature t f,f held constant, we have 

The smaller the time constant, the more rapidly a collector will respond to 

short periods of insolation. 

Over a time period dT, efficiency is determined to be 

For each data point, the efficiency is the average over a period of 5 minutes 

or T c (whichever is larger?, during which insolation is steady and flow is 

maintained at 14.7 lbm/h ft (0.02 kg s-I m2) for a liquid collector and both 

1.96 and 6.0 cfrn/ft2 (0.01 and 0.03 m3 s-I mq2) for an air collector. (The 

efficiency of an air collector is more sensitive to flow rate than that of a 

liquid collector.) Efficiency is measured for four different values of 

(Tf - Ta): lo%, 30%, 50%, and 70% of the difference between stagnation temper&ture and ambient temperature at the given conditions. For each case, four 

data points are taken symmetrically about solar noon. The resulting 16 points 

are plotted on a graph of n versus (Tf - T,)/I, and, for flat-plate collectors, a straight line is fitted using a' f east-squares analysis. 

These efficiency tests should be conducted close to solar noon with the collector positioned normal to the sunts.direct rays. If the collector is left 

in this position, its efficiency will drop during morning and late afternoon 

hours because of the decreasing value of I and consequent increase of AT/I,. 

However, the efficiency curve determined above is valid only for near-normal 

incidence. At other angles, the optical efficiency will be less, thereby moving the whole efficiency curve downward. The incident-angle modifier quantifies this change in optical efficiency. 

Two efficiency tests are performed on the collector for each of four different 

incident angles: 0' (normal), 30°, 45O, and 60'. In each case, the inlet 

temperature is controlled to within flOc (f 1.8'~) of the ambient. Then, we 

have 
since tf,i = ta, nc = FRno. The incident angle modified KaT is defined as: 

where ('lo)n is '1, for the normal incidence case. 

Since nc = FRqo for these tests, we have no = T\~/FR, and 

The nc values are determined for each angle, and FR(n0), is the efficiency 

value only for the 0' case. The KaT values allow one to take the normal incidence efficiency curve and determine the appropriate curve for off-normal 

incident solar radiation. 

The ASHRAE 93-77 test standard was written for nonconcentrating collectors; it 

does not uniformly apply to concentrating collectors. A test standard for 

concentrating collectors has been developed by SERI (ASTM Document No. 127) 

and is currently under review and ballot by an ASTM committee. However, considerable efficiency testing of parabolic troughs has been done. Sandia 

National Laboratories in Albuquerque has performed many efficiency tests on 

parabolic troughs [for example, Harrison (1980)l. Both instantaneous efficiency and incident-angle modifier tests are performed. Efficiency data are 

reported in the form of 

where al and a2 are constants fit to the data points, and Tf is the average 

fluid temperature. 

As we mentioned, this form of an efficiency fit is accurate only for one value 

of irradiance, Ia. To convert this form of efficiency fit to the preferred 

form of 

it is necessary to divide out an I, from the second-order term of the Sandia 

equation. Since collector testing is performed on clear days, an I, value of 

1000 w/m2 is recommended. We also assume for these tests that FR PI Ff , because in the Sandia tests, the average fluid temperature was only-' a few 

degrees hotter than the inlet fluid temperature. With these assumptions, the 

values of the first- and second-order UL terms are calculated as 
The design procedure developed in this handbook is based on a single overall 

collector heat loss coefficient, UL. 

For a given AT = Tf,i - Ta, UL can be calculated as 

or, using Sandia's constants, 

UL = al + a2/1000 (AT) .. (5-18) 

Test results should be obtained for any collector being considered for a solar 

IPH system. This information can often be obtained from collector manufacturers. In that case, it is important that the testing was done according to the 

standard test procedure by a reputable collector test facility. Also, make 

sure that the test data pertain to the particular collector model you are 

interested in. A great deal of performance test data on solar collectors have 

also been generated by national laboratories and test programs funded by the 

Department of Energy (see Harrison 1980; Mather 1980; and Sun Designs 1982). 

The collector selection procedure is usually a two-step process. First, the 

appropriate type of collector is determined; then, a particular brand is 

chosen. The collector type is ordinarily selected during the conceptual 

design phase, and the particular brand is often determined in the preliminary 

design stage. Choosing the collector type at an early stage accelerates the 

rest of the system design process. The algorithm by which a collector type is 

selected requires a minimum number of inputs at this early stage. 

In this section, we present a simple method for making a judgment on the 

appropriate type of collector. After various types are compared on performance and cost bases, one collector often emerges as a clear best choice. If, 

however, two types seem equally appropriate, it is best to defer the final 

selection until more information is available. Sections 6.0 and 10.0 explain 

the more detailed evaluation procedure. 

Selecting the best collector for a particular IPH application involves weighing two quantities: solar system performance and solar system cost. The most 

meaningful measure of solar system performance is the average annual energy 

delivery of the system. A way of estimating it is described in Sec. 5.3.1. 

The second quantity, total system cost, must include direct costs such as collector hardware, piping, insulation, heat exchangers, controls, and pumps, as 

well as indirect costs such as installation, maintenance, and design fees. 

Guidelines for estimating their contributions are contained in Sec. 10.0. 
3 A PreliaLnary Comparison of Collector Performance 

Since the type of collector is preferably chosen early in the design process, 

that decision must be based on quite limited data. Fortunately, the relative 

performance of flat-plate, evacuated-tube, and parabolic-trough collector 

systems is governed largely by only a few variables: site characteristics, 

collector characteristics, and process load temperatures. Detailed information such as system configuration, storage tank size, collector field layout, 

heat exchanger effectiveness, and piping network geometry are not required at 

this stage because, if the system is well designed, their effects on performance are small (or at least nearly equal for all three types). Thus, the 

dominant performance quantities are as follows: 

the average collector operating temperature 

the performance characteristics of each collector type, described simply 

by an optical efficiency and an overall heat-loss coefficient 

the average annual direct normal and total horizontal irradiance at the 

proposed IPH site. 

The average collector operating temperature is not precisely known. Section 6.0 describes how to account closely for this average temperature based 

on the process temperatures, load profile, load flow rate, system configuration, and storage size. However, this much detail is usually not necessary at 

the conceptual stage. Instead, we recommended a simpler approach, as follows. 

Typically, the average collector operating temperature of a hot water or hot 

air system is higher than the load return temperature but lower than the process load temperature. In low solar fraction systems, the average collector 

temperature is nearer the load return temperature. In systems with higher 

solar fractions, more collector area is needed, and the average collector temperature increases. For very large solar fractions, the average collector 

operating temperature may actually exceed that of the process load, but this 

situation is not likely to be economically justified. Therefore, the average 

collector operating temperature of a hot water or air system is likely to be 

bounded by the load and load return temperatures. The approach here is to 

consider the relative performance of the principal types of collectors at both 

temperatures. The differences in system performance and cost are often substantial enough that the same collector type will be the preferred choice at 

both temperatures. If, however, ope collector type is preferred at the load 

return temperature and a different type is preferred at the load temperature, 

it is best to defer the final selection until more detailed information is 

available. 

In steam systems, the average collector operating temperature will be somewhat 

above the steam saturation temperature. A reasonable approximation of the 

average collector operating temperature is 20'~ above the saturation temperature of the process steam. 

The performance characteristics of the different types of collectors are the 

next important parameters to consider. Collector optical efficiencies and 

heat-loss coefficients are obtained from standard collector test procedures 

and are readily available from manufacturers. Further, the ranges of optical 
efficiency and U-value are confined to relatively narrow bands for each collector type by their geometries and according to the materials used in them, 

Typical values are shown in Table 5-1, 

The average annual daytime irradiance ? (based on 4380 annual daylight hours 

or an average of 12 hours per day per year) a-t the proposed IPH site can be 

estimated from Figs. 5-10 and 5-11, yearly insolation maps for average total 

horizontal daytime irradiance Ih and average daytime direct normal irradiance - 

Ib. These contour maps differ from Figs. 3-1 and 3-2 in that they denote 

average yearly irradiance and not average daily irradiation. The total horizontal map should be used for flat-plate and evacuated-tube collectors, and 

the direct normal map should be used for parabolic troughs. Of course, if 

better long-term irradiance data are available for the proposed site, they 

should be used instead. The industrial owner must supply only the average 

process load return temperature, the number of hours and days the process 

operates, and an estimate of collector field size or solar fraction. 

With this information, Fig. 5-12 can help to provide annual performance estimates of the principal types of IPH collectors. The figure permits a graphical determination of qc, the average annual energy collection rate of an 

unshaded collector operating with a constant collector inlet temperature. 

This figure was derived from hundreds of detailed hour-by-hour computer simulations (as described in Appendix E) and essentially enables us to determine 

annual collector performa6ice from instantaneous efficiency data. The ordinate 

of the graph is simply &- divided by the product of collector optical ef f iciency and annual average daytime irradiance for the particular site. The 

ordinate can be determined once the abscissa, a simple grouping of known 

quantities, is defined. The abscissa here is the ratio of the collector's 

critical intensity to the average intensity of the sun's radiation, the 

intensity ratio (see Sec. 6.1). The critical intensity is that irradiance at 

which heat lost from the collector just balances the heat gained. A collector ' s critical intensity is calculated as follows : 

critical intensity = U~(Tcollector - Tanbient ) 

qo 

- 

Use Fig. 5-10 to define the annual average daytime irradiance. level I for 

flat plates and evacuated tubes and Fig. 5-11 for parabolic troughs. After 

defining the abscissa, read the ordinate from the graph for the latitude of 

Table 5-1. Typical Ranges of Liquid Collector 

Performance Characteristics 

Collector Type Effective Optical U-v lue 

Efficiency (t~9-K) 

Flat-plate 

single glazing 0.65-0-8 2.6-4.4 

double glazing 0.6-0.7 1.9-2 -8 

Evacuated tube 0.5-0.7 0-5-1.0 

Parabolic trough 0.65-0.8 0.25-0.75 



the site* The ordinate is then muztiplied by the product of the collector 

optical efficiency and an average irradiance level to arrive at <c, the 

average annual energy collection rate per unit of collector area. Note that, 

for parabolic trough collectors, the ordi ate is multiplied by the average 

annual- direct -normal irradiance plus 50 W/2.* 

In referring to Fig. 5-12 for parabolic troughs, both north-south and eastwest rotational-axis orientations are shown. If land or rooftop area considerations do not preclude north-south orientation, it is best to utilize the 

north-south performance curves because of the greater annual energy delivery 

associated with this orientation. The flat-plate and evacuated-tube performance curves are for collector panels that are oriented south and tilted from 

horizontal at the latitude angle. This is optimum for collector systems that 

operate year round as is the case for most IPH applications- (A more detailed 

dimension of Fig. 5-12 is contained in Sec. 6.1.) 

The average annual energy collection prediction just obtained is used to normalize the total solar system cost (see Sec. 10.1.2) to provide a measure of 

the cost effectiveness of the particular type of collector. This measure is 

often called capacity cost. me lower the capacity cost is, the better the 

investment- This measure can, therefore, be used to judge which collector 

type is best suited for a particular industrial plant and process. While the 

procedure yields a measure in'units. of energy cost, note that this value is 

not the actual cost of energy. These values are intended only for comparing 

collector system options. Determining the actual cost of delivered energy 

requires many other factors not included in this procedure, and, therefore, a 

. life-cycle economic analysis is necessary (see Sec. 10.2). 

5.3.2 Other Considerations in Selecting an Appropriate Collector 

While capacity cost (total installed system cost divided by annual collected 

energy) should be a major factor in deciding which collector is best for the 

IPH system, other factors should also be considered. Some of these are as 

follows: 

Determine if flat-plate glazing materials or parabolic-trough reflector 

materials deteriorate rapidly because of industrial contaminants at the 

solar IPH site by placing material samples at the site as early as 

possible. 

Consider the maintenance and replacement costs that each type of collector might require. Maintenance and replacement costs are not included in 

capacity costs, but they certainly affect the life-cycle cost of the 

solar system. 

Determine if the industrial plant has maintenance personnel to repair and 

maintain a tracking collector. Parabolic trough collectors may require 

maintenance and replacement of electric motors, gear reducers, bearings, 

and sun-tracker electronics, for example. 

2 *This extra additive irradiance of 50 ~/m is necessary only because it permits 

a better empirical correlation of annual performance. 
If a rooftop area is being considered for placement of the collectors, 

determine if the roof is structurally adequate for that purpose. If it 

is not, consider the roof modifications that each type of collector would 

necessitate. 

ASHRAE Standard 93-77. Collector Test Procedure of the American Society of 

Heating, Refrigeration, and Air Conditioning Engineers. 343 W. 43rd St., 

New York, NY. 

ASTM Document No. 127. "Test Method for Determining the Thermal Performance 

of Tracking Solar Collectors." American Society for Testing and 

Materials. 

Casamajor, A. B.; Parsons, R. E. 1979 (Jan.). Design Guide for Shallow Solar 

Ponds. UCRL-52385 (Rev. 1). Livermore, CA: Lawrence Livermor e 

Laboratory. 

Duffie, J. A*; Seckman, W. A. 1974. Solar Energy Thermal Processes. New 

York, NY: John Wiley and Sons. 

Edesess, M.; Henderson, J. ; Jayadev, T. S. 1981 (Revised). A Simple Design 

Tool for Sizing Solar Ponds. ~ER1/~~-351-347~. Golden, CO: Solar Energy 

Research Institute. 

Franta, G.; et al. 1981 (Jan.). Solar Design Workbook. s~RI/S~-62-308. 

Golden, CO: Solar Energy Research Institute. 

Gee, R. C., 1982 (May). An Experimental Performance Evaluation of Line-Focus 

Sun Trackers. SERIITR-632-646. Golden. CO: Solar Enerm Research 

Institute. 

Gee, R. C.; et al. 1980 (Mar.). Long-Term Average Performance Benefits of 

Parabolic Trough Improvements. SE~1/TR-632-439. Golden, CO : Solar 

Energy Research Institute. 

Harrison, T. D. 1980 (Nov.). Midtemperature Solar Systems Test Facility 

Program for Predicting Thermal Performance of Line-Focusing, Concentrating 

Solar Collectors. SAND80-1964. Albuquerque, NM: Sandia National 

Laboratories. 

Lunde, P. J. 1980. Solar Thermal Engineering. New York, NY: John Wiley and 

Sons. 

Mather, G. R., Jr. 1980 (Nov.). "AS- 93-77 Instantaneous and All-Day 

Tests of the Sunpak Evacuated-Tube Collector." Journal of Solar Energy 

Engineering. Vol. 102. 

Rabl, A. 1976. "Comparison of Solar Concentrators." Solar Energy. Vol. 18; 

p. 93. 
Solar Energy Research Institute. 1981 (Nov.). Solar Ponds: A Selected 

Bibliography. ~~~1/~~-752-711. Golden, CO: Solar Energy Research 

Institute. 

Sun Designs. 1982 (July). Solar Collector Data Manual. SERI/TR-254-1515. 

Golden, C0:- Solar Energy Research Institute. 

Tabor, HI 1980. Letter to the Editor. Solar Energy. Vol. 24; pp. 113-115. 

Tabor, H. 1981. "Solar Ponds. " Solar Energy. Vol. 27 (No. 3) : 

pp. 181-194. 

Winston, R. 1974. "Solar Concentrators of a Novel Design." Solar Energy 16; 

p. 89. 

PART XI1 

PRELlMI~ DESIGN 
Because the objective of a solar IPH system is to deliver energy efficiently 

to a process load, we need an accurate 'method of calculating the performance 

of that solar system. Further, to size the system components and to help make 

the trade-offs necessary in using any solar system, we must have a performance 

analysis that takes into account the impact of all important parameters. Such 

a system performance analysis should be efficient, accurate, easy to use, and 

not require the use of a computer. This section presents some performance 

analysis design tools that were developed to meet all these requirements, 

Many of these design tools were generated with the help of a detailed hour-byhour computer model, SOLIPH. Thousands of SOLIPH runs were made to formulate 

generalized design tools . The primary difficulty encountered in developing 

these tools was the number of variables that affect annual system performance. 

Because there are so many variables, detailed hour-by-hour computer models are 

often utilized during the design stages of a solar system. This can make the 

process very time-consuming and significantly increase system design costs. 

However, by grouping variables into physically meaningful groups and using 

regression analysis techniques, we can correlate the performance of solar systems with a great degree of accuracy and display the results graphically. The 

methodology used to generate these design tools was influenced greatly by the -- 

work of Ari Rabl. The simplified energy collection correlations he formulated 

(1981) provided valuable insight and greatly aided development of the design 

tools presented here- The IPH system computer model and a comparison of its 

results with other computer codes is contained in Appendix C. Our design tool 

methodology is presented in more detail in Appendix D, along with the accuracy 

(rms error) of each design tool. The reader is cautioned that the energy prediction design tools were developed for the continental United States only, 

and use in other areas can result in less accuracy than that indicated in the 

Appendix. 

Each subsection in this section addresses one aspect of IPH system performance 

and presents design tools for predicting its impact on the annual performance 

of the entire IPH system. The annual energy collection design tool introduced 

in Sec. 6.1 is the fundamental correlation upon which the performance analysis 

is based. It is applied to a variety of IPH system configurations for hot 

air, hot water, and steam systems. Section 6.2 describes how to account for 

incident-angle modifier effects and end losses (for a parabolic trough) on an 

annual basis. In Sec. 6.3, annual correction factors for row-to-row shading 

losses are presented. Section 6.4 provides a method of calculating annual 

losses from field piping, including steady-state losses, overnight losses, and 

freeze protection losses. Section 6.5 presents annual correction factors that 

account for downtime ?nd utilization of the solar system. Section 6.6 summarizes the design tool information step-by-step. 

6-1 ANNUAL ENERGY COLLECTION FOR SKVERAL IPB SYSTEM CONFliGIJRATIONS 

The first step in determining how much energy is delivered from the solar system to the process load is to calculate how much energy is produced by the 

collector field. Energy collection depends on the type of collector, its 
fluid specific heats, heat exchanger effectiveness, storage tank size, process 

load supply temperature, process load energy requirement, and the hours the 

process operates. Because there are so many variables, detailed hour-by-hour 

computer models are often employed to make IPH system trade-off decisions and 

to size various components. Fortunately, some of these variables can be 

accounted for in closed-form analysis. .Other key variables have been appropriately grouped and correlated empirically with the annual performance 

results of SOLIPH. The resulting basic annual energy correlation is presented 

here, and its application to specific IPH system configurations is treated in 

subsections that follow. 

As shown in Sec. 5.0, the instantaneous energy collection of a collector can 

be described in the form 

The heat transfer efficiency factor FR accounts for the temperature rise 

across the collector and the resultant decrease in energy collection due to 

this elevation in collector operating temperature. This factor, as shown in 

Sec. 5.2, is calculated as 

Equation 6-1 is useful when the collector inlet temperature is known. In 

direct hot water and air systems (see Figs. 4-1 and 4-3), the collector inlet 

temperature is the load return temperature. However, in indirect systems that 

incorporate a heat exchanger between the collector loop and the load (see 

Figs. 4-2 and 4-4), the collector inlet temperature is higher than the load 

return temperature because of the finite heat transfer area of the heat 

exchanger. The collector inlet temperature is also not specifically known for 

steam systems. As we show later in this section, simple modifiers can be 

developed that account for the effects of intermediate heat exchangers, 

unfired boilers, and steam flash tanks. We define this system-dependent modifier to be Fs. With it, energy collection can be written as 

Here, Tin is a known temperature which is also dependent on system configuration. In hot air and hot water systems, Tin is the load return temperature; 

in steam systems, Tin is the saturated steam temperature. Although Eq. 6-3 is 

useful in defining instantaneous performance, it does not quantify the most 

important quantity--long-term average performance of a collector. We need 

only three primary quantities to quantify long-term collector performance (see 

Appendix D): primarily the intensity ratio, the geographic latitude, and the 

product of collector optical efficiency and the average intensity of the sun's 

irradiation during daylight hours at the solar site. 

The intensity ratio is the critical intensity of the collector divided by the 

aveEage intensity of the sun's irradiance during daylight hours and is denoted 

as I. The critical intensity of a collector is that irradiance at which heat 

loss just balances heat gain. A collector's critical intensity (based on 4380 

annual daylight hours, or an average of 12 hours per day per year) is 

calculated as 
FRUL(T~~ - Ta) critical intensity = FR~ 0 

. 

All the quantities necessary to define the intensity ratio are readily available and, therefore, provide a simple method for calculating energy collection. Simple empirical correlations for energy collection based on the 

intensity ratio are shown graphically in Flg. 6-1 (which is Fig. 5-12 with the 

addition of polynomials for use with hand calculators). Evacuated-tube and 

flat-plate collectors are assumed to be oriented south and tilted at the latitude angle. Parabolic troughs are assumed to be mounted horizontally. 

To use the figure, first define the intensity ratio, which is the variable 

grouping 

Both FRUL and FRmo are collector properties. The collector optical efficiency 

term FRno is often lowered to account for the long-term optical degradation of - 

the collector from dirt and dust. The amount by which FRn, should be reduced 

is highly site dependent and should be based on observed degradation of mater- - 

ial samples placed at the site (see Sec. 3.1). I is the long-term - average 

irradiance during daylight hours for the site being considered. 1 is to be 

taken as for parabolic troughs (see Fig. 5-11). For flat-plate and evacu- b ated-tube collectors, use yh(see Fig. 5-10). T, is the average annual daytime 

temperature for the site (see Appendix F). The correct temperature to use for 

Tin depends on the configuration of the system. Use the load return temperature of the process for hot air and hot water systems, and use the saturated 

steam temperature for steam systems. This is explained more fully in the subsections that follow. 

With the x-axis defined, the quantity [h /FsFRn can be read directly from 

the graph along the y-axis for the latitude of the site. Multiplying this 

ordinate value by the product of Fs, FR, the collector optical efficiency, and 

.$he appropriate annual average daytime irradiation results in the quantity 

q,, which is the annual average energy collection' rate, per unit of collector 

area, for the unshaded collector for a co stant value of Ti,. Note that, for 

parabolic troughs, an additional 50 W/n? is. added to the annual average 

irradiance used on the y-axis, which allows a better empirical fit than one 

based on the annual average irradiance alone. * 

Note that the parabolic trough performance curves extend to intensity ratios 

of 0.7, while for flat plates and evacuated tubes they extend to 1.4. This is 

consistent with the operating temperature range in use for each type of collector. This covers temperatures up to about 90'~ for flat plates and up to 

about 300'~ for parabolic troughs. Because a flat-plate collector loses more 

heat at 90'~ than a parabolic trough does at 300°c, the curves extend to 

higher intensity ratios for flat plates. 

*If a second-order efficiency equation is provided by the collector supplier, 

use the UL value at the load temperature. As noted in Sec. 5.2, UL should be 

evaluated as UL = ULS1 + UL,$T1 - Ta). 
Another characteristic of these curves is that those for flat plates are well 

above those for parabolic troughs at low intensity ratios. This is so because 

f lat-plate and evacuated-tube curves are based on average daytime total horizontal irradiance, but parabolic-trough curves are based on average daytime 

direct normal irradiance. For many sites., direct normal irradiance values can 

be significantly higher than the total horizontal irradiance values. Only one 

curve is shown for east-west rotational axis troughs. In that particular 

orientation, performance is essentially independent of site latitude, because 

the incident angle of incoming irradiance is the same for all latitudes. Note 

that the north-south orientation outperforms (on an annual basis) the eastwest orientation, but they approach each other at high latitudes. Shading 

losses tend to further diminish this performance difference, as shown in 

Sec. 6.3. 

The annual performance of a parabolic trough with a rotational axis oriented 

between north-south and east-west limits is typically between that of a northsouth trough and an east-west trough. At some sites, performance may be 

slightly enhanced with a small off-north-south orientation because of weather 

patterns marked by very cloudy mornings or afternoons. However, this asymmetry is usually slight on an annual basis, and the annual performance of a 

parabolic trough oriented between north-south and east-west can be approximated (Harrigan 1981) by: 

- qc,w + Pc,n-s + qc,n-s - qc,e-w qc s8 axis - 2 2 cos(2 eaXis) 3 (6-4) 

where 

. 

qc,O,is = annual energy collection rate of trough with rotational axis 

between east-west and north-south 

. 

qc,e-w .- 

- annual energy collection rate of east-west rotational axis 

trough (from Fig. 6-1) 

. 

qc,n-s = annual energy collection rate of north-south rotational axis 

trough (from Fig. 6-1) 

axis = direction of trough rotational axis measured from south 

(north-south = oO, east-west = 90'). 

Note that the polynomial expressions for the annual collector performance 

curves are provided at the bottom of Fig. 6-1. These polynomials are given 

for those wishing to use a hand-held calculator rather than the graphical 

representations. 

Hot Water and Hot Air Systems 

An indirect hot water or hot air system is shown in Fig. 6-2. The term "indirect" is used to denote that a heat exchanger is used between the collector 

loop and the load. As noted in Sec. 6.1, this heat exchanger affects system 

performance because the temperature of the fluid entering the collector system 

is higher than the process return temperature. The heat exchanger factor Fx 

can be used to account for this effect (dewinter 1975). The heat exchanger 

factoriC is defined as 

where E is heat exchanger effectiveness. Therefore, for hot air and hot water 

systems, the system-dependent modifier Fs is equal to Fx. Also, for hot air 

and hot water systems, the process return temperature is used for T in 

referring to Pig. 6-1. If a heat exchanger is not part of the system &?.e., 

it is a direct system), set Fs equal to unity. 

Figure 6-2 shows a collector flow loop and a secondary loop. If no storage is 

provided, the secondary loop fluid must be delivered to the process load. If 

storage is added, the secondary loop fluid can either be delivered to the process load or stored for later use. Whether to choose a storage or a nostorage system depends to a great extent on the hours that energy is needed by 

the process, and such process heat requirements are governed by the production 

schedule of the industrial plant. Typically, industrial plants operate on 

either a single-shift, two-shift, or three-shift schedule, so that process 

loads of 8, 16, or 24 hours per day are common. A no-storage system and two 

systems with storage are described in the subsections that follow. 

I I o rrocess g or Storage 0 

I I Exchanger 

I Process 

Return 

Pump Pump 

Figure 6-2. An Indirect Solar FIot Water or Hot Air System 

 q qua ti on 6-5 assumes that the collector loop flow capacity rate is less than 

or equal to the load loop flow capacity rate. A more general form is given in 

Sec. 7.5. 
6.1.1.1 Htorage IPE System 

An IPH system without storage would be configured as shown in Fig. 6-2. Whenever solar energy is collected, both pumps are turned on, and all the return 

water (or air)-is heated as it passes through the heat exchanger. The collector system should be sized so that, under the best conditions for solar collection, the heated fluid does not exceed the required process temperature, 

Thus, when the collectors are producing less than their peak energy output, 

the heated process fluid leaves the heat exchanger at less than the required 

process temperature. The additforial energy needed to bring the preheated 

fluid to that temperature must be supplied .by a back-up boile@ which is 

placed in series with the solar heat exchanger. 

A no-storage solar system should be considered for industrial plants with process loads that occur during all or nearly all daylight hours. If the plant 

operates only a single shift (8 hours) per day, the no-storage system is not a 

good choice because there will be too many daylight hours when no process load 

exists. During such nb;load periods, collectable energy is lost, which can 

significantly reduce the annual performance of the collector system. 

The no-storage system is also a poor choice if the industrial plant shuts down 

on weekends. Without storage, collectable energy is lost two days of every 

week. This significantly reduces the cost effectiveness of the solar system. 

But a no-storage systemis a good choice for industrial plants having daytime, 

7-day-per-week loads. Many two- .and three-shift industrial operations fall 

into this category. 

To size the collector area for a no-storage system, we follow the guideline 

that under the best conditions for solar collection, the solar collector field 

should not produce more energy than the process can use. This is consistent 

with the belief that no collected energy should ever be dumped. Actually, a 

small amount of dumping is economTcally justified [Gordon and Rabl (forthcoming) j . But the economic advantages of a slightly oversized system over a nodump system are slight. For purposes of preliminary solar system design, the 

no-dump philosophy is entirely adequate. 

To find the maximum collector area needed for a no-storage system, we simply 

equate the rate at which the process load requires energy to the rate at which 

the collector field can deliver energy under the best solar collection 

conditions: 

*The impact of operating a boiler at variable heating rates is discussed in 

Appendix A. 
where 

Imax = peak irradiance available to collector 

Ta ,max = highest expected ambient temperature. 

zg 

2 It is su gested that Lx be set to 1000 W/m for parabolic troughs and to 

1100 W/m for flat-plate and evacuated-tube collectors. These values may be 

slightly too high for some locations and slightly too low for others, but on 

the average they represent good design values. The design value of high ambient temperature may be estimated for the site from ASHRAE 99% guidelines 

(ASHRAF, 1981). Alternatively, a value of 40'~ may be used since it represents 

a typical maximum temperature for much of the United States. 

Values for FRno and FRUL are taken directly from the performance data of the 

collector. Tin is the process return temperature, and F is the heat 

exchanger factor (see Eq. 6-5), which is a function of the ezfectiveness of 

the heat exchanger. Again, if no heat exchanger is present, use Fx = 1. 

After determining all the appropriate values, we solve for the maximum collector area for a no-storage system as follows: 

This collector area represents the maximum; smaller collector fields can also 

be used with a correspondingly smaller amount of fossil fuel energy displacement. If, for example, available land is limited, a collector area smaller 

than Ac ,max may be necessary. 

The annual performance of the solar system can be predicted using Fig. 6-1. 

Use the process return temperature for Tin and the calculated value of Fx for 

Fs. Assuming that the no-storage system configuration has been selected 

because a process load exists during all daylight hours, the total annual 

energy collected is calculated as 

where 

Qc = total annual average energy collection 

qc = annual average energy collection rate per unit of collector 

area during daylight hours (from Fig. 6-1) 

A, = collector area (< A,, 1 

Ndaylight = number of daylight hours in year (= 4380). 

The total annual process load is as follows: 
where 

tload = average process load energy rate {= 1; c (T~ - T~,~) J } load p 

Nload = nmber of hours load operates during the year. 

Now, the solar fraction (fraction of total process load that is displaced by 

solar energy system) can be calculated as: 

An example illustrates this procedure. A chemical =nu£ acturing plant near 

Columbus, Ohio, is considering adding a solar system to provide some of its 

process heat. Chemical reaction vessels are heated 24 hours per day, 7 days 

per week with 120~~ hot water. After heating the reaction vessels, the water 

is returned at 90'~ for reheat. The chemical plant uses 38,000 kg/h 

(84,000 Ib/h) of hot water for this chemical process. The 24 h/day load 

ensures that a process load exists during all. daytime hours; hence, a nostorage system is a good choice. 

The roof area of the plant is too cluttered with ventilation equipment to 

accommodate solar collectors. However, the plant has 2.5 acres of vacant land 

adjacent to it. First, we must calculate how much of the 2.5 acres of land 

may be used for the solar system, assuming a ground cover ratio (collector 

aperture width divided. by row-to-row spacing) of 0.4- Then, we calculate the 

solar fraction that the collectors can meet. 

Assume that evacuated-tube collectors will be used that have the following 

performance characteristics (as tested with a water flow rate through the collectors of 0.02 kg s-' mo2) : 

The collector loop will 'use a heat transfer fluid other than water because of 

both freeze protection concerns and the load temperature requirement of 120°C. 

Because the process load loop uses water, a heat exchanger between the two 

loops is necessary. Assme that fhe heat exchanger factor F, has a value of 

0.95. The process load use rate, Qload, 1s calculated as 

Based on this load use rate, the maximum collector area for the no-storage 

system is calculated (see Eq. 6-7) as 
TR-1356 san 

Using this collector area and a ground cover ratio of 0.4, land requirements 

are 

or about 1.4 acres of land area. 

Because the assumed collector FRUL and FRqO values correspond only to the 

tested flow capacity rate, it is necessary to adjust their values for the actual flow capacity of this application. Using a collector loop flow rate equal 

to half the load flow rate (see Sec. 7.5.4), adjustment of FR for different 

flow capacities, as shown by Lunde (1981), can be calculated as 

('R'L) old - (FRuL) old 

2(;c ) p new 2( mtpl 

Therefore, the FRUL and FRno values assumed are 3.5% too high. This correction is small enough that it is not necessary to recalculate a new value of 

Ac,max' After is an approximate value. However, the FR correction should be included in the annual performance calculations. To do so, use 

corrected FRqo and FRUL values of 
With these values,* Fig. 6-1 can help to provide an annual energy collection 

prediction. Because the collector is an wacuated tube, the correct T value 

to use is average daytime total horizontal irradiance. The annual average 

total horizontal irradiance during daylight hours at Columbus is about 

350 w/m2 .(as read from Pig. 5-10). The annual average ambient temperature is 

13O~ (from Appendix E) . The value of the intensity ratio (x-axis of Fig. 6-1) 

is, therefore, 

For the 40' latitude of Columbus this provides a y-axis value of 0.81. 

Now, qc can be calculated as 

The total annual energy collected can be calculated (from Eq. 6-9) as 

g, = (156 w/m2)(2250 m2) (4380 h) 

The total annual process load is 

The solar fraction is then given as 

6-1.1-2 Mixed-Td, Recirculation Ill3 System 

A mixed-tank, recirculation (four-pipe storage) system such as that illustrated in Fig. 6-3 is historically the most common configuration for a system 

with storage. This configuration has been used in several IW systems and in 

almost all solar domestic hot water systems. As noted in Sec. 4.4, this configuration is best suited for applications where the load is not continuous, 

or where the temperature difference between load supply and load return is 

*As we describe latex, incident-angle modifier effects can be included with a 

modification of the FRq0 term. 
Figure 6-3. Mixed-Tank Recirculation System 

small.* The storage tank has two inlets and two outlets, one pair for each 

of the flow loops. The storage tank is assumed to be completely mixed at one 

average temperature. This is slightly conservative from a performance viewpoint, because a small amount of thermal stratificati'on usually occurs within 

the tank. 

A mix valve is shown in Fig. 6-3. This valve is needed so that the temperature of the fluid provided to the process will not exceed the required process 

temperature. The valve mixes some of the process return fluid with the hot 

fluid from the storage tank to maintain a temperature at or below the process 

temperature. When the storage tank is below the required process temperature, 

the mix valve is fully open, and no fluid bypasses the storage tank. 

The mixed-tank recirculation system shown in Fig. 6-3 has a heat exchanger 

between the collector loop and the storage tank/load loop. This heat 

exchanger is usually used in conjunction with a nonfreezing fluid in the collector loop. In that case, the heat exchanger factor should be calculated as 

shown in Eq. 6-5. When the same fluid is used throughout the system and no 

heat exchanger is present, set F, = 1. 

The heat exchanger factor allows us to use the inlet temperature on the cold 

side of the heat exchanger as the value on which to base performance. In the 

*An alternate mixed-tank, recirculation (two-pipe storage) system configuration 

that allows bypass of storage is described in Sec. 4.4. 

9 4 
no-storage system configuration, the cold side inlet is simply the process 

load return temperature. In the mixed-tank recirculation system, the cold 

side of the heat exchanger is fed by the storage tank. However, the storage 

tank temperature is not constant, because it heats up and cools down during 

the day as energy is added or removed from the tank. Therefore, another performance modifier is introduced that relates the storage tank temperature to a 

known temperature-the process load return temperature. Because this modifier 

accounts for the effects of the storage tank* and is also a strong function of 

the process load profile, it is known as the load-storage modifier. Appendix E derives the functional relationships important to it. For a specified 

collector type and load profile, three variable groupings define the loadstorage modifier: 

The first term is the ratio of the average energy collection rate of the collector field (assuming infinite storage size) divided by the average process 

load demand rate. The second term accounts for the size of the storage tank 

relative to the sensitivity of the collectors to increased temperature. The 

third accounts for the heat withdrawal rate from storage as defined by the 

load flow capacitance. Figures 6-4 to 6-11 graphically represent the loadstorage modifiers for single-shift (8 h/day) and three-shift (24 h/day) load 

profiles. Seven-day-per-week operation is assumed. A separate figure is 

given for flat plates, evacuated tubes, north-south parabolic troughs, and 

east-west parabolic troughs. 

A separate figure is needed for each of the two trough orientations because of 

their different seasonal outputs (due to incident-angle effects) and their 

subsequent impact on annual performance . The north-south orientation shows a 

greater drop in performance than that of the east-west orientation as the 

ratio of collection rate to load rate increases (moving to the right along the 

x-axis). This is the result of the large variation in energy collection that 

occur seasonally with north-south oriented troughs. As we increase collector 

area, excess energy can be collected during the summer with the north-south 

orientation. This drives the average storage temperature up; the result is a 

higher inlet temperature to the collectors and a loss in collection efficiency. East-west-oriented troughs vary less in seasonal output and, therefore, their performance drops less significantly as collector area is 

increased. 

The impact of the energy collection rate normalized to the load demand rate 

(along the x-axis) is the most important quantity. As the ratio of energy 

collection rate to energy demand rate increases, the performance penalty also 

increases. This performance degradation occurs because the collectors are 

providing a larger fraction of the process load, which drives storage tank 

temperatures up and causes the collectors to operate at higher temperatures. 

Smaller storage capacity, larger collector UL values, and smaller load flow 

*The load-storage modifier also accounts for the impact of the mixing valve and 

load flow rate. 
rates also result in larger performance losses and storage-load modifiers farther below unity. 

Three storage sizes are shown, as defined by the values of [(Mc ) 

(A FxFRU~)]. They span the range of storage capacity typically considePe3 for 

sosar systems. Note that storage capacity is considerably less important to 

annual performance for the single-shift load profile than the three-shift load 

profile. Storage size is more important for a 24-hours-per-day load because 

storage can considerably extend the number of hours that part of the load can 

be met with stored solar heat. For example, stored heat may permit energy to 

be withdrawn from the tank late into the evening. In the single-shift load, 

no load exists in the late afternoon or evening; thus, stored energy can be 

withdrawn only during cloudy, daytime periods. 

The curves shown on Figs. 6-4 to 6-11 extend over the range of storage capacitance, load flow rates, and ratios of collection rate to load demand rate for 

which SOLIPH computer results were generated. These ranges are in part 

defined by the range in process load temperatures that was considered: up to 

90°c for flat plates, up to 150~~ for evacuated tubes, and up to 300~~ for 

parabolic troughs. Zxtrapolation beyond these limits is not recommended. 

The annual performance of a mixed-tank, recirculation system can now be predicted by first using Fig. 6-1 to determine the annual energy collection rate 

of the collector. Use the process load return temperature for Tin and use the 

calculated value of F, for Fs if a heat exchanger is present. Now, use the 

result to compute the load-storage modifier for a given storage size, collector area, load flow rate, load demand, and collector UL value. Because the 

load-storage modifiers are defined by three quantities, interpolation may be 

necessary for two of the quantities when reading from Figs. 6-4 to 6-11. 

The total annual energy collected by a mixed-tank, recirculation system is 

calculated as 

where 

Qc = total annual average energy collection 

9c,, = annual average energy collection rate during daylight hours 

(from Fig. 6-1) 

Ac = collector area 

= annual load-storage modifier (from Figs. 6-2 to 6-9) 

Ndaylight = number of daylight hours in year (= 4380) . The total annual process load is 








where 

bead = average process load energy demand [= kloadCP(~a - %,r)] 

ITload = number of hours load operates during the year , 

Now, the solar fraction can be calculated as 

The following example illustrates the procedure. A solar industrial process 

heat system is to be installed at a medium-sized fluid dk-processing plant 

located in Fort Worth, Texas .* A major use of low-temperature process heat is 

to generate hot water for cleanup. A minimum water temperature of 43'~ 

(110~~) is required to dissolve milk fats. The dairy uses 16,000 kg/h 

(35,000 Ib/h) 'of such water from 8 AM to 4 PM seven days per week. The hot 

water is produced in a steam-to-water exchanger and is piped throughout the 

plant to the various wash stations. Inlet water temperature is 20'~ (68'~). 

The contaminated nature and low temperature of the wash water effluent make 

heat recovery impractical. The dairy has 800 m2 (8650 ft2) of usable roof 

space, but much of that is over warehousing; only minimal increases in roof 

loads are permissible. -Bowever, the dairy owns three acres of vacant land, 

within 46 m (150 ft) of the process building, that are available for a solar 

energy system. 

For a thorough analysis , we should compare f la t-plate , evacuated-tube , and 

parabolic-trough collectors. For purposes of demonstrating the procedure, 

however, we will examine only flat plates, because of the very low temperature 

requirement in this application. The total annual load is as follows: 

Let us start by determining how much energy the roof area could provide. A 

good, single-glazed, selective-surface flat plate would have the following 

values (from Table 5-1): 

FRno = 0.65 - 0.8 + use 0.72 

20 

'R'L = 2.6 - 4.4 + use 3.1 W/m C . 

In Fort Worth, Tex., the annual average total horizontal irradiance during 

daylight hours is about 400 w/m2 (from Fig. 5-10). The AT needed for Pig. 6-1 

is the difference between load return and ambient. The load return is 20'~ 

and the average daytime ambient in Fort Worth is 21'~. Thus, AT = 0. The 

*This example is based upon a case study from a SEBI report by Hooker et al. 

(1980) 
value of F will be set to one because no heat exchanger is expected to be 

needed. ?The load return water will be circulated directly through the 

collectors.) So, the value on the x-axis of Fig. 6-1 is 

With latitude = 32.s0 and X = 0, Fig. 6-1 yields a value along the y-axis of 

1.0. 

qC ," 

- = 1.0 . Solving for , we obtain FsF~nol 

c ,OD 

Now, use Fig. 6-8 to determine the load-storage modifier. Looking at 

Fig. 6-8, we see that for this load profile, mi~imal storage is needed. We 

will use a value of 20 h as our baseline for [(MC )stor/(AcP F U )] . Since 

we have an 800 m2 roof, we will start with a coll&tor area OF %& m2 (ground 

cover ratio of 0.5). 

The value of 

The process load use rate, ?) load' is calculated as 

(4.84 x 1012 ~)(~~t~ ) - - yr 5 

Qload days = 4.60 x 10 W . (365 7)(8 &) 

We can now calculate the y-axis value to be used with Fig. 6-8: 

From Fig. 6-8, the load-storage modifier is 0.934. 

Now, the annual energy collected by 400 m2 of flat-plate collectors is given 

by 
The solar fraction is 

To increase the solar fraction substantially above 0.35, it would be necessary 

to mount collectors on the land adjacent to the plant. Selecting the optimum 

collector area for a mixed-tank recirculation system requires a trade-off of 

the increased energy collection that occurs as collector area is added against 

the increased costs of the system. Typically, several collector areas will be 

selected, and the life-cycle costs of these options will be compared. 

The collector area with the most favorable life-cycle economics. is usually 

selected. Sometimes, however, other considerations dictate a different 

choice* For example, the land or roof area available for mounting the collectors may constrain maximum collector area. Or, if an industrial plant must 

operate at a certain minimum capacity to be profitable, sufficient collector 

area may be installed so that, in the event of an interruption of fossil-fuel 

supply, the solar system can maintain the thermal needs of that minimum 

capacity. 

6.Imlm3 Variable-Volume Storage System 

A variable-volume storage system is shown in Fig. 6-12. In this configuration 

there is no recirculation of fluid between the storage tank and the collector 

field. Heating the collector loop fluid is accomplished with a single pass 

through the collector field. The hot water is stored in a tank that can be 

completely drained and used by the industrial process. When solar energy is 

being collected, hot water is added to the tank. When a process load exists 

and hot water is available in the tank, the hot water is pumped from the tank 

to the process load. If the industrial process is an open loop (i.e., the hot 

water is consumed and not returned for reheat), the cold tank is not needed. 

Make-up water is then supplied from the water main during the day. If the 

industrial process is a closed loop, the return water must be stored in an 

additional tank (see Fig. 6-12). 

An advantage of the variable-volume storage system is that the collector array 

is always supplied with the coldest possible fluid, whenever it is operating, 

regardless of whether the load is on or off. In this respect, it is similar 

to a no-storage system. However, because this configuration has storage, it 

is an efficient system configuration for all load profiles, daytime or nighttie shifts. 

Our approach to the design and performance analysis of a variable-volume system follows the basic precept that thermal energy delivered by the collector 

system should never be dumped. This no-dump requirement is equivalent to 
Variable 

Volume 

Hot 

Tank Load Supply 

Load Return 

I I 

L - - Variable-Volume 

Cold Tank 

(Not Needed for 

Open Load Loops) 

Figure 6-12. Variable-Volume Storage Configuration 

s.izing the system so that the peak daily energy collection of the solar system 

does not exceed the daily process load. Further, the volume of water heated 

during the day by the collectors and delivered to the storage tank should not 

exceed the volume of water the process needs. for one day of operation. The 

maximum daily energy collection of the solar system can be estimated as 

where 

2 A, = collector area (m ) 

4a ,max = maximum daily total irradiation available to collectors per 

unit of collector area 

= day-long efficiency of collector. 

The day-long efficiency of the collector can be estimated as 

2 where I, daily is the average irradiance (W/m ) available to the collector on 2 a clear day. A value of 650 W/m for Ia daily is a good average for clear-day 

irradiance and can be used as an approx'imation. Values of FRTlo and FRUL can 
be taken directly from the collector performance data sheets. Tin should be 

set to the process load return temperature. The maximum ambient temperature 

can be taken as 40'~. Values of q,, are provided in Table 6-1 for the various collector types at latitudes of 24' to 56'. These values have been 

derived from clear-day design tables provided in the ASERAE Handbook of ~unda-' 

mentals. The maximum daily energy collection obtained from Eqs. 6-15 and 6-16 

is approximate but sufficient for system design. The constraint that the maximum energy collected in one day is less than or equal to the daily process 

load demand can be expressed as 

Substituting front Eq. 6-15, the maximum collector area that can be utilized 

and still satisfy this condition is calculated as 

The constraint that the maximum volume of water provided to storage in one day 

must be less than or equal to the volume of water used by the process every 

day can be used to determine the maximum pump mass flow rate. 

M - - /t 

pump c,mx 

where 

= daily process water usage (kg) 

c ,,, = maximum operating time of pump (collectors) in one day. 

Table 6-1. Maximum Daily Irradiation Available for Several Collector Typesa 

Latitude 

(degrees) 

- -- -- - 

Flat-Plate East-West North-South 

and Evacuatedb Parabolic Parabolic 

Tube Collectors Trough Collectors Trough Collectors 

~~~alues are given in MJ/m2 (~tu/ft* in parentheses). 

b~alues for flat plates and evacuated tubes are for collectors tilted at latitude angle. 
The maximum operating time for a parabolic trough can be estimated from the 

number of daylight hours during the longest summer day. The number of hours 

between sunrise and sunset on the summer solstice is given (in hours) by 

where L = local latitude of site, in degrees. 

Realistically, two hours may be subtracted from this length of time because 

the solar irradiance will not be sufficient to maintain collector operation in 

the earliest morning hour or latest afternoon hour. Thus, the maximum operating time of a parabolic trough, for a single day, can be approximated (in 

hours) by 

With a flat-plate or evacuated-tube collector, no energy can be collected on a 

summer day until the sun is sufficiently high in the sky that sunlight falls 

on the front of the tilted collector. With a collector tilted at the local 

latitude angle, a maximum of twelve hours of sunlight is available for solar 

collection (Liu and Jordan 1977): 

tc,max = 12 for flat plates . The flow rate determined from Eq. 6-18 will ensure that the volume of water 

heated by the solar system can always be used by the process; hence, no energy 

will have to be dumped. This is also consistent with a design philosophy that 

minimizes the operating temperature of the collector and, hence, maximizes 

collector efficiency, within the constraints of a single-speed pump and a nodump requirement. 

Having determined the pump flow rate, we can now determine the correct value 

of FR (see Eq. 6-2) for any given collector area up to A t,max' the maximum 

collector area for which no dumping occurs. Adding col ector area up to 

*c ,max for a constant system flow rate results in a lower value of FR because 

the average collector operating temperature increases. Conversely, decreasing 

the collector area lowers the average collector operating temperature, and FR 

approaches one. Now, the annual performance of the variable-volume storage 

system can be predicted using only Fig. 6-1. Use the process load return temperature for Tin. AS with the other systems, if a heat exchanger is used the 

heat exchanger factor Fx should be calculated and used as Fs. The value of FR 

should be calculated based on the calculated system flow rate and the collector area being considered. The total annual energy collected is then calculated as 

where 

Qc = total annual average energy collection 

. 

qc = annual average energy collection rate during daylight hours 

(from Fig. 6-1) 
A, = collector area (c A,,mx 1 

Ndaylight = nmber of daylight hours in a year (= 4380). 

The total annual process load is 

where 

Qload = average process load energy rate [= mc (Tg - T )] P g,r 

Nload = number of hours load operates during the year. 

The solar fraction can then be calculated as 

6.1.2 Steam Systems 

The largest share of the total industrial process heat requirement is currently met by steam. An alternative to generating steam with a packaged steam 

boiler is a steam-generating solar system. In either case, the steam is 

delivered to the point of use in a saturated state. This saturated steam is 

used typically to heat a vessel to drive a chemical reaction, or it may be 

employed for evaporation, crystallization, etc. The steam is condensed during 

the process; after treatment, the hot water is returned to the boiler or solar 

system for revaporization. Generating steam with a solar system requires a 

significantly different system configuration than that for air or water process heating. Two system approaches to generating steam are considered here: 

flash steam systems and unf ired-boiler systems. The operating temperatures 

needed for steam generation ordinarily preclude using water as a heat storage 

fluid, because an expensive high-pressure storage tank would be required. 

Instead, an oil is usually the heat-storage medium. Such fluids are quite 

expensive. Therefore, because storage for steam systems is so expensive, it 

is not likely to be used widely in the near future and is not discussed here. 

Information on the performance of steam systems using thermocline storage can 

be found in Harrigan (1981). 

6.1 -2 -1 Unf ired--% ler Steam Systems 

In an unfired-boiler steam system (see Fig. 4-4), an organic heat transfer 

fluid is pumped through the collector field and then to an unfired boiler. 

The hot fluid within the tubes of the boiler vaporizes the water next to the 

tubes; this saturated steam is fed to the existing steam header, which delivers energy to the industrial process. As the steam is generated, additional 

condensate is supplied to the boiler. The hot condensate is assumed to be 

saturated. Steam generation is a latent-heat process; therefore, no temperature change occurs on the water side of the boiler. Because heat is being 

transferred from the collector loop fluid to the water, the fluid in the collector loop must always exceed the steam saturation temperature. Therefore, 
the temperature of the fluid at the inlet to the collector fluid must exceed 

the steam saturation temperature. To account for the temperature elevation of 

the collector loop inlet above the steam temperature, a performance modifier 

is introduced--the unfired boiler factor, FB. It is calculated as follows: 

where 

FRUL = the collector heat-loss coefficient 

k = collector loop flow rate 

C 

; = collector loop flow rate per unit collector area (= %/A,) C , 

c = collector loop fluid specific heat P 

UbAb = unfired-boiler heat transfer coefficient, boiler surface 

area product. 

The unfired-boiler modifier is shown to be a function of the unfired-boiler UA 

value, the collector loop flow rate, and the collector UL value. The derivation of this modifier is given in Appendix E. It assumes that the collector 

loop flow rate is constant. A constant collector loop flow rate is usually 

used for steam systems, although variable flow rate systems that maintain a 

constant collector outlet temperature are sometimes employed. However, the 

greater complexity of a variable flow rate system is usually unwarranted. 

More details on variable flow control systems are given in Sec. 8.0. 

The unfired-boiler modifier allows energy collection for an unfired-boiler 

steam system to be written as 

To size the maximum collector area for an unfired-boiler system without storage, follow the guideline that no collected energy should be dumped, the same 

as for the no-storage hot air and hot water systems. The rate at which the 

process load requires energy is equated to the rate at which the collector 

field can deliver energy under the best solar collection conditions: 

2 As suggested in Sec. 6.1.1.1, a value of 1000 W/m can be used for parabolic 

troughs and 1100 w/m2 for flat-plate and evacuated-tube collectors. Also, a 

maximum ambient temperature (Ta,max ) of 40'~ is recommended. Values of FRno 

and FRUL are taken directly from the performance data of the collector. Tin 

should be set to the steam saturation temperature. After all the appropriate 

values are determined, the maximum collector area for the no-storage system is 

then solved as 
This collector area is the maximum amount that can be used within the no-dump 

constraint. Smaller collector fields can also be used with a resulting 

smaller amount of solar system energy collection. Now, the annual performance 

of the solar system can be predicted using Fig. 6-1. Use the unf ired boiler 

factor FB for -F and the steam saturation temperature for Tin. The total 

annual energy coflected is then calculated as 

where 

qc = annual average energy collection rate during daylight hours 

per unit collector area (from Fig. 6-1) 

A, = collector area (( 1 

Ndaylight = number of daylight hours in year (= 4380). 

The total annual process load is 

where 

hload = average process load energy rate [= kloadcp(T~ - TQ,~)] 

Nload = number of hours that process load operates during year. 

Now, the solar fraction can be calculated as 

6.1.2.2 Flash Steam Systems 

In a flash steam solar system (see Fig. 4-3), pressurized water is circulated 

through the collector field and flashed to low-quality steam across a throttling valve into a flash, or separator, tank. Flashing is a constant enthalpy 

process that converts the sensible heat of the water into a two-phase mixture 

of saturated water and saturated steam at conditions prevailing in the flash 

tank. The steam quality (fraction of total mass flow that is flashed to vapor) usually is less than 10%. Steam separated in the flash tank is fed into 

the plant steam distribution system to be used by the industrial process. The 

saturated liquid is recirculated through the collector field. To maintain the 

necessary liquid level in the flash tank, boiler feedwater is injected into 

the pump suction. 

To prevent boiling within the collectors or the collector field piping, the 

water must be pressurized. Pressure is maintained by the recirculation pump 

which, in the simplest control mode, operates at constant flow. The pump is 

sized so that water exiting the collector field is under sufficient pressure 

to prevent boiling. The collector field outlet temperature must be considerably above the steam delivery temperature to obtain reasonable steam qualities 
downstream of the throttling valve. Higher steam qualities allow the water to 

be recirculated through the collector field fewer times. Therefore, the average collector operating temperature is usually significantly above the steam 

saturation temperature. A performance modifier accounts for this temperature 

elevation--the-flash system factor FF. It is calculated as follows: 

where 

m = collector loop flow rate per unit collector area 

C 

Ahfg = heat of vaporization of steam at its saturation temperature 

c = specific heat of saturated water P 

Ts = steam saturation temperature 

Tf = feedwater temperature. 

The derivation of this modifier is given in Appendix E. It allows energy collection for a flash system to be written as 

This is identical to the unfired boiler (Eq. 6-26) except that FF is substituted for FB. Therefore, Eqs. 6-27 to 6-31 can be used for the flash system 

sizing and performance analysis, using FF. 

6 -2 INCIDENT-ANGLE EFFECTS 

The incident angle of solar radiation on a solar collector is defined as the 

angle between the normal-to-the-collector aperture and the direction of the 

sun. In describing off-normal irradiance, only the direct or beam component 

of irradiation is considered. Diffuse irradiance does not affect incidentangle corrections because it is nondirectional by.definition. 

The incident angle of solar radiation has an impact on energy collection in 

several ways. First, the intensity of the beam irradiance component available 

to the collector decreases at offnormal incidence according to the cosine of 

the incident angle. This effect has been incorporated into the performance 

curves of Fig. 6-1, because the hour-by-hour computer model from which the 

figure was generated computed the incident angle for each hour and provided 

for this correction. 

Second, off-normal irradiation typically reduces the optical efficiency of a 

collector below that for normally incident irradiation. The effect is 

described by an incident-angle modifier that shows how the optical efficiency 
of a collector changes with incident angle, relative to its optical efficiency at normal incidence. The impact of a collectorls incident-angle modifier upon the annual performance of a collector is-described in Sec. 6.2.1. 

The third effect .applies to parabolic-trough collectors but not to flat-plate 

or evacuated-tube collectors. This incident-angle effect, end loss, refers to 

energy lost from the end of a parabolic trough when the incident radiation is 

not normal. Some of the radiation reflected at the end of a parabolic concentrator will spill off the end of the row and not be intercepted by the 

receiver. This loss is accounted for in Sec. 6,2.2, 

6.2.1 Incident-hgle Modifiers 

The optical efficiency of most collectors decreases as the incident angle of 

incoming irradiation increases. This is shown in Fig. 5-9, which provides 

typical incident-angle modifiers of various collectors. In some cases, 

however, a collectorls optical efficiency can increase with of faormal irradiation. Evacuated-tube collectors without specular reflectors can have incident-angle modifiers that increase with that angle because, as the sun angle 

gets lower, the effective gap between tubes shrinks and intercepted irradiation increases. Flat-plate collectors decrease in optical efficiency at offnormal incidence because, as incident angles increase, the transmittance of 

glazing materials and the absorptance of the absorber coatings decrease. Parabolic troughs exhibit a reduction in optical efficiency at off-normal incidence because of glazing and absorber properties as well as because of the 

increase in path length of the reflected radiation at off-normal incidence. 

That increased path length permits a wider spread in the reflected beam and 

causes the amount of radiation intercepted by the receiver to drop. 

For each of the three types of collectors, a typical incident-angle modifier 

has been assumed in the curves of Fig. 6-1. For energy-collection predictions 

for collectors with other than these assumed incident-angle modifiers, correction factors are used. Correction factors for flat plates, evacuated tubes, 

and parabolic troughs are given below. 

As noted in Sec. 5.2, the incident-angle modifier for a flat-plate collector 

can be correlated by an equation of the form: 

k,, = 1 - bo[(cos - 11 

where bo is the incident-angle modifier coefficient. 

Figure 6-1 assumes a bo value of 0.11, which is typical of single-glazed flatplate collectors with black painted absorbers. However, b values down to 

about 0.06 have been found, and bo values up to about 0.17 are typical of 

double-glazed flat-plate collectors. We need a way to account for these differences to provide an accurate collector performance analysis. Figure 6-13 

provides a simple graphical correction factor for the performance impact of 

incident-angle modifiers of flat-plate collectors. The x-axis is simply the 

incident-angle modifier coefficient bo for the given flat plate. Along the 

y-axis, the graph provides a value of the annual incident-angle modifier. 

This annual modifier yields a correction term to the optical efficiency of a 
collector that closely accounts for the performance impact of the incidentangle modifier on an annual basis. Note that because a bo value of 0.11 was 

assumed for Fig. 6-1, the annual modifier for a bo value of 0.11 is one; i.e., 

no correction is necessary. For bo values other than 0.11 we must correct the 

optical efficiency term no in Fig. 6-1, on both the x-axis and y-axis. 

The incident-angle modifiers of evacuated-tube collectors usually cannot be 

expressed in the form of Eq. 6-34; therefore, Fig. 6-13 does not apply. 

Instead, a simple equation helps us to arrive at an annual modifier that 

closely accounts for incident-angle effects. The evacuated-tube annual modifier correction can be calculated as 

The K values are the incident-angle modifiers at the particular incident angle 

denoted by the subscript. Essentially, Eq. 6-35 breaks up a collector's incident-angle modifier curve into 15O intervals and applies a weighting factor to 

each interval. These empirical weighting factors are defined largely by the 

fraction of collectable energy that occurs within each incident-angle span. 

Equation 6-35 allows the performance impact of the incident-angle modifier of 

an evacuated tube to be evaluated quickly even if it is highly irregular, as 

it is for some evacuated tube collectors. Because the same curves on Fig. 6-1 

are used for both flat plates and evacuated tubes, the baseline evacuated-tube 

incident-angle modifier was assumed to be also given by Eq. 6-34. Therefore, 

the correction factor calculated with Eq. 6-35 is relative to the same baseline incident-angle modifier as the flat-plate collectors. As before, the 

modifier calculated with Eq. 6-35 is applied to the optical efficiency in 

using Fig. 6-1. 

Parabolic-trough incident-angle modifiers, like those of evacuated-tube collectors, are not well correlated by an equation like Eq. 6-34. Typically, 

parabolic-trough incident-angle modifiers decrease more rapidly with incident 

angle than do those of flat-plate collectors (Gaul and Rabl 1980). To account 

for these differences, an annual modifier correction (similar to that for an 

evacuated tube) is provided. The annual incident-angle modifier correction 

for an east-west parabolic trough is calculated as: 

As before, the K values are taken from the incident-angle modifier curve for 

the collector at the incident angles denoted by the subscript. Because little 

energy is available for collection at high incident angles, the weighting factor for them is small. Most of the energy available to a parabolic trough 

occurs at small incident angles; thus, the weighting is greater there. 

A general equation with constant weighting factors (of the simple form of 

Eq. 6-36) is not accurate for north-south parabolic troughs because of the 

impact that latitude has on the average incident angles of north-south troughs. 

The weighting factors are a function of the latitude of the site, as shown in 

Fig. 6-14. The weighting is larger at low incident angles for low latitudes 

Incident 'Angle (degrees) 

Figure 6-14. Annual Optical Efficiency Incident-Angle Weighting 

Factors for a North-South Rough 

because, at low latitudes, the bulk of the energy striking a north-south parabolic trough occurs at low incident angles. At high latitudes, north-south 

troughs often operate when incident angles are high; therefore, the weighting 

is smaller at low incident angles. 

6.2.2 End Losses 

Radiation spillover, or end loss, from parabolic troughs of finite length can 

be calculated (Gaul and Rabl 1980) as: 

where 

Lend = end loss factor (1 - fraction lost) 

f = trough focal length 

R = trough length 

w = trough aperture width 

8 = incidence angle. 
This equation assumes that the receiver has the same length as the concentrator. The end-loss factor is shown to decrease as parabolic trough lengths 

increase and incident angles decrease, 

Gaul and Rabl (1980) evaluated the all-day average of the end-loss factor for 

a typical parabolic trough on a seasonal basis. Their results are shown in 

Table 6-2. An additional column of data has been added for the annual endloss factor, based on the average of the summer, autumn, winter, and spring 

end-loss factors. For typf cal parabolic trough drive strings with R/f ratios 

exceeding 25, the annual end-loss factor is above 0.96.* Therefore, less than 

4% of the collectable energy is lost because of end spillage. The annual endloss factor should be estimated from Table 6-2 for the particular collector 

drive string to be configured for the IPH collector system, This end-loss 

factor should then be used to modify the energy predictions computed from 

Fig. 6-10 

6.3 ROW-TO-RW SHADING EFFECTS 

Typical IPH collector fields are arranged with multiple rows of collectors. 

These collector rows are set quite close together to minimize land area 

requirements and collector field piping. However, this close proximity causes 

row-to-row shading losses. These shading losses are not accounted for in the 

curves of Fig. 6-1. The graphs in this subsection quantify these row-to-row 

shading losses on an annual basis. The analysis of row-to-row shading loss is 

greatly simplified if end effects are ignored and each row is assumed to be 

much longer than it is wide, a good approximation for typical IPH collector 

rows. With this assumption in mind, consider parallel raws of collectors 

Table 6-2. All-Day Average of End-LOSS Factors (Lend) 

R East-West Axis North-South Axis - 

f Summer Equinox Winter Year Summer Equinox Winter Year 

- -- .-. . . - -. - - -- - . - - - . - . .- -- - - - 

a~op number represents cutoff time one hour before sunset; bottom number 

represents cutoff time two hours before sunset. 

Source: Gaul and Rabl 1980. 

*This assumes that the losses that occur between adjacent modules on a drive 

string are negligible. 
(either tracking or nontracking) as shown in Fig. 6-15a. The row-to-row spacing is designated as R and the aperture width of the collector is W. We 

define the ground cover ratio (GCR) to be the ratio of W to R: 

W GCR = - R * (6-38) 

First, let us consider the beam component of radiation. Either the beam component is shaded from one row to another, as shk in Fig. 6-15b, or the beam 

component is not shaded from row to row, as shown in Fig. 6-15c. Note that 

when shading does occur, no beam irradiance reaches the ground; that is, all 

the beam irradiance that would normally reach the ground has been intercepted 

by the collectors. Hence, the radiation incident on the collector array is 

A 1 COS eh , gb 

where 

Ag = ground area 

I,, = beam irradiance (direct normal) 

= incident angle of direct irradiance on the horizontal surface. 

Whenever no shading occurs, the radiation incident upon the collector is 

where 

A, = collector area 

0 = incident angle of beam irradiance on the aperture of the 

collector. 

Therefore, as given by Rabl (1981), the beam irradiance available per unit of 

collector aperture area is 

I COS eh 

Ia = Ib * Min cos 8, GCR 

Therefore, the direct irradiation available to a collector, including shading 

effects, is a function of incident angles (which are defined by the collector 

type and the site latitude) and the ground cover ratio. The collector tilt 

angle is assumed to be equal to the site latitude. 

Now, consider the diffuse component of radiation for flat-plate and evacuatedtube collectors. A fraction of the diffuse component of radiation that would 

normally fall upon a collector is blocked by the row immediately in front of 

it. To the extent that diffuse radiation is isotropic (as is typically 

assumed), the fraction of the diffuse radiation incident on a horizontal surface that is available to a tilted collector can be calculated as the view 

factor of the sky as seen by the collector. This view factor can be calculated using a crossed-string method (Jones and Burkhart 1981) as 

Fd = 0.5 (1 + [sin ($ + B)/sin $1 - [sin &/sin $1) , (6-40) 

where the angles $ and B are shown on Fig. 6-15a. 

The ground cover ratio can be defined in terms of the angles $ and B as 

GCR = (cos B + sin B/tan $)'I . (6-41) 

Therefore, the fraction of diffuse radiation available to a flat-plate or 

evacuated-tube collector is a function of the collector tilt angle and the 

ground cover ratio. The collector tilt angle is assumed to be equal to the 

site latitude. 

Because the direct and diffuse radiation losses due to row-to-row shading are 

principally dependent only on collector type, site latitude, and ground cover 

ratio, they can be expressed in graphical form as shown in Figs. 6-16 to 6-18. 

These figures show annual row-to-row shading correction factors as a function 

of latitude for parabolic troughs, flat-plate collectors, and evacuated-tube 

collectors. As explained above, these correction factors account for the loss 

of beam irradiation and, for flat-plate and evacuated-tube collectors, the 

loss of diffuse irradiation due to the reduction in view factor from the collector to the sky. 

The shading factor obtained from Figs. 6-16 to 6-18 applies only to the rows 

being shaded--that is, all rows but the first. To account for the unshaded 

row, use the following equation to compute an average field shading factor: 

where 

Fshad = shading factor as determined from Figs. 6-16 to 6-18 

N = number of rows in field. 

Row-to-row shading losses increase' for all types of collectors as site latitude increases, because the sun is, on the average, lower in the sky at high 

latitudes, resulting in more shading. Collector rows can, therefore, be 

spaced much closer together at low latitudes than at high ones. The impact of 

row-to-row shading losses is especially significant for north-south rotational-axis parabolic troughs. Therefore, north-south parabolic troughs 

should be spaced significantly farther apart than east-west troughs. 

6-4 'ANNUAL IXlSSES CW COLLECTOR FIELD PIPING AND STORAGE 

Thermal losses from the collector field piping and storage tank (if any) can 

reduce the energy delivery of a solar system significantly. Section 7.0 

describes how to arrange collector field piping and how to determine how much 

insulation should be added around' the piping and the storage tank. Here, we 



describe how to account for the annual thermal losses from these components, 

so that annual energy delivery can be predicted for the solar system. Three 

different thermal losses are considered: steady-state losses, overnight 

losses, and recirculation losses. . - 

6.4-1 Steady-State bsses 

Steady-state losses are thermal losses that occur during operation of the 

solar system. By a simple adjustment of the collector parameters no and UL, 

it is possible to account for most of the thermal losses from piping and storage on an annual basis. The derivation of the corrected no and UL values follows the analysis of Beckman (1978) and is included in Appendix E, which shows 

that by replacing the collector parameters no and UL with modified values no' 

and UL1, we can account for the steady-state losses. These modified values 

are defined as 

and 

where 

$cp = 'collector loop flow capacitance 

UoAo = overall heat loss coefficient of piping and other components 

located on outlet (hot) side of collector field 

Ui$ = overall heat loss coefficient of piping and other components 

located on inlet (cold) side of field 

A, = collector area. 

The modified n and UL values defined by Eqs. 6-43 and 6-44 can be used 

directly with F!?~. 6-1 to determine the annual energy delivery of the collector system. To determine the steady-state thermal losses from the field 

piping, storage tank, and other components, it is neccesary to group the components in either UoAo or UiAi. Components included in UoAo will have a 

greater impact on energy delivery because they operate at a higher average 

temperature. 

UA values for insulated pipes can be obtained from Sec. 7.1.3, in which a 

method of determining the most economic pipe insulation thickness is given. 

(For purposes of conceptual design, the designer should estimate the insulation thickness based on past experience; detailed design requires iteration 

between insulation thickness and the resulting cost of delivered solar 
energy.) Note that pipe UA values in Sec. 7.1.3 are values per unit length of 

pipe; thus, they should be multiplied by the pipe lengths involved to obtain 

overall UA values. 

Estimates -of UA values for pumps, valves, fittings, and pipe anchors, for 

example, are not as straightforward as they are for pipes. We can use the 

equations in Sec. 7.1.3 to estimate U values for these components, however. 

The U value can then be multiplied by the estimated total hot surface area of 

these components to arrive at an overall UA value. In practice, care must be 

taken to achieve low U values for such components as exposed valve stems, pipe 

supports, and anchors, as they will act as fins to conduct heat away to the 

environment. (It is worthwhile to isolate pipe supports and anchors from the 

pipes thermally with a noncompressible insulation.) 

Piping, valves, fittings, pipe anchors, and the like, located on the inlet 

side of the collector, should be added to the inlet overall heat loss coefficient UiAi, and those on the outlet piping should be added to UoAo. Pump UA 

values should account for the overall heat loss from the pump's surface as 

well as the heat required for cooling the pump seal, which could possibly 

cause significant thermal losses. Seal configurations that reduce sealcooling requirements are recommended. The collector loop pump is located on 

the inlet side of the collector field; thus, it should be grouped into Ui+. 

If storage is used in the system, the appropriate UA value can be calculated 

based on its size and the amount of insulation that surrounds it. When it is 

multiplied by the storage tank surface area, this U value provides an estimate 

of the storage tank UA value, which should be added to the outlet side overall 

heat-loss coefficient. This.is a conservative analysis of a mixed-tank recirculation system, because the storage tank temperature will be lower than that 

of the collector outlet fluid. For a variable-volume system, however, the 

storage tank is filled directly from the co~lectors; hence, the fluid exiting 

the collectors is the same average temperature as the storage. (In the 

detailed design and construction phase, efforts should be made to minimize 

heat leaks from storage tanks associated with pipe penetrations and support 

structures.) When UA values for all components have been determined, then UA 

values for components at like temperatures are summed to provide UiAi and 

6.4.2 Overnight Usses 

When a solar system is shut down at the end of a day, the piping, components, 

and fluid inventory are often still hot but can lose heat during the night. 

These nightly thermal losses have been termed nonoperating, overnight, or cool 

down losses, and they represent energy collected but never delivered to the 

process load. Overnight losses can be estimated by calculating the total heat 

capacitance of the components and the fraction of heat lost overnight. The 

most significant components in terms of overnight losses are the storage tank, 

the collectors, the field piping and insulation, and the heat transfer fluid 

they contain. 

The total heat capacitance of flat-pla te collectors should include contxibutions from the absorber plate, the fluid it contains, and any interconnecting pipirig between collectors. For evacuated tubes, the heat capacitance of the 
absorber surface, the fluid within each tube, the headers that connect adjacent tubes, and the fluid within the headers should be summed. For parabolic 

troughs, the heat-capacitance contributions are from the absorber tube, the 

fluid in the absorber, flexhoses, and the fluid they contain. . - 

The piping that runs to and from the collector field usually does not cool 

down to ambient overnight. If an insulated fluid-filled pipe has negligible 

internal resistance, it will exhibit a uniform temperature as it cools, given 

by 

T = Ta + (Ti - Ta) e -At/? 3 

where 

Ta = ambient temperature 

Ti = initial temperature of pipe 

At = length of time pipe has cooled 

T = time constant of pipe given by Mc /UA. P 

The total amount of heat lost is 

For an example, consider a water-filled 12.7-cm (5-in.), schedule 40 pipe 

covered with 7.6- cm (3 in.) of insulation having a thermal conductivity of 

0.156 k~/h/Oc per meter of length (0.214 ~tu/h/O~ per foot). The total heat 

capacity Mc of such a pipe is about 64 k~/k per meter of length (10.2 Btu/F 

per foot). 'The time constant r is, then, about 48 hours. In a 16-hour cooldown period (system shut-down to start-up the next morning), the total amount 

of heat lost is 

Thus, the pipe in the example theoretically loses only about 28% of its heat 

overnight. Smaller pipes, or pipes with less insulation, exhibit higher heat 

losses. In practice,' valve stems, pipe supports and anchors, etc., provide 

conduction paths that significantly increase heat loss. Until such additional 

heat losses can be quantified experimentally (tests are being done at Sandia 

National Laboratories in Albuquerque), it is recommended that half the energy 

left in the piping and associated components be counted as lost overnight. 

Storage tank insulation should keep thermal losses to a small fraction of the 

solar energy delivered to storage, as noted in Sec. 7.6. Because of the large 

thermal mass of typical storage tanks, the temperature of the storage fluid 

will not decrease substantially overnight. Hence, storage loss overnight can 
be based on a constant heat loss rate. This heat loss rate can be calculated 

as 

. -- 

where 

Usto, = storage tank heat-loss coefficient 

Asto, = storage tank surface area 

Tst0, = storage temperature 

Ta = ambient temperature. 

The storage tank temperature Is reasonably assumed to be the same as the process load return temperature, because energy typically is withdrawn from storage until the tank approaches the process return temperature. Also, the 

initial temperature Ti of the field piping and collectors is assumed to be the 

same as the process return temperature, because when the collectors shut down 

at the end of the day, they usually are not producing much energy, and the 

average temperature of the piping is close to the load return temperature. 

Therefore, the total annual overnight losses of a collector system can be 

estimated as 

The factor No er is the number of days of operation per year, which determines 

the number o? days of cooldown losses . A value of 300 days is a conservative 

assumption. The factor 16 in the final tern of Eq. 6-49 is the average number 

of nonoperatlonal hours per day that the storage tank loses heat, and the 

factor Nd is the number of days per year that the storage tank does so. A 

value of 365 can be used because the storage tank will lose heat even if the 

collectors did not operate every day. The value of T,, the average nighttime 

ambient temperature, may be determined from the tables in Appendix F for many 

U.S. cities. That appendix contains average daytime temperatures, but by simply subtracting 6'~ from the daytime values, average nighttime temperatures 

are closely approximated. 

6.4.3 Freeze-Protection Heat Usses 

In addition to the energy lost as pipes, components, and fluids cool down 

overnight, heat losses will occur in the freeze-protection system if warm 

water is circulated through the collectors in freezing weather. Such circulation freeze-protection systems are usually appropriate only in mild climates. 

A -typical freeze-protection strategy is to circulate warm water (usually from 

storage) with the collector loop pump when sensors located in the collector 
plumbing indicate that near-freezing temperatures are being reached. The flow 

is halted after the low-temperature signals stop, and the system is allowed to 

cool down with no flow until the low-temperature alarm is activated again. 

The average heat loss rate from this freeze protection system when it is in 

operation-is expressed by 

where 

& = heat loss rate (W) 

Ta = ambient temperature when freeze protection is used (OC) 

Tr = recirculation fluid temperature (OC) 

U%, UAo = UA values of pipes going to and from the collectors (W/K) 

UL = heat loss coefficient of collectors (w/m2-K) 

2 A, = collector area (m ) 

Tset = temperature set-point for recirculation ('2). 

In most systems, ULAc is much greater than UP4 + UAo, and the losses from the 

collectors dominate the solution. 

To use Eq. 6-50 to estimate the annual energy lost by such a freeze-protection 

system, it is necessary to know how many hours per year the system will be 

operated. Fig. 3-4 shows the incidence of freezing days in the United States 

on an annual basis. To estimate the number of hours of freezing weather per 

year, data from the SOLMET sites were analyzed to find a correlation between 

the number of days of freezing weather and the number of hours of freezing 

weather per year when the collectors are not operating. The results of that 

analysis are plotted in Fig. 6-19, both as the least-squares curve fit to the 

data and the actual data points, so that the range of error can be seen. 

Using the two figures together, we can estimate the total number of hours of 

freezing weather that will occur at a given location in the United States. 

The average ambient temperature when freeze protection is needed,Ta,can be 

determined from Fig. 6-20 as a function of the average January daytime temperature for the particular site. Average January daytime temperatures are given 

in Appendix E for 72 U.S. cities. The correlation shown in Fig. 6-20 was 

based on data from all 26 SOWT sites. T, is defined as the average ambient 

temperature for all times when ambient temperature is both below freezing 

(0'~) and the collectors are not operating because of insufficient irradiation. This restricts temperature averaging to times when recirculation is 

necessary for freeze protection. 

Average January Daytime Temperature (O C) 

Figure 6-20, Average BelmFreezing Temperaturesas a 

Function of Average January Daytime Temperature 

6.5 UTILIZATION AND AVAILABILITY 

After we have taken into account climatic conditions, collector performance, 

amount of storage, and the load profile using the energy collection design 

tools presented here, we must consider how the process will utilize the solar 

system and how reliable the solar system itself will be. 

The overall economics of a solar system depends not only on how much energy 

the system can collect in a year, but also on how much of that energy will be 

used by the industrial process and on how much time the system will be able to 

collect that energy. It is of no use to have either a solar system that collects energy that the process cannot use or one that can never collect and 

deliver energy because of malfunctions. The two indices that quantify these 

effects, then, are utilization and availability. Strictly defined, these 

indices should be based on energy quantities. Thus, energy collected but not 

delivered to the industrial process because that process is unavailable 

should be accounted for in the utilization term. Energy lost because of solar 

system downtime should be accounted for in the availability term. Because 

these energy quantities are very difficult (if not impossible) to determine 

during the solar system design process, an approximation based on time estimates is recommended. Solar system utilization and availability are defined 

in terms of time fractions as follows: 
Periods of Operation of the 

Solar System to Collect Energy 

Solar Systems - - for the Process* 

Utilization Total Period Periods of Solar (6-5 1) - of Time System Downt be 

and 

Total Period - Periods of Solar 

Solar System - - of Time System Downtime 

Availability Total Period (6-52) 

of Time 

Availability is based on the total period of time, so that all periods of 

solar system downtime are included, even if the industrial plant happens to be 

down at the same time. If only a portion of the collector field is down, this 

should be reported as a reduction in availability. (For example, if half the 

field is down during a 10-hour collection day, downtime would be 5 hours.) 

Utilization is based on the amount of time the solar system is available, so 

that it measures system usage by the industrial plant without a penalty for 

system downtime. The two indices are multiplied together to obtain the overall system capacity factor, the factor by which the yearly collected energy 

must be multiplied to determine the annual usable energy collection, including 

system and plant operation effects. Ideally, an industrial process would use 

solar energy all year (high utilization), and the solar system would be reliable enough to supply its portion of the load whenever it was called upon to do 

so (high availability), so that the system operation factor would be nearly 

equal to one. 

Because we lack long-term experience with solar IPH systems, solar system 

availability is difftcult to predict with confidence. It is encouraging, however, that even in the first-round DOE field tests, which were among the first 

large IPH projects built, the availabilities of. all but one project were 

greater than 85%, and two of the seven were greater than 97% (Kutscher and 

Davenport 1981). These were all nontracking collector fields, however. Preliminary data from new systems employing parabolic troughs indicate significantly lower availabilities. A characteristic of solar systems that leads to 

high availability is that collector field maintenance can be conducted at 

night or on cloudy or rainy days without affecting system performance. It is 

also possible to perform maintenance tasks during the day on some sections of 

a collector field while continuing to operate others. 

Utilization is also difficult to approximate, but may have a sizable impact on 

the actual amount of useful energy a solar system collects. The energy collection design tool presented in this handbook assumes tliat the collectors 

will operate every day that weather permits. Zowever, if plant operation 

scheduling causes the collectors to be idle for significant periods when they 

could be operating, the actual solar energy collected will be less than that 

predicted by the design tool. For industrial processes that are seasonal or 

*That is, the total period of time less solar system downtimes and periods of 

time the collectors were idled when they could have been used to collect 

energy. 
san g TR-1356 

shut down for considerable lengths of time, the utilization factor can be 

quite significant. 

For systems with storage, calculating utilization is difficult and, at best, 

approximate. Engineering judgment is required to estimate the contribution of 

various effects on utilization, and no clear-cut rules apply. If periods of 

no load are very long in comparison to the amount of storage available (e.g., 

seasonal shutdowns or extended plant holidays), storage will be of little 

value. The solar system can continue to be operated for a short time, but 

only the amount of energy that can be stored in the fully-charged storage system will be useful, and any extra energy collected after storage is charged 

will be wasted. However, for no-load periods of the same order as the time it 

takes to charge storage, we must determine what the effect will be on the 

energy collected. Occasional no-load periods of just a few hours have little 

effect and can be ignored. 

For solar systems with no storage, utilization is relatively easy to estimate 

if we know the annual plant operation schedule. In such a case, we need only 

total the periods of time that the system would be idle because of plant maintenance, seasonal shutdowns, holidays, etc., and subtract this total, along 

with the estimated downtimes of the solar system (allowing for any overlap), 

from the total period of time for which the analysis is performed, to obtain 

the numerator of Eq. 6-51. 

A further difficulty in estimating utilization is associated with the effect 

of seasonal variations. Although the definition of utilization given in 

Eq. 6-51 does not mention when the operation of the solar system takes place, 

it does matter; a shutdown in winter will have a smaller effect on energy collection then one in summer. 

It is important to keep in mind that calculating the system utilization is 

merely a crude attempt to quantify the effect of process scheduling on the 

amount of energy that will be collected and delivered by a solar system, and 

is a refinement to the general annual energy collection design tool. As such, 

its usefulness is determined largely by the insight and judgment of the 

designer. Careful consideration of how the solar system will be operated can 

bring about useful corrections. In any case, the result will be an energy 

collection estimate more conservative than the estimate obtained with the 

energy collection design tool. 

Some examples will illustrate how utilization and availability factors might 

be calculated for actual systems. 

Example 1: A food processing firm is considering using solar energy for a 

fruit-drying operation. Because the fruit is available only seasonally, the 

system will be operated for only seven months of the year, from May through 

November. During that time, processing occurs seven days per week. No storage will be provided. Since five months are available for maintenance, the 

system availability should be high, estimated at 98%. The utilization is 

approximately 

Utilization = 31 + 30 + 31 + 31 + 30 + 31 + 30 

365 
The system capacity factor is (0.98)(0.60) x 100 = 59%. 

Example -2: Aii oil and gas company is contemplating using solar energy in 

remote location to heat crude oil before pumping it. The process would be in 

use daily, and storage would be provided for some additional operation at 

night. Because of the nature of the crude oil, clogging of the main solar 

heat exchanger is expected to lead to downtimes of the solar system of one day 

per month. The area is one of frequent hailstorms, and 10 days of operation 

per year are expected to be lost because of the storms. The process is shut 

down completely for two weeks every year for major maintenance and parts 

replacement. 

Availability = 365 days - 12 days of downtime 

365 days 

365 days - 12 days of downtime - 14 days of process down time Utilizatf on = 365 days - 12 days of downtime 

Thus, the overall system capacity factor is (0.97)(0.96) x 100 = 93%. Note 

that the incidence of hailstorms does not affect availability; only shutdowns 

caused by mechanical problems with the solar system are included. Weather 

effects are considered only in the calculation of the energy available for 

collection. 

To smmarize the calculation of the annual energy collection of an IPH solar 

system, a step-by-step procedure is provided here. Note that the inputs 

required of the industrial owner or system designer are largely readily available items of information, and the outputs of this procedure are quantities of 

significance to the industrial owner. 

Step 1 - Obtain necessary information 

Define collector and obtain its FRUL and FRno values and K, data. 

Define process load with its load schedule and TE,~, Tg, and mload for 

hot water and Ts and Tf for steam systems. 

Define latitute and average ambient temperature (see Appendix F) of proposed site and obtain long-term irradiance data from Figs. 5-10 and 5-11. 

Define land availability at proposed IPH site. 

Define system-dependent heat exchange factor F,. Use F, for hot air and 

hot water systems. Use Fp for steam flash systems and FB for unfiredboiler steam systems. 
Correct the value of FRUL to account for steady-state pipe losses by 

Eq. 6-44. 

Step 2 - Calculate long-term average optical efficiency 

Define dirt and dust optical losses based on material coupon degradation. 

Calculate or look up incident-angle modifier annual correction 

(Figs. 6-13 and 6-14 and Eqs. 6-35 and 6-36). 

Multiply normal incidence optical efficiency by both modifiers to arrive 

at long-term average optical efficiency. 

Correct the optical efficiency to account for steady-state pipe losses by 

Eq. 6-43. 

Step 3 - Calculate annual average collection rate for unshaded collector 

If a variable-volume storage system is selected, calculate the maximum 

collector area Ac ,plax based on the maximum daily process load requirement. 

If a no-storage hot air, hot water, or steam system is selected, calculate the maximum collector area Ac,max based on the maximum instantaneous 

process load use rate. 

Determine the collector heat transfer efficiency factor FR for the given 

flow rate and for the specified collector area (Ac,max - or less). If a 

mixed tank recirculation system is selected, use the collector flow 

rate recommended by the collector manufacturer. 

Determine value of variable grouping in - ~a)] and locate on 

abscissa of Fig. 6-1. FR~ To 

(Use the load return temperature T2 for Tin with hot air and hot water 

rr systems. Use steam temperature T for Tin for both unfired-boiler and 

flash steam systems. Use = Ih ?Fig. 5-10) for flat-plate and evacuated-tube collectors. Use T = Tb (Fig. 5-11) for parabolic trough 

collectors.) 

Iacate value of ~c/~s~Rno~ on ordinate of Fig. 6-1 consistent with value 

of abscissa and site latitude. 

Multiply ordinate by F~F~~~~ to determine qc. [Note $hat Y = yh for flat 

plates and evacuated tubes, but that I = + 50 (W/m ) for troughs.] 

If the system chosen is a recirculation system, select the collector area 

and storage tank sizes. On the load-storage modifier figure appropriate 

for the collector type and.process load schedule (see Figs. 6-4 to 6-11), 

determine FQ-s. Correct qc for storage and load effects by multiplying 

by Fg-,. 

Step 4 - Calculate annual shading loss factor and end-loss factor for parabolic troughs 
a Determine proposed ground cover ratio (GCR = collector length/row-to-row 

spacing) . Calculate required collector field size as A g = A=/GCR. 

Detefinine' whether enough collector field area is available. If not, 

increase GCR or reduce Ac. 

a Locate annual shading-loss factor (FShade) on Figs. 6-16 to 6-18 for 

specified GCR and latitude of site. 

Correct qc for shading losses by multiplying by Fshade,field (see 

Eq. 6-42). 

For parabolic troughs, determine end-loss factor for specified row length 

(see Table 6-2). 

Correct qc for end losses by multiplying by Lend. 

Step 5 - Calculate annual energy collection 

hltiply the energy collectipn rate per unit of collector area :c by the 

collector area to determine G, the average annual energy collection rate 

of the collector field. 

Since Qc is an average collection rate based on all daytime hours, multiply Q, by 4380 (the number of daylight hours in a year) to obtain annual 

energy collection in watt-hours. 

Step 6 - Calculate collector overnight and freeze-protection losses from field 

piping and storage 

Calculate total collector field piping thermal capacitance and total collector area thermal capacitance. Calculate UA value for storage. Use 

these values to determine overnight thermal losses using Eq. 6-49. 

If a warm-water circulation freeze-protection system is used to protect 

the collector system from freezing, u.se Figs. -6-19 and 6-20 to determine 

the annual nmber of freezing hours and average ambient temperature when 

freeze-protection is needed. (Data from a local weather station or from 

the U.S. Climatic Atlas are preferred if available for the site in 

question. ) 

Calculate UA values for piping and collector field and use this information to evaluate Eq. 6-50 for the annual freeze protection thermal loss. 

Step 7 - Estimate utilization and availability of solar system 

Estimate solar system utilization based on plant operation schedule and 

any expected plant shutdowns (see Eq. 6-51), 

+ Estimate solar system availability based on expected solar system downtime and likelihood of doing maintenance work during the evening or night 

(see Eq . 6-52) . 
Step 8 - Calculate annual energy delivery and solar fraction 

Subtract annual overnight losses and freeze-protection losses (from 

Step 6) from the annual energy collection determined in Step 5. 

Multiply this value by both solar system availability and utilization to 

obtain solar system annual energy delivery. 

To obtain that fraction of the process load met by solar energy (neglecting parasitics), divide the annual energy delivered by the annual process 

load. 

ASHRAE Handbook, 1981 Fundamentals. New York, NY: American Society of Heating, Refrigerating,. and Air Conditioning Engineers, Inc. 

Beckman, We 1978. "Duct and Pipe Losses in Solar Energy Systems." Solar 

Energy. Vol. 21 (No. 6); p. 531. 

dewinter, F. 1975. "Heat Exchanger Penalties in Double-Loop Solar Water Heating Systems." Solar Energy. Vol. 17; p. 335. 

Gaul, H. ; Rabl, A. 1980 (Feb. ) . "Incidence-Angle Modifier and Average Optical 

Efficiency of Parabolic Trough Collectors." Journal of Solar Energy Engineering. Vol. 102. 

Gordon, J.; Rabl, A. (Forthcoming in Solar Energy.) "Design, Analysis, and 

Optimization of Solar Industrial Process Heat Plants Without Storage." 

Harrigan, R. 1981 (July). Handbook for the Conceptual Design of Parabolic 

Trough Solar Energy Systems - Process Heat Applications. SAND-81-0763. 

Golden, CO: Solar Energy Research Institute. 

Hooker, D.; May, E. K.; West, R. 1980 (May). Industrial Process Heat Case 

Studies. SERI/TR-733-323. Golden, CO: Solar Energy Research Institute. 

Jones, Re Jr.; Burkhart, J. 1981. "Shading Effects of Collector Rows Tilted 

Toward the Equator." Solar Energy. Vol. 26; p. 563. 

Jordan, R. ; Liu, B. 1977. Applications of Solar Energy for Heating and Cooling of Buildings. ASERAE GRP170. 

Kutscher, C.; Davenport, R. 1981 (June). Preliminary Operational Results of 

the Low-Temperature Solar Industrial Process Heat Field Test. SERI/TR-632- 

385R. Golden, CO: Solar Energy Research Institute. 

Lunde, P. 1980. Solar Thermal Engineer4ing Space Heating and Hot Water Sys- 

- tems. New York, NY: John Wiley and Sons. 

Rabl, A. 1981 (Jan.). Yearly Average Performance of the Principal Solar 

Collector Tv~es. - ~~~1)~~-631-716. Golden. CO: Solar Energy Research * 

Institute. 
THE ENERGY TEUWSPORT SYSTEM 

This sect'on presents the design requirements of the energy transport system-- 

the piping, pumps, valves, heat exchangers, and storage components that convey the energy absorbed by the solar collectors to the proper place in the 

process stream. Because the energy transport system can be a source of significant system inefficiency, it is important to , avoid design errors in this 

area. 

In Sec. 7.1 we discuss piping and insulation and review collector field layouts and pipe sizing, including a method of optimizing pipe insulation thickness. Heat transfer fluids that can be used if water is impractical are discussed in Sec. 7.2. Effects of fluid properties on heat transfer and pumping 

power are reviewed, and the heat transfer efficiency factor (HTEF), an effective ratio of heat transfer ability to pumping power requirements, is 

explained. In Sec. 7.3, we review the kinds of pumps available for solar IPH 

systems and discuss how to select the proper pump. The many types of valves 

needed in an ZPH system are covered in Sec. 7.4, and sizing various types of 

heat exchangers is discussed in Sec. 7.5. Section 7.6 summarizes characteristics and methods of thermal storage. 

7.1 PIPING AND INSIJL&TION 

71 Oollector Field Piping Configurations 

Three basic types of collector field layouts are employed in solar IPH systems. These layouts--direct return, reverse return, and center f eed--are 

shown schematically in Fig. 7-1. In each case, the hot outlet piping is 

shorter than the supply piping, to minimize thermal losses. There are advantages and disadvantages to each of these configurations. 

The direct-return piping configuration (shown in Fig. 7-la) is the simplest, 

and probably most extensively used, of the three. Its main disadvantage is 

that there is a much greater pressure differential across the collector row 

nearest the field inlet than across the last collector raw, so that balancing 

valves must be used to maintain equal flows through each row. These valves 

are responsible for most of the pressure drop in the beginning of the array; 

thus, their contribution to the total head loss in the system is significant. 

The result is a higher parasitic energy requirement for the direct-return system than for the reverse-return system, in which the fluid enters the collector array at the opposite end. Of course, larger headers can also be used to 

balance array flow, since the imbalance is caused by pressure drop and pressure recovery along the headers. Using larger headers will also result in 

lower parasitic power requirements, but these could be offset by increases in 

initial costs and energy losses. 

The reverse-return design (Fig. 7-lb) has an inherently better balanced flow; 

balancing valves may still be required, but they add much less head loss to 

the system than they would in a direct-return configuration. (Alternatively, 

header pipes can be stepped down in size on the inlet side and stepped up on 

the outlet side to maintain constant velocity in the headers, thereby providing uniform flow.) The extra length of supply piping Is a disadvantage in the 

reverse-return array because of additional heat loss, although this depends 

greatly on the supply fluid temperature.- If supply fluid temperatures are 

near ambient, additional heat loss is negligible. Adding length to the pipes, 

however, results in higher piping, insulation, and fluid inventory costs . The center-feed configuration is gaining favor with some IPH system designers, 

As with the direct-return design, balancing valves contribute a significant 

portion of the head loss; but the design minimizes the amount of piping needed 

by eliminating a pipe that runs the length of the collector row. Also, direct - access to each collector row is possible without having to bury any pipes. 

7-1-2 Optimum Array Flw Bate and Collector Configuration 

Along with the array configuration, we must also determine the optimum array 

flow rate and the nmber of collectors to be connected in series and in parallel Determining the optimum collector flow rate involves a trade-off between 

collector and heat exchanger performance and parasitic ene5gy requirements. 

Consider the effect of changing the collector mass flow rate %. If we ignore 

changes in collector efficiency as a function of AT, (the temperature rise 

through the callectors), the mass flow rate is inversely proportional to AT . Thus, halving the .flow rate doubles AT,. Whether that is desirable depends gn 

whether the inlet temperature to the collectors drops (increasing n,) or the 

outlet temperature rises (decreasing nc). 

As is reduced, the effectiveness of the heat exchanger drops slightly 

because of a reduction in the heat transfer coefficient of the .collector 

fluid. Since the heat transferred through the heat exchanger is &c@T, if 

M, is halved, the AT across the heat exchanger will be slightly less than 

doubled. If the heat exchanger has a high effectiveness, the temperature of 

the exiting collector fluid will already be close to the cold inlet temperature on the other side of the heat exchanger; thus, the change in Mc has 

little effect on the collector inlet temperature. Therefore, decreasing Mc 

increases the collecror outlet temperature and reduces efficiency, 

With this effect in mind, we want a collector flow rate large enough to keep 

array outlet temperatures low (providing good efficiency) but not so large 

that greater array efficiency is offset by greater parasitic energy requirements. We also want a heat exchanger large enough to provide a minimum collector inlet temperature. The optimum mass flow rate will be somewhat higher 

in a parallel-configured array (with lower AT ) than in a series array because 

of the lower parasitics associated with paralfel flow. 

Along wfth choosing an optimum overall flow rate, we must make certain tradeoffs between the collectors -in parallel and those in series. For n collectors 

in parallel, the head losses for a given total flow rate are 

For collectors in series with the same total flow rate, 
3 Thus, Hs/Hp = n , so the head loss in a series system is n3 times the head 

loss in a system plumbed in parallel. To minimize parasitics, therefore, we 

should probably have more collectors configured in parallel than in series. 

On the other hand, collector performance decreases as the flow rate is 

decreased, because FR changes with flow rate. Lunde (1980) gives the following expression for FR: 

where 

= mass flow rate through the collector 

c = specific heat of collector fluid P 

UL = collector heat loss coefficient 

Ac = collector aperture area 

nF = fin efficiency of absorber plate 

Uf = heat transfer coefficient from absorber to collector fluid 

Af = area of heat transfer to collector fluid. 

For small changes in flow rate, the following approximate formula holds: 

This leads to lower collector efficiency in parallel collectors compared with 

series collectors at the same total flow rate. 

Thus far, we have mentioned only collector pressure drops and have ignored 

interconnecting piping. A parallel array requires more of such interconnecting piping, which adds to cost and parasitics, especially in a trough array 

where the collectors must be spaced far apart enough to minimize row-to-row 

shading- Also, the troughs themselves are marked by fairly low pressure 

drops. These factors suggest that an optimum trough field will have more collectors in series than an optimum field of flat-plate or evacuated-tube collectors. On the other hand, collectors with high individual pressure drops, 

such as some evacuated-tube designs and flat plates with serpentine flow, are 

more likely to function optimally with parallel plumbing. 

Note also that measures must be taken in parallel configurations to ensure 

reasonably uniform flow through each collector. This can be done by balancing 

valves, which add to pressure drops and pumping costs, or by increasing the 

size of the header pipes, which adds to pipe costs. Again, this problem is a 

function of collector pressure loss characteristics: collectors with higher 

AP have more uniform flow. So, the optimum plumbing configuration is the 

result of a cost trade-off. Adding more series collectors decreases field 
piping AP (and both piping and life-cycle pumping costs) but rapidly increases 

collector AP. Any final arrangement will be a series/parallel combination, 

but the actual configuration will be a function of the particular collector 

pressure drop and, to a lesser extent, electricity costs for pumping and local 

installed piping costs. 

7.1.3 Pipes and Sizing Techniques 

Piping material must be capable of withstanding stagnation temperatures for a 

long period of time, which rules out PVC and CPVC pipe in most cases. 

Although certain plastics are appropriate for low-temperature applications, 

Schedule 40 steel pipe is a common, readily available choice. In small sizes, 

copper pipe can be used well with copper flat-plate collectors because it 

eliminates the galvanic corrosion problem associated with multiple metals. 

Note that dielectric insulation should be used at the junctions of any dissimilar metals to prevent such galvanic corrosion. 

Many pipe sizing techniques are available. One technique of ten used ,is the 

method found in the Chemical Engineerst Handbook (Perry and Chilton 1973). 

The Perry and Chilton method uses pipe cost correlations, physical property 

data, and flow rates to estimate opti&m pipe diameter. Table 7-1 summarizes 

typical results of economic fluid velocities for turbulent flow in Schedule 40 

steel pipes that were obtained using this method. 

Another complex sizing method is that employed in the ETRANS computer program 

(Barnhart 1981). ETRANS optimizes piping in a solar field by searching for 

the combination of pipe diameter and insulation thickness with the lowest 

life-cycle cost. This technique uses cost estimates for piping, insulation, 

valves, fittings, labor, heat loss, and pumping power, and incorporates features of previous work by Powell (1974), Caputo (1975), Williams (1978), and 

Iannucci (1980). 

A number of pipe sizing analyses for solar thermal systems [e .g . , Alexander 

and Kutscher (1978) and Thornton (forthcoming)] indicate that economically 

optimum pipe velocities, based on pumping power versus installed cost and heat 

losses, are usually greater than good design practice allows. So, considerations such as erosion-corrosion (HUD 1977) limit that maximum velocity and 

thereby determine pipe size. In the collector array, header pipe sizes may be 

larger to provide for more uniform flow. 

Table 7-1. Economic Fluid Velocities for Schedule 40 Steel 

Pipes, Obtained Using the Perry and Chilton Method 

Density, kg/m3 (lb/ft3) 1600(100) lOOO(62.4) 800(50) 15(1.0) 

Viscosity, centipoise 1.0 1 .O 1.0 0 -02 

Economic velocity, m/s (ft/s) 2(6.5) 2.3(7.4) 2.4(7.9) 9.5(31) 
TR-1356 sin + 

7.1.4 Insulation and Beat Losses 

Collecting thermal energy with a solar system involves considerable expense; 

therefore, as much of that energy as possible should be retained by insulating 

the system piping. This does not mean, however, that a builder should purchase the thickest possible pipe insulation, because there is a point where 

the additional cost of thicker insulation is higher than the value of the 

energy saved over the lifetime of the system. Optimum insulation is achieved 

with an appropriate insulating material at a thickness that provides the lowest total lif e-cycle costs in materials, installation, maintenance, and 10s t 

energy. 

The effect of insulation thickness on the cost of energy delivered by a solar 

system is illustrated in Fig. 7-2. Increasing the amount of insulation on a 

hot pipe surface decreases the amount of energy lost from that surface, and it 

reduces accordingly the amount of energy that would otherwise have to be made 

up by additional collector area or by an auxiliary source. The effect is 

inversely logarithmic, however, so each additional increment of insulation 

saves less energy than the one before. To this decreasing cost of lost 

energy, we must add the increasing cost of the insulation itself. The total 

cost exhibits a minimum value at some optimal insulation thickness. (Adding 

insulation to small-diameter tubes can increase heat loss up to a point by 

increasing the area available for heat loss. This is not the case for the 

pipe sizes we are addressing here, however.) 

Optimum 

Insulation 

I Total Cost 

\ ~hickness / - Insulation Cost 

r - Cost of Energy Saved 

1 

Insulation Thickness -4 

Figure 7-2. Effect of Insulation Thickness on Delivered Energy Cost 
san :el -1356 

As a rough guide, Table 7-2 gives typical thicknesses of pipe insulation at 

different temperatures (Perry and Chilton 1973). Another rough rule of thumb 

is that optimal insulation thickness is approximately the maximum thickness of 

a single layer of insulation that can be installed without introducing proti 

lems associated with thermal expansion of the pipe or vessel (Allen 1981). 

Additional insulation requirements, including- flammability, durability, and 

permeability to water, should be satisfied before a least-cost optimization is 

conducted. The optimization process described here does not deal directly 

with such requirements, but information on flammability and other properties 

of insulating materials is given in Table 11-1. 

The following model is based on both thermal and economic parameters and permits a solar system designer to select an insulating material-and thickness 

with the lowest total life-cycle cost for a particular application. The 

method follows and extends the work of Jones and Lior (1979), who developed 

the method for solar space-heating systems. Whereas Jones and Lior considered 

a maximum nominal pipe diameter of 127 mm (5 in.) and a maximum insulation 

thickness of 152 mm (6 in.), the present work addresses pipe diameters up to 

610 mm (24 in.) at insulation thicknesses up to 254 mt (10 in.). 

The heat transfer model is based on an insulated pipe like that shown schematically in Fig. 7-3. A heat transfer fluid flows axially through the pipe and 

loses heat through the pipe wall, insulation, and finally to the surrounding 

air via convection and radiation. The equation governing the total radial 

heat loss per unit length of pipe between the fluid and surrounding air is 

Figure 7-3. Insulated Pipe Model 

145 
Table 7-2. mical Thicknesses of Calcim Silicate Hpe 

Insulation (inches) 

Nominal Temperature of Pipe - 

(?F) 

Pipe Size 

(in* 100-199 200-299 300-399 400-499 500-599 

1.5 and less 

2 

2.5 

3 

3.5 

4 

4.5 

5 

6 

7 

8 

9 

10 1.5 2.5 3 3.5a 4a 

11 1.5 2.5 3 3 .5a 4a 

12 1.5 2.5 3.5 4a 4.5a 

14 and up 2 2.5 3.5 4a 4 .5a 

Source: Perry and Chilton 1973. 

a~vailable in single or double layer. 

where 

Tf = fluid temperature (K) 

Ta = air temperature (K) 

L = pipe length (m) 

Ri = thermal resistances (mK/W) - 

2 U = overall heat transfer coefficient (~/m -K) 

2 A = heat transfer area (m ) 
Inserting the appropriate expressions for the thermal resistance, we have 

where 

Dp,i = pipe inside diameter (m) 

Dp,o = pipe outside diameter = insulation inner diameter (m) I 

Di = insulation outside diameter (m) 

hi = heat transfer coefficient inside pipe (w/m2-K) 

hc = convective hea transfer coefficient between insulation and surroundings (W/mh) 

h, = radiative heat transfer coefficient between insulation and sur 

roundings ( w/m2-~) 

kp = pipe thermal conductivity (w/m-K) 

ki = insulation thermal conductivity (W/m-K). 

Combining Eqs. 7-1 and 7-2, and using the relation 6 = UAAT, we obtain 

Physically, UA/L represents the rate of heat loss per unit temperature differ 

ence between the fluid and ambient per unit length of pipe. The three heat 

transfer coefficients, 9, he, and hr, can be determined as follows. The 

inside film coefficient hi can be obtained from 

where 

0.8 NuI = 0.023 Ref prgo3 [see Dittus and Boelter (1930) for cooling of 

the fluid] 

kf = fluid thermal conductivity (~/m-K) 

Ref = fluid Reynolds number 

Prf = fluid Prandtl number. 
For outdoor piping, where forced convection dominates because of the wind, the 

convective heat-loss coefficient can be calculated (Kreith 1973) from 

where . - 

ka = air thermal conductivity (W/m-K) 

Rea = air Reynolds number based on the outside diameter of the 

insulation 

Pr, = air Prandtl number " = air dynamic viscosity at ambient temperature (kg s-I m-l) 

pas = air dynamic viscosity at insulation film temperature (kg s-I m-I 

For indoor piping, where free convection dominates, the convective heat transfer coefficient is* 

where T = insulation outside surface temperature (K). i,o 

The radiative heat transfer coefficient is 

where 

a. = Stefan-Boltnnann constant (5.67 x 10'~ w/~~-K~) 

E = insulation surface emissivity 

Tr = effective radiative temperature of surroundings (K). 

It is important to note that the outside surface temperature T is not known i,o a priori and must be calculated iteratively. For that reason, the expression 

for UA/L was evaluated for all combinations of the 18 Schedule 40 pipe sizes 

and 20 insulation thicknesses using nominal values of the independent variables listed in Table 7-3. Tables 7-4 through 7-11 present the resulting UA/L 

values for indoor and outdoor piping and four values of insulation conductivity. The conductivities investigated span the range of those for the most 

common types of pipe insulation. For example, fiberglass insulation has a 

co ductivity that varies between approximately 0.032 ~/m-5 (0.22 Btu-in./ 9 ft -h-F) at OOC (32'~) and 0.089 W/PK (0.62 Btu-in./ft -h-F) at 260'~ 

(500~~)~ and the conductivity of calcium silicate varies between 0. 53 ~/m-K 9 (0.37 Btu-in./ft2-h-F) at 35'~ (95'~) to 0.125 W/WK (0.87 Btu-in./ft -h-F) at 

*For English units (~tu/hr*ft~-~F) the coefficient 1.32 becomes 0.27 with 

temperatures in degrees F and DI in feet (Lauer 1953). 
TR-1356 sea (el 

Table 7-3. Average Values of Tndependent 

Variables Used in Calculation of 

UUL 

-- 

-.. Fluid 

Fluid temperature 

Flui ~5 velocity 

Pipe conduc ti-vi ty 

Water 

2oo0c 

2 m/s 

Insulation surface emissivity 0.5 

Wind velocity 5 rn/~,~ 0 m/sb 

Ambient temperature ~oOC,~ 250~~ 

a~tdoor pipes. 

b~ndoor pipes. 

540'~ (1000~~). Figure 7-4 shows variations in thermal conductivity with temperature of common rigid insulating materials. This information is usually 

available from insulation manufacturers. 

In evaluating heat loss through insulation, the average insulation conductivity should be used. Since the conductivity of many insulating materials is 

approximately linear with temperature, as shown in Fig. 7-4, the average conductivity is simply the average of the values at inside and outside insulation 

surface temperatures. To find the heat-loss coefficient per unit length of 

pipe, average conductivity is estimated and interpolated with the appropriate 

table (Tables 7-4 through 7-11). 

Sensitivity .studies examined the effect of changes i'n the independent variables in Table 7-3 on UA/L; the results are shown in Fig. 7-5 for outdoor pipes 

and in Fig. 7-6 for indoor pipes. The value of (uA/L)/(uA/L),, where (uA/L), 

is the value of UA/L for the nominal inputs in Table 7-3, is graphed as a 

function of (X - Xo)/Xo, where X represents one of the varied parameters and 

X, is the nominal value of that parameter (also from Table 7-3). As indicated 

by the values of (X - x,)/x, the fluid t.emperature was varied between 100' 

and 300°c, the fluid velocity was varied between 0.2 and 4.0 m/s, and the 

insulation outside surface emisstvity was varied between 0.1 and 0.9. The 

ambient temperature was varied between -30' and 40'~ [(X - X,)/X, = -4 to +3] 

for outdoor pipes and 0' and 40'~ for indoor pipes. The wind velocity was 

varied between 1 and 20 m/s [(X - xo)/xO = -0.8 to +3] for outdoor pipes only. 

The pipe thermal conductivity was not varied, because only Schedule 40 commercial steel pipe was used to develop the uA/L values; however, since metal pipe 

will provide much less resistance to heat flow than any insulation, we can 

assume that different pipe materials and thicknesses (schedules) will have a 

minuscule effect on the value of UA/L as long as alternative pipe is compared 

with Schedule 40 pipe of comparable actual diameter. 

Figures 7-5 and 7-6 show that the effects of parameter changes on UA/L are 

limited to a few percentage points and are greater for indoor pipes than outdoor ones. These effects are greatest for large pipes with thin insulation, 

and for this combination [part (c) of each figure] , the deviation in uA/L is 
Table 7-4. Outdoor Pipe UA/L alues (w/K-~ of length) for Insulation k = 0.0288 ~/m-K l- (0.20 Btu-inlhr-f t 9) 

,;&I, 

Nom. ' - 

Pipe Insulation Thickness, mm (in.) I 

~iirn., 

mm 13 25 38 51 64 76 89 102 114 127 140 152 165 178 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2.0) (2.5) (3.0) (3.5) (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8.0) (8.5) (9.0) (9.5) (10.0) 
Table 7-5. Outdoor Pipe UA/L Values (w/K-m of length) for Insulation k = 0.0577 W/PK 

(0.40 Btcin. /hrf t2wo~) 

Nom. Insulation Thickneae, mm (in.) , Pipe 

Diam., 

mm 13 25 38 51 64 76 89 102 114 127 140 152 165 178 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2.0) (2.5) (3.0) (3.5) (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8.0) (8.5) (9.0) (9.5) (10.0) 

25 0.629 0.388 0.303 0.258 0.230 0.211 0.196 0.185 0.176 0.168 0.162 0.156 0.152 0.147 0.144 0.140 0.137 0.135 0.132 0.130 
Table 7-6. Outdoor Pipe UA/L Values (w/K-~ of length) for Insulation k = 0.0865 W/m-K 

(0.60 Btu-in. /hr-f OF) 

Nom. Insulation Thickness, [mm (in.)] Pipe I 

Diam., 

mm 13 25 38 51 64 76 89 102 114 127 140 152 165 178 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2.0) (2.5) (3.0) (3.5) (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8.0) (8.5) (9.0) (9.5) -(10.0) 
Table 7-7. Outdoor Pipe UA/L Value (w/K-~ of length) for Insulation k = 0.1154 W/WK 

(0.80 ~tu-in. /hr-f t2-~l?) 

ul 

111 

Y 

Nom. I;*, 

Insulation Thickness, mm (in.) '- 

Pipe I 

~iam., 

mm 13 25 38 51 64 76 89 102 114 127 140 152 165 .I78 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2.0) (2.5) (3.0) (3.5) (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8.0) (8.5) (9.0) (9.5) (10.0) 
Table 7-8. Indoor Pipe UA/L Values (~1K-m of length) for Insulation k = 0.0288 W/PK 

(0.20 ~tu-in. /hrf t2-OF) 

Nom. - 

Pipe Insulation Thickness, mm (in.) I 

Diam., 

mm 13 25 38 51 64 76 89 102 114 127 140 152 165 178 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2.0) (2.5) (3.0) (3.5) (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8.0) (8.5) (9.0) (9.5) (10.0) 

25 0.271 0.179 0.144 0.124 0.111 0.103 0.096 0.091 0.086 0.083 0.080 0.077 0.075 0.073 0.071 0.070 0.068 0.067 0.066 0.065 

(1.0) 

32 0.322 0.209 0.165 0.141 0.126 0.115 0.107 0.101 0.095 0.091 0.088 0.085 0.082 0.080 0.078 0.076 0.074 0.073 0.071 0.070 

(1.25) 

38 0.358 0.229 0.179 0.152 0.135 0.123 0.114 0.107 0.102 0.097 0.093 0.090 0.087 0.084 0.082 0.080 0.078 0.076 0.075 0.073 

(1.5) 
Table 7-9. Indoor Pipe UA/L Values (w/R-~ of length) for Insulation k = 0.0577 WWK 

(0.40 ~tu-ia./hrf ?-OF) 

Nom. Insulation Thickness, mm (in. ) Pipe I uraur., -- - 

rnm 13 25 38 51 64 76 89 102 114 127 140 152 165 178 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2-0) (2.5) (3.0) (3.5) (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8,O) (8.5) (9.0) (9.5) (10.0) 
Table 7-10. Indoor Pipe UA/L Va ues (w/K-~ of length) for Insulation k = 0.0865 W/m-K 

(0.60 Btu-in. /hrf ti-OF) 

Nom . i*,, ' - ' 

Pi~e Insulation Thicknees, mm (in.) i 

- 

mm 13 25 38 51 64 76 89 102 114 127 140 152 165 178 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2.0) (2.5) (3.0) (3.5) (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8.0) (8.5) (9.0) (9.5) (10.0) 

25 0.657 0.475 0.395 0.348 0.317 0.294 0.276 0.262 0.251 0.241 0.233 0.226 0.220 0.215 0.210 0.205 0.201 0.197 0.194 0.191 

(1.0) 

32 0.774 0.549 0.451 0.394 0.356 0.328 0.307 0.291 0.277 0.266 0.256 0.248 0.241 0.234 0.228 0.223 0.219 0.214 0.210 0.207 

(1.25) 

38 0.854 0.600 0.489 0.424 0.382 0.351 0.328 0.309 0.294 0.282 0.271 0.262 0.254 0.247 0.241 0.235 0.230 0.225 0.221 0.217 

(1.5) 

51 1.011 0.698 0.562 0.483 0.432 0.395 0.367 0.345 0.327 0.312 0.300 0.289 0.280 0.271 0.264 0.257 0.251 0.246 0.241 0.236 ,.. .. 
Table 7-11. Indoor Pipe UA/L Va ues (w/K-~ of length) for Insulation k = 0.1154 W/WK 

(0.80 Btu-in. /hr-ft4-~F) 

,;a,, Nom. '-' Insulation Thickness, mm (in.) Pipe I 

Diam., 

mm 13 25 38 51 64 76 89 102 114 127 140 152 165 178 191 203 216 229 241 254 

(in.) (0.5) (1.0) (1.5) (2.0) (2.5)'(3.0) (3.5). (4.0) (4.5) (5.0) (5.5) (6.0) (6.5) (7.0) (7.5) (8.0) (8.5) (9.0) (9.5) (10.0) 



as much as +13X to -21% indoors when all parameters are at their maximum and 

minimum values, respectively. If we use smaller pipes or thicker insulation, 

however, the thermal resistance of the insulation becomes increasingly important and possible deviations in UA/L are less significant. 

In the economic model, three cost sources are considered: the cost of insulation material and labor, of maintenance, and of the solar energy provided by 

the system. Following Jones and Lior (1979), the equation that expresses the 

total present-value average cost per unit length of piping insulation is 

where 

[El(l)/n] (ci + Cj + C1) = cost of insulation material and labor 

[E2(1)/n]Cm = maintenance costs 

FCsUA(Tf - T,) = cost of solar energy provided by the system, 

and where 

El(l) ,E2( = economic coefficients for converting cash flows to present 

values, 

n = period of economic analysis (usually, the life of the system, in years) 

Ci = base cost of the insulation material, including the cost of 

fitting and valve insulation prdrated over the straight 

pipe length ($/m) 

Cj = base cost of insulation jacketing ($/m) 

C1 = base cost of insulation labor ($/m) 

C, =' base cost of maintenance during the first year ($/m) 

F = annual usage factor (0 < F < 1) of the insulated component 

(the annual fraction of time during which the solar collection system or storage tank loses heat; consideration must 

b$ given to the working fluid remaining in piping and 

exposed to ambient temperatures after the solar collection 

system has stopped) 

Tf,Ta = average annual Kelvin working fluid and ambient temperatures, respectively 

C, = present-value annual average cost of solar heat, $/GJ-yr 

(may be a given value or could be calculated by using methods presented in Sec. 10.0 of this handbook). 
Dividing Eq. 7-7 by CsF(Tf - Ta), we obtain 

Cm = CT/CsF(Tf - Ta) = CR + UA* 9 

where 

- - 

== 0.0315 -- x UA (GJ/~-yr-K) , 

and 

The E-terms used to convert cash flows to present values (Barley and Wynn 

1978) are defined as follows: 

E2 = (1 - tl)P(d,rm,n) 

where 

a = down-payment fraction of first cost 

B = investment tax credit fraction, if applicable 

o = fractional salvage value at end of equipment life 

g = annual general inflation rate (percent 5 100) 

d = annual discount rate, designated either as that for inflation, 

for an opportunity cost of money, or for a required return on 

investinent (percent 3 100) 

t = annual incremental income-tax rate (applicable only in business, where capital expenses are income-tax deductible; otherwise, t = 0) (percent + 100) 

tl = same as t, but applicable only if maintenance, operating, and/ 

or fuel expenses are hax-deductible; otherwise, tl = 0 (percent 

3 100) 

p = actual annual property tax rate (per cent/100) 

h = annual insurance cost as a fraction of the first cost 
and 

P(d,r,n) = [(I + d)n - (1 + r)n]/(l + d)" (d - r) for d # r 9 

P(d,r,n) = n/(1 + r) for d = r , (7-14) . -. 

where 

n = period of economic analysis, usually the life of the system 

(years) 

i = annual interest rate on loan or mortgage (per cent/100) 

m = period of loan or mortgage (years) 

B = cumulative present -mrth of depreciation tax credits per dollar 

invested . With straight-line depreciation: 

BSL = t(l - a)~(d,O,k)/k . 

With declining balance : 

BDB = t6P(d - G/k,k)/k 

With sum of years digits: 

where 

k = depreciation lifetime 

8 = declining balance multiplier 

r, = annual fractional rate of increase in maintenance expense 

The optimal insulation thickness for a particular pipe size is determined as 

follows : 

a Obtain insulation material and jacketing costs for each insulation thickness, starting with the smallest thickness available for the particular 

pipe size of interest; from economic and system, design information and 

labor costs that apply to the project, calculate CR for each thickness, 

using Eq. 7-10. 

a From the applicable table, find the value of UA/L that corresponds to the 

particular pipe size under consideration for the proper value of k and 

for the range of insulation thicknesses being investigated. 
Find UA* from Eq. 7-9. 

Obtain Cm from Eq. 7-8 by adding the values of UA* and CR that correspond to the same pipe-size and insulation-thickness combination. 

The optimal insulation thickness is the value that gives us the smallest 

value. of -Cm. For this optimal insulation thickness, the total annual 

cost per unit length of piping is 

and the total annual heat loss per unit length of insulated pipe is 

The procedure can be repeated for different insulation materials with different k values to determine the economic optimal insulation material for a par 

ticular pipe size. The system variables F, Cs, Tf, and Ta can be determined 

by methods described elsewhere in this handbook. 

7.2 HBBT TIWSFER FLUIDS 

Water is a popular heat transfer fluid because it is nontoxic, nonflammable, 

inexpensive, and has excellent heat transfer characteristics. It does, however, attain high vapor pressures at elevated temperatures: 1 MPa at 180'~ 

(135 psia at 350'~) to 7 MPa at 285'~ (1050 psia at 550~~). Because highpressure design adds to overall system costs, water is not economical for 

high-temperature systems. However, the extra cost of high-pressure design may 

be offset by the savings realized from using smaller pipes and heat exchangers 

and from avoiding the costs of other heat transfer fluids and extensive fire 

protection systems. But because water freezes at a relatively high temperature, it may be an impractical if not unfeasible heat transfer fluid. 

If water cannot be used as the working fluid, the designer faces the troublesome task of determining which of over 50 other fluids can best serve the 

needs of the IPH system. Alternative fluids include water-glycol mixtures, 

silicone compounds, fluorocarbons, inorganic salt mixtures, and petroleumbased and synthetic hydrocarbons. Comparing them is not easy, because different manufacturers present their data in different ways. And in the majority 

of cases, complete property information over the total operating range of a 

fluid is simply not available. The designer must also compare the fluids' 

flammability, toxicity, corrosiveness, and thermal stability, as well as cost. 

Detailed tables of Pnformation on many heat transfer fluids appropriate for 

solar applications are presented in Appendix B. 

In the following section, we summarize some general characteristics of different types of fluids, particularly as they relate to a solar IPH system. Glycols, silicone fluids, and hydrocarbons are discussed in some detail. Inorganic salts, because of their high melting points, are best suited to very 

high-temperature systems and thus have little relevance as IPH collector 

fluids. Fluorocarbons are used in some two-phase domestic hot water systems 

but have not been suggested for larger IPH systems. 
san TR-13 56 

7.2.1 Types of Fluids 

We have already noted several characteristics that make water a valuable working fluid (it is nontoxic, nonfl~ble, inexpensive, has good thermal properties, etc.). But we should expand here on some of its disadvantages: 

Water has a low boiling point. This is a problem not only in concentrating collectors, where the temperature routinely surpasses 10oOc, but also 

in flat-plate collectors, if they are allowed to stagnate while filled 

with water and exposed to sufficient sunlight. 

a Water has a freezing point higher than the lowest temperature that occurs 

in most parts of the United States. Thus, freeze-protection methods are 

required for most water systems. 

a Water will corrode most metals, unless it is treated. Water treatanent 

technology is advanced enough, however, that this problem is not as 

severe as the others. 

7.2.1 .2 Wter-6lycol Mixtures 

Aqueous solutions of ethylene and propylene glycol are the most commonly used 

nonfreezing fluids in solar systems. In proper concentrations, these mixtures 

freeze only at temperatures below -45'~ (-50'~); thus, they can provide adequate freeze protection in most parts of the United States. These mixtures 

still boil at relatively low temperatures [about 110'~ (230~~)], however, so 

they are usually restricted to process temperatures less than 100~~. Another 

reason for this temperature limit is that glycols decompose into organic acids 

if they are exposed to air and elevated temperatures; thus, glycols increase 

corrosion problems. Glycol manufacturers of ten add inhibitors to their products to reduce the rate of decomposition and provide corrosion~protectfon for 

various metals. Since different manufacturers use different inhibitors, a 

solar system designer should ascertain whether the inhibitors in a candidate 

glycol heat-transfer fluid will provide adequate protection. 

7.2.1.3 Aliphatic Hydrocarbons 

Aliphatic hydrocarbons consist of open-chain structures and include olefins 

and paraffinic oils. They can be natural petroleum fractions or synthetic 

oils, and they can be used at higher temperatures than water (but become 

fairly viscous at lower temperatures). They exhibit low toxicities and are 

thermally stable at high temperatures if there is no air in the system and 

stagnation is avoided. Excluding air generally requires that expansion tanks 

be pressurized with nitrogen. 

7.2.1.4 Aromatic Eydrocarbons 

By definition, aromatic hydrocarbons contain at least one benzene ring. 

Biphenyls, terphenyls, and naphthenic oils are examples of these cyclic 
ssn a$ TR-1356 

molecules. Aromatic hydrocarbons have lower viscosities than aliphatic hydrocarbons and slightly higher maximum operating temperatures, but they also have 

relatively low flash points. Aromatic compounds dissolve roofing tar and 

asphalt shingles; thus, they may not be suitable for roof-mounted systems. 

They also degrade elastomeric materials, so gaskets and hoses must be chosen 

carefully; - 

7.2.1.5 Silicones 

Silicone fluids on the market today (all polydimethylsiloxanes) have the highest permissible operating temperatures of any of the heat transfer fluids discussed in this handbook. They are also nontoxic, have high flash points, and 

will not harm roofing materials--all attractive qualities for solar systems. 

On the other hand, their relatively high viscosities and low specific heats 

require high flow rates (thus, a great deal of pumping power) for adequate 

heat transfer. Silicone fluids are incompatible with neoprene or butyl rubber, and because they have very low surface tensions, they leak through joints 

tight enough to contain other fluids. Silicones are also the most expensive 

heat transfer fluids marketed, costing three to ten times as much as alternative fluids. 

7.2.2 Temperature-Dependent Thermal Properties 

Certain thermal properties of fluids determine a fluid's ability to transfer 

heat as well as the pumping power required to pump it through a given circuit. 

These properties include density (P), thermal conductivity (k), specific heat 

(cP), and kinematic viscosity (v) [dynamic viscosity (p) can also be used: 

1.1 = P V] . Although vapor pressure does not enter into the heat transfer or 

pumping calculations, it is important, too, because it reveals the atmospheric 

boiling point of a fluid as well as the absolute pressure that must be maintained to prevent the fluid from boiling. All of these properties vary with 

temperature. Appendix B summarizes these properties for many fluids appropriate for solar IPH systems. 

The most important trade-off to make in selecting a heat transfer fluid for a 

solar application is between heat transfer properties and pumping power 

requirements. In this section, we present an index to use in making this 

trade-off, the heat transfer efficiency factor (Fried 1973). To begin with, 

we consider the effect of a fluid's thermal properties on its heat transfer 

characteristics. Heat transfer to or from a fluid flowing through a circular 

pipe or tube can be determined from the Dittus-Boelter equation (Dittus and 

Boelter 1930), 

where 

Nu = Nusselt number (h~/k) 

Re = Reynolds number (pv~11.1) 

Pr = Prandtl number (PC /k) P 
n = 0.4 for heating the fluid, 0.3 for cooling the fluid 

D = hydraulic diameter of pipe 

V- = fluid flow velocity. 

The heat transfer coefficient h is obtained from the definition of the Nusselt. 

number: 

Substituting the thermal property expressions into the dimensionless numbers 

gives us, in the heating case, 

Thus, for a given flow velocity and pipe diameter, we see that high density, 

specific heat, thermal conductivity, and Low viscosity enhance heat transfer. 

Now, we must consider the effect of fluid properties on pumping power (pp) . From the first law of thermodynamics for fluid flowing in a tube (see Shames 

1962) , we have 

where pp is the pumping power required to move fluid at a mass flow rate m 

through a path with a head loss hQ. Head loss is determined from 

where f is the friction factor. If A is the pipe cross-sectional area 

(a~'/4), then 

Substituting the expressions for hQ and m into the equation for pp and divid- 

.ing through by L (the pipe length) yields 

For long, smooth pipes with Re between 5,000 and 200,000 (McAdarns 1954), we 

have 
With Re = pVD/,, substituting f from Eq. 7-28 into Eq. 7-27 gives us 

Thus, for a given flow velocity and pipe diameter, fluids with low density and 

viscosity minimize pumping power requirements. 

Comparing h in Eq. 7-23 with pp/L in Eq. 7-29, we find that c and k should be P high and u should be low for high heat transfer and low pumping power, but it 

is unclear whether high or low density is desired. However, by solving the 

pp/L equation for V and then substituting for V in the h equation, we obtain 

The first term is simply a numerical constant, C. The second term, following 

the work of Fried (1973), is the heat transfer efficiency factor HTEF:, 

p4/7 ci0.4 k0.6 

HTEF = ,16135 

Combining Eqs. 7-30 and 7-31 yields 

h . D3/7 

HTEF = c(PP/L)~/~ 

Equation 7-32 shows that, for a particular pipe diameter, fluids with high 

values of HTEF will have relatively low pumping power requirements or, alternatively, a high heat transfer coefficient per unit pumping power. Note that 

HTEF is independent of mass flow rate but is a function only of temperaturedependent fluid properties. Therefore, it 'varies with temperature.* 

Water is the znost thermally efficient fluid available in its temperature 

range. If freeze protection is needed and process temperatures are not high, 

ethylene glycol-water solutions are the next most efficient. Several of the 

Dowtherm@ fluids (A, E, and J) also have relatively high efficiencies. In the 

mid-range efficiency band, the Syltherm@ 800 silicone fluid, the "Sun-Tempw@ 

fluid, and DowthermQ G appear best at various temperatures. There are only 

slight differences among the remaining petroleum fluids. Figure 7-7 shows 

heat transfer efficiency factors for a number of fluids. 

*Fried (1973) originally defined HTEF as (p4I7c 113k2/3) 1 (y16135), where the 

difference in the exponents of c and k result's from using n = 113 as the P Prandtl number exponent when calculating the Nusselt number. Fried' s 

development of HTEF considered cooling a fluid by means of a heat exchanger 

rather than heating by means of a solar collector. Fried also included the 

numerical constant in HTEF in the text of his paper, though.his graphical 

results did not contain it. 

7.2.3 Other Thermal Properties 

A heat transfer fluid should not be selected on the basis of the HTEF alone. 

The solar system designer may find that more efficient fluids are also more 

toxic, flammable, or corrosive, or more prone to thermal degradation. Fluid 

manufacturers -usually specify recommended operating temperature ranges for 

their fluids. The range is usually viscosity-limited at low temperatures 

(because the fluid becomes too difficult to pump) and degradation-limited at 

high temperatures. The high limit usually refers to bulk fluid temperature; a. 

somewhat higher maximum film temperature may also be specified. Operating 

ranges are given for many fluids in Appendix B (see Table B-3). 

The flammability of a fluid is usually defined by the flash point, the fire 

point, and the autoignition temperature. The flash point is the lowest temperature at which an air-vapor mixture will burn when it is exposed to a spark 

or flame; but if the ignition source is eliminated, the mixture will not keep 

burning. The fire point is the lowest temperature at which an air-vapor mixture will burn when it is exposed to a spark or flame and will continue to 

burn after the source is removed. The autoignition temperature (AIT) is the 

temperature at which the vapor will burn spontaneously when it is exposed to 

air; and here, no separate ignition source is needed. The fire point of a 

fluid is slightly higher than the flash point, and the AIT may be several hundred degrees higher. These values are also presented in Appendix B (see 

Table B-6). Fluids are often operated at temperatures above their fire 

points; therefore, system operators should be aware of the possible dangers 

and should know what actions to take if a fluid leak develops. 

Toxicity levels were established by the National Academy of Sciences Committee 

on Hazardous Materials and are given in Appendix B (see Table B-8). Propylene 

glycol is nontoxic and often used in food-processing systems, sometimes as a 

food additive; silicone fluids are also nontoxic. However, ethylene glycol is 

considered toxic. And adding corrosive inhibitors and pH buffers can render a 

pure, nontoxic fluid toxic. High temperatures (for example, like those 

occurring in stagnation) can cause oxidation, which also increases a fluid's 

toxicity. 

Temperatures, pressures, and the kind of heat transfer fluid used in an IPH 

system as well as pump materials, drivers, couplings, and seals all affect the 

choice of an appropriate pump. Although using relatively small pipes throughout the solar field may minimize piping costs, this could result in high head 

losses which could, in turn, necessitate a bigger, more expensive pump. Thus, 

both capital and operating pump costs should be an integral part of the piping 

design process. Because pump technology is so well known and developed, 

detailed pump selection criteria are not presented in this handbook; rather, 

some basic information regarding types of pumps and preliminary sizing techniques is given. The solar IPH system designer is urged to evaluate this 

information with each project, and then to consult pump suppliers or manufacturers for assistance in the final selection of a pump. 
Pumps fall into two broad categories: centrifugal pumps and positive displacement pumps. Figure 7-8 summarizes the various subcategories of each 

type. The basic difference between the two is that, at a constant pump speed, 

a positive displacement pump maintains a constant capacity (i.e., it always 

delivers the same volume of fluid per unit time), but the capacity of a centrifugal- pump -depends on the head that it must work against. In both cases, 

the brake horsepower required of the driver and pump efficiency vary with the 

head. A typical pump curve for a centrifugal, pump showing efficiency and 

head-versus-flow-rate characteristics at various speeds is displayed in 

Fig. 7-9. Similar pump curves for a positive displacement pump would be 

nearly vertical and would show the flow rate increasing nearly linearly with 

the pump speed. Efficiencies of positive displacement pumps tend to increase 

with speed because slippage losses have less effect at higher speeds. Both 

types of pumps have been used in solar IPH systems. 

Before choosing a pump for a particular application, certain preliminary 

information is needed: 

The tentative system piping layout should be designed and the system - 

head-flow curves calculated for all conditions, including cold start-up. 

The required pmp capacity Q should be determined. This capacity is a 

function of the energy collected by the collector field, field inlet and 

preferred outlet temperatures, and fluid specific heat and density. 

a The system head loss to be made up by the pump B must be calculated, 

using system head-flow curves. Since the head loss depends on the pipe 

sizes used in the system layout, piping and pumping sizing are iterative 

procedures. 

The net positive suction head available (NPSHA) to the pump must be 

determined. This parameter represents the amount of energy in the fluid 

at the pump datum. NPSHA is the absolute pressure at the pump inlet plus 

the velocity head, minus the vapor pressure of the fluid at the inlet 

temperature. 

With this information, pump size can be estimated. 

7-3-1 Sizing a Single-Speed Centrifugal Pump 

To size a centrifugal pump, first calculate the specific speed Ns: 

where 

N = an initial estimate of the pump speed in rpm, chosen from the 

approximate full-load speeds of induction motors: 3500, 1750,- 

1160, 875, and 700 rpm for 60-Hz motors, or 2900, 1450, 975, 730, 

and 585 rpm for 50-Hz motors 

Q = flow rate, in gpm 

H = head, in feet. 
Centrifugal 

Vertical 

Turbine Type 

Volute Type 

Sump Type 

Chemical Type In-line 

High Speed In-Line 

Can Type (Low NPSH) 

Mixed Flow 

Propeller 

d 

- 

(D 

2 

00 

Displacement 0 

Horizontal 

General Service 

Chemical (ANSI) 

High Temp. (API) 

Multistage 

Slurry 

Self-priming 

Mixed Flow 

Propeller 

Sealed Rotor i 

Screw 

Progressing Cavity 

Vane 

Power Frame Type 

Plunger or Piston 

Horizontal or Vertical 

Plunger Type 

Diaphragm Type 

Number of Feeds 

Types of Stroke 
Flow rate - 

SOURCE: Johnson 1981 

Figure 7-9. Typical Eea&Flw Curves for a Centrifugal Pump 

N ranges from 7,000 to 10,000 in a typical impeller design. Values between 

18,000 and 13,000 indicate special impeller designs that might be unstable 

when operated at less than 50% of the capacity for maximum pump efficiency 

(Lobanoff 1979). 

Next, use Fig. 7-10 to find the point of maximum efficiency for the value 

obtained for Ns. Then, read the corresponding value of specific diameter D, 

from the vertical axis of the figure. Ds is defined by 

which can be solved for D, the required impeller di'ametex (in inches). 

Figure 7-11 enables the designer to estimate the net positive suction head 

required (NPSHR) by a pump sized for N = 3550 or 1760 rpm; NPSHR is a characteristic of pmp design and is the net positive suction head necessary to 

avoid cavitation in-the pump. To use Fig. 7-11, find the range of NPSm corresponding to 7000 Ns 10,000 at design capacity Q. For a viable pump 

selection, NPSHA should exceed NPSHR by at least 2 or 3 ft to provide a margin 

of safety. If the value of NPSHR is lower than the value of NPSHA, or unreasonably high, the designer should select a different pump speed or consider 

double-suction pumps and develop another preliminary pump design. 

At this point, pump manufacturerst catalogs can be scrutinized for pumps 

closely matching the required values of Ns, D, Q, H, and NPSHR that are also 

suitable for the fluids and temperature that will be encountered in the system. When a candidate pump is selected, its performance curve should be compared with the system head-flow curve to ensure that it is appropriate for all 

Based on suction specific speed 

Nss = - N = rpm Q = Flow, gpm ti. = NPSH required, ft H,34 

For single-suction pumps: -.. 

3,550 rpm 1,750 rum 

Capacity; U.S. gal/min 

For double-suction pumps: 

3.550 rom 1.760 rprn 

I with pump manufacturer 

I I I I I 

500 1,000 2,000 5.000 10,000 20,000 

Capacity, U.S. gal/min 

SOURCE: Neerken 1978 

Figure 7-11. Net Positive Suction Head Required by Pump 

conditions of operation. It is critical that the normal operation point (the 

intersection of the pump head-flow curve and the system normal operation 

curve) is near the "knee" of the pump curve, so that errors in estimating system head loss will cause little change in the flow rate. It is also important 

to make sure that the pump generates sufficient head and flow for all modes of 

system operation, especially cold start-up. Finally, a pump driver (usually 

electric) must be selected with adequate torque and power to drive the pump 

under all circumstances. 

7.3.2 Multispeed Centrifugal Pumps 

A designer may want to vary the flow rate from the collector pump for several 

reasons. Fox example, varying solar radiation requires a variable flow rate, 

if we want a constant collector array outlet temperature. For freeze protection by means of circulation, a lower flow rate might be desirable. Changes 

in fluid viscosity and density caused by temperature variations during system 

operation can lead to undesirable, uncontrolled flow-rate changes during the 

day. Typically, the flow from a single-speed pump is controlled by throttling 

down its outlet, although this procedure can lead to higher parasitic losses. 

An alternative is to use a variable-speed driver (Johnson 1981, Morton 1980). 

Multispeed or variable-speed pumps, as their names imply, are driven at different speeds in response to changing H-Q requirements. The effect of varying 

the speed of a typical pump may be seen in Fig. 7-9. And an interesting study 
by Morton (1980) compared the operating costs of a single-speed, a two-speed, 2 2 and a variable-speed pump and electric driver in a 4650 m (50,000 ft ) collector field. The field produced 315'~ $600~~) heat transfer oil at flow 

rates between 11.4 m3/h (50 gpm) and 68.1 m /h (300 gpm). The resultingpmp 

motor power requirements are shown in Fig. 7-12. Morton determined that the 

additional amortized capital cost of the variable-speed driver would be more 

than offset by the savings in required electrical energy, and so he chose the 

variable-speed pump for his application. Figure 7-13 relates capacity to 

NPSHR for variable-speed pumps for which water is the fluid. Methods for controlling flow rate to maintain a constant outlet temperature are discussed in 

Sec. 8.2.1. 

Two or more single-speed pumps in parallel also represent a viable configuration for solar IPH systems. A large pump in parallel with a smaller pump is 

analogous to a single pump with three speeds; each pump can be operated alone 

or the two can be operated together. Such flexibility can significantly 

reduce parasitic power. When they are working together, both pumps operate 

against the same head but contribute only a portion of the total flow rate. 

An example H-Q curve for parallel centrifugal pumps is shown in Fig. 7-14. 

However, the size difference between pumps must not be so great that the 

smaller one cannot operate under the head produced by the larger. 

As we noted in Fig. 7-8, positive displacement pumps come in three types: 

rotary, reciprocating, and controller volume. Of these, the rotary types are 

probably best suited to IPH applications, because they are readily available 

SCR Variable 

7 8 9 10 11 12 13 14 15 16 17 

Hour of Day 

SOURCE: Morton 1980, 

Figure 7-12. Pumping Paver Required by Different Pump Configurations 

176 


in appropriate sizes, provide a smooth flow, and are relatively efficient. 

However, reciprocating or controller volume pumps may also be suitable for 

certain applications; for example, a diaphragm pump might be most appropriate 

for a fluid that tends to leak. 

Several -characteristics of positive displacement pumps make them attractive 

for solar IPH applications. They are often self-priming, reducing the suction 

head requirement in system design. The flow rate of a positive displacement 

pump is nearly proportional to its speed and insensitive to the head against 

which it must pump; thus, precise flow rate control and cold start-up, even 

with ,a viscous fluid, are not difficult* These pumps can be used in hightemperature applications, and have generally higher efficiencies than centrifugal pumps. They are also relatively inexpensive in small sizes compared with 

centrifugal pumps [less than about 6 L/S (100 gpm) ] and when used for highhead applications (Perry and Chilton 1973). 

But other characteristics of positive displacement pumps may be less benef icial. Because of the close clearances needed for efficient pump operation, 

the fluid must be clean and nonabrasive. Many pumps require a fluid with good 

lubricating properties, since the fluid must lubricate internal bearings. 

Thus, pumps for water or other fluids with few lubricating qualities may have 

to be specially designed to ensure long life. The insensitivity of these 

pumps to the head against which they operate can cause a rapid, large pressure 

buildup at the pump outlet if flow is blocked. Pressure relief ,valves are 

usually added to the pump casing to vent fluid from the outlet back to the 

suction side of the pump* However, if an overpressure condition is allowed to 

persist for any length of time, provision must be made for removing the excess 

heat or the pump will overheat. A system design employing a positive displacement pump must include protection for components and sensors against such ' 

overpressure conditions. 

Selecting a positive displacement pump involves first determining the system 

head curves, the design flow rate and head loss, and NPSHA, the same as for a 

centrifugal pump system. Next, the manufacturers' literature must be scanned 

to find a pump that matches these requirements. As with a centrifugal pump, 

care must be taken to ensure that the pump will operate under all conditions 

and that the pump driver is adequate, especially in the case of a variablespeed system. 

7.4.1 Qlaracteristics of Solar Systems 

Valves regulate and isolate flow in a mechanical system. The number and kinds 

of valves for a solar system should be selected carefully because valves add 

to system cost and are sources of pressure drop and heat loss during operation 

and overnight cool-down. Some characteristics of solar systems, such as overnight shutdown, that provide daily intervals for maintenance, make fewer 

valves necessary in the system than for a conventional process plant. 
Solar systems that operate at low temperatures allow for great flexibility in 

the choice of valves. In addition, solar systems, particularly closed systems, usually do not operate at high pressures. Sealing pressures are low, 

and absolute shutoff is generally not necessary. Isolation valves would most 

often be closed only when the solar system is down and some amount of leakage 

would then; be acceptable. 

7.4.2 TvDes of Valves 

With the proper seat elastomers, butterfly valves are operational at temperatures up to 135'~ (275'~). Butterfly valves combine many attributes that are 

favorable to solar system applications: they are inexpensive, have low 

thermal mass, present little resistance to fluid flows, and are quick-acting, 

opening and closing over a one-quarter turn. These valves are a good choice 

for isolation or crude throttling in a low-temperature solar system. They are 

available in large diameters but generally not in sizes of less than 2 in. and 

should not be used when absolute shutoff is required. 

With teflon seats, ball valves are suitable for service at temperatures up to 

200'~ (400'~). These valves are more expensive than butterfly valves, but 

they are also lightweight, compact, and quick-acting over a one-quarter turn. 

In addition, the straight-through flow characteristic of these valves minimizes pressure drop. They provide positive flow shutoff and can be used for 

flow throttling. In solar systems, they are a good choice for vent, drain, 

and flow-balancing valves. Ball valves come in sizes ranging from 1/4 in. to 

over 12 in., with screwed or flanged fittings or connections suitable for 

soldering. Ball valves equipped with pressure taps simplify flow-balancing 

procedures. 

In high-temperature solar systems, steel valves (or metal alloy, as required) 

must be used: gate valves for isolation and globe valves for throttling. 

Gate and globe valves are considerably more massive than butterfly or ball 

valves, and their stems provide a considerable surface for heat loss. Gate 

valves should be used only in the fully open or fully closed position. In the 

partially open position, the gate is subject to rapid wear and positive sealing is not possible. When it is fully open, however, a gate valve causes minimal pressure drop. Globe valves are always associated with a considerable 

pressure drop. Flow through the valve is almost proportional to the number of 

screw turns that the valve is open. 

It is generally preferable to weld steel valves in place in a solar system, 

particularly when it is operating under high pressure or contains synthetic 

heat transfer oils. Compared with flanges and screwed fittings, welds are 

less massive, are leak free, have lower friction losses, and are more easily 

insulated. The disadvantage of welding, in addition to a generally higher 

initial cost, is the lack of flexibility that results in the piping system. 

For example, a line cannot be broken for cleaning. Care must be taken not to 

gall the seat of welded-in-place valves because they are so difficult to 

replace. 

Control valves are usually globe-type, although butterfly control valves with 

plastic or all-steel construction are available. Three-way control valves 
should be avoided, because field experience indicates that leaks into the 

shutoff line soon develop. Check valves are needed in nondraining solar collector loops to prevent thennosiphon heat loss, which could result in the heat 

exchanger freezing. They should be selected to minimize pressure drop, which 

usually requires the use of a swing check. A flow-through valve with a check 

that swings clear of the flow is preferred. Fluid velocities should be high 

enough to keep the check fully open at all times. Partial opening or fluttering will increase pressure drop and wear, and lead to less efficient sealing. 

7,4,3 Gzidelines for Selecting Valves 

Solar system designs have been quite conservative in the past, employing a 

great number of isolation and throttling valves. This trend has also 

increased the chances for leakage and large thermal losses. Too few data are 

available to make definite rules about the placement and type of valves suitable for solar IPH systems; but the following guidelines, based on minimizing 

the number of valves, should be considered by the system designer. 

Isolation valves should be placed around pumps, and butterfly valves should be 

used for temperatures of less than 135'~ (275'~), if possible. A clear-away 

swing check valve should be located on the pump discharge between the isolation valves, and storage tanks and other vessels should be isolated with 

valves. 

Ball valves should be used for vents and drains as well as to isolate instruments such as pressure and flow indicators. Ball valves are unsuitable only 

for the highest pressure steam flash systems and for systems using oil heat 

transfer fluids. If piping is sloped correctly with as few slope changes as 

possible, a minimum number of vent and drain valves can be located to serve 

large lengths of line. 

Most of the valves in an industrial solar system are used for flow balancing 

and isolating individual rows of collectors. The block-in capability of each 

collector string invariably dictates placement of safety valves in each 

string, but this further increases thermal losses and makes fluid leaks more 

likely. Unless isolation capability is required for proper maintenance, however, omitting these valves should be seriously considered; they should not be 

necessary in an industrial solar system. While small leaks can be tolerated, 

large fluid leaks will shut down the entire collector field. But an ability 

to operate a portion of a col1ecto.r field while the rest is shut down gains 

little energy, because maintenance can be performed at the end of each day. A 

good compromise for large collector fields is to provide isolation valves for 

various sections of the field. Eliminating isolation valves on each row 

allows the use of fewer safety valves, and these can be located in the header 

piping. 

Flow equalization between individual collector strings is a major concern in 

solar system design. Flow equalization can be accomplished using reversereturn, multiple-diameter piping configurations, but this increases piping 

costs, thermal losses, and pumping power requirements. An alternative is to 

use balancing valves to achieve sufficient pressure loss across each collector 

string to eliminate the effect of pressure drops along the header. piping. 

These balancing valves can be located at either the inlet or outlet of the 
collector. An outlet location can be more convenient for making adjustments, 

because this is where the temperature reading will be taken. In any case, 

however, balancing flows with valves is a time-consuming process. Valve settings change easily over time, as the valves wear or through accidental interference. An alternative to using conventional valves for flow balancing is to 

use automatic -variable-orifice valves. These valves are designed to control 

the flow rate to within 5% over the desired range of operating pressure drop. 

Another alternative is to use fixed-orifice plates instead of valves to induce 

the needed pressure differential in combination with appropriate pipe sizing. 

Orifice plates are cheaper, more reliable, and result in less thermal loss 

than valves. Although perfect flow balancing using orifice plates requires an 

extremely detailed pressure analysis of the piping system, this is not necessary because a small degree of liquid maldistribution has little effect on 

system performance. In an oil system operating close to the temperature limit 

of the oil, or a flash-steam system operating near the pressure limitation of 

the collectors, maintaining flow equality could be more crucial. If collector 

outlet temperatures indicate serious maldistribution of flow, it is possible 

to change the orifice plate to a different diameter, although the effect of 

this procedure on pump performance and overall flow rate must be considered. 

Control valves are required in an IPH solar system in which control of the 

collector outlet temperature is desired. Butterfly control valves are, again, 

particularly suitable here and have been advocated for more demanding process 

applications (Baumann 1979). Since few control valves are likely to be 

employed in the solar site, and they could be widely scattered and remote from 

the system control station, electrical activators should be considered. 

Pneumatic systems with a compressor and large lengths of piping are not as 

economical for the small number of valves involved, and pneumatic leaks are 

bothersome. 

Often, process fluid should not pass directly through the collector field; 

thus, many solar applications require heat exchangers. A closed-loop solar 

system allows the use of nonfreezing collector fluids that are less corrosive 

and less prone to scaling than the process fluid. Possible contamination of 

the process fluid is another factor to take into account in selecting a 

closed-loop system. However, incorporating a heat exchanger in a solar system 

introduces cost penalties associated with that exchanger and with auxiliary 

piping; and the performance of the solar system is reduced by virtue of the 

increased operating temperature of the collector system working fluid. 

Another penalty is the result of the greater pumping power needed because of 

the increase in system pressure drop and the need for an additional pump. 

Thus, the objective in designing an exchanger for a solar IPH application is 

to size the exchanger so that performance and pumping power penalties and heat 

exchanger costs are minimized. 

7.5.1 Heat Transfer Relations 

For the sy-stem illustrated in Fig. 7-15, the heat transferred across the heat 

exchanger Q in watts (~tu/h) is 

182 
From 

- : 

Solar 

Collectors 

To 

Solar 

h;tCcp,. To 

- 

r * Storage 

TC., Tss0 Tank 

4- Heat Exchanger 

,I c From 

: Storage 

Collectors Tank 

Figure 7-15. Example Heat Exchanger System 

where &and is are flow rates (kg/s , ib/h) and cp,, and c are specific 

heats kg K, I3tu/lbo~) of the collector and storage f l~ixs',~ respectively. 

It is convenient to define the capacity rate W (w/K, ~tu/h'~) for each fluid 

as 

In a heat exchanger of infinite area, the heat transferred would be at a maximum and would be 

where Wdn is the smaller of Wc and Ws. 

Heat exchanger effectiveness E is defined as 

and, thus, 

and 

E = Tc,i - =c,o when Wc ( Ws , Tc,i - Ts,i 
sin + TR-1356 

TS ,o 

- 

E = Ts'i when Wc > Ws . Tc,i - Ts,i 

7.5.2 Overall Heat Transfer Coefficient 

The heat transferred between fluids within a counterflow heat exchanger with 

constant fluid specific heats is given as 

2 where %is the overall heat transfer coefficient between the fluids (W/m K, 2 2 ~tu/ft F), A is the area of heat transfer surface (m , ft ), and ATm is the 

log mean temperature difference: 

Typical values for overall heat transfer coefficients for some of the fluids 

likely to be encountered in a solar system are shown in Table 7-12. If 

greater accuracy is required to size the heat exchanger, the following simplified procedure can be employed. (More detailed procedures that take into 

account the physical characteristics of the heat exchanger are employed by 

heat exchanger suppliers, but are not required for the initial stage of 

design. ) 

The overall heat transfer coefficient is generally based upon the exterior 

tube surface and can be defined as 

where % is the total resistance to heat transfer. The resistances to heat 

transfer are in series, so that 

Table 7-12. Typical Overall Heat Ransfer Coefficient Values for 

Thbular Heat -changers 

Tube-Side 

Fluid 

Shell-Side Overall Heat Transfer 

Fluid Coefficient [w/m2~ (~tu/h-f t2-'I?) ] 

Water Water 1140-1420 (200-250) 

Water Demineralized water 1700-2840 (300-500) 

Feed water Steam 2270-5680 (400-1000) 

Heat transfer fluid Boiling water 570-850 (100-150) 

Water Air 114-142 ( 20-25) 
sin :el TR-1356 

where Do and Di are the outside and inside tube diameters (m,ft), 

respectively; kt is the thennal conductivity of the tube material (w/~PK, 

I3tu/h-ft0~); ho and hi are the outside and inside film coefficients (w/rn2-~, 

~tu/h-ft*~~), respectively; and Rf and Rf are the outside and inside foul- 2 ing resistances (m K/W, hO~f t2/~t$, respe'ctively. The fouling resistance? 

account f6r the reduced heat transfer efficiency caused by scaling. Typical 

values for fouling resistances are listed in Table 7-13. In general, fouling 

In the solar collector side of the exchanger should be minimal, and the collector working fluid should be selected to minimize scaling. Scaling on the 

process side could be much greater, depending on the characteristics of the 

process fluid. 

The thermal conductivity of the tube material is readily obtainable. Typical 

materials are steel (142 ~/m-K, 25 ~tu/h-ftO~) and brass (340 ~/m-K, 

60 ~tu/h-ftO~). The remaining unknowns in Eq . 7-45 are the film coefficients. 

The inside heat transfer coefficient can be calculated using the DittusBoelter (1930) equation: 

where 

Nui = Nusselt number (hpi/ki) 

Rei = Reynolds number (P.D.v. /U ] 111 i 

Pri = Prandtl nlnnber (c Y. /ki) psi 1 

n = 0.4 for heating the fluid, 0.3 for cooling the fluid. 

The dimensionless numbers are calculated using fluid properties evaluated at 

the mean operating temperature: 

pi = is the density of the fluid inside the tubes (kg/J, lb/f t3) 

Vi = the fluid velocity (m/s, f t/s), and 

wi = the viscosity (kglm-s lb/ft-h). 

Table 7-13. Typical Foaling Resistances 

Type of Fluid 

Distilled water 

Treated boiler feed water 

City water below 52% 

City water above 52O~ 

Heat transfer media 

Refrigerant liquids 

Industrial air 
The Dittus-Boelter equation assumes turbulent flow within the tubes (Re > 

10,000). Establishing turbulent flow conditions should be a requirement for a 

solar heat exchanger design, because heat transfer under laminar or transition 

flow is much less efficient. In industrial solar systems, the use of forced 

convective heat transfer equipment is assumed. Natural convective heat trans- 

, fer is inefficient; placing exchanger coils within a heat storage tank would 

cause maintenance problems. The procedure described by Cole et al. (1980) can 

be used to determine the shell-side heat transfer coefficient. A similar 

Nusselt number relation is used to correlate the film coefficient, 

where 

and 

&, = the shell-side mass flow rate (kgls, lb/h) 

I+, = the number of tube rows across the diameter of the shell 

Sbaf = the baffle spacing (m, ft) in the longitudinal direction along the 

exchanger 

'min = the minimum spacing between tubes (m, ft) 

bin = the min'imum cross-sectional area between the tubes. 

After calculating the fluid film coefficients, the overall heat transfer coefficient can be calculated using Eqs. 7-44 and 7-45. The effectiveness of a 

counterflow heat exchanger is related to the overall heat transfer coefficient 

by 

e = 1 - exp(-B) 

Wmin * 

1 -- exp ( -B 

wmx 

where 

B A O (L Wmin Wmax 

The number of heat transfer units, NTU = UoAJWmin, is a dimensionless measure 

of the adequacy of heat exchanger area. For proper heat exchange, NTU will 
generally be in the range of 1 to 10 (Lunde 1980). Equation 7-48 can be 

solved for E when a heat exchange area must be found for a particular 

effectiveness. 

When the flow capacity rates on both sides of the exchanger are equal, 

Eq. 7-48 becomes 

€ = NTU 

1+mu 

7.5.3 Heat Exchanger Factor for Solar System Performance 

The following analysis applies to the collector system illustrated in 

Fig. 4-4. It describes a factor that can account analytically for the presence of the heat exchanger between the co~lectors and storage. The basic collector performance equation can be written as 

-- - ,,,a - FflL(Ti - T,) , (7-51) 

*c 

where 

2 A, = collector aperture area (m , ft2) 

FR = heat transfer factor based on collector inlet temperature 

Ta = collector optical efficiency 

UL = overall heat transfer coefficient for heat loss from the collector (w/m2 K, ~tu/h-ft~~~) 

T~ = collector inlet temperature 

T, = ambient temperature (OC, OF). 

Rearranging Eq. 7-35 and assuming that line losses in the collector loop are 

negligible (i.e., Ti = TC,, and To = T,,i), then 

Substituting this equation into Eq. 7-51 yields 
Using Eqs. 7-40 and 7-41 and assuming a well-mixed storage tank, Ts,i = Ts, a 

general expression for the heat transferred can be derived: 

The expression 

is known as the dewinter heat exchanger factor (dewinter 1975). Thus, F 

represents the penalty imposed on an open-loop system, where Ts would equaf 

Ti, by the incorporation of the heat exchanger to form the double-loop configuration shown in Fig. 4-6. 

The performance of flat-plate collectors is generally categorized in terms of 

the collector inlet temperature. Parabolic trough performance is often correlated in terms of the collector outlet temperature or the average of the inlet 

and outlet temperatures. The heat exchanger factor FX,? for a collector performance equation in terms of the outlet temperature To 1s 

where Fo is the heat transfer factor based upon the collector outlet temperature. The heat exchanger factor Fx,m, in terms of the average collector operating temperature Tm, is 

The performance curve of a parabolic trough collector is generally presented 

as a quadratic function of ATII, unlike flat-plate collectors whose performance curves are linearized. Consequently, for a parabolic trough collector, 

an appropriate operating temperature (whether inlet, average, or outlet) must 

be selected. Given this temperature, the term FRUL, FOUL, or F U can be 

m .L determined by evaluating the slope of the performance curve at thls point. 

Selecting the appropriate operating temperature involves a judgment based on 

the nature of the solar heating process, the storage temperature, and the 

variations likely in collector temperatures. In any case, given that the performance curve of a line-focus collector is fairly flat over a wide temperature range, the operating temperature selection is not critical. An overestimate of temperature is conservative, leading to an increased value of FUL and 

a larger heat exchanger. 
7.5.4 Economical Heat Exchanger Area 

The foregoing analysis indicates that a heat exchanger reduces the performance 

of the solar system by a constant factor F,. Thus, to meet a given load, the 

collector area must be increased in inverse proportion to F,. For economical 

heat exchanger sizing, the heat exchanger factor typically has a value of 

about 0.95. Such information can be used for preliminary heat exchanger sizing by solving Eq. 7-55, 7-56, or 7-57 for E. The heat exchanger area can 

then be calculated using Eq. 7-49. 

The optimum heat exchanger area represents a trade-off between the cost of the ' 

heat exchanger and the cost of the solar collectors. The total system cost CT 

can be represented by 

where C, and Cx are the costs of the collectors and heat exchanger per unit 

area, respectively, and A, and A, are their respective areas. The energy' 

delivered by the system is 

where F is FR, F,, or Fm. The minimum cost of delivered energy with respect 

to exchanger surface area is 

For equal flow capacity rates (Wc = Ws) , and assuming that the overall heat 

transfer coefficient Uo does not vary with Ax, the optimum (minimum cost) 

ratio %/Ac is 

According to Horel and dewinter (Cole et al. 1979), the optimum heat exchanger 

invariably has a storage capacity rate Ws higher than its collector capacity 

rate Wc. They found that the ratio wC/W for the optimum exchanger is 0.5 to 

0.6, and that Eq. 7-61 can still be use1 to find the optimum heat exchanger 

area because that value varies from the value determined in the optimum 

(unmatched capacity rate) case by about 1%. The optimum storage capacity rate 

is generally greater than the collector capacity rate because of the effect of 

the individual flows on collector operating temperature. Increasing the storage flow rate has a greater effect on reducing collector inlet temperature 

(and thus the temperature of the entire collector field) than an equivalent 

increase in the collector flow rate. Increasing the storage flow rate would 

result in less of an increase in electric power consumption than an equal 

increase in collector flow, because the pressure drop through the collector 

loop is usually larger. 
7.5.5 Practical Considerations in Selecting a Heat Exchanger 

In previous sections, heat exchanger sizing has been discussed in terms of 

perfect countercurrent flow. Such conditions are attainable only in doublepipe exchangers that are generally economical only in small sizes. Shell-andtube heat-exchangers accommodate large heat exchanger areas in a compact volume. A diagram of a floating tubesheet shell-and-tube heat exchanger is shown 

in Fig. 7-16. Since steel shell-and-tubes are the most economical type of 

heat exchanger, they are the most likely kind to be incorporated into a solar 

IPH system. This section presents some of the practical aspects of selecting 

a heat exchanger. Operating experience with heat exchanger systems in industrial solar systems is limited. Consequently, only some general points about 

heat exchangers are incorporated here and tend toward a rather conservative 

exchanger design. 

A major variable in a shell-and-tube heat exchanger is the number of shellside and tube-side passes; i.e., the number of times the fluid changes direction from one end of the exchanger to the other. Because some means must be 

built into the exchanger to compensate for thermal expansion, flows into and 

out of the tube side are generally at the same end of the exchanger. Thus, 

normally, the number of tube-side passes is even. By appropriate baffling it 

is easy to produce two, four, or more tube passes. However, the greater the 

number of passes, the greater the deviation from countercurrent flow, the 

greater the path length, and hence, the.greater the pressure drop of the tubeside fluid. 

A single shell pass is the most common shell-side configuration because of the 

difficulty of adequately sealing a multi-shell pass exchanger. The effect of 

multiple shell-side passes can be achieved by connecting identical single-pass 

exchangers in series. Because multiple-pass heat exchangers are not associated with perfect countercurrent flow, correction factors must be applied to 

the log mean temperature differential. Such correction factors are available 

from graphs (Kreith 1973, Perry and Chilton 1973). 

The unique characteristics of a solar system must be considered in determining 

the number of exchanger passes. In general, compared with conventional 

thermal processes, a solar system involves larger flows and smaller temperature differentials. Because solar collector performance depends more on operating temperature than conventional heating equipment does, a closer similarity between the hot side (collector) and cold side (process) temperatures is 

desirable. This demands maximum heat exchanger efficiency and a minimum number of heat exchanger passes. Other considerations working in this direction 

are pumping power and thermal losses (both operational and overnight). Thus, 

as a general rule, unless a large mismatch of flows precludes it, a two-tube, 

single-shell pass exchanger is probably the most appropriate configuration for 

a solar system. 

The designation of tube-side and shell-side fluids is another, largely practi-. 

cal, decision that must be made. It is more difficult to clean the shell side 

of an exchanger than the tube side, so a dirty, scaling, or corrosive fluid is 

generally placed on the tube side. A great difference in operating pressure 

would place the high-pressure fluid in the tubes. Placing the hottest fluid 

in the tubes reduces insulation requirements on the exterior shell. Turbulence is more easily achieved on the shell side; thus, the fluid with poorer 

heat transfer characteristics would be placed in the shell. Shell-side pressure drop for a given flow is also generally lower. These characteristics of 

exchanger fluids are not entirely consistent in the choice of flow path, so 

engineering judgment must be used. Moreover, the cleaning and maintenance 

factor will often place the collector fluid in the exchanger shell. 

. -: 

Finally, with the help of the exchanger manufacturer, the type of exchanger 

must be specified. A major factor in this decision is the degree of differential thermal expansion and cycling. Fixed-tube sheet exchangers are usually 

less expensive, but the severe strains placed on the exchanger seals by the 

diurnal solar cycle must be fully considered. Hairpin exchangers readily 

accommodate thermal expansion but are difficult to clean and are often unsuitable for dirty or scaling fluids. They are, however, applicable in unfired 

steam generators with a heat transfer fluid in the tubes. Generally, 90:lO 

copper-nickel tubes are specified for such service. 

For most solar energy systems, floating-head exchangers appear to be preferable. The tubes are easily cleaned without requiring removal of the tube bundle, and they are designed to accommodate thermal expansion. Although the 

operating pressure of a solar system is generally low, because of the high 

level of thermal cycling it is probably wise to specify a heat exchanger rating beyond that dictated by operating pressure alone. 

Liquid-to-air exchangers invariably pass the air on the shell side. Since the 

air-side heat transfer coefficients are the major resistors to heat flow, 

extended surface-finned tubes are generally employed. Passing the air transverse to the tubes in a direction parallel to the fins results in little 

' increase in shell-side pressure drop, but the air-side heat transfer coefficient typically increases two to three times. 

7.5.6 Plate Eleat Excha~~~!ers 

Plate heat exchangers are ideally suited for certain solar applications and 

should also be considered. However, plate heat exchangers are not normally 

suitable for pressures exceeding 2.2 MPa (300 psig), temperatures over 200'~ 

(400°~), or for heat exchange involving a phase change (Raju and Chand 1980). 

The plate exchanger becomes economically attractive when an expensive construction material is required or if a double-walled shell-and-tube heat 

exchanger (for leak protection) is the alternative. This is often the case in 

food industries (which usually offer excellent potential for solar energy 

applications) when any possibility of product contamination must be eliminated. -As long as the integrity of the plates is maintained, the sealing 

mechanism of the plate exchanger precludes cross-contamination of exchanger 

liquids. The plate exchanger cost is comparable to or cheaper than equivalent 

shell-and-tube exchangers constructed of stainless steel. It does not have to 

be insulated, it can be supported on a less expensive foundation, and it 

requires less energy for pumping than a shell-and-tube exchanger. Plate 

exchangers generate highly turbulent conditions that result in high heattransfer rates, and approach temperatures may be as low as 1°c. In addition, 

plate exchangers have lower thermal mass and hold-up volumes than shell-andtube heat exchangers. These are important considerations in solar system 

design. 
7.5.7 Summary 

The following generalizations can be made about heat exchangers: 

Forced-convection heat exchange should be used for industrial solar 

systetns. - 

a Fluid velocities in the heat exchanger should be adequate to maintain 

turbulent flow (Re > 10,000). 

For proper heat exchange, the nmber of heat transfer units (NTU = 

UA/W~~) will generally range from 1 to 10. 

The economical heat transfer area is obtained from the expression 

This generally results in a value of about 0.95 for the dewinter heatexchanger factor. 

The flow capacity ratio for the optimum heat exchange, wc/wS, generally 

ranges from 0.5 to 0.6. 

The most appropriate shell-and-tube heat exchanger configuration is probably two tube passes and a single shell pass. 

a If scaling, corrosion, or dirt buildup preclude the use of a hairpin 

exchanger, either a fixed or floating tube sheet (depending on the amount 

of thermal expansion) exchanger is probably the most appropriate 

alternative. 

Consider a plate heat exchanger if the alternative is a double-walled 

shell-and-tube heat exchanger or if p1ai.n steel is unsuitable as a construction material. 

7.6 STORAGE 

In conventional IPH applications, fuel consumption (oil, gas, electricity) is 

adjusted to match the load. The supply of solar energy, however, cannot be 

regulated. To reduce the mismatch between solar supply and process demand, 

storage systems are often deemed appropriate. The cost-effectiveness of storage depends on the particular application, however. For systems in which 

solar energy supplies only a small fraction of the load, storage would ordinarily not be warranted unless the collectors might not be used for significant 

periods of time (e.g., if the plant is shut down on weekends). Storage can be 

worthwhile, however, if the collector array is large enough to supply more 

energy than the load requires during times of peak insolation. 

There are many ways in which energy can be stored; these include mechanical, 

electrochemical, chemical, and thermal means. We are concerned here only with 

thermal energy storage (TES) because the energy delivered by the collectors to 

the load is thermal in solar IPH systems. 
Thermal energy storage is most commonly sensible heat or latent heat. In a 

sensible heat application, the thermal energy to be stored raises the temperature of the storage material. When the energy is later extracted, the storage 

temperature drops. Latent heat storage uses the heat of fusion of a storage 

material as it undergoes a phase change (melting when heat is added, freezing 

when heat-is extracted) to store energy, usually at a nearly constant temperature. Both types of thermal energy storage can be used on either an annual or 

short-term basis. Because of the cost of annual storage systems,* we address 

only short-term storage here. (Solar ponds, which act both as collectors and 

long-term sensible storage, can be cost-effective but thus far have not been 

used in industrial applications and so are not addressed here.) Short-term 

storage allows the solar energy collected during the day to be used at night, 

and also allows energy to be collected on days when the plant is shut down, 

such as on weekends and holidays. 

7.6- 1 Storaee Media 

7-6.1-1 Sensible Eeat Storage 

The vast majority of existing solar IPH systems use sensible heat storage. 

Liquid systems typically use water or oil storage; steam systems employ water, 

oil, or a mixture of oil and rock; air systems usually use a rock bed. 

When liquid collectors are used, it is easiest to store sensible heat in a 

liquid medium since this permits straightforward heat exchange. The same 

characteristics that make water an excellent heat transfer fluid also make it 

an ideal fluid for law-temperature storage. It has a high volumetric heat 

capacity, is easy to pump, is cheap, and is readily available. At higher 

storage temperatures, materials other than water must be considered if high 

pressures and the associated high cost of storage tanks are to be avoided. 

Using other low vapor pressure fluids is an alternative; however, they can 

also be expensive. Another alternative is to use solid storage. Ordinarily, 

the high-temperature heat transfer fluid is brought into direct contact with 

the solid medium. Because of its low cost, rock is a common choice for a 

solid storage medium. 

When a storage tank is filled with a mixture of rocks and a heat transfer 

fluid, a great deal of stratification is possible because of the large surface 

area of the solid, the corresponding rapid heat transfer, and low thermal conductivity. This setup distributes high-temperature fluid to the load from the 

top of the tank and low temperatures to the collectors from the bottom. 

The stratification associated with a solid storage device is well utilized at 

lower temperatures as well, specifically in air collector heating systems 

using rock storage. Air collectors generally have lower FR values than liquid 

f lat-plate collectors (-0.7 versus -0.9), because of the lower heat-transf er 

coefficients associated with air. Rock-bed stratification provides low inlet 

collector temperatures which compensate for the low FR values and result in 

*That is, storage systems with capacities comparable to energy collected on an 

annual basis. 
efficiencies similar to those of liquid collectors. It is important that the 

rocks used not vary much in size, however, and that they be loaded carefully, 

otherwise nonuniform flow will be the result. Cole et al. (1980) describe the 

design of rock storage bins for air heating systems in detail. 

. -. 

7.6.1.2 Latent Heat Storage 

Utilizing the latent heat capacity of storage materials permits us to have 

smaller storage volumes. And the relatively constant temperature of storage 

can maximize collector efficiency and minimize storage heat losses. An ideal 

phase-change material (PCM) should have the following characteristics: 

appropriate phase-change temperature 

a high latent heat 

a low cost 

ready availability 

nontoxicity and nonflamm~bility 

uniform.phase-change characteristics (no subcooling or separation). 

Two basic material types have been used for short-term phase change storage-- 

organic compounds and salt hydrates. A good example of an organic compound is 

paraffin. Like other organics, it suffers certain limitations--flammability, 

low thermal conductivity , and volume trlc change during phase change (causing 

separation from container walls). The latter two problems make it difficult 

to get heat into and out of the material. As a result of such limitations in 

organic compounds, most of the work in phase-change materials has centered on 

salt hydrates. Maria Telkes, who has done much of the pioneering work in this 

field, has concentrated on one salt hydrate In particular because of its low 

cost--sodium sulfate decahydrate, or Glauber's salt. The chemical reaction 

involved in the phase change of Glauber's salt (Na2S04 10 H20) is 

Heating 

Na2S04 10 820 + 251 KJ/kg (108 Btu/lb,) ' Na2SOq + 10 820 . Cooling 

When the solid hydrate is heated, Na2S04 dissolves in the water of hydration; 

the result is a liquid. When it cools, the hydrate is reformed and 251,000 J 

of heat are released for each kilogram that solidifies. To illustrate the 

volumetric storage capacity of Glauber's salt, consider 100 kg (220 lb) undergoing a 30 K (54'~) temperature swing that includes the phase change at 32'~ 

(89O~) : 

where 

hfg = latent heat of fusion, 251 k.J/kg (108 ~tu/lb,) 
c = specific heat at constant pressure, 1.2 k~lkg K (0.5 ~tullb~'~) P 

AT = temperature change, 30 K. 

Substituting numerical values, we have . -- 

Note that the latent heat term is a constant independent of temperature. The 

smaller the temperature swing, the less the contribution from sensible heat. 

In this example of a 30 K change, 87% of the heat stored is latent and 13% is 

sensible. 

In Table 7-14 one can readily see the advantage in both mass and volume inherent in using Glauber's salt rather than rocks or water. The comparison is 

based on each material sized for a heat storage capacity of one gigajoule over 

a 30 K (54'~) temperature swing (typical for a solar space heating system). 

Only 3200 kg of Glauber's salt is needed, compared with 8000 kg of water and 

38,100 kg of rock. 

Unfortunately, the commercialization of Glauber's salt storage has faced a 

number of obstacles, arising from the phase-change behavior of this salt. 

Glauber's salt is considered an incongruent material because, upon melting, 

two distinct phases result: a saturated solution of Na2S04 in water and an 

excess amount of insoluble Na2S04 which precipitates out. Once the precipitate settles to the bottom, it no longer participates in the reaction, which 

causes a decrease in overall heat capacity with each meltinglfreezing cycle. 

Various approaches have been used to address this problem, such as using 

thickeners like paper, pulp, and thixotropic agents (similar to those used in 

thickening paints), active mixing, and thin containers. 

Table 7-14. Storage Size Comparison of 

Different Media Based on 

1 GJ,Storage and 30 K 

Temperature Suing 

Medium Weight 

(kg 

Rocks 38,100 20.3 

Water 8,000 8.0 

Glauber' s salt 3,200 2.1 
Another problem with Glauber's salt is its tendency to supercool below the 

normal freezing point. To solve this problem, nucleating agents (such as 

borax) have been added. A cold rod can also be inserted in the salt hydrate 

to serve as an initiating nucleation site. 

Although storage devices containing Glauber's salt have been marketed, the 

problems discussed above have not yet been completely solved. As a result, 

some manufacturers have looked into other salt hydrates--calcium chloride hexahydrate, for example. Considered a semicongruent material, it does not 

exhibit the same degree of separation as Glauber's salt, and according to one 

manufacturer, it only supercools for the first several cycles [to llOc (20'~) 

below its freezing point]. Unfortunately, it is expensive [over $2/kg 

($l/lb) J in package form and has a lw melting point 127'~ (81°~)], which 

makes it unsuitable for all but the lowest-temperature storage applications. 

For higher temp 

bonates can be 

anticorrosion c 

erature applications, other materials must be considered. Caruseful at temperatures as high as 700°c, and they have good 

haracteristics. Below 500°c, nitrates are good candidates that 

are also relatively noncorrosive and inexpensive. Figure 7-17 shows the storage capacities of various candidate phase-change materials, and the temperatures at which the phase change occurs. Work 'in phase-change storage continues. Problems with containment, heat addition/extraction, and in some cases, 

corrosion still need to be resolved. 

7,6-2 Storage Vessels 

Whatever fluid is used, the storage capacity is a function of specific heat of 

the fluid, its mass, and the ,temperature range over which it can be used. The 

following section focuses on sensible heat storage units, but some parts of 

the discussion can also apply to latent heat systems. We must keep in mind 

that phase-change storage units store a large amount of heat at a particular 

temperature. The heat stored in a sensible storage tank is expressed by 

Thus, for a given fluid and minimum operating temperature, the storage capacity can be increased by increasing the amount of fluid or raising the maximum 

storage temperature. Often, however, the temperature is limited by the heat 

transfer fluid. 

To enhance any stratification that might occur, storage tanks are usually 

plumbed so that solar return and load supply lines are connected near the top 

of the tank where the temperatures are the hottest. Load return and solar 

supply lines are connected near the tank bottom, allowing the coolest fluid to 

be pumped to the collectors, which in turn maximizes efficiency. In actual 

practice collector flow rates are often high enough to disrupt stratification. 

Some stratification may occur in direct systems as well, if loads are drawn 

from storage when there is no collection, and if the flow rates are small. 

The design of a stratified tank usually requires that the height of the tank 

be at least twice its diameter, that diffusers be used, and that the tank volume is passed only once each day. Various devices such as baffles, perforated 

headers, and floating membranes have been studied to help maintain a vertical 

temperature gradient; however, these add to system cost. Multiple tanks are 

also sometimes used with each tank operated at a different temperature to 

achieve a measure of stratification; but, as we might expect, several small 

tanks cost more than one large tank and also provide greater area for heat 

loss. For instance, in a solar water heating study, higher heat losses were 

identified-,as -the major factor causing single-tank domestic hot water tank 

systems to outperform two-tank systems (Farrington, Murphy, and Noreen 1980). 

Typically, several different materials are used to construct storage tanks; of 

these, steel is the most commonly used. It is also the only material used in 

pressure applications. Steel tanks are readily available and, when they are 

not the pressurized type, are inexpensive. Steel tanks are subject to corrosion, however, and have less resistance to underground loads than concrete 

tanks. Fiberglass tanks have good corrosion resistance and are lightweight, 

Resins typically limit the maximum operating temperature to between 65'~ 

(150~~) and 95'~ (~oo'F), however. Fiberglass tanks are usually more expensive and are less readily available than steel tanks. Concrete tanks can be 

formed in any shape or size, are corrosion resistant, and resist underground 

loads well. However, they are heavy and often require a liner to prevent 

leakage. Wood tanks, properly lined, can be cost-effective in applications 

that require unpressurized storage. Their durability must be considered, however. Liners are used to prevent leakage and, in steel tanks, corrosion. 

Butyl rubber, EPDM, PVC, and polyethylene are common materials. Polyethylene 

has less puncture resistance than the others; and PVC is limited to a maximum 

temperature of about 70'~ (160~~). 

The optlmum size of storage is a function of collector area, load profile, and 

solar fraction. Experience in the solar heating of buildings and hot water 

showed that the optimum size was a,bout 200 to 300 u/m2 of collector area/^ 

(10 to 15 ~tu/ft~-'~) which translates to about 60 to 90 liters of water per 

square meter of collector area (1.2 to 1.8 gal/f t2). ' Because IPH applications 

can have such different load profiles, however, optimum storage size can be 

significantly different from these figures; it can be determined using the 

procedure given in Sec. 6.0. 

7.6.3 Storaere Tank Insulation 

Storage heat loss can cause a significant drop in system performance. There 

are various standards for tank insulation; for example, the SMACNA standard 

for solar heating systems specifies that insulation must be of sufficient 

thickness to keep heat loss less than 2% in 12 h. This means 2% of storage - capacity, defined as,McpATuseful, where ATuseful is the temperature range over 

which storage is operated. The maximum temperature to determine a AT can be 

somewhat arbitrary, yet it affects the result greatly. In general, the U 

value 'for storage required to meet such a standard can be written as: 
where 

f = fraction of stored heat loss specified by the standard (0.02 for 

SWCNA) 

-t-= specified time period (12 h for SMACNA) 

M = storage mass 

c = specific heat of storage medium P 

Tmax, Tmin = maximum and minimum operating temperatures of storage 

Tavg = average storage temperature 

Tamb = ambient temperature. 

An alternative to the SMACNA standard is to calculate the most economic insulation thickness for a storage vessel, based on a comparison of the cost of 

collecting an additional amount of energy versus the cost of insulating the 

storage tank to save an additional amount of energy (Cole et al. 1980). If 

the cost of collecting additional energy is higher than the cost of saving it, 

the system needs insulation; but if the cost of collecting energy is less than 

the cost of saving it, the system has too much insulation. The economic 

thickness is the thickness that makes the cost of saving additional energy 

equal to the cost of collecting it. In many cases, the resulting insulation 

thickness will be close to that required by the SMACNA standard. 

The incremental cost of collected energy is calculated by adding a small 

amount of collector area and determining the increment of additional energy 

collected over a year AQc and the additional cost associated with the additional collector area ACc. Using an economic factor Ec to convert initial 

costs to an annual equivalent cost, the ratio EcACc/A~c is the incremental 

cost of collecting energy, in $/J ($/B~u). This quantity is compared with the 

cost of saving energy to determine the optimum insulation thickness. If we 

assume the same economic basis for calculating the cost of saving energy, the 

economic factor can be ignored and the costs can be compared on an initial 

cost basis. 

Next, the energy lost and the cost of insulation are calculated as a function 

of the insulation thickness. For a cylindrical tank surface, the following 

procedure is used. The insulation is assumed to have three parts: an inside 2 surface thermal resistance Ri (in m K/w), a layer of insulation with thickness 

s (in m) to be determined, and an outside surface thermal resistance Ro (in 

m2~/w). The annual heat loss from such a surface is 
where 

L = height (length) of storage tank (m) 

- 

T . -.. = average temperature (OC) of the storage during the time it is hot 

(a good estimate is the average of the peak storage temperature 

and the minimum temperature during operation) 

- 

Ta = average ambient temperature (OC) , also averaged during the time 

the storage. tank is used (the temperature at the tank location, 

either indoors or outdoors) 

D = diameter of the tank (m) 

2 \ 

Ri = inside surface thermal resistance (m K/w), calculated similarly 

to R in Eq. 7-1 

r* = them1 resistance of the insulating material per unit thickness 

(~K/w), adjusted for parallel heat loss (without parallel heat 

loss, it is the inverse of the thermal conductivity of the 

material) 

2 Ro = outside surface thermal resistance (m K/w), also calculated like 

R in Eq. 7-1, 

Differentiating with respect to the insulation thickness, we have 

We assume that the cost of the insulation consists of a fixed cost CIS a cost 

proportional to the outside surface area C2, and a cost proportional to the 

insulation volume C3, as follows: 

The derivative of the.insulation cost with respect to insulation thickness is 

Combining Eqs. 7-63 and 7-65 yields the incremental cost of saving energy: 
Finally, the two incremental costs are set equal to one another. Since the 

incremental cost of saving energy E=~C~/~Q~ must equal the incremental cost of 

collecting energy ECACc/A~, at the optimum insulation thickness, then, assuming equal economic factors (EI = Ec), we obtain 

* AC 

r Dy Iln y 

(7-67) 

where y = 1 + ~s/D. 

We can solve for y in terms of C2, C3., D, q, Ro, and r* .using' Eq. 7-67 either 

by trial and error or by more sophisticated methods such as the Newton-Raphson 

method. Once y is obtained, the optimum thickness of insulation is simply 

If the surface to be insulated is flat, such as the top or bottom of a tank, 

or the radius of curvature is large compared with the insulation thickness, a 

similar analysis yields a closed-form solution for the optimum insulation 

thickness 

where R* is the thermal resistance of the surface before the insulation is 

applied, adjusted for parallel heat loss (m2w/~). In insulating a storage 

tank, it is important to pay attention to the top and bottom (particularly the 

latter, because of conduction paths), and not just the sides. 

7.6.4 Storage Location 

7.6.4.1 Interior Storage 

When space is available inside a building, it is valuable for storage because 

the system can then use shorter pipe runs and waterproofing is not needed. 

Any losses from storage can add to a building's cooling load, although mechanical equipment rooms are often not air conditioned. There must be some provision for containing or draining leaks as well as access to all parts of the 

tank. Mounting pads should be designed to isolate the tank thermally from the 

floor. 
7.6.4.2 Exterior Storage 

If interior 

insulation 

insulation 

space is scarce, exterior storage problems must be addressed. The 

must be waterproof, which usually necessitates a closed-cell foam 

if temperatures permit. Because of the lower ambient temperatures 

and wind effects, more insulation is needed for .an outside tank than an 

interior one. All penetrations fox valves, pipes, supports, and instrumentation must be waterproofed. In freezing climates, a drainable sight gauge is 

r ecomended. 

For aesthetic reasons, or to conserve ground area, storage tanks can be 

located underground. Of primary concern in such an application is the height 

of the local water table. If the bottom of the tank is below the water table, 

a holddown structure or added dead weight is needed to prevent flotation of 

the tank when it is empty. A commonly used support structure consists of a 

concrete footing with tank saddles to supportthe weight of the tank and steel 

straps to hold it down. High-density insulation must be used to withstand 

both upward and downward loads. &cause of the serious problems a high water 

table can cause, most experienced solar system designers avoid using underground tanks under these circumstances. A current method of installing an 

underground tank involves prefoaming the tank with urethane, wrapping it with 

nylon fabric and mastic material, and setting it in a sand bed. 

Alexander, Em L.; Kutscher, C. Fa 1978 (Aug.). Thermal Storage Subsystem 

Parameter Study. Solar Ten Megawatt - Project Off ice Report No. 40X5131056-R. 

Canoga Park, CA: Rockwell ~nternationai Inc. Energy systems Group. 

Allen, David, 3. 1981. Personal communication. 

Barley, C. D.; Wynn, C. B. 1978. "Optimal Sizing of Solar Collectors by the 

Method of Relative Areas." Solar Energy. Vol. 21 (No. 4); pp. 279-89- 

Barnhart, 3. S. 1981. "Energy Transport System Optimization for Distributed 

Networks of Solar Collectors." ASME Paper No. 81-SOL-1. Presented at the 

Energy Sources Technology Conference and Exhibition. 18-22 Jan. 1981, 

Houston, TX. 

Baumann, He Dm 1979 (May). "A.Case for Butterfly Valves in Throttling Applications ." Instruments and Control Systems. 

Caputo, R. 1975. An Initial Study of Solar Power Plants Using a Distributed 

~etwork of Point Focusing; - Collectors. JPL 900-724. Pasadena. CA: Jet 

Propulsion Laboratory. 

Cole, R. L.; Nield, K. J.; Rohde, R. R.; ~olosewicz, R. M. 1980. Design and 

Installation Manual for Thermal Energy Storage. 2nd Edition. ANL-79-15. 

Argonne, IL: Argonne National Laboratory. 

dewinter, Fa . 1975. "Heat Exchanger Penalties in Double-Loop Solar Water 

Heating Systems." Solar Energy. Vol. 17; pp. 335-337. 
TR- 1 3 56 sm + 

Dittus, F. W.; Boelter, M. K. 1930. University of Calif. (Berkeley) Pub. 

Eng. Vol. 2; p. 443. 

Farrington, R. B.; Murphy, L. M.; Noreen, D. L. 1980 (April). A Comparison 

of Six Generic Solar Domestic Hot Water Systems. SERI/TR-351-413. 

Golden, COf Solar Energy Research Institute. 

Fried, J. R. 1973 (28 May). "Heat Transfer Agents for High Temperature Systems." Chemical Engineering. 

HUD International Minimum Property Standards Supplement, Solar Heating and 

Domestic Hot Water Systems. 1977 Edition. Washington, DC: U.S. Department of Housing and Urban Development. 

Iannucci, J. J. 1980 (June). "Thermal Energy Centralization Network: 

Design, Cost, and Performance for Disk, Trough, and Central Receiver Systems ." Paper presented at International Solar Energy Society Meeting,. 

Phoenix, AZ. 

Johnson, J. D. 1981 (10 Aug.) . "Variable-Speed Drives Can Cut. Pumping 

Costs . " Chemical ~n~ineerin~. 

Jones, G. F.; Lior, N. 1979. "Optimal Insulation of Solar Heating System 

Pipes and Tanks ." Energy. Vol. 4 TNO. 4); pp. 593-621., -. -- 

Kreith, F. 1973. Principles of Heat Transfer. Third Edition. New York: 

Harper and Row Publishers, Inc. 

Lauer, B. E. 1953. How to .Evaluate Film Coefficients for Heat-Transfer Calculations. A technical manual reprinted from the Oil and Gas Journal. 

Tulsa, OK: Petroleum Publishing Co. 

Lobanoff, V. 1979 (June). "Specific Speed is a Useful Index for Pump Design 

and Selection." Power. Vol. 123 (No. 6);,pp. 70-71. 

Lunde, P. J. 1980. Solar Thermal ~ngineerin~: Space Heating and Hot Water 

Systems. New York: John Wiley and Sons. 

McAdams, W. H. 1954. Heat Transmission. Third Edition. New York: McGrawHill. 

Morton, R. E. 1980 (Sept.). "Design of Collector Subsystem Piping Layouts." 

Line-Focus Solar Thermal Energy Technology Development Seminar. Albuquerque, NM: Sandia National Laboratories. 

Neerken, R. F. 1978 (3 Apr.). "Selecting the Right Pump." Chemical 

Engineering. pp. 87-98. (See also, "How to Select and Apply PositiveDisplacement Rotary Pumps."). 

Parts, L.; Miller, D. R.; Leffingwell, J. W.; Thompson, Q. E. 1980 (Sept.). 

Superior Heat Transfer Fluids for Solar Heating and Cooling Applications. 

AL0/45356-2. Monsanto Research Corp. 
sin :al TR-1356 

Perry, R. H.; Chilton, C. H. 1973. Chemical Engineers Handbook 5th Edition. 

New York:- McGraw-Hill Book Co. 

Powell, J. C.; et al. 1974. Dynamic Conversion of Solar-Generated Heat to 

Electricity. NASA CR-134724, Washington, DC : National Aeronautics and . -: Space Administration. 

Raju, K. S.M.; Chand, J. 1980 (11Aug.). "Consider the Plate Heat 

Exchanger." Chemical Engineering* pp. 133-144. 

Seider, E. N.; Tate, C. Em 1936. "Heat Transfer and Pressure Drop of Liquids 

in Tubes." Ind. Eng. Chem. Vol. 28; pa 1429. 

Shames, I. H. 1962. Mechanics of Fluids. New York: McGraw-Hill. 

Thornton, J. ; Herlevich, A. ; Hooker, D. ; Kriz, T. Forthcoming. Comparative - 

Evaluation of Solar Thermal Systems for Thermal Applications. 

SERI/TR-253-1706. Golden, CO: Solar Energy Research Institute. 

Williams, 0. M. 1978. "Thermal Chemical Energy Transport Costs for a Distributed Solar Power Plant." Solar Energy. Vol. 20, pp. 333-342. 

SECTION 8.0 

As in nonsolar process applications, controls and instrumentation play an 

important role in solar IPH systems. In this section, we describe the design 

aspects of controls and instrumentation in solar IPH systems. In Sec. 8.1, 

control fundamentals needed to design a solar control system are explained. 

Subsections address such items as controllers, control loops, measurement 

dynamics, noise, and control valve characteristics. In Sec. 8.2, the special 

control problems of solar energy systems are addressed, beginning with normal 

operating modes, and including start-up/shutdown, freezing/stagnation, emergency conditions, operator training, and checkout. Instrumentation is covered 

in Sec. 8.3, particularly including irradiation, temperature, flow, pressure, 

and level measurements. 

In this section, it is assumed that the designer already has some knowledge of 

process control, although several excellent textbooks are referred to. It is 

also assumed that the designer is familiar with the major elements of a closed 

control loop: the process, feedback (measuring) element, controller, control 

variable, feedback variable, manipulated variable, reference variable (set 

point), and uncontrolled variable (disturbance) (Grader 1970). 

8.1.1 Controllers 

The controller is the part of the control loop that implements corrective 

action as the process variable deviates from a desired set point. The control 

modes that characterize the corrective action include on-of f , proportional, 

integral (reset), and derivative (rate). There are no adjustments to "on-off" 

control (unless a deadband is included), and the controller output changes 

full-scale as the process variable crosses the set point. The corrective 

action implemented with proportional control is normally a linear function of 

the error signal (process variable minus set point). The proportionality constant (i-e., the gain) is equal to the percent controller output change 

divided by the percent error change. 

Integral control (reset) is usually combined with proportional control. It 

forces the controller output to change in accordance with the time integral 

function of the error signal and can reduce steady-state error. It also 

repeats initial proportional output response as long as the error signal persists. Derivative control is combined with proportional control to change the 

controller output in accordance with the rate of change of error signal. This 

action ceases when the error signal stops changing. 
Common Control Loops 

The common types of control loops are flow, pressure, level, and temperature. 

Some rules of thumb are as follows. 

Flow loops: Proportional plus reset controllers are used almost exclusively. The process typically is very fast and noisy, and the flow measurement is usually nonlinear (square). The controller is characterized by low 

gain and fast reset. 

Pressme loops: For a liquid, the process is fast and noisy with most of the 

lags in the control system, and the measurement is nonlinear (square). Linear 

valves and proportional plus reset controllers with low gain and fast reset 

are used. For a gas, the process is simple: linear with no dead time and no 

noise. Proportional controllers with high gain suffice, and valve characteristics are not critical. For vapor pressure control, equal percentage 

valves and proportional-reset-derivative controllers are employed. This process is slow compared with other pressure processes. Controller settings 

include moderate gain, a reset rate of 0.5 repeats per minute or less, and a 

derivative time of 0.5 minute or more. 

Level loops: High-gain or proportional-plus-reset controllers are used for 

precise control, low gain proportional-plus-reset controllers for averaging 

control. Valve characteristics are important. 

T-erature loops: Temperature control loops can vary greatly in complexity, 

because there really is no such thing as a typical temperature application. 

Almost all the temperature control problems in solar applications are heat 

transfer problems characterized by long time constants and slow reaction 

rates. Distance-velocity lag (also known as dead time) is common. The measurement lag can pose a serious problem, especially if the thermal system is 

protected with a well. The measurement time constant depends on the mass and 

surface area of the bulb (or the well), the measured fluid, and its velocity 

past the bulb. Special care should be taken in locating the bulb to maximize 

heat transfer; usually, the bulb should be placed at bends in the flow path. 

Nonlinearities also cause complications in the temperature loops. Heat transfer processes have parameters that vary with flow, so that time constants and 

distance-velocity lag vary with load or operating point. Distance-velocity 

lags are not as evident as in other systems and are often overlooked in analysis. Imperfect mixing is a good example of hidden dead time. 

Processes dominated by one large capacity, e.g., storage tanks in air heating 

systems, can be controlled with on-off controllers. Some cycling results, but 

only about 1% of span. Proportional plus reset control is used in smaller 

capacity systems where load changes are large and where distance-velocity and 

measurement lags are important. Most shell-and-tube heat exchangers fall into 

this category. Derivative action becomes helpful, provided the process is 

dominated by linear lags (e.g., a batch reactor). 
sin :el TR-1356 

Controlling temperature by mixing hot and cold streams is more of a blending 

problem than a heat exchange problem. Good mixing and fast temperature measurement are the keys to simplifying the control job. Proportional-plus-reset 

controllers should be used. 

In general, the following guidelines can be used in selecting controllers: 

Use proportional control where 

the cyc.1ing action, due to on-off control, is undesirable; 

a set-point changes are small or infrequent; and 

a the steady-state deviation between the set point and the process variable 

(Lee, the offset) can be tolerated. 

Add integral control where 

the offset must be reduced or eliminated, and 

the set point changes are frequent. , 

Do not add integral control when 

start-up overshoot must be eliminated, and 

the process can be controlled with high-gain proportional control. 

Add derivative action to proportional control when 

the distance-velocity lag (e.g., dead time in the pipes) is negligible 

compared with either of at least two linear lags (e.g., storage tanks) in 

the process loop. 

Do not add derivative action if 

the distance-velocity lag is a major time lag in the process; and 

noise is present--unless the noise/signal ratio is low. Do not use on 

flow control. 

The time lag associated with a typical control loop can be linked to three 

distinct causes: the lag inherent in the process, the response lag of the 

detecting element, and the signal transmission lag- To minimize lag effects, 

detection response should be considered first and its lag effect reduced, if 

possible. These measurement lags can cause serious errors as the process is 

changing; i.e., the slower the response, the more inaccurate the measurement. 
A classic example of detecting element lag is a temperature measurement using 

a filled system. The lag depends on the thermal capacity of the element and 

the surrounding fluid. Of the common methods for detecting temperature 

changes, the filled system has the slowest response speed. To ensure quicker 

responses, the following precautions should be taken: . - 

The element should fit snugly inside the protecting well. 

The protecting well surface should always be clean. 

A high velocity of the fluids to be nneasured must be maintained: 0.3 m/s 

(1 ft/s) or more for liquids and 3 m/s (10 ft/s) minimum for gases. 

Protecting wells of minimum thicknesses consistent with plant specifications should be selected (pressure requirements must also be met). 

Protecting wells should be immersed deeply into lines and vessels. 

In general, if the dynamics of the temperature measuring system are fast, compared with the major secondary dynamic elements in the control loop, they can 

be ignored. Measurement dynamics cannot be ignored, however, if the temperature is controlled by mixing hot and cold streams. They can usually be 

ignored in slow-responding tank heating systems, but they are usually important in small heat exchangers. Finally, relative to temperature measurement, 

flow, pressure, and level elements respond instantaneously to process changes. 

8.1.4 Noise 

Noise comprises random, unwanted signals that can occur in many parts of the 

control loop, usually those associated with measurement. Examples of solar 

system noise are turbulence in differential-measured flow signals, random pulsations in pressure signals, and surface waves in level signals. Since 

derivative action amplifies high-frequency signals, it cannot be used if noise 

is present. Moreover, high controller gain can be a problem; hence, low-gain, 

reset controllers are generally used. Flow contro'l is dominated by noise that 

is difficult to filter out because the process itself is fast. 

In solid-state control systems, grounding practices have a significant ef fecr 

on immunity to noise. Each ground should be connected to its respective 

reference point by no more than one wire (single-point grounding). Under no 

circumstances should two or more systems share a common single-ground wire, 

either equipment ground or control common. In general, noise entering the 

control system must be kept as low as possible by employing appropriate 

installation practices, especially when the anticipated noise signal is quite 

similar to the desired control input signal. 

8-1.5 Valves 

Most control valves are marked by one of three flow characteristics: quickopening, linear, or equal percentage. These different characteristics provide 

control-loop stability over the expected range of.operating conditions. 
The quick opening characteristic provides a maximum change in flow rate at low 

stem travel while maintaining a linear relationship through most of the stem 

travel. Usually, about 90% of valve capacity is achfeved with 30% valve 

opening. This valve is used primarily for on-off service or in systems with 

constant pxessure drops where linear characteristics are needed. - -: 

A valve with a linear characteristic produces flow directly proportional to 

the valve lift; e.g., 50% of valve lift corresponds to 50% of maximum flowThis characteristic is commonly specified for liquid level control and for 

control applications requiring constant gain. 

An equal-percentage flow characteristic is one in which equal increments of 

stem travel produce equal percentage changes in existing flow. For example, 

when the flow is small, the change in flow is small; when the flow is large, 

the change in flow is large. The change is proportional to the quantity 

flowing before the change. Equal-percentage valves are often used when the 

pressure drop available over the control valve is not constant. 

From a control point of view, the following conditions apply: 

a For simple processes, valve characteristics are relatively unimportant. 

The less expensive quick-opening valve can be considered appropriate for 

on-off applications. 

a If the required flow range is 3:l or less, there is little difference 

between linear and equal-percentage valves. If the flow range is 8: 1 or 

more, linear valves are preferable. 

If the pressure drop across the valve varies more than 2:l or 3:l with 

valve opening, equal percentage is probably the better choice, even if 

linear is the desired theoretical characteristic. 

a If the valve is oversized, the equal-percentage characteristic allows 

somewhat better control because an oversized linear valve requires a 

lower controller gain at the operating point. 

a For flow control, where the primary element is an orifice plate or 

another differential pressure device, use a linear valve if the pressure 

drop across the valve decreases as the valve opens. The installed characteristic will compensate for measurement nonlinearity. 

Because these characteristics assume the pressure drop across the valve to be 

constant, the installed characteristic is usually quite different from the 

theoretical one. Equal-percentage valves tend to become linear, linear valves 

tend toward quick-opening , and quick-opening valves become useless except for 

on-off service. The larger the pressure drop across the valve, the better the 

flow -control, and the control system will be able to handle large disturbances 

and upsets. From a heat exchanger and pump design standpoint, however, the 

valve pressure drop should be kept as small as possible. Thus, an engineering 

compromise must be made between controllability and power requirements. A 

good rule of thumb is to design the system so that the control valve in its 

half-open position takes about 25% of the total system pressure drop at design 

flow rate. The control valve range must also be considered in designing a 

control system- Most control valves work effectively. between 10% and 90% of 

the valve characteristic curve. At low flows, the control valve may be almost 

on its seat, and poor flow regulation can be the result. 
sin + TR-1356 

Other control elements include dampers, louvers, and variable-speed pumps. 

Dampers and louvers are used to throttle gas flows where control quality is 

not critical and pressures are low. Leakage rates can be high, but they may 

be reduced to very low levels (less than 0.1%) by using soft edging on the 

damper blades. Pumps are often used for flow control by adjusting the stroke 

length or. by -varying the speed of a motor-driven shaft . Reciprocating pumps, 

which displace a known fixed value of fluid with each stroke, and diaphragm 

pumps, which have a flexible diaphragm, are commonly used. The latter cost 

less, but are limited to lower operating pressures because of their material 

strength limitations. 

8-1.6 Miscellaneous Considerations 

The control system will respond to disturbances according to their location in the control loop. Response is affected by the size of the time 

constants and gain elements in the loop. 

A good first guess of the time constant is the ratio of the volume to 

throughput. 

An index of controllability is the ratio of controller gain to the period 

of oscillation; the higher the gain and shorter the period, the easier 

the control job. 

The higher the controller gain, the less the offset (difference between 

the variable and set-point) following a load change. If controller gain 

is high, reset is unnecessary. 

8.1.7 Multivariable Control Iaops 

8.1.7.1 Cascade 

A cascade loop has two feedback controllers; the output signal of the master 

controller goes to the set point of the slave controller. The output of the 

slave controller goes to the final control element. The major time constant 

must not be in the slave loop in order to maintain control. Cascade control 

is most useful in temperature control systems and is not normally applied in 

fast control loops such as flow and pressure. 

8.1.7.2 Feed-Forward 

The basic notion of feed-forward control is to detect disturbances as they 

enter the process and make adjustments in manipulative variables so that 

output variables are held constant. The control does not wait until the disturbance has worked its way through the process to produce an error signal. 

If a disturbance can be detected as it enters the process, the feed-forward 

control takes immediate action to compensate for its effect on the process. 
san ce TR-1356 

The temperature-flow cascade loop just described can handle the collector outlet thermal lag problem. However, oscillation and overshoot of temperature 

responses have been found in a system where the controlling temperature sensor 

is not located properly. In such a case, the midfield temperature can be used 

together with the outlet temperature for temperature control. A simple way to 

implement'. this multiple-temperature approach is to feed-f onrard an average 

temperature obtainable from the sumation of all applicable temperatures so as 

to damp out temperature variations during transient periods and still properly 

represent the collector temperature under steady operating conditions. 

8-1-7-3 Split-Bange Control 

Split-range control indicates two control valves operated by the same controller. For example, nitrogen make-up normally maintains the correct vessel 

pressure. However, under certain conditions, the vessel pressure may become 

too high, and the excess must be vented off. In these conditions, one valve 

is used for venting and one used for pressurizing. Usually, a small deadband 

is provided between valve operations ; for example, the nitrogen make-up valve 

closes from 0% to SOX of signal range and the vent valve opens from 55% to 

100% of signal range. In some cases, no deadband is required; in others, 

overlap is necessary. 

In IPH solar systems, it may be necessary to take more drastic control action 

on a primary control variable to maintain safe operation or protect process 

equipment. The primary variable maintains control as long as a second variable does not exceed a safe limit, at which point the second variable assumes 

control. For example, a mid-row temperature variable can be used to override 

an outlet-row temperature when overtemperature conditions are met 

(Schindwolf 1981). 

A sequencing computer, such as a programmable logic controller (PLC), is very 

useful in a solar IPH system. The PLC assists in start-up and shutdown, and ' 

performs alarm, relay, and motor control functions. This system costs approximately $25,000 (1981 dollars). Its advantages include 

Flexibility: logic can be changed in most cases without hardware modificat ion. 

Reliability: it uses solid-state electronics. 

Reusable options: the controller can be reused no matter what logic 

changes are implemented. 

Maintenance reduction: indicator lights can assist in diagnostics and 

troubleshooting. 

Power savings: it uses less power than relay panels. 
It may also be wise to consider continuous control capability in addition to 

the sequencing logic. Although digital control may seem inappropriate initially, it allows the flexibility to implement other control logic for a low 

incremental cost as more process experience is gained. Information on equipment, materials, and services for process control can be found in the Chemical 

~ngineering Deskbook (1979). 

8-2 CO-OL DESIGN 

The regulatory ability required of a process control system varies significantly for each of the three IPH system applications (steam, hot water, hot 

air); therefore, the designer must understand the dynamics of the process 

before making a decision about the degree of control required. A total systems approach is the key to the success of the control system. In general, 

the energy collection loop must be coordinated with the energy utilization 

loop, yet operate independently. In addition, the control system must protect 

the process in all emergency conditions. 

There are many possible process configurations for solar industrial applications. Here three basic control systems are discussed: constant flow rate, 

constant flow rate with a three-way diverting valve, and variable flow rate 

generated by a throttling valve or a variable-speed pump. Also, control 

designs (Su and Castle 1979) are suggested that take into account the process 

dead time and insolation characteristics of solar IPH applications. 

8-2.1 Normal Operating Modes 

In the normal production mode, the control system.must maintain a balance 

between energy collection, storage, and usage. For example, the energy flow 

path could be one in which the energy collected is consumed only by the load, 

the energy is accumulated only in the storage device, or the energy is fed to 

the load and storage simultaneously. When the collector field is incapable of 

providing the energy delivery rate required by the load, alternative operations can be considered, such as activating the auxiliary heat source or 

thermal storage or even using the system 'to supply lower-temperature energy 

needs. 

The control system is relatively simple for a constant flow-rate process (see 

Fig. 8-1). The designer does not have to be concerned with keeping the collector field outlet temperature constant, and the industrial process can 

handle any heat surges or slumps that occur. An auxiliary heat source can be 

used to make up any heat not produced in the collectors; however, this may 

complicate the controls because of heat source interactions. Two different 

pumps can be used: one for low flows and cold fluids at start-up and one for 

higher flows and temperatures at normal conditions. The instrumentation is 

standard for this concept and includes flow switches, level switches, pressure 

gauges, and thermocouples. The process information can be forwarded to a PLC 

to relate alarm and status conditions and can be forwarded to a data acquisition computer. The information is not, however, used in any continuous control capacity. 
Figure 8-1. Constant Flov-Rate Control 

The designer may enhance control capabilities by using a three-way diverting 

. valve (or preferably 2 two-way valves) in a constant flow system (see 

Fig. 8-2). This valve can divert flow as the collector outlet temperature' 

swings. The valve may be capable of throttling flow and providing more consistent energy flow to the industrial end user than the system shown in 

Fig. 8-1. The controls are more complicated because a sensor signal must be 

transmitted to the valve. Such a system controls the outlet temperature by 

adjusting the field inlet temperature. However, this type of control is 

characterized by large time delays and provides poor control *over the outlet 

temperature. 

The next step in improving system performance involves implementing variable 

flow control. This control is not necessary unless the industrial user 

requires a constant temperature input. In that case, the flow must vary as 

insolation increases or decreases to maintain a constant field outlet temperature (Fig. 8-3). 

Three optfons are available in constructing a variable flow control system: 

use a throttling valve with a constant speed pump, 

use a variable speed pump, or 

use a throttling valve with a two-speed pump. 

To determine which method is best for a given application, the value of the 

energy delivered by the solar energy system and required by the flow controller and the pump motor, along with the cost of each control system, should be 

considered. The first option listed above is the more traditional method. 

According to Baumann (1979, 1981), this method has an economic advantage over 

a variable-speed pump for a process where operating conditions are maintained 

between 80% and 100% of design capacity. On the other hand, the second option 

is preferable when static head is not significant and when the average quantity of liquid being pumped is less than two-thirds of the maximum design flow 

rate. Unfortunately, typical solar IPH systems do not fit either of these 

models. Systems do not always operate near design conditions. Frequent 

start-ups and the wide-ranging viscosity of heat transfer fluids require the 

characteristics of both the first and second option. Therefore, the third 

option is a good compromise--using a throttling valve with a two-speed centrifugal pump. (See Sec. 8.1.5 for more on pumps and valves .) 

The final control element, whether it is a valve or a pump, is manipulated by 

a signal from an analog controller or a microcomputer. The analog controller 

is more commonly used, but the microcomputer has advantages in flexibility 

and, in some cases, price. For example, if a designer first decides on proportional-only control, an analog controller might be used- If a vapor pressure should be needed later for a set point and this pressure were to be calculated from a temperature, a microcomputer would be needed. In retrospect, 

the computer would have been the better purchase, because it can handle both 

cases. 

Tuning constants in an analog controller or a microcomputer algorithm are crucial to the control of flow in the solar system. Figures 8-4, 8-5, 8-6, and 

8-7 have been prepared to help the designer specify controller tuning constants necessary for . stable operation of the system. The constants selected 

areLa function of sensor location, process dead time, instrument spans, valve 

characteristics, and type of collector. The tools were generated by a frequency response analysis by Wright (1980) and were tested by means of a realtime dynamic computer simulation. 

To use these tools, follow this procedure: 

Pick transmitter spans for temperature and flow. 

Pick the temperature set point. 

Calculate the AT across the solar field at steady-state conditions. 

Calculate the AP across the field (APp) at steady-state conditions. 

Calculate the AP across the valve (AP,).at steady-state conditions. 

Calculate the steady-state flow rate Mss . a Specify p (dimensionless)., which is the ratio of the thermal mass of a 

unit length of fluid (p c A)p to the thermal mass of a unit length of the 

fluid - and receiver tube 8 C~A)~: 

where 

p = density 

c = heat capacity P 

A = cross-sectional area. 



X, Equivalent Lag 

Figure 8-7. m~ionless Integral The as a Function of Equivalenf Lag and 

Chpawftamce Batio (p) for Proportional-httqgral Cantrol 

a Specify X (dimensionless) for a single row of collectors. X is the dead 

time associated with the piping from the end of the collector row to the 

sensor location divided by the. collector row residence time. 

An equivalent lag is an arithmetic average for the X associated with each 

row in the collector field. For example, if we have three rows and only 

one sensor that is 12.2 m (40 ft) from the end of the first row, 6.1 m 

(20 ft) from the second row, and 3.05 m (10 ft) from the third row, then 

40A S1 =- 20A , S2=- 10A , and Sg =-, 

Qv, 1 Qv, 2 Qv.3 

where Q,,, Qv,2, and Qv,3 are the steady-state volumetric flow rates in 

each row, and A is the cross-sectional area of the pipe. Now, the lag 

for each row (assuming each row is L meters long) is 

Xl = s1 , x2 = s2 , and X3 = s3 

(L)A/QV, 1 (L)A/Qv, 2 (L)A/Qv, 3 ' 

and the equivalent lag is 

a Determine whether the system has linear or equal-percentage valve characteristics by examining the ratio of APp/APv. If the ratio is small 

(less than l), equal percentage is appropriate. If the ratio is greater 

than 1, the system has a linear characteristic. 
smn a(~ TR-1356 

If the system has an equal-percentage characteristic, the suggested controller tuning constants will be stable for insolation turndown ratios of 

5:l or more- i-e., if the tuning constants are picked at a design poin 2 of 1000 W/m , they will be stable even if the insolation dips to 200 W/m 5 

or lower. 

If the system has a linear characteristic, Fig. 8-4 must be used. After 

defining P and X, read the turndown ratio from the graph. The design 

insolation should be the minimum operating insolation multiplied by the 

turndown ratio. If a low turndown ratio is encountered, a smaller valve 

could be installed to increase APV and give the system more of an equalpercentage characteristic. This enhances the controllability of the 

field, but it also increases pumping requirements. 

Use Fig. 8-5 to pick a proportional-only constant &. If proportional 

integral control is desirsd, use Figs. 8-6 and 8-7 to pick a proportional (Kc) and integral (T~) constant. (Note that these constants are 

dimensionless numbers.) 

Calculate the fractional change for a lo change in AT across the field, 

TF = l/AT across field. 

Calculate the corresponding change in the signal to the controller [use 

103 to 21 kPa (15 to 3 psi) span for pneumatic controllers; use 4 to 

20 mA for electronic controllers]: 

PT = (103 kPa - 21 kPa) (lo change) 

temperature transmitter span 

8 Calculate the corresponding change in flow rate per lo change in temperature: 

Calculate the change in controller signal for the change in flow rate: 

for linear characteristics, 

PQ = (20mA-4mA)(FF) . flow transmitter span ' 

for equal percentage characteristics, 

where R is the valve characteristic (typically 20-50). 
Calculate the gain 

100 and proportional band (typically OX-500%) = - K 

Calculate the integral time 

where T~ is the process residence time* The reset rate (typically 0 to 5 

repeats per minute) = l/rI. 

&-leg* Following the procedure we outlined: 

Temperature transmitter span is -18' to 538'~ (0' to 1000~~). 

Flow transmitter span is 0 to 10 gpm (6.31 x m3/s) . Temperature setpoint is 316. l0c (601~~). 

AT across the field at steady-state conditions is 160'~. 

qe ratio APp/AP, > 1. The steady-state flow rate is 8.1 gpm (5.1 x .lom4 

m /s). 

a Since each collector row is 97.5 m (320 ft) long, and the temperature 

sensor is 6.1 m (20 ft) from the end of each row, then 

a Because AP~/AP, > 1, the system has a linear characteristic. 

a For proportional-only control, use Fig. 8-5: 

for proportional-integral control, use Figs. 8-6 and 8-7: 

and 

- 

TI = 1.7 . a TF = 1/160° = 0.00625. 

a PT = (12)/(1000-0) = 0.012. 

a For proportional-only control : 

*Note: This realistic example is taken from Schindwolf (1981). 

223 
sin TR-1356 

For proportional-integral control: 

For equal-percentage characteristics, 

Proportional: PQ = (12)(0-147) = 0.0557 (8.1 (In 50) 

proportional-integral: PQ = (12)(0-1) = 0.038 . (8.1) (In 50) 

Proportional : K = 000557 = 4-64 . 0.012 

~d = (1-in. pipe, 320-ft row, 8.1 gpm) , 

- - (320 ft)(0.006 ft2) - min 

60 s = 1.6 min ; 

0.02 ft31s 

TI = (1.7)(1.6) = 2.7 min . 

Reset rate - --- I - 0.37 repeatslmin . 2.7 

In this case, the large temperature transmitter span is producing high 

control loop gain. An improvement may be made by reducing the span from 

-18O to 538'~ (0' to 1000~~) to 204' to 482'~ (400' to 900 F). 

To test the tuning constants given above, a dynamic simulation of a solar IPH 

system was conducted. Again, for comparison and verification purposes, the 

model was made similar to the work of Schindwolf (1981). The numerical solution and process control analysis were done via the Advanced Computer Simulation Language (ACSL). ACSL is a control-oriented language useful in dynamic 

analysis. 

Figures 8-8 and 8-9 show the solar system response to proportional and proportional-integral control for an inlet water temperature of 226.7'~ (440°F), an 

outlet temperature setpoint of 316'~ (601°~), and an insolation which is 


changed from 0 to 600 w/m2. The design insolatiori was 800 w/m2. Note that 

the addition of integral control eliminates the offset between the final temperature and the setpoint. Depending on the requirements of the system (i.e., 

off set and overshoot), ' designers may choose proportional-integral control 

rather than proportional-only control. . - 

In general 

system. 

incorrect 

designer a 

, these tools should be helpful during the design phase of the solar 

They will handle problems ranging from poor sensor location to 

transmitter span specifications. They are intended to give the 

feel for control system performance before the system is built. 

The best way to manage the frequent start-ups and shutdowns of a solar IPH 

system is with a microcomputer or a PLC. These tools can implement relay 

logic and time delays that can stow tracking collectors and start or stop flow 

consistently and sequentially. 

The start-up mode enables us to start process heat generation rapidly at sunrise. When sufficient light intensity is sensed by the trackers (if any) or 

when a sufficient collector-storage AT is reached, the circulating pump is 

turned on. The control logic may include a start-up for low flows or viscous 

heat transfer oils. 

If the solar system tracks, the start-up controls and safety logic include 

. moving the collectors into a sun-tracking position and maintaining flow at a 

minimum. A well-designed tracking system is critical in optimizing energy 

production as well as in providing protection against overpressure, overtemperature, and other emergency modes. The system should be able to (1) accept 

demand flow signals; (2) start the flow through the collectors; and (3) sense 

fluid temperature, AC power, solar intensity, and wind speed. Typical features of a shadow-band collector tracking system (the most popular tracker) 

are as follows: 

Each collector array is equipped with a shadow-band device, control circuit, and drive motor.' With centralized control, a master controller is 

used to control all collector arrays. 

The system is capable of tracking in both rotational directions. Twospeed or multiple-speed tracking is desirable and allows the collectors 

to quickly reach a stow condition. 

A digital shaft encoder is used to measure the angular position of the 

collector shaft. Limit switches mounted on the collectors are used for 

fail-safe end travel to prevent mechanical damage. 

a A standby emergency power source is needed to defocus and stow collectors 

to prevent equipment damage from overheating in the event of power 

failure. 

Figure 8-10 is a flow chart of a typical collector control loop. As an example, the master controller uses the system-permissive signal and low-flow 

detection before sending a start-permissive signal to the individual collector 

array controllers. The individual array controller is responsible for detecting excessive temperatures and for determining when there is sufficient insolation for an operation. 

Computer-command psi tion tracking is another approach to collector focusing. 

It can be' the- primary control method or a backup. . With this system, a microcomputer implements a tracking algorithm that calculates the position of the 

sun and commands the motor to drive the collector trough to the correct angle. 

Normal shutdown occurs near the end of the solar day and during periods when 

the time-averaged radiation falls below a specified level. The collector 

array is stowed in the safest position (minimum wind loading and maximum 

reflective surface protection). The circulating pump is stopped after a time 

delay, and the whole system is shut down according to a predetermined 

sequence. Overnight thermal losses may be lessened by extracting as much 

energy as practical from the collector field. 

Two strategies for freeze protection in a water-filled loop-are a drain-back 

system and a circulation loop. The drain-back system can reduce overnight 

losses, but can also cause corrosion in the collector piping and pressure 

surges at start-up. Water circulation from a storage or flash tank may be 

associated with significant heat losses over a year of operation, however. 

Generally, this type of freeze protection should be considered only in mild 

climates. In both cases, the freeze-protection point should be at least 2'~ 

above the freezing temperature of the fluid. The fluid temperature must also 

account for night radiation losses, a significant factor in dry climates* To 

ensure that the coldest point in the system is known, several sensors in different locations should be monitored* In the circulation system, a time delay 

should be used which is sufficient to ensure that the entire loop is warmed to 

above freezing before the pump shuts off. Freeze protection should be automatically implemented in emergency conditions, such as during a power outage* 

Stagnation caused by overpressure, overtemperature, or thermal shock can harm 

the collector system (thermal shock can be especially damaging to evacuatedtube collectors). The control logic should prevent stagnating collectors from 

being filled with cold fluid when they are above a critical temperature. For 

example, if evacuated-tube collectors stagnate during the day, the circulating 

pump should not be restarted until they have cooled to a safe temperature. 

Circuit-breakers should be located in a locked box to prevent tampering. 

Overtemperature and overpressure may be controlled by increasing the fluid 

flow rate, stowing the collectors, or both. 

8.2-4 Emergency Conditions 

Typical emergency shutdown conditions include abnormal temperature, pressure, 

flow rate, or fluid level; pump failure; excessive wind speed; and loss of 

power. The conditions are set by maximum temperatures and pressures that collectors can withstand and the vapor pressure, toxicity, and autoignition point 

of the heat transfer fluid. In the checkout phase, the necessary limit 
switches that indicate these emergency conditions must send the correct 

signals to the control area. For example, a low-flow or high-temperature condition requires stowing the collectors. Also, emergency conditions must be 

signalled to the operator by means of visual and audible alarms. The emergency shutdown logic should be fail-safe, and the control valves should go to 

the safest position if instrument air or electrical power is lost. If a PLC 

implements alarms and relays, the critical functions should be hard-wired to 

circumvent controller problems. A total system kill switch should also be 

provided for fire protection. The switch should stop fluid flow, stow collectors, and be accessible to firemen. Finally, checking out the automatic 

emergency conditions will be easier and safer if electrical simulation of control inputs are provided for. 

8.2.5 Operator Training/Msplay 

Operators should be trained in all normal and emergency modes of the system. 

They must be able to react quickly to alarms and know how to perform diagnostic procedures. They should be trained in emergency procedures and should 

keep a daily log of unusual occurrences, corrective actions, and routine 

maintenance activities. They should maintain upto-date piping and instrumentation diagrams, post signs indicating If a control loop is on manual or if an 

alarm or over=ide has been bypassed, and keep records of relief valve, interlock, and controller settings. 

A process display should be visible to the operator, along with the solar 

field. The display should show flow directions and control loops. If a data 

acquisition system is used, the operator should be familiar enough with it to 

start it up, handle problems, and replace paper and tapes. 

8.2.6 Control System Checkout 

A complete, sequential checkout can save plant personnel time and prevent 

equipment damage during start-up. A checkout may include the following steps. 

Before the electricity is turned on: 

Check the equipment and process configuration. Label equipment, flow 

direction, fuel lines, etc. 

Use an ohmmeter to perform point-to-point wiring checks. Check the continuity between instruments and terminal boxes, master terminal cabinets, 

and the motor control center. Note whether switch and alarm contacts are 

normally open or normally closed, and verify that the action is correct. Also check the continuity of the analog controller, the PLC, and 

the emergency shutdown relays. 

Adjust temperature, pressure, and flow limit switches. Also, adjust the 

valve travel limit switches. 

Dial in analog controller set points and tuning constants. 
With the electrical power on: 

a Program the PLC to accept alarm conditions. 

Check the power distribution. Verify activation of the proper elements 

when -individual circuits are activated on the operator panel. 

Verify functions of the Uninterruptible Power System transfer switch to 

alternate supply by operating the main power breaker. 

Perform a control loop function check. Input "dummy" signals at the sensor element, possibly using a resistance decade box. Verify that the 

controllers and the final control elements are working as signals are 

changed. Reconfirm that travel limit switches on valves are working properly by observing annunciator and control panel displays. 

a Check the alarm functions. From the PLC keyboard, activate all alarms 

and status signals generated by the PLC. Simulate alarm conditions at 

the sensor element by manipulating instrument contacts (on or off). 

Verify that the corresponding alarms are activated and that the correct 

motor action is taken. 

8- 3 I1OSTRUMENTATION AND nATA ACQUISITIOB 

An extensive treatment of this topic is beyond the scope of this section, but 

some observations are in order. First, instrumentation is needed both for 

system control and to provide information about the system's performance. And 

instrument control systems must be evaluated in terms of cost versus efficiency. In instrument applications, quality is often sacrified to minimize 

original costs, but such shortcuts can result in increased maintenance costs . 

and loss of production time. Most instrument control systems are installed 

with a life expectancy of 10, rather than 25, years. A system must also be 

evaluated in terms of available operating personnel. Sophistication and cow 

plexity can work against plant efficiency without proper staff support 

(Andrew 1974). 

To ensure continued accuracy, all sensors should be calibrated frequently 

according to the manufacturers' recommendations. The use of dependable visual 

gauges near control sensors is recommended to facilitate troubleshooting. 

When possible, the use of locally serviceable equipment will reduce the amount 

of downtime. 

8-3-1 Flow Measurement 

Basic flow measurement instruments can be categorized as 

a head meter (differential pressure across an engineered restriction) 

variable area or rotometer (weight) 

magnetic meter (velocity) 

a turbine meter (velocity) 
a target meter (weight) 

a vortex shedding meter (turbulence). 

In choosing the correct instrument for the solar application, consider the 

operating-conditions. Note the range of flow rates required and the normal 

expected flow. The most common flow measurement, the head meter, is applicable only from a 3:l to 5:l ratio of flows. For indication only, a 5:1 ratio 

is acceptable; for closed-loop control, however, 3:l is preferable. If a 

higher range is needed, it is necessary to use two head devices in parallel or 

use another type of device with a 10:l or 20:l range. Temperature and pressure variations must be known so that compensation can be included. Corrosion 

and viscosity effects must also be taken into account. 

The orifice plate is the most common restrictive device used in head flow measurements. Orifice plates are inexpensive up to the larger pipe sizes and are 

very reliable. From a pressure-loss standpoint, venturi tubes have a decided 

advantage over orifice plates; from an accuracy standpoint, the two are 

similar. Because more test data are available on orifice plates, more 

certainty exists about their coefficients, especially at low Reynolds numbers. In the process industries of the United States, the American Gas 

Association (AGA) standards for installation of these devices are the most 

widely accepted. 

Pitot tubes and (for air systems) hot wire anemometers can be used to measure 

flow rate. To determine total volumetric flow, however, a properly weighted 

array of point measurements must be employed. 

The rotometer is a variable-area flowmeter consisting of a vertical 'tapered 

tube with a float that is free to move up and down within the tube as the flow 

varies. Rotometers are available in a variety of styles and can meet a wide 

range of service conditions. These flowmeters have an accuracy of f2% and a 

range of about 10:l. The pressure drop across the meter is constant once the 

float lifts off the float stop and ranges from a few centimeters of water 

(small-sized meters) to about 7 kPa (1 psi) (larger meters). 

Magnetic flowmeter measurement is independent of viscosity, density, temperature, and pressure. The meter's desirable features include 

a no flow obstructions 

a minimal pressure drop 

a flexibility of pipe configurations, because the meter measures average 

velocity. 

The following precautions need to be taken in installing the magnetic flowmeter: 

a Conductivity must be above the recommended minimum. 

a The meter must be full at all times. Air bubbles will cause errors. 

Turbine meters consist of a straight-flow tube within which a turbine or fan 

is free to rotate about an axis fixed along the centerline of the tube. 
Accuracy is obtained by operating the meter in the linear portion of its rang 4 (10% to 100%). At low fluid velocities, the number of pulses generated per m 

of flow is small and changes appreciably with flow rate. At about 10% of 

rated flow, however, a linear relation is maintained between pulses and 

flow. Within these limits, accuracy is normally f0.25X to f0.5X; the repeatability of 'the -turbine meter is excellent, ranging from f0.25% to M.02%; and 

the ranges are generally 10:l or 20:l. The pressure drop across the meter 

varies with the square of the flow. But because the meter is inserted into 

the flow line, the entire mechanism is subject to dirt and erosive action. 

Turbine meters work best when they are used in a lubricating fluid. 

Target meters function by measuring the force on a disc centered in the pipe 

with the plane of the disc at right angles to the direction of flow. The 

accuracy is 39.5% to 3% of flow range. Target meters are especfally useful in 

measuring heavy, viscous, dirty, or corrosive fluids. They can handle pressures up to 10 MPa (1500 psig) and temperatures up to 400~~ (750'~). 

Whatever flow measuring device is used, it is important to follow the manufacturer's recommendations regarding the lengths of straight pipe required upstream and downstream or to consult available standards. 

8.3.2 Level Measurement 

Level measurements fall into two general groups--direct and inferential. 

Direct level measurements, such as sight gauges, .are not easily adapted to 

signal transmission, but they are simple and economical. Inferential methods 

utilize properties such as buoyancy, hydrostatic head, sonar, conductance, 

capacitance, radiation, and weight. Caution must be used in applying inferred 

level measurement; the measured property must have a well-defined relationship 

to the level. Otherwise, large errors can occur. 

8.3-3 Pressure .&asure~ent 

Well-known pressure elements include manometers, Bourdon tubes, bellows, diaphragms, and strain gauges. These instruments must also be compensated for 

process conditions, especially temperature. Pressure gauges account for a 

large percentage of pressure measuring elements used- Their accuracies vary 

from H.lX to *5%. Their ranges vary from a few centimeters of water to about 

700 MPa (100,000 psig) and from 0.1 to 760 mm of mercury absolute. 

The most common methods of measuring temperature are by means of thermocouples, filled systems, bimetallic elements, resistance elements, and 

thermistors. The choice of sensor depends primarily on four factors: system 

cost, accuracy, dependability, and adaptability to the process- The first 

consideration speaks for itself. The second factor requires a balance between 

different requirements; e.g., while one process must be controlled within a 

degree or two, others may vary several degrees with no loss of efficiency or 

quality. The third factor, dependability, 2s also a factor of process conditions. For example, high temperatures and oxidation may cause early failures 
in system elements. Adaptability to the process is simply selecting and 

locating a sensor so as not to upset the process functions; e.g., not placing 

a thermocouple in the path of an agitator or a thermowell in a stream that 

coats the well and thereby causes inaccurate measurements. 

The thermocouple (TC) is the most versatile electronic temperature sensor. 

Various standard TCs are available in temperature ranges between -185'~ 

(-300'~) and 1760'~ (3200'~). Greater accuracies can be achieved by paying 

special attention to grounding and shielding: 

Ground all shields. An ungrounded shield does not provide noise protection. 

Ground a shield at only one point. Grounding at two points produces 

rather than prevents noise. 

For common mode noise rejection with a grounded couple, ground the shield 

on the extension wire at the couple. The shield should not be grounded 

in the control room. 

Thermocouples are seldom placed directly in a process stream. Rather, they 

are placed inside protecting wells so that they may be removed or replaced 

without shutting down the process. The wells slow response time appreciably, 

but reduce the cost of replacement. In using thermocouples, one must ensure 

that sufficient immersion depth is provided to reduce conduction heat loss. 

High-quality extension wire should be uniformly calibrated and wires should 

not pass through sudden large temperature gradients. 

Sealed metal bulbs or tubes, partially or completely filled with liquids or 

gas, are widely used as temperature sensors. Bulbs completely filled with 

liquid have high accuracies and fast response rates, but are limited to ranges 

of -18'~ (0'~) to 315'~ (600'~). Partially filled vapor-pressure sensors are 

less expensive and can be specified for ranges between 230'~ (450~~) and 540'~ 

(1000~~). Bimetallic sensors utilize dual strips, with different heat coeff icients of expansion joined together. Most of ten employed in on-of f control 

systems, they have ranges of -75'~ (-100~~) to 1100~~ (2000°F), but slow 

response times and poor repeatabilities. 

Resistance temperature detectors (RTD) are also common. These sensors are 

more expensive than TCs and require a current source and signal conditioning, 

but they are very stable. They provide good linearity from -240'~ (-400'~) to 

900~~ (1650°F), and their unamplified signals can often be transmitted over 

distances up to 100 m without degradation. Care should be taken to position 

the RTD at bends in the flow path to maximize heat transfer. Four-wire types 

are recommended to eliminate lead resistance effects, unless signal conditioning is located close to the measurement point. 

Thermistors are the preferred sensor when great sensitivity is required. They 

are extremely nonlinear, which has limited their application; however, this is 

not a problem for a PLC or microcomputer. An excellent article by 

L. M. Tierstein (1978) reviews the companies that manufacture temperature sensors, regulators, and controllers. 
8-3-5 Irradiation Measarerent 

A number of different types of instruments measure the intensity of solar 

radiation. Pyranometers that employ a photovoltaic cell are relatively inexpensive and have an accuracy of 3% to 5%. For greater accuracy, the ~~pley 

Precision 'Spectral Pyranome ter (PSP) is commonly used. It utilizes a copperconstantan thermopile attached to a Parson's black recefver beneath two concentric glass dones with compensation for ambient temperature. 

Measuring total radiation in the plane of the collectors is sufficient to 

determine array efficiency in nontracking collectors. Concentrating collectors essentially collect no diffuse radiation, but a measurement of direct 

radiation is required. A pyrheliometer that tracks the sun in two axes measures only direct radiation. To determine direct radiation normal to the 

aperture of tracking concentrators (needed for an array efficiency calculation), the measured radiation must be multiplied by the cosine of the angle 

between the collector aperture normal and earth-sun line. Since this value 

changes continuously during the day, the conversion would be performed by a 

data acquisition system* 

One problem with the pyrheliometer is that it requires periodic adjustment, 

and its power cord must be unwound often. Solar field measurements are of ten 

not maintained well, so data are lost. A less accurate but more reliable 

means of determining direct radiation in the collector plane is to mount both 

total and shadow-band pyranometers (one each) on a collector. The shadow band 

blocks direct radiation, permitting only diffuse radiation to be measured, 

The direct radiation in the plane is the difference between total and diffuse 

radiation. If the shadow band is mounted parallel to the tracking axis, it 

will never require adjustment. Of course, if the collector is not tracking 

accurately, the measured radiation will be too low. Modern trackers, however, 

track accurately enough so that this should not be a problem. 

8-3-6 Converters 

Converters link electronic and pneumatic control systems together, change 

signal levels in the application of computers to control problems, and convert 

easily obtained sensing signals to other forms more easily transmitted. The 

units can be classified into five groups: 

current-to-pneumatic (I/P) 

pneumatic-to-current (P/I) 

voltage-to-current (E/Z) 

voltage-to-pneumatic (E/P) 

current-to-current (111)- 

The first three converters--I/P, P/Z, and E/I--are the most common. Inputs to 

I/P converters are normally 1-5, 4-20, or 10-50 mA. These shockproof and 

vibrationproof units may be mounted upright but not tilted more than 10% from 

the vertical centerline, and they may be mounted on or away from the actuating 

or control element. Finally, they can either signal a pneumatic positioner or 
can direct-load the control valve if a spring-loaded actuator and volume 

booster are used. 

P/I converters are used when pneumatic signals must be converted to electronic 

signals, for example, a pneumatic transmitter connected to an electronic controller. - They are also used when instrument air is not available at the controller and when long transmission distances are involved (more than 

500 ft). The units may be installed in any orientation, have the ability to 

operate in vibrational environments, and have a built-in power supply. 

E/I converters are widely used in the processing industries. For example, 

thermocouples, the most common millivolt-generating sensing element, require 

E/I units to convert the signals to 1-5, 4-10, or 10-50 mA for inputs to controllers or other receivers. E/I temperature converters are designed to 

accept standard thermocouple inputs directly, converting them to high-level DC 

current outputs. These units normally have built-in temperature compensation 

and thermocouple burn-out protection. 

8.3-7 Data Acquisition 

Because the DOE-sponsored IPH field tests were experiments, they utilized 

fairly expensive, detailed data acquisition systems (DAS). Because of their 

complexity, these systems were kept separate from the control system so as not 

to compromise the reliability of the latter. Industrial owners funding their 

own IPH systems will probably want a much less sophisticated US. In that 

case, the small amount of data needed could simply be taken from the control 

system, thereby eliminating the extra costs that would be incurred by having 

two separate systems. 

Data acquisition varies from a simple reading of energy collected to a 

detailed breakdown of all system energy balances. A study of different types 

of systems is given in Bush and Kutscher (1980). A discussion of the more 

sophisticated system can be found in Kutscher (1979) and Kutscher and 

Davenport (1980). Experience has shown that no matter what type of DAS is 

used, care must be taken to ensure reliability. 

The data acquisition hardware (data logger or minicomputer, tape drives, 

printer, etc.) should be located in a sheltered environment with a temperature 

control. The area should be free from dust, steam, water leaks, and vibrations. It should also not be exposed to direct sunlight. Isolation trans- 

.formers are recommended for systems that are susceptible to damage by voltage 

spikes. Ideally, the DAS should be capable of taking data whether or not the 

solar system is operating. Battery back-up should be employed so that the DAS 

can keep track of time and maintain memory during a power outage. It is also 

very important to select components that are compatible. Poor matches of data 

loggers and tape drives have caused problems in the past. 
Andrew, W. G. 1974. Applied Instrumentation in the Process Industries. 

Houston, TX: Gulf Publishing Co. ; Vol. 1. 

Baumann, 'H. 0. 1981 (29 June). "Control-Valve vs. Variable-Speed Pump." 

Chemical Engineering. p. 81. 

Baumann, H. 0. 1979 (May). "A Case for Butterfly Valves in Throttling 

Applications." Instruments and Control Systems. p. 35. 

Buckley, P. S. 1964. Techniques of Process Control. New York: John Wiley & 

Sons, Inc. 

Bush, G.; Kutscher, C. F. 1980 (June). "Data Acquisition for Solar 

Industrial Process Beat Field Tests. " Proceedings of the 1980 Annual 

Meeting. American Section of the International Solar Energy Society. 

Phoenix, AZ. 

Campbell, Donald P. 1958. Process Dynamics. New York: John Wiley & Sons, 

Inc . 

Chemical Engineering Deskbook. 1979 (15 Oct.). New York: McGraw-Hill. 

Considine, D- M.; and Ross, S. D. 1964. Handbook of Applied Instrumentation. New York: McGraw-Hill. 

Eckman, Do Po 1958. Automatic Process Control. New York: John Wiley & 

Sons, Inc. 

Grader, Jerome. 1970. Basic Process Control. Taylor Instrument Company. 

Harrfott, Peter. 1964. Process Control. New York: McGraw-Hill. 

Kutscher, C. I?. 1979 (30 Mar.). SPIPS Data Acquisition System Guidelines. 

Golden, CO: Solar Energy Research Institute; memorandum to SPIPS 

contractors. 

,Kutscher, C. F. ; Davenport, R. L. 1980. (Sept .). Monthly Reporting Require- . 

ments for Solar Industrial Process Heat Field Tests. SERI/MR-632-714. 

Golden, CO: Solar Energy Research Institute. 

Luyben, W. L. 1973. Process Modeling, Simulation, and Control for Chemical 

Engineers. New York: McGraw-Hill. 

Schindwolf, R. 1981 (July). Frequency Response Analysis of Fluid Control 

Systems for Parabolic-Trough Solar Collectors. SAND80-0385. Albuquerque, 

NM: Sandia National Laboratories. 

Shinskey, F. G. 1967. Process Control Systems. New York: McGraw-Hill. 

Su, W. S.; Castle, J. N. 1979 (July). State-of-the-Art of Solar Control Systems in Industrial Process Heat Applications. SERL/TP-39-240. Golden, 

CO: Solar Energy Research Institute. 
Tierstein, L. M. 1978 (Dec.). "Selecting Temperature Regulators and Controllers. " ~nstrumentatik Technology. - pp. 52-59. 

Torkelson, L. E. 1980 (Sept.). Pump Power Consumption Test Report. 

SAND80-1707. Albuquerque, NM: Sandia National Laboratories. . .. 

Wright, J. D. 1981 (July). "Analytical Modeling of Line-Focus Solar Collectors." Presented at the - JACC, San Francisco, CA; Aug. 1980. 
The reliability and performance of a solar system depend to a great extent on 

the quality of the original installation. Installation should conform to all 

applicable engineering standards and codes and should be consistent with good 

engineering practices. Although many facets of system installation will be 

familiar to contractors, some will be outside their range of experience, and 

these can cause unexpected difficulties . The following discussion focuses on 

items that are unique to a solar installation. 

9 1 1 Scheduling 

Constructing an industrial solar energy system requires a considerable amount 

of equipment and a variety of skilled personnel. Proper scheduling during 

both the equipment procurement and construction phases can do much to contain 

costs. For example, collectors should be delivered so that they are kept a 

minimum amount of time in storage. Collector components are fragile and 

easily damaged, so collectors should be inspected for damage upon receipt, and 

any damage claims should be filed as quickly as possible. 

, Final copies of all system drawings, specifications, codes, operation and 

maintenance manuals, and other appropriate documents should be available on 

site for reference. A detailed log should be kept to record progress and to 

note difficulties . Adequate tools, equipment, and spare parts should also be 

provided to complete all aspects of installation and start-up with a minimum 

of delay. 

9-1.2 Installing the Collectors 

The collector field should be located in an area that is not subject to shading from surrounding buildings and vegetation, and for this reason, the growth 

of vegetation in the collector field should be controlled. 

9.1.2.1 Installing Flat-Plate Collectors 

Flat-plate collectors are, of course, nontracking, but they are usually tilted 

to maximize solar energy collection. However, neither the tilt nor the 

azimuth orientation of the collector is critical as long as they are within a 

few degrees of the desired angles. Consequently, some latitude is allowed in 

the accuracy of the support structure for tilt and azimuth angles. However, 

most flat-plate collectors have internal manifolds; thus, it is important to 

align connecting pipes correctly along the collector rows. Also, since the 

size of the internal manifold is fixed, only a limited number of collectors 

can be placed in parallel without the danger of flow maldistribution. 
ssn ;el TR-1356 

Generally, connections are made with synthetic rubber connectors clamped over 

the tubes, leaving a sufficient gap to accommodate thermal expansion. Care 

should be taken not to overtighten these connectors, since this can lead to 

early system failure. Spring clamps are often used instead of screw clamps to 

prevent overtightening. Collectors and pipes should be sloped slightly in 

case it is necessary to drain the system. Slope requirements [0.010 to 

0.021 m/m (0.125 in. to 0.25 in. per ft)] for drainable systems must be 

checked carefully. For collectors with external 'mnifolds, it is important 

that thermal expansion of the header does not impose stresses on the connections to the absorber plate. Cyclic stresses can cause the connection to 

fail. 

The largest flat-plate collectors are usually 1.2 m (4 ft) wide by 2.4 m 

(8 ft) long and can be handled by two people. The collectors should be 

mounted rigidly to prevent the structure from flexing, which could break the 

glazing. Before choosing a collector initially, be sure to consider how 

easily glazing can be replaced in the field. It is also advisable to prevent 

liquid collectors from stagnating before they are turned on. Collectors are 

sometimes shipped with a black plastic cover; it should not be removed until 

the system is fully checked out under cold-flow conditions and is ready for 

heat collection. This is a sensible precaution, even though liquid flat-plate 

collectors should be designed to withstand stagnation conditions, which can 

produce temperatures in excess of 150'~ (300'~). In general, collector 

installation is fairly rapid once the structure is in place, so it should be 

postponed to the latest possible date. 

With roof-mounted structures, care should be taken to completely waterproof 

the points of attachment to the roof. Wind loads can cause the collector 

structure to move; the resulting damage to the roof can cause rainwater to 

leak into the building. This applies not only to flat plates but to other 

types of collectors as well. 

9.1.2.2 Installing Evacuated-Tube Collectors 

Current evacuated-tube designs incorporate integral manifolds. Consequently, 

installation procedures are very similar to those of flat-plate collectors. 

Connectors should be made of elastomers such as Viton that are designed to 

withstand high temperatures. As with flat-plate collectors, stagnation of the 

collectors during construction should be avoided. Evacuated-tube collectors 

containing copper heat conduction fins will suffer oxidation and subsequent 

spallation at stagnation temperatures, which can reach 371'~ (700'~). Allglass types, less susceptible to degradation under dry stagnation conditions, 

could pose a danger to construction personnel if they should handle the collector near the open ,end of the tube. All types of evacuated-tube collectors 

can suffer tube breakage if a cold fluid is inadvertently admitted while they 

are stagnating. Nondrainable evacuated-tube collectors made entirely of glass 

should be filled with liquid only during nighttime or cloudy conditions when 

the solar system is ready for heat removal. Heat removal from such collectors, once they are filled, should not be stopped, since stagnation under 

wet conditions can cause the tubes to break. Drainable collectors require 

strict adherence to pipe slope requirements. 
9.1.2.3 Installing Line-Focus Collectors 

The construction tolerances of the foundation work of tracking collectors are 

critical if the collector structure is to be aligned accurately. Twelve or 

more collector modules, with each module perhaps 3 m (10 ft) long, can be 

driven by 'a &tor in a single string, so accurate alignment of the modules 

along the row is essential. This is generally achieved by placing studs precisely in the concrete foundation and adjusting the support structure on the 

studs. Al'though the concrete foundations along each row must be aligned . 

accurately, it is not critical that all .the rows be precisely parallel. Also, 

it is not necessary that the receiver tube of a parabolic trough collector be 

mounted absolutely horizontally- Some amount of slope can be tolerated, 

depending on the design of the bearing. In fact, construction on a southfacing slope in northern latitudes increases energy collection. Similarly, 

some differences in grade between modules of a two-axis tracking Fresnel lens 

collector can be tolerated, provided that the orientation of the receiver 

tubes can be maintained in parallel planes. As we have noted elsewhere, 

spacing of collector rows involves a compromise between shading losses and 

land use. Row-to-row spacings of two to three times the aperture width of the 

collector are usually appropriate for line-focus collectors. In latitudes 

below 45', this spacing keeps the annual shading losses to reasonable levels 

(see also Sec. 6.2). 

To ensure accurate tracking in windy weather, the support structure of a linefocus collector must be very rigid. This requirement increases the weight of 

the structure, so lifting equipment is generally required for installation. 

Substantial foundations are also required to support the weight of the collectors and, more important, to withstand wind loads both when the co~lectors are 

tracking and when they are stowed. At the same time, the foundation design 

must prevent water or ice from causing the supports to "heave," which would 

misalign and possibly damage the collectors. If soil conditions are favorable, an augered concrete foundation is typically the most economical support 

structure. A floating pier structure requires larger volumes of concrete and 

generally must extend below the frost line. A foundation test program was 

undertaken at Sandia Laboratories in 1979 (Auld 1979) and suggested some economical foundation designs for parabolic troughs (Auld 1980). 

Load-bearing requirements of struts and pylons vary according to their positions in the collector array. Exterior collectors are subject to higher wind 

loads than interior modules* Drive pylons must also be reinforced. Such considerations lead to considerable economies in construction. Wind tunnel tests 

have been carried out to characterize the wind loads experienced by parabolic 

troughs (Randall, McBride, and Tate 1980). The tests showed that interior 

collector modules installed in a collector field experience a SOX-65% reduction in peak wind loads. Also, a collector field surrounded by a fence or 

berm that is three-fourths of the maximum collector height exhibits a reduction in wind load nearly equivalent to that of the inside rows of collectors. An assessment of exlsting studies of wind loading on solar collectors (Murphy 1981) discusses these effects, particularly in regard to wind 

fences and berms. 

On site, the collectors should be assembled according to the manufacturer's 

instructions. Once again, great care must be taken not to damage components. 
The selective surface of the receiver tube and the Pyrex glass envelope of a 

parabolic-trough collector should be cleaned carefully before installation, 

successively with detergent and organic solvent (Solar Kinetics, Inc. 1980). 

After cleaning, bodily contact 'with the selective surface should be avoided, 

because skin oils (and other substances) can cause the surface to degrade. 

The glass -envelope should be installed concentric with the receiver to obtain 

the maximum benefit from the insulating air gap around the receiver. O-ring 

seals are used at the end of the glass tubes to reduce dirt penetration into 

the annular air gap. Sufficient spacing between adjacent tubes is required 

for thermal expansion of the glass, which otherwise can result in breakage. 

Factory assembly in a sealed cavity should ensure the cleanliness of the 

receiver tube of a Fresnel lens collector. 

An all-welded receiver tube is desirable but makes disassembly difficult (to 

replace a broken glass envelope, for example). Ferrule fittings joining collector tubes must be installed correctly to prevent possible leakage, especially in oil systems. 

Flexhoses, installed at the ends of a parabolic trough receiver tube to accommodate the rotation of the collector, are points of weakness in the integrity 

of the collector piping system. Flexhoses should not be flexed past their 

minimum bending radius, and they function most effectively when they are 

installed to flex in one dimension only. Torsional stress can cause early 

failure; thus, imposing such stresses during installation and operation 

(e.g., after an incorrect installation) 'should be avoided (Boyd 1980). An 

example of correct flexhose installation with either rotatable or nonrotatable 

receivers is shown in Fig. 9-1. The flexhose is supported, and high radii of 

curvature are generally provided, by a stripwound metal insulation cover. 

Caution is required when welding near a flexible connection so as not to alter 

the properties of that connection. Flexible insulation is recommended if the 

flexhoses are to function effectively while in continuous motion. The insulation must be installed on the flexhose before it is connected to collector and 

field piping. 

Other points to note when checking out a line-focus system are correct installation and alignment of the sun tracker (final adjustments can be made when 

fluid flow is initiated and the collectors are tracking); ensuring the presence of an overtemperature switch for each collector row (particularly for oil 

systems, which present the greatest fire hazard); and ensuring that adequate 

shielding from concentrated solar radiation is provided for instrument or 

electrical wiring and any other system components (e.g., bleed valves). The 

collector tracking mechanism should be tested after final assembly over its 

full range of travel, but only on a cloudy day. Sun tracking can take place 

only with full fluid flow through the receiver. The flexhoses should rotate 

freely. 

9.1.2.4 Piping, Fittings, and Insulation 

Piping is a major consideration in solar installations. Piping design shovld 

conform to the guidelines presented in previous sections. In checking a solar 

installation., be sure that adequate allowance is made for thermal expansion. 

Solar system components frequently cycle through large temperature variations, and to prevent the buildup of thermal stresses, sufficient expansion 

loops, expansion bellows, or flexible connections are required. 

Pipe schedules, gaskets, and fittings should conform to engineering drawings. 

Before being connected, pipe segments should be emptied of any dirt or gravel 

that may have accumulated in them, as that could damage the equipment. Fittings should be installed in the correct orientation to flow. Generally, 

valves in an oil system are installed with the stems positioned horizontally 

so that leaks will not drip into the insulition-. Installing the valves upside 

down is inadvisable, because dirt can then accumulate in the valve body. When 

the valve is moved, the dirt will be forced into the fitting causing damage 

and eventual leakage. Where a fluid leak is possible, nonwicking insulation 

(e.g., foamed glass) can reduce the risk of fire to a great extent. And electrical or steam-tracing lines, if present, should be checked and turned on 

before they are insulated. In winter, the steam lines should be tested and 

completely drained until they are ready for reactivation, after the solar system is completed. 

Valve packing, gaskets, and flange ratings should be checked carefully, particularly in oil systems. Graphite-impregnated asbestos ("grafoil") packing 

seems most effectfve in reducing oil leaks. Spiral-wound asbestos-filled gaskets should be used in raised-face flanges for oil systems if welded fittings 

cannot be employed. Oil suppliers often specify heavy-duty flanges and highstrength studs. Plain asbestos gaskets on raised-face flanges are generally 

satisfactory for high-pressure water systems. In low-temperature systems, 

rubber gaskets on smooth-face flanges or O-ring joints can be used. In all 

cases, flanges should be joined with studs rather than machine bolts, and nuts 

should be tightened so as to avoid short bolting; equal lengths of exposed 

pipe.thread should be visible at each end of the stud. 

The solar system should be pressure-tested before insulation is installed, and 

insulation must be thoroughly waterproofed. Insulation covers should be 

lapped to shed water and the seams should be caulked. Because the insulation 

cools at night, it is susceptible to moisture penetration. Insulating ability 

is seriously reduced when the insulation is wet and its structural integrity 

is compromised. Closed-cell insulation resists moisture better and can be 

worth the added cost. In systems that use flammable fluids, a nonwicking 

insulation should be used at any point that is susceptible to leaks to prevent 

fires that could result from oxidation-induced high temperatures. 

Heat losses through supports, fittings, and instrument connections can and 

should be reduced. Pipe hangers and supports should be insulated from hot 

pipe. One way to do this is to use rigid insulation at support points and to 

loop the hangers around the insulation (see Fig. 9-2). Valves and fittings, 

including flanges, should be insulated as thoroughly as possible, consistent 

with safe operation of the system. 

If possible, locate piping away from personnel walkways, because walking on 

nonrigid insulation can cause serious damage. However, the collector field 

should be accessible to personnel and vehicles as required. Underground piping is best installed inside a rigid conduit that is specially waterproofed 

with asphalt compounds. Conduits should be sealed to prevent the intrusion of 

rain or groundwater. If piping with conventional insulation is used in a culvert, the culvert should be free-draining, and water should not be able to 

enter it. 

An adequate nwber of vents and drains should be located in the piping system, 

but these fittings should be confined to essential locations because they act 

as heat sinks. Dead ends, such as drain valves, are also possible freezing 

sites in water systems. The piping system should be designed to minimize 

pressure drop, which means that additional attention must be paid to pipefitting practices. For a drain-back system with sewer-flow, Y connectors should 

be substituted for T connectors, and pipe slope requirements are critical. 

Locate relief valves wherever a section of piping or components can be 

isolated that is subject to possible pressure increases caused by thermal 

expansion. The number of relief valves required can be minimized by 

minimizing the number of isolation valves. Relief valves should be installed 

vertically (upward) and vented to a safe location. Valves vented to the 

atmosphere should have weep holes in outlet piping to prevent their filling 

with rainwater. Liquid relief valves should be free-draining downward. In a 

heat transfer fluid system, it is necessary to pipe the relief valves to a 

collection point to prevent fluid from spilling. 

9.1.3 Installing Heat lhchangers 

Heat exchangers mst be mounted to provide sufficient clearance for disassembly or for removing the tube bundle. Piping should be supported so that 

forces are not directly applied to the heat exchanger. The shell should be 

fixed only at one end, and a shoe should be provided for free thermal expansion at the other end. Connections should be provided on the inlet and discharge lines for pressure and temperature gauges, as required. Locate vents 

and drains on both the shell and tube sides of the exchanger. 

9.1.4 Installing Pumps 

The pump foundation and grouting should be carefully constructed according to 

the manufacturer's recommendations. Suction and discharge piping should be 

fully supported, so that forces are not transferred to the pump. There should 

also be adequate access to the pump so that it can be serviced. Pump life is 

largely determined by the correct alignment of the pump and the motor. Final 

adjustments are often made under operating conditions. If mechanical seals 

are installed, seal flushing lines should be correctly located and should usually include a centrifugal strainer. Seal cooling is generally not required 

unless fluid operating temperatures exceed 260'~ (500'~). Heat rejection to 

cooling water can be a major source of thermal loss from a solar system. 

Fittings for each pump should generally include a check, a suction strainer, 

and a discharge pressure gauge located within the pump isolation valves. Pump 

and motor nameplate data should be checked against design specifications. The 

design point should be located to the left of the maximum efficiency point on 

the pump curve so that flows greater than design do not overload the motor. 

The suction head on the pump should also be checked against the pump curve. 

Pumps and motors, and other equipment in the system, should be grounded. 
The cyclic nature of a solar system imposes severe stresses on mechanical components, especially those operating at high temperatures. This is particularly true for solar system pumps that are remotely controlled. Under such 

stress, correct installation and maintenance are even more important than for 

equipment operated continuously. A standby pump may be highly desirable. . - 

Under normal operations, mechanical pump seals are highly reliable, cause minimal friction, and reduce leakage along the pump shaft to a negligible amount. 

However, these seals require. skilled installation, and they are expensive. If 

the seals should leak, they can spray liquid over a wide area. A packed 

stuffing box does not provide such a positive seal. Their leakage rates may 

be too high for an oil system but perfectly acceptable for water systems, and 

they should be considered as an alternative. Adjustments are easily made by 

unskilled personnel and repacking is equally simple. Failure is not likely to 

be catastrophic, evident only as increased leakage, and it is possible that 

packing glands could better tolerate the thermal cycling imposed on the cow 

ponents in a solar system. It appears that the greatest reliability can be 

attained by using redundant pumps. 

9.1.5 Install- Pressme Vessels and Storage Tanks 

Pressure vessels and storage tanks must be mounted on adequate foundations 

with thermal expansion taken into account. Fittings such as sight glasses 

(which should always be installed in conjunction with automatic level controls), level controllers, and valving must be insulated carefully to prevent 

localized freezing that could damage control systems. Relief-valve settings 

should be bench-tested for correctness. Ladders should be installed to provide easy access to all instruments and valves. 

Care should be taken to avoid damaging the insulation covering when installing 

tanks underground. Sand or other suitable material should form a bed at least 

15.6 an (6 in.) thick below the tank and at least 5.4 an (2 in.) thick around 

the tank as backfill. Drainage must be provided for all vessels. Underground 

tanks may require a sump pump. The placement and fabrication of baffles, vortex breakers, demisters, etc., should also be checked against shop drawings. 

Storage tanks and pressure vessels act as heat reservoirs as the solar system 

cools down overnight. Thermosiphon heat transfer can then cause significant 

heat loss. Connecting piping should, theref ore, be constructed to prevent 

thermosiphoning in poorly insulated sections of the solar system. A downward 

sloping U bend has been effective in preventing thermosiphoning from heat 

storage tanks. In drainback systems with return lines discharging into the 

top of the drain tank, considerable overnight heat losses can result from a 

"heat pipe effect," where water vapor condenses on the cooled pipe walls and 

returns to the tank in a continuous cycle. A solution devised by Sunmaster 

Corporation (Nest16 1981) resolves this problem. The return lines are constructed with a dip tube that extends below the surface of the liquid. To 

allow the return piping to drain completely, a small vent line with check is 

constructed from the tank to the top of each return line (see Fig. 9-3). Correctly filling the tank is obviously critical to the success of this technique. 
V) 

- Collectors Empty 2 a) r 

E 1 

Collectors FUII 

Vent Line Check c I1 I 0 

0 

I r - Return Line 

----- 

---- -- 

Figure 9-3. Design for Reducing Overnight Heat Losses in Drainback Systems 

9.1.6 Installing Controls, Electrical Mnes, and Instrumentation 

It is particularly important to check controllers and instruments for correct 

labeling. Instrument wiring should be adequately shielded and grounded to 

eliminate signal interference. The fail-safe position of control valves 

should conform to specifications. The valves should be stroked manually to 

ensure that they open and close smoothly. 

Flow measuring .devices should be installed with. adequate straight runs of 

upstream and downstream piping. Thermowells should be located so as to be 

sufficiently immersed in the fluid stream and should be insulated to prevent 

heat loss and incorrect readings. The operation of the auxiliary power supply, if any, should be checked. Similarly, the uninterruptible power supply 

to the data acquisition system should be fully charged and the battery charger 

should be operational. 

Since there i's little need to enter the collector field at night except for 

repairs, permanent outdoor lighting is not required; but it can be helpful 

where vandalism is a problem. However, sufficient electrical cable should be 

available so that power for lighting and equipment can be supplied to any part 

of the field. 

9.1.7 Perso~el and Environmental Safetv Precautions 

During the entire checkout of the solar system, the safe operation of the system should be ensured. Sharp edges or exposed piping that could cause injury 

or burns should be eliminated. Guard rails and ladder cages, as needed, 
should be required for roof-mounted structures. Depending on the types of 

fluids used in the solar system, safety showers and eye baths may be necessary 

at strategic locations. Pressure relief valves should be vented carefully. 

In high-pressure water systems, it may be necessary to restrict access to the 

operating collector field. . *. 

The fire protection system and alarms should be tested, and personnel should 

be instructed in the use of related equipment. Portable fire extinguishers 

should be strategically located. An emergency system shutdown switch should 

be easily accessible. Personnel should be equipped with eye-protection equipment when they enter fields of concentrated solar radiation. 

Heat transfer fluids that could be harmful to the environment must be collected. Care should be exercised in the selection and use of herbicides to 

control the growth of vegetation in the collector field. More details on 

safety and environmental issues are given in Sec. 11.0. 

9.2 START-UP 

The purpose of checkout and start-up procedures is to test the system thoroughly, so that future operations are as trouble-free as possible. With adequate supervision, as many start-up procedures as possible should be carried 

out by the saw plant personnel who will later operate and maintain the solar 

system. Such work provides exceptional training and helps the staff to become 

familiar with the details of the system. Start-up procedures necessitate the 

close coordination of several people. Portable, two-way radios could be provided to personnel to ensure smooth operation. 

9.2.1 Line Flnkhinp: 

During system fabrication, lines and vessels invariably collect earth, scale, 

welding rods, and other debris. Vessels large enough for a person to enter 

should be wire-brushed and swept out. Lengths of piping should be isolated 

into sections and thoroughly flushed with water that is then discharged 

through an open line. Vessels, heat exchangers, and solar collectors should 

be valved off or isolated with blanks. Control valves and flow measurement 

devices should be removed or bypassed to prevent damage. 

After their first flush, piping should be connected in a continuous circuit 

through a pump using temporary piping or fire hose. This is a good time to 

run in the pumps and-motors, although the motors should be checked for correct 

rotation and run in before being connected to the pumps. (Note, however, that 

gear pumps, for example, which depend on a fluid for lubrication, may not be 

designed to pump water.) Each pump should be primed and the impeller and 

motor checked to ensure free rotation. The bearing case should be filled to 

the correct level with lubricating oil. Initially, the pump should be started 

against a closed discharge. This minimizes start-up current and avoids overloading the motor. After a few seconds, the discharge valve should be opened 

slowly. 
Table 9-1. Installation Checklist 

Documentation 

Piping and instrument diagram 

System- drawings 

Component specifications and drawings 

Equipment list 

Construction codes 

Operation and maintenance manuals 

Progress log 

, Spare-parts list 

Flat-plate and evacuated-tube collectors 

Vegetation 

Support structure 

Collector alignment for tilt and azimuth 

Row spacing 

Manifold alignment 

Manifold connectors installation and materials 

Slope for drainage 

Stagnation cover during construction 

Support structure meets specifications 

Rigidity of support and collector attachment 

Access to collector field as necessary 

Line-focus collectors 

Collector alignment for azimuth 

Alignment of receiver tubes 

Row spacing 

Access 

Support structure 

Assembly of receiver tube and cover 

Cleanliness of receiver tube and cover . 

Alignment and support of flexhoses 

Attachment of flexhoses 

Alignment of sun trackers (check during fluid flow) 

Travel of collector 

Components shielded from concentrated radiation 

Piping, fittings, and insulation 

Provision for thermal expansion 

Schedules and material of pipe and fittings 

Orientation of fittings to flow 

Gaskets and packing 

Short bolting of flanges 

Adequate vents and drains 

Valves for oil system installed horizontally 

Relief valves installed vertically, vented to safe location, weep hole 

Field pipefitting practices minimize pressure drop 

Pipe placement allows access but isolated from foot traffic 

Heat tracing check before installing insulation 

Waterproofing insulation, particularly underground 

Pipe supports isolated from pipe 
Table 9-1. Installation Checklist (Concluded) 

Heat exchangers 

Clearance for disassembly 

Connecting* piping fully supported 

Thermal expansion 

Instrument connections 

Vents and drains 

Pumps 

Foundation 

Connecting piping fully supported 

Alignment of pump and motor 

Seal flushing and cooling lines 

Isolation valves, strainer, check, discharge pressure gauge 

Free and correct rotation 

Grounding 

Suction head 

Lubricating oil 

Bearing temperatures, discharge pressure, motor current 

Pressure vessels and storage tanks 

Foundations 

Thermal expansion 

Conformity to construction drawings 

Vessel intemals 

Placement, thickness, and type of backfill for underground tanks 

Waterproofing 

Thermosiphon breakers 

Safety-valve settings 

Controls, electrical and instrumentation 

Labelling of instruments and controllers 

Wiring shielded and grounded 

Fail-safe position of valves 

Free movement of valves 

Orientation to flow of valves and instruments 

Immersion of themowells 

Inlet and outlet pipe lengths around flow pressuring devices 

Auxiliary power supply, uninterrupt ible power supply,. battery charger 

Safety and environmental 

No sharp edges or exposed hot piping 

Guard rails, ladder cages 

Safety showers, eye baths 

Fire extinguishers 

Emergency shutdown 

Collection of heat transfer fluids 

Personnel training 

SECTION 10.0 

When an iGdustria1 firm considers installing a solar IPH system, the primary 

deciding factor, in most cases, is whether or not such a system is economically feasible. In this section, we turn our attention to the economic 

analysis of solar IPH systems. Two simple methods of estimating total system 

cost are presented in Sec. 10.1- The Dickinson-Brown methodology for economic 

analysis of solar IPH systems is summarized in Sec. 10.2. Section 10.3 presents financing alternatives for solar IPH systems. 

Two methods of obtaining a rough cost estimate of a solar IPH system are presented in this section. The first method uses the results of recent studies 

by Mueller Associates, Znc. (Mueller Associates, Inc. 1980 and 1981; Franta et 

al- 1982), in which the investigators determined actual constructi on costs for 

10 solar IPH systems and 24 solar heating and cooling systems by interviewing 

the various contractors involved in each project. The second cost-estimating 

method is that used in a computer program developed at SERI known as ECONMAT 

(see Stadjuhar 1982; and Brown et al. 1980). The approach is modular cost 

estimating (Guthrie 1969), and it- enables one to estimate the total system 

installed cost from the cost of collector equipnient (FOB) and a series of 

multiplicative factors that account fox all other direct and indirect costs. 

This method is explained in more detail in Sec. 10.1.2. 

10-1.1 Historical IPE System and Subsystem Casts 

Mueller Associates (1980) summarized actual, normalized, and modified costs 

for 10 federally funded solar IPH systems. The systems they studied include 

those with both manufactured and site-built flat-plate collectors, evacuated 

tubes, and tracking concentrating col~ectorsm These systems provide hot air, 

hot water, and steam to a variety of industrial processes. Later, ~eller 

Associates added 24 solar heating and cooling systems to their analysis, and 

the results were presented by Franta et al. (1982). 

In these studies, system costs were divided into the following nine 

categories: 

Collector array (including tracking devices, if applicable) 

Collector support structure 

~iping/ductwork (including external collector manifold material cost, 

pumps, valves, expansion tanks) 

a Insulation 

a Heating/cooling equipment (a carryover term from an earlier Mueller Associates study of solar heating and cooling systems, including special nonauxiliary equipment ) 
a Storage (including storage insulation) 

a Controls 

a Electrical 

General construction (roofing, equipment rooms, excavation, painting). 

Each category includes costs for materials, delivery, and installation 

labor. Actual costs reported by Mueller are the true year-of-construction 

costs and do not include the contractor's overhead and profit markup (OH&P), 

design costs, or costs for data acquisition and recording equipment. Normalized costs account for inflation from the year of construction to 1981 and for 

differences in contractual configurations, and include a uniform OH&P percentage for all projects. Modified costs are reported in 1981 dollars, including 

actual 1981 collector and control costs. They incorporate nominal OH&P rates 

for the general contractor (25% on bare materials and labor and 10% on subcontracts), subcontractors (15% on bare costs), and use the national average 

skilled labor rate ($14.25/h). Site-specific costs, such as those for extralong piping runs, excessive system check-out labor, collector repairs, and 

special construction, were not included in the modified costs. Modified costs 

are the most useful in terms of cost estimating, although the cost of any particular design may deviate significantly in various areas, and design costs 

themselves are not included. 

10.1.1.1 Historical System Costs 

Table 10-1 summarizes the modified costs as determined by Mueller Associates, 

Inc., for the 10 solar IPH systems that were examined in their first study. 

[Other characteristics of the systems are presented in Table 2-3- (see 

Sec. 2.3).] Subsystem costs are presented in Table 10-1 on a per unit collector area basis and also as a percentage of total system cost. Note that system costs vary considerably, and within each subcategory, large variations in 

cost are also evident. In this and the following subsections, largely 

excerpted from Franta et al. (1982), we examine the total and subsystem costs 

of the 10 IPH and 24 heating and cooling systems in more detail. Although the 

statistical analyses presented here are not based solely on solar IPH systems, 

there are so many similarities between large heating and cooling systems and 

IPH systems that certain generalizations are appropriate. 

Statistical tests show that the system's application is an important factor in 

total system cost. Of active systems, hot water systems cost the least, followed by direct air heating systems, liquid-to-air heating systems, and steamproducing systems, in that order. Unfortunately, the statistical tests did 

not indicate whether new systems were more or less expensive than retrofit 

systems, but most of the more expensive steam and cooling systems were retrofit projects. 

Total cost data were also analyzed to determine whether economies-of-scale 

effects occur. To determine whether economies of scale affected these systems, the slope of a line plotted on a graph of log system cost versus log 

collector area was used. This approach produced a slope of 0.81, significantly less than one, suggesting that economies of scale do exist. The 
Table 10-1. Modified Solar IPH Subsystem Costs 

Array Total Total Collector Support Heating/ 

Array Structure %:$ Insulation Cooling Storage Control Electrical 

solar IM system Equipment 

Construction 

Coat 

$/m2 $ /m2 $/m2 $/m2 $/m2 

($/ft2) ($/tt2) % ($I&) 

$/m2 $/m2 

($/ft2) ($/ft2) ($/ft2) ($/ft2) 

Campbell Soup 681.4 330,850 485.1 240.9 19.7 60.7 12.5 39.3 8.1 13.8 2.8 -- -- 62.7 12.8 11.0 2.3 32.5 6.7 24.7 5.1 

(7,335) (45.1) (22.4) (5.6) (3.7) (1.3) (5.8) (1.0) (3.0) (2.3) 

Gilroy Foode 552.8 307,850 556.9 297.1 53.3 58.4 10.5 82.7 14.9 31.0 5.6 8.0 1.4 -- - 36.3 6.5 22.7 4.1 20.7 3.7 

(5 950) (51.7) (27.6) (5.4) (7.7) (2.9) (0.7) (3.4) (2.1) (1.9) 

Home Laundry 603.5 750,950 1,244.3 411.1 33.1 187.7 15.2 329.5 26.5 30.1 2.4 15.0 1.2 13.3 1.0 91.0 7.3 67.7 5.4 98.0 7.9 

(6,496) (115.6) (38.2) (17.4) (30.6) (2.8) (1.4) (1.2) (8.5) (6.3) (9.2) 

Johnson & Johneon 1,070.2 809,190 756.1 307.0 40.6 104.9 13.9 112.8 14.9 20.9 2.8 -- -- 51.6 6.8 67.2 8.9 59.6 7.9 32.1 4.2 

N (11,520) (70.2) (28.5) (9.7) (10. 5) (1.9) . (4.8) (6.2) (5.5) (3 -0) Cn 

a ~a~our 214.0 130,160 608.2 195.8 32.2 95.6 15.7 193.0 31.7 7.2 1.2 -- -- 42.2 6.9 16.3 2.7 19.9 3.3 38.2 6.3 

(2,3Q4) (56.5) (18.2) (8.9) (17.9) (0.7) (3.9) (1.5) (1.9) (3.5) 

York Building 832.4 490,110 588.8 403.9 68.6 69.6 11.8 37.4 6.4 7.7 1.3 -- -- - -- 62.5 10.6 7.7 1.3 - - Produc ts (8,9601 (54.7) (37.5) (6.5) (3.5) (0.7) (5-8) (0.7) 

Average 807.6 461,019 632.0 284.4 46.6 84.0 12.5 113.5 17.1 22.1 3.7 15. 2.8 17.2 7.2 45.9 6.9 30.1 4.6 27.1 3.6 

(81 693) (58.7) (26.4) (7.81 (10.5) (2.1) (1.4) (3.5) (4 3) (2.8) (2.4) 

Source: Mueller Aeeociatee, Inc. 1980. 
largest system by far, at Lamanuzzi and Pantaleo Foods, was also the least 

expensive, possibly because of design factors rather than an economies-ofscale effect. When that data point was removed from the analysis, the 

resulting slope was 0.77, strengthening the argument for the existence of 

economies of scale. . -.~ 

An expectation of the solar community is that solar energy construction costs 

will decline as experience is gained in the design, installation, and mass 

production of solar components. Therefore, Mueller Associates tested total 

unit costs to determine whether the year in which a project was constructed 

was a significant cost factor. Since all costs were expressed in 1981 dollars, inflation was not a factor in the statistical test. Unfortunately, the 

results showed no significant evidence that costs are coming down. Similarly, 

the total unit cost data were tested to determine whether regional variations 

in labor and material costs were a cost-impacting factor. The regional cost 

factors used were taken from the city cost index for mechanical construction 

from Means Mechanical and ~lectrical- Cost Data 1981. These cost variations 

proved not to be a significant factor. 

10.1.1.2 Historical Subsystem Costs 

Collectors. Solar collectors represent one target area for cost reduction. 

Cost data for collectors, grouped according to the type of collector, show 

that site-built collectors are the least expensive, followed by liquid flat 

plates, air flat plates, evacuated tubes, and tracking collectors, in that 

order. The collector costs listed in Table 10-1 include the cost of mounting 

the collector on the support structure and the cost of connecting collectors 

to a manifold system, as well as the cost of the panels themselves. Thus, for 

example, while air flat-plate panels generally cost less than liquid ones, 

more labor is required for ductwork manifold connections than for piping manifold connections. 

Support Structures. Col ector support structure costs vary from $8.20/mL of 

collector area to $188/m 2 . Statistical tests performed by Mueller Associates 

show that the single factor that most influences support structure costs is 

whether the structure is used for functions other than supporting the collector. These additional functions may include the following: 

House equipment 

Improve system appearance 

Provide ref lectors 

Form building roof structure 

Form building waterproof membrane. 

It is generally easier for the support structures of new systems to serve multiple functions. Fewer constraints are imposed by new building conditions, 

allowing designers to use'more complex support systems. Retrofit conditions, 

however, are more constraining. Support structure data were also tested to 

determine whether ground/roof mounting, newlretrofit, and materials 
distinctions were cost factors, but they all proved not to be significant. In 

most cases, the support structure does not contribute to performance, so that 

"cheaper" could be "better" in many support structure designs . The wide variation in support structure costs certainly suggests that this subsystem can 

benefit from more cost-conscious design. 

Energy Transport Equipment. Although these subsystem categories are reported 

separately in Table 10-1, it is appropriate to combine them here because they 

all fall within the general mechanical construction category. These subsystem 

costs were statistically tested to see whether the particular IPH applications 

and the new-versus-retrofit distinction influence costs. Both proved to be 

significant cost factors. Air systems appear to be the least expensive, followed by hot water systems, liquid-to-air systems, and steam systems, in that 

order. The last is more expensive partly because of the additional heat 

exchange equipment required and because high-pressure piping must be used. 

New systems were about $50/m2 of collector area cheaper than retrofit systems 

in this subsystem category. The difficulty of fitting an energy transport 

system into an existing building raises costs. It is interesting to note that 

higher support structure costs tend to balance out the energy transport system 

cost savings in new construction. 

Storage. Because of the wide variations in storage capacity per collector 

area encountered among the projects, storage costs are expressed in Table 10-1 

in terms of storage capacity rather than collector area. Statistical tests 

showed that storage costs depend both on the type of storage vessel used and 

the location of the vessel. Unpressurfzed steel tanks were the least expensive, followed by fiberglass tanks, rock bins, and pressurized steel tanks. 

In terms of location, buried storage was least expensive, followed by exterior 

and interior storage. These costs do not include the added cost of extra 

piping on ductwork to and from buried and exterior stprage. Nevertheless, the 

results are surprising, since most estimation techniques suggest that interior 

tanks, which do not require waterproofing, would be less expensive. Storage . 

costs on the average represent only 7% of total system cost, and storage performance (particularly heat loss) has a great effect on system thermal performance. Therefore, it is important that storage subsystems be designed and 

built for optimum performance. 

Electrical Systems and Controls. Electrical systems and controls costs were 

also tested to determine whether application and new/retrofit distinctions 

were cost factors. New systems were found to be significantly less expensive 

than retrofit systems. Retrofit electrical and controls costs were about 

$30/m2 higher than those for new installations. Projects with tracking collectors tended to have higher electrical and controls costs than those that 

did not, because of the tracking system controllers and the need to wire power 

lines out to the collector array. This was one reason steam system costs were 

significantly higher in this area. Otherwise, little difference in cost 

between the applications was evident. 

10.1-103 Estimating Construction Costs Using the Wller Data 

This subsection, also excerpted from Franta et al. (1982), presents a method 

of estimating the construction cost of a solar system based on the historical 
data discussed above. However, because some of the projects no longer represent the state of the art, allowance has been made for cost data considered 

nonrepresentative. 

The engineering fee varies and is difficult to estimate. Data on engineering 

fees were not collected for the demonstration projects, but some general 

guidelines for estimating such fees for solar energy systems can be established. Engineering fees include the cost of conceptual design, detailed 

design and specifications, bid supervision and evaluations, and construction 

supervision. Designing a commercial-scale solar energy system takes at least 

three person-months , if complete detailed specifications and drawings are to 

be provided. The designer's fee increases as the solar construction contract 

size increases and as the system becomes more complex. Design costs will also 

be higher if an architect or a structural engineer is required. 

Cost-estimating manuals commonly allocate a percentage of the mechanical construction cost as an estimate of the mechanical engineer's fee, which ranges 

from 4% to 10%. In solar design, this percentage is pomewhat higher-- 

typically, 6% to 20%. Only smaller systems (less .than 100 m ) or very complex 

ones would normally be associated with engineering fees higher than 15%; only 

very large systems would entail fees less than 10%. 

Cost Estimating at the Conceptual Phase. During the conceptual phase, the 

designer needs an estimate of construction costs to perform feasibility and 

system sizing studies. At this point, the designer has, at best, a rough system design. The cost estimate can, therefore, only be approximate. 

Table 10-2 is a guideline for making "f irst-pass" estimates for the feasibility and sizing analysis. The table lists the various subsystems that make up 

a solar energy system, the design categories for that subsystem, the range of 

costs that might be expected, and what the authors consider to be 3 typical 

cost. Note that all costs are expressed in either 1981 dollars/m of net 

aperture collector area or as 1981 dollars/liter or thousand kilograms of 

rocks, for the storage subsystem. No value is given for a fixed-cost component of the total system, because statistical tests of the demonstration proj- 2 ects' costs suggest that, for large systems 030 m ), this cost component is 

too small. System costs can be described accurately solely as a variable cost 

per collector area. 

To use the table to arrive at a total system cost estimate, add the typical 

subsystem costs associated with each appropriate design category. Use the 

ranges with your own judgment. For example, if you anticipate that an expensive support structure will be required because of roof structure design constraints, or if long piping runs will be required, then use values from the 

upper end of the ranges for the support structure and energy transport subsystems. However, try to avoid being too optimistic or pessimistic in choosing 

values. Table 10-3 describes in detail the sort of design factors to consider 

in selecting cost values from the ranges provided. 

Because a significant economies-of-scale effect is seen among the demonstration projects, the preliminary cost estimates should be adjusted by an economies-of-scale factor. Figure 10-1 has been provided for that purpose. To use 

the figure, simply find the appropriate collector area, read up to the curve, 

and read over to the economies-of-scale factor. Then, multiply the total cost 

estimate by that factor. 
Table 10-2. Conceptual Phase Cost Esttmating Guide 

(Includes materials, labor, contractor's 

overhead and profit fn 1981 dollars) 

Subsystem Category Cost Typical 

Range Cost Units 

Collector array Site-built 65-130 110 

~iqufd flat plate 130-215 

Air flat plate 150-250 

Evacuated tubes 260-325 300 

Tracking concentrator 215-430 32 5 

Support Single functton 30-160 95 1 $/m2 

structure Mu1 t iple functions 75-270 160 collector area 

Storage (air) Rock bin 110-220 150 1 $11000 kg rocks 

L 

- - - - - - - - . -- - 

Electrical and Hot water 20- 55 

controls Liquid-to-air heat 30- 95 

Air heating 20- 85 

Steam 20-195 

Heating and Coollng 45-215 

Energy Hot water 85-185 150 

transport Liquid-to-air heat 170-325 235 

- - 

General N/A 

construction 

$/m2 

0-160 

collector area 

Air heating 55-195 110 ) collector area 

Steam 110-325 195 

Heating and cooling 215-540 375 

Storage Unpressurized s tee1 0.23-0.77 

(liquid) tank 

Pressurized steel 0.53-1.80 ,::: I $,liter 

tank 

Fiberglass tank 0.45-0.66 0.53 - 

. - - - - - -- - - - 

Source: Mueller 1981. 

Cost Estimating Ikuring the Design Phase. As the designer actually performs 

the detailed desigq work, he or she constantly makes decisions that will 

affect the project's construction cost. Many of these decisions involve cost/ 

performance trade-offs; for example, using higher efficiency collector panels 

will improve thermal performance but may also increase costs. An analysis of 

cost/performance trade-offs frequently need only consider "differential" costs 

of the more expensive options and incremental energy output additions that 

they provide. Other decislons may not a£ fect thernal performance as much; for 

example, support structure design. By maintaining an attitude of cost consciousness and applying value engineering concepts, the designer helps to keep 
Table 10-3. Design Cost Factors 

Subsys tem Cost Factor Comments 

Collector Manif old type Internally manifolded collectors cost about the same 

array as externally manifolded collectors, but require less 

than half the labor to connect. 

Panel size 

Support Roof-imposed 

structure . structural 

constraints 

Larger panels may require less labor per collector 

area for mounting and connection. 

In some retrofit situations, the support structure 

must span large distances, requiring larger, more 

expensive structural members. 

Flat/sloped roof In general, support structures for sloped roofs 

require less material and labor. 

Number of penetrations Roof penetrations are expensive and should be kept to 

through roof membrane a minlmum. 

Reflectors Reflectors add materials costs. 

Esthetic constraints "Cosmetic" details for support structures add significantly to costs. 

Energy Long pipelduct runs Long runs to and from an isolated collector array or 

transport storage vessel add to materials and labor costs. 

Freeze protection Direct systems are probably less expensive. The type 

and size of heat exchanger used in an indirect system 

can affect energy transport costs significantly. 

Complexity/number of Obviously, the simpler the system, the greater the 

modes opportunity for cost savings. 

Storage Size The most important cost factor is size--the storage 

capacity per collector area. 

Electrical Number of modeslnumber The more complex the control system, the higher the 

and of actuators cost. 

controls 

Monitoring equipment Instrumentation- and performance-monitoring equipment 

can be very expensive. 

construction costs down. See also Table 10-3 for some of the design-related 

factors that impact construction costs. These factors can be useful to 

designers in two ways. First, they can help designers decide when to use the 

values in the range column in Table 10-2, to thereby refine the initial cost 

estimate at the same time that the initial conceptual design is refined. Second, the list -may help designers maintain an attitude of cost-consciousness. 

While this list is by no means complete, these factors are among the more 

important cost-impacting decisions that designers face. 

Cost Estimating in the Post-Design Phase. After the system has been designed, 

complete with drawings and specifications, a detailed cost estimate (or takeoff) is normally prepared by' the bidder or by the contractors who will bid on 

the project. The take-off allows the contractor to submit a bid that provides 

a reasonable profit over his costs without jeopardizing his chances of winning 

the bid. Often, the designer will also prepare a cost estimate, although this 

estimate is usually less detailed than the contractor's. This design estimate 

can be useful in assessing the bids. If all the bids are much higher than the 

estimate, perhaps additional contractors should be invited to bid. If the 

lowest bid is much lower than the estimate, perhaps the contractor's ability 

to perform should be questioned. 

Contractors differ in the processes they use to prepare the take-off, but the 

following description represents what normally happens. First, the contractor 

looks at the design drawings, reads the specifications, and formulates a construction plan as a series of tasks. He then prices the major components by 

contacting suppliers and subcontractors. He then estimates the material and 

labor cost required to complete each task. He will obtain estimates or firm 

bids from any subcontractors he plans to use on the job. He will then add his 

overhead and profit rate and a contingency to arrive at a bid value. The 

labor and material cost estimates are often obtained from cost estimating manuals, although many contractors rely instead on cost data compiled from their 

own previous experience. However, these are generally insufficient in themselves for preparing a detailed take-off for a solar construction job. 

Table 10-4 provides additional cost information for the following solar construction tasks: 

Collector panel mounting--labor 

Collector array manifold-labor 

Support structure--labor and materials 

Rock bin storage--labor and materials. 

The table format is similar to that found in cost-estimating manuals. 

Non-Design-Related Cost Factors. Some of the factors that are not directly 

related to system design but that may affect system cost are listed below: 

Number of bidders for the construction contract. Substantial cost 

decreases can almost be ensured by inviting a large number of contractors 

to bid. 
Table 10-4. Cost Estimating Guide 

Mat er fa1 Labor Labor Total Total 

($) ($) (hours) ($1 (incl. sub. 

OH&P) ($) 

Item 

Mount and connect 9.70 10.80 1 1 20.50 25.30 

collector panels (not 

including cost of panels)a 

For air collectors, 

add : 0.00 10.80 1.1 10.80. 13.50 

For tracking collectors, 

add : 10.80 5.40 0.54 16.20 19.90 

For external manif old, 

add : 0 . 00 15.10 1.1 15.10 18.80 

Collector support 

structurea 

Maximum : 

Minimum: 

For ref lectors, 

add : 

For multiple functions, 

add : 

For sloped roof, 

add : 

Rock binb 

Maximum : 

Minimum: 

a~osts are per m2 - of collector area. 

b~osts are per 1000 kg of rocks. 
Number of contractors in area/general economic conditions. Contract bid 

values are sensitive to the laws of supply and demand. Contract bids 

will be lower if there are many contractors and little current construction in the area. The converse is also true. 

Transportation requirements. Transportation of materials to an isolated 

site may boost material costs. 

Time constraints. A 'tight completion deadline may require the use of 

overtime labor and boost labor cost. 

Material delivery delays. Construction schedules may be interrupted if 

delivery of important materials and equipment must be delayed which leads 

to increased costs. 

Weather/season. Inclement weather may interrupt construction schedules. Labor productivity may be reduced during cold winters and hot summer s. 

Regional variations in labor and material costs. While this was not a 

significant factor in the demonstration projects, costs for a particular 

project may be affected by variations in local costs. 

Legal restrictions. Local building code restrictions and local union 

regulations may affect system cost. 

Contingency. The contingency allowance added to the contractor's bid 

depends heavily on the extent and nature of the contractor's experience 

with solar and government projects. 

In-house construction supervision versus construction management versus 

general contractor. Exploring the various contractual arrangements possible for the solar system construction can sometimes help reduce total 

construction cost. 

Example of Cost EstimatinrFairfield. The Fairfield solar energy system was 

designed in 1979 and 1980 and constructed in 1980. The system provides hot 

water for a nursing care facility. The solar energy system was retrofit onto 

the existing building, but the original roof was constructed with steel tubing 

stub-ups so that a solar collector support structure could be added more 

easily later on. Early in the design phase, the following design parameters 

were determined: 

Collectors. There was room for 144 liquid flat-plate collectors. 

Support structure. The stub-ups would enable a lightweight, steel support structure to be constructed relatively inexpensively. 

Energy transport. Freeze protection would use a glycol solution in the 

collector loop, separated from the rest of the system by a heat 

exchanger. A relatively long piping run would be required to connect the 

collector array to the mechanical room. 

Storage. A pressurized steel tank with a capacity of about 18,900 L 

(5000 gal) would be used. 
At this point, a preliminary cost estimate can be prepared using the values in 

Table 10-2, as follows: 

Collector area: 144 pan Is x 1.8 m /panel 5 4 = 268 m2 

Collector array: $160/m x 268 m = $ 42,850 

Support *structure: $65/m2 x 268 m2 = 17,420 

(A figure from the lower end of the range 

would be used because of the stub-ups.) 

Energy transport: $170/m2 x 268 m2 

(A figure from the high end of the range would be 

used because of the long pipe runs.) 

Storage: $0.771~ x 18,900 L = 14,550 

Electrical system and contro : $30/$ x 268 m2 = 8,040 

General construction: $45/m3 x 268 m = 12,060 

Total $140,480 

This totas is then multiplied by the economies-of-scale factor from Pig. 10-1 

for 268 m , or 1.16, to arrive at a total estimated construction cost of 

$163,000. In the detailed design phase, the design was finalized with the 

following changes : 

2 a The collectors selected had a net aperture area of 1.719 m (18.50 ft 

(2,664 ft ). 

per pane3 for a total net aperture area of 1.719 x 144 = 247.5 m 

a The storage tank selected had a capacity of 15,140 L (4000 gal). 

Using these final figures, a total construction cost estimate could be calculated as follows.: 

Collector array: $160/m~~x 247.5 m2 = $ 39,600 

Support structure: $65/m x 247.5 m2 

2 = 16,088 

Energy transport: $170/m2 x 247.5 m = 42,075 

Storage: $0.77/L x 15,140 L = 11,658 

Electrical system and contro s: $30/m2 x 247 .5 m2 = 7,425 8 General construction: $45/m x 247.5 m2 = 11,138 

Total $127,984 

This value would the2 be multiplied by the economies-of-scale factor from 

Fig. 10-1 for 247.5 m , or 1.18, for a total estimated construction cost of 

$151,000* 

10.1.2 Modular Cost Estiaatinpr 

Modular cost estimating (Guthrie 1969) calculates total system costs using a 

number of multiplicative factors applied to FOB cost. The procedure used in 
ECONMAT (Stadjuhar 1982) is diagrammed in Fig. 10-2, and the various factors 

that are applied are defined in Table 10-5. 

To begin, the collector FOB cost is multiplied by CAMAT to arrive at the cost 

of auxiliary materials for the collector array. This cost is added to the 

collector cost- to get the collector array materials cost. The collector array 

materials cost is then multiplied by PIMAT to obtain the cost of process 

interface materials. The sum of the materials costs are multiplied by ED0 and 

FRTTAX to obtain estimates of engineering design, offices, freight, and tax 

costs, which are the indirect costs for the system. Separately, the collector 

array and process interface materials costs are multiplied by CALAB and PILAB, 

respectively, to estimate labor costs for installation of the array and interface equipment. These labor costs are multiplied by COVRHD to compute the 

construction overhead, which is added to the indirect costs previously calculated. Adding the materials and labor costs for the collector array and the 

process interface yields the total direct costs for the system. Finally, the 

sum of the direct and indirect costs is multiplied in turn by CNTG and FEE to 

obtain contingency cost estimates and the contractor's fee. Adding these cost 

components to the sum of the direct and indirect costs produces the estimated 

total system cost. 

Certain values, based on data from previously built systems, are recommended 

for the parameters in Table 10-5; some depend on the collector type and others 

on the system type. These values are given in Table 10-6. Although the modular cost es timating method is usually accurate to within f 20%, because historical solar system cost data are limited, we cannot justify more than a 230% 

accuracy for solar IPH systems. 

10-2 LIFE-CYCLE COST ANALYSIS 

There are a number of methods to evaluate the economic feasibility of a solar 

IPH system. An important consideration, in addition to the performance of the 

system itself, is the cost of the conventional fuel that the solar system displaces. Thus, solar systems may be proposed for areas where sunlight is not 

plentiful but conventional fuels, like oil or natural gas, for example, are 

expensive or face curtailments in supplies. 

The most popular methods of evaluating economic feasibility include net present value, payback, and internal .rate of return. The simple payback method 

does not accurately reflect the profitability of an investment because it does 

not account for cash flows after the payback period. It is often used, 

though, to make initial estimates as to the value of an investment, particularly during uncertain economic times. The internal rate of return required 

of a solar investment is that rate of return giving a levelized (or 

annualized) cost of solar energy equal to the levelized cost of conventional 

fuel. The levelizing technique expresses annual required revenue as an equivalent constant revenue payable each year in current-year dollars. The method, 

proposed by Dickinson and Brown (1979), can be summarized as follows 

(Stadjuhar 1982): 

Table 10-5. Factor Definitions for Modular Cost Estimating 

CAMAT - Ratio of auxiliary collector array materials cost to collector FOB 

cost for each collector type. Auxiliary collector array materials 

iilclude controls, supports, foundation, field piping insulation, etc. 

CAW - Ratio of collector array installation cost to total collector array 

materials for each collector type. Includes all installation labor 

for collector field construction. 

PIMAT - Ratio of process interface materials to total collector array materials for each system type. Includes heat exchangers, boilers, and 

other materials. 

PILAB - Ratio of process interface installation to process interface materials for each system type. 

ED0 - Ratio of engineering design and office costs to total (collector 

array plus process interface) material cost. 

FRTTAX - Ratio of freight and taxes to total material cost. 

COVREID - Ratio of construction overhead to total labor cost. 

CNTG - Ratio of contingency to total direct and indirect costs. 

FEE - Ratio of contractor fee to total direct and indirect costs. 

Source: Stadjuhar 1982. 

Table 10-6a. Recommended Values for Modular Factors 

(Collector-dependent values) 

Flat Evacuated CPC Parabolic Parabolic 

Plate Tube Trough Dish 

Source: Stadjuhar 1982. 
Table 10-6b. Reccnmended Values for Modular Factors 

(System-dependent values) 

Hot Water Aot Air Steam 

Flash Unf ired Direct Indirect Direct Indirect Boiler Boiler 

- -- 

Source: Stadjuhar 1982. 

Calculate the levelized price of the conventional fuel, including the 

effects of fuel escalation and fuel utilization efficiency. 

a Calculate the levelized price of solar energy. 

- Calculate the initial capital investment for the solar system using 

modular cost estimating or some other technique and adding land costs, 

if any. 

- Calculate the annual energy delivered by the system. 

- Calculate the annual energy capacity cost: 

Capacity cost .= Capital cost $ 

Annual energy delivered 'G3/yr 

- Calculate the M-factor (Dickinson and Brotin 1981), where M is the 

single levelizing factor incorporating the effects of annual operation, maintenance, property, and insurance costs (OMPX), composite 

(federal and state) income tax rate, investment tax credit, depreciation, and required market discount rate (or rate of return) over the 

project lifetime. 

- The levelized price of solar energy is the product of the M-factor and 

the annual energy capacity cost of the solar system: 

Levelized price of solar energy = M x capacity cost . 

The internal (or project) rate of return of the solar system is that rate 

of return (or discount factor) for which the levelized price of solar 

energy is equivalent to the levelized price of the conventional fuel. 

This is the annual after-tax rate of return on the unamortized equity 

investment and does not imply or require reinvestment (Stemole 1974, 

p. 57). 

To calculate the required levelizing factors, use the capital recovery 

factor. It is defined as 
si?l + TR-1356 

where 

R = internal rate of return or discount rate 

N = the number of years covered by the analysis, usually taken as the 

system lifetime. 

The capital recovery factor represents the constant revenue (or payment) 

required each year for N years for each dollar of capital invested (or debt 

owed) today. Values of CRF for various values of R and N are given in 

Table 10-7. 

Table 10-7. Values of Capital Recovery Factor 
The levelized price of conventional fuel can be calculated by 

where . -. 

Pfo = the fuel price in the year zero 

LF = the levelizing factor, a function of the assumed total fuel cost 

inflation rate g' (includes the general inflation rate), the system life N, and the discount rate R. 

Defining 

the levelizing factor is given by* 

Some sample values of LF for several values of g', R, and N are given in 

Table 10-8. 

Some elaboration is warranted here on the concept of "capacity cost." .Up to 

this point, solar IPH system costs have been discussed in terms of total 

installed cost per unit of collector aperture area, a figure that is convenient for estimating the Investment but does not reflect the energy benefit. 

The capacity cost, however, defined as the investment I divided by the annual 

energy delivery from the solar system Es, represents the investment required 

to purchase one GJ (or MBtu) of annual energy output and is similar in meaning 

to other common capacity costs (e-g., $/kwe for conventional electric power 

plants). 

*This formulation of LF assumes that g' is constant. If a variable fuel 

inflation rate is desired, where gt is the rate in year t, then the levelizing 

factor is 
Table 10-8. Values of the Tevelizing Factor Zdir to Convert a ZeroYear Fuel Rice to a Levelized Price Over N Years 

Fuel Escalation Market ROR Rll 

Rate g' (x)~ R(X) (%) CRF(R,N) CRF(R1",N) LF 

Source: Dickinson and Brown 1981. 

a~his is an overall escalation rate including general inflation. If 

the general inflation rate is g and the differential fuel escalation rate is e, the overall fuel escalation rate g' is given by 

1 + g' = (1 + g)(l + e). 

The levelizing factor M for solar energy is defined by Dickinson and 

Brown (1981) as 

--- Tc T DEP +(a)tc m(tC)(l - TC -T DEP) l+R 
This equation is derived from an expression that can be solved for the 

levelized required revenue for the solar energy system Cs that includes the 

following terms: 

C, = expenses + loan repayment + r (C, - expenses - depreciation - loan 

interest) + equity repayment - investment tax credit + major 

replacement costs - net salvage value, 

where T is the marginal composite (state plus federal) income tax rate. 

The terms in the equation for M are defined in the list of economic terms at 

the front of this handbook. Multiplying M by the capacity cost of the system, 

the levelized price P, of solar energy is 

- 

Some values of M for various combinations of OMPI,, tax credits, loan fraction, loan interest rate, system lifetime, depreciation period, and required 

rate of return on investment are listed in Table 10-9. A simplified form of 

the equation for M is valid for cash investments (no loan) where no major 

replacement costs occur and salvage value is negligible (Brown et al. 1980): 

In comparing Ps and Pf, we should remember that a unit of energy provided by 

the solar system may displace more than a unit of conventional energy when 

boiler or burner efficiencies , stack losses, and other factors are involved. 

Defining a solar effecttveness factor E as 

E = fuel energy saved by solar system 

solar energy delivered 9 

we find that P should be compared with s Pf for meaningful interpretations 

of this economL evaluation. Except in very unusual process arrangements, s 

is ordinarily the reciprocal of full-load boiler efficiency. Effects of variable boiler efficiency on E are, however, actually very small, as shown in 

Appendix A. 

The rate of return R that satisfies the expression 

will be the required internal rate of return (.IROR) for the solar system. 

This quantity generally indicates the profitability of a new endeavor. A 

graphical solution to Eq. 10-10 is very informative and is recommended. An 
Table 10-9a. Values of ac actor^ 

(R = 0.10) 

OMPIO + 

f (Loan 

Fractton) DP(yr) + 

Add to 

above for: 

m(t - -- 0.017 0.020 -- 0.017 0.020 -- 0.013 0.016 -- 0.013 0.016 -- 0.005 0.008 -- 0.005 0.008 

0.55(10) 

S p 0.20 -0.045 -0.022 -0.022 -0.045 -0.022 -0.022 -0.045 -0.022 -0.022 -0.045 -0.022 -0.022 -0.045 -0.022 -0.022 -0.045 -0.022 -0.022 

'~ixed parameters: g - 6X, T - SOX, SOYD depreciation, LP - 10 yr (for N - 10 yr), LP - 20 yr (for N - 20 yr), m(tc) - 0, and S - 0. 

Source: Dickinaon and Brown 1979. 

c7 
Table 10-9b- Values of ac actor^ 

(R = 0.15) 

OMPIO + 0.01 0.04 0.01 0.04 0.01 0.04 

f (Loan 

Fraction) DP(yr) + 7 16 7 16 7 16 7 16 7 16 7 16 

- 

N(yr) + 10 20 20 10 20 20 10 20 20 10 20 20 10 20 20 10 20 20 

Add to 

above for: 

'~ixed parametere: g - 6%, T - 50%, SOYD depreciation, LP - 10 yr (for N - 10 yr), LP - 20 yr (far N 1 20 yr), m(tc) - 0, and S = 0. 

Source: Dickinson and Brown 1979. 
Table 10-9c. Values of If-l7actora 

(R = 0.20) 

TC + 0.2 0.3 0.5 

OHPIO + 0.01 0.04 0.01 0.04 0.01 0.04 

f (Loan 

Fraction) DP(yr) + 7 16 7 16 7 16 7 16 7 

- 

16 7 16 

N(yr) + 10 20 20 10 20 20 10 20 20 10 20 20 10 20 20 10 20 20 

Add to 

above for: 

'Fixed parameters: g - 6%, T = 50%, SOYD depreciation, LP - 10 yr (for N - 10 yr), LP - 20 yr (for N - 20 yr), m(tc) - 0, and S - 0. 

Source: Dickinson and Brown 1979. 
example of such a solution is presented in Fig. 10-3, and shows both the rapid 

increase in IROR as the loan fraction is increased and the sensitivity of IROR 

to the assumed fuel cost inflation rate. 

This section presents three financing methods for solar IPH systems, taken 

lareelv from the Proceedinns of the 1980 Solar Industrial Process Heat Conference, particularly from the- paper by Dickinson (1980). The first is the 

conventional method, in which the IPH user finances the system from in-house 

capital or loans. Second, conventional lease financing is discussed. 

Finally, we present the Solar Management Company (SMC) concept for financing 

solar IPH projects. 

10.3.1 Conventional Financing 

The usual assumption, in analyses of solar economics, is that the solar system 

will be conventionally financed. In this method of financing, the solar IPH 

user purchases the system using internal capital and funds obtained from 

external sources, such as front loans or the sale of bonds. This financing 

method is simple, but it has some drawbacks. For example, the IPH user is 

responsible for the construction and operation of the solar system, which 

might entail some risk to the company. 

10.3.2 Conventional Iease Arrangements 

Leasing is an option that eliminates the need for owners to make the large 

initial capital investment required by conventional financing. It can also 

reduce the risk to IPH users, usually because the responsibility for 

constructing and operating the solar system rests with a third party and 

because payments are constant over the lease period. Lease payments, being 

expense items, axe also tax deductible to users. Lessors, however, may be 

able to take advantage of an accelerated depreciation allowance that users, 

if they owned the system themselves, could not. 

10.3.3 Solar Management Company/Lim.ited PartnersMp 

This concept, proposed by Charles Wilde of Winthrop Financial Co. 

(San Francisco, Calif. ) is similar to methods of financing large construction 

projects like shopping centers and commercial buildings, oil and gas development programs, and other projects in the real estate and equipment industries. In this system, an agency, the Solar Management Company (SMC), enters 

into partnerships with groups of investors, each group being concerned with a 

particular solar IPH project . The investors, as limited partners, provide the 

equity part of the investment and participate in any income or losses from the 

project. They also obtain the tax credits and other advantages from the 

investment. The SMC acts as the general partner. The partnership owns the 

solar system and is responsible for its construction, operation, and maintenance. In turn, the IPH user agrees to purchase a11 energy delivered by the 

solar system at stipulated rates less than those expected for the competing 

fossil fuel. 

It is important to note that the concepts of project financing are complicated 

by an abundance of tax legislation. It is recommended that a reputable tax 

accountant- be -consulted before embarking on any innovative financing arrangements. More information on financing alternatives can be found in Nevitt 

(1979) 

Brown, K. Cm et al. 1980 (Jan.). End-Use Matching for Solar Industrial Process Heat. SERI/TR-~~-O~I. Golden, CO: Solar Energy Research Institute. 

Dickinson, W. C. 1980 (Dec.) . "The Role of Financing in the Marketability of 

Capital Intensive Solar Technologies for Industry." Proceedings of the 

Fifth Annual Solar Industrial Process Heat Conference. SER1/CP-632-952. 

Golden, CO: Solar Energy Research Institute; pp. 41-46. 

Dickinson, W. C. ; Brown, K. C. 1981 (11 Aug.). Economic Analysis of Solar 

Zndustrial Process Heat Systems. UCRL-52814, Rev. 1. Livermore, CA: 

Lawrense Livermore National Laboratory. 

Franta, G. E. 1981 (June). Solar Design Workbook. SERI/SP-62-308 .. Golden, 

CO: Solar Energy Research Institute. 

Guthrie, K. M. 1969 (24 Mar.). "Capital Cost Estimating." Chemical Engineering. pp. 114-133. 

Means Mechanical and Electrical Cost Data 1981. Robert Snow Means Company, 

Inc., Kingston, MA. 

Mueller Associates, Inc. 1981 (3 Aug.). Solar Energy System Construction 

Costs. Draft report 81-183. 

Mueller Associates, Inc. 1980 (12 Dec.) . The Analysis of Construction Costs 

of Ten Industrial Process Heat Systems. MU Report No. 210; MAI Project 

No. 80-168. 

Nevitt, P. R. 1979. Project Financing. London: Euromoney Publications. 

Stad juhar, S. 1982 (Feb.) . PROSYS/ECONMAT Users' Guide - Solar Industrial 

Process Heat Feasibility Evaluation. ~E~I/T~-733-724. Golden, CO: Solar 

Energy Research Institute. 

SECTION 11.0 

SAFE= BND ENVIROHMENTBI, ISSUES 

Solar IPH. systems call for many of the same safety measures as other industrial thermal systems. Some are unique to solar energy systems, however, and 

must be recognized and dealt with in the design phase. Solar energy systems 

are generally regarded as environmentally benign because they do not have 

smokestacks, they do not discharge toxic substances, and they do not have a 

direct impact on land or on plants and animals. While solar systems lack such 

obvious indications of environmental degradation, they do have impacts, both 

positive and negative, on their environments. In designing these systems, it 

is necessary to assess these environmental effects so that their acceptability 

to plant management and to local, state, and federal agencies may be determined. This section addresses safety and environmental issues that pertain 

particularly to solar IPH. A summary of laws and agencies created to ensure 

that energy systems will be operated safely and in accordance with environmental quality constraints has also been included. We have tried to cover all 

the relevant laws and agencies in this section; however, detailed questions on 

specific requirements should be referred either to a lawyer or to an appropriate agency. 

The philosophy behind solar energy system safety is that systems should be 

designed, built, and operated without creating additional hazards greater than 

those that already exist without the solar system. The major safety concerns 

in solar systems fall into six categories: fire safety, physical hazards, 

handling and disposal of hazardous fluids, overtemperature and overpressure 

protection, product contamination, and noise. Each of these is discussed in 

the following sections, and the regulations and governmental agencies involved 

in enforcing the safety requirements are described. 

111 Fire Safety 

There is a definite need for fire prevention and control measures in solar 

systems, for several reasons. Heat transfer fluids are often flammable or 

produce flammable products when they decompose. Sunlight, especially when it 

is concentrated, can heat exposed surfaces to very high temperatures, and this 

can result in degradation, outgassing, or ignition. Storage tanks are usually 

filled with hot, sometimes hazardous, fluids. To reduce risk to personnel and 

equipment and lessen the damage from a fire if one should occur, we must 

address two aspects of fire safety: (1) the materials used in solar systems 

and (2) the equipment and procedures necessary for fire protection. 

11.11 Materials 

The most important solar IPH materials to consider in regard to fire protection are the heat transfer fluids used in the systems. This is especially 
true in steam systems that employ an unfired boiler, where fluids may be under 

pressure at temperatures well above their flash points, so that leaks could 

pose severe fire hazards. The National Fire Protection Association (NFPA) 

(1973) defines flammable liquids as those with flash points below 37.8'~ 

(100'~) and combustible liquids as those with flash points of 37.8'~ (100'~) 

or higher, The Minimum Property Standards published by the Department of 

Housing and Urban Development (HUD) for solar heating and hot water systems 

prohibits the use of flammable liquids in solar systems and restricts the use 

of combustible liquids to temperatures well below their flash points (1976). 

This type of restriction is, however, not always possible in IPH systems 

because of the high temperatures involved. In IPH systems, while it is best 

to use fluids below their flash points, other factors may be decisive in the 

selection of a fluid, such as its vapor pressure characteristics or whether it 

can be pumped at low temperatures. Heat transfer fluids of interest in solar 

IPH systems are discussed in Sec. 7.2 and their properties are summarized in 

Appendix B. 

In addition to the direct hazard posed by combustible fluids, fire hazards may 

occur from exposure of heat transfer fluids or insulation materials to high 

temperatures, resulting in degradation or ignition. The flammability and 

flame-spread characteristics of insulating materials in a solar system should 

be considered, particularly when they are used in conjunction with a combustible working fluid. This is especially important in regard to fibrous insulation materials, where leaks may soak the insulation, making a large surface 

area subject to oxidation. The relevant properties of some popular insulating 

materials are given in Table 11-1. 

Solar system components and structures must have adequate fire-retardant properties. The system design must avoid exposing flammable materials to elevated 

temperatures and to concentrated sunlight. In designing for the second of 

these, it is necessary to consider that solar energy can be focused off the 

ends of parabolic troughs onto support structures, flex hoses, etc. and can be 

focused at locations other than the absorber tube if the array is not tracking 

the sun properly. Adding collectors on roof structures may result in additional fire hazards because access becomes more difficult. Finally, lightning 

protection should be provided to all parts of the system to reduce the risk of 

fire from that source. 

11.1.1.2 Equipment and Procedures 

Fire safety equipment can prevent a considerable amount of damage in the event 

of a fire. One item highly recommended is a total system "kill switch" that 

will shut off collector flow and defocus or stow concentrators in the event of 

an emergency. This minimizes damage by cutting off the supply of fuel to a 

fire (the heat transfer fluid) and removing the concentrated sunlight that may 

be the heat source for the fire (in concentrators). Placing appropriate firefighting equipment at various locations around the system is recommended so 

that small fires can be extinguished immediately. Finally, the fire hazard 

from storage tanks containing combustible liquids may be reduced by placing a 

berm around the tank to contain leaks and keep a fire from spreading. 

Procedures must also be set up for fire prevention and control. Plant personnel should be trained in using fire safety equipment, and drills should be 
Table 11-1. Fire-Resistance Properties of Various Insulating Materials -. 

Approximate Water Vapor 

General Specific Fire- Flame Fuel Moisture Smoke Toxic Cases Temperature Permeability Absorbtion 

Types Types Ilesistancea spreadb contributedb ~eveloped~ Emitted Limite 

(OC) [kp,/(!tlfim)l (X by volume) 

Cellular plastic Extruded C 5-25 5-80 10-400 Yea(C0) 7 5 0.6-1.3 1 

polystyrene 

Molded C <2 5 5-80 10-400 Yes(C0) 7 5 0.9-4.4 2 

polystyrene 

Polyurethane C 30-50 14-25 116-233 Yes(C0) 110 1.7-4.4 Negligible 

Polyiaocyanurate C 2 5 0-5 55-200 Yes(C0) 120 2.9-4.4 Negliqble 

Urea-formaldehyde C 0-25 0-30 0-10 --C 215 6.6-146 -- 

Glass 

Looee fill 

Fiberglass bolts NC 15-20 5-15 0-20 Yes 540 146 0.1-0.2 

Glass foam NC 5 0 0 Yes(C0, E2S) 480 0 Negligible 

Vemiculi te 

Perlite 

Cellulose 

NC 0 0 0 No 540 High 0 

NC 0 0 0 No 650 High Low 

C 15-40. 0-40 0-45 Vsa(C0) High 5-20 

Miscellaneoua Mineral wool NC 15 0 0 No 1000 >I46 2 

Calcium silicate NC 0 0 0 No 816 0 Negligible 

Ineulating concrete NC 0 0 0 No 540 Varies 

SOURCE: Adapted from Versar (1979) and Hees (1979). 

a~~~ E-136, C = combustible, NC - noncombuetible. 

'NO more toxic than burning wood. 

d0.2 to 0.4 depending on relative humidity, up to 46% by immersion. 
scheduled to ensure that correct procedures are known. The system should be 

designed so that the collector array is accessible and fire-fighting equipment 

is nearby, and egress paths should be available for plant personnel from all 

sites of possible trouble. It is recommended that the system design be 

reviewed for fire safety by the factory's insurance carrier. Finally, local 

fire departments should be made aware of the nature of fire hazards associated 

with the solar system. An inspection by fire prevention experts is also recommended to identify potential problems. 

11.1.2 Physical Hazards 

The most obvious physical hazards associated with solar systems involve high 

temperatures and concentrated sunlight. Because the hot absorbing surface on 

a solar collector must be exposed to sunlight, it cannot be covered with insulation. Although protecting personnel from accidental burns is difficult, 

warning labels and personnel training are the most effective approaches. Sunlight, either reflected off glazings or concentrated by reflectors or lenses, 

can cause a range of problems from annoyance to severe injury. Regular sunglasses may not provide adequate vision protection against this hazard. Sunlight is even more difficult to protect against than hot surfaces, because 

sunlight can be concentrated at a point in space that is not near any physical 

object; therefore, the danger is almost impossible to detect before an injury 

occurs. 

Scalding from hot fluid leaks can also occur. This danger is aggravated by 

the large amount of piping present in most solar systems, so that there are 

more joints, flex hoses, and other materials that can leak. A perimeter fence 

installed around a ground-mounted collector array will not only enhance 

safety, but will also serve to deter vandalism. Of course, the advantages 

must be weighed against the cost. 

The glazing on solar collectors is another source of hazards. Glare from 

poorly placed arrays can annoy personnel and contribute to accidents if . it 

should temporarily blind machine operators and drivers. In collectors glazed 

with glass, hazards arise from sharp fragments if the glazings are broken by 

impact or thermal shock or if they are in a position where personnel may fall 

through them. Falling on the glazings, and thereby coming into contact with 

the absorber plate, could cause burns. 

Physical hazards may also emanate from the structural design of a solar energy 

system. Wind loads on support structures and collectors must be considered to 

avoid the possibility of parts blowing free in strong winds. Static loads, 

such as the buildup of snow between collectors in a sawtooth array, should be 

considered in design to reduce chances 0.5 breakage, leakage, and overstressing 

of components. Collectors are normally tilted at fairly high angles and have 

smooth surfaces. They also heat up rapidly so that snow and ice tend to fall 

off suddenly; this can be a problem with an overhead array under which people 

may walk . Finally, the hazards associated with maintenance of solar systems also include 

glare, possible burns and cuts from glazings, and concentrated sunlight. Protective measures like handrails and lifelines can reduce in juries, and lock- 
out switches can be used to keep trackers or circulating pumps from operating 

while maintenance is being performed. An additional hazard from high temperatures and high pressures may result from stagnation of flat-plate or evacuated-tube collectors, or if an emergency causes a tracker to remain focused on 

the sun with no flow and maintenance work is attempted. 

11.1.3 Fluid Todcitp Considerations 

Safety problems related to hazardous fluids in solar energy systems nearly 

always involve the heat transferfluids used in the system. Water is used 

extensively for low-temperature applications, but because of its vapor pressure characteristics, other fluids are often used for high-temperature applications. Even in low-temperature systems, however, water is often made toxic 

when antifreeze agents, rust inhibitors, or biocides are added. Thus, the 

problems associated with hazardous working fluids are not restricted to hightemperature systems. 

The hazards involved in dealing with toxic materials are greatly reduced if 

the toxicity of the material is known, but this can be difficult, For 

example, it was noted that additives which make a fluid suitable for a solar 

system may also make that fluid toxic; this can be a problem if personnel are 

not aware that the additives are there or that they might be dangerous. For 

many solar fluids, the toxicity is not well-documented to begin with,* and in 

the environment of a solar system, many processes can work together to create 

toxicity in even the most innocuous fluids. For example, exposing fluids to 

high temperatures and pressures can cause them to break down chemically. This 

degradation can in turn create toxi; substances or toxic or flammable fumes 

that could escape from the system and cause injury. 

Bacterial and fungal growth may occur in low-temperature projects, posing dangers of disease, blocked flow, or product contamination. Many harmless materials may become toxic when brought into contact with products of corrosion 

from copper piping or surface coatings on alainum collector 'panels. Toxic 

products of combustion may be released from.fires. Even in the most carefully 

controlled system, mistakes may be made in which contaminants are inadvertently added to the system. Only by constant monitoring and maintenance of 

solar system fluids and proper labelling of all fill locations can most of 

these problems be eliainated. 

1.14 Protection from Overtemperature and Overpressure 

Solar energy systems are different from conventional systems in that if the 

energy they can deliver is not needed, that energy supply cannot be shut off. 

The systems heat up unless the collectors can be covered or defocused. Occasions when a system or collector could become stagnated include plant shutdowns, holidays, maintenance, system breakdown, lw utilization of heat by the 

process, and blocked flow or imbalance in the collector piping. If this happens during a period of high irradiation, very high temperatures soon develop 

*See Table B-8 in Appendix B. 
in the collectors that can degrade heat transfer fluids, damage mechanical 

components from thermal stress, cause outgassing of toxic or flammable gases 

from insulation, cause ruptures and leaks in pipes from high pressures, and 

increase the fire danger. Also, if flow is restored to collectors that have 

been stagnating, damage from thermal shock can occur when a cold fluid enters 

the hot co~leciors. 

The solutions to problems of overtemperature and the overpressure that accompanies it are relatively straightforward. To avoid dangerous pressure 

buildup, it is necessary to install pressure relief valves in every section of 

the system that receives heat and that can be isolated from the rest of the 

system. An important safety consideration in using pressure- and temperaturerelief valves is to ensure that the discharge from the valves is piped to a 

safe location. Otherwise, injuries to personnel or serious damage to roofing 

materials or other equipment may result. To avoid stagnation of tracking collectors facing the sun, the emergency stow operation should be made as failsafe as possible so that collectors can be stowed under any circumstances. To 

- reduce the incidence of thermal shock damage, the control system should be 

designed to lock out the pumps or make-up water lines when collector temperatures are above those considered safe enough for adding cool fluid. 

11.1.5 Product Contamination 

Product contamination from a solar energy system can be caused by spillage, 

leakage, or carryover of system fluids into the product, or by improper processing of the product (for example, if a poorly designed system permits 

unacceptable temperature variations to occur). Both physical and biological 

contamination are possible. Contamination can affect the palatability and 

wholesomeness of foodstuffs, soil or degrade nonfood items such as textiles, 

or cause products to spoil. 

One of the most common concerns is the protection of potable process water 

from contamination by a solar system. The usual approach is to keep toxic 

system fluids physically separated from the potable water. Double separation, 

provided by a double-walled heat exchanger, a plate-type heat exchanger, or 

two regular heat exchangers in series, is normally employed; periodic tests 

for leakage are performed on the intermediate fluid to ensure that double 

separation is maintained. Usually, higher pressure is maintained on the product side to further guard against leaks into the product. Another specific 

concern is the possibility of contamination of the water supply by back flow 

from solar system make-up water lines. Normally, back flow preventors or air 

gaps in the make-up lines will solve this problem. 

In addition to these concerns, which involve direct contamination of the process from within the solar system, indirect contamination is also possible. 

Discharges from pressure-relief or overflow valves or leaks from the system 

may release contaminants to the plant environment that can come in contact 

with the product. These sources of contamination can be dealt with by properly 

disposing of system wastes and discharges and by proper system maintenance to 

reduce leakage. 
Noise rarely presents a safety problem in solar IPH projects. The noisiest 

parts of the system are usually the circulating pumps. However, if a system 

does include noisy equipment, operating and maintenance personnel must be adequately protected from harm. 

11-1-7 Applicable Regulations and Agencies 

The most comprehensive set of laws dealing with safety in industrial operations is the Occupational Safety and Health Act (OSHA), which details safety 

standards for exposure to toxic fluids and gases, exposure to noise, and many 

other areas. The Consumer Product Safety Act deals with human safety questions derived from the use of consumer products, including devices and equipment. Laws dealing with hazardous fluids include the Toxic Substance Control 

Act and the Hazardous Substance Act of 1971. The Food and Drug Administration 

(FDA) sets limits for contamination of foodstuffs, and the United States 

Department of Agriculture (USDA) regulates the processes that are used in food 

industries. Legislation on noise safety is contained in the Walsh-Healey Public Contracts Act (for the Department of Labor), the Williams-St eiger Occupational Safety and Health Act of 1970, and in OSHA. Many guidelines for safe 

handling of discharges, toxic substances, and other materials are part of the 

environmental protection legislation discussed in Sec. 11.2. Finally, there 

are state and local safety regulations which must be followed at a particular 

site. A summary of regulations and the safety concerns they address is given 

in Table 11-2. 

Table 11-2. Safety ~gulatfons and Agencies 

-- -- - - - - - - - - - 

Safety Concern Appropriate Regulations or Agencies 

Personnel safety Occupational Safety and Health Act (OSHA) 

Consumer Product Safety Act 

Hazardous substances Toxic Substance Control Act 

Hazardous Substance Act of 1971 

Food processing Food and Drug Administration 

U.S. Department of Agriculture 

Noise Walsh-Healey Publlc Contracts Act (Department 

of tabor) 

Williams-Steiger Occupational Safety and Health Act 

of 1970 

OSHA 
11.2 WIROmNTAL dSPECTS OF SOUR IPH SYSTEMS 

In recent years, there has been a gradually increasing awareness of environmental effects associated with nearly every aspect of social and industrial 

functions. One of the major reasons for the interest in solar energy is the 

belief thgt replacing conventional fuel sources with solar energy technologies 

will reduce damage to the environment without requiring changes or sacrifices 

in life style. This section examines the environmental impacts of solar IPH 

systems and describes applicable environmental protection laws. 

11.2.1 EP1vironmental Impacts of Solar IPH Systems 

Both positive and negative environmental impacts accompany solar energy systems. On the positive side, solar systems in normal operation emit no carbon 

dioxide or other atmospheric pollutants. Since solar systems require little 

auxiliary energy to operate, they reduce the environmental damage and pollu-. 

tion resulting from the exploration, mining, processing, transportation, and 

storage of fossil fuels. Water requirements are normally low and are usually 

restricted to periodic washing and,blow-down of the tanks. This enhances the 

suitability of solar energy systems in arid regions. And because a solar 

energy system uses solar energy--energy that would have heated the earth 

anyway--it is not a source of thermal pollution. 

Negative environmental impacts of solar energy systems include land displacement and possible air and water pollution resulting from the construction, 

normal and emergency operations, and demolition of the solar system. Land use 

becomes a problem in IPH systems because of the large energy needs of many 

processes and the diffuse nature of solar energy. Roof mounting, which eliminates some of the problem by using the land area for two purposes, is frequently impractical because of cost, structural requirements, accessibility 

problems, or requirements for larger arrays (too large for roofs) to satisfy 

the energy needs of the process. The environmental ramifications of operating 

large, ground-mounted arrays are not yet well understood, but they could 

include changes in microclimate that occur because of a different energy 

balance on the ground below the collectors and changes in local ecology that 

result from the use of herbicides and other inhibitors under the collector 

array. 

Direct environmental effects on local air and water quality during normal 

operation include pollution from herbicides and biocides used around the collectors to control weeds and pests, cleaning solutions and debris, disposal of 

wastes from the system, and release of products of outgassing and degradation. 

Fires and leaks can also cause damage as toxic fumes and liquids are released 

into the environment. The indirect environmental impacts of a solar energy 

system (which, however, are usually not all charged against the system) 

include those associated with the production and assembly of components, the 

construction of the system, the disposal of the system at the end of its useful life, and the generation and distribution of electricity needed to operate 

the system. 
11,2,2 National Environmental Protection Laws and Organizations 

The United States government has made a national commitment to preserve the 

envfronment, which is stated as follows: 

. - . .. To declare a national policy which will encourage productive 

and enjoyable harmony between man and his environment; to promote 

efforts which will prevent or eliminate damage to the environment 

and biosphere and stimulate the health and welfare of man.... 

The Congress has backed this commitment with a series of Laws designed to 

regulate and control environmental pollution and to work toward reducing it. 

The National Environmental Policy Act (NEPA) of 1969 (P.L. 91-190), from which 

the quote above was taken, is the most general of these environmental laws. 

Its purpose was threefold: to establish a national environmental policy, to 

require the generation of Environmental Impact Analysis (EIA) reports on federally supported projects, and to set up a Council on Environmental Quality 

(CEQ) to advise the President on environmental matters. 

The greatest impact of the act has been the EIA report requirement. These 

environmental impact analyses have become very important in decisions about 

whether or not projects are environmentally acceptable. A major function of 

the CEQ has been to generate guidelines to assist planners in writing EIA 

reports and to detail many of the responsibilities and requirements not specified in the NEPA (CFR Title 40, Chap. V, Part 1500). Laws dealing with specific environmental concerns are discussed in the following sections, 

including air-pollution control, water-pollution control, waste disposal, 

noise, and land use. Table 11-3 summarizes the information contained in the 

following sections, listing applicable regulations, agencies, and requirements 

for different aspects of environmental protection. 

112.2 Air-Pollution Control 

The Clean Air Act of 1963 (P.L. 88-206), amended in 1970 (P.L. 91-604), provides the basis for air-pollution control. Under this act, all new "stationary sources" are required to install air-pollution cdntrol devices, and new 

and existing sources are required to monitor the generation and dispersal of 

air pollutants. The Environmental Protection Agency (EPA) was empowered to 

establish standards of air quality. and to enforce those standards. Fines of 

up to $25,000 per day and prison sentences of up to one year were authorized, 

and the EPA was allowed to supersede state programs in its enforcement of 

standards if the state programs proved ineffective. Another law governing air 

pollution is the Toxic Substance Control Act, which considers the production, 

use, distribution, and disposal of toxic substances. It also covers the 

release of toxic gases during fires. 

11.2.2.2 Water-Pollution Control 

The major laws for water-pollution control are the Federal Water Pollution 

Control Act (FWPC) of 1956 (P.L. 84-660) as amended in 1972 (P.L. 92-500) and 

the Water Quality Act of 1965 (P.L. 89-234). Some of the provisions of these 
Table 11-3. Summary of Environmental Agencies and Regulations 

Environmental Area Appropriate Regulations and Agencies Func tions 

All Environmental Protection Agency (EPA) Sets and enforces standards for pollutants, 

discharges, emissions; monitors compliance with 

regulations 

Council on Environmental Quality (CEQ) Generates guidelines to assist in preparing Environmental Impact Aasessments (EIAs); details 

requirements not specified in NEPA 

National Environmental Policy Act of 1969 (NEPA) Requires EIA for projects with federal funding 

Air pollution Clean Air Act of 1963, amended in 1970 

Toxic Substance Control Act 

Requires all new stationary sources to install 

air-pollution control devices 

Requires new and existing sources to monitor air 

pollutants discharged 

Empowers EPA to set standards and enforce them with 

fines and prison sentences 

Covers toxic gases released in fires 

Water pollution Federal Water Pollution Control ,Act (FWPCP of 1956, Requires permits and licenses from federal 

amended in 1972 government for discharging pollutants 

Water Quality Act of 1965 Empowers EPA to control and enforce standards 

Safe Drinking Water Act Requires National Pollutant Discharge Elimination 

permits; covers disposal of hazardous fluids 

Resource Conservation and Recovery Act of 1976, Covers liquid and solid waste disposal 

Resource Recovery Act of 1970 

Noise Environmental Noise Control Act of 1972 Empowers EPA to control and enforce standards on 

noise pollution 

Land use Local ordinances and zoning laws 

Right-to-sun ordinances 
laws aim to eliminate pollutant discharges into U.S. waters by 1985, require 

that permits and licenses be obtained from the federal government to discharge 

pollutants, and empower the EPA to control and enforce standards. The Safe 

Drinking Water Act requires National Pollutant Discharge Elimination System 

permits and provides for the disposal of hazardous system fluids. 

11020203 &st@ Disposal 

The Resource Conservation and Recovery Act of 1976, which replaced the Solid 

Waste Disposal Act of 1965 (P.L. 89-272) and its later amendments in the 

Resource Recovery Act of 1970 (P.L. 91-512), is the national law that deals 

with waste disposal. This includes both solid and liquid wastes (such as 

spent working fluids) . Despite these national laws, however, waste control 

remains mostly a function of local government. 

11020204 Noise 

As mentioned in Sec. 11.1.6, noise is not normally a problem with solar IfH 

systems. The Environmental Noise Control Act of 1972 (P.L. 92-574), included 

among the amendments to the Clean Air Act, authorizes the EPA with control of 

noise pollution and allows that agency to override state authority. 

1102.205 fand Use 

At present, there are no federal guidelines for land use, although such regulations are possible in the future. The important regulations concerning land 

use are normally found in local zoning laws and in state and local sun rights. 

11.2.3 State Envfrommental Ekgulations 

Many states have enacted laws to protect their natural environments. Although 

a detailed discussi.on of each of these state laws is beyond the scope of this 

handbook, Table 11-4 summarizes the requirements of states that have adopted 

environmental restrictions beyond or in addition to the federal laws, as of 

April 1978. State officials should be contacted before construction begins to 

obtain the latest requirements. 

13 BIBLIOGRAPHY 

Arbuckle, J. Gordon; et ale 1978. Environmental Law Handbook . Washington, 

DC: Government Institutes, Inc. 

Heer, John Em, Jr.; Hagerty, D. Joseph. 1977. Environmental Assessments and 

Statements. New York: Van Nostrand Reinhold Co. 

Kutscher, C. F., editor. 1981 (Mar.). Design Considerations for Solar Industrial Process Heat Systems. ~~~1/~~-632-783. Golden, CO: Solar Energy 

Research Institute. 
Searcy, Jimmy Q., editor. 1978 (Aug.). Hazardous Properties and Environmental Effects of Materials used in Solar Heating and Cooling (SHAC) Technologies: Interim Handbook. SAND78-0842. Albuquerque, NM : Sandia 

National Laboratories. 

Stro jan; Carl -J. 1980 (Sept. ) . Environmental Aspects of Solar Energy Technologies. SERIITP-743-826. Golden, CO: Solar Energy Research Institute. 

U.S. Dept. of Energy. 1979 (Aug.). Environmental Readiness Document: Solar 

Agricultural and Industrial Process Heat. DOEIERD-0025. Washington, DC. 

Wakeman, David; Holton, John. 1978 (Sept.). Environmental and Safety Considerations for Solar Heating and Cooling Applications. NBSIR 78-1532. 

Washington, DC: National Bureau of Standards. 

11.4 REFERENCES 

Hess, L. Y., editor. 1979. Insulation Guide for Buildings and Industrial 

Processes. Energy Technology Review #43. Park Ridge, NJ: Noyes Data 

Department of Housing and Urban Development. 1976 (Apr.). Intermediate Minimum Property Standards for Solar Heating and Domestic Hot Water Systems. 

Interim Report. NSBIR 76-1059. Washington, DC: National Bureau of Standards. 

National Fire Protection Association. 1973. NFPA 321: Basic Classification 

of Flammable and Combustible Liauids. 

Versar, Inc. 1979 (May). Survey and Evaluation of Available Thermal Insulation Materials for Use on Solar Heating and Cooling Systems. Interim 

Technical Progress Report Under Contract No. EX-78-C-04-5363. 
Table 11-4. State Environmental Impact Statement Requirements 

(as of 1 April 1978) 

I. States vith Comprehensive Statutory Requirements 

California 

Source : California Environmental Quality .Act, 

Cal. Pub. Reg. Code Section 21000 et seq. 

(Cum. Supp. 1978) (West). 

Guidelines: Guidelines for Implementation of the California Environmental Quality Act of 

1970, Cal. Admin. Code tit. 14, Section 

15000 et seq., as amended March 4, 1978. 

Guidelines are issued by the Resources 

Agency of California. 

Contact : Assistant to the Secretary for Resources, 

N The Resources Agency, 1416 Ninth Street, a 

4 Sacramento, California 95814 

Connecticut 

Source : Connecticut Environmental Policy Act of ' 

1973, Conn. Gen. Stat. Ann. Section 

22a-la et seq. (Cum. Supp. 1978) (West). 

Guidelines: No guidelines have been iseued. 

Contact : Planning and Coordination Unit, Department of Environmental Protection, 118 

State Off ice Building, Hartford, ConnectGuidelines: Rules of Practice and Procedure and Environmental Impact Statement Reguiremente, 

issued by the Environmental Quality Commission on June 2, 1975. 

Contact: Chairman, Environmental Quality Commission, Office of the Governor, Room 301, 

550 Halekauwila Street , Honolulu, Hawaii 

96813 

Indiana 

Source : Indiana Environmental Policy Act, Ind. 

Code Ann. Sectfon 13-1-10-1 et aeq. 

(1973) (Burns). 

Guidelines: EMB-2 and EMB-3, Ind. Admin. Rules and 

Regs. Ann. Section 13-1-10-3 et seq. and 

Section 13-7-5-1 et seq. (Supp. 1977). 

The Environmental Management Board prepared guidelines. 

Contact: Coordinator of Environmental Programs, 

Indiana State Board of Health, 1330 west 

Mfchigan Street, Indianapolis, Indiana 

46202 

Maryland 

icut 06115 Source : 

Hawaii 

Guidelines: 

Source : Governor's Executive Order of August 21, 

1974, as supplemented by Environmental 

Quality Commission and Environmental Impact Statementa, Haw. Rev. Stat. Section Contact : 

343-1 et seq. (1976 Replacement). 

Maryland Environmental Policy Act of 

1973, Md. Nat. Res. Code Ann. Section 

1-301 et seq. (Cum. Supp. 1977). 

Revised Guideline6 for Im~lementatf on of 

the Maryland Environmental Policy Act, 

issued by the Secretary of the Department 

of Natural Resources, June 15, 1974. 

Administrator, Clearing Rouse Review, Department of Natural Resources, Tawes 

State Office Building, Annapolis, Maryland 21401. 
Table 11-4. State Environmental Impact Statement Requirements (Continued) 

(as of 1 April 1978) 

Massachusetts 

f:#j$ 

Montana \ - 

I 

Source : Massachusetts Environmental Policy Act, 

Mass. Ann. Laws Ch. 30, Sections 61 and 

62 (Cum. Supp . 1977) (Michie/~aw. Co-op), 

as amended by 1978 Mass. Acts Ch. 947, 

January 10, 1978. 

Guidelines: Regulations Governing the Implementation 

of the Massachusetts Environmental Policy 

- Act, issued by the Executive Office of 

Environmental Affairs on February 16, 

1978. 

Contact : Director, Massachusetts Environmental Impact Review Office, Executive Office of 

Environmental Affairs, Room 2001, 100 

h, 

\O Cambridge Street, Boston, Massachusetts 

03 02202 

Minnesota 

1 

Source : Minnesota Environmental Policy Act of 

1973, Minn. Stat:Ann. Section 116D.01 et 

seq. (1977) (West). 

Guidelines: Rules and Regulations for Environmental 

Impact Statements, issued by the Minnesota Environmental Quality Council on 

April 4, 1974, and amended on February 

13, 1977 

Contact: Director, Environmental Planning, Environmental Quality Board, Capital Square 

Buiding, 550 Cedar Street, St. Paul, Minnesota 55101 

Source : Montana Environmental Policy Act, Mont. 

Rev. Codes Ann. Section 69-6501 et seq. 

(Cum. SUDD. 1977). 

Guidelines: uniform *Rules implementing the Montana 

Environmental Policy Act. Final version 

adopted by the Montana Commission on Environmental Quality on January 15, 1976. 

Contact: Montana Commission on Environmental Quality, Capitol Station, Helena, Montana 

59601. 

New York 

Source : New York State Environmental Quality Review Act, N.Y. Envir. Conserv. Law Section 8-0101 et seq. (Cum. Supp. 1977- 

1978) (McKinney) as amended by 1976 N.Y. 

Laws, Ch. 228, Section 5 and 1977 N.Y. 

Laws, Ch. 252, Section 9, et seq., 

Guidelines : 6 N.Y .C.R.R. Park 617, revised .January 

24, 1978 by the Department of Environmental conservation. - 

Contact: Environmental Quality Review Section, Office of Environmental Analysis, New York 

State Department of Environmental Conservation, 50 Wolf Road, Albany, New York 

12233. 

North Carolina 

Source : North Carolina Environmental Policy Act 

of 1971, N.C. Gen. Stat. Section 113A-1 

(1975 Replacement). 
Table 11-4. State Environmental Inpact Statement Requirements (Continued) 

(as of 1 April 1978) 

Guidelines: North Carolina Department of Admtnistra- Virginia 

tion, Guidelines for the Implementation 

of the Environmental Policy Act of 1971, Source : Virginia Environmental Quality Act of 

revised March I, 1975. 1973, Va. Code Section 10-17.107 et seq. 

Contact : Policy Advisor for Natural Resources, Division - of Policy Development, Department 

of Administration, 116 West Jones Street, 

Raleigh, North Carolina 27603. 

Puerto Rico 

Source: Public Environmental Policy Act, P.R. 

Laws Ann. tit. 12, Section 1121 et seq. 

(Cum. Supp. 1976). 

13 Guidelines: duidelinei for the Preparation, Evalua- LO tion and Use of Environmental Impact 

Statements, issued' by the Environmental 

Quality Board on December 19, 1972. 

Contact : Executive Director, Environmental Quality , Board, 4th Floor, 1550 Ponce de Leon Avenue, Santurce, Puerto Rico 19910 

South Dakota 

Source : South Dakota Environmental Policy Act, 

S.D. Codified Laws Section 34A-9-1 et 

seq. (1977 Revision). 

Guideli nes : Informal guidelines issued by the Department of Environmental Protection in 1974. 

Contact: South Dakota Department of Environmental 

Protection, Foss Building, Pierre, South 

Dakota 57501 

(Cum. Supp. 1977). 

Guidelines: Procedures Manual for Environmental Im3 

pact Statements in the Commonwealth of 

Virginia, revised June 1976, by the Governor s Council on the Environment. 

Contact : Environmental Impact Statement Coordinator, Council on the Environment, 903 9th 

Street Office Building, Richmond, Virginia 23219. 

Waehington 

Source : State Environment Policy Act, Wash. Rev. 

Code Ann. Section 43.21C.010 et seq. 

(Supp. 1976). 

Guidelines: State Environmental Policy Act1 Guidelfnes. - - Wash. Admin. Code Section 197-10. 

revieid January 21, 1978, by the ~e~artment of Ecology. 

Contact : Environmental Review and Evaluation, Of - fice of Planning and Program Development, 

Department of Ecology, Olympia, Washington 98504 

Source : Wisconsin Environmental Policy Act of 

1971, Wis. Stat. Ann. Section 1.11 (Cum. 

Supp. 1977-1978) (West). 
Table 11-4. State Environmental Impact Statement Requirements (Continued) 

(as of 1 April 1978) 

Guidelines : Revised Guidelines for the Implementation Utah 

of the Wisconsin Environmental Policy - 

- Act, issued by Governor's Executive Order Source: State of Utah Executive Order, August 27, No. 26 (February, 1976). 1974. 

Contact: State WEPA Coordinator, Office of State Guidelines: No guidelines have been issued. 

Planning and Energy, Room R-130, 1 West Contact : Office of the Attorney General, State 

Wilson Street, Madison, Wisconsin 53702 Capitol Building, Salt Lake City, Utah 

84114 

11. States with Comprehensive Executive or 

Administrative Orders 

Michigan 

Source: Michigan Executive Order 1974-4 (May, 

Cc, 

o 1974). 

0 Guidelines: ~uidelines for the Preparations and Review of Environmental Impact Statements 

under Executive . .. . - - - - - - - - - - - . - Order - - - - - 1974-4. - - . . I issued ------ hv - J 

the Environmental Review Board in November, 1975. 

Contact: Environmental Review Board, Department of 

Management and Budget, Lansing, Michigan 

48913 

New Jersey 

Source : New Jersey Executive Order No. 53 (October 15, 1973). 

the Office of the Commissioner, Department of Environmental Protection, and revised in February 1974. 

Contact: Chief, Office of Environmental Revew, De111. States with Umited EIS Requirements 

Arizona 

Source: (a) Game and Fish Commission Policy of 

July 2, 1971. 

(b) Power Plant Transmission Line Siting 

Act, Ariz. Rev. Stat. Section 40-360 

et seq. (Cum. Supp. 1977-1978). 

Guidelines: (a) Memorandum by the Arizona Game and 

Fish Commission, "Requiremehts for 

Environmental Impact Statements," 

issued June 9, 1971. 

(b) No guidelines have been issued. 

Contact : (a) Chief, Wildlife Planning and Development Division, Arizona Game and Fish 

Department, 2222 West Greenway Road, 

Phoenix, Arizona 85023 

(b) Chairman, Power Plant Transmission 

Line Siting Committee, Attorney General's Office, Room 200, 1700 West 

Washington, Phoenix, Arizona 85007 

Arkansas 

partment of Environmental Protection, 

P.O. Box 1390, Trenton, New Jersey 08625 Source : Utility Facility Environmental and Economic Protection Act, Ark. Stat. Ann. I$ Section 73-276 et seq. (Cum. Supp. 1977)- 
Table 11-4. State Phviroamental Inrpact Statement Requirements (Continued) 

(as of 1 April 1978) 

Guidelines: Informal guidelines issued by the Arkansas Public Service Commission. 

Contact: Public Service Commission, Just ice Buf lding, Little Rock, Arkansas 72202 

Delaware 

Source : (a) Delaware Coastal Zone Act, Del. Code 

Ann. tit. 7, Section 7001 et seq. 

(1974). 

(b) The Wetlands Act, Del. Code Ann. tit. 

7, Section 6601 et seq. (1974). 

Guidelines : (a) permit Application I& truct ions and 

Forms and Information Material on 

W 

o Reauired . Procedures for the Coastal 

Zone Act, adopted by the Delaware Office of Management, Budget, and PlanGuidelines: Developments Presumed to be of Regional 

Impact, Fla. Admin. Code Ch. 22F-2 

Contact : Bureau Chief, Bureau of Land and Water 

Management, Division of State Planning, 

Department of Administration, 660 Apalachee Parkway, Tallahassee, Florida 

,32304. 

Georgia 

Source: State Tollway Authority Act, Ga. Code 

Ann. Section 95a-124l(e)(l) (1976). 

Guidelines: Policy and Procedure Manual: State Tollway Authority, revised by Georgia's Tollway Adminiatrator's Off ice in February 

1973. 

ning on ~ul~-l, 1977. Contact : 

(b) Wetlands Regulations, adopted by the ! 

Department of Natural Resources and 

Environmental Control, December 23, 

1976. 

Contact : (a) Manager, Coastal Management Program, Maine 

Delaware Office of Management, Budget, and Planning, Dover, Delaware Source : 

19901 

(b) Wetlands Manager, Department of Natural Resources and Environmental Con- Guidelines: 

trol, Division of Environmental Control, Dover, Delaware 19901. 

Contact : 

Florida 

Source : The Florida Environmental Land and Water 

Management Act of 1972, Fla. Stat. Ann. 

Section 380.012 et seq. (Cum. Supp. 1977) 

(Vest) 

State Location Engineer, Division of Preconstruction, Department of Transportation, 2 Capitol Square, Atlanta ,' Georgia 

30334 

Site Location Law, Me. Rev. Stat. tit. 

38, Section 481 et seq. (Cum. Supp. 1977- 

1978). 

Site Law Regulations and Guidelines, iesued by the Department of Environmental 

Protection. 

Information and Education Division, Department of Environmental Protection, 

State House, Augusta, Maine 04333. 
Table 11-4. State Znviromaental Impact Statement Requirements (Continued) 

(as of 1 April 1978) 

Mississippi Contact : Chairman, Public Service Commission of 

Nevada, Kinkead Building, Carson City, 

Source: Coastal Wetlands Protection Law, Miss. Nevada 89701. 

Code Ann. Section 49-27-1 et seq. (Cum. 

Supp. 1977), to be amended by sen. Bill 

3498 (1978) (passed but not yet signed as 

of ~~ril 1, 1978). 

Guidelines: ~ules and -~e~ulations Pertaining to the 

Coastal Wetlands Protection Law, revised 

by Mississippi Marine Resources Council, 

~iril 15, 1975. 

Contact : Marine Projects Manager, Mississippi Marine Resources Council, P.O. Drawer 959, 

Long Beach, Mississippi 39560 

New Hampshire 

Source : Electric Power Plant Transmission Line 

Siting and Construction Procedure, N.B. 

Rev. Stat. Ann. Section 162-F:1 et seq. 

(Supp. 1975) 

Guidelines: No guidelines have been issued. 

Contact: Secretary of Public Utilities Commission, 

8 Old Suncook Road, Concord, New Hampshire 03301. 

W Nebraska New Jersey 

N 

Source and Nebraska ~e~artme~t of Roads, Department 

Guidelines: of Roads Action Plan (1973), as revised 

by the State of Nebraska Environmental 

Action Plan, prepared by the Nebraska Department of Roads and approved by the 

Federal Highway Administration, June 24, 

1975. 

Contact : Comprehensive Planning Coordinator, Office of Planning and Programming, P.O. 

Box 94601, State Capitol, Lincoln, Nebraska 68509 

Nevada 

Source : Utility Environmental Protection Act, 

Nev. Rev. Stat. Section 704.820 et seq. 

(1973). 

Guidelines : No guidelines have been issued. 

Source : (a) Coastal Area Facility Review Act, 

N.J. Stat. Ann. Section 13:19-1 et 

seq. (Cum. Supp. 1977-1978). 

(b) The New Jersey Wetlands Act 'of 19'10, 

N.J. Stat. Ann. Section 13:9A-1 et 

seq. (Cum. Supp. 1977-1978). 

Guidelines : (a) CGRA Rules and Regulations, N. J.A.C. 

7 : 7D-1 .l et seq . , effective November 

(b) ~roceedural Rules and Regulations, 

N.J.A.C. 7:7A-1.1 et seq., - - revised 

September 3, 1976. 

Contact: (a) Chief, Office of Coastal Zone Management, New Jersey Department of Environmental Protection, P.O. Box 1889, 

Trenton, New Jersey 08625. 
Table 11-4. State Environmental Xmpact Statement Requirements (Concluded) 

(as of 1 April 1978) 

(b) Supervisor, Off ice of Wetlands Management, Division of Marine Services, 

Department of Environmental Protection, P.O. Box 1889, Trenton, New 

Jersey 08625 

South Carolina 

Source : South Carolina Coastal Management Act, 

S.C. Code Section 48-39-10 et seq. (Cum. 

SUPP. 1977). 

W 

o Guidelines: Final Rules and Regulations for Permits 

w of Alterations of Critical Areas, issued 

by the South Carolina Coastal Council 

(1977) in the South Carolina State Register. 

Contact : Executive Director, South Carolina Coastal Council, 116 Bankers Trust Tower, 

Columbia, South Carolina 29201. 

IV. City EXS Bequft-~ts 

Bowie, Maryland 

Source and The bowie, Maryland Environmental Policy 

Guidelines : and Impact Statement Ordinance, passed by 

the City Council on May 3, 1971; Ordinance 0-2-73, Declaring an Environmental 

Policy and Providing for Environmental 

Impact Statements, passed by the City 

Council on July 16, 1973; and Ordinance 

0-14-76, Changing Notification and Referral Requirements under the Ordinance, 

passed by the City Council on September 

8, 1976. 

Contact : Planning Director, Office of Planning and 

Community Development, City Halla, Bowde , Maryland 20715. 

New York City 

Source and Executive Order No. 87, October 1973 and 

Guidelines: Executive Order No. 91, June 1, 1977. 

Contact : Director, Office of Environmental Impact, 

New York City Department of Environmental 

Protection, 2344 Municipal Building, New 

York, New York 10007. 


APPENDIX A 

EFFECTS OF SOLAR SYSTEMS ON TEE EFFICIENCY OF HOT WATER BOILERS 

In this- appenaix, we analyze an apparent problem in interfacing solar hot 

water systems with industrial processes--backup hot water boilers, in particular. Figure A-1 shows a boiler efficiency curve* typical of many industrial 

boilers. The efficiency is nearly constant at 80% over most of the load 

range, but drops drastically below 20%-30% of full load. In solar IPB systems, full backup is usually required, so the backup boiler is sized for the 

entire load. However, if the solar energy system is capable of supplying a 

large fraction of the load, the backup boiler will be forced to run at much 

less than full load and, hence, at greatly reduced efficiency. If this happens, the solar effectiveness will decrease, In order to evaluate this pro& 

lem, it is necessary to understand some details of boiler operation and how 

solar IPH systems interact with boilers. In the following sections, the operation of boilers is described, a simple analytical model is developed to consider long-term boiler efficiency, and the results of interfacing a boiler 

with a solar system are investigated. 

A.1 PRACTICAL OPERATION OF HOT WATER BOILERS 

Understanding practical boiler operation requires some knowledge of physical 

aspects of boiler efficiency and how boilers are controlled in normal applications. Basically, there are two sources of inefficiency in hot water boilers: 

heat losses from the boiler case, and losses in exhaust gases. Figure A-2 

shows a breakdown of these losses for the boiler for which an efficiency curve 

was plotted in Fig. A-1. In Fig. A-2, the boiler losses, expressed as percentages of efficiency loss, are plotted as a function of the firing rate. 

The inefficiency at low firing rates results mainly from skin losses. Note 

that the skin losses depend primarily on the temperature of the boiler shell, 

so that whenever. the boiler is operated, the skin losses are constant regardless of the firing rate. For the boiler shown, the size of these losses is 

about 1.5% of the energy delivered at full load. The variation in the skinloss effect shown in Fig. A-2 is from this constant 1.5% of full load, which 

becomes more important relative to the energy delivered as energy delivered 

decreases. Stack losses, on the other hand, are a relatively constant fraction of the energy delivered over the entire range of the load. These boiler 

characteristics will be used later to develop the analytical model of boiler 

operation. 

Three control strategies are generally used for industrial boilers: on-off 

control, high-low firing, and full modulation. On-off control is used on 

small boilers, up to about 500 kWt (50 hp). High-low firing, which affords 

some additional load-following capability, is used on boilers up to about 

1 MWt (100 hp). Modulating burners are used with larger boilers, and are usually designed with a limit in turndown ratio of about four to one. Thus, the 

boiler can be modulated continuously over a range from one-fourth of full load 

*Based on a 13,000 lb/h (about 3.7 MWt) natural-gas-fired hot water boiler. 

up to full load. These control strategies and the boiler sizes to which they 

are applied are summarized in Table A-1. In the discussions that follow, full 

modulation of the firing rate is assumed, which is the most general case and 

from which the other types of control can be understood as limiting cases. 

A-2 ANALPTICAL MODEL OF A TYPICAL HOT WA!J!ER BOZIER 

Considering the characteristics of boiler efficiency and operation described 

above, it is possible to develop a simple model of boiler operation. The definition of instantaneous boiler efficiency is 

where 

Qdel = the energy delivered to the process 

Qfuel = the energy in the fuel consmed. 

We can relate these energy values through an energy balance on the boiler: 

where 

QsHn = the skin loss 

Qstack = the heat loss in the exhaust flue gases. 

Solving Eq. A-2 for Qfuel, and substituting in Eq. A-1, 

Table A-1. Control Systems Used With Industrial Boilers 

Control System Sf ze of Boiler . - - 

On-off Up to 500 kW (50 hp) 

~igh-low-of f up to 1 MW~ f100 hp) 

Modulating Iarger than 1 MWt (100 hp) 

(typical turndown ratio of 4: 1) 
Dividing top and bottom by QfUll oad, the energy delivery at full load, and 

defining the firing rate F as Qde~fQfull-load, Eq. A-3 becomes 

ng = F 

+ Qskin + Qstack 

Qf ull-load Qfull-load 

As stated above, the skin losses are essentially constant, so that the quantity Qskin/Qfull-load may be replaced by a, a constant. Also, the stack 

losses are approximately a constant fraction of the energy delivered, so that 

Qst k/Qfull-load can be written as BF, where B is also a constant. This 

yief2s 

According to Eq. A-6, skin losses cause the variation in qB seen with the firing rate. Without skin losses, the efficiency would be essentially constant 

over the full load range; but with skin losses included, the efficiency drops 

rapidly at low firing rates. The instantaneous efficiency given by Eq. A-5 

may be used to obtain the average boiler efficiencyover a time period. Integrating both the numerator and denominator of Eq. A-5 over time, we have 

- 

- 0 (A-7) 

J~F(~ + B)dt + ~~adt 

0 0 

Since B and a are constants, then defining = I ltFdt as the average firing t rate over the time period, the average efficiencyqs 

where T is the fraction of time that the boiler is turned on during the time 

period. 

Dividing through by F, we obtain 

Thus, the average efficiency is a function of F/T. 
The function given by Eq. A-9 is plotted in Fig. A-3 for the nominal conditions a = 0.015 and B = 0.25 to correspond to the typical boiler described 

earlier. With T = 1, the curve in Fig. A-3 is t_he same as the instantaneous 

efficiency curve from Eq. A-6 with F replaced by F. Therefore, it is possible 

to compare the efficiency curve predicted by the model with the actual boiler 

curve plotted in Fig. A-1. The shape of the analytical curve is very similar 

to the real boiler curve, with a maximum deviation from the real curve of less 

than 3%. The deviation is less than 1% over 60% of the firing-rate range. 

This excellent agreement indicates that the analytical model describes the 

actual boiler well. 

8.3 EFFECT OF SOIAR SYSTEMS ON BOIIER EFFICIENCY 

8.3-1 Solar System Znfluence on Boiler Fractional On-Tfme 

The configuration of a solar system has an influence on T, the fractional ontime for the auxiliary hot water boiler. The three types of systems considered here are series, series-bypass, and parallel (Fig. A-4). We assume that 

each system is connected to a sensible heat load that requires a certain flow 

rate of heated fluid at a particular temperature and returns the fluid at a 

lower temperature. In the series and series-bypass systems, solar energy preheats the process fluid. These system configurations are used for hot air and 

hot water process loads and for preheating make-up water in steam systems. 

The series-bypass system Ts set up so that ,the backup boiler can be bypassed 

and shut down when the solar system can supply the full load; in the simple 

Figure 8-3. Boiler Efficiency from Aualytical Model 

series system, the boiler must maintain a low firing rate whenever the load is 

on to replace the energy lost from the skin of the boiler. In both the series 

and series-bypass systems, the boiler is modulated to make up the difference 

between the load and the solar contribution when the solar system cannot 

supply the full load. In the parallel system, the boiler is operated in an 

on-off manner and the solar system supplies heat only when it can carry the 

entire load. 

The influence of each system configuration on T depends on how many hours the 

boiler may be shut down while the load is supplied totally by solar energy. 

As we noted, the simple series system does not allow for shutdown, because the 

boiler is always kept hot. Thus, T for a series system is equal to one. In 

the series-bypass system, the boiler may be shut down when solar energy supplies the entire load, so the value of T may be less than one. Increased collector areas and small amounts of storage tend to decrease T because the solar 

system heats up faster and can supply the full load more often. Moreover, T 

has a minimum value for a given collector area and storage size in a parallel 

system, because any time the solar system delivers energy, the boiler can be 

shut down. Therefore, the boiler always either operates at full load efficiency or is shut down. 

Reducing the value of r decreases skin losses and increases overall boiler 

efficiency at a given average firing rate (Eq. A-9). This seems to favor parallel systems, or at least series systems with low turndown ratios* for the 

backup boiler (a parallel system can be thought of as a series system in which 

the turndown ratio of the boiler is one) to maximize the boiler's efficiency. 

However, because of the operational characteristics of solar systems, this is 

not the best approach to adopt for maximum overall fuel savings. In particular, the performance of the solar system decreases as the inlet temperature to 

the collectors increases. Therefore, a series system (or series-bypass) is 

much more efficient, because the inlet temperature to the collectors is lower 

than that of a parallel system. In a parallel system, the minimum temperature 

to the collectors is approximately the same as the load supply temperature, 

since the storage tank cannot be drawn down below that temperature. For a 

series system, however, the minimum collector inlet temperature is close to 

the make-up or load return temperature. More energy is provided by a series 

system, resulting in much higher fuel savings as boiler load is reduced--even 

if boiler efficiency is also slightly reduced. 

A.3.2 The Effect of Boiler Turndm Ratio on Solar not Water Systems 

The effect of the boiler turndown ratio on energy savings in a solar IPH system is also related to the way collector performance varies with inlet temperature. When the solar, system is capable of supplying a large fraction of the 

load, most of the time the boiler will either be operated at its minimum fiting rate or be turned off. Consider the effect of boiler turndown ratio on 

such a solar system. The solar system collects much more energy than the load 

requires at peak times, thereby carrying the entire load at those times while 

*Turndown ratio is the ratio of full load firing rate (energy delivery) to the 

minimum firing rate possible with that boiler. . 
also charging the storage. During those times, the boiler can be shut off. 

When the collection rate becomes less than the load, the system may continue 

to supply the whole load for a while if there is sufficient energy in storage, 

but eventually the storage tank temperature will decrease below the load temperature. To continue supplying the load, the backup boiler would then be 

turned on and operated at its minimum firing rate, Energy extraction from the 

solar storage would have to be reduced to the difference between the load and 

the minimum firing rate of the boiler so the load could be met. The lower 

energy extraction rate would cause the storage tank temperature to decrease 

more slowly than before the boiler was started. The reduced energy extraction 

rate from storage would continue until the storage tank cooled to where the 

boiler would have to modulate. The net result is that the storage tank would 

be warm the next day when collection starts. 

The lower the minimum firing rate of the boiler, the greater the amount of 

energy that can be extracted from storage and the lower the collector inlet 

temperature the next day. Since a lowered inlet temperature leads to higher 

energy collection, a boiler with a large turndown ratio (i-e., one that can be 

operated at a low firing rate) improves the performance of the solar system. 

This, in turn, leads to greater energy savings, even if the boiler is somewhat 

less efficient at low firing rates. 

To illustrate these effects, SOLIPH runs were made for solar IPH systems with 

a variety of collector areas and storage sizes. A constant water-heating load 

of 25 GJ/day was specified, with water entering at 20'~ at a flow rate of 

1.15 kgls and a required load temperature of 80°c. The turndown ratio of the 

auxiliary boiler in each case was varied from one (corresponding to an on-off 

boiler or parallel setup) to infinity (corresponding to a series system with a 

boiler capable of being modulated down to zero load). The results of these 

runs are plotted in Fig. A-5 as curves of annual energy savings versus the 

minimum firing rate of the backup boiler. The curves are labeled with the 

collector area and the number of hours of storage for the systems depicted by 

the curves. In all cases, reducing the minimum firing rate increased the performance of the solar system and increased fuel savings. For small collector 

areas, there is an obvious knee in the curve which occurs where the minimum 

firing rate becomes low enough that the storage is essentially exhausted overnight. Further decreases in minimum firing rate continue to decrease the 

storage temperature slightly but do not have as great an effect. 

To put the effect of lowered boiler efficiency at low firing rates into perspective, the analytical model derived above can be used to calculate the 

extra fuel energy that must be used because the boiler efficiency changes-with 

firing rate from its ,full load value. For a given average firing rate F the 

fuel energy needed by the boiler is given by 

- which is derived from the definition of efficiency. Because FQ~~~

- 

Qdel , We have 

where nB(F) is the average boiler efficiency at the average firing rate F. 

Consider the worst case: a boiler that must be fired all the time, as in a 

simple series system. The extra energy that must be used because the boiler 

efficiency drops as the firing rate decreases is the difference between the 

fuel used at a firing rate F and a boiler efficiency of i'iB(F) and that used at 

the same firing rate and an efficiency of :B(l), or 

- FQ~ ull-load FQf dl-load' Qextra - - 

- - - 

Substituting for TB from Eq. A-9 and gathering terms, noting that T = 1 for a 

system in which the boiler is never shut down, we obtain 

With the nominal condition of a = 0.015, this function is plotted in Fig. A-6. 

The maximum effect of 1.5% of Qf ll-load is very small compared with the 

changes in total fuel use that resuyt from small changes in such things as the 

turndown ratio, which in turn lead to.changes in the solar system performance. 

To illustrate this point, Fig. A-7 shows the total fuel use plotted along with 

the extra fuel use caused by the boiler efficiency effect. Clearly, any pen- 

.alty in fuel use caused by reducing the minimum boiler firing rate is very 

, small compared with the savings in overall fuel use. In fact, such a penalty 

would be easily outweighed by the advantages of the reduced storage tank temperatures we discussed earlier. 

Firing Rate (% of full load) 

Figure 8-6. Extra Energy Use 
0 10 20 30 40 50 60 70 80 90 100 

Firing Rate (% of full load) 

Figure A-7. Extra Fuel Energy Use Compared With Total Use 

In conclusion, the decrease in boiler efficiency that results from decreasing 

the firing rate appears not to be a problem in solar hot water systems. The 

temperature dependence of the performance of solar systems has a profound 

effect on overall fuel savings, so that decreasing the minimum firing rate of 

the backup boiler to enhance the solar system's performance is more rewarding 

than raising it to enhance the efficiency of the boiler. 

APPENDIX B 

PROPEETIES OF HEAT FLUIDS* 

Table Page 

13-1 Addresses of Manufacturers of Heat Transfer Fluids ................... 319 

B-2 Melting. Pour. and Boiling Points of Heat Transfer Fluids ........... 323 

B-3 Useful Temperature Ranges and Thermal Degradation 

Temperatures of Heat Transfer Fluids ................................ 325 

B-4 Surface Tensions and Colors of Heat Transfer Fluids ...............,, 327 

B-5 Beats of Vaporization and Coefficients of Thermal 

Expansion of Heat Transfer Fluids ................................... 329 

B-6 Flash Points. Fire Points. and Autoignition Temperatures 

of Heat Transfer fluid^....................^..^^^^^=-^^^^. 331 

B-7 Recommended Fire-Extinguishing Agents for Heat Transfer 

Fluids .............................................................. 334 

B-8 Physiological Properties of Heat Transfer Fluids .................... 335 

B-9 Summary of Density Data ............................................. 341 

B-10 Summary of Viscosity Data ........................................... 343 

B-11 Summary of Specific Heat Data ....................................... 345 

B-12 Summary of Thermal Conductivity Data ................................ 347 

B-13 Summary of Vapor Pressure Data ...................................... 349 

*Source: Adapted from Parts et a1 .. 1980. Superior Heat Transfer Fluids for 

Solar Heating and Cooling Applications. Monsanto Research Corp . 

Table B-1. Addresses of Manufacturers of Heat Transfer Fluids 

Flu1 d Manufacturer Address ?hone 

Hydrocarbons 

Pet roleum-based 

aliphatic hydrocarbons 

Caloria RP-43 Sxxon Company, U.S.A. 

Dials AX Shell Oil Company 

llobiltherm 603 Nobil Oil Corporation 

Silogram Reat Transfer 

Fluid 13 A. Margolis & Sons Corp. 

Sunoco Heat Transfer Oil 21 Sun Oil Company 

Sunoco Heat Transfer Of1 25 Sun oil Company 

Texa t he m 

Thermia Oil C 

Synthetic aliphatic 

hvdrocarbons 

Srayco 358 

Brayco 588 ItT 

Texaco, Inc. 

Shell Oil company 

Sray Oil Company 

Sray Oil Company 

Ethyl Corporation 

Ethyl Corporation 

Ethyl Corporation 

?.lark Xnnterprises , Inc. 

Mark Enterprises, Inc. 

Uniroyal, Inc. 

P.O. Sax 2180 

Houston, TX 77001 713-656-5318 

One Shell Plaza 

P.O. Box 2463 

Bouston, TX 77001 713-241-4334 

150 East 42nd Street 

New York, Ny 10017 212-583-2630 

1504 Atlantic Avenue 

Brooklyn, NY 11216 212-773-6270 

1608 Walnut Street 

Philadelphia, PA 19103 215-972-4150 

1608 Walnut Street 

Philadelphia, PA 19103 215-972-4150 

42nl River Road 

Cincinnati, OH 45204 513-h51-5151 

he Shell Plaza 

P.O. Box 2463 

Bouston, TX 77001 773-241-4336 

9550 Flair Dr., /I301 

El Xonte, CA 7L731 

9550 Flair Dr., $301 

El Yonte, CA 91731 

1600 West Sight Nile Rd. 

Ferndale, MI 43220 

1600 Vest Eight Mile Rd. 

Ferdale, MI 48220 

1500 West Zipht Mile Xd. 

Fernd.de, XI 48220 

50 3azel Terrace 

!?oodbridge, CT 06525 

50 Hazel Tarrace 

SToodbtidge, CT 06525 

Spencer Street 

?Taugatuck, CT g6770 
Table B-1. Addresses of Manufacturers of Heat Transfer Fluids (Continued) 

Fluid Manufacturer Address Phone 

Aromatic hydrocarbons 

Dowtherm J 

Dowtherm LF 

Plohiltherm 6nO 

MCS-1958 

NCS-1980 

MCS-2046 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Dowtherm SR-1 

Prestone I1 

Sunsafe 100 

Sunsafe 130 

The Dow Chemical Co. 

The Dow Chemical Co. 

Gulf Oil Chemicals Co. 

Xobil Oil Corporation 

!4onsanto Company 

Monsanto Company 

Monsanto Company 

Vonsanto Company 

Honsanto Company 

Xonsanto Company 

Xonsanto Company 

2020 Dow Center 

Rarstow Building 

Midland, MI 48640 

2020 Dow Center 

Barstow Building 

Midland, MI 48640 

P.O. Box 2900 

Shawnee Mission, KS 

66201 

150 East 42nd Street 

New York, NP 10017 

800 N. Lindbergh Blvd. 

St. Louis, MO 63166 

800 N. Lindbergh Blvd. 

St. Louis, X0 63166 

800 N. Lindbergh Blvd. 

St. Louis, NO 63166 

800 N: Lindbergh Blvd. 

St. Louis, MO 63166 

900 N. Lindberoh Blvd. 

St. Louis, YO 63166 

800 N. Lindbergh Blvd. 

St. Louis, MO 63166 

800 Y. Lindbergh 31vd. 

St. Louis, >fO 63166 

The Dow Chemical Co. 2o20 Dow Center 

Rarstow Building 

Xidland, MI 48640 517-636-3155 

Union Carbide Corp. Tarrytown Center 

Tarrytown, XY 10591 914-345-22b1 

Xuclear Technolonv Corp . l 2050 North Szoad Street 

:IPD Energy Systems, Inc. Lansdale, PA 19446 215-362-1178 

Nuclear Technology Corp./ 2050 Vorth Rroad Street 

?IPD Pnergy Systems, Inc. Lansdale, PA 19445 215-362-1178 
Table B-1. Addresses of Manufacturers of Heat Transfer Fluids (Continued) 

Fluid Manufacturer Address Phone 

UCAR m-17 

Zerex 

Propylene glycol-base3 

fluids 

Dowf rost 

Practical Solar Fluid 

Solar Winter Ban 

Sunsafe 200 

Sunsafe 230 

Sunsol 60 

UCAR FF-35 

Cs r ers 

Stauf fer 36hh-A 

Cthers 

Dowthen A 

Union Carbide Corp. Tarrytown Center 

Tarrytown, ?lY 10591 914-789-3578 

PPG Industries, Inc. P.O. Box 4026 

Corpus Chtisti, TX 512-883-4301 

78405 

The Dow Chemical Co. 

Practical Solar Reat, Inc. 

Camco Xanuf actur ing , Inc . 

Nuclear Technology Corp . / 

NPD Energy Systems, Inc. 

FTuclear Technology Cotp . / 

NPD Energy Systems, Inc. 

Sunworks 

Union Carhide Corp. 

2020 Dow Center 

Bars tow Building 

Midland, FIX 48640 517-636-3158 

2216 i-tontgomery Streec 215-865-5646 

Bethlehem, PA 18027 

2804 Patterson Street 

Greensboro, NC 27407 919-292-4906 

2050 Xorth Broad Street 

Lansdale, PA 19446 215-362-1178 

205n Xorth Broad Street 

Lansdale, PA 19446 215-362-1175 

P.O. Box 1904 

New Haven, CT 06508 203-934-6301 

Tarrytown Center 

Tarrytown, NY 19591 911-789-3573 

Stauffer Chemicai Company Nyala Farm Road 

Westport, CT 068PO 203-222-3166 

Honsanto Company 800 N. Lindbergh Blvd. 

St. Louis, YO 63166 314-694-2153 

The !hw Chemical Conpany 2020 Dow Center 

Rarstow Building 

Nidland, X1 $8660 517-636-399 3 

The Dow Chemical Company 2020 Dow Center 

3ars:ow Building 

Xtdland, Y1 48640 517-536-3993 

Xonsanto Conpany ROO ??. Lindbergh 31vd. 

St. Louis, YO 63166 315-694-2153 
Table B-1- Addresses of Manufacturers of Heat Transfer Fluids (Concluded) 

. -.~ 

Fluid Manufacturer Address Phone 

Silicones 

SF-96(20) 

?luorocarhons 

Freon 11 

Freon 114 

Freon TA 

Union Carbide Corp. 

General Electric Company 

Dow Corning Corporation 

Dow Corning Corporation 

E. I. duPont de Nemours 

h Co. 

PI. I. duPont de tkmours 

& Co. 

E. I. dePont de Nemours 

h Co. 

Tarrytown Center 

Tarrytown, NP 10591 924-759-3578 

Silicone Products Ikpc. 

Waterford, NY 12188 518-237-3330 

3901 S. Saginaw Road 

Midland, W 48640 517-496-4000 . 3901 S. Saginaw Road 

Xidland. XI 48640 517-496-4000 

Xemours Building 

Wilmington, DE 19898 302-774-2192 

Nemours 3uilding 

Wilmington, DE 19898 302-774-2192 

?Ternours Building 

(Jilmington, DE 19899 302-774-2192 
Table B-2. Melting, Pour, and Boiling Points of Heat Transfer Fluids 

Me1 ting Point Pour Point Boiling Point 

Fluid 

(Oc) (OF) (Oc) (OF) (OC) (OF) 

Hydrocarbons 

Petroleum-based 

aliphatic hydrocarbons 

Caloria HT-43 

Diala AX 

Mobilthena 603 

Silogram Xeat Transfer Fluid 43 

Sunoco Heat Transfer M1 21 

Sunoco Reat Transfer Oil 25 

Texatherin 

Thermia Oil C 

Synthetic aliphatic 

hydrocarbons 

Brayco 888 

Rrayco 888 HF 

ESH-4 

ESH-5 

ESH-6 

H-30 

11-30C 

Unirogal PAO-13C 

Aromatic hvdrocarbons 

Dowtherm J 

Dowtherm LF 

3XE 

?fobilthem 600 

MCS-1958 

MCS-1980 

NCS-2046 

Theninol 55 

Therminol 6rl 

Thenninol 66 

Themino 1 SP 

i 

Glvcals 

Ethylene glvcol-based 

fluids 
Table B-2. Melting, Pour, and Boiling Points of Heat Transfer Fluids 

( Concluded) 

Melting Point Pour Point Boiling Point 

Fluid 

- -- 

Sunsafe 100 (33 vol-Z) 

Sunsafe 130 (50 vol-X) 

UCAR TF-17 (50 wt-X) 

Zerex 

Propylene glvcol-based 

fluids 

Dowfrost (50 wt-X) 

Solar Vinter Ran 

Sunsafe 200 (33 vol-%) 

Sunsafe 230 (50 vol-Z) 

UCAR FF-35 (50 wt-Z) 

- Esters 

Stauf fer 3664-A 

Thenninol 44 

Ethers 

Dowthern A 

Dowtherm G 

Therninol VP-1 

UCON HTF-500 

Silicones 

Fluorocarbons 

Freon 11 

Freon 114 

Freon TA 

- Water 

anitial boiling point. 

holidifies slowly at 21°c ~70~~). 

L~elting range. 

9rystallization begins at this temperature unon cooling. 

$The data pertain to water solution of the glycol. 

3he data pertain to the concentrate. 
Table B-3- Useful Temperature Ranges and Thermal Degradation 

Temperatures of Heat Transfer Fluids 

Fluid 

-- - 

Thermal 

Degradation 

Temperature Range Temperature 

(OC) (OF) (OC) (OF> 

Hydrocarbons 

Pe troleum-based 

aliphatic hydrocarbons 

Caloria HT-43 -7 to 316 20 to 600 >350 >680 

Dfala AX -40 to 163 -40 to 325 

Mobilthenn 603 93 to 288 200 to 550 >316 >600 

Silogram Beat Transfer Fluid 43 -9 to 316 15 to 60& 

Sunoco Heat Transfer Oil 21 -15 to 316 5 to 600 

Sunoco Reat Transfer Oil 25 -15 to 316 5 to 600 

Texatherm 

Thennia Oil C -9 to 288 13 to 550 

hydrocarbons 

Brayco 888 

ESR-4 

ESH-5 

XSH-6 

H-30 

Uniroyal PAD-13C 

Aromatic hydrocarbons 

Dowthem J 

Dowtherm LF 

Nobiltherm 600 

YCS-1958 

?fCS-1980 

YCS-2046 

Theminol 55 

herminol 60 

l'herminol 66 

Therminol 85 

Glycols 

Ethylene glycol-based 

fluids 

Dowthern SR-1 (50 wt-7:) 

?yestone 11 (50 vol-X) 

Sunsafe 100 (33 vol-%) 

Sunsafe 130 (50 vol-X) 

CCAR TF-17 (50 wt-X) 

Zere:r 
Table B-3. Useful Temperature Ranges and Thermal Degradation 

Temperatures of Heat Transfer Fluids (Concluded) 

Fluid 

- -- -p - 

Thermal 

Degradation 

Temperature Range Temperature 

(Oc) (OF) , (OC) (OF) 

Propylene glycol-based 

fluids 

Dowfrost (50 wt-X) 

Practical Solar Fluid 

Sunsafe 200 (33 vol-%) 

Sunsafe 230 (50 vol-%) 

Sunsol 60 

UCAR FP-35 (50 vol-X) 

- Esters 

Stauffer 3664-A 

Therminol 44 

- Ethers 

Dowthen A 

Dowthen G 

Themino1 VP-1 

UCON HTF-500 

Silicones 

SF-96(20) 

Syltherm 444 

X2-1162 

Freon 11 

Freon 114 

Freon TA 

3~sable up to 204'~ (4n0O~) in presence of air, and up to 316~~ (600~~) in

inert atnosphere. 

kJse temperature range extends ur, to 250'1: (500'~) in inert atmosphere. 

2ate of :henna1 degradation at this :emperature is 0.1 vt-9: per week. 

3etermined isoteniscopically . Aower use temperature value is heine; determined. f 4se temperature range for solution in water. 

Bpon contact with steel at 121'~ (250°?), 0.5% degradation per year. 

%?on contact with steel at 2W0c (NOOF), 0.5% deqradation per year. 

.he upper use tenperature aay be affixed by the pressure tolerance of the 

system. The temperature indicated her* corresponds to a maxinum allowable 

fluid pressure of 50 atn (750 psig). 
Table B-4. Surface Tensions and Colors of Heat Transfer Fluids 

Fluid Surf ace Tens ion 

(kN/m) Physical Appearance, Color 

Hyd tocarbons 

Petroleum-based 

aliphatic hydrocarbons 

Caloria HT-43 r 

Diala AX 

Mobiltherm 603 

Silogram Ffeat Transfer Fluid 43 

Sunoco Reat Transfer Oil 21 

Sunoco FIeat Transfer Oil 25 

Texatherm 

Thennia Oil C 

Synthetic aliphatic 

hydrocarbons 

Brayco 888 

Rrayco 888 ffF 

ESH-4 

ESH-5 

XSH-6 

U-30 

H-30C 

Uniroyal TAO-13C 

Aromatic hydrocarbons 

Dowtfterm J 

kwtherm LF 

DXE 

Zobilthem 600 

HCS-1958 

MCS-1980 

YCS-2046 

Themino1 55 

Therminol 60 

Thenninol 66 

Therninol 58 

Glycols 

Ethylene ~lycol-based 

fluids 

Dowt hem 

Prestone I1 

Sunsafe 1r)O 

Pale yellow, L1.O ASTY coloe 

Pale yellow, L0.5 ASTN color 

Pale yellow 

Pale yellow, L1.O ASTM color 

Pale yellow, L1.O ASTM color 

Pale yellow, 0.5 ASTA color 

Pale yellow, L0.5 ASTM color 

Pale yellow, 0. ,5 ASTM color 

Red 

Red 

Colorless 

Colorless 

Colorless 

Green 

Blue 

Colorless 

Colorless 

Colorless to light yeliow 

Colorless to pale yellow 

Clear liquid 

Colorless to light yellow 

Red liquid at 75'~ (167~~) 

-3& Amber-redd is h 

30.48 at 25'~ (77O~) Yellow 

35.24 at 25'~ (77'~) Light yellow 

37.99 at 25O~ (77'~) Clear, pale yellow 

Crumbly, wax-like flakes at 

ambient temperature. Light 

amber liquid above nelring 

point. 

Re d 

Golden yellow 

Colorless 

Sunsafe 130 
Table B-4. Surface Tensions and Colors of Heat Transfer Fluids (Concluded) 

Fluid Surface Tension 

(kN/rn) Physical AppearUCAR TF-17 

Zerex 

Propylene glycol-based 

- fluids 

Dowf ros t 

Practical Solar Fluid 

Solar Winter Ban 

Sunsafe 200 

Sunsafe 230 

Suns01 60 

UCAR FF-35 

Esters 

Stauffer 33644 

Therminol 44 

- Ethers 

Dowtherm A 

Dowtherm G 

Theminol VP-1 

UCON IIT9-500 

Silicones 

SF-96(20) 

Syltherm 444 

X2-1162 

Freon 11 

Freon 114 

Freon TA 

47 .Pale yellow 

48.E at 20'~ (68'~) Orange 

4e Colorless 

Blue 

42.e at 25'~ (77'~) Red 

4d at -4'~ (25'~) 

455 at -4'~ (25OF) Colorless 

42.e 

35S. at 25'~ (77'~) Colorless 

Amber 

Yellow 

Colorless to light strawcolored 

Light amber 

Colorless to pale yellow 

Reddish-amber 

Colorless 

Colorless 

Colorless 

Colorless 

Colorless 

Colorless 

Colorless - - - - - -- -- 

3~~4 1976. 

%st imated value. 

L~he data pertain to 504 solution in water. 

&he data ~ertain to 33Z solution in water. 

z~he data pertain to undiluted concentrate. 5 

;International Critical Tables. 1928. 
Table B-5. Heats of Vaporization and Coefficient of Thermal 

Ehrpansion of Heat Transfer Fluids 

Heat of Vaporization Coefficient of Thermal Fkpansiona 

Fluid 

(cal/g) (~tu/lh) (oc-') ( oF-l) 

Hydrocarbons 

Caloria RT-43 

Fiohiltherm 603 

Texatherm 

Synthetic aliphatic 

hydfocarbons 

Brayco 888 

3-30 

Uniroyal PAD-13C 

Aromatic hydrocarbons 

Dowthem J 

Dowtherm LF 

Nobiltherm 600 

MCS-1958 

YCS-2046 

Therminol 55 

Therminol 60 

Therminol 66 

Glycols 

Ethylene glycol-based 

fluids 

Dowtherm SR-I 

Prestone I1 

Sunsafe 200 

Sunsafe 130 

IJCAQ TF-17 

Zerex 

Propylene slycol-based 

fluids 

Dowfros t 

Sunsafe 200 
Table B-5. Heats of Vaporization and Coefficient of Thermal 

Expansion of Heat Transfer Fluids (Concluded) 

6 

Heat of Vaporization Coefficient of thermal expansiona 

Fluid 

(callg) (~tu/lb) (OC-l) (oF-l) - - 

Sunsafe 230 6.1 3.4 lo-4= 

UCAY FF-35 164 296 7.0 x 1r42 3.9 x At 20'0 (68OF) 

Esters 

Stauf fer 36644 

Therminol 44 

- Ethers 

Dowtherm A 

Dowtherm G 

Therminol VP-1 

UPICON HTF-500 

Silicones 

SF-96(20) 

Fluorocarbons 

Freon 11 

Freon 114 

Freon TA 

3he coefficient of thernal expansion is defined by 

vt - v700~ L J = V700~ t OF -70 ' 

unless a different temperature interval is indicated in the table. 

heported by t'le manufacturer to be similar to values for conventional petroleum oils. 

5s timated value. 

&t atmospheric Dressure. 

ahe data pertai? to 50: solution in water. 

2he data pertain to 33'5 solution in water. 

393'~ (740'~). 

4t 63.6'~ (110.5O?). at 3.8'~ (38.8'~). 

At 23.8'~ (74.9'~). Lt 10oOc (~15~~). 
Table B-6. Flash Points, Fire Points, and Autoignition Temperatures 

of Heat Transfer Fluids 

Flash Point, Flash Point, Autoignition 

ul 

Fire Point Temperature 

III 

Fluid Open CUP Closed Cup 4J 

m 

(Oc) (OF) (Oc) (OF) (Oc) (OF) (Oc) (OF) 

Hydrocarbons 

Petroleum-based 

aliphatic hydrocarbons 

Caloria HT-43 204 

Diala AX 149 

Mobiltherm 603 

Silogram Heat Transfer Fluid 43 216 . 

Sunoco Heat Transfer Oil 21 227 

Sunoco Heat Transfer Oil 25 229 

Texatherm 221 

Thermia Oil C 235 

Synthetic aliphatic 

hydrocarbons 

Brayco 888 

Brayco 888 HF 

ESH-4 

ESH-5 

ESH-6 

H-30 

H- 30C 

Uniroyal PA+13C 

Aromatic hydrocarbons 

Dowtherm 2 

Dowtherm LC 

Dm 

Mobilthe m 600 

MCS-19 8 58-- 

MCS-1980 

MCS-2046 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Dowtherm SR-l 

Prestone I1 

Sunsafe 100 

Sunsafe 13 P UCAR TF-17- 

Zerex 

&-Lee footnotes at end of table. 
Table B-6. Flash Points, Fire Points, and Autoignition Temperatures 

of Heat Transfer ~luids (Continued) 

Flash Point, Flash Point, Fire Point Autoignition 

Fluid Open Cup Closed Cup Temperature 

C0c) (OF). (OC) (OF) (OC) (OF) (Oc) (OF) 

Propylene glycol-based 

fluids 

~owf ros t (LO,?)* (215g 05 (221)29%sf -5 -5 47e(41g+% 87e (788~~ 

Practical Solar Fluid - f 

f (153F* (307F% (-153e2 f (--307*2 48& (424FE 907A (795+2 Solar Winter Ban - - Sunsafe 200 - f - f 

Sunsafe 230 - f - f 

Sunsol 60 - f - f 

UCAR FF-~& (116)c (240g (99g (210)E (421)c (7901% 

Esters 

Stauffer 3664-A 243 470 219 41e 282 540 427 800 

Therminol 44 207 405 19e 38e 225 438 374 705 

W 

W 

h) 

Ethers 

Dowtherrn & 124 255 115% 23e 135 275 621 1,150 

Dowtherm 152 305 13e 27& 157 315 554 1,030 

Therminol VF-1 116 240 115E 23e 127 260 621 1,150 

DCON HTF-500 282 540 244 471 316 600 399 750 

Silicones 

SF-96(20) 

Syltherm 444 

X2-1162 

Fluorocarbons 

Freon 11 

Freon 114 

Freon TA 
Table B-6. Flash Points, Fire Points, and Autoignition Temperatures 

of Heat Transfer Fluids (Concluded) 

3alue determined in present work. 

kFlammability limits in air: lower flammability limit, 0.8 vol-% at 54'~ (130~~) and also at 171°c (340'~); upper flammability limit, 5 vol-X at 

88O~ (190~~) and also at 171°c (340~~). 

9lammability limits in air: lower flammability limits, 0.8 vol-% at 14g0c (300~~) and 0.5 vol-X at 260'~ (500~~); upper flammability limits, 

3.3 vol-% at 149'~ (300'~) and 6.2 vol-% at 260'~ (500'~). 

sot manif old ignition temperature -816°~ (~1,500~~). I 

!?The data pertain to undiluted glycol base stock. I 

fSolutions containing 50 vol-X water do not have measurable flash and fire points. I 

.&olutions containing up to 85 vol-X Prestone I1 in water do not have detectable flash and fire points. I 

k~he autoignition temperatures of Prestone I1 Summer/Winter Concentrate and its 40 vol-% solution in water are reported as 632'~ (1,170'~) and 

688'~ (1 ,270°F'), respectively. 

LE"1ammability limits in air: lower Elammabi2ity limit, 3.2 vol-%; upper flammability limit, 15.3 vol-X. I 

&erex solutions in water, at concentrations lower than 80 vol-X, do not have detectable flash and fire points. I 

%?lammability limits in air: lower flammability limit, 2.6 vol-X; upper flammability limit, 12.5 vol-X. I 

~lammabiliry limits in air: lower flammability limits, 0.8 vol-% at 149'~ (300~~) and 0.5 "01-X at 260'~ (500'~); upper flammability limits, 

3.3 vol-X at 149'~ (300'~) and 6.2 vol-% at 260'~ (500'5'). I 

!!Flammability limits in air: lower flammability limits, 1.2 vol-XI at 171'~ (340~~) and 0.6 vol-X at 260'~ (500~~); upper flammability limits, 

1.2 vol-X at 171'~ (340'~) and 3.3 vol-% at 204'~ (400'~). 

%reon 11, Freon 114, and Freon TA are reported by the manufacturer not to exhibit flash and fire points. I 
Table B-7. Recommended Fire-Extinguishing Agents for Heat Transfer Fluids 

Fluid Recommended Fire Extinguishing Agents 

Hydrocarbons 

Petrolem-based 

aliphatic hydrocarbons 

Caloria HT-63 

Hobilthenn 603 

Silogram Heat Transfer Fluid 43 

Synthetic aliphatic 

hydrocarbons 

Brayco 888 

Brayco 888 HF 

X-30 

Uniroyal PAO-13C 

Aromatic hydrocarbons 

Dowtherm J 

Dowtherm LF 

DXE 

Xobilthem 600 

XCS-1958 

?lCS-1980 

YCS-2046 

Thenninol 55 

Theminol 50 

Therminol 66 

Th'erninol 88 

Glycols 

Ethylene glycol-based 

- f l11ids 

Dowthem Sil-1 

Prestone I1 

VCAX TE-17 

Zerex 

Provylene glvcol-based 

fluids 

Dowfrosz 

Zsters 

Therninol 44 

- Ethers 

Dowthem A 

ilowt>en G 

Cog, dry chemical, foam, water spray or fog 

C02, dry chemical, foam 

Same fire extinguishing agents that are applied to oil fires 

C02, dry chemical 

C02, dry chemical 

C02, foam 

C02, dry chemical, foam, water 

Dry chemical, steam, water spray, or mist 

Dry chemical, steam, water spray, or mist 

C02, dry chemical, foam, water spray; water spray Day be 

used to flush spills away from exposure 

CO,, dry chemical, foam; firefighters must use selfcontained breathing apparatus 

C02, dry chemical, foam, water spray, or mist 

C02, dry chemical 

C02, dry chemical, foam, water spray, or nist 

C02, dry chemical, foam, water spray, or mist 

C02, dry chemical, foam, water spray, or mist 

Cog, dry chemical, foam, water spray, or mist 

Cop, dry chemical 

Cog, dry chemical, foam, water mist for neat fluid; none 

needed for diluted fluid 

C02 or dry chemical for snall fires; foam for large fires 

CO or dry chemical for small fires; foam and water for 

Zarge fires 

Cog, dry chemical, water 

C02, dry chemical, foam, water mist for neat fluid; none 

needed for diluted material 

Cog, dry chemical for snall fires; foam and water for large 

rires 

C02, dry chemical, foam 

lky chemical, steam, water spray, or mist 

Dry chemical, steam, water spray, or sist 

Silicones 

SF-96(20) :by common firefighting agent 

Sylthen 444 C02, dry chemical 

X2-1162 Cop, dry chemicai 
Table B-8- Physiological Properties of Heat Transfer Fluids 

Fluid Physiological Effects 

Hydrocarbons 

Caloria FiT-43 Acute oral LD50 >10 g/kg body weight for rats. Skin 

contact : prolonged contact may cause mild irritation. 

Mutagenicity: Ames test negative 

Diala kY Not reported 

Yobiltherm 603 Safe and nontoxic by Federal Hazardous Substances Act tests 

Silogram Reat Transfer Fluid 43 Mutagenicity: Ames test negative 

SUnOcO Heat Transfer 21 Acute oral LDS0 >30 g/kg body v ight for rats. Inhalation: 

no effect expected at 25 mg/m 5 of air. TLV 5 mg/m3 as oil 

mist. Skin contact: dermal LDSO g/kg body weight. 

Yuragenicity: Ames test negative 

Sunoco Reat Transfer M1 25 Acute oral LDSO >30 g/kg body w ight for rats. Inha ation: 3 3 no effect expected at 25 mg/m of air. TLV 5 mg/m as oil 

mist. Skin contact: no irritation expected unless 

prolonged or repeated contact is allowed. Not expected co 

be toxic by dernal absorption 

Low toxicity and nonirritating to operating personnel 

?Jot reported 

Texathera 

Thermia Oil C 

Eirayco 858 

Aromatic hydrocarbons 

Dowtherm J 

Acute oral LDgO >40 &/kg body weight by ingestion or 

subcutaneously. Eye contact: no irritation by the Dtaize 

test. Mutagenicity: hes test negative 

LD50 >40 mL/kg. Eye contact: non-irritating; Draize 

lndex 0. Skin contact : nonirritating 

Physiological effects similar to those of paraffin oils 

Physiological effects similar to those of paraffin oils 

PhysiologLcal eEfects similar to those of paraffin oils 

Oral LD5* >30 g/kg body weight. TLV >17 mg/liter. 

Mutagenicity: hes test negative 

Not reported 

LDS0 >40 &/kg body weight. Skin contact: causes 13 

irritation. Xutagenicity: Ames rest negative 

LDS0 (rats) is in the range of 1-2 g/kg body weight. Eye 

contact: up to rnild irritation; no corneal icjury 

Likely. Skin contact: up to mlld irritation upon single 

exposure; up to noderare irritation upon prolonged 

exposure, possi5ly mild edema and superficial burn. Xor 

likely to be absorbed in acutely toxic amounts. 

?Iutageaicity: Ames test negative 
Table B-8. Physiological Properties of Heat Transfer Fluids (Continued) 

Fluid Physiological Effects 

Dowthern LF 

XCS-1980 

YCS-2046 

Therminol 55 

Theminol 50 

Theminol 66 

LDSO (rats) is in the range of 2-4 g/kg body weight. 

Inhalation: exposure should be limited to 1 ppm according 

to OSHA guide (1975). Eye contact: may cause pain, slight 

transient irritation; no corneal injury. Skin contact: 

prolonged or repeated exposure aay cause slight to moderate 

irritation. Not likely to be absorbed in toxic amounts. 

Mutagenicity: Ames test negative 

TLV not established. Suggested limiting exposure criterion 

of mist is 5 mg/m3. Skin contact: prolonged or repeated 

contact may cause irritation. Prolonged exposure to mist 

may cause irritation of mucous membrane. Eye contact: may 

cause irritation 

Not reported 

Acute oral LD50 (rats) is approximately 8 g/kg body weight. 

Xutagenicity: Ames test negative 

Xutagenicity: Ames test negative 

Yutagenicity: hes test negative 

LD50 (rats) >15.8 glkg body weight. TLV is not 

established. Inhalation: due to low volatility, no 

observable effects on rats during and after 6-hr 

exposure. Eye contact: mild, reversible irritation to the 

eyes of rabbits. Skin contact: nonlethal at the dose rate 

of 7.04 g/kg body weight. Muta,oenicity: Ames test 

negative 

Acute oral LDSO (rats) is 13.9 g/kg body weight. TLV is not 

established. Inhalation: due to low volatility, no 

observable effects on rats during and after 6-hr 

exposure. Eye contact: sild, reversible irritation to the 

eyes of rabbits. Skin contact3 nonlethal at the dose rate 

of 7.94 g/kg body weight. Pfutagenicity: hes test 

negative 

Acute oral LD (rats) is 10.2 g/kg body weight. TLV is 

5 mg/m3 (0.2Oppm). Inhalation: due to low volatility, no 

observa3le effect on rats during and after 6-hr exposure. 

Eye contact: aild, reversible irritation to the eyes of 

rebbits. Skin contact: dermal LD50 (rats) is 6.3 g/!cg 

body weight. Irritation upon exposure of abraded rabbit 

skin to Thenin01 66. ?lutagencity: Ames test negative 

Acute oral LD59 is 50 glkg body weight. TLV is not 

established. Eye contact: mild, reversi3le irritation t? 

the eyes of rabbits. Skin contact: no irritation upon 2Lhr contact with intact rabbic skin. ?futagenicity: .hes 

test negative 
Table B-8- Physiological Properties of Heat Transfer Fluids (Continued) 

Fluid Physiological Effects 

Glycols 

Ethylene glycol-based 

fluf as 

Dowtherm SR-1 

Prestone 11 

Sunsafe 100 

Sunsafe 130 

UCAR TF-17 

Zerex 

Provylene glycol-based 

fluids 

Ingestion: moderate to low single dose oral toxicity to 

humans. Inhalation: 7-hr exposure to saturated vapors 

generated at 38O~ (100°~) caused no adverse effects to 

rats. Eye contact: nay cause pain and mild irritation; is 

not likely to cause corneal injury. Skin contact: 

prolonged or repeated exposure may cause minor irritation, 

even minor burn. Not absorbed in toxic amounts through 

skin. Mutagenicity: Ames test negative 

TLV 100 ppm. Confirmed cases of harmful effects relate only 

to swallowing. It causes drunkenness, rapidly passi3q into 

coma. Serious or fatal kidney injury. Yutagenicity:. Xmes 

test negative 

Not reported 

Not reported 

Acute oral.LD5* (rats) is j.54 g/kg body weight. TLV is 

100 ppm (vapor), 10 mg/m (particulate). Eye contact: 

flooding the rabbit eye with UCM TF-17 caused a reaction 

no more severe than moderate inflammation. Skln contact: 

undiluted UCAR TF-17 on rabbit belly caused faint redness 

for a short duration 

Single dose of 100 mL of ethylene glycol can be fatal to 

human beings. .Animal studies have indicated that small 

oral doses over a lonq period can produce severe kidney 

injury, bladder stones, and liver damage. Inhalatios: 

TLV, recommended by the American Conference of Gover mental 

Industrial Xygienists is 100 ppm of vapor or 10 mg/m S 

particulates. Inhalation nay be a problem if ethylew 

glycol is hot, or if fog or mist is generated by heat or 

violent agitation. Va,por inhalation overexpQsure may cause 

irritation of the throat, mild headache, and low 

backache. Yutagenicity: .hies test negative 

Acute oral LD5,, (rats) >30 g/kg body weight. As auch as 2% 

to SO% of propylene glycol ingesced by humans appears 

unchanged in the urine in 24 hrs. Chronic oral toxicity is 

also very low. Xats receiving drinking water containing u? 

to 1OZ propylene glycol over a period of 140 days develo~ed 

no ill effects. Rats receiving b.9Z in their diet for 2G 

nonths were normal in their growth. They sustained slight 

liver injury. Eye contact: proaylene glycol is not 

expected to cause irritation. Skin contact: ~ropylene 
Table B-8. Physiological Properties of Heat Transfer Fluids (Continued) 

Fluid Physiological Effects 

glycol does not cause serious skin irritation. Very 

severe, prolonged exposure may produce slight maceration of 

the skin. Mutagenicity: Ames test negative 

Practical Solar Fluid Mutagenicity: .hes test negative 

Solar Winter Ban Not reported 

Sunsafe 200 ?lot reported 

Sunsafe 230 Not reported 

Sunsol 60 Xanufacturer's literature claims that Sunsol 60 is nontoxic 

and does not contain hazardous ingredients 

UCAP FF-35 Acute oral LDSO (rats) is 26.3 g/kg body weight. TLV not yet 

established. Inhalation: air saturated with propylene 

glycol vapor at room temperature killed no animals exposed 

for eight hours. Skin contact: LD50 >20 mL/kg body 

weight. Undiluted propylene glycol caused no irritation on 

the tender skin of the rabbit belly 

- Esters 

Stauf fcr 3664-A 

Ethers 

Dowthem, A 

Accidental ingestion of large doses aay produce symptoms of 

nonspecific irritation of the gastointestinal tract, 

nausea, vomiting, cramps and diarrhea. Inhalation: high 

vapor concentrations may cause nonspecific irritation of mucous membranes in the upper respiratory tract. Skin 

contact: no irritation was observed when this material was 

applied onto the skin of rabbits. Xutagenicity: .bes test 

negative 

Acute oral LDgO (rats) is 13 g/kg body weight. Inhalation: 

rats survived 6-hr exposure and 10-day observation period 

with no noticeable effects, when exposed to air aspirated 

through Theminol 44. Eye contact: slight, reversible 

irritation to rabbit eye. Skin contact: mild irritation 

upon contact with rabbit skin. Hutagenicity: hes test 

negative 

Acute oral LD50 (rats) 2-L g/kg body weight. Inhalation: 

TLV 1 ppm. Eye contact: up to mild irritation but no 

corneal injury. Skin contact: short single exposure not 

likely to cause significant irritation. Prolonged or 

repeated exposure may cause up to mild irritation. 

:?utagenicity: hes test negative 

Acute oral LDgp (rats) 2-4 g/kg body weight. Inhalation: 

suggested TLJ 1 ppm. Eye contact: aild gain, mild 

transient irritation and corneal haziness. Skin contact: 

nild skin irritation. Dermal L3g0 >2 g/kg body weight. 

Mutagenicity: Ames test negative 
Table B-8. Physiological Properties of Heat Transfer Fluids (Continued) 

Fluid Physiological Effects 

Themino1 VP-1 Acute oral LD50 (rats4 1.46 g/Lg body weight. Inhalation: 

TLV 1 ppm or 7 ng/m . Eye contact: slight, reversible 

irritation to rabbit eye. Skin contact: mild irritation 

upon contact with intact and abraded rabbit skin. Dernal 

' LDS0 >5.01 g/kg body weight. Xutagenicity: hes test 

negative 

UCON HTF-500 Not yet established 

Silicones 

SF-96(20) 

Sylthem 444 

%luorocarbons 

Freon 11 

Acute oral tD5,, >20 g/kg body weight. Inhalation: LCSO 

>500 mg/m3 for 1-hr inhalation. Eye contact: minor 

transient irritation by Draize test. Skin contact: no 

irritation. Mutagenicity: Ames test negative 

Information about physiological effects of Sylthem 444 was 

not available from the manufacturer. Rowever, Dow Corning 

Corporation supplied a report on the toxicology of 

silicones. On the basis of this report, 

poly(dimethylsiloxane), the base fluid of Sylthem 444, has 

very low toxicity in rats, whea supplied orally. No 

deleterious effects were detected when fed at a 

concentration of 1% of the diet over a period of 90 days. 

Inhalation: vapor toxicity is low, partly because of the 

very low vapor pressure. Eye contact: transitory 

conjunctive irritation may be caused; no Ternanent 

effect. Skin contact: cause no acanthosis, are not 

absorbed through skin; used in protective skin creams and 

sprays. Mutagenicity: Ames test negative. 

Information about physiological effects of X2-1162 was nor 

available. However, Dow Corning Corporation supplf ed a 

reporr on the toxicology of silicones. On the basis of 

this report, poly(dimethylsiloxane), the base fluid of X2- 

1162, has very low toxicity in rats, when supplied 

orally. Yo deleterims effects are detected when fed at a 

concentration of 1X of the diet over a period of 90 days. 

Inhalation: vapor toxicity is low, parzly because of the 

very low vapor pressure. Eye contact: transitory 

conjunctive irritation nay be caused; no pernanent 

effect. Skin contact: cause no acanthosis, are not 

absorbed through skin; used in protective skin cream and 

sprays 

Inhalation: no effects at 1,000 ppm; LC50 (rats) 

26,200 ppm. Cardiac sensitization in beagle dogs at 

3,500 ?Dm. Xutagenicitp: .hes test negative. 

Teratogenicity: no indications 
Table B-8. Physiological Properties of Heat Transfer Fluids (Concluded) 

Fluid Physiological Sffects 

Freon 114 

Freon TA 

Inhalation: no effects at 1,000 ppm; LC50 >600,000 ppm. 

Cardiac sensitization in beagle dogs at 25,000 ppm. 

Xutagenicity: no indications. Teratogenicity: no 

indications 

No data available for Freon TA. It is composed of 892 

trichlorofluoroethane and 10% acetone. The following data 

pertain to trichlorofluoroethane. Inhalation: LCs0 (rats) 

90,000-100,000 ppm; TLV 1,000 ppm. Cardiac sensitization 

in beagle dogs at 5,000 ppm. Mutagenicity: hes test 

negative. Teratogenicity: no indications 
Table B-9. Summary of ~ensit~'Data (kg/m3) 

Temperature (OC) 

Fluid 

-50 -2 5 0 2 5 5 0 7 5 100 125 150 175 

Brayco 888 

Brayco 888 HF 

Caloria HT-43 

Diala AX 

Dowf rost 

Dowtherm A 

Dowtherm G 

Dowtherm J 919.8 

Dowtherm LF 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Them 600 

Mobil Them 603 

PA0 13C 

Practical Fluid 

Prestone 11 

SI-96 

Silogram 43 

Solar Winter Ban 

Stauffer 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Sunsol 60 

Sylrherm 444 

Texatherm 

Thermia C 

Therminol 44 977.3 

'Rierminol 55 

Therminol 60 1041.1 

Therminol 66 

Therminol 88 

Therminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 
Table B-9. Summary of Density Data (kg/$) (Concluded) 

Temperature (OC) 

Fluid 

200 225 250 275 300 325 350 375 400 450 

Brayco 888 

Brayco 888 HF 

Caloria HT-43 727.4 709.8 692.5 674.3 656.3 639.0 

Diala AX 

Dowf rost 

Dowtherm A 907.5 883.3 858.8 833.4 806.8 779.0 749.2 715.4 680.8 

Dowtherm G 964.7 944.5 924.3 904.1 884.7 865.9 847.6 830.3 

Dowtherm J 710.8 685.1 657.1 626.5 

Dowtherm LF 897.4 877.2 858.1 839.3 821.3 804.0 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 1133.1 1112.7 1086.4 

MCS 1980 983.4 964.9 945.2 

MCS 2046 

Mobil Them 600 829.1 813.5 797.7 781.8 765.2 747.9 

Mobil Them 603 752.5 737.8 722.4 706.5 

PA0 13C 725.5 708.2 690.9 - Practical Fluid 

Prestone I1 

SI-96 735.3 710.3 686.8 

Silogram 43 

Solar Winter Ban 

Stauf fer 3664-A 

Sunoco 21 754.6 735.9 716.1 695.0 673.4 651.8 

Sunoco 25 754.6 735.9 716.1 695.0 672.7 649.6 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Sunsol 60 

Syltherm 444 

Texatherm 752.0 737.8 721.3 704.9 689.8 675.3 

Thermia C 761.8 746.2 727.3 

Therminol 44 783.4 

Therminol 55 762.1 745.1 727.8 710.5 693.9 678.0 

Therminol 60 877.2 859.2 840.5 823.4 806.9 789.6 

Therminol 66 884.1 868.0 851.1 833.8 816.5 799.2 781.9 

Therminol 88 964.1 944.1 926.4 908.2 890.2 869.1 844.4 827.1 

TherminolVP-1 912.3 889.3 865.2 840.7 814.8 786.8 757.2 724.8 688.8 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 909.5 893.6 

Water 865.1 834.1 798.3 

X2-1162 800.2 776.0 749.4 721.2 690.2 657.0 

Zerex 
Table 35-10, Summary of Viscosity Data (cp) 

Temperature (OC) 

Fluid 

0-50 0-25 0 25 5 0 7 5 100 125 150 175 

Brayco 888 

Brayco 888 HF 

Gloria NT-43 

Diala AX 

Dowfrost 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

Dm 

ESH 4 

ESH 5 

ESH 6 

Freon I1 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Them 600 

Mobil Them 603 

PA0 13C 

Practical Fluid 

Prestone I1 

SI-96 

Silogram 43 

Solar Winter Ban 

Stauffer 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Suns01 60 

Syltherm 444 

Texathem 

Thermia C 

Therminol 44 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Therminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 
s=pI +, TR-1356 - \=/ 

Table B-10. Summary of Viscosity Data -(cp) (Concluded) 

Temperature (OC) 

Fluid 

200 225 2 50 275 300 325 350 375 400 425 

Brayco 888 

Brayco 888 HF 

Caloria HT-43 

Diala AX 

Dowf rost 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Them 600 

Mobil Them 603 

PA0 13C 

Practical Fluid 

Prestone I1 

SI-96 

Silogram 43 

Solar Winter Ban 

Stauf f er 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Suns01 60 

Syltherm 444 

Texatherm 

Thermia C 

Therminol 44 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Therminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 
Table B-11. Summary of Specific &at Data [J/ (kg K) 1 

Temperature (OC) 

Fluid 

-50 -25 0 2 5 5 0 7 5 100 125 1 SO 175 

Brayco 888 

Brsyco 888 BF 

Caloria HT-43 

Diala AX 

Dowf rost 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

B 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Them 600 

Mobil Them 603 

PA0 13C 

Practical Fluid 

Prestone I1 

S 1-96 

Silogram 43 

Solar Winter Ban 

Stauffer 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Suns01 60 

Syltherm 444 

Texatherm 

Thennia C 

Therminol 44 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Theminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 
Table B-11. Summary of Specific Heat Data kg K) 1 (Concluded) 

Fluid 

Brayco 888 ' 

Brayco 888 HF 

Caloria HT-43 

Diala AX 

Dowf rost 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Therm 600 

Mobil Therm 603 

PA0 13C 

Practical Fluid 

Prestone I1 

SI-96 

Silogram 43 

Solar Winter Ban 

Stauf fer 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Sunsol 60 

Syltherm 444 

Texatherm 

Thermia C 

Therginol 44 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Therminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 

-- 

Temperature (OC) 

200 225 250 275 300 325 350 375 400 425 
Table B-12. Summary of Thermal ~onductivity Data [W/(m K) ] 

Temperature (OC) 

Brayco 888 

Brayco 888 HF 

Caloria HT-43 

Diala AX 

Dowfrost 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Them 600 

Wbil Them 603 

PA0 13C 

Practical Fluid 

Prestone I1 

SI-96 

Silogram 43 

Solar Winter Ban 

Stauffer 3664-A 

sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Sunsol 60 

Syltherm 444 

Texatherm 

Thermia C 

Therminol 44 

Theminol 55 

Therminol 60 

Therminol 66 

Thermlnol 88 

Therminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 
TR-1356 SSP1 3 

Table B-12. Suntmary of Thermal Conductivity Data [w/ (m K) 1 (Concluded) 

Fluid 

Brayco 888 

Brayco 888 HF 

Caloria ET-43 

Diala AX 

Dowf ros t 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Them 600 

Mobil Them 603 

PA0 13C 

Practical Fluid 

Prestone I1 

SI-96 

Silogram 43 

Solar Winter Ban 

Stauffer 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Suns01 60 

Sylthem 444 

Texatherm 

Thermia C 

Therminol 44 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Therminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 

Temperature (OC) 
'Eable B-13. Sumary of vapor Pressure Data '(pa) 

Temperature (OC) 

Fluid 

-50 -25 0 25 5 0 7 5 100 125 150 175 

Brayco 888 

Brayco 888 HF 

Calotia HT-43 

Dfala AX 

Dowf rost 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

Dm 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Therm 600 

Mobil Therm 603 

PA0 13C 

Practical Fluid 

Prestone I1 

S 1-96 

Silogram 43 

Solar Winter Ban 

Stauf fer 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Suns01 60 

Syltherm 444 

Texa them 

Thermia C 

Themino1 44 

Thermtnol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Therminal VF1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 
TR-1356 

Table B-13, Summary of Vapor Pressure Data (Pa) (Concluded) 

Fluid 

Brayco 888 

Brayco 888 HF 

Caloria HT-43 

Diala AX 

Dowf ros t 

Dowtherm A 

Dowtherm G 

Dowtherm J 

Dowtherm LF 

Dowtherm SR-1 

DXE 

ESH 4 

ESH 5 

ESH 6 

Freon 11 

Freon 114 

Freon TA 

H 30 

MCS 1958 

MCS 1980 

MCS 2046 

Mobil Them 600 

Mobil Them 603 

PA0 1X 

Practical Fluid 

Prestone I1 

SI-96 

Silogram 43 

Solar Winter Ban 

Stauf f er 3664-A 

Sunoco 21 

Sunoco 25 

Sunsafe 100 

Sunsafe 130 

Sunsafe 200 

Sunsafe 230 

Sunsol 60 

Syltherm 444 

Texatherm 

Thermia C 

Therminol 44 

Therminol 55 

Therminol 60 

Therminol 66 

Therminol 88 

Therminol VP-1 

UCAR FF-35 

UCAR TF-17 

UCON HTF-500 

Water 

X2-1162 

Zerex 

Temperature (OC) 
APPENDIX C 

THE SOLIPH COMPUTER PROGRAM 

The SOLIPH computer program was written specificallya for the purpose of generating design tools for this handbook. Like other solar simulation codes 

(e.g., TRNSYS, SOLTES, etc.), SOLIPH is a quasi-steady-state, hour-by-hour 

model. For each hour of the year, climatological data (time, direct normal ' 

insolation, total horizontal insolation, and ambient temperature) are read 

from a TMY (Typical Meteorological Year) weather tape, available for 26 different weather stations. The executive routine reads all the system and climatological input data, and then calls various subroutlnes (collector, pipe, 

heat exchanger, storage, etc.) around closed piping loops. A starting point 

temperature is chosen for each pipe loop (the collector array inlet temperature in the collector loop), and energy balances are performed on each component. The program cycles through each loop as many times as necessary until 

the temperature distribution is essentially unchanged from the previous iteration (to within a specified temperature convergence criterion). Each hour, 

new climatological and loads inputs are used, and the program arrives at a new 

steady-state solution, until the entire year has been modeled* 

A simple SOLIPH model is shown in Fig. C-1. The starting point for this configuration is the inlet collector temperature, The executive routine calls 

the collector subroutine, SOLCOL, which, based on input collector parameters 

PIPE 1 PIPE 3 

PIPE 2 PIPE 4 

Figure C-1. A Simple SOLIPH Configuration 
and climatological data, supplies a collector array outlet temperature. This 

is used as the inlet temperature for pipe 1. The pipe subroutine, PIPE, is 

called and, based on input pipe insulation and ambient temperature, supplies 

an outlet temperature. The outlet temperature is used as the hot-side inlet 

temperature to the heat exchanger. The heat exchanger routine, HX, uses input 

effectiveness and the hot and cold inlet temperatures to compute the two outlet temperatures. The hot outlet temperature is then used as input for 

pipe 2. The PIPE subroutine is again called, and its outlet value replaces 

the inlet collector temperature we started with. If these two temperatures 

are not sufficiently close, the loop must be repeated. 

First, however, the second loop is computed. The cold-side outlet temperature 

of the heat exchanger is used as input for pipe 3. The outlet from PIPE is 

used as the inlet storage temperature. The LOADS subroutine is called to 

determine the load at that hour and to allow a complete energy balance on the 

storage tank, and then STORE is called to determine a new storage tank temperature. This temperature is used as the input for pipe 4, and the output 

temperature from PIPE is compared with the inlet cold-side heat exchanger temperature originally assumed, thus completing the second loop. If either loop 

has not converged within the specified tolerance, both are reiterated. 

To make the code as easy to understand. as possible, energy calculations are 

done in the subroutines where they are most appropriate rather than at the end 

of the executive routine. So, for example, pipe energy loss is calculated in 

the PIPE subroutine, storage loss in STORE, etc. Since only temperature values are needed for loop iteration, calculating all energy values during each . cycle would waste computer time. SOLIPH is set up to do these calculations 

only on the last iteration. 

Output temperatures and energy values are supplied on hourly, daily, and 

monthly bases with an annual cumulative summary. Energy collected by the 

array, energy delivered to the load, and pumping energy are outputs. Energy 

losses are given separately for piping and storage and are also broken down 

according to whether they are operational (durfng collector pump operation) or 

nonoperational losses. Collector array efficiencies are given relative to 

useful energy in the plane of the collectors as well as to total horizontal 

energy. System efficiencies are supplied as the ratio of energy delivered to 

the .load to insolation. Table C-1 is a sample monthly summary. 

Before we describe the various subroutines, we must point out that SOLIPH is 

not a highly user-oriented code like TRNSYS or SOLTES. To change the system 

configuration, the user does not change input data as he or she would for one 

of the other codes. Rather, the user changes the Fortran programming statements in the executive program. Thus, a CALL STORE might be replaced by a 

CALL HX. Although this is not an elegant approach, it saves the code from 

complexity and results in shorter run times. SOLIPH was designed to generate 

design tools, not for public use; therefore, it is not documented for such 

use. Rather, the design tools generated from SOLIPH should make detailed 

computer models unnecessary. The following section describes the basic algorithms used in each SOLIPH subroutine. 
Table 0-1. Sample Monthly ~kry Output 

IBN 

~GJ) 

IAVAIL IAPER 

(GJ) (GJ) 

QCOLL 

(GJ) 

QDEL 

(GJ) 

OLOSS NOLOSS SLOSS ETA(2) 

(GJ) (GJ) (GJ) (XI 

EPAR 

(GJ) 

0.0 

25.9 

29.6 

47.8 

54.0 

52 a5 

SO. 1 

49.8 

42.3 

22.3 

0.0 

42 -8 

33.5 

46.8 

36.9 

48.6 

31.0 

47.5 

50.6 

52 -0 

51.0 

47 .O 

49.8 

53.0 

41.5 

45.8 

0.0 

46 .O 

39.3 

45;9 

- 

14.6 

41.8 

= Total daily horizontal irradiation times collector array aperture area (GJ). 

IBN = Daily direct normal irradiation times collector aperture area (GJ). 

IAVAIL = Daily usable irradiation in collector plane times collector aperture area (GJ). 

IAPER = Daily irradiation in collector plane times collector aperture area (GJ). 

QCOLL = Daily energy collected by collector array (GJ). 

ETA(1) = Collector array efficiency--QCOLL/ITH. 

ETA(3) = Collector array efficiency--gCOLL/IAFER. 

QDEL = Daily collected energy delivered to the load (GJ). 

QLOSS = Daily operational thermal system losses (during pump operation) (GJ). 

NOLOSS = Daily nonoperational system thermal losses (during pump shutdown) (GJ). 

SLOSS = Daily thermal losses from storage tank (GJ). 

ETA(2) = System thermal efficiency--QDEL/IAVAIL. 

EPAR = Daily parasitic (pumping) energy (GJ). ' 

hnthly total or average. 
C.l THE SOLIPH SUBROUTINES 

C.1.1 Subroutine SOLCOL 

This subroutine models a stationary solar collector 'array. Direct normal and 

total horizontal radiation and ambient temperature from the weather tape are 

used. Values of FRTa, FRUL, incident angle modifier coefficients, and the 

collector time constant are input, as well as collector tilt, azimuth, and 

ground-cover ratio. 

First, insolation in the collector plane is calculated. SOLIPH does this in 

the following steps: 

Calculates hour-angle and declination. (A day-of-the-year function is 

used to determine declination.) 

Calculates incident angle and converts normal beam radiation to collector 

plane. 

Calculates diffuse radiation in horizontal plane. 

Converts diffuse to collector plane (including ground and sky terms). 

Adds direct, diffuse, and reflected beam in plane. 

Now, it must be determined whether the collector pump is on. If the pump has 

been operated, this determination is based on the difference between previous 

collector outlet temperature and storage. If the pump is not on, as in early 

morning, a stagnation temperature is calculated as follows: 

where no is the optical efficiency. The stagnation temperature is compared 

with the storage tank temperature, and if it is sufficiently higher, the pump 

is turned on. Several flags provide a deadband temperature range which allows 

for a typical ATon/A~off control scheme. If the pump is on, collector efficiency is calculated from the Hottel-Whillier-Bliss equation (incident-angle 

corrected) and multiplied by insolation and collector area to yield energy 

collected. Collector outlet temperature is then 

Qcoll 

Tout = Tin + 7 

If the pump is off, cooldown loss from the collectors is determined. For collector mass M, specific heat C, and loss coefficient U, we solve a timedependent, first-order ordinary differential equation: 

I.C. : 
Soln. : 

The KaTnol/U term in the differential equation accounts for stagnation heating. The ME value for the collectors is found from the collector time constant rc as determined by ASHRAE 93-77 and input as 

where is the collector mass flow rate value used in the ASHRAE test. Once 

the array temperature is calculated, energy loss is determined as MC times the 

difference between that temperature and the one for the previous time step. 

(At shutdown, the average of inlet and outlet temperatures is used for the 

first value.) These calculations apply only to the collectors and not the 

header pipes. The headers are lumped into the pipe runs to and from the collector array, and their losses are determined with the supply/return pipe 

losses. 

C 1 2 Subroutine TROUGH 

- The parabolic trough subroutine first calculates incident angle for a northsouth or east-west trough array. Direct insolation on the aperture is then 

calculated, correcting for row-to-row shading losses. Pump status is determined by comparing available radiation to an input critical intensity, If the 

radiation is sufficient, an incident-angle modifier is calculated from input 

coefficients. The average fluid temperature T is determined as follows: the 

energy collected per unit area is the product of efficiency and irradiation 

and also the product of mass flow rate, specific heat, and fluid temperature 

rise. Setting these quantities equal, we have 

SOLIPH then uses the quadratic formula to solve this equation for T. When 

the average fluid temperature is known, efficiency can be calculated from the 

input coefficients. (Second-order equations are used for the troughs.) The 

energy collected is then II IA and outlet temperature is calculated just as c' it is for stationary collec6ors. 

Fox situations in which the pump is off, the decaying receiver temperature and 

associated energy loss are calculated just as for stationary collectors. The 

exception is that an input receiver mass is used, so that it does not have to 

be calculated from an input time constant. The stagnation term is not 

included because parabolic trough collectors would be defocussed when the pump 

is off. 
sin TR-1356 

C.1.3 Subroutine PIPE 

If the pump 

temperature, 

a first-order 

B.C.: 

Soln. : 

is operating, pipe outlet temperature is determined from inlet 

ambient temperature, and input insulation, using the solution of 

, ordinary differential equation (see Fig. C-2): 

UrD 

X 

T = Tamb + (Tin - Tamb)e Mc~ 

Energy lost is then 

. Qloss = Mcp(Tout - Tin) 

To determine parasitic power, the Reynolds number is calculated first to 

determine which flow regime is present. The Colebrook equation determines the 

friction factor when flow is turbulent, and f is calculated as 64/Re when flow 

is laminar. For transitional flow, a simple linear interpolation between the 

two is used. Values for total equivalent pipe LID, including fittings and 

elbows, are user inputs. Head is then determined as H = f (L/D) (v2/2g). For 

simplicity, a user input for average collector and heat exchanger pressure 

drops are added here, although they could also be in separate subroutines. 

I 

I 

I I 

I I I Qin - Qouc = h;l cpdT 

F;1 Qin i 

T,n - 1 + Tout 

TI . I I 

I I 

I 

X x + dx 

Figure C-2. Steady-State Pipe Loss Energy Balance 

35 6 
If the pump is off, the solution for temperature decay is similar to that for 

the collectors: 

The Mcp product includes both the fluid and pipe metal. (Insulation heat 

capacity is usually neglected.) The cooldom energy loss is then the product 

of Mcp and the average temperature change over a time step. Note that this 

can be negative for the collectors and pipe. If they have cooled down to 

ambient and the ambient temperature rises, there will be a heat gain. 

C.1.4 Subroutine HX 

The heat exchanger subroutine uses the flow rates, hot and cold inlet temperatures, and the input effectiveness E to compute the hot and cold outlet temperatures using simple heat exchanger effectiveness equations (see Fig. C-3) . Thus, we have 

and 

" 

Figure C-3. SOLIPH Beat Exchanger Model 
. where C refers to heat capacitance flow rate, i.e., Mcp. Heat exhanger 

thermal losses are considered to be negligible. 

C.1.5 Subroutine LOADS 

The LOADS subroutine supplies the load flow rate and return temperature at 

each hour needed to perform the loop energy balances. Load profiles and load 

delivery control schemes are changed by changing the code in LOADS. In a typical setup, LOADS first checks to see if a load exists for a given hour. If 

so, it calculates the difference between the storage tank and load return temperatures to determine whether flow should occur through storage. Several 

flags allow for a deadband, so that a AT,,/AT,~~ control strategy can be 

used. The LOADS subroutine also has a mix valve capability that allows only a 

fraction of the load return fluid to pass through storage and then be mixed 

with bypassed load return fluid to limit the load supply temperature to a set 

value. 

C.1.6 Subroutine SMRE 

The basic storage subroutine assumes mixed storage and takes skin losses into 

account. Flow into and out of storage occurs both on the collector side and 

the load side. If we call the inlet temperature on the collector (hot) side 

Th and the load return (cold) temperature to the tank Tc, and the mixed storage temperature T (same as return to collectors and load supply) (see 

Fig. C-4), we have 

Figure C-4. SOLIPH Storage Tank Heat Balance 

358 
I.C. : TI =To 

t=O 

Soln. : 

where 

Note that, in the case of no flow on either side, the solution reduces to the 

same form as that for the pipe. 

If To is the storage tank temperature at the beginning of the time step, substituting in the time step (one hour) for t in the above solution will give 

the tank temperature at the end of the time step. For the energy balance to 

work, however, we must use the average tank temperature during the time step 

t' ; i.e., we must integrate the above solution and divide by the time step. 

Thus, 

The solution is 

where X = %cp + Qcp + UA. The energy lost from storage is determined by 

integrating the product of UA and the difference between instantaneous 

storage-tank temperature and ambient temperature. Thus, 

t ' 

the solution of which is 

(We should emphasize here that, in all cases, SOLIPH merely uses the solution 

to a differential equation or integral rather than solves it.) The energy 

delivered to the load is calculated as the product of the load mass flow rate, 

specific heat, and difference between load return temperature and average 

storage temperature: 
C -1.7 Subroutine TCSTOBE 

The thermocline storage subroutine (TCSTORE) is a simple 2-node model that 

works by stacking two mixed storage tanks, one on top of the other, and 

calling STORE twice. The storage volume and UA are divided equally between 

the two tanks. Energy delivered is the product of load flow rate, specific 

heat, and the difference between the top tank temperature and the load return 

temperature. Total energy loss is the sum of the losses from each tank. 

C -1 -8 Subroutine BOILER 

This subroutine models an unfired boiler. The boiler is divided into a preheat section and a boiling section; total area is held constant. The temperature of the saturated steam to be delivered is specified, as are inlet hot 

(collector) and cold (load) temperatures and overall U value. Because thermal 

resistance on the oil (hot) side is dominant in both sections, using one U 

value for both is a reasonable approximation. Oil flow can be varied to yield 

a constant steam flow (up to a specified limit), or a constant hot flow can 

yield a variable steam output. Outputs of the subroutine are hot-side outlet 

temperature and the unknown flow. 

The algorithm solves four simultaneous equations. Two are heat exchanger 

equations (using Q = UA LMTD), one for the preheater, the other for the 

boiler. The other two are energy balance equations, one across the preheater, 

the other for the boiler (see Fig. C-5). 

Boiler: 

Preheater: 
Figure C-5. SOLIPB Unf ired Boiler Model 

TH : * Mw, 

Boiler 

U, A1 

This gives us four equations in four unknowns: Tc, Ti, Al, or A2, and the 

unspecified flow. (We know the total area A + A2, but do not know the breakdown.) Since the equations are nonlinear (Itwo contain log terms), we cannot 

solve them by Ggussian elimination. We must combine them into one equation in 

R, defined as (MC~)~~~/(MC~)~ to obtain 

Thus, we have one equation in one unknown, R. Subtracting U(A1 + A*) from 

both sides, we have an equation of the form f(R) = 0. SOLIPH solves for the R 

root by the Newton-Raphson method. Typically, fewer than five iterations are 

required. Once R, and hence the unknown flow rate, is determined, the energy 

delivered is calculated as 

Water 

Ts Side Oil ,-i Side 

Preheater 

U, A2 

- Tc 1 - = ~w, 

, ' 
and the oil return temperature as 

C-1-9 Subroutine FLASH 

This subroutine models a flash valve, flash tank, and feedwater make-up valve 

(see Fig. C-6). All enthalpies are calculated as the product of specific heat 

and temperature, with the exception of saturated steam enthalpy h which is g' determined from a separate steam properties subroutine (McClintock and 

Silvestri 1968). 

C.1.9.1 Flash Valve 

We assume that the pressure upstream of the flash valve is maintained at 5 psi 

greater than the saturation pressure (determined from the steam properties 

subroutine) in order to prevent boiling. Saturation pressure depends on the 

temperature at that point. The AP across the flash valve is, then, the difference between that upstream pressure and the saturation pressure of steam at 

- 

, xhh, _ 

: Saturated Steam 8 

to Load 

I 

From uh, thh, L h,l 

Collectors - Y- Flash 

Flash Tank 

Valve 

To 

Collectors A - Feedwater 

Llha 

Valve 

Figure C-6. SOLIPH Flash System Components and Energy Values 
the desired (input) delivery temperature. Parasitic power is calculated using 

this AP, If the upstream temperature is insufficient to supply steam at the 

desired temperature, the flash valve AP is arbitrarily set at 5 psi. 

C.1.9.2 Flash Tank - 

First, the flash tank temperature is calculated as a function of time, with 

the same algorithm as that used in the storage tank subroutine. We assume for 

this calculation that no steam is delivered. Since the flash valve is a constant enthalpy device, this calculation is performed as if the upstream water 

were directly entering the flash tank. Thus, 

where 

ihcp~h i- UATamb 

Too = 9 

Mhcp + UA 

a 

and %ch is determined upstream of the flash valve. If the temperature T at 

the end of the time step is less than the steam delivery temperature, no steam 

is delivered, and tank.loss is calculated as it is in the storage subroutine: 

where X = Mhcp + UA. If the final calculated temperature exceeds the steam 

delivery temperature, and the initial temperature was less than the steam temperature, we must determine how long it took to reach the delivery temperature, since heating above this point is not physically possible. To do this, 

we replace T with TSteam in the temperature equation and solve for time, 

tboil. Energy loss during the heat-up period can be determined by substituting tboil for t' in the energy loss equation. For time step t', the time left 

after boiling is tleft = t' - tboll* During time tleft, the tank loss is 

simply 

To determine the amount of steam delivered, the steam quality must be calculated from an energy balance: 

Enthalpy in = steam enthalpy + recycled water enthalpy + heat losses + tank 

energy increase, 

Solving for quality x, 

X = h. - ha - koss - 6inc 

G(hg - h!L) 
The tank energy increase term is just 

Energy delivered to the load is the difference between enthalpy of delivered 

steam and enthalpy of the make-up water: 

C-1.9.3 Make-up Valve 

One more energy balance is needed to determine the temperature of the water 

returned to the collectors. Referring to Fig. C-6, we find 

Energy to collectors = energy from the tank + energy of make-up water, 

The return temperature to the collectors T2 is, then, h /c 2 P' 

Because SOLIPH was written to make thousands of runs to generate design tools, 

it was important to check its accuracy. This was done using two methods: a 

"point" comparison of a specific detailed model with other recognized computer 

models and a parametric analysis compared with a recognized simplifed method. 

Fortunately, an IPH system had already been modeled simultaneously with several other codes. In mid-1979, a Systems Simulation and Economic Analysis 

Working Group sponsored by DOE modeled a sample problem IPH system with TRNSYS 

(two different programmers), DOE-2, and a code written at Los Alamos Scientific Laboratory which we will refer to as LASL. An attempt was also made to 

use the SOLTES program, but the user was unable to obtain satisfactory results 

in time. The example problem consisted of a CPC solar collector array, a heat 

exchanger, and a thermocline storage tank (Freeman 1980). 

To check SOLIPH1s performance, one of the task members modeled the sample 

problem with SOLIPH. Approximately 10 hours elapsed from the time work began 

until good results were output. Much of this time was spent incorporating a 

thermocline storage tank and mix valve which SOLIPH did not have at that time. 

Table C-2 shows monthly energy output results from SOLIPH compared with energy 

values supplied by the other programs. This comparison shows very good agreement for both the low- and high-temperature load cases. 

Hourly plots of the storage tank temperature are given in Fig. C-7. Comparisons between the codes of energy collected and energy delivered on an hourly 

basis are shown in Figs. C-8 and C-9. In all cases, the codes are shown to 

agree very well. 
Table 02. Camparison of SOLIPB Energy Outputs With Other 

Computer Models Used in SSEA Sample IPH Problem 

Open-Loop Closed-Loop 

Low-Tempera t ure High-TemperaComputer Load ture Load 

Model 

IHOR ICIN IACPT QCOUT QSOUT QCOUT QSOUT 

(w/m2) (GJ) (CJ) (GJ) (GJ) (GJ) (GJ) 

January 

DOE-2 345.0 441.0 419.0 171.0 164.0 96.0 73.0 

TRNSYS (UW) 345.0 444.0 421.0 172.0 167.0 98 -0 74.0 

TRNSYS (ALTAS) 345.0 444.0 423.0 173.0 166.0 100.0 76.0 

LASL 345.0 444.0 425.0 172.0 170.0 90.0 72.0 

SOLIPH 344.6 443.4 424.4 172.9 166.8 98.4 77.4 

July 

__L 

DOE-2 876.0 652.0 590.0 241.0 235.0 183.0 166.0 

TRNSYS (UW) 875.0 645.0 584.0 241.0 235.0 179.0 163.0 

TRNSYS (ALTAS) 875.0 645.0 588.0 242.0 234.0 184.0 167.0 

LASL 875.0 647.0 593.0 243.0 239.0 174.0 163.0 

SOLIPH 874.7 644.3 592.8 241.8 235.1 183.3 167.9 

Yearly Total 

DOE-2 7625.0 6950.0 6408.0 2622.0- 2472.0 1838.0 1559.0 

TRNSYS 7625.0 6987.0 6396.0 2626 -0 2485.0 1828.0 1552 -0 

TRNSYS (ALTAS) 7625.0 6987.0 6431.0 2646.0 2482.0 1880.0 1588.0 

LASL 7628.0 6980.0 6468.0 2639.0 2531.0 1762.0 1545.0 

SOLIPH 7624.7 6970.0 6492.0 2653.0 . 2501.0 1863.0 1595.0 

To test SOLIPH over a wide range of parameters, a variation study was conducted against FCHART 4.0. FCHART 4.0 is widely recognized and simple to run. 

A total of 20 annual runs of a simple flat-plate collector configuration were 

made with various combinations of the following 14'parameters: 

Collector peak optical efficiency 

Collector UL value 

Collector tilt 

Collector area 

Collector incident-angle modifier 

Ground reflectance 

Collector loop flow rate 

Steady-state pipe losses 

Storage size 

I SOLIPH 

Month 

Figure C-9. Energy Delivery Coaparison of SOLIPE-and SSBh Besults 

(The shaded area represents the range of SSEA results.) 

Storage skin losses 

Load flow rate 

Storage tank minim discharge temperature 

Load profile 

Load return temperature. 

To permit a good comparison, all runs were made for one city, Albuquerque, and 

FCHART monthly insolation values were adjusted to agree with the TMY tape. 

Energy delivery values from SOLIPH and PCHART agreed to within 5% for 15 of 

the 20 runs. This agreement is considered good, since FCHART is a monthly 

code, and its accuracy is expected to be in the range of 5%. Five of the 

runs, however, showed differences of from 5% to 11%. In these runs, temperatures were higher than in the other cases. To determine the cause of these 

differences, we consulted with the University of Wisconsin Solar Laboratory, 

which developed FCHART and TRNSYS, the detailed hour-by-hour code from which 

FCHART was derlved. The Solar Laboratory made several TRNSYS runs fox direct 

comparison with SOLIPH runs. TRNSYS and SOLIPH agree in each case to within 

1-l/2%, but both exhibited differences from FCHART. The hypothesis was that 

the lower energy values from FCWT resulted because PCHART algorithms are 

more conservative at higher temperatures. In any case, the agreement between 

SOLIPH and TRNSYS further supported the accuracy of SOLIPH. 
To check the accuracy of the SOLIPH TROUGH subroutine, parabolic trough runs 

were compared with Sandia-Albuquerque trough predictions. Again, excellent 

agreement was found. Thus, the basic nonsteam components of SOLIPH have been 

verified. However, the unfired-boiler and flash-tank subroutines, the most 

recently developed SOLIPH capabilities, have not yet been verified. Indeed, 

TRNSYS and FCHART do not have these capabilities. Comparisons of SOLIPH 

outputs with hand calculations and checks on energy balances, however, lend 

credibility to their accuracy. 

No attempt has yet been made to validate SOLIPH against field measurements, 

although TRNSYS has been validated for some solar heating cases. In general, 

differences between energy values measured in the field and those of a good 

computer model arise from inaccurate inputs to the computer model, rather than 

from inaccuracies in the model algorithms. For example, when SOLIPH models 

the heat loss from a 500-ft run of collector array return pipe, it uses an 

overall pipe loss coefficient as input. If the user inputs a U value based 

only on the amount of pipe insulation, SOLIPH will probably underpredict the 

temperature drop in the pipe as compared with a field measurement, since 

piping in the field contains many heat loss mechanisms (such as, for example, 

uninsulated flanges and pipe supports). 

In that case, code "validation" often involves simply trying higher U values 

until the code results agree with the field measurements. The model has not 

been changed, but the input has been improved, although we do not know that 

the new U-value is entirely accurate. And we cannot be sure that the results 

are extremely accurate. In a well-insulated pipe, the temperature drop may be 

less than 1°c. With a large mass flow rate, thermal losses can still be significant. But it is very difficult to measure them with great accuracy 

because of the problems associated with measuring a very small AT. Thus, the 

experimental measurement used for the benchmark may itself only be accurate to 

within, say, 15%. The point of all this is that experimental validation of a 

computer model does not ensure good results. The results can only be as accurate as the inputs. 

C.3 THE USE OF SOLIPH 

Because of its lack of user-oriented special features, SOLIPH is relatively 

fast running. A year-long, hour-by-hour simulation of a system that includes 

a collector array, heat exchanger, .storage, and associated piping takes about 

10 CPU seconds of execution time. This amounts to a total cost of about $3.00 

on SERI's CDC 7600 computer. However, the thousands of runs needed to generate design tools resulted in a substantial expenditure for computer time. 

Since the original version of SOLIPH was completed in early 1981, IPH handbook 

task members have contributed a large number of improvements to the model. 

The authors hope that future funding might permit SOLIPH1s capabilities to be 

exploited further, to generate results that could not be obtained before publication of this handbook. More details on SOLIPH can be found in work by 

Kutscher (forthcoming). 
Freeman, To L. 1980 (Jan.). "A Comparison of the Predicted Performance of 

Several Solar System Simulation Codes for an Industrial Process Heating System." . Proceedings of the Systems Simulation and Economic Analysis Conference. SE~I/~~-351-431. Golden, CO: Solar Energy Research Institute. 

Kutscher, C. F. Forthcoming. SOLIPH--A Detailed Computer Model of Solar 

Industrial Process Heat Systems. SERI/TR-253-1481. Golden, CO: Solar 

Energy Research Institute. 

McClintock, R. Be; Silvestri, G. Jo 1968. Formulations and Iterative Procedures for the Calculation of Properties of Steam. New York: The American 

Society of Mechanical Engineers. 

APPENDIX D 

DERIVATION OF ANNUAL-PERFORMANCE EMPIRICAL COBllELBTIONS 

An accurate closed-form solution for the annual energy collection of a solar 

system is not feasible because of the dynamic nature of the many variables 

that affect solar system performance. Instead, empirical correlations, as 

presented in Sec. 6.0, have been used. This appendix describes the approach 

used to provide those empirical correlations, presents the derivation of 

appropriate variable groupings for the key empirical correlations, and discusses the accuracy of the correlations. 

The empirical correlations in Sec. 6.0 were based on the annual results of a 

detailed, hour-by-hour IPB system computer model, SOLIPH, described in Appendix C. Numerous SOLIPH runs were made to provide a sufficiently large data 

base to use in developing the empirical correlations. We made these computer 

runs so that the resulting empirical correlations would largely eliminate the 

need for others to make detailed computer simulations for each IPH system they 

design. 

Simple first- or second-order polynomials were found to provide accurate, 

easy-to-use empirical correlations. They were generated with a multivariable 

regression analysis computer routine which provided polynomial fits to the 

annual results of detailed IPH system simulations. The regression analysis 

routine provided coefficients to the specific polynomial that minimized the 

sum of the squared differences between the SOLIPH-generated data points and 

the empirical fit. 

First- or second-order polynomials were used to keep the empirical correlations as simple as possible. If high-order polynomial fits with many coefficients are provided, the fit may not correlate physically significant characteristics. Instead, extraneous polynomial tenas may be fitting random 

fluctuations. This potential problem is especially significant with a small 

data base. The general rule in generating these empirical correlations is to 

keep the order of the polynomial as low as possible while maintaining a better 

than 4% accuracy (rms error). 

The empirical annual' energy correlations are somewhat subject to the weather 

and dependent on the solar irradiation data base used by the computer model. 

SOLIPH read hourly weather and solar irradiation data from Typical Meteoroloc 

ical Year (TMY) tapes. We selected these tapes because they were generated 

from long-term average weather and insolation information for each site. TMY 

tapes were available for the 26 stations of the SOLMET network. These stations are well distributed over the continental United States, as shown in 

Fig. D-I, and provide a suitably broad data base for empirical correlations. 

The total horizontal irradiation data on the tapes were measured values, while 

the direct normal insolation data were calculated from an algorithm, derived 

by the Aerospace Corporation, that measured direct normal irradiation data for 

five stations. 

Dm2 DERIVATION OF VBBIBBLE GROUPINGS 

The key factor in making accurate empirical correlations is to properly select 

the variable groupings used in the empirical correlation. Appropriate variable groupings are determined by investigating the algebraic form that the 

empirical solution (or in some cases, multiple solutions) would take. The 

form and the variables of these expressions indicate which variable groupings 

will produce accurate empirical correlations. Examples of the derivation of 

several correlations in Sec. 6.0 are given in the subsections that follow. 

D.2-1 The Base Annual Energy Collection Correlation 

The principal empirical correlation given. in Sec. 6.0 is the correlation for 

average energy collection rate qc, shown in Fig. 6-1. The variable groupings 

that produced these accurate, but simple, empirical correlations were identified in Eqo 6-3, the instantaneous rate energy collection equation. 

Consider replacing all of these instantaneous values with long-term average 

values. (Long-term average values are denoted by a bar.) We can then write 

FR and Fs are constants for constant loop flow rates and a given heat 

exchanger. 

- 

Dividing through by F~FG~ no, we obtain 

This equation suggests -- that the average energy collection rate (normalized by 

the grouping FsFRIaTlo) can be correlated as a function only of the variable 

grouping 

However, the closed-form solution implied by Eqo D-1 cannot be used directly, 

because --- it solves for an - instantaneous collection rate, given the average values of UL, Ta, Ia, and no. This is not the same as the long-term average - 

collection rate, given the average, but time-varying, values of cL, Ta, I,, 

and c. The value of Eqo D-1 lies in its suggestion that the long-term average energy collection rate, when normalized by the terms Fs, FR, Ig, and &, 

can be correlated as a function of only one variable grouping. With this form 

of an empirical correlation, an accurate, long-term average energy collection 

rate correlation has been determined. However, the empirical correlation 

given in Sec. 6.0 involves several further simplifications. 
First, we must replace the average collector heat-loss coefficient EL with a 

single value. Usually, UL is considered to be a constant; this allows no compromise. Sometimes a collector's efficiency equation is fit to second order, 

and UL becomes a function of temperature. If so, we use the UL value as 

defined by the process load temperature. This assumption causes little loss 

in the accuracy of the empirical correlation'because the second-order term is 

usually relatively small. 

Next, we replace the long-term average optical efficiency with the peak 

normal incidence optical efficiency no, which eliminates the need to account 

for incident-angle modifier effects at this point in the performance analysis. 

(Incident-angle effects are accounted for in Sec. 6.2.1.) 

Finally, we deal with the quantity Ta, the long-term average available irradiance on the aperture of the-collector. This quantity is not easily defined, 

so we prefer a readily available irradiance measure that requires no further 

calculations. If such an irradiance - measure is available and is directly proportional to yay it can replace 1,. The constant of proportionality is 

accounted for in the formulation of the empirical correlations. Adding 

another variable, site latitude, the long-term average values of total horizontal irradiance and direct normal irradiance yield this proportionality. 

For flat-plate and evacuated-tube collectors, the total horizontal irradiance 

is used. For parabolic trough collectors, the direct normal irradiance is 

used. Both of these irradiance measures are readily available from contour 

maps (see Figs. 3-1 and 3-2) . Now long-term average energy collection can be correlated as a function of the 

variable grouping - 

UL(Tin - Ta) 

for flat-plate and evacuated-tube collectors, and 

for parabolic troughs. This variable is the intensity ratio and serves as the 

basis of the empirical correlations given in Fig. 6-1. As noted in this discussion, the only additional variable needed is the site latitude. 

D.2.2 Mixed-Tank, Recirculation System Loadlstorage Annual Modifier 

The modifier F2-s provided in Sec. 6.1.1.2 accounts for the impact that storage size and process load profile have on energy collection for a recirculation system. The analysis that provided the variable groupings that define 

F2-s follows. 

As described In Sec. 6.1, instantaneous energy collection for a recirculation 

system can be written as 
where Ts is the storage temperature. 

However, the average storage tank temperature for a recirculation (four-pipe 

storage) system is not a known quantity. Storage tank temperature varies 

during collector operation as the tank is charged and discharged. The effect 

of this variation on energy collection can be examined by considering the 

average elevation of the storage tank temperature. If Qstor is the average 

energy stored in the tank over a given time period, then 

Qstor = Qc - Qd , (D-3) 

where 

Qc = energy collected by the solar system 

Qd = average process demand provided from storage while the collectors 

are operating. 

The process load use rate is given by ' 

where 

Ta = load supply temperature 

Tg,r = load return temperature. 

Because all the process flow is preheated through the solar storage tank, the 

energy delivery rate to the process load is 

where Ts is the temperature of the mixed storage tank. 

Equations D-4 and D-5 can,be combined to yield 

If TQ is greater than T,, the solar system sup~lies only a port:on of the 

delivered energy. However, if Ts exceeds T%, Qd is limited to Qr, which 

means that the energy delivery from the solar storage tank cannot exceed the 

process demand. This is generally accomplished by using a mixing valve which 

limits the load supply temperature to TQ. Thus, over an average daytime 

period, the energy delivery from storage is 
where 

- 

Ts = average storage tank temperature during the time period 

C = a - constant to account for the difference in operating hours of 

the process and the solar system. 

Thus, the energy provided from the collectors to storage and then to the 

process load depends on the storage tank temperature. The elevation in 

storage tank temperature during a given time increment At is 

and since the tank is generally only discharged down to TR the average tank 

temperature is approximately ,r' 

From Eqs. D-3 and D-7, the average storage tank temperature can be written as 

The two solutions are now separated--one when the mixing valve is not being 

used and one when it is. 

D.2.2.1 Case 1: No Mixing Valve 

Solving Eq. D-10, when 

we have 

(D- 1 1) 

Now, substituting the solutions for % in;o Eq. Ib2 and solving for 6c on a 

per unit collector area basis (denoted as q,), 
where (mcp) tor is the storage tank thermal capacitance per unit collector 

area. Note that the numerator is the energy collection rate for a solar 

system with infinite storage in which the collector inlet temperatur;e never 

rises above the load return temperature. This quantity is defined as qc,=: 

Dividing Eq. D-12 by Eq. 0-13 to obtain the load/storage modifier, 

D12*2.2 Case 2: Mixing Valve 

Solving Eq. D-10, when 

we have 

Substituting into Eq. D-2 as before, yields 

- 

~~~~[y~n~ - UL(TQ,, - T,)] FXFR%4 AtC 

- - + 

qc FXFRULAt (mco) s tor 

(D- 16) 

Again, dividing by ic,, to obtain the load/storage modifier, 
- c FxFRULA t I-' + CF~F~U~:~~[~~ , 2(mcp)stor~ 

- - = [1 + . (D-18) 

qc ,O0 2(mcp) s tor 1 + F~F~U~ 

2(,mcp)stor 

Note that in both cases the loadlstorage correction terms can be expressed in 

terms of only three variable groupings: 

FXFRUL qc ,=' , and (mcp )load 

2(mcp)stor ' 

qp 

2(mcp)stor . 

These three variable groupings are sufficient to define the storage/load. correction term. If the constant C in Eqs. D-15 and D-18 were known, and if it 

were possible to combine the solutions of Eqs. D-15 and D-18 based on the 

knowledge of h~w often the mixing valve is actually mixing fluid, one could 

conceivably solve directly for the storagelload correction factor. However, 

since this information is not available, the three variable groupings are correlated empirically with the results of the hour-by-hour computer simulations. The resulting polynomial expressions can be evaluated quickly for 

the impact of load profile and storage size. The value of deriving Eqs. D-15 

and D-18 lies, in finding the number and form of the variable groupings that 

will provide accurate empirical correlations. 

Each of the three variable groupings is independent of the others in that none 

can be expressed as a combination of the others. Because they are 

independent, one variable grouping can be divided by another grouping and 

still remain independent. The third variable grouping was divided by the 

first grouping because the third grouping's range of values can be large, and 

if is inconvenient to express it graphically. The third grouping then becomes 

(mcp)load/(~X~R~L). Thus, the three independent variable groupings used for 

the graphic presentations of the storagelload modifiers are 

D-3 ACCURACY OF TEE EMPIRICAL CORRELATIONS 

Several of the annual energy design tools given in Sec. 6.0 were based on 

regression analysis of the annual results of the computer code SOLIPH. In 

this section, we discuss the accuracy of these empirical correlations and the 

extent of the SOLIPH-generated data base upon which these fits were based. 

First, consider the base energy collection correlations of Fig. 6-1. Data 

from all 26 stations were initially used in deriving energy collection correlations. These correlations are fundamental to the energy collection procedure; therefore, the entire weather data base was used. Hundreds of hour-byhour computer simulations of flat-plate, parabolic-trough, and evacuated-tube 

IPH systems were made to map the effects of various system-level variables. 

However, the empirical correlations that were generated from all of these data 
contained an anomaly. At high intensity ratios, the dependence of energy 

collection upon latitude was reversed for north-south parabolic troughs. 

The source of -this anomaly was the Seattle data--the TMY station with the 

lowest annual direct normal irradiation. The annual energy collection at this 

site, as determined by computer simulations, differs substantially from values 

calculated from the empirical fit. While the error is within 4% for intensity 

ratios below 0.3, it increases to 5% at a critical intensity of 0.4 and then 

to 10% at a critical intensity of 0.6. Above a critical intensity of 0.6, the 

error remains at about 10%. All of these errors are underestimation errors-- 

that is, the empirical fit underestimates north-south parabolic trough energy 

collection for Seattle by up to 10%. Because the data points for Seattle, 

which has a latitude of 47.5', show such high deviations from the other data 

points, an empirical fit shifts to the Seattle data points. The shift is the 

natural result of a least squares fit. The resulting fit shows performance at 

high latitude locations to be as good as at low-latitude locations at the same 

direct normal irradiance, and at high intensity ratios. To avoid skewed 

correlations, the Seattle data points were not used in the regression 

analysis. 

The Seattle data were also significantly different from the other 25 TMY sites 

for the flat-plate and evacuated-tube correlations. For these nontracking 

collectors, the Seattle data points were well below those predicted by the 

empirical fit. The empirical correlations provided in this handbook were 

found to be 11% to 17% too high for flat-plate and evacuated-tube collectors 

used in Seattle. 

The uncharacteristic performance of Seattle solar systems as predicted by the 

TMY tape is puzzling. Although Seattle represents an extreme site because of 

its low annual irradiation, it is not clear why collector performance would be 

so atypical. The fact that the flat-plate correlation for Seattle is an 

overestimate butthe parabolic-trough correlation is an underestimate suggests 

that its diffuse-to-total-irradiation ratio is significantly higher than that 

of any of the other 25 sites. However, a thorough investigation of this 

anomaly was beyond the scope of this handbook. The fact that the empirical 

fits do not closely predict Seattle performance was not judged a great 

liability; this or a similar area is not likely to be a potential IPH site in 

the near future because of its poor annual irradiation. IPH systems in 

Seattle can be designed with the correlations in this handbook, but corrected 

according to the errors given above. 

The accuracy of the unshaded annual energy collection correlations is shown in 

Table D-1. The accuracy is tabulated in terms of relative rms error over the 

25 stations. The relative nns error is defined as 

- 

where qactual is the actual energy collection as determined by the detailed 

hour-by-hour computer code, and qfit is the predicted energy collection as 

calculated from the empirical correlation- 
Table D-1. Accuracy of Annual Energy 

Correlations in Fig. 6-1 

Type of Collector rms Error 

Flat platelevacuated tube 2.8 

East-west axis trough 3.5 

North-south axis trough 3.2 

The summation is taken over all the data points that were generated for that 

particular type of collector. About 300 computer runs for each type were sufficient to map out collector performance. ~h'e runs contained variations in 

collector operating temperature, collector UL value, and collector optical 

efficiency for the 25 TMY sites. 

The loadls torage modifiers provided in Sec. 6.1.1.2 for mixed-tank recirculation systems involved numerous variables. This variable quantity necessitated 

many annual SOLIPH runs, and over 400 SOLIPH runs were necessary for each 

SOLMET site considered. To keep the total number of runs needed for this 

design tool to a reasonable level, only 5 of the 26 SOLMET sites were 

considered. They were: Albuquerque, N. Mex.; Erownsville, Tex.; Caribou, 

Maine; Dodge City, Kans.; and Omaha, Neb. These sites were chosen because 

they represent wide ranges in annual irradiation and geographic latitude. 

For each of the five cities and for all four types of collectors (parabolic 

troughs are counted twice because of the two tracking orientations), annual 

SOLIPH results were generated for parametric variations in load flow rate, 

load AT, storage size, and collector performance characteristics. The accuracy of the empirical correlations with respect to the SOLIPH runs is summarized in Table D-2: 

Table D-2. Accuracy of ~oadlstorage 

Modifiers in Figs. 6-4 

Through 6-11 

Type of Collector rms Error 

(%I 

Single-Shift Modifiers (8-hr day) 

Flat plate 3.2 

Evacuated tube 3.4 

East-west axis trough 2.9 

North-south axis trough 3.8 

Three-Shift Modifiers (24-hr day) 

Flat plate 3.6 

Evacuated tube 3 .O 

East-west axis trough 1.6 

North-south axTs trough 2.4 
The row-to-row shading-loss factors given in Sec, 6.3 were generated using all 

26 SOIMET sites as the data base. As the FShade figures show, shading losses 

are defined by the latitude of the site and the ground-cover ratio. Other 

factors influence shading losses, but to a much smaller extent, For example, 

the operating temperature of the collector affects the time the collector 

begins operation. Collectors providing energy at high temperatures (high 

intensity ratios) require more irradiance before they can provide useful heat; 

therefore, they start slightly later in the morning than if they were providing lower-temperature energy. However, over the year, start-up time appeared 

to influence Pshade only slightly. A relative rms error of less than 2% was 

found, and the largest errors occurred for large ground-cover ratios. In 

fact, for ground-cover ratios of 0.4 or below, the largest error in FShade for 

any of the 26 SOLMET sites was just above 1%. 

DERIVATION OF ANNUAL PEB-FORMANCE MODIFIERS 

This appendix presents the derivation of several annual performance modifiers. FB is the unfired-boiler steam system modifier used in Sec. 6.1.2.1. 

Fp is the flash-steam system modifier. The modified optical efficiency nor 

and heat loss coefficient UL' are derived and shown to account for steadystate piping losses, as discussed in Sec. 6.4.1. 

E .I FBs THE UNFLREIFBOILEB FACTOR 

Typically, energy collection of a solar collector (see Sec. 5.0) is written as 

where 

qc = energy collection rate of solar collector per unit collector 

area 

FR = collector heat removal efficiency factor 

TI, = collector optical efficiency 

I, = available irradiance on collector plane 

UL = collector overall heat-loss coefficient 

TCsi = temperature of fluid at inlet to collector 

T, = ambient temperature. 

However, the collector inlet temperature is not a known quantity for an 

unfired-boiler system. Using the unfired-boiler factor FB permits energy collection to be written as 

where T, is the steam saturation temperature. 

To illustrate the derivation of FB, consider the unfired-boiler system of 

Fig. E-1. Saturated water at temperature Ts is supplied to the boiler and 

vaporized to produce saturated steam. The thermal energy required to vaporize 

the water is supplied by the fluid heated by the solar collectors. The tem- , 

perature of this heated fluid is T 

"3"; As this fluid passes through the 

boiler, it cools to a temperature c,i' The unfired boiler has a heat 
sin TR-1356 +I 

Existing Parabolic Trough Equipment Solar System Tc, Check ---- 

\ \ 1 

I I I 

Heat Transfer Steam '' Boiler Fluid LOOP 

Expansion Tank 

Circulating 

Pump 

Steam 

Header 

Figure E-1. Unf ired-Boiler System 

exchanger area A and an overall heat transfer coefficient of Ub. This leads 

to the energy ba ? ance 

where 

GC = collector loop flow rate 

c = collector loop fluid specific heat 

P 

AT, = log-mean temperature difference across unfired boiler. 

The log-mean temperature difference for the unfired boiler is 

Substituting Eq. E-4 into E-3 and solving for Tc,i results in 
From Eq. E-3, we have 

where &, is the collector loop flow rate per unit collector area (&/A~). 

Substituting Eq* E-6 into Eq. E-5 provides 

Solving for TCsi yields 

This can be reduced to 

If we substitute this expression for Tcpi into Eq. E-1, we get 

Solving for qc, we get 
Equation E-11 can now be written a.s 

where 

(E- 12) 

This expression is used in Sec. 6.1.2.1 to define the annual performance of an 

unfired boiler steam system. 

E.2 FF, THE FLASH ST- SYSTEn FACTOR 

The flash-steam system factor is solved in the same manner as FB. A flashsteam system is shown in Fig. E-2. Consider the collector/flash valve/flash 

tank as a "black box" in which feedwater enters and steam leaves. The feedwater mass flow rate must equal the steam mass flow rate. The feedwater typically enters the tank at a temperature well below the saturation temperature, 

so that the solar system requires two heating steps. First, the feedwater is 

heated to saturation, and then the saturated water is vaporized into saturated 

steam. The solar system energy collection rate is therefore related to the 

feedwater (or steam) mass flow rate as 

;C = mf [cp(TS - Tf) + bhfg] , (E- 13) 

Figure E-2. Flash-Steam System 

Steam a 10 * to 

Process ; 

Ts 

i - bQ Flash 

Ftas h Tank 

Valve 

A 

! 

Recirculated 

Water 

T, 

- - Feedwater 
sm?l :el TR-1356 

where 

mf = feedwater mass flow rate per unit collector area 

c = specific heat of feedwater' P 

T, = steam saturation temperature 

Tf = feedwater temperature 

Ahfg = heat of vaporization of feedwater to steam. 

Equation E-13 can be written in terms of the feedwater mass flow rate as 

The flow scream feeding the collectors is made up of two mixed flow, streams. 

One flow stream is the feedwater and the other is recirculated water from the 

flash tank: 

where 

mc = mass flow rate through collector field per unit collector area 

kf = feedwater mass flow rate per unit collector area 

w 

mr = mass flow rate of recirculated' water from flash tank per unit 

collector area. 

The temperature of the fluid entering the collectors TCpi is the mixed stream 

temperature: 

Substituting Eq. E-16 and Eq. E-14 into Eq. E-17, the collector inlet temperature can be written as 
If we substitute this expression for Tc,i into Eq. E-1, we obtain 

Solving for qc, we have 

Equation E-20 can now be written as 

sc = F~[FR~OI~ - FRUL(T, - ~a)] 3 

where 

This expression is used in Sec. 6.1.2.2 to define the annual performance of 

flash-steam solar systems. 

E-3 Tho' AND x', TBE STEBDY-STATE PIPE LOSS XIDIFIERS 

By a simple adjustment of the collector parameters UL and no, we can include 

the effects of steady-state thermal losses from the piping to and from the 

collector array. 

Consider the solar system shown in Fig. E-3. The inlet piping and outlet piping have overall heat loss coefficien;~ UiA and UoAo, respectively. The mass 

flow rate of the collector fluid is mc, an2 the specific heat of the fluid is 

c . The temperature delivered at the end of the outlet is T, and that at 

tRe entrance of the inlet pipe is T~,~. The temperature drops ayong the inlet 

and outlet pipes are ATi and ATo, respectively. 

The useful power delivered to the heat exchanger from the collectors is 

. . Qu = Mccp(Tc,o - Tc,~) (E- 2 2) 

Using the collector efficiency equation, Qu can also be expressed as 
sin TR-1356 

1 

Storage 

Tank 

1 I 

Pigure E-3. Double-Loop Solar System 

where 

A, = collector area 

I, = irradiance in the plane of the collectors 

Ta = ambient temperature 

@,tot = total heat losses from the inlet and outlet pipes. 

To calculate we consider first the losses from the inlet pipe. The 

governing differential equation is 

(E- 2 4) 

where 

Ai = outside surface area of the inlet pipe 

Ui = heat loss coefficient of the inlet pipe. 

This has the following solution for the outlet temperature of the pipe: 
Since the heat loss is MccpATi, the heat loss QQ ,i from the inlet pipe is 

The solution is similar for the outlet pipe, with T,,, + ATo replacing Tcyi, 

and ATo replacing ATi: 

. so that the heat loss from the outlet pipe is qcpATo, or 

Adding the contributions from the inlet and outlet pipes (Eqs. E-26 and E-28), 

(E-29) 

Rearranging this equation and substituting QU from Eq. E-22, 

(E-30) 

Now we can substitute Eqs. E-25 and E-30 into Eq. E-23, obtaining 

Solving for Q,, 
This can be written in the same form as Eq. E-23: 

except that now the piping losses are included in the modified values TI ' and 

lJLt which are defined as follows: 0 

The modified no and U values defined by Eqs. E-34 and E-35 can be employed 

directly in the variable groupings used for calculations of energy collection 

in Sec. 6.0. 

APPENDIX F 

AMBIENT TEHPERATIJBE DATA FOR 72 U.S. CITIES* 

Albuquerque, NM 16 

Apalachicola, FL 22 

Astoria, OR 9 

Atlanta, GA 18 

Bismarck, ND 7 

Blue Hill, MA 10 

Boise, ID 16 

Boston, MA 12 

Brownsville, TX 25 

Cape Hatteras, NC 19 

Caribou, ME 4 

Charleston, SC 21 

Cleveland, OR 12 

Columbia, MO 14 

Columbus, OH 13 

Davis, CA 18 

Dodge City, KS 15 

East Lansing, HI 7 

East Wareham, MA 11 

El Paso, TX 19 

E~Y, ?sfv 10 

Fort Worth, TX 21 

Fresno, CA 19 

Gainesville, FL 23 

Glasgow, MT 7 

Grand Junction, CO 17 

Grand Lake, CO 5 

Great Falls, MT 9 

Greensboro, NC 16 

Griffin, GA 19 

Hatteras, NC 18 

Indianapolis, IN 13 

Inyo Kern, CA 20 

Ithaca, NY 10 

Lake Charles, LA 22 

Lander, WY 8 

Las Vegas, NV 

Lemont, IL 

Lexington, KY 

Lincoln, NE: 

Little Rock, AR 

Los Angeles, CA 

Madison, WI 

Medford, OR 

Miami, FL 

Midland, TX 

Nashville, TN 

Newport, RI 

New York, NY 

Oak Ridge, TN 

Oklahoma City, OK 

Omaha, NE 

Phoenix, AZ 

Portland, ME 

Rapid City, SD 

Riverside, CA 

St. Cloud, MN 7 

Salt Lake city, UT 13 

San Antonio, TX 22 

Santa Maria, CA 16 

Sault Ste. Marie, MI 6 

Sayville, NY 13 

Schenectady, NY 10 

Seattle, WA 12 

Seabrook, NJ 14 

Spokane, WA 10 

State College, PA 9 

Stillwater, OK 18 

Tampa, FL 24 

Tucson, AZ 22 

Upton, NY 13 

Washington, DC 15 

*These data have been compiled from Table C-1 of Applications of Solar Energy 

for Heating and Cooling of Buildings, ASHRAE GRP 170, 1977. 

**T, = average annual daytime temperature, OC; T = average January daytime 

temperature, OC. j 

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(Write for free Solar Energy Bibliography #9) 
Availability-the fraction of time that a solar energy system is available to 

be used by an industrial process. It does not include climatic conditions 

that might render the system unusable, but is meant to be a measure of the 

mechanical reliability of the solar system. Availability is defined as 

Solar System - Total Time Period - Periods of Solar System Downtime 

Availability - Total Time Period x 100%. 

Beam Irradiance--solar radiation that has not been scattered by dust or water 

in the atmosphere and is, therefore, capable of being focused. 

Central Receiver--a concentrating solar energy collector consisting of a field 

of ground-mounted heliostats that reflect sunlight onto a receiver mounted on 

a tower. The heliostats track the sun to maintain reflected sunlight on the 

receiver. 

Clearness Index--the ratio of the clear-day beam irradiance at a location to 

the irradiance calculated for the standard atmosphere at the same location and 

date. 

Collector Efficiency--the ratio of energy collected by an individual solar 

collector or an array of collectors to the energy incident on the collector or 

array. The energy incident is normally the energy within the acceptance angle 

of the collector, or, for flat-plate collectors, the total energy in the collector plane. 

Diffuse Zrradiance--solar radiation that is scattered by air molecules, dust, 

or water droplets before reaching the ground and so cannot be focused. 

Direct Normal Irradiancen-beam irradiance measured perpendicular to the direction of the sun. 

Direct System Configuration--a system configuration in which the process working fluid is heated directly in the solar collectors before being delivered to 

the process. 

Double-Walled Heat Exchanger--a heat exchanger with two physical walls to separate the fluid being heated and the fluid being cooled to prevent mixing. An 

intermediate fluid transfers the heat between the two walls (see Fig. H-1) . Double-walled heat exchangers are used primarily to avoid contamination of one 

fluid (usually potable water) by another fluid (usually a toxic heat-transf er 

oil) 

End Loss--energy that is focused off the end of a parabolic trough collector 

when it is not at normal incidence to the sun. This energy normally misses 

the receiver and is not, therefore, collectable. 
Visual 

Indicator 

Toxic Heat L 

Transfer Medium = 

Expansion Chamber Containing 

Intermediate Transfer 'Fluid 

Innermost Potable 

Water Tube 

Figure H-1. Double-Walled Heat Exchanger 

Evacuated-Tube Collector--a solar collector in which the absorber is contained 

within a glass envelope (usually two concentric cylinders sealed together at 

one or both ends), and the envelope is evacuated to eliminate convection heat 

transfer. Several tubes are usually contained in a collector module (see 

Fig. H-2). 

Fluid Out ;l Fluid In 

Figure XI-2. Concentric Glass Evacuated-Tube Collector 
F-CHART Procedure--a solar system performance and sizing procedure, developed 

by the University of Wisconsin, for solar heating and cooling applications. 

The procedure is expressed in terns of a universal f-chart family of curves. 

Flash-Steam System--a system configuration in which water at a pressure sufficient to prevent boiling is circulated'-through the collector field and then 

flashed to steam across a throttling valve into a separator where the steam is 

removed for delivery to the process. 

Flash Tank--the tank In a flash-steam system in which steam and water are 

separated. 

Flat-Plate Collector-a solar collector consisting of a flat, black absorber 

plate of metal or other suitable material insulated on the bottom and edges 

and covered by one or more transparent covex(s) . Beat is removed from the 

collector by air or liquid that circulates through or around the absorber 

plate (see Fig. H-3). 

Global Irradiance-the total solar irtadiance (beam plus diffuse) incident on 

a flat surface. 

Ground Cover Ratio--the ratio of collector aperture area to the land area 

occupied by the collector array. 

H-Q Curve--the characteristic locus of operational points for a pump, 

.expressed as a curve of flow rate versus head on the pump. 

Heat Pipe--a heat transfer device with a very low thermal resistance that consists of a sealed chamber containing a liquid and its vapor. Heat is transferred by liquid evaporation at the hot end of the chamber, vapor flow to the 

cool end, and vapor condensation at the cool end of the chamber. The liquid 

is returned to the hot end by a wick, by gravity, or by means of a pump. 

Absorber Surface - 

Figure Ff-3. Flat-Plate Collector 
Heat Transfer Efficiency Factor (HTEF)--an index that relates the heat transfer coefficient and the pumping power requirement for a heat transfer fluid, 

independent of mass flow rate. A fluid with a high HTEF value will have relatively low pumping power requirements for a given heat transfer coefficient. 

Heliostat--a ground-mounted reflector assembly-that tracks the sun to reflect 

sunlight onto the absorber of a central receiver. 

Industrial Process Heat (1PH)--thermal energy used in an industrial process 

(usually heated air or liquid, steam, or radiant heat). 

Incident-Angle Modifier--the factor by which the optical efficiency of a solar 

collector is multiplied to account for the angle of incidence of the sunlight 

on the collector. 

Indirect System Configuration--a system configuration in which the collector 

loop contains a fluid separate (and usually different) from the fluid used in 

the industrial process. The process fluid is heated by heat exchangers. 

2 Irradiance--radiant power flux on a surface (Wlm ). 

2 Irradiation--the time integral of irradiance (~/m ) . Life-Cycle Costing-an economic analysis method that considers all of the relevant costs over the life of a system, including acquisition, maintenance, 

operation, and disposal. The method compares design and ownership alternatives, and also analyzes the present worth of all future costs. 

- Linear Concentrating Collector-a solar collector in which the sunlight is 

focused in one dimension, either by reflectors or other optical devices, onto 

a linear absorber smaller in surface area than the collector aperture. Except 

at low concentration ratios, these collectors must track the sun to keep the 

focused sunlight on the receiver; they collect primarily the beam component of 

sunlight. 

Optical Efficiency--the efficiency at which a solar collector would operate if 

no thermal losses occurred and, therefore, optical losses were the only constraints on performance. The intercept of the efficiency curve of a collector 

for the fluid parameter (ATII), equal to zero. 

Parabolic Dish Collector--a point-focus solar collector consisting of a 

reflector in the shape of a paraboloid of revolution, a receiver fixed at the 

focal point of the reflector, and a two-axis tracker to point the collector at 

the sun. 

Parabolic Trough Collector--a linear concentrating solar collector in which 

the sunlight is collected by reflection off a parabolic reflector (Fig. H-4). 

Parasitic Energy--the energy (usually electricity) required to run the solar 

system, including pumps, trackers, and the control system. 
Figure E-4. Parabolic Trough Collector 

Phase-Change Material (PCM)--a substance that undergoes a reversible phase 

change when energy is' added to it at a nearly constant temperature. Such 

materials are used to store energy in latent heat, which is more efficient in 

terms of stored energy density than sensible heat systems. 

Point-Focus Collector--a solar collector in which beam radiation entering the 

collector aperture is focused in two dimensions to a point at a receiver. 

concentrating the sunlight in two dimensions requires that the collector track 

the sun in both elevation and azimuth; theoretical concentration ratios of 

about 11,000 are possible. 

Pyranometer--an instrument for measuring global irradiance (see Fig. H-5). 

Figure -5. manometer 
Figure R6. Pyrhelio~leter 

Pyrheliometer--an instrument for measuring direct normal irradiance 

(Fig. H-6). The instrument must track the elevation and azimuth of the sun. 

R-Value-a measure of the thermal resistance, of a particular thickness of 

insulating material. 

Rock Bin Storage-a thermal storage component for air systems consisting of a 

large container filled with rocks and fitted with plenums so that air can be 

blown through the device, transferring heat to or from the rocks by 

convection. 

Solar Heating and Cooling (SHAC)--a program begun in the 1970s by the U.S. 

Department of Energy to demonstrate solar energy applications for heating and 

cooling buildings and for hot water production for residential and commercial 

use. 

Sawtooth Array Configuration--a collector array layout with flat-plate collectors arranged in parallel east-west rows (Fig. H-7). 

Selective Surface--a surface treated so that its absorptance for solar radiation is increased relative to its emittance for infrared radiation. 

Shading Loss--the loss of available sunlight due to shading of the collectors 

by other collectors in the array at low elevation angles of the sun. 

Solar Effectiveness--the ratio of fuel energy saved because of energy delivered by the solar system to the energy delivered by the solar system. This 

factor is used in comparing the cost of enere delivered by a solar energy 

system to the cost of energy from conventional sources. 

Solar Fraction--the fraction of the total process load that is supplied by the 

solar energy system. 

Solar Pond--a low-cost solar collector concept. Two kinds of solar ponds are 

the most popular: shallow solar ponds and salt gradient solar ponds. Shallow 

solar ponds consist of bags of water heated by the sun during the day and 

drained at night. They supply energy at temperatures up to 50°C. Salt gradient solar ponds work on the principle that solar-heated water with high concentrations of dissolved salt will remain at the bottom of the pond by virtue 

of its higher density. Salt gradient ponds produce heat at temperatures up to 

90'~ and provide for seasonal storage as well as solar collection. 

SOLMET-an acronym for the National Oceanic and Atmospheric Administration 

(NOAA) network of 26 meteorological measurement stations and the data obtained 

from that network. Locations of the SOLMET sites are listed in Table H-1 and 

are shown in Fig. I)-1. 

Stagnation--the condition in which a solar collector is allowed to be in a 

sun-facing position with no coolant flow. Temperatures reached in stagnation 

are much higher than normal operating temperatures, especially in evacuatedtube collectors and concentrating collectors. 

System Thermal Efficiency--the ratio of the thermal energy delivered to the 

process by the solar energy system to the solar energy incident on the collector array. The energy incident is normally the energy within the acceptance 

angle of the collector, or the total in the collector plane for flat-plate 

collectors. 

Typical Meteorological Year (TMY)--a set of typical-year, hour-by-hour meteorological values - for SOLMET locations derived from statistical analysis of 

many years of.data from each SOLMET station (see SOLMET). 

Unfired Boiler--a vessel designed to produce steam using hot heat transfer oil 

as the heat source. Normally, such vessels come as a package with their own 

condensate level control, etc. 

Utilization--a measure of how well a solar system is utilized by the industrial plant to which it is attached. It is further defined as the ratio of 

the period of time that the solar system is operated by the industrial plant 

to the period of time that the solar system is available for use (i.e., the 

time it is not down for maintenance), or 

Periods of Operation of the Solar System 

Solar System to Collect Energy for the Process 

Utilization = Total Period of Time - Periods of Solar x 100% . System Downtime 
Table R1. 26 SOIMET Sites 

-- 

WBAN North West Approximate 

Location Latitude Longitude Elevation Number (degrees) (degrees) (m) 

Phoenix 

Fresno 

Santa Maria 

Washington 

Apalachicola 

Miami 

Dodge City 

Lake Charles 

Caribou 

Boston 

Columbia 

Great Falls 

Omaha 

E~Y 

Albuquerque 

New York 

Cape Hatteras 

Bi smarck 

Medf ord 

Charles ton 

Nashville 

Brownsville 

El Paso 

Fort Worth 

Seattle 

Madison 

APPENDIX f 

CONVEBSIOH TABLES 

Adapted with permission from the Annual Book of ASTM Standards, Part 41. 

Copyright, American Society for Testing and Materials, 1916 Race Street, 

Philadelphia, Pa. 19103. 

CLASSIFIED LIST OF UNITS 

To convert from 

ACCELERATION 

f t/s2 metre per second squared (m/s 2 ) 

free fall, standard (g) metre per second squared (m/s 2 ) 

gal 2 metre per second squared (m/s ) 

ids metre per second squared (m/s 2 ) 

degree (angle) 

minute (angle) 

second (angle) 

acre 

are 

bar 

circular mil 

darcy 

ft2 

hestare 

inL 

mi2 (international) 

mi2 (U.S. statute) 

yd2 

dyne* cm 

kgfom 

ozf*in 

Ibfoin 

Ibfoft 

lbf f t/in 

Ibf*in/in 

ANGLE 

radian (rad) 

radian (rad) 

radian (rad) 

AREA 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

BENDING MOMENT OR TORQUE 

newton metre (N*m) 

newton metre (Nam) 

newton metre (Nom) 

newton metre (Nom) 

newton metre (Nom) 

BENDING MOMENT OR TORQUE PER UNIT LENGTH 

newton metre per metre (~*rn/m) 

newton metre per metre (~*m/m) 

Multiply by 

Note: An asterisk (*) after the sixth decimal place indicates that the conversion factor is exact and that all subsequent digits are zero. A11 other 

conversion factors have been rounded to the figures given in accordance 

with ASTM E-380 Sec. 4-4. Where less than six decimal places are shown, 

more precision is not warranted* 

409 
sen 8 TR-1356 

To convert from - to 

CAPACITY (SEE VOLUME) 

DENSITY (SEE MASS PER UNIT VOLUME) 

ELECTRICITY AND MAGNET ISM^ 

abampere 

abcoulomb 

abf arad 

abhenry 

abmho 

abohm 

abvolt 

ampere hour 

EMU of capacitance 

EMU of current 

EMU of electric potential 

EMU of inductance 

EMU of resistance 

ESU of capacitance 

ESU of current 

ESU of electric potential 

ESU of inductance 

ESU of resistance 

faraday (based on carbon-12) 

f araday (chemical) 

faraday (physical) 

gamma 

gauss 

gilbert 

maxwell 

mho 

oersted 

ohm centimetre 

ohm circular-mil per foot 

s tatampere 

statcoulomb 

s tatfarad 

stathenry 

s tatmho 

statohm 

s tatvolt 

unit pole 

ampere (A) 

coulomb (C) 

farad (F) 

henry (H) 

siemens (S) 

ohm (Q) 

volt (V) 

coulomb (C) 

farad (F) 

ampere (A) . volt (V) 

henry (H) 

ohm (Q) 

farad (F) 

ampere (A) 

volt (V) 

henry (H) 

ohm (52) 

coulomb (C) 

coulomb (C) 

coulomb (C) 

tesla (T) 

tesla (T) 

ampere (A) 

weber (Wb) 

siemens (S) 

ampere per metre (A/m) 

ohm metre (Q.m) 

ohm metre (Q.m) 

ampere (A) 

coulomb (C) 

farad (F) 

henry (H) 

siemens (S) 

ohm (Q) 

volt (V) 

weber (Wb) 

ENERGY (INCLUDES WORK) 

British thermal unit 

(International Table) joule (J) 

British thermal unit (mean) joule (J) 

British thermal unit 

( thermochemical) joule (J) 

Multiply by 

'ESU means electrostatic cgs unit. EMU means electromagnetic cgs unit. 

410 
To convert from - to 

British thermal unit (39'~) 

British thermal unit (59'~) 

British thermal unit (60'~) 

calorie (~nternational Table) 

calorie (mean) 

calorie (thermochemical) 

calorie (15'~) 

calorie (20'~) 

calorie (kilogram, Internat Tonal Table) 

calorie (kilogram, mean) 

calorie (kilogram, 

t hermochemical) 

electronvolt 

erg 

f t* lbf 

f t-poundal 

kilocalorie (International 

Table) 

kilocalorie (mean) 

kilocalorie (thermochemical) 

kl4 . h 

them 

ton (nuclear equivalent of TNT) 

+ Wwh 

Wws 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

joule (J) 

ENERGY PER UNIT AREA TIME 

2 Btu (thermochemical) / (f t s) 

Btu (thermochemical) / (ft2*min) 

Btu (thermochemical) / (f t2*h) 

Btu (thermochemical) /(in2* s) 2 cal (th rmochemi cal) / (cm win) 

erg/lcm'* s) 

~/cm 

a/ in2 

watt 

watt 

watt 

watt 

watt 

watt 

watt 

watt 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

square metre 

FLOW (SEE MASS PER UNIT TIME OR VOLW PER UNIT TIME) 

FORCE 

dyne 

kilogram-f orce 

kilopond 

kip (1000 lbf) 

ounce-f orce 

pound-f orce (lbf) 

Ibf /lb (thrus t/weight 

[mass] ratio) 

poundal 

ton-force (2000 lbf) 

newton (N) 

newton (N) 

newton (N) 

newton (N) 

newton (N) 

newton (N) 

Multiply by 

newton per kilogram (~Ikg) 

newton (N) 

newton (N) 
To convert - to 

lbf If t 

lbf /in 

FORCE PER UNIT AREA (SEE PRESSURE) 

FORCE PER UNIT LENGTH 

newton per metre (~/m) 

newton per metre (~/m) 

HEAT 

Btu (In ernational Table) *f t/ 5 (haft *OF) (k, thermal 

conductivity) watt per metre kelvin [W/(m*K)] 

Btu (th rmochemical)*f t/ 5 (heft *OF) (k, thermal 

conductivity) watt per metre kelvin [W/(moK) ] 

Btu (International Table) *in/ 

(h* f t2*'F) (k, thermal 

conductivity) watt per metre kelvin [W/(m0K)] 

Btu (thermochemical)*in/ 

(h* f t2* OF) (k, thermal 

conductivity) watt per metre kelvin [w/(~*K) ] 

Btu (International Table) *in/ 

(s*ft2*'F) (k, thermal 

conductivity) watt per metre kelvin [W/(m*K)] 

Btu (thermochemical) *in/ 

(s*ft2*~F) (k, thermal 

conductivity) watt per metre kelvin [W/(m*k)] 2 Btu (International able) /f t2 joule per square metre (J/m ) 

Btu (thermochemical) /f t2 joule per square metre (~/m 2 ) 

Btu (International Table)/ 

(h* f t2*'F) (C, thermal watt per square metre kelvin 

conductance) [w/(m2*)1 

Btu (thennochemical)/ 

(h*ft2e0F) (C, thermal watt per square metre kelvin 

conductance) [ W/ (m2 .R) 1 

Table)/ watt per square metre kelvin 

[w/(m2*K> 1 

watt per square metre kelvin 

[w/(m2*K) I 

Btu (International Table)/lb joule per kilogram (J/kg) 

Btu (thermochemical) /lb joule per kilogram (~/kg) 

Btu (International Table)/ joule per kilogram kelvin 

(1be0F) (c, heat capacity) [ J/ (kg*K) 1 

Btu (thermochemical) / (,lbAF) joule per kilogram kelvin 

(c, heat capacity) [ J/ (kg*K) 1 

Btu (International able) /f t3 joule per cubic metre (~/m~) 

Btu (thermochemical) /f t3 joule per cubic metre (J/m 3 ) 

cal (thermochemical) / (cm*s*OC) watt per metre kelvin [W/ (m0K) ] 

cal (thermochemical) /cm2 joule per square metre (J/m 2 ) 2 cal (thermochemical) / (cm2*min) watt per square metre (W/m ) 

2 cal (thermochemical)/(cm2*s) watt per square metre (~/m ) 

Multiply by 
To convert from 

cal (International able) /g 

cal (thermochemical) /g 

cal (Internatignal Table) / 

(g* OC). 

cal (thermochemical) /(g*O~) 

cal (thermochemical) /min 

cal (thennochemical) /s 

clo 

~~*h*ft*/~tu (International 

Table) (R, thermal 

resis ance) 5 O~mh* ft /~tu (thermochemical) 

(R, t9ermal resistance) 

O~*h*ft /(Btu [International 

Tablejein) (thermal. 

resis ivity) 

OF* h* f t 5 / (~tu [thermochemical] 

*in) (thermal resistivity) 

ft2/h (thermal diffusivity) 

angstrom 

astronomical unit 

chain 

fathom 

femi (femtometre) 

foot 

foot (U.S, survey) 

inch 

light year 

microinch 

micron 

mil 

mile (international nautical) 

mile (U- S nautical) 

mile (international) 

mile (U.Se statute) 

parsec 

pica (printer's) 

point (printerT s) 

. rod 

yard 

cd/in2 

footcandle 

footlambert . 

lambert 

joule per kilogram (J/kg) 

joule per kilogram (~/kg) 

joule per kilogram kelvin 

[ J/ (kg*~) 1 

joule per kilogram kelvin 

J/ (kg*~) 1 

watt (W) 

watt (W) 

kelvin square metre per watt 

(K*~~/w) 

kelvin square metre per watt 

(K*~~/w) 

kelvin square metre per watt 

(Pm2/w) 

kelvin metre per watt 

(Kam/W) 

kelvin metre per watt 

(K*m/W) 2 square metre per second (m /s) 

LENGTH 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

.metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

metre (m) 

Multiply by 

LIGHT 

2 candela per square metre (cd/m ) 1,550 003 EM3 

lux (Ix) 1.076 391 E+Ol 

candela per square metre (cd/m2) 3.426 259 EM0 

2 candela per square metre (cd/m ) 3.183 099 E+03 
To convert from 

carat (metric) - 

grain 

gram 

hundredweight (long) 

hundredweight (short) 

kgf* s2/m (mass) 

ounce (avoirdupois) 

ounce (troy or apothecary) 

pennyweight 

pound (lb avoirdupois) 

pound (troy or apothecary) 

slug 

ton (assay) 

ton (long, 2240 lb) 

ton (metric) 

ton (short, 2000 lb) 

tonne 

denier 

lb/f t 

lblin 

tex 

MASS 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

kilogram (kg) 

MASS PER UNIT AREA 

Mu1 t i ply by 

2 kilogram per square metre (kg/m ) 3.051 517 E-01 2 kilogram per square metre (kg/m ) 3.390 575 E-02 

kilogram per square metre (kg/m2) 4.882 428 EM0 

MASS PER UNIT'CAPACITY (SEE MASS PER UNIT VOLUME) 

MASS PER UNIT LENGTH 

kilogram per metre (kg/m) 1.111 111 E-07 

kilogram per metre (kg/m) 1.488 164 EM0 

kilogram per metre (kg/m) 1.785 797 E+O1 

kilogram per metre (kg/m) 1.000 OOO*E-06 

perm (0'~) 

perm (23'~) 

perm* in (0'~) 

perm* in (23'~) 

lb/h 

lb/min 

lb/s 

lb/ (hp*h) (SFC, specific 

fuel consumption) 

ton (short) /h 

MASS PER UNIT TIME (INCLUDES now) 

kilogram per pascal second square 

metre [kg/(~a*s*m2)] 

kilogram per pascal second square 

metre [kg/(pa*s*m2) ] 

kilogram per pascal second 

metre [kg/(Pa0s*m) ] 

kilogram pr pascal second 

metre [kg/(pa0s*m) ] 

kilogram per second (kg/s) 

kilogram per second (kg/s) 

kilogram per second (kg/s) 

kilogram per joule (kg/J) 

kilogram per second (kgls) 
To convert from - to 

MASS PER UNIT VOLUME (INCLUDES DENSITY AND MASS CAPACITY) 

grainlgal (U.S. liquid) 

g /em3 

oz (avoirdupois)/gal 

(U.K. liquid) 

oz (avoirdupois)/gal 

(U.S. liquid) 

oz (a oirdupois) /in3 

lb/f t 3 

lb/in3 

Ib/gal (UeK. liquid) 

lb/ga) (U. S. liquid) 

Ib/yd 

slug/ft3 

ton (long) lyd3 

ton (short) lyd3 

Btu (International Table) /h 

Btu (International Table)/s 

Btu (thermochemical) /h 

Btu (t hennochemical) /min 

Btu (thermochemical) /s 

cal (thermochemical) /min 

cal (thennochemical) /s 

erg/s 

f t*lbf/h 

f t* lbf/min 

f t* lbf /s 

horsepower (550 ft.lbf/s) 

horsepower (boiler) 

horsepower (electric) 

horsepower (metric) 

horsepower (water) 

horsepower (U.K.) 

kilocalorie (thermochemical) /min 

kilocalorie (thermochemical) /s 

ton (refrigeration) 

kilogram per cubic metre (kg/m 3 ) 

3 kilogram per cubic metre (kg/m ) 

kilogram per cubic metre (kg/m 3 ) 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

kilogram per cubic metre 

POWER 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (W) 

watt (w) 

watt (W) 

watt (W) 

PRESSURE OR STRESS (FORCE PER UNIT AREA) 

atmosphere (standard) pascal (Pa) 

atmosphere (technical = 

1 kgf/cm2) pascal (Pa) 

bar pascal (Pa) 

centimetre of mercury (0'~) pascal (Pa) 

centimetre of water (4'~) pascal (Pa) 
To convert from - to 

dyne/cm2 

foot f water (39.2'~) 9 gf /cm 

inch of mercury (32'~) 

inch of mercury (60'~) 

inch of water (39.2'~) 

inch o water (60'~) 

kgf /cy 5 

kgf /m 

kg f /mm2 

kip/in2 (ksi) 

millibar 

millimetre of mercury (0'~) 

poundal/f t2 

lbf/ft2 

lb f /in2 (psi) 

psi 

torr (mmHg, OOC) 

degree Celsius 

degree Fahrenheit 

degree Fahrenheit 

degree Rankine 

kelvin 

d ay 

day (sidereal) 

hour 

hour (sidereal) 

minute 

minute (sidereal) 

second (sidereal) 

year (365 days) 

year (sidereal) 

year (tropical) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

pascal (Pa) 

SPEED (SEE VELOCITY) 

STRESS (SEE PRESSURE) 

TEMPERATURE 

kelvin (K) 

degree Celsius 

kelvin (K) 

kelvin (K) 

degree Celsius 

TIME 

second (s) 

second (s) 

second (s) 

second (s) 

second (s) 

second (s) 

second (s) 

second (s) 

second (s) 

second (s) 

TORQUE (SEE BENDING MOMENT) 

VELOCITY (INCLUDES SPEED) 

metre per second (m/s) 

metre per second (m/s) 

metre per second (m/s) 

metre per second (m/s) 

metre per second (m/s) 

Multiply by 

1.000 000*E-01 

2.988 98 EM3 

9.806 65@E+Ol 

3.386 38 EM3 

3.376 85 E+03 

2.490 82 EM2 

2.4884 E+O2 

9.806 650*E+04 

9.806 65WE+OO 

9 e806 650*E+06 

6.894 757 E+06 

1.000 OOO*EM2 

1.333 22 E+02 

1.488 164 EM0 

4.788 026 E+01 

6.894 757 EM3 

6.894 757 E+03 

1.333 22 EM2 

TK = toC + 273.15 

to = (to - 32)/1.8 

TK = ?toF + X59.67)/1.8 

TK = TO /1.8 

toc = TK - 293.15 
To convert from 

knot (international) 

mi/h (international) 

mi/min (international) 

mils (internatfonal) 

mi/h (international) 

centipoise 

centistokes 

ft2/s 

poise 

poundal* s/ f t2 

lb/ (f t* h) 

lb/(ft* sj 

lbf* s/ft_ 

lbf* s/inL 

rhe 

slug/ (f t* s) 

stokes 

metre per second (m/s) 

metre per second (m/s) 

metre per second (m/s) 

metre per second (m/s) 

kilometer per hour (km/h) 

Vf SCOSITY 

pascal second (Pa* s) 2 square metre per second (m /s) 2 square metre per second (m /s) 

pascal second (Pa* s) 

pascal second (Pa* s) 

pascal second (Pa* s) 

pascal second (Pa* s) 

pascal second (Pa* s ) 

pascal second (Pa* s) 

1 per pascal second [l/(Pa* s)] 

pascal second (Pa* s) 2 square metre per second (m /s) 

VOLUME (INCLUDES CAPACITY) 

acre-f oot cubic metre (m 3 ) 

barrel (oil, 42 gal) cubic metre (m 3 ) - 

board foot cubic metre (m 3 ) 

bushel (U.S.) cubic metre (m 3 ) 

CUP 3 cubic metre (m ) 

fl id ounce (U.S.) Y 3 cubic metre (m ) 

ft cubic metre (m 3 ) 

gallon (Canadian liquid) cubic metre (m 3 ) 

gallon (U.K. liquid) cubic metre (m 3 ) 

gallon (U.S. dry.) cubic metre (m 3 ) . 

gallon (U. S . liquid) cubic metre (m 3 ) 

gill (U.K.) .cubic metre (m 3 ) 

gill (U.S.) 3 3 cubic'metre (m ) 

in 3 cubic metre (m ) 

litre cubic metre (m 3 ) 

ounce (U.K. fluid) cubic metre (m 3 ) 

ounce (U.S. fluid) cubic metre (m 3 ) 

peck (U.S.) cubic metre (m 3 ) 

pint (U.S. dry) cubic metre (m 3 ) 

pint (U.S. liquid) cubic metre (m 3 ) 

quart (U.S. dry) cubic metre (m 3 ) 

quart (U.S. liquid) cubic metre (m 3 ) 

stere cubic metre (m 3 ) 

tablespoon cubic metre (m 3 ) 

teaspoon cubic metre (m 3 ) 

tog (register) cubic metre (m 3 ) 

~d 3 cubic metre (m ) 

Multiply by 

- - - -- 

2~lthough speedometers may read b/h, the SI unit is m/s. 

417 
To convert from Multiply by 

VOLUME PER UNIT TIME (INCLUDES now) 

ft3/min cubic metre per second (m 3 1s) .4.719 474 E-04 

f t3/s cubic metre per second (m 3 1s) 2.831 685 E-02 

gallon (U.S. liquid)/(hp.h) 

(SFC, specific fuel 

3 consumption) cubic metre per joule (m J) 1.410 089 E-09 

in /min cubic metre per second (m 1 1s) 2.731 177 E-07 

yd3 /min cubic metre per second (m 3 1s) 1.274 258 E-02 3 gallon (U.S. liquid) per day cubic metre per second (m 1s) 4.381 264 E-08 

gallon (U.S. liquid per min cubic metre per second (m 3 1s) 6.309 020 E-05 

WORK (SEE ENERGY) 
Bold-face page numbers in this index refer to pages containing an fllustration, a table, or both. The page may also contain text supporting 

the entry. For definitions of technical terms, the reader is referred 

to the glossary, Appendix H. 

Absorber plates 

coatings, 53, 55 

materials used in, 54 

selective surfaces of, 55 

Absorptance, of absorber plate 

coatings, 55 

ACSL, computer language, 224 

American Gas Association, standards 

for meter installation, 232 

American Society of Heating, Refrigerating, 

and Air Conditioning Engineers (ASHRAE), 

and test standards, 69 

American Society for Testing and 

Materials (ASTM), and test standards, 72 

Argonne National Laboratory 

and CPC design, 63 

and hot water system 

design, 38 

Array, sawtooth, 53, 403 

Auxiliary heater 

in direct hot air systems, 35 

in series and parallel configurations, 50 

Availability, 132-35 

Bimetallic sensors, 234 

Boiler turndown ratio, 311-312, 313 

Boilers 

backup, 305-309, 310, 311-15 

controls for, 305, 307 

Capacity cost, 79, 273, 275 

Checkout procedures, 230-31, 

239-49 

Collectors, 53 (see also f lat-plate 

collectors, evacuated-t'ube collectors, 

line-focus collectors, and parabolic trough 

collectors) 

central receivers, 65 

compound parabolic concentrators, 

63, 64 

.cost comparison of, 259, 260 

energy balance of, 67 

evacuated-tube, 56-58 

flat-plate, 53-56 

for hot water systems, 38 

instantaneous efficiency of, 67 

instantaneous performance of, 65-73 

line-focus, 63, 65 

liquid, 38 

locating, 32 

multiple-reflector, 65 

operating temperatures of, 12 

parabolic dish, 65 

parallel and series, 141-42 

performance of, 66-68 

point-focus, 63, 65 

stowing, 65, 73-80, 286 

testing materials for, 28 

Computer simulations, IPB, 1, 2, 75, 78 

(see also SOLLPH, SOLTES, TRNSYS) 

Computers 

in control systems, 213-14, 217, 227, 229 

in data acquisition, 236 

Conservation, and solar energy use, 8, 13, 33 

Control loops, 208-209 

dampers in, 212 

flow chart of, 228 

louvers in, 212 

measurement dynamics of, 210 

measurement lag effects in, 209-10 

multispeed pumps in, 212 

multfvariable, 212-13 

Control systems, 207-3 1 

checkout, 230-3 1 

computers in, 213-14 

for constant flow-rate process, 214, 215, 216 

dead time in, 208 

error signals, 207 

freezinglstagnation problems with, 229 

proportional-integral and 

proportional-only compared, 

224, 225-26, 227 

in start-up/shutdown, 227-29 

tuning constants in, 217, 

218-21, 222-24 

variable flow, 215, 216, 217 

Controller, analog, 217 

Controllers 

guidelines for selecting, 209 

integral and proportional, 207, 209 

Controls, installing, 248 

Converters, 235-36 

Corrosion 

caused by heat transfer fluids, 165 

galvanic, in pipes, 143 

minimizing, in hot-water systems, 12 

in seacoast climates, 28 

Cost estimating 

in conceptual design, 262, 263 

ECONMAT used in, 270, 271 

economies-of-scale effects in, 258, 260 

example, 268-6 9 

in design phase, 263, 264, 266 

modified costs in, 258, 259 

modular, 257, 269-70, 271, 272, 273 

in post-design phase, 266-68 - - - . . -.- 

Cost, installed, 28 

Costs 

of construction, estimating, 262, 263 

of conventional fuels, 32, 33 

of electrical systems, 259, 261 

of energy transport equipment, 259, 261 

historical subsystem, 260-61 

of insulation, 161-64, 201-202 

of support structures, 259, 260-61 

Critical intensity, 75, 84-85 
(Continued) 

Data acquisition, in IPH field tests, 236 

Degradation 

caused by atmospheric pollutants, 28 

of collector glazings, 55 

of collectors in industrial environments, 8 

observed in IPH field tests, 19, 20 

underground piping minimizes, 32 

Department of Energy, U.S. 

funded collector efficiency tests, 73 

funded IPH, SHAC field tests, 1 

publications of, 395 

Design 

conceptual, elements of, 2-4 

control system, 214-31 

methodology, 2-4 

preliminary, elements of, 2-4 

Drain-back system, freeze protection in, 229 

Drying and dehydration, 13-15 

ECONMAT, used in cost estimating, 257 

Economics, solar IPE system, 257-83 

affects future of solar energy in industry, 22 

capital-intensive nature of, 32 

federal and state tax credits affecting, 32 

and industries with greatest solar potential, 

33-34 

Economies of scale, effects, in cost 

estimating, 258, 260 

'- Economies-of-scale factor, 265 

Efficiency, boiler, 305-15 

effect of firing rate on, 306, 312, 314-315 

and fractional on-time, 309, 311 

losses in, 305, 306 

Efficiency, collector 

and high temperatures, in 

f lash-steam systems, 41 

in hot water systems, 50 

testing, 69-72 , 

Efficiency, instantaneous 

of collectors, 65 

curves for IPH collectors, 67-68, 68 

Efficiency, optical 

and collector performance, 68-69 

and incident-angle weighting 

factors for north-south troughs, 118 

Efficiency, system, vs. temperature, 28 

Energy collection, annual 

determining correlation for, 84-114 

key variables in, 83-84 

Emergency controls, 229-30 

Energy collection, annual 

derivation of, 371-81 

step-by-step method of calculating, 135-38 

Energy collection rate, average annual, 

75, 78, 79 

Energy use, in U.S. industry, 7, 8, 10, 11 

End-loss factor, in parabolic troughs, 

115, 118, 119 

Enthalpy, in flash-steam systems, 40 

Environmental issues, 292-303 

air pollution effects, 292 

EIA reports, 293 

environmental agencies and regulations, 

293, 294, 295 

environmental regulations, state, 295, 297-303 

impacts of IPH systems, 292 

industrial contamination of collectors, 8 

land use, 295 

NEPA, 293 

waste disposal, 295 

water pollution, 292-93, 295 

Evacuated-tube collectors, 56, 57, 58 

annual recirculation system storage-load 

modifiers for, 98, 102 

advantages of, 56 

installing, 240 

mounting, 56 

operating temperatures of, 56, 58 

selective surfaces of, 56 

vacuum in, 56 

Field tests, IPH, 16-22 

list of projects, 17-18 

major types of collectors in, 53 

problems encountered in DOE-funded, 20-22 

Financing alternatives, 281-83 

Flash-steam system factor, 

derivation of, 386-88 

Flash-steam systems, 16, 40, 41 

Flat-plate collectors, 53, 54, 55-56 

advantages of, 53 

annual incident-angle modifier 

cortection for, 117 

annual recirculation-system 

storage-load modifier for, 97, 101 

enclosures for, 55-56 

installing, 239-40 

mounting, 53 

Flexhoses, installing, 243 

Flow meters, 231-33 

Flow rate 

optimum collector, 141 

in unfired-boiler system, 42 

in variable-volume storage system, 109 

Fluid loading, 251 

Fouling resistances, 185 

Freeze protection 

in flash-steam systems, 39 

heat losses from, 129-30 

in hot water systems, 36, 38, 39, 40 

when water is the heat transfer fluid, 165 

in unfired-boiler systems, 16 

Fresnel lens collectors, 63, 64, 65 

Fuels, conventional 

antipollution laws could limit use of, 28 

costs of, 32, 33 

used in industry, 8, 10 

Glazing 

degradation of, 55 

for flat-plate collectors, 55 

hazards associated with, 288 

problems with, in DOE-funded IPH field tests, 

20-22 

replacing, in the field, 240 

transmittance properties of, 55, 56 

Ground-cover ratio, 120, 122 

Heat exchanger factor, 88, 187-88 

1. + 
INDEX (Continued) 

Heat exchangers, 182-92 

example of, 183 

floating heads in, 192 

in hot water storage systems, 43 

installing, 246 

optimum, 189 

plate, 192 

selecting , 190-93 

two-tube, single-shell pass, 190 

sizing techniques for, 184-87 

Beat loss 

annual, 200-201 

coefficient, for collectors, 66 

reducing, in drainback systems, 248 

underground piping minimizes, 32 

Heat removal efficiency factor, 66 

Heat transfer coefficient, 184, 185-87 

Heat transfer efficiency factor, 139, 166-68, 

169, 170 

Heat transfer fluids, 164-69, 317-50 

aliphatic hydrocarbons, 165 

aromatic hydrocarbons, 165-66 

as corrosion inhibitors in hot water systems, 

38 

flammability of, 170 

in flash-steam systems, 41 

relative efficiencies of, 168 

silicones, 166 

thermal properties of, 166-70 

toxicity of, 170 

water, 164-65 

water/glycol mfxtures, 165 

Heliostats, 65 

Hot water solar IPH systems, 36-38 

direct, 36, 37 

example, 13 

indirect, 36, 37, 38 

industrial uses of, 12 

multiple reflector collectors in, 13 

shell-and-tube heat exchangers in, 13 

Hot-water-to-air solar IPH systems, 14 

Incident-angle modifiers, 68 

for collectors in IPH applications, 69 

effect of, on annual performance, 115-18 

Incident-angle modifier coefficient, 117 

Insolation 

direct normal, 27 

global, 26 

Installation, 239-49 

checklist, 254-55 

of collectors, 239-42 

of cont'rols , electrical lines, and 

instrumentation, 248 

of heat exchangers, 246 

of pipfng, fittings, and insulation, 242-44, 

245, 246 

of pressure vessels and storage tanks, 247 

of pumps, 246-47 

Instantaneous energy balance, steady-state, 66 

Instrumentation, 231-36 (see also instruments, 

measurement ) 

installing, 248 

Instruments, measurement, 231-35 

for flow, 231-33 

for irradiation, 235 

for level, 233 

for pressure, 233 

for temperature, 233-34 

Insulation 

of flat-plate collectors, 54 

installing, 242, 244, 245, 246 

of piping, 144-64 . 

SMACNA standard for, 199-200 

of storage tanks, 199-202 

thermal conductivity of rigid materials 

for, 158 

typical thicknesses, at various temperatures, 

146 

Intensity ratio, 75, 78, 84-87, 93 

Irradiance 

direct normal, 75, 77, 86 

losses, direct and diffuse, in row-to-row 

shading, 122 

total horizontal, 76, 86 

Irradiation, maximum daily available, 109 

"Kill switch," 286 

Life-cycle cost analysis, 270-281 

capacity cost in, 273, 275 

capital recovery factor in, 273, 274 

internal rate of return in, 270, 273-74, 277, 

281, 282 

levelized cost of conventional fuel, 275 

levelized cost of solar energy, 270, 273 

levelizing factor, 275, 276 

M-factor, 273, 276-77, 278-280, 281 

payback in, 270 

Lfne-focus collectors 

direct steam generation in, 43 

installing, 242-43 

in steam systems, 40 

Load-storage modifiers, 95, 97-104 

Materials 

in storage tanks, 199 

tests of, for environmental effects, 28 

thermal conductivity of insulating, 158 

Mueller Associates, Inc . , 257-58, 261-69 

National Bureau of Standards, and collector 

performance tests, 69 

No-storage IPH solar sys tern 

appropriateness of, 89 

predicting annual performance of, 90-93 

sizing techniques for, 89-90 

Noise, 291, 295 

Orifice plates, 182, 232 

OSHA, 291 

Outgassing 

in flat-plate collectors, 56 

hazards of, 285, 290 

Overpressure, hazards of, 290 

Overtemperature, hazards of, 289-90 
INDEX (Continued) 

Parabolic trough collectors, 59, 60-61 

advantages of, 59 

annual recirculation system storage-load 

modifiers for, 99, 100, 103, 104 

end losses of, 118-19 

maximum operating time of, 110 

mounting of, 59 

orientation of, 60-61 

in steam systems, 15 

suitability of, in U.S. IPH aplications, 9 

Payback period 

expected by industry, 8 

in life-cycle cost analysis, 270 

Performance, annual 

climatic effects on, 130, 131, 132 

of flash-steam systems, 113-14 

of a mixed-tank, recirculation system, 93-107 

of a no-storage system, 90-93 

overnight losses and, 127-29 

steady-state losses and, 126-27 

and thermal-loss effects , 122, 126-30 

of unfired boiler systems, 111-13 

of variable-volume storage systems, 107-11 

Performance, collector, 74, 75 

Performance modifiers, annual, derivation of, 

383-91 

Performance tests, 252-53 

Phase-change materials 

Glauber's salt, 195-97 

in latent heat storage, 195-97 

Pipe sizing techniques 

fluid velocities in, 143 

Perry and Chilton method, 143 

Piping 

advantages of underground, 32 

collector field configurations, 139, 140, 141 

flushing, 249-50 

installing, 242, 244, 245, 246 

insulation of, 144 

optimal insulation thickness for, 163-64 

Piping configurations 

center-feed, 140, 141 

direct-return, 139, 140 

pressure drop in, 142-43 

reverse-return, 139, 140, 141 

Pressure tests, 250-51 

Pressure vessels, installing, 247 

Product contamination, 290 

Pumping power 

effect of fluid properties on, 167-68 

required by various pumps, 175-176 

Pumps, 170-79, 263 

Pumps, centrifugal 

capacity vs. NPSHR for, 177 

head-f low curves for, 173, 178 

multispeed, 175-76 

NPSHR for, 173, 175 

selection curves for, 174 

single-speed, 171-75 

Pumps, positive displacement, 176, 179 

Pyranometers, 235, 401 

Pyrheliometers, 235, 402 

Reflective coatings, 60 

Resistance-temperature detectors, 234 

Rock-bin storage, 13, 36 

Row-to-row shading effects, 119, 122 

geometries, 121 

shading-loss modifiers for flat plates, 

evacuated tubes, 123 

shading-loss modifiers for parabolic troughs, 

124, 125 

Safety, 285-91 

flammable fluids and, 285-86 

fire prevention and control, 285-86, 287, 288 

insulation hazards and, 286, 287 

in installation, 248-49 

"kill switch" for, 286 

materials hazards and, 285-86 

physical hazards and, 288-89 

regulations and agencies, 291 

Sandia National Laboratories 

and AR-coated receivers, 61 

and SOLTES, 2 

and trough efficiency , 72-73 

and trough foundations, 241 

Shell-and-tube heat exchangers, 190, 191 

SI conversion factors, 407-18 

Solar Energy Research Institute 

and SOLIPH simulation, 2 

and test standard for concentrating 

collectors, 72 

Solar management company, concept of, 281, 283 

Solar ponds, 61, 63 

SOLIPH, 2, 83, 96, 351-69 

SOLTES, 2 

Start-up procedures, 249-53 

Steady-state pipe loss modifiers, 388-91 

Steam systems, 38, 40-43 

in IPH, 15-16 

line-focus collectors in, 40 

unfired-boilers in, 15-16 

Stefan-Boltzmann constant, 148 

Storage, 88, 193-203 

calculating annual performance for system 

with. 93-107 

costs, 259, 261 

depends on process schedule, 32 

latent heat, 195-97 

location of, 202-203 

media, 194-95, 196, 197 

optimum insulation thickness of, 200-202 

rock-bin, 194-95 

sensible heat, 194-95 

Storage systems 

comparative study of, 47, 49, 50 

dual-mediim rock/oil, 47 

four-pipe, 45, 46 

hot water, 43, 44, 45, 46 

mixed-tank. 47, 48 

two-pipe, 46 

variable-volume, 45, 47, 48, 107, 108, 109-11 

Storage tanks, 197-202 

installing, 247 

insulation of, 199-202 

materials for, 199 

multiple, 199 

single, 199 
INDEX (Concluded) 

Stratification (see thermocline tanks) 

Suitability of solar systems 

economic factors in, 32-33 

environmental factors in, 25-27, 29-31 

factors that determine, 8 

of parabolic trough collectors in IPH, 9 

plant maintenance factors in, 33 

process factors in, 28, 32 

Sun trackers 

flux-line, 60 

shadow-band , 60 

and control systems, 227 

System configurations, 35-51 

parallel, 50-5 1 

principal, in IPH applications, 35 

series, 50-51 

Systemlprocess interface, 50-51 

Themi stors , 234 

Thermocouples, 233-34, 236 

Tanks, pressurized vs. unpressurized, 38, 39, 40 

Temperature 

distributions among IPLI users, 11 

of process deternines appropriate collector, 

10, 12 

Temperatures, ambient 

average daily freezing, in U. S. , 31 

January daily averages, U.S., 29 

July daily averagea, U.S., 30 

in selected U.S. cities, 393 

Tempecatures, operating 

when glycols are heat transfer fluids, 165 

of parabolic troughs, 59 

when ater is heat transfer fluid, 165 

Thermal conductivity 

of rlgid insulating materials, 158 

Thermocline tanks, 45, 46, 47, 48 

Thermosiphoning, prevention of, 38 

TMY, SOLIPtl used data of, 377-87 

Toxicity, of IFE fluids, 289 

TRNSYS, 2 

Tubes 

in flat-plate collectors, 54 

in evacuated-tube collectors, 56-57 

Unfired-boiler factor, 112, 383-86 

Unfired-boiler systems, 42 

circulating fluids in, 42 

sizing collectors for, 112-13 

storage methods for, 47-50 

Utilization, 132-35 

Valves, 179-82, 210-12 

Variable-volume storage systems , 45, 47, 48, 

107, 108, 109-11 

Water-to-air systems, 36 

dewinter heat exchanger factor, 188, 193 

Wisconein, University of, 2 
3. Rectptent's Accessron No. 

5. Publication Date 

Auqust 1982 

6. 

8. Performing Organ~zatton Rept. No. 

' 

10. ProjecVTask/Work Unit No. 

1 007.99 

11. Contract (C) or Grant (G) No. 

(C) 

(G) 

13. Type of Report 8. Perlod Covered 

Technical Report 

14. 

Document Control 

Page 

4 Title and Subtttle 

Design Approaches for Solar Industrial Process 

Heat Systems 

7 Author(s) Char1 es F. Ku tscher , Roger Davenport, Kenneth May, 

Doug1 as Dougherty , Randy Gee, Michael Masterson 

9. Performtng Organizatton Name and Address 

Solar Energy Research Institute 

1617 C01 e Boulevard I 

Go1 den, Col orado 80401 

12. Sponsoring Organtzatton Name and Address 

15 Supplementary Notes 

1 SERI Re~ort NO. 

TR-253-1356 

16. Abstract (Ltmtt: 200 words) This document is meant to serve as a handbook for the design of 

solar industrial process heat systems. It is divided into three parts: I. Objectives 

and Fundamentals; 11. Conceptual Design; and 111. Preliminary Design. Part I describes 

the design methodology and gives an overview of the use of solar energy in industry. 

Part I1 describes how to determine whether solar energy makes sense for a particular 

application, discusses the basic system configurations used to supply hot water or 

steam, and supplies computer-generated graphs that allow the user to select a collector type. Part I11 provides for detailed energy calculations including the effects of 

thermal losses and storage, describes the selection of subsystem components (e.g. , fluids, piping, heat exchangers, pumps, valves), and explains control systems, instal - 

1 ati on and start-up detai 1 s , economics, and safety and environmental issues. A number 

of appendices supply important data and explain how results used in the text were 

derived . 

17 Document Analysts Solar drying : Solar Drocess heat ; Steam generation ; Manuals : 

a. Descr~ptors Design ; Economics ; Performance ; Evacuated tube collectors ; Flat late 

collectors : Parabolic trough collectors : Heat transfer ; Heat transfer fluids ; 

Control equipment Cost ; Safety : Hazards 

b Identtfters/Open-Ended Terms System design ; Desim tools ; Conce~tual design ; Preliminary 

design ; Com~uter simulations ; System performance : Industrial process heat systems ' 

Cost estimating 

c UC Categories 

6 2 

2. NTlS Accession No. 

18 Availabtllty Statement 

National Technical Information Service 

U .S . Department of Commerce 

5285 Port Royal Road 

qnrinofi~ld - Viroinia 771 61 

19 No. of Pages 

452 

20 Prlce 

$14.50