Refwene®

STAND & TECH R.I.C.

INTERNATIONAL ENERGY AGENCY

program

to develop and test

solar heating

and cooling systems

Task 1

INVESTIGATION OF THE PERFORMANCE OF

SOLAR HEATING AND COOLING SYSTEMS

DATA REQUIREMENTS AND THERMAL

PERFORMANCE EVALUATION PROCEDURES

FOR SOLAR HEATING AND COOLING SYSTEMS

-QC

100

.U56

80-1980

1980

August 1979
This report is part of the work of the

lEA Solar Heating and Cooling Program

Task I: Investigation of the Performance

of Solar Heating and Cooling Systems

Subtask B: System Measurement Procedures

Document 9 Distribution: Unrestricted

Additional Copies can be ordered from:

National Technical Information Service (NTIS)

Springfield, Virginia 22151
DATA REQUIREMENTS AND THERMAL PERFORMANCE EVALUATION

PROCEDURES FOR SOLAR HEATING AND COOLING SYSTEMS

The following persons and groups have contributed to this report.

Faculte Poly technique de Mons , Mons , Belgium

Andre Pilatte

In

MA’TlOMAh MUKKAO w ttJMAaxm

UHUUIT

NOV 2 4 1980'

nOi (UC.

OCy I Oo

3o mo

'Qi-:'

Technical University of Denmark, Lyngby, Denmark

J. Lemming

Ove Jorgensen

Faber Computer Operation Ltd., St. Albans, Hertfordshire, England

David Curtis

Phillips Research Laboratory, Aachen, Germany

Richard Bruno

Nikken Sekkel Ltd., Osaka, Japan

Tatsuo Inooka

Eindhoven University of Technology, Eindhoven, Netherlands

Chris van Koppen

The Royal Institute of Technology, Stockholm, Sweden

Per Isakson

Ecole Polytecnique Federale de Lausanne, Lausanne, Switzerland

Guy-Roland Perrin

Andre Faist

The report was edited by

Elmer R. Streed

National Bureau of Standards

Washington, D.C. 20234

i
ABSTRACT

This document provides standardized nomenclature and procedures to serve as a guide to monitor and evaluate research or demonstration type solar hot water or heated and/or

cooled systems, components and buildings. Performance factors, data requirements,

measurement parameters and data analysis methods are described for typical solar energy

systems. The document has resulted from the review and comments submitted by representatives of countries participating in Task 1. Material developed by the United

States for use in the National Solar Heating and Cooling Demonstration Program and

published as NBSIR 76-1137 [1], was used as the primary reference. The contact persons

for each country participating in Task 1 are listed in Appendix A.

11
TABLE OF CONTENTS

PAGE

1.0 Introduction 1 2.0 Program Objectives 2 3.0 Performance Evaluation Procedure 3 3.1 Standard Designations for Sensors and Subsystems 3 3.2 General Solar Energy System Descrlptln and Energy Balance 5 4.0 Active Systems Description and Performance Calculations 10

4.1 Energy Collection and Storage Subsystems 10

4.2 Hot Water Subsystem 14

4.3 Space Heating Subsystem 16

4.4 Space Cooling Subsystem 19

4.5 Building Systems Summary 22

5.0 Systems Performance Evaluation Summary (Active Systems) 25

5.1 Performance Factors - General 25

5.2 Energy Saved - General 27

5.3 Climatic Primary Performance Factors 28

5.4 Energy Collection and Storage Subsystem (ECCS) Primary

Performance Factors 29

5.5 Hot Water Subsystems (HWS) Primary Performance Factors 31

5.6 Space Heating Subsystem (SHS) Primary Performance Factors 33

5.7 Space Cooling Subsystem (SCS) Primary Performance Factors 35

5.8 Solar Energy System/Bulldlng Summary 37

5.9 Secondary Performance Factors and Measurements ^0

6.0 Uncertainty Analysis of Solar Performance Factors 47

6.1 Sensitivity Analysis Methods 47

6.2 Derivation of the Overall Instrumentation Accuracies 50

6.3 Summary 59

7.0 Application of Performance Factors 61

7.1 Solar Energy System Thermal Performance 61

7.2 Solar Energy System Thermal Effectiveness 61

7.3 Analytical Predictions 64

7.4 Solar Collector Array 64

7.5 Component Predicted Performance 66

7.6 Climatic Data 66

7.7 Recommendations 70

8.0 Conclusions 72 9.0 References 73

10.0 Appendix A 74

111
TABLES AND FIGURES

TABLES PAGE

1. Primary Performance Evaluations Factors 4

2. Summary of System/Building Performance Evaluation Factors 24

3a&b. CSU Sampled Data Using Differential Sampling Intervals 55

4. Range of Measured Daily Variance with Data Extrapolated for Weekly,

Monthly and Yearly Periods 56

5. Sampling Rate as a Function of Time Interval for Several Data Requirement Types 57

6. Instrumentation Range, Accuracy and Measurement Frequency 60

7. Comparison of Collector Perfoirmance Coefficients Derived from Testing

and Analysis 67

8. Application of Specific Performance Factors to Evaluation Areas 71

FIGURES

1. Energy Flow Diagram between Subsystems and Building 6

2. Energy Collection and Storage Subsystems (ECSS) 11

3. Primary and Secondary Performance Factors for Energy Collection and Storage

Subsystem (ECSS) 12

4. Hot Water Subsystem Flow Schematic, Sensors and Performance Calculations .. 15

5. Space Heating Subsystem Flow Schematic, Sensors 17

5a. Primary and Secondary Performance Factors for Space Heating Subsystems ig

6. Space Cooling Subsystem Flow Schematic, Sensors and Performance

Calculations 20

7. Energy Flow Diagram Showing the Relation between the Installed Systems

and the Building 23

8. Accuracy in Calculated Solar Energy Collected (QlOO) 52

9. Accuracy in Calculated Solar Used for Hot Water (Q300) 53

10. Monthly Heating and Cooling Loads and Auxiliary Energy Requirement 62

11. Cummulative Energy Use for the MIT Solar House IV During Two Winter

Heating Seasons 63

12. Comparison of Collector Panel and System Collector Array Performance 65

13. Illustration of Detecting Collector Degradation from Thermal Performance

Measurements 68

14. Global Radiation on Horizontal Surface at Stockholm, Sweden 69

iv
NOMENCLATURE

P COP

"FG

K

ItNm

N

Q

Qu

T

Collector aperture area Specific heat

Coefficient of Performance

Collector panel heat removal factor

Latent heat of vaporization

Sampling interval factor

Total incident solar radiation in plane of array

Mass

Mass flow rate

Performance index, number of samples

Cummulative thermal energy

Rate of useful energy extraction from collector

Temperature

TU or T Time

UA Overall heat transfer coefficient

Collector heat loss coefficient

GREEK LETTERS

“ Collector panel solar absorptance

(“T)g Effective product of solar absorptance and transmittance of cover and absorber

panel

A Difference

n Efficiency

o Sensor or measurment uncertainty, standard deviation

Integration time 1, etc.

T Collector cover transmittance at air mass 2 or time

SUBSCRIPTS

a

f

f. i

Iin

out

AT, TD

SW

Air, ambient

Mass flow

Fluid inlet

Insolation

Inlet

Exit

Temperature difference

Sampling rate

Water, Flow
The International System of Units (SI) used in this document are generally consistent

with the International Standard (ISO) 1000-1973-02-01, "SI Units and Recommendations for the

Use of Their Multiples and of Certain Other Units." Ihe conversion factors for some common measurements used in solar energy heating and cooling applications are listed for convenience

purposes when other units are still customary.

Length

1 mm = 0.040 in.

1 cm = 0. 3937 in.

1 m = 3.2808 ft.

Area

1 cm^ = 0.1550 in^

1 m^ = 10.764 ft^

Volume

1 cm^ = 1 mil = 0.061 in^

1 m^ = lO^il = 264.2 gal (U.S. Liquid)

Mass

1 kg = 35.2858 ounces (avoirdi:q5ois)

1 kg = 2.2045 pounds

Pressure or Stress

-4

1 pascal = 2.9612 xlO inch of Mercury (60°F)

-4 2

1 pascal = 1.4503 xlO pound- force /inch (psi)

Ene rgy

1 joule = 0.7375 foot-pound force (ft.*lbf)

1 joule = 0.9479 xlO ^ Btu (International Table)

1 Kilowatt-hour = 3.6 xlO^ joule = 3.412 xlO^ Btu

Power

1 Watt » 1x10^ erg/second

1 Watt •• 3.412 Btu/hr

Temperature

to^ - 5/9 (top - 32)

Heat

1 W/m-^K - 6.9306 Btu- in/h- f t^- °F

1 J/kg-“K - 2.390 xlO"^ Btu/lbm-“F

1 langley 4.124 xlO^ J/m^ 1 cal/cm^ 3.69 Btu/ft^

vl
PREFACE

INTERNATIONAL ENERGY AGENCY

j In order to strengthen cooperation in the vital area of energy policy, an Agreement on an

I International Energy Program was formulated among a number of industrialized countries

in November 1974. The International Energy Agency (lEA) was established as an autonomous

body within the Organization for Economic Cooperation and Development (OECD) to administer

that agreement. Nineteen countries are currently members of the lEA, with the Commission

of the European Communities participating under a special arrangement.

As one element of the International Energy Program, the participants undertake cooperative

I activities in energy research, development, and demonstration. A number of new and imI proved energy technologies which have the potential of making significant contributions

I to our energy needs were identified for collaborative efforts. The lEA Committee on

j Energy Research and Development (CRD), assisted by a small Secretariat, coordinates the

energy research, development, and demonstration program.

SOLAR HEATING AND COOLING PROGRAM

Solar Heating and Cooling was one of the technologies selected by the lEA for a collaborative

I effort. The objective was to undertake cooperative research, development, demonstrations

I and exchanges of information in order to advance the activities of all Participants in the

j field of solar heating and cooling systems. Several sub-projects or "tasks" were developed

I in key areas of solar heating and cooling. A formal Implementing Agreement for this

I Program, covering the contributions, obligations and rights of the Participants, as well

as the scope of each task, was prepared and signed by 15 countries and the Commission of

the European Communities. The overall program is managed by an Executive Committee, while

the management of the sub-projects is the responsibility of Operating Agents who act on behalf of the other Participants.

The tasks of the lEA Solar Heating and Cooling Program and their respective Operating

Agents are:

I. Investigation of the Performance of Solar Heating and Cooling Components - Technical University of Denmark

II. Coordination of R & D on Solar Heating and Cooling Components - Agency of Industrial Science and Technology, Japan

III. Performance Testing of Solar Collectors - Kernforschungsanlage Julich, Federal Republic of Germany

IV. Development of an Insolation Handbook and Instrumentation Package - United States Department of Energy

V. Use of Existing Meteorological Information for Solar Energy Application - Swedish Meteorological and Hydrological Institute

Collaboration in additional areas is likely to be considered as projects are completed or fruitful topics for cooperation identified.

vii
TASK I - INVESTIGATION OF THE PERFORMANCE OF SOLAR HEATING AND COOLING SYSTEMS

In order to effectively assess the performance of solar heating and cooling systems and

improve the cost-effectiveness of these systems, the Participants in Task I have

undertaken to establish common procedures for predicting, measuring, and reporting the

thermal performance of systems and methods for designing economical, optimized systems.

The results will be an increased understanding of system design and performance as well as reports and/or recommended formats on each of the task activities.

The sub tasks of this project are:

A. Assessment of modeling and simulation for predicting the performance

of solar heating and cooling systems

B. Development of recommended procedures for measuring system thermal

performance

C. Development of a format for reporting the performance of solar heating

and cooling systems

D. Development of a procedure for designing economical optimized systems

E. Validation of simulation programs by comparison with measured data.

The Participants in this Task are: Belgium, Denmark, Germany, Italy, Japan, the Netherlands,

New Zealand, Spain, Sweden, Switzerland, United Kingdom, United States, and the Commission

of the European Communities.

This report documents work carried out under subtask B of this Task. The cooperative

work and resulting report is described in the following section.

vill
DATA REQUIREMENTS AND THERMAL PERFORMANCE EVALUATION

PROCEDURES FOR SOLAR HEATING AND COOLING SYSTEMS

1.0 INTRODUCTION

One overall objective of the International Energy Agency's (lEA) Solar Heating and

Cooling Project is to increase the cost effectiveness of these systems by establishing cooperation in the calculation, measurement and reporting of system thermal

performance. The purpose of this document is to provide standardized nomenclature

and procedures which will serve as a guide to monitor and evaluate experimental or demonstration type solar hot water or heated and/or cooled systems. Performance

factors, data requirements, measurement parameters and data analysis methods are described for typical solar energy systems.

The thermal performance data obtained from experimental or demonstration projects may

serve a variety of users including engineers, architects, manufacturers, contractors,

developers, homeowners, code officials and government planners for energy conservation,

economic and building technology applications. Therefore, it is intended that the

document provide a comprehensive coverage of state-of-the-art technology and the user can select the evaluation factors and monitoring system complexity to satisfy particular interests and needs.

The relatively large possible number of solar systems, auxiliary energy systems and

building combinations makes it impractical to precisely define the equations, data

requirements and instrumentation for every application. Therefore, it is expected

that modifications will be required as dictated by the characteristics of the specific

system under evaluation.

The approach used assumes that on-site measurements are used to determine the solar

energy system contribution to the heating and/or cooling load, auxiliary energy

requirements, building heating and/or cooling load, climatic conditions and comfort

level maintained by the system. In addition, the equations and instrumentation for

evaluation of critical subsystems such as collector, storage and heat transfer are treated as integral units and may not be evaluated at the component level. Additional

field test or laboratory data on critical components for part load performance, heat

leaks or thermal losses may be required to conduct diagnostic evaluation of a particular system.

1
2.0 MEASURMENT OBJECTIVES

The objectives of the measurement and evaluation program are to provide data which

can be utilized by the various users. The following factors are considered to be

of the greatest need and interest in the order listed:

1. Determining the savings in fossil fuel and electrical energy resulting from the use of solar energy for space heating, space cooling and/or hot water.*

2. Determining the total heating, cooling and/or HW thermal energy loads and the

fraction of each load supplied by solar energy for monthly, seasonal and/or annual

periods

3. Measuring the solar energy system efficiency for converting solar radiation into

useful thermal energy for monthly and seasonal or annual periods.

4. Measuring the thermal performance of major subsystems or components and the

thermal interactions between collector array, storage and energy conversion equipment.

5. Measuring the occupants use of the system by means of parameters such as the tem- perature level maintained and hot water demand.

6. Determining the major system operational characteristics and degradation over the

life of the demonstration (1 to 5 years).

7. Obtaining records of the incident solar radiation and other pertinent site

environmental parameters that could affect the performance of the system over the

life of the demonstration.

* The term hot water (HW) as used in this report includes both residential hot water (DHW)

and commercial service hot water (SHW). The commercial service hot water may either be

potable or nonpotable depending on its intended use.

2
3.0 PERFORMANCE EVALUATION PROCEDURE

Performance factors and associated data requirements have been classified into three

categories. Category one (primary) items are required for a data summary that is

considered essential to adequately measure the solar energy system or subsystem

thermal effectiveness and determine the energy saved by the solar energy system in

comparison with the energy that would have been used by conventional hot water, space

heating, or space cooling systems. Without this data, comparative evaluations of

different solar energy subsystems and systems would be incomplete or impossible.

These primary performance evaluation factors are shown in Table 1 and described in

detail in Section 5.0.

Category two (secondary) requirements are for data deemed important and useful in

evaluating different subsystems or components. Such data make it easier to understand the component interactions that occur in system operation and serve as an aid

in comparative analysis or simulation but are not essential. In general category two

data can be determined by appropriate calculations or approximations using category

one measurements however in some cases the data can only be obtained by measurements.

An example of a secondary performance factor is the storage efficiency. The

average storage medium temperature is the significant parameter in determining the

amount of stored energy available. The change of storage medium temperature during

a time period with no addition or withdrawal of energy can provide a measure of the

storage efficiency. The storage medium temperature is thus very useful but is not

unique to the system thermal evaluation.

Category three data are obtained from special measurements which are not particularly

essential for current analysis needs, but which serve to define system operational

conditions. System operating pressure or component pressure differential are examples

of such measurement.

3.1 Standard Designations for Sensors and Subsystems

In order to standardize the performance calculations and identify sensors according

to type and location, and alpha-numeric name is provided for each performance factor

and sensor, A five character name is used consisting of one or two letters which

designate either the sensor type or the measured or calculated quantity and three

digit number which identified the subsystems or data group as follows: (designations

are shown as either text or computer because of the limitations in using some letters

on the computer).

3
4 I

TABLE 1

PRIMARY

PERFORMANCE

EVALUATION

FACTORS
Letter Designations

C = Specific Heat (use Cp for text)

D = Direction or Position

EE = Electric Energy

EP = Electric Power

F = Fuel Flow Rate

I = Incident Solar Flux (Insolation) (use i for text)

N = Performance Parameters

P = Pressure

PD = Differential Pressure

Q

= Thermal Energy

T = Temperature

TD = Differential Temperature

V = Velocity

W = Heat Transport Medium Mass Flow Rate (use ill for text)

TI = Time

Subsystem Designations

Number Sequence Subsystem/Data Group

001 to 009

100 to 199

200 to 299

300 to 399

400 to 499

500 to 599

600 to 799

800 to 899

Climatological

Collector and Heat Transport

Thermal Storage

Hot Water

Space Heating

Space Cooling

Building /Load

Swimming Pool

Thus the sensor designation TlOl defines an absolute temperature measurement in the

collector subsystem and the variable name Q600 defines a thermal energy measurement

or calculation for a building load grouping.

3.2 General Solar System Description and Energy Balance

Prior to discussing the performance evaluation and measurement requirements of solar

energy systems, it is useful to describe in general terms the equipment and subsystem

that comprise a solar energy system and to describe the flow of thermal energy from

the solar equipment, through the energy conversion and distribution equipment to the

building. As shown in Figure 1, the basic elements of a solar hot water, space heating and space cooling system include a solar energy collection and storage subsystem

(ECSS), an energy conversion and distribution subsystem (ECDS) and the building.

5
1 “I f

r

I

6

Figure

1

Energy

Flow

Diagram

between

Solar

Energy

Subsystems

and

Building
3.2.1 Functions

The function of the collector subsystem, collector energy transport subsystem, and

storage subsystem (ECSS) is to convert the relatively variable incident solar radiation to a relatively steady source of thermal energy in the form of elevated

temperature heat transport fluid or storage medium. This solar source acts as a significant thermal energy source to the building's energy conversion equipment.

The major purpose of the ECSS is to reduce the consumption of non-renewable energy

sources such as natural gas, oil, and electricity normally used to provide the hot

water, heating, and cooling for the building.

The energy conversion and distribution subsystem is comprised of three subsystems to provide the distinct functions of HW heating, space heating- and space cooling and

utilizes conventional HVAC equipment such as electric or fuel fired heating furnaces,

hot water heaters, heat pumps, absorption chillers and their associated pumps, fans,

heat exchangers, controls, piping and ductwork. The function of this equipment is to combine the energy available from the solar subsystem with the auxiliary energy available from the conventional energy sources when the supply of solar energy is inadequate, and to convert the solar energy to a useful energy form for the building. To

accomplished this conversion and distribution function, additional electrical energy

is required to power the pumps, fans, and controls.

The building consists of the various structural elements in which the transfer of

thermal energy between the outdoor and indoor environments occurs primarily by the

process of conduction, convection, radiation, and infiltration. When the solar heat

gain and the structural heat losses and gains are combined with the internal heat

gains from the lights, appliances and other equipment and the metabolic heat from the

occupants, and these loads are absorbed by the air in the temperature controlled spaces

of the building, they comprise the building thermal load. If the HVAC equipment's

rate of heat removal or addition to the building is exactly equal to the building

thermal load, the air temperature is stabilized and the building is in balance.

Figure 1 includes the use of energy recovery devices to provide for the return of

waste or excess energy back to the appropriate subsystem. Provisions for the exchange

of energy between the building and the solar energy subsystem is also shown. Elevated

temperature operation of the ECSS usually results in energy flow to the building as discussed in Section 3. 2. 2.1 Subsystem Heat Loss.

3.2.2 Thermal Energy Flow

A primary tool which can be used in the location and choice of measurements is the

concept of heat balances. For a given component, the amount of energy input must

equal the energy output plus the change in stored energy with the component.

7
This tool can be particularly useful as a check on the Installed instrumentation.

By obtaining the heat balance periodically on a component or subsystem, evaluation

of the losses and accuracy of the installed data instrumentation can be made. Only

when the heat balance "error" is no longer within acceptable limits will selected

investigation (on the particular subsystem) be required to determine the need for sensor recalibration or subsystem maintenance.

The performance evaluation factors can be defined in terms of the thermal energy

quantities shown for the generalized system of Figure 1, in which an arrow leading

into a box represents the net flow of a particular thermal energy quantity into a subsystem. The quantities shown represent the Integrated rate of thermal energy

flow over a sufficient period of time such that thermal storage in each subsystem

(with the exception of the storage subsystem) is negligible. For example, in

Figure 1 the quantity Q203 represents the net flow of thermal energy out of the ECSS

system and into the energy conversion and distribution subsystem. The quantity Q602

represents the net flow of thermal energy between the building and the energy con- version and distribution subsystem; i.e., the total building heat lodd.

3. 2. 2.1 Subsystem Heat Loss

Examination of Figure 1 indicates a quantity called "heat loss" (or "heat gain")

associated with each subsystem element. This quantity represents the difference

between the total energy that originally entered the subsystem and the thermal

energy delivered by the subsystem. In most cases, the subsystem heat loss represents thermal energy transferred to the subsystem environment by heat loss through

the component insulation.

Depending on the physical location of the component, the subsystem environment can

be outside the building either above or below ground or inside the building either

in a temperature controlled or a non-controlled space. No further use is made of

the heat lost by components located outside the building and above ground. However,

the heat lost by components in the other locations can affect the performance of

the solar energy system.

For example, with a buried non-insulated storage unit some heat lost to the environment when the storage medium temperature is relatively high may eventually be

recovered when the storage medium temperature is low. In addition, for those

components located within the building, some or all of the subsystem's heat loss

may find its way into the temperature controlled portion of the building which is

shown in Figure 1 as a miscellaneous heat loss/heat gain for the building. The

entire subsystem heat loss for those components located within a temperature

8
controlled space will be effective in reducing the building's heat load during the

heating season and in increasing the building's cooling load during the cooling

season.

In the case of a subsystem having components located in a non-temperature controlled

room in a building, the effects of subsystem heat loss on the solar energy system

performance are difficult to assess. The heat loss from a storage unit located in an unheated basement will certainly raise the air temperature of the room, which

will reduce the heat losses for the heating equipment and increase the heat gains

for the cooling equipment located in that room. However, little benefit of the

subsystem heat loss will be realized unless specific means are provided to utilize

the heat loss to reduce the building heating requirements.

Examination of each subsystem element in Figure 1 reveals the energy quantities

that must be either measured or estimated to determine the subsystem heat balance.

Subsystem heat loss is probably the most difficult quantity to measure, therefore,

it must be determined from the heat balance by measuring or calculating all the

other quantities.

In the following description of subsystem equipment measurements and performance

evaluation, the basic approach to performance measurement is to Instrument all

energy flow quantities except subsystem heat loss and to determine this quantity

by the energy balance method. Additional instrumentation is recommended for the

solar collector subsystem and storage subsystem to enable correlation of heat loss

with observed temperature differentials and thus more effectively monitor these

important subsystems. It is recognized that this approach to Instrinnentation may

not always be practical, because of other constraints such as sensor cost,

reliability and performance, available data channels, etc. When such reductions

in measurement are considered, it will be necessary to assess the Impact on overall evaluation and accuracy of the stated objectives of performance analysis.

In the subsequent sections describing the performance evaluation of solar energy

systems, the performance equations are developed on the basis that subsystem heat

loss does not affect the performance of a solar energy system with respect to such

primary evaluation factors as energy saved, heating and cooling load, and the

solar fraction of the heating and cooling load. However, it is necessary that the

heat loss for solar energy transport and storage subsystems located in temperature

controlled spaces be determined. When significant losses are calculated , the

pertinent equations (energy saved, heating and cooling load, and solar fraction of

the heating and cooling load) must be modified to indicate heat loss effects.

9
4.0 ACTIVE SYSTEM DESCRIPTIONS AND PERFORMANCE CALCULATIONS

The following section describes the flow schematic drawings and instrumentation

requirements for several typical solar energy systems, which are used for hot water,

space heating and space cooling, to illustrate the methods of evaluating performance.

The objectives of this section are to define the various subsystems sufficiently to enable an analyst to convert a site contractor's solar energy system mechanical

drawings (showing the equipment, piping, ducting, controls etc.) into the various

system, subsystems and components as shown in Figures 2, 3, 4, 5 and 6. The location

and type of sensors can then be selected and the performance evaluation equations

defined based on the guidelines established herein.

In order to illustrate the sensor locations and performance evaluation factors, the

subsystem component configurations shown in Figures 2,4, 5 and 6 assumed to represent reasonable subsystems that are capable of utilizing solar energy to reduce the

consumption of conventional energy. It is recognized that numerous variations on these subsystem and component configurations are possible. It is therefore re- emphasized that the schematic drawings are Illustrative only and should not be interpreted as recommendations as to the most efficient means to use solar energy to reduce conventional energy consumption in satisfying the hot water heating and space

heating and cooling requirements of buildings.

In order to provide some flexibility in the selection of sensors, three different

categories of performance evaluation have been defined; primary, secondary and

special. Primary factors are deemed mandatory for each system and therefore all sensors used to calculate primary performance factors must be provided. Secondary

performance factors are desireable and these data will normally be provided as a fallout of the data provided with the primary sensors, however, whenever additional

non-primary sensors are required to calculate a secondary performance factor,

the requirement to provide the additional sensor is optional. Special performance

factors are calculated from data taken with special sensors, which are provided

as determined by the needs of each particular system and site.

4.1 Energy Collection and Storage Subsystem (ECSS)

Figure 2 describes the flow schematics, instrumentation and performance calculations

required to characterize two alternate energy collection and storage subsystems

(ECSS) and to define the required sensor locations and performance evaluation factors.

Subsystem element common to both systems Include a collector subsystem, energy

transport subsystem and a storage subsystem. In System A, the heat transfer

medium is a liquid and the storage subsystem is in series with the collector subsystem and the energy conversion and distribution subsystem (ECDS) jtherefore all thfe

10
SYSTEM A

(Liquid Medium, Series Storage) SOLAR HEATED

COLLECTOR

CIRCULATING

PUMP

SYSTEM B (Air Medium, Parallel Storage)

11
CATEGORY VARIABLE

p QOOl

SM Q002

S Q003

P QlOO

S QlOl

S Q102

S Q103

S Q105

S Q151

S Q152

S Q153

S Q200

S Q201

S Q202

P Q203

S Q204

s Q205

s Q250

s Q252

s Q255

s NlOO

s NlOl

s N102

s N103

s N104

s N105

s N106

s N107

s NllO

p Nlll

s N112

p N113

p N114 SH Nils

SM N116

SM N117

P N208

SM N209

DESCRIPTION Total Solar Incident

Direct Solar Incident Incident Solar During Collection

Solar Energy Collected Collector Heat Loss

ECSS Operating Energy^^^

Collector Transp. Heat Loss (3)

Collector Heat Loss to Bldg. Collector Energy Transp. SS Heat Loss to Bldg. Collector Heat Loss to Environment Collector Energy Transp. SS Heat Loss to Environment

Energy to Storage

Energy from Storage

Hourly Increase In Stored Energy

Total Solar Energy Utilized

Storage Heat Loss

ECSS Total Heat Loss Storage Heat Loss to Bldg

Storage Heat Loss to Environment

ECSS Heat Loss to Bldg

Dally Integrated Collector Efficiency

Instant Collector Efficiency

Collector Panel Efficiency Factor Collector Panel Factory F^ (t«) Collector Panel Factor F^Uj^ Collector Hx Effectiveness

DHV Hx Effectiveness Collector Transp. Efficiency

ECSS Coefficient of Performance

ECSS Conversion Efficiency

ECSS Utilization Efficiency

Avg. Ambient DB Temperature

Avg. Wind Velocity

Avg. Wind Direction

Avg. Collector Pressure Differential

Avg. Storage Pressure Differential

Storage Efficiency

Storage Heat Loss Parameter

DEFINING EQUATION

/lOOdT /Cl001-I002)dT

/lOO dx (during system operation)

(l/Ac)/W100*C100*TD100dT

/[I001-(1/Ac) (W100*C100*TD100)dx, WlOOj‘0 3413/EPlOldx. SYSTEM A

3413/0*EP4Oldx, SYSTEM B Aj,*Q100+NPUMP*Q102-Q200, SYSTEM A Aj.*Q10(>+NFAN*Q102-Q200, SYSTEM B/MODE 1 A|,*Q100+NFAN*Q102-Q203, SYSTEM B/MODE 2 Q201+NFAN*Q102-Q203 , SYSTEM B/MODE 3 A^/HF600dx

System dependent, determine from Q103

Q101-Q150

System dependent, determine from Q103

/W100*C101*TD101dx

/W100*C101*TD101dx

QQ300+Q4004<)500

0/W400*C101*TD101dx

(MC„)„[T200(t)-T200(t

Q300-M)400+Q500

0/W400*C401*TD401dx

, SYSTEM

, SYSTEM

, SYSTEM

, SYSTEM

, SYSTEM

, SYSTEM

-1)1

, SYSTEM

, SYSTEM

, SYSTEM

Q200-(Q201-H)202)

Q101-H)103+Q204

AB/MODE 1 B/MODES 2 & 3 AB/MODES 1 & 2 B/MODES 3

AB/MODE 1 B/MODES 243

System dependent; determine from Q204

System dependent; determine from Q204

Q150+Q151+<)250

/Q100dx//Q001dT

W100*C100*TD100/Ac*T001, QUASI-STEADY CONDITIONS^^^ (I/TI)/[(T100-T001/I0011dx, QUASI-STEADY CONDITIONS^^^ COMPUTER SUBROUTINE, QUASI-STEADY CONDITIONS^^^ COMPUTER SUBROUTINE, QUASI-STEADY CONDITIONS^^^ (1/TI/[TD101/(T10I-T200) ]dx, WlOOj^O, SYSTEM A (I/TI)/[TD300/(T200-T300) Idx, W300)‘0, SYSTEM A (l/TI)/[(Q100-Q103)/Q1001dx, WlOOi^O /Q203dx/Q102dT

/Q203dx/Ac*/Q00IdT

/Q203dT/Ac*/Q100dx

(l/TD/TOOldx

(l/TD/VOOIdx

(l/TI)/DOOIdx

(l/TI)/PD100dx, WlOOitO (l/TI)/PDIOIdx, SYSTEM B/MODES 143

/(Q201+Q202)dx//Q200dT

(l/TI)/(T200-T201)dr

(P - Primary

8 " Secondary

8M - Calculated)

(1) Provided for concentrating collector only

(2) 0 ~ Ratio of Pressure Drop in ECSS to Total Pressure Drop

(3) NPUMP, NFAN - Ratio of pump or fan shaft work to electrical energy input (when piaspa or fan Is cooled by the working fluid, do not Include In Q103)

(4) QUASI-STEADY Conditions occur when 1001, TOOl, TlOO, WlOO are essentially

constant for IS minutes.

Figure 3 Primary and Secondary Performance Factors of Energy Collection and Storage Subsystem (ECSS).

12
thermal energy collected is transferred through the storage tank before going to the ECDS- In System B, the heat transport medium is air and the storage subsystem

is in parallel with the collector subsystem and the ECDS, thus permitting collected

solar energy to be transferred to either the storage subsystem or to the load.

In System A, during sunny periods the collector circulation pump circulates the

heat transport fluid through the collector array where it is heated by absorbed

solar radiation. The absorbed energy is transferred to the storage tank via the

collector heat exchanger.

In SYSTEM B a fan combined with five motorized dampers (MDS) permits operation of the

system in three different modes. In Mode 1 on a sunny day when there is no demand

for space heating, the fan circulates air between the collector and storage unit and

thereby temporarily stores thermal energy for future use. In Mode 2 when a demand

exists for space heating and there is solar radiation available, the fan circulates

air between the collector and the building load. In Mode 3 when a demand exists

for space heating and there is insufficient solar radiation available, the fan circulates

air between the storage unit and the building load and thus makes available the

previously stored thermal energy for space heating. In Modes 2 and 3, whenever

the building heating load is not satisfied by the available energy either from

the collector or from storage, a final stage of heating is provided by an auxiliary

source using conventional fossil fuel or electrical energy.

To obtain data for full evaluation of all performance factors, the sensor types and

locations shown in Figure 2 are required. These include the sensors for a local

weather station which consists of total (direct plus diffuse) solar radiation at the

solar array tilt angle and ambient dry bulb temperature. Wind velocity and

direction sensors are provided on certain selected sites as special measurements.

On solar energy systems using concentrating collectors, an additional sensor measuring diffuse radiation is also required. The collector and heat transport

subsystems have temperature sensors at the collector array inlet, on the absorber

plate of one panel and at the collector heat exchanger inlet in addition to differential temperature sensors across the collector array and collector heat

exchanger. The storage subsystem temperatures Include the average storage

medium and exterior ambient temperatures. Storage subsystems utilizing stratification to improve performance should measure Interior temperatures at specific

locations rather than average storage medium temperature.

13
In SYSTEM A, a single mass flow sensor is required to determine the liquid flow rate

between the collector and storage subsystems. In SYSTEM B, two mass flow sensors are shown as being required by the solid symbols. One flow sensor measures the air flow

rate through the collector and the second sensor measures the air flow rate to the

load. The air flow rate to the storage system is determined by the difference in

flow rate to the two sensors, assuming negligible air leakage. However, experience to date with air systems has indicated that the extensive of leaks in ducts and dampers can cause significant errors in measuring the system performance. Therefore, additional flow sensors are shown by the dash s 5rmbols to accout for these leaks from the

collector and storage. Operational power measurement is required for the circulating

pump of SYSTEM A, or the building fan of SYSTEM B and for the operating controls of

both systems. Since the building fan of SYSTEM B also provides the energy to move air through the non-solar equipment and the building, only a portion of this power

is charged against the solar energy system. Pressure differential sensors are provided across the collector arrays in both systems and across the storage unit in

SYSTEM B as special measurements.

Figure 3 also defines the performance calculations necessary for each type of energy

system. As indicated, many of the questions are appropriate for both system types

and where different equations are required, the particular system is noted. However,

not all active solar systems types to be considered for the demonstration program can

be described by the listed equations. In that case, the equations must be written as required, to define the desired performance factors for the specific systems to be

evaluated. In addition to the performance calculations noted, several of the calculated quantities are considered of special significance and are categorized as primary

performance evaluation factors. These variables will be discussed in greater detail

in Section 6.

4.2 Hot Water Subsystem

Figure 4 shows the flow schematic, instrumentation requirements and performance

calculations required for the HW subsystem. The subsystem selected for illustration

consists of the HW storage tank, circulation pump, auxiliary heat exchanger, piping

and controls but does not Include the HW heat exchanger which is located within the

solar storage tank and is therefore considered a part of the storage subsystem. (Had

the HW heat exchanger been located on the outside of the solar storage tank, it

would been considered a part of the HW subsystem).

In operation, heat is transferred from the storage subsystem to the HW storage tank

by circulating potable water through the HW heat exchanger which is located in the

storage tank. Whenever a demand is made for hot water, solar preheated watere is

14
c/> 2

s

KvVWvW//A

I

I

os

? ?fn O O cn fO ? I

|H <VJ

S 5

i i

1 §

15

FIGURE

4

HOT

WATER

SUBSYSTEM

FLOW

SCHEMATIC,

SENSORS

AND

PERFORMANCE

CALCULATIONS
withdrawn from the top of the HW storage tank and replaced by cold make-up water at

the bottom. If the temperature of the water leaving the HW tank is insufficient,

auxiliary energy is added either electrically or by combustion of fuel to provide

the desired HW temperature.

Temperature sensors are located at the HW heat exchanger inlet and at the

makeup to the HW storage tank and across the auxiliary heating unit.

Liquid flow measurements are required for the HW circulation loop and for

the HW flow to the load. Operating power measurements include electrical

energy consumed by the pump and controls. Electrical power or fuel flow rate

must be measured depending on the auxiliary energy source.

Figure 4 also lists the performance calculations required for the HW subsystem. A further discussion of the primary performance factors is given in

Section 5.

4.3 Space Heating Subsystem

Figure 5 shows the flow schematic, instrumentation requirements and performance

calculations for two alternate space heating subsystems using a liquid

heat transport medium. In SYSTEM A, an all-electric heating system » a llquld-to-alr heat exchanger is located in the air duct as the primary

solar heating component, a liquid-to-alr heat pump is the secondary

solar-heating component and an electric resistance heating coll is the

backup auxiliary component which is used when the solar energy storage is

depleted. In SYSTEM B, an all fossil fuel heating system, solar heated

liquid is passed through a liquid-to-air heat exchanger located in a con- ventional fan-coil heating unit. Auxiliary energy is provided in the heat

transport loop by a conventional gas or oil fired furnace to supplement

the solar energy source during peak demand periods or when insufficient

solar energy is available. In both systems the building supply

air is heated as it flows across the various heat exchangers located in

the air duct and this increase in sensible energy represents the amount

of heat provided to the space heating load.

In SYSTEM A, four distinct modes of operation are considered, which are numbered in order of increasing electrical energy consumption and therefore

decreasing preference. In Mode 1, when the temperature of the storage

medium is sufficiently high to carry the building heating load, the two-way

16
SYSTEM A

Supply Air

FIGURE 5 SPACE HEATING SUBSYSTEM FLOW SCHEMATICS AND SENSORS

17
uaTEGURY variabu. PESCRIPTION DEFIMINC. EOCATinN

Q400

0401

Q402

1)40 J

Q404

Q405

Q406

Q407

Q408

Q409

0410

Q411

Q412

1)413

Q414

Q415

Q416

Q417

Q4S0

Q4S1

Q460

N400

N401

N402

X403

M404

N405

N406

M407

P - PrlMry

t • S«cond«r7

Solar Enersy Delivered to Space

Heating

Auxiliary for Space Heating

Space Heating Load

Operating Energy

Heat Pump Compressor Energy

Solar to Heat Pump

Solar Co Building Air

Heat Pump Load

Heating Loop Load

Electric Energy £or Aux.

Fossil Energy For Aux.^^^

Total Energy Consumed

SHS Fraction of ECSS Elec. Energy

Elec. Engy. for Solar Space Htg.

/W400-C400-TD400dT

p'U600-C602(TD600-TD601)dT , SYSTEM A/MODES 3 4 4 I/W400.C401.TD401d’

/W600-C600-TD600dT

3413/(EP401+EP402)dT

3413/EP403dx

/W400-C400-TD402dT

/W400-C401-TD401dT

/W600-C601-TD601dT

/W400-C402-TD402dx

3413/EP400dx

HVF/F400dx r Q400+q403

I Q400-K)403+Q404 J Q400+Q403+Q404+Q409

I

Q403+Q409

1^Q400+Q403+Q410

Q400/N110

^403+Q412

Q403+()404+Q412 Q403+Q404+<)409+Q412 Q403+Q409

J3403+Q412

(I)

(3)

Elec. Engy. for Conv. Space Htg.

Elec. Energy Saved

Fossil Engy. for Conv. Space Htg

Fossil Engy. Saved

SHS Heat Loss to Bldg.

SHS Heat Loss to Envlronasntal

ENERGY FROM HEAT RECOVERY SS TO SHS

Q402/:i'HTE

Q414-Q413

Q402/NHTF

0416-Q410

System Dependent

Systee Dependent

SYSTEM B

SYSTEM a/ MODES 243

SYSTEM A/ MODES 243

SYSTEM A/MODE 1

SYSTEM A/MODES 243

SYSTEM B

SYSTEM A/ MODES 344

SYSTEM B

SYSTEM A/MODE 1 SYSTQl A/MODE 2 SYSTEM A/MODE 3 SYSTEM A/MODE 4 SYSTEM B

SYSTEM A/MODE 1 SYSTEM A/MODE 2 SYSTEM A/MODE 3 SYSTEM A/MODE 4 SYSTEM B

SYSTEM B

SYSTEM B

Solar Fraction of Energy Delivered

to Space Heating

Solar Fraction of Energy Consumed

SHS Coefficient of Performance

Heat Pump Coefficient of Perf.

Elec. Aux. Thermal EfflcianUiy

Fossil Aux. Thermal Efficiency

Avg. Bldg. DB Temp.

Avg. Bldg. Supply Air DB Temp.

(1) HVF • Heating Value of Fuel

(2) :nfTE » Thermal Efficiency of Conventional Electric Heating Unit

(3) .NHTF - Thermal Efficiency of Conventional Fossil Fuel Heating Unit

FIGURE 5a PRIMARY AND SECONDARY PERFORMANCE FACTORS

FOR SPACE HEATING SUBSYSTEMS

SYSTEM A { SYSTEM B

/(Q405-H)406)dx/.fQ402

/Q400dx//Q402dx

/Q400dx//Q411dx

/Q402dx//(Q403+Q404+<)409)dx, SYSTEM A

/Q407dx//(Q4034<J404)dT

/Q401dx//Q409dx

/Q401dx//Q410dx

(l/TI)/T600dx

(l/TI)/(T600-fTD600)dx

SYSTEM A/MODES 243

SYSTEM A/MODES 344

SYSTEM B

18
valve directs the flow of solar heated liquid to the heating loop load

heat exchanger. If the temperature of the solar heated liquid is insufficient

to carry the building load, Mode 2 operation is initiated in which the two-way

valve diverts the heating loop flow to the heat pump's evaporator heat exchanger

and the heat pump is turned on. This mode uses solar energy indirectly in

that the solar heated liquid is used to increase the heat pump's Coefficient

of Performance (COP) and thus reduce the consumption of electrical energy

required to carry the building heating load. In Mode 3, the heat pump's

heating capacity is augmented by the electric resistance heaters in the air

duct and in Mode 4 the heat pump and heating loop circulation pump are off and the entire building heating load is carried by the electric resistance

heaters.

Figure 5 shows the measurements required for the space heating subsystem.

Absolute temperature sensors are located at the heating loop inlet to the

solar storage subsystem and at the building return air duct inlet to the heat

pump or fan coil unit. Differential temperature sensors are located in the

heating loop across the solar storage subsystem, across the heat pump heat

exchanger in SYSTEM A and across the heating loop load heat exchanger. A

differential temperature sensor is required in the building air loop to sense

the dry-bulb temperature difference between the building air supply and return

and in SYSTEM A to sense temperature difference across the combined heat

pump condensor heat exchanger and the electric auxiliary coil. A liquid mass flow sensor is located in the heating loop and an air mass flow sensor

is located in the building air flow circuit. Operating power measurements

are required for the heating loop pump, building fan and controls for both

systems, and for the heat pump compressor of SYSTEM A. Auxiliary energy

consumption, using an electric meter for SYSTEM A and a fuel flow sensor for

SYSTEM B are also required.

The performance calculations required for the space heating subsystem are also listed in Figure 5. The primary performance evaluation factors used to characterize the operation of the subsystem are further described in Section 5.

4.4 Space Cooling Subsystem

Figure 6 shows the flow schematic. Instrumentation requirements and detailed

performance calculations for the space cooling subsystem using a thermal energy

actuated absorption chiller as the cooling component. In operation, the solar

heated liquid from storage is circulated through the absorption chiller's

generator by way of the auxiliary heat exchanger and this provides the re- quired thermal energy source.

19
20
The absorption chiller's useful thermal output consists of the energy indirectly

removed from the building air using an intermediate heat transfer fluid (chilled

water or brine) which is pumped through the evaporator. The heat rejection

required by the absorption thermodynamic cycle is provided by another intermediate

heat transfer fluid (water) which absorbs heat in passing through the absorber

and the condensor sections and then rejects this heat to ambient air via a cooling tower. The energy removed from the building air flowing over the load

heat exchanger represents the space cooling load. Since most space cooling

applications include both sensible cooling and dehumidification processes,

it is important to account for the removal of water vapor from the building air

in determining the building's cooling load.

Figure 6 shows the measurements required to fully evaluate performance of a solar assisted space cooling subsystem. The temperature, flow and power sensors

for the heating loop and fan coil unit are identical to those previously described for the system B configuration space heating subsystem. Additional

temperature and flow sensors are required to measure absorption chiller heat

rejection and building air dehumidification. Building air dehumidification

is determined using a modified rain gauge to determine the rate of condensation

at the building load heat exchanger. An additional power sensor is required

to measure the operating power of the various pumps, fans and controls used in

the absorption chiller.

In measuring wet-bulb temperature (or alternatively measuring relative humidity)

it is recognized that the relative high expense and reduced accuracy of the

commercially available sensors may not be justified, particularly for the

residential portion of the demonstration program. Alternatively , the building

cooling load could be defined as the energy added to the chilled water circulating between the absorption chiller and load heat exchanger at the load

heat exchanger. This approach does not account for the energy gains in the

fan coil unit but does eliminate the requirement for the condensate measurement.

Measurement of the alternative building cooling load at the absorption chiller

requires coolant mass flow and inlet temperature to the load heat exchanger

and temperature difference across the load heat exchanger.

Figure 6 also lists the performance calculations required for the space

cooling subsystem and the primary items which characterize the operation of the

subsystem and are reported in the overall performance summary. These items are further discussed in Section 5.

21
4.5 Solar Energy System/Bulldlng Performance Factors

Figure 7 illustrates the energy flows in terms of heat gains or losses to the building from the various subsystems, heat recovery devices and the exterior or interior

environment. The associated primary and secondary factors used to evaluate the

heating or cooling system/building performance are listed in Table 2.

Direct measurement of the energy flows may not be possible or practical and the

performance evaluation will be dependent upon indirect determination from energy

balance calculations. Factors such as air infiltration, venting and metabolic heat

release from occupants may be obtained by special measurements over short time

period and then correlated with climatic conditions or occupancy profiles. The

temperature and humidity in non-air conditioned rooms responding to randomly

fluctuating outdoor climatic conditions can be obtained from hourly simulation of

heat gain, heat storage and climate using algorithms published by ASHRAE (2).

22
!'II ij

i:

;i Ii

,1 iII1

•aC • at Ik Pi m e £ 3

4) Pi +*m +> >» c4

(0 4) £

T)

«> cd 1—

iH TD

Ctf P

4» at

laC toU

4>

«> tiD Ca c o

4>

K

0) 4) »

•P P>

0> (d4> Co 0)

•rH 4> +» T3

(4 3

(H iH

4>

Uc

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4)

g»o

fi c to •H e o 4) X P>

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23
PRIORITY

P

PP

P

PP

S

S

S

S

S

S

S

S

S

S

P

P

S

S

S

P

S

S

S

S

s

s

s

s

s

s

VARIABLE Q600

Q601

Q602

Q603

Q604

Q605

Q621

Q622

Q624

Q625

Q626

Q650

Q651

Q652

Q66I

Q662

N60I

DESCRIPTION

Total Auxiliary Energy

Total Operating Energy

Total Energy Delivered

to Bldg.

Total Energy Consumed

Total Electric Energy Saved

Total Fossil Energy Saved

Building Mechanical Equip. Heat Loss Building Infiltration Heat Loss or Gain

Building Transmission Heat Loss or Gain

Solar Energy Gain through Windows

Energy Loss Through Windows

Energy from Lighting and Appliances

Metabolic Heat Load

Energy Recovered from Exhaust Air

Energy Recovered from Waste Water

Avg. Bldg. DB Temperature (hourly)

Solar Fraction of Delivered to Total Load

DEFINING EQUATION

Q301+Q401+ Q501

Q102+Q303+Q403-K)503

Q255+Q35(H<)351

-K)450+<)55(H<)302+<)402

Q102+Q307+Q411+Q515

Q311+Q415+Q512

Q313+Q417+Q514

System Dependent

(can be measured or calculated)

t

(I/TI)m00dT

/[N300 •Q302+N400 »Q402+N500 •Q502 1 dr /(Q302+Q402+Q502dT

N602

N700

N701 N702

N703

N704

N705

Q800

Q801

Q802

Q803

Q854

Q855

Q856

N800

System Performance Factor

Space Dry Bulb Temp, (avg.)

Space Maximum Temperature

Space Minimum Temperature

Space Mean Radiant Temp, (avg.)

Space Relative Humidity (avg.)

Space Effective Temp, (avg.)

Solar Energy Delivered to Swimming

Pool (SP)

Auxiliary for SP

SP Load

SP Heat Loss Total Heat Loss

SP Heat Loss to Bldg.

SP Heat Loss to Environment

SP Temperature (avg.)

JQ602dT ; ; [Q306-K)410+Q508+(Q601+Q305-K)^09 ) /NELECJ

(l/TI)/T600dT

Ti

(

t)^^^@Ti ’ ( t)=0&Ti " ( t) <0

^1 (T)n,in®Ti(x)-0&Ti"(t)>0

(l/TI)/Tjj^T*dT

(l/TI)/RH^*dT

ET* - ET (T^j^, T^)

System Dependent , (similar to DHW instrumentation)

TABLE 2 SUMMARY OF BUILOING/SYSTEM PERFORMANCE EVALUATION FACTORS

24
5. SYSTEMS PERFOBMANCE EVALUATION SUMMARY

As Indicated in Figures 3 to 6, numerous calculations are performed for the

elements comprising a system, subsystem or for the individual components in

the solar assisted heating and cooling system. As previously described,

performance evaluation factors are classified into three categories, primary,

secondary and special. The primary performance evaluation factors are listed

in Table 1 and consist of those evaluation factors that summarize the

performance of each subsystem, the solar energy system, the building and

climate and the utilization of the solar energy system by the occupant.

The secondary performance evaluation factors include the detailed performance

of the solar collectors, storage tanks, heat exchangers and other solar energy

components as well as the components of the conventional HVAC equipment used

such as hot water heaters, furnaces, heat pumps and other energy conversion

equipment. Special evaluation factors include those calculations performed

using data from certain optional sensors such as the diffuse pyranameter or

the collector absorber panel temperature.

This section will describe each term of the primary system performance

evaluation summary to clearly define the terminology and calculation method.

In addition, some of the more important terms of the secondary and special

performance calculations are described.

5.1 Performance Factors - General

Two types of performance factors are Indicated in Table 1; a thermal energy

quantity defined by the letter "Q", and a performance index defined by the

letter "N".

5.1.1 Performance Factors Based on Thermal Energy Quantity

In the evaluation of the net thermal energy flow into or out of a subsystem,

the general expression for energy addition to a fluid flowing through a subsystem or component is determined by integrating the measured instantaneous

• rate of heat addition as follows

:

Q = / me (T ^ T . )dx

p out in (5.1)

where m is the fluid mass flow rate in LB/HR , Cp is the fluid specific heat at constant pressure in J/kg-K (BTU/LB ®F)

,

25
T - T, is the fluid temperature rise in the subsystem or component

out in

in °C and

T^, are the initial and final times of the integration period*

In general, both T and T. are functions of time, m is a function of both

time and temperature and c^ is a function of temperature; therefore, evaluation

of Equation (5.1) usually involves a numerical integration procedure in which

the total time interval is broken down into subintervals that are sufficiently

small so that during the subinterval each variable in the integrand can be

considered constant.

Ideally continuous data measurement is desired, however, in the actual data

acquisition system the sensors are scanned at periodic Intervals and the

Instantaneous measured values are used to evaluate equation (5.1). Changes

in the variables between data scans are not determined and errors are introduced

into the calculated results. Section 6 describes these errors due to data

sampling and presents the results of a study of sampling errors based on data from one of the solar demonstration houses at the Colorado State

University ^ •

In general, for all thermal energy quantities the smallest Integration period

desired will be one hour, with additional integration periods to provide

cumulative dally, monthly, and seasonal or annual data.

5.1.2 Performance Indices

In the evaluation of a performance index which depends on the ratio of two thermal quantities such as the energy conversion efficiency, the index N

is given by:

^2

Ql

N ± (5.2)

I

^ Q2 dx

"1

In this equation and Q2 are hourly thermal energy quantities calculated by

Equation (5.1). For meaningful results the Integration times must be sufficiently

long, not only to preclude division by zero, but to assure that a true average

value Is obtained. Thus, the performance index calculations involving the ratio

of thermal energy quantities may require evaluation on a dally, monthly, or annual basis using hourly values of the thermal energy quantity.

26
Other performance indices such as average temperature are determined by

integrating the measured temperature and dividing by the integration period as follows

:

dx (5.3)

where is the actual temperature measurement,

and ^2 are the initial and final times of the integration period and

TI= T2 “ represents the total time period over which the average

temperature Is evaluated.

The minimum integration period varies depending on the particular temperature.

For example, outdoor dry bulb temperature would be desired for hourly, daily and

monthly periods whereas storage tank ambient temperature might be evaluated on

a monthly basis.

5.2 Energy Saved - General

Since the energy sources for both conventional and solar assisted heating and cooling

include different energy types such as gas, oil or electrical, it is important to distinguish between at least the fossil sources and the electrical sources. It is conceivable that when a conventional system is replaced with a solar system,

the solar system could require more electrical energy to run (due to operating power

for the solar pumps, fans or controls) than the conventional system; however, the

solar system should significantly reduce the consumption of fossil energy. Due to the difference in energy costs in various parts of the country, the same solar

system and same type building in different locations may have wide variance in the

cost effectiveness or payback period.

The basic approach to determining the energy saved is to first measure the total

electrical energy and the total fossil fuel energy consumed by the solar assisted

system to provide a given building energy demands at a given occupant utilization

level. An assessment of a non-solar system must then be made to determine the

type of equipment that would be provided if there were no solar equipment.

Since available performance data of energy conversion equipment are usually

based on measurements taken at a design condition for steady state equipment

operation, the effects of off-design operation and duty cycling on equipment

performance must be estimated to Improve the accuracy of the predicted energy

consumption. Alternatively, equipment performance based on seasonal efficiency

rather than design point efficiency should be used. The electrical energy

27
and fossil energy consumption of the non-solar system must then be calculated

assuming some equipment performance coefficients and operating efficiencies

based on the same building load and occupancy utilization that was measured

for the solar system. The energy saved Is then the difference between the

calculated value of energy consumed by the non-solar system and the measured

value of energy consumed by the solar system. In reporting these results,

the assumed non-solar system must be described as well as the assumed performance

characteristics and efficiencies.

5.3 Climatic Primary Performance Factors

5.3.1 Total Solar Energy Incident (Q001tQ002*)

Total Incident solar radiation Is measured by a sensor mounted In the plane

of the collector array on either a continuously Integrated or frequently

sampled basis. Data are recorded at specified Intervals for use In the calculation of collector arid system efficiencies. For those solar energy systems

having a significant dependence on direct solar radiation (such as concentrating

collectors) , diffuse Insolation will also be measured Independently with a separate sensor located In the plane of the collector array and the direct

conq>onent of Incident solar radiation Is determined by subtraction of diffuse

from the total Incident solar radiation. The total and direct Integrated

values of Incident solar radiation are calculated by Integrating the

Instantaneous values as follows:

1001 dx (5.4)

Q002* (1001-1002) dx (5.5)

Where 1001 and 1002 are the Instantaneous values of Incident total

solar radiation and diffuse solar radiation respectively, and Xj^, X2 are the Integrating time Intervals.

Q002* Is not Identified as a primary performance factor In Table 1 however. Its Importance for certain solar collectors warrants

Inclusion as a special measurement for some active and passive solar

energy systems.

28
5.3.2 Average Ambient Dry Bulb Temperature (N113)

Average outdoor dry bulb temperature is a significant parameter in determination of

system performance and comparison of alternate solar energy systems in different

climatic regions. It is obtained by integration of the instantaneous ambient dry

bulb temperatures as follows;

^2

N113 = —^ f r TOOl dT (5.6) TI ^1

where TOOl is the instantaneous dry bulb temperature, and TI is the

integration period ^2“^1*

N113 is obtained for the hourly, daily and monthly data summaries.

5.4 Energy Collection and Storage Subsystem (ECSS) Primary Performance Factors

The primary performance factors are based on the ECSS shown in Figure 2.

5.4.1 Solar Energy Collected (QlOO)

The amount of solar energy collected in a given time period is obtained by

evaluating Equation 5.1 using the appropriate sensors in the ECSS as follows:

QlOO = —L- / W100*C100*TD100 dT (5.7)

^c "l

Where A^ is the total collector area defined by the aperture dimensions of

the collector array,*

WlOO = Collector array fluid mass flow rate,

ClOO = Specific heat of collector fluid,

TDIOO = Fluid temperature increase across the collector array.

Additional data may be required to correct the fluid specific heat of temperature,

concentration, etc.

5.4.2 Total Solar Energy Delivered CQ300, Q400, Q500, Q203)

For the demonstration program, solar energy is used in as many as three applications

i.e., hot water heating, space heating, and space cooling. For each application,

* Solar collector test procedure [4] rates flat plate collector performance on gross

frontal area Instead of aperture area, therefore, thermal comparison of results will

require adjustment by appropriate area ratio.

29
Equation (5.1) is evaluated using the appropriate neasureaents In the HW loop

and In the heating or cooling loop. Since some of the measurements used for

the heating and cooling calculations are the same, additional Information must be

supplied (such as the operating status of the absorption unit) to determine

whether the calculation pertains to heating or cooling. The following equations

are used to calculate each component for the ECSS using a liquid heat transfer

medium (SYSTEM A In Figure 2):

5. 4.

2.1

Solar Energy Delivered Hot Water

^2

Q300 - / W300*C301*TD301 dx

^1

(5.8)

5. 4. 2.Solar Energy Delivered to Space Heating

^2

Q400 - / W400-C400«TD400 dx

"l

(5.9)

5. 4. 2. 3 Solar Energy Delivered to Space Cooling

^2

Q500 - / W400*C400*TD400 dx (5.10)

^1

5. 4. 2. 4 Total Solar Energy Delivered (Liquid Heat Transfer Medium)

The total solar energy utilized Is the sum of the solar energy used In each

application and Is given by:

Q203 - Q300 + Q400 + Q500 (5.11)

5. 4. 2. 5 Total Solar Energy Delivered CAlr Heat Transfer Medium)

For the ECSS using air as the heat transfer medium (SYSTEM B In Figure 2 )

the total solar energy delivered Is given by:

^2

Q203 - / W400*C401*TD401 dx (5.12)

"l

5.4.3 ECSS Conversion Efficiency (Mill)

The ratio of total solar energy actually utilized to the total solar energy

Incident on the collector array Is termed the solar subsystem conversion

30
efficiency and is a measure of the ability of the ECSS to convert incident solar

radiation into useful thermal energy. ECSS conversion efficiency is calculated by

^2 ^2

Nlll = f Q203 dr/A- ^ ^ QOOl dr (5.13)

^1 ^1

Because of the solar energy storage time dependence, ECSS conversion efficiency

(Nlll) should be determined only for the monthly, seasonal and annual data

summary

5.5 Hot Water Subsystem (HWS) Primary Performance Factors

5.5.1

Hot Water Load (Q302)

The total thermal energy required for heating HW from the inlet (makeup) to

delivery temperature is given by:

^2

Q302 = f W301-C301-(TD301 + TD302)dT (5.14)

"l

The HW load (Q302) should be obtained for the hourly, daily, monthly and annual

data summary.

5.5.2

Solar Fraction Energy Delivered to the HW Load (N300)

The solar fraction of the energy deliverd to the HW load is calculated by:

N300 = Q300 = / W300 ‘CiBOO •TD300 ^3015^0 (5.15)

Q302 "^1 W301 *C301 ^ (TD301+TD302) ’

where TD301 and TD302 are the temperature differences across the HW storage

tank and auxiliary heat exchangers, respectively, when there is flow to the

HW load (W301?^0).

This parameter should be evaluated on a dally, monthly and annual basis.

5.5.3

HW Electrical Energy Saved (Q301)

The measured electrical energy used by the HW subsystem of Figure 4 is given by:

Q309 = Q303 + Q305 + Q308 (5.16)

where Q303 is the enrgy required to operate the circulation pump, Q305 is

the energy input to the auxiliary heater (Q305=0 for a fossil auxiliary),

and Q308 is the HW fraction of the ECSS operating energy.

31
The calculated electrical energy required to operate a conventional hot water

suheysten Is given by:

Q310 = Q302/NHWE (5.17)

where Q302 Is the hot water load previously described,

and NHWE is the thermal efficiency of a conventional HW subsystem using

electricity as an Mergy source.

The electrical energy saved is the difference between the calculated electrical

energy to operate a conventional system having the same source and

delivery temperature and usage rate as the solar energy system and the

measured electrical enerev required to ooerate the solar energy system as follows:

Q311 = Q310-Q309 (5.18)

If a negative value is obtained for Q311 this implies that the particular

solar HWS consumes more electrical energy than the assumed conventional

system it is replacing.

5.3.4 HW FosbII Energy Saved (Q313) '

The fossil energy used by the solar HWS is calculated in the following manner:

Q306 = HVF / F300 dx (5.19)

where HVF is the fuel heating value in J/kg (BTU/LB) and F300 is the

measured mass flow rate of fuel to the auxiliary in kg/HR (LB/HR).

The fossil fuel energy required to operate a conventional HWS is calculated from;

Q312 = Q302/NHWF (5.20)

where Q302 is the HW load and NHWF is the thermal efficiency

of a conventional HW system using fossil fuel as an energy source,

The fossil fuel energy saved

energy required to operate a energy required to operate a

is the difference between the calculated fossil

conventional HW system and the measured fossil

solar energy system as follows:

Q313 - Q312-Q306 ( 5 . 21 )

32
5.6 Space Heating Subsystea (SHS) Primary Performance Factors

The primary performance factors are based on the SHS shown in Figure 5 5.6.1

Space Heating Load (Q402)

The space heating load is the sensible energy added to the air in the building

and is given by:

^2

Q402 = / W600-C600-TD600 dx

"l

(5.22)

where W600 is the building air flow rate,

C600 is the specific heat,

anH TD600 is the temperature rise of the air flow across all the heat

exchangers in the air handling unit.

The space heating load should be deirermlned for the hourly, monthly

and seasonal data summary.

5.6.2

Solar Fraction of Energy Delivered to the Space Heatlilg Load (N400)

The solar fraction of the energy delivered to the space heating load for SHS comprised

of a heat pump and electric atixlllary (SYSTEM A) is given by:

N400 = / (Q406 + Q407)dx// Q402 dx (5.23)

^1 ’'l where Q406 is the energy delivered to the heating loop load heat

exchanger in mode 1,

and Q407 is the energy delivered to the heat pump evaporator in modes 2 and 3.

The solar fraction of the energy delivered to the space heating load for the SHS

comprised of the fossil fuel auxiliary (SYSTEM B) is given by: .

N400 = ; Q400 dx// Q402 dx (5.24)

where Q400 is the energy delivered to the heating loop load heat

exchanger

,

and Q402 is the space heating load previously described.

This parameter should be determined for the dally , monthly and seasonal data

summary.

5.6.3

Space Heating Electrical Energy Saved (Q415)

The electrical energy used by the heat pump system shown as system A in Figure

33
(6.25)

5 Is given by:

Q413 - Q403 + Q404 + Q409 + Q412

where Q403 Is the energy consuiaed by the heating loop circulation

pump, bulldlnR fan and all controls,

0404 Is the energy to operate the heat pump compressor,

Q409 is the energy to the electric auxiliary heat exchanger and

Q412 is the SHS fraction of the ECSS operating energy.

The electrical energy consumed by a non-solar heat pump heating system is

given by:

Q414 * Q402/NHTE (5.26)

where Q402 is the measured space heating load,

and NHTE is a modified coefficient of performance of the non-solar

heat pump system which as defined in reference [ 2 ] includes

electrical energy required to operate the compressor, supply fan,

return fan, outdoor air fan and HVAC control circuit.

The modifications to the equipment COP Include the supplemental energy required

for defrosting and auxiliary heating and the reduction in performance due to cyclic operation at off design conditions. Reference [6 ] presents data

describing off-design heat pump performance and the discrepancy between manufacturers

performance data and measured performance primarily due to defrosting requirements.

The electrical energy saved is therefore the difference between the calculated

electrical energy required to operate a conventional heating system and the

measured electrical energy required to operate khe solar energy system as follows:

Q415 - Q414-Q413 (5.27)

6.6.4 Space Heating Fossil Energy Saved (Q417)

The fossil energy saved by an all electric-heating system is obviously zero,

therefore, to Illustrate this calculation, the fossil energy used by the alternate

SYSTEM B is given by:

Q410 HVF / F400 dr (5.28)

where HVF is the heating value of the fuel,

P400 is the mass flow rate of fuel consumed by the auxiliary.

The fossil-energy consumed by a non-solar heating system must be calculated for

the measured load conditions based on the performance characteristics and/or

component efficiencies of the equipment as follows:

Q416 - Q402/NHTF (5.29)

34
where Q402 is the space heating load and,

NHTF is the assumed thermal efficiency of the equipment.

The fuel energy saved is given by the difference between the calculated

fossil energy consumption of the non-solar heating system and the

measured fossil energy consumption of the solar energy system as follows

:

Q417 = Q416-Q410 (5.30)

5 .7 Space Cooling Subsystem (SCS) Primary Performance Factors

The primary performance factors of the space cooling subsystem are based on

the SCS shown schematically in Figure 6.

5.7.1 Sgace Cooling Load (Q502)

The space cooling load is the total heat, including sensible and latent,

removed from the air in the building and is given by:

^2

Q502 = / [W600-C600*TD600+W601-h,,_] dx (5.31)

^1

where W600 is the building supply air flow rate,

TD600 is the temperature differential across the fan-coil unitj

W601 is the flow rate of condensed water vapor from the cooling coil,

and h„„ is the latent heat of vaporization of the condensate.

Alternatively if air side measurements are not practical, the space cooling

load can be approximated from Q507 shown in Figure 6 which is the measured

absorption chiller load.

5.7 .2 Solar Ftaction of Energy Delivered to the Space Cooling Load (N500)

The solar fraction of the energy delivered to the space cooling load Is given by:

N500 = /

^ Q500 dx// Q506 dx (5.32)

where Q500 Is the solar energy delivered to the SCS,

and Q506 Is the total thermal energy delivered to the absorption

chiller generator consisting of solar and auxiliary thermal energy.

This parameter should be determined for the daily, monthly and seasonal data

summary.

35
5. 7.3 Space Cooling Electrical Energy Saved

The electrical energy used by the solar assisted space cooling subsystem is given

by:

Q510 = Q503 + Q509 (5.33)

where Q503 is the cooling subsystem operating energy including

power for the heating loop circulation pump, building fan, absorption

unit pumps, cooling tower fans and all subsystem controls,

and Q509 is the space cooling subsystem fraction of the ECSS

electrical energy consumption.

The electrical energy consumed by a non-solar cooling system must be calculated

for the measured load conditions, source and sink temperatures using the appropriate conversion efficiency as follows:

Q511 = Q502/NCLF (5.34)

where Q502 is the measured cooling load,

and NCLF is the electrical efficiency of the non-solar cooling

equipment

.

The electrical energy saved is the difference between the calculated electric

energy consumption of the conventional cooling system and the measured electric

energy consumption of the solar energy system as follows:

Q512 = Q511-Q510 (5.35)

5.7.4 Space Cooling Fuel Energy Saved (Q514)

The fossil fuel energy used by the solar space cooling subsystem

is given by:

Q508 HVF / F500 dT (5.36)

where F500 is the fuel mass flow rate to the auxiliary unit,

and HVF is the heating value of the fuel.

The fuel energy consumed by a non-solar cooling subsystem must be calculated

for the measured load conditions' based on the component performance characteristics

and/or efficiency as follows:

36
Q513 = Q502/NCLF (5,37)

where Q502 is the measured space cooling load,

and NCLF is the thermal efficiency of the non-solar equipment.

The foaail fuel energy saved is given by the difference in the calculated fossil

energy consumption of the non-solar cooling system and the measured fossil

energy consumption of the solar energy system as follows:

Q514 = Q513-Q508 (5.38)

5.8 Solar Energy System/Building Summary

The following primary performance factors summarize the performance of the

overall solar energy system and the building.

5.8.1

Average Building Dry Bulb Air Temperature (N40 )

Average building temperature is an occupant utilization parameter that will have a strong influence on system performance for both heating and/or cooling and is

therefore useful for comparison of alternate systems. Average dry bulb temperature

should be evaluated as follows

This paraimeter should be determined for the hourly, daily, monthly and seasonal

data summary. Variations in this parameter can also be used as a measure of system's

ability to provide thermal comfort.

5.8.2

Total Auxiliary Energy (Q301, Q302 , Q303, Q600)

Auxiliary energy is required for HW, space heating and space cooling whenever

the solar system is not capable of meeting the demand. The amount of auxiliary

energy required is determined using the same basic approach described in Section

6.4.2

for solar energy utilized and is calculated as follows:

5. 8,2.1 Auxiliary Used for HW

1 ^2

N406 = / T600 dx (5.39)

where T600 is the measured building air dry bulb temperature.

T

2 Q301 = f W301-C302- TD302 dx (5.40)

X 1

37
5. 8. 2.

2

Auxiliary Used for Space Heating

For SYSTEM A of Figure 5, the auxiliary energy used for space heating is given

by:

X Q401 = /

^ W600*C602(TD600-TD601)dT (5.41a)

"l

For SYSTEM B of Figure 5, the auxiliary energy used for space heating is given

by:

T- Q401 = / W400-C401-TD401 dr (5.41b)

5.8.2. 3 Auxiliary Used for Space Cooling

T- Q501 = f

^ W400-C401- TD401 dr (5.62)

"l

5. 8. 2. 4 Total Auxiliary Energy Utilized

The total auxiliary energy utilized Is the sum of the auxiliary energy used for

each application and Is given by:

Q600 = Q301 + Q401 + Q501 (5.43)

Total auxiliary energy should be determined for hourly, daily, monthly and

seasonal/annual data summary.

5.8.3 Total Operating Energy (Q601)

The total operating energy is the thermal equivalent of the electrical energy

required to run the pumps , fans , compressors and controls but excludes the

electrical energy used for auxiliary heating purposes. The total operating

energy is composed of the individual components as follows:

Q601 - Q102 + Q303 + Q403 + Q503 (5.44)

where Q102 is the solar subsystem operating energy defined in Figure 3,

Q303 is the HW operating energy defined in Figure 4,

Q403 is the space heating operating energy defined in Figure 5,

Q404 is the heat pump compressor energy defined in Figure 5,

Q503 Is the space cooling operating energy defined In Figure 6.

38
Total operating energy should be determined for the hourly, dally, monthly and

seasonal/annual data summary.

5.8.4 Total Energy Delivered to Building Load (Q602)

The total building energy load Is the sura of the HW load, the space heating load

and space cooling loads previously defined, and Is calculated by:

Q602 = Q302 + Q402 +Q502 (5.45)

The total building energy load should be determined for the hourly, dally,

monthly, seasonal/annual data summary.

5.8.5 Total Energy Consumed (Q603)

Total energy consumption consists of the total solar, fossil and electric

energy consumed by all of the subsystems as follows:

Q603 = Q102 + Q307 + Q411 + Q515 (5.46)

where Q102 Is the ECSS operating energy.

Q307 Is the HWS total energy consumption defined In Figure 4

Q411 Is the SHS total energy consumption defined In Figure 5,

and Q515 Is the SCS total energy consumption defined In Figure 6.

Total energy consumed should be determined for the hourly, dally, monthly and

seasonal/annual data summary.

5.8.6 Total Electric Energy Saved (Q604)

The total electric energy saved Is given by:

Q604 = Q311 + Q415 + Q512 (5.47)

where Q311, Q415 and Q512 are the electric energies saved for HW,

space heating and space cooling, respectively.

5.3.7 Total Fossil Energy Saved (Q605)

The total fuel energy saved Is given by:

Q605 = Q313 + Q417 + Q514 (5.48)

where Q313, Q417 and Q514 are the fossil fuel energies saved for

HW, space heating and space cooling respectively.

Energy saved should be determined for the hourly, dally, monthly and seasonal/

annual data summary.

39
5.8.8

Solar Fraction of Energy Delivered to the Building Load (N601)

The solar fraction of the energy delivered to the building load is determined by

averaging the solar fractions of the individual subsystem loads as follows:

N601 = [N300-Q302 + N400 Q402 + N500 Q5Q2]dT

f

^ [Q302 + Q402 + Q502]dx

"l

where N300, N400 and N500 are the solar fractions, respectively, of

the energy delivered to the HW load, heating load and cooling load,

and Q302, Q402, Q502 are, respectively, the HW load, heating load

and cooling load.

5.8.9 System Performance Factor (N602)

The ratio of the total energy delivered to the building load to the total

equivalent fossil fuel energy expended is defined to be the system performance

factor and is calculated as follows:

X T N602 = / ^ Q602 dt// ^ [Q306 + Q410 + Q508 +(0601 + 0305 + Q4fl9)]d x (5.50)

X T NELEC

1 ^1

where Q306, Q410 and Q508 are the fossil fuel energies consumed,

respectively, for the HW, space heating and space cooling auxiliaries,

Q305 and Q409 are the electrical energies consumed respectively for

the HW and space heating auxiliaries,

NELEC is the overall thermal efficiency for conversion of fossil energy

at the power plant to electrical energy at the building.

The system performance factor should be determined for the dally, monthly and

seasonal /annual data summary.

5.9 Secondary Performance Factors and Measurements

In addition to the primary system performance factors described in Section 5.3 to 5.8 , certain secondary performance evaluation factors for the ECSS and ECDS are of sufficient importance to warrant further discussion.

40
5.9.1 Dally Integrated Collector Efficiency (NlOO)

The ratio of the dally Integrated solar energy collected by the array to the dally

Integrated total solar energy Incident on the array Is termed the dally Integrated

collector efficiency and Is a measure of the ability of the solar collector to convert dally Incident solar radiation Into thermal energy available either

Immediately or for storage and subsequent use thereof to support the building

thermal energy load. Dally Integrated collector efficiency Is calculated by:

^2 ^2

NlOO = / QlOO dx// QOOl dx (5.51)

where the numerator represents the total thermal energy collected

per day for one square meter of collector and the denominator represents

the total solar radiation Incident on one square meter of collector

per day.

5.9.2 Collector Array Instantaneous Performance (NlOl, N102, N103, N104 )

The performance of a flat plate collector operating under steady state

conditions can be described by the following equation:

^

- Fj t(I^) (T>)^ - Uj^(T - T^)] (5.52)

c

where = rate of useful energy extraction from the collector

= collector area, aper ture

= Actual useful energy collected

useful energy collected If the entire

collector were at the fluid temperature

I.J. = total Incident solar radiation

(x«)^ = effective transmission absorptance product of collector

= heat transfer loss coefficient for the collector

T^ = fluid temperature

T^ = ambient air temperature

Defining the solar collector efficiency as the ratio of useful energy extracted

from the collector to the total solar radiation Incident, equation (5.52) Is rearranged to give collector efficiency as follows:

T T

N101=Fj^ [(T*)g - ^

] (5.53)

41
A plot of equation (5.53) as a function of (Tf - Ta)/lj for a range of

operating conditions yields a first or second order curve with the y axis

intercept equal to (t “)g and slope equal to Fj^Ul.

If an Individual collector panel is instrumented the same as the collector

array with inlet and exit temperatures and flow rate monitored, or if the

entire collector array is co-planer, then by evaluating the two factors

F„(t“) and over the life of the demonstration, degradation of the array

due to changes in the product or (heat transfer loss coefficient) will

be revealed.

Meaningful efficiency measurements are obtained when essentially steady state

is achieved for the previous 15 minutes (three data scans, if the scan occurs every five minutes). The following measurements should be constant:

TOOl (ambient dry bulb air temperature)

TlOO (array fluid temperature)

WlOO (array flow rate)

1001 (total Incident solar radiation)

Other constraints for the procedure as obtained from reference (4 ) are to limit the calculation to times during which the angle between the sun and the

collector array normal is less than 30® degrees and the total incident solar

2 2 radiation is greater than 630 w/m (200BTU/hrft ). If all the above constraints

are satisfied, then data taken at the last data scan are used to calculate the

following performance indicies.

5. 9. 2.1 Instantaneous Collector Array Efficiency (NlOl)

WIOO-CIOO-TDIOO

r:iooi

c

5. 9.2.2 Collector Panel Efficiency Factor (N102)

(5.54)

N102 - (TlOO-TOOl)/ 1001 (5.55)

5. 9.2.3 Collector Panel Factors (N103, N104)

The newly calculated values of the parameters NlOl and N102 are used together

42
with previously calculated values of NlOl and N102 using the previously described

slope/intercept linear curve fit and new values of the collector panel factors

N103 and N104 are obtained, where:

N103 = (toc)^ (5.56)

and.

N104 = F^U

R L (5.57)

The above described procedure should be performed at the start of each hour

until a data scan occurs which satisfies all specified constraints. For that

scan, the calculated values of NlOl, N102, M103 and N104 are reported in the

hourly data summary and no further scans are required for the remainder of the

hour. At the start of the next hour the procedure is repeated.

Collector Heat Exchanger Effectiveness (N105)

For the ECSS where the thermal capacitance of the storage container is much

greater than the flow capacitance of the collector loop, the collector heat

exchanger effectiveness is given by:

Evaluation of collector heat exchanger effectiveness can be done on a monthly

and annual basis.

HW Heat Exchanger Effectiveness (N106)

The hot water heat exchanger effectiveness is determined as follows:

Due to the requirement for double walled heat exchangers to prevent any possible

contaoiinatlon of potable water with non-potable water, the HW heat exchangers

may present a substantial thermal resistance to heat transfer and thereby

reduce the amount of solar energy available. Any tendency for fouling of the

heat exchangers would be revealed by changes in the calculated values of heat

exchanger effectiveness

(5.58)

(v5.59)
5-9.5 Storage Subsystem Efficiency (N108, N109)

The storage subsystem efficiency is defined as the ratio of the sum of the

output of stored thermal energy and the increase in stored thermal energy to the input of thermal energy to storage as follows

N108 -

''l W20Hq

202 ) ,d,

(5 ^2

/ Q200 dr

^1

where Q201 is the hourly output of thermal energy from the storage

device,

Q202 is the hourly increase in stored energy,

and Q200 is the hourly input of thermal energy to the storage device.

The normal source of thermal energy input to storage is from the solar energy

collectors, however, other thermal energy sources, such as off-peak auxiliary

energy must also be included. Where more than one storage container is used,

individual evaluation is required.

Storage efficiency is related to the subsystem heat losses which may be

either deliberate (such as the dumping of energy to ambient) or non-dellberate

due to air leakage or insulation losses. Heat loss through insulation is related

to the following parameter:

1 ^2

N109 - ^ (T200-T201)dT (5.61)

"l

where T200 is the average storage medium temperature, and

T201 is the ambient temperature surrounding the storage container.

Evaluation of these parameters (N108 and N109) should be performed for the

monthly and seasonal/annual data summary.

5.9.6 Average HW Load Temperature (N307)

The average HW delivery temperature to the load is a significant parameter

in the comparison of alternate HW solar systems, in that this temperature

is controlled by the occupants and subsystem performance will depend

on the actual control point setting.

1 ^2

N307 - / (T301 + TD301 + TD302)dx (5.62)
where T301 is the make-up water temperature,

TD301 is the temperature difference across the hot water storage,

and TD302 is the temperature difference across the HW auxiliary

heat exchanger.

5.9.7 Average Gallons HW Consumed (N308)

The time of day at which hot water is used and the total daily consumption

are significant parameters in evaluating performance and comparison of

alternate HW solar systems. The average HW consumption in liters is given

by:

^2

N308 = 1/3600 f W301 dx (5.63)

^1

where W301 is the measured flow rate in kg/s and ~ ^ hour

The HW consumption should be determined for the hourly, dally, monthly

and annual data summary.

5.9.8 Energy Conversion Equipment Coefficient of Performance

Energy conversion equipment uses electrical or thermal energy to

raise heat from a low temperature source to a higher temperature sink and

is rated by the ratio of the useful heat transferred to the energy input

.

Useful heat transferred consists of heat delivered to the sink in the heating

mode and heat extracted from the source in the cooling mode.

5. 9. 8.1 Space Heating Equipment COP (N404)

Measurement of the Coefficient of Performance (COP) is desired for energy

conversion equipment such as heat pumps in which the useful thermal energy

delivered to the building is significantly greater than the electrical

energy consumed. Referring to the heat pump system shown as SYSTEM A in

Figure 5, Space Heating COP is calculated from:

^2 ^2

N404 » / Q407 dr// (Q403 + Q404)dx (5.64)

"l . -^1

where Q407 is the useful thermal energy added to the building

supply air from the heat pump,

Q403 is the electrical energy required to operate the SHS pumps,

fans and controls.

45
QA04 is the electrical energy required to operate the heat pump

compressor.

This parameter should be determined for the dally, monthly and seasonal

data sumnary.

5. 9. 8. 2 Space Cooling Equipment COP CN503)

Measurements of the Coefficient of Performance (COP) are desired for thermally

actuated equipment such as the absorption chiller for Figure 6 and for other

equipment such as solar assisted Ranklne Cycle equipment or dessicant

dehumldlfIcatlon systems as appropriate.

Referring to the absorption chiller shown in Figure 6, the Coefficient of

Performance is calculated as:

N503 Q507// Q506 dx (5.65)

where Q507 is the useful thermal output of the absorption

chiller as defined In Figure 6,

and Q506 is the thermal energy input to the absorption chiller

as defined In Figure 6.

5-9.9 Space Comfort

The space comfort can be characterized in several ways depending upon the instrumentation complexity and the methods of heat distribution or removal. The space

average dry bulb temperature N600 Is commonly used as a measure of comfort level

and is a significant parameter in evaluating building energy use and energy saved

5.9.9. 1 Space Mean Radlent Temperature (N702)

The space mean radiant temperature is defined as the temperature of a uniform black

enclosure In which a solid body or occupant would exchange the same amount of radiant

heat as In the existing non-uniform environment. It Is expressed by:

N703 (1/TI) / T^^ • mrt

dx or

where A area of surface, r

r

’

(l/TI)/( E A^- T^)-

r-1

n

d

X

T^ temperature of surface, r
6.0 UNCERTAINTY ANALYSIS OF SOLAR PERFORMANCE FACTORS

The uncertainty of determining the performance evaluation factors lor a particular solar energy system/building/climate combination is related to the data

requirement accuracy for sensor signal conditioning, data acquisition sampling

rate and data processing method. Non-instrumentation variables such as building

heating or cooling load, occupancy, conventional heating and air conditioning

equipment operation and meteorological parameters must also be considered when

comparing the performance of solar energy systems in different buildings or climatic regions.

To establish acceptable tolerances in the performance evaluation factors, the

contribution of sensor accuracy and sampling rate error to the total performance

factor uncertainty must be derived and set in perspective by comparison with

the pertinent non-instrumentation sources of the performance factor uncertainty.

The approach, rationale and sensitivity analysis for several performance factors

are described in the following sections

:

° Sensitivity Analysis Methods

° Specific Error Analysis

° Overall Instrumentation Errors

° Recommended Sampling Rates and Data Requirement Accuracies

Two methods are in general use for combining precision errors in measuring

several variables to estimate the error in a calculated function of those

variables. The particular method used depends on whether the component errors

are considered to be absolute limits or statistical bounds (such as 3a limits)

the form of the relationship between the variables and the calculated function,

and the specification of component errors (percent of reading or absolute in

terms of measured units)

.

If the component precision errors are considered to be absolute limits and a functional relationship exists such that

6.1 Sensitivity Analysis Methods

6 . 1.1 Absolute Limits

T = f(x,y,z) ( 6 . 1 )

The component errors in x, y, and z are Ax, Ay and Az respectively,

and f(x,y,z) is expanded in a Taylor series; then:

47
ff , , . , . » N ct \ , 3fAv . 3fAy , 3fAz f(x + Ax, y + Ay, z + Az) = f(x,y,z) + ^

^ ^ ^

+1/2 ( 6 . 2 )

Neglecting the second order and larger terms because Ax, Ay, Az are assumed

small ('\'1%) , the total measurement error is:

Af + (6.3)

In the general case for a function R (a function of any number of variables)

the error can be expressed as:

i«l

6.1.2 Statistical Bounds

(6.4)

In the absence of a function relating the component error sources, a general

equation can be used to find the measurement error. If the measurement is

defined by R(X, , X„ X ), where R is the desired measurement and AX,, AX

are the individual

i z error

nsources, the following equation can be used:

11

AR = (6.5)

This equation assumes that the errors are random and uncorrelated. The precision

errors will be expressed as + AX. As a probable error in either of the two cases (functional or non-functional relationship) , the true value of R will be

between R - AR and R + AR for some percentage of all readings. The percentage

involved depends upon the error expressions used for the component errors.

6.1.3 Error Analysis - Daily Integrated Collector Array Efficiency

An error analysis of the calculations of daily integrated collector array

efficiency is presented to illustrate using both methods discussed in the

preceding paragraphs.

48
From Figure 3, the daily integrated collector array efficiency is calculated as;

NlOO = /Q100dT//Q001dT = /WlOO ClOO TDIOO dx/Ac lOOldx ( 6 . 6 )

If the component errors are independent of time then the uncertainty in the integrated daily efficiency is the same as the uncertainty in the instantaneous

efficiency given by performance factor NlOl as:

For purposes of illustration, the following reference conditions and tolerances in

each variable are assumed with water as the heat transfer fluid:

WlOO = 40 £/HR m2 X 3 m^ = 120 i/HR - 120kg/HR ±2.4 kg/HR), collector flow

ClOO = 4.19 kJ/kg C, specific heat (NO TOLERANCE)

TDIOO = 10“C +1.7% (±0.17®C), temperature rise through collector

1001 = 1000 WHR/m^ +3% (30 WHR/m^), incident solar radiation

The nominal array efficiency is determined from equation (6.7) by substitution of

the assumed variables at the reference point as:

Equation 6.7 is differential with respect to each variable having a non-zero

tolerance and each partial derivative is evaluated at the reference condition as follows:

Mim = WlOO ClOO TDIOO

Ac IlOOl

(6.7)

Aj, 3 m2 +1% (±.01 m2), collector area

NiOl = 120kg/HR (4.19) kj/kg °C (10)°C 1(HR) = ^455

3 m2 1000 (W HR/m2) (3.6) (kJ/W HR)

3N101 = ClOl TDIOO = (4.19) (10)

9W101 Aj. 1001 (3) (1000) (3.6)

0039

9N101 = WlOO ClOO = (120) (4.19)

3TD100 A^ 1001 (3) (lOOO) (3.6)

0466

49
3N101 ^ W100‘C100«TD100 = _(120) (4.19 (10)

3A, 2*1001

= -.1552

(3)^ (1000) (3.6)

3N101 ^ _ W100»C100*TD100 ^ _ (120) (4.19) (10) = .00013

31001

Ac*(10001)2 (3) [(1000) (3.6)]'

The error by absolute limits is obtained by substitution of the partial derivatives

and tolerances in equation (6-4) as follows:

ANIOI = |(.0039) (2.4) (+ |(.0466) (.17) |+ | (-.1552) (.01) | +[(-.00013) (98)|

ANIOI - .0313

NlOl = ,465+. 031

Thus the calculated value of instantaneous efficiency based on absolute error limits

indicates an uncertainty of + 6.7 percent.

The error by statistical bounds is obtained by substitution of the partial derivatives and tolerances in equation (7,5) as follows:

NlOl = [(.0039 X 2.4)2 ^ (.0466 x .17)2 + (-.1^552 x .01)2 + (_.00013 x 98)2]^^^

ANlOl = .0176

NlOl = .465+. 0176

The statistical or rms method indicates about a + 3.8 percent uncertainty in the

calculation of collector efficiency. As indicated by the sample calculations the

absolute limit method gives a larger error value than the statistical method.

Because of the randomness of the measurement process for the solar energy systems

(l.e., errors among the many different sensors are not correlated), the statistical

method is used for the uncertainty and error analysis calculations reported in this

document.

When comparing the data reported by different organizations for similar type measurements, consideration of systematic uncertainties must also be considered. For

instance, the possible data scatter attributed the systematic facility errors were calculated to be as large as the error resulting from the absolute measurement

uncertainty (12).

6.2 Dervlation of the Overall Instrumentation Accuracies

Instrumentation accuracies are caused by sampling errors and by systematic

sensor errors due to inaccurate calibration, drift, and non-linearities. To

evaluate the effect of sensor and sampling errors on the performance factors,

the following information is necessary: the analytical expression for each

50
performance factor, the range of loads and operating points for the solar energy

systems and the sampling period. Application of the error analysis method to determine the uncertainty in solar energy system conversion efficiency is

described to illustrate the analysis performed for most of the primary factors.

6.2.1 Temperature Sensor Accuracy

There are several ways of expressing temperature sensor accuracy. If all

temperature sensors used to compute energy flows are differential sensors,

meaning that a temperature rise or drop, not an absolute temperature is

measured then accuracy of measuring a temperature differential is expressed as percent (degrees accuracy in measuring the differential divided by the total

differential). If the differential is to be measured using two sensors, then

the accuracy is the square root of the sxam of the individual accuracies squared

divided by the temperature difference or

accuracy + 0^ / AT ( 6 . 8 )

Thus, a 2% load temperature accuracy requirement and 20®C assumed load temperature

difference means that the temperature accuracy should be .4°C for a differential

sensor and .3°C for individual sensors. Similarly, a 4% accuracy and 10®C

rise across a collector requires a temperature accuracy of .4°C differential

or .3®C for individual sensors.

Other combinations of flow and temperature sensors which fulfill instrumentation

accuracy requirements can be determined from Figures 8 and 9. These two

graphs were computed from the two error equations that constrain flow and

temperature sensor errors.

6.2.2 A Description of Sampling Errors

Sampling errors develop when a signal waveform is not sampled quickly enough

so that the exact waveform can be reproduced. Because many solar parameters

change quite rapidly (e.g., auxiliary fuel flow or Insolation), it is not

feasible to sample to reproduce the entire waveform. However, it is

possible by sampling a large number of times to statistically reproduce the mean of a waveform. For Instance, for a monthly measurement period and a 10-minute sample interval, each parameter mean is based on approximately 2,000

samples. It is the statistics of large nxunbers which governs sample accuracy

(provided correlation effects do not arise)

.

51
QlOO

«

moO-ClOO-TDlOO

dT

VO

o o

o o

CVl

CVJ GO

CVJ GO

rH ^

>-

a:DO

o

<

cro

CO

z

liJ CO

llJ cr3

a:

UJ

a.uH

_J<

H

Z

UJ

(TUJ

U.

u.

o

o

AOVdnODV dOSN3S MOld

cd CJ

a

cd

ViDO

o<

00

0)

ViD

60

•H

52

FOR

LIQUID

(AIR)

SYSTEM
53

(.78)

(1.17)

(1.56)

OC

(1.94)

(Air)

DIFFERENTIAL

TEMPERATURE

SENSOR

ACCURACY

FOR

LIQUID

(AIR)

SYSTEM
In general, lengthening the sampling period (e.g., from one month to one year)

by some factor k decreases sampling error by 1/J^. Similarly, shortening the

sampling interval (e.g., from 30 minutes to 5 minutes) decreases sampling error.

The errors due to sampling can be predicted for the three common types of signals.

"ON-OFF," "slowly varying," and "rapidly varying." Error in measuring "ON-OFF"

signals is a function of the total number of samples N and the duty cycle, d

0 (ON-OFF) (6.9)

For "slowly varying" signals (signals that cycle much fewer than once in 2tt samples) error is a function of the number of samples, N, and the mean percent

change of the signal during one sample interval, a:

a < (slowly varying) ( 6 . 10 )

For "rapidly varying" signals (signals that cycle much faster than once every

2ir samples), error is a function of the number of samples, N, and the ratio of

the varying to steady signal component, b:

0 < (rapidly varying)

/N (1-b)

( 6 . 11 )

Decreasing the sample interval by a factor of k results in an error decrease

of approximately 1/k for "ON-OFF", l/kj k for "slowly varying" and 1/^ k for

"rapidly varying." Examples of "ON-OFF", slowly varying, and rapidly varying

signals might be auxiliary input to load, storage temperature, and Insolation,

respectively, for a 2 minute to 60 minute sampling Interval. Actual standard

deviations for different sampling rates and periods have been computed for

insolation, collector output, auxiliary output, etc., using Colorado State

House No. 1 data [3]. Typical data for insolation values integrated from

measurements made at different intervals are listed in Tables 3a and 3b.

Assuming the 2 minute sampling rate represents the most accurate value obtained,

the actual sampling error results are listed in Table 4 and scaled to different

sampling Intervals and periods. There is wide variation in the monitoring Interval

required by the different parameters. For exeunple, the analysis indicates

insolation need only be monitored once every 20 minutes to maintain a weekly

variance below about 1%, but auxiliary sampling with a non- Integrating sensor

must be made at Intervals more frequent than 5 minutes.

54
Table 3a CSU Sampled Data Using Different Sampling Intervals (Summer 1975)

Parameter Insolation [3]

Table

Minutes

Date 2 5 10 20 30 60

6/21 1132.9 1130.0 1118.9 1128.3 1124.2 1160.7

7/9 1111.3 1119.0 1089.9 1100.4 1035.5 995.4

7/13 1768.2 1776.2 1772.6 1763.9 1759.3 1765.7

7/17 1255.3 1266.6 1270.9 1273.0 1242.9 1227.0

7/21 1248.0 1271.6 1254.3 1241.1 1153.9 1072.2

7/23 1263.4 1246.8 1253.1 1204.3 1259.7 1271.7

7/25 1815.2 1811.4 1809.0 1799.1 1792.0 1767.3

7/27 1850.4 1846.6 1840.5 1827.7 1815.1 1779.6

7/29 1564.5 1558,1 1534.4 1515.9 1633.1 1513.0

7/31 1205.6 1207.8 1245.6 1229.3 1219.8 1233.3

S.D. per day 0.82 1.3% 2.0% 3.3% 5.3%

Parameter Insolation (Winter 1974-75)

'

Date 2 Minutes

5 10 20 30 60

12/21 455.0 449.1 446.4 455.2 466.6 465.9

12/23 165.9 159.5 158.0 152.2 159.7 143.7

12/25 1478.9 1476.0 1472.7 1457.4 1445.9 1396.3

12/27 1238.6 1235.8 1235.1 1228.9 1251.7 1270.1

12/29 948.0 937.8 933.3 916.6 896.7 846.5

12/31 1108.1 1102.0 1086.0 1034.4 1045.6 976.0

1/4 1248.4 1242.6 1246.7 1246.2 1205.9 1224.6

1/6 1395.4 1388.1 1380.4 1345.3 1327.4 1228.9

1/15 730.9 741.1 725.0 735.6 778.2 755.0

1/17 1022.4 1017.6 1015.6 1112.4 111.3 1173.3

S.D. :per day 0.7% 1.1% 4.3% 5.1% 9.6%

55
TABLE 4

RANGE OF MEASURED DAILY VARIANCE WITH DATA EXTRAPOLATED

FOR WEEKLY, MONTHLY, AND YEARLY PERIODS.

SAMPLING INSOLATION

FREQUENCY (MIN) 5 10 20 30 60

Daily .7 - .8 1.1-1.

3

2.0-4.

3

3. 3-5.1 5. 2-9.

6

Weekly .3 .4 - .5 .8 - 1.6 1. 2-2.0 2. 0-3.

6

Monthly .1 .2 .4 - .7 .6 - .9 1.0-1.

7

Yearly .1 .1 .1 - .2 .2 - .3 .3 - .5

COLLECTOR

SAMPLING

OUTPUT

FREQUENCY (MIN) 5 10 20 30 60

Daily 3. 3-4.

6

5.3-11.1 13.9-20.1 18.2-21.5 19.7-23.8

Weekly 1.2-1.

7

2. 0-4.0 5. 2-7.

5

7. 0-8.0 7. 5-9.0

Monthly .6 - .8 .9-2.0 2. 5-3.

7

3. 3-3.

9

3. 6-4.

3

Yearly .2 .3 - .6 .7-1.0 .9-1.1 1.0-1.

3

AUXILIARY TO

SAMPLING

LOAD

FREQUENCY (MIN) 5 10 20 30 60

Daily 6.7-23.6 6.3-30.9 10.2-43.3 15.8-66.5 23.3-111.8

Weekly 2. 5-9.0 2.5-11.5 4.0-16.5 6.0-25.0 9.0-42.0

Monthly 1.2-4.

3

1.1-5.

6

1. 8-8.0 2.8-12.0 4.2-20.0

Yearly .7 .7 1.1 1.7 2.6

56
Using the CSU data and the suggested sampling accuracies from Section 6.2.2,

sampling rates for various sensors are determined as listed In Table 6.

Data Requirements Weekly Summations Monthly Summations Yearly Summations

(minutes) (minutes) (minutes)

load flow <5 5 30

collector flow and

temperature 5 10 60

auxiliary input <5 5 60

insolation 30 60 60

Based on Insolation at Colorado State University, Fort Collins, Col. 1974-75.

Table 5 Sampling Rates as a Function of Time Interval for Several Data Requirements Types

Sensors requiring sampling rates greater than once every five minutes can be

continuously Integrated and then sampled. It Is recognized that the data

utilized Is for a specific system, load and climatic conditions and will only

provide estimates of sample rates for other combinations of these factors. For

example. Insolation sample rates are a function of the weather variability and

a rate of 3 minutes is used in the Washington, D.C. area to obtain an uncertainty

of about 1% [7]. A sampling rate of 1 minute or less is recommended for both

Insolation and auxiliary energy related measurements

6.2.3 Solar Energy Conversion Efficiency (Nlll)

The conversion efficiency of a heating and HW solar energy system is determined

by dividing the solar energy delivered to the load by the available insolation.

Instrumentation uncertainty (a ) is given by:

+

2 \f Q400 \

J^300 + Q400

J + a

2I + a SOOl ( 6. 12 )

where o^ ando^^.^ are uncertainties in solar—to- load flow and temperature

difference sensors, Og is the sampling uncertainty, Q300 and Q400 is

solar energy to hot water and heating respectively, is insolation

sensor uncertainty, and is the Insolation sampling uncertainty.

57
Assuming conditions such that Q300>>Q400, the instrumentation accuracy is:

2 2^2

°INS

“ + + a. SOOl

(6.13)

The sensor accuracy and sampling rate accuracy necessary to achieve a 6%

instrumentation uncertainty is determined as described in the following sections.

6.2.4 Sensor Accuracy

The two worst case RMS instrumentation error equations that determine necessary

sensor accuracies for system and collector array efficiencies respectively are

INS

2^INS

2 2 2 2 °W301 ®TD301 ®I001 °S300 ®S001

(7.14)

2 2 2 2 ‘^WlOO ‘^TDIOO ®I001 ‘^SlOO

. 2 ®S001

(7.15)

where

“ flow sensor accuracies W301 vn.00

Otd3oi “ 103*^ temperature sensor accuracy (10®C differential)

c^TDioo “ temperature sensor accuracy (5°C differential)

^1001

° insolation sensor accuracy

*^S300

" error for solar or auxiliary to load

^SOOl

* sampling error for insolation

°S100

" error for collector output

On the basis of performance a reasonable strategy for initial selection of sensor accuracy and sampling rate is to balance the error terms of the error equations. For example, using the Instrument error equation for system

conversion efficiency and a* 6% Instrument error criterion, the error terms

would be balanced according to:

67. a. 2-2% 1 1 °tD301 - ®I001 - ®S300 - °S001 (6.16)

58
Using this term balancing strategy, sensor and sampling accuracies are selected

and iteratively refined to reasonable values using tradeoff charts shown in

Figures 8 and 9. The results for the projected sensor accuracy and sampling

requirements are as follows

Sensor Sensor Accuracy Sampling Accuracy

load flow + 2% + 2%

load temp. + 2% —

collector flow + 2%(liq)+ 3%(air) + 2%

collector temp. + 4%(liq)+ 3Z(alr)

insolation + 3% + 2%

auxiliary input + 2.5% + 2%

SUMMARY

The final instrumentation accuracy and performance factor uncertainty will

depend upon economic tradeoffs of sensor cost, installation and maintenance.

Using the instrument error equations and selecting a desired instrumentation

uncertainty of 6% as being reasonable and achievable, the values of sensor accuracy and sampling rate were assigned to the various measurements as shown in

Table 6.
TYPE DESIGN DATA REOUIREMENT RANGE ACCURACY MEASUREMENT FREOUENCY

1001 Total Radiation 0-1100 + 3Z FS (W/m^) 1 min or less

1002 Diffuse Radiation 0-600 + 6Z FS (W/m^) 5 min TOOl Outdoor DB Temperature -25 to 50 + 1*C Avg/hr

9 VOOl Wind Velocity 0 to 45 + 1 (m/s) Avg/hr

•S DOOl Wind Direction 0 to 360 + 20* Avg/hr U T002 Outdoor Wet Bulb Temp 0 to 40 + 1*C Avg/hr

6

4» w TlOO Collector Inlet Temp 50 to 150 + 0.3*C (L) + 0.6*C (A) 5 min

>. TDIOO Collector Temp Dlff -5 to 40 + 0.15*C (L) + 0.7*C (A) 1 min

C ^ TlOl Storage Inlet Temp 15 to 120 + 0.3*C (L) + 1*C (A) 5 min

OT TDIOX Storage Temp Dlff 0 to 60 + 0.15*C (L) + I'C (A) 1 min

0 w T102 Collector Absorber Temp 0 to 260 + 2*C Dally at solar noon

U O WlOO Collector Flow Rate varies + 2Z (L) + 3Z (A) FS 1 min ^ OBC

0 9 U WH

PDIOO Collector Press Dlff varies + 5Z FS Dally at solar noon

S

PC fct T200 Storage Media Ave Temp . 15 to 120 1*C hr

u ^ T201 Storage Ambient Temp -25 to 50 + 1.5*C hr.

4J -3

CO 3

CO PDlOl Storage Press Dlff (Air) varies + 2Z hr.

T301 Makeup Water Temp 0 to 30 + 0.3*C Avg/hr.

6 T300 HX Inlet Temp 5 to 100 + 0.3*C 5 min

« «

4J TD300 HX Temp Dlff 0 to 30 + 0.15*C (L) + 0.5*C (A) 1 min

9 m TD301 Storage Temp Dlff 0 to 40 + 0.15*C (L) + 0.5*C (A) 1 min

a

4J ^

TD302 Auxiliary Temp Dlff 0 to 60 + 0.15*C 1 min S 3^ W300 Circulation Flow Rate varies + 2Z FS 1 min

W301 Load Flow Rate varies + 3Z FS Continuous & Cummulat

T400 Load Return Temp 30 to 80 + 0.3*C (L) + 1*C (A) 1 min i TD400 Storage Temp Dlff 0 to 30 + 0.15°C (L) + 1*C (A) 1 min

<«4 (B TD401 Auxiliary Temp Dlff 0 to 60 + 0.15*C (L) + I'C (A) 1 min

« m W400 Circulation Flow Rate varies + 2Z (L) + 3Z (A) FS 1 min X *3

CO TD402 HTG Load Temp Dlff 0 to 60 + 0.15Z (L)

1 min

e

K T500 Load HX Inlet Temp 5 to 20 + 0.3*C 1 min

TD500 Load HX Temp Dlff 0 to 50 + 0.15*C 1 min X T501 Cooling Tower Inlet Temp 5 to 50 + 0.3*C 5 min

CO TD501 Cooling Tower Temp Dlff 0 to 15 + 0.15*C 1 min

NSOO Load HX Flow Rate varies + 2Z FS 1 min

O

0

CJ

U501 Cooling Tower Flow Rate varies + 2Z FS 5 min

>>

00

EPIOI

EP301

EP401

Collector Clrc Pump Power HW Clrc Pump Power HTG Loop Clrc Pump Power

AKW varies AKW varies AKW varies

+ 5Z FS + 5Z FS + 5Z FS

5 min or on/off

5 min or on/off

5 min

u «! EP402 Bldg Fan Power AKW varies + 5Z FS 5 min

i “ EP403 Heat Pump Compress Power AKW varies + 2Z FS 5 min or less

a. >« EP501 Absorp Chiller Oper Power AKW varies + 2Z FS 5 min or less

00 • EP300 HW Elec Aux Power AKW varies + 2Z FS 5 min or less EP400 HTG Elec Aux Power AKW varies + 2Z FS 5 min or less

n H F300 HW Aux Fuel Flow varies + 2Z FS 1 min or less

« < F400 HTG Aux Fuel Plow varies + 2Z FS 1 min or less o *« F500 Cooling Aux Fuel Flow varies + 2Z FS 1 min or less

T600 Bldg Return Air DB Temp 10 to 35 + 1*C 5 min TD600 Supply/return Air Temp Dlff 10 to 50 + 1*C 5 min

5 8

T601 Bldg Return air WB Temp -5 to 30 + 1*C 5 rain T602 Bldg Supply Air WB Temp -5 to 30 + 1*C 5 min U600 Building Air Flow Rate varias + 2Z FS 5 min

«• U601 Condeneate Plow varies + 5Z 1 5 min

3 CO

«3 MF600 Heat Flow Meter 0.1 to 15*C (AT) + 5Z 5 min

1 TD601 HT Pump Cond & Load HX Temp 0 to 30 + 1*C 5 min

1 Dlff

Tahl.; 6 INSTRUMENTATION RANGE, ACCURACY AMD MEASUREMENT FREQUENCY

60
7.0 APPLICATION OF PERFORMANCE FACTORS

The performance factor data generated during an experimental program will provide

the basis to directly determine parameters such as energy saved, thermal efficiency

and energy contributions to the various functional loads. However, to fulfill

the national program goals the data will also be applied to determine correlations

between building types, climates and heating and cooling system designs, to verify

design methods and to establish reasonable performance goals.

Although exact system or subsystem comparisons must await the selection of specific

solar system/building/climate combinations, examples of the format and general use

of performance factors are presented as Illustrations of how the data can be

utilized.

i.l Solar Energy System Thermal Performance

The technical selection of a solar system is based primarily on the thermal

performance in terms of energy collected on monthly or annual/seasonal periods.

Data such as shown in Figure 10 presents the amount of energy utilized for

auxiliary energy as well as for the heating and cooling functions and the total

energy supplied for a single site. Individual comparisons of solar energy systems

(in similar climates) and collector areas can be made using this type of chart.

For systems with varying collector size, the energy quantity can be expressed per

unit collector area. Comparisons are made for each unique type of solar system

to include air, liquid, active and passive. The data should be tabulated for

monthly, seasonal and annual time periods to cover the following functional areas

as appropriate.

Functions

A. Hot Water

B. Space Heating

C. Space Cooling

D. Space Heating and Space Cooling

E. Space Heating and Hot Water

F. Space Heating and Cooling and Hot Water

G. Space Cooling and Hot Water

7.2 Solar Energy System Thermal Effectiveness

The effectiveness of a solar energy system to meet the total functional loads on a cumulative basis for each building type can be illustrated for a single site as shown in Figure 11. Comparison of the effectiveness of similar solar system types

61
..01 X ON lN3W3yin03y AOy3N3

62

'igure

10

Monthly

Heating

and

Cooling

Loads

and

Auxiliary

Emrgy

Requirement
001

(g.OL X OH) A9y3N3

63

Figure

11

Cumulative

Energy

Use

for

the

MIT

Solar

House

IV

during

Two

Winter

Heating

Seasons

[9]
and climates on a seasonal basis is done by normalizing the building size and load

per degree day of heating or cooling and presenting the data in tabular form for

monthly, seasonal and annual time periods.

7.3 Analytical Predictions

The design of solar systems is currently based on analytical models and calculated

performances. A monitoring program will provide the measured data for com- parison with prediction of the following performance factors:

(1) Energy Delivered to Load (HW, heating, cooling, total)

(2) Solar Fraction of Energy Delivered to Load (HW, heating, cooling, total)

(3) Solar Energy Conversion Efficiency

(4) Energy Saved (Electric and Fossil)

(5) Collector Array Efficiency

Comparisons can be made on an individual site basis as illustrated in Figures 10

and 11 or tabular data for many sites can be used to determine standard deviations

as a function of climate and building characteristics for monthly and annual

periods

.

7.4 Solar Collector Array

Technical Innovations are needed in the development of collectors, therefore,

comprehensive characterization, measurement, and comparison of operating

performance data for the many collector varieties will be necessary. Because of

the influence of site integration and operating mode, comparison of preinstallation

performance data for individual panels and the array performance, as Illustrated

in Figure 12, is desirable using instantaneous and daily, monthly and annual

efficiencies. Other comparisons based upon design or material properties are listed

as follows:

A. Flat Plate

1. Absorber Coating

a. Flat Black

b. Selective

2. Covers

a. Number

b. Material Type

64

A
FLAT

PLATE

COLLECTOR

DOUBLE-GLAZED,

0.3

cm

TEMPERED

GLASS

ALUMINUM

ROLL-BOND

ABSORBER

COATED

WITH

FLAT-BLACK

PAINT

7.6

cm

GLASS

FIBER

BACK

INSULATION

65

Figure

12

Comparison

of

Collector

Panel

and

System

Collector

Array

Performance

[9]
B. Concentrator

1. Cylindrical

2 . Tubular

3. Trapezoidal

4. Other

7.5 Component Predicted Performance

It is not the intent of the test and evaluation program to develop components

but the influence of the operating mode and environment will be determined on major subsystems or components as listed below:

A. Collector Array

B. Storage

C. Energy Transport

D. Energy Conversion Equipment

An example of the comparisons in collector performance between predicted and

experiment are shown in Table 7 for the three key heat transfer areas: (a) solar

absorptance-transmlttance product (b) heat removal efficiency factor

(Fj^) ; and (c) heat loss coefficient (U^^) . These values are obtained by

reducing the collector performance data during selected periods of quasi-steady

state to plot in the slope-intercept form.

An example of the use of the slope-intercept plot to Illustrate collector

material degradation is shown in Figure 13. Tabular values of and for

similar materials as a function of climatic exposure will reveal the differences

related to environmental conditions.

7.6 Climatic Data

Climatic data measured during the program will be reported for hourly, monthly and

annual data as follows:

A. Total solar radiation at collector tilt angle

B. Direct solar radiation at collector tilt angle for selected sites

C. Ambient dry bulb temperature

D. Ambient wet bulb temperature at selected sites

E. Wind direction and velocity at selected sites

As example of reporting monthly values of global solar radiation on a horizontal surface at Stockholm, Sweden is shown in Figure 14 (10).

66
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67
a» BLACK NICKEL. 2 CLASS COLlfCTOR

Figure 13 Illustrations of Detecting Collector Degradation From

Thermal Performance Measurements.

68
MJ/m^ kWh/m^

month month

540

360

180

0

1958-1969

1975-1976

J A s 0 N D J F M A M J

16 4^ I2jps 7^3 3^70 1^7 4.5S 1C|,73 2^3 7 4,62 11 0,66 16qS3 16^

IS (,64 13^57 6 VO 4 1.63 10,13 6,14 1 ip7 2 3^03 6%7S — 14 vs 17S97

Figure 14 Global Radiation on a Horizontal surface

at Stockholm, Sweden.
7.7 Reconnnendatlons

Table 7 lists a number of data correlations and evaluations possible with the

available measurements and calculated performance factors. Due to the large

number of building types* solar energy systems and climatic regions, it is

obvious that computerized data reduction will be necessary to perform the necessary

evaluation. It is therefore recommended that additional study of the data format

and computerized data reduction requirements be under taken to more efficiently

implement the various correlations studies planned and to assure availability of the

results to the potential users •

70
PERFORMANCE

FACTORS

EVALUATION

AREA

71

Table

8

Application

of

Specific

Performance

Factors

to

Evaluation

Areas
8.0 Conclusions

The quantity and type of measurements described reflect a level of instrumentation

that will provide a capability for full efaluation of each solar energy system

and for each building, partial evaluation of most components performance and

measurement of local climatic data.

To reduce instrumentation costs, as assessment of the significance of the performance factors should be made for each system/building combination. The four

factors considered essential for the performance evaluation of solar energy

systems are;

o conventional energy saved by the solar energy system

o solar fraction of total load

o solar energy system conversion efficiency

o solar energy collected per unit sol lector area

The primary tool used to determine the data requirements and the selection of

instrumentation is the analytical heat balances. Sufficient heat balance calculations are required to equate the total energy input to the total energy output

for the subsystem or component plus an acceptable heat loss to provide an energy

balance closure of about ten percent. Errors greater than approximately ten per

cent will not permit useful comparison between different systems. Error analysis

of most performance evaluation factors for active solar energy systems have shown

that the experimental data can be obtained with an accuracy of about ± 6 per cent

using commercially available- sensors

72
9.0 REFERENCES

1. Streed, E. R., McCabe, M. , Waksman, D., Hebrank, J,, Rlchtmyer, T., "Thermal Data

Requirements and Performance Evaluation Procedures for the National Solar Heating and

Cooling Demonstration Program," NBSIR 76-1137, U.S. Gov't Printing Office, Washington,

D.C. 20402, SD Cat. No. C13

2. "Procedures for Determining Heating and Cooling Loads for Computerized Energy Calculations," The Task Group on Energy Requirements for Heating and Cooling, ASHRAE, 345 East

47th Street, New York, 1971.

3. ASHRAE Standard 90-75, "Energy Conservation in New Building Design," 1975. Available

American Society of Heating and Refrigerating and Air Conditioning Engineers, Inc.,

345 East 47th Street, New York, N.Y. 10017

4. ASHRAE Standard 93-77 "Method of Testing for Determine the Thermal Performance of

Solar Collectors," Corrected Pringing August 1978, ASHRAE, 345 East 47th Street, New

York, N.Y. 10017.

5. Personal Communication, Dr. Dan S. Ward, Colorado State University, Ft. Collins,

Colorado; and Study on "Instrumentation Type, Range, Accuracy, and Measurement

Frequency Required to Monitor and Evaluate the Thermal Effectiveness of Solar Heating

and Cooling and Hot Water System," NBS Purchase Order No. 608692, March 1976.

6. Kelly, G. E., "Potential of Air-to-Air Heat Pumps for Energy Conservation in Residential

Buildings," NATO Advanced Study Institutes, Series E: Applied Science No. 15, Noordoffleyden, 1976 (Available from National Bureau of Standards, Washington, D.C. 20234).

7. Personal Communication, Dr. William H. Klein, Radiation Biology Laboratory, Smithsonian

Institution, Rockville, Maryland, Jaunary 1976.

8. Engebretson, C.D., The Use of Solar Energy for Space Heating, M.I.T. Solar House IV,

"Proceedings of the United Nations Conference on New Sources of Energy ," Rome, August

21-31, 1961, Vol. 5 III e.2 pp. 159-172.

9. Hill, J. E., Richtmyer, T. E., and Jenkins J., "Initial Test Results for a Solar

Cooled Townhouse in the Mid-Atlantic Region," National Bureau of Standards, Washington,

D.C. 20234, Presented at ASHRAE Semi-Annual Meeting, June 1976.

10. Ahlstrom, B., Hedman, E., Dattermark, B.> "Solar Energy House in Lin oping," Swedish

Council for Building Research, Stockholm, NP-23368, 1977 (Also NTIS, U.S. Dept, of

Commerce, Springfield, Va.)

11. Ramsey, J. W., Borzoni, J. T., and Holland, T, H. , "Development of Flat-Plate Solar

Collectors for the Heating and Cooling of Buildings, "NASA CR-134804, June 1975.

12. Streed, E. R. , et al, "Results and Analysis of a Round-Robin Test Program for LiquidHeating Flat-Plate Solar Collectors," NBS Tech Note 975, U.S. Gov't Printing Office

Stock No. SN003-003, 3., August 1978.

73
APPENDIX A

National Contact Persons for TASK 1

BELGIUM Prof. Andr§ Pilatte

Faculte Polytechnique de Mons

Boulevard Dolez 31

B-7000 Mons

Tel: (065) 338191

DENMARK Mr. Ove Jorgensen

Thermal Insulation Laboratory

Technical University of Denmark

Building 118

DK-2800 Lyngby

Tel: (02) 883511

GERMANY Dipl.-Ing. F.J. Friedrich

Projektleitung Energieforschung

Kernforschungsanlage Julich GmbH

Postfach 1913

D-5170 Julich

Tel: (02461) 614621

Tlx: 0833556 kfa d

FRIEDRICH PLE

ITALY Professor Aldo Fanchiotti

Instituto di Macchine e Technologie Mechaniche

Facolta d'Ingegneria

Via Eudossiana 18

Roma 00184

Tel: (06) 4754141

JAPAN Mr. Taira Sunami

Senior Officer for Solar Energy Development Prograun

Agency of Industrial Science and Technology

MITI

3-1 Kasumigaseki, Chiyoda-Ku

Tokyo

Tel: 03-501-1511 ex. 4658

. Tlx: EIDMITI J22916

NETHERLANDS Prof. Ir. C.W.J. van Koppen

Eindhoven University of Technology

P.O.Box 513

Eindhoven

74
SPAIN Mr. Eduardo G. Mezqulda

Institute Naclonal de T§cnlca Aeroespaclal

Torrejon de Ardoz

E-Madr id

Tel: 6750700, ex. 479

SWEDEN Prof. Ingeraar Hoglund

The Royal Institute of Technology

Division of Building Technology

S-10044 Stockholm 70

Tel; 08/236320

SWITZERLAND Dr. Phys. Andr# Faist

Ecole Polytechnique F§d§rale

de Lausanne

33 Av. de Cour

CH- Lausanne

Tel: 021/264621

U.S.A. Mr. James Hedstrom

Los Alamos Scientific Laboratory

Mail Stop 571

Los Alamos

New Mexico 87545

Tel: (505) 667-6441

United Kingdom Mr. David Curtis

Faber Computer Operation Ltd.

18 Upper Marlborough Rd.

St. Albens, Herts

75
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