NATL INST. OF STAND & TECH R I.C,

AlllDS lDBm3

NIST

PUBLICATIONS

NBSIR 76-1137

THERMAL DATA REQUIREMENTS AND

PERFORMANCE EVALUATION

PROCEDURES FOR THE NATIONAL

SOLAR HEATING AND COOLING

DEMONSTRATION PROGRAM

Office of Housing and Building Technology

and Thermal Engineering Section

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D C. 20234

August 1976

Prepared for

Energy Research and Development Administration

Division of Solar Energy

Washington, D.C. 20545

and

Department of Housing and Urban Development

Division of Energy, Building Technology and Standards

Washington, D.C. 20410

U.S. DEPARTMENT OF COMMERCE, Elliot L Richardson, Secretary

O. Vetter, Under Secretary

QC sy Ancker-Johnson, Assistant Secretary for Science and Technology

100

,U56

NO. 76-1 157

1976

BUREAU OF STANDARDS, Ernest Ambler, Acting Director

PREFACE

The overall goal of the National Solar Heating and Cooling Demonstration Program is "to stimulate industrial and commercial capability, including that of small businesses, to produce and distribute solar heating and cooling systems, and through widespread applications, reduce the demand on present fuel supplies." To help achieve this goal, the

I Demonstration Act further provides that solar heating and combined heating and cooling

j systems will be installed in a substantial number of buildings in the climatic regions

existing in the different United States geographic areas. Evaluation of the performance

and reliability of the current technology can be expedited by testing under carefully

controlled conditions and by demonstration in the field.

The purpose of this document is to provide the rationale and description of the data

requirements, instrumentation types and data analysis methods used to monitor and evaluate

the field demonstration systems. It is recognized that complete instrumentation and subsequent technical evaluation of each system/building/ climate combination cannot be

performed because of the cost and data analysis limitations. Therefore, only selected

unique installations will be completely instrumented and as the exact design and location

of all sites becomes available, optional measurements will be made to evaluate significant

features . «

The report has been prepared at the National Bureau of Standards under the general guidance

and review of the Solar Heating and Cooling Performance Evaluation Committee, Mr. H. J. Hale,

Solar Division, Energy Research and Development Administration (ERDA) , Chairman. Members

of the committee include:

M. McCabe National Bureau of Standards (NBS)

W. Christensen Department of Defense

W. Freeborne Department of Housing and Urban Development

A. Kromis NASA - Marshall Space Flight Center (MSEC)

W. Littles NASA - MSEC

F. Morse ERDA

E. Streed (Secretary) NBS

Specific acknowledgments are extended to Dr. Dan Ward, Colorado State University, for providing operational data and technical inputs and to David E. Galehouse, Consulting Engineer,

for sensitivity and error analysis calculations. The consultation and technical reviews of

Dr. J. Wayne Littles, NASA-MSFC, Dr. Mike Nash and Mr. John Bartlett, International Business

Machines, and Dr. James E. Hill, NBS, have contributed significantly to this document.

Thanks are also expressed to Mr. Frank Bridgers, Dr. Jack Duffie, Dr. Gerald Lowery, Prof.

John Yellott, and Dr. George 0. G. Lof for general review and comments regarding organization,

completeness, and terminology. The encouragement and support of Mr. Jack Hale, ERDA, and

Mr. Robert Dikkers, NBS/CBT, Solar Program Manager, to prepare the document in final form,

is gratefully appreciated.

This report was prepared as a reference document to prescribe a standard list of thermal

performance factors and data analysis methods that can be used to evaluate solar heating

and cooling systems for the National Demonstration Program. In describing these factors

and the associated measurements, specific solar energy system designs have been identified

and their features characterized to illustrate the type and location of sensors. Inclusion

of a particular design in this report in no case implies a recommendation or endorsement

by the Federal government, and the presentation should not be construed as a certification

that any component, subsystem, or system is preferred at the current state of technology

development. Similarly, the omission of a component, subsystem, or system does not imply

that the capabilities are less than those that are included. The designs presented were

obtained primarily from the open literature and are intended to be used for illustration

purposes only.

The thermal performance data obtained from the Demonstration Program are intended to serve a variety of users including architects, engineers, manufacturers, developers

and homeowners, code officials, standards writing organizations, and government planners

for energy conservation, economic and building technology applications. An attempt has

been made to identify and determine the many factors needed to satisfy the interest and

needs of these diversified disciplines. However, recognizing that requirements or technology will change during the course of a five-year program, the evaluation factors and

measurements can be modified.

Comments and suggestions are welcome and should be sent to:

Manager, Solar Energy Program

National Bureau of Standards

Building 225, Room A-114

Washington, D.C. 20234

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NOMENCLATURE

Collector gross 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

Time

Overall heat transfer coefficient

Collector heat loss coefficient

Collector panel solar absorptance

Effective product of solar absorptance and transmittance

of cover and absorber panel

Difference

Efficiency

Sensor or measurement uncertainty, standard deviation

Integration time 1, etc.

Collector cover transmittance at air mass 2 or time

Air, ambient

Mass flow

Fluid inlet

Insolation

Inlet

Exit

Temperature difference

Sampling rate

Water, Flow

iii

SI CONVERSION UNITS

In view of the present accepted practice m this country for building technology, common

U.S. units of measurement have been used throughout this document. In recognition of

the position of the United States as a signatory to the General Conference of Weights

and Measures, which gave official status to the metric SI system of units in 1960,

assistance is given to the reader interested in making use of the coherent system of

SI units by giving conversion factors applicable to U.S. units used in this document.

Length

1 in = 0.0254 meter (exactly)

1 ft = 0.3048 meter (exactly)

Area 2 _4 2

1 in„ = 6.45 X 10 meter

1 ft = 0.09290 meter

Volume. ^ . 1 in = 1.639 X 10~ meter

1 gal (U.S. liquid) = 3.785 x 10 meter

_2

1 ounce-mass (avoirdupois) = 2.834 x 10 kilogram

Mass

11 pound-mass (avoirdupois) = 0.4536 kilogram

Pressure or Stress (Force/Area)

1 inch of mercury (60"?) = 3.377 x 10^ pascal

1 pound-force/inch (psi) = 6.895 x 10 pascal

Energy

1 foot-pound-force (ft-lbf) = 1.356 joule

1 Btu (International Table) = 1.055 x 10 joule

Power

^ 1 watt = 1 X 10 erg/second

1 btu/hr = 0.2929 watt

Temperature

to^ = 5/9 (top - 32)

Heat

1 Btu-in/h-ft^-'p = 1.442 x 10"^ W/m-K (thermal conductivity)

1 Btu/lbm - 'F = 4.184 X 10^ J/kg-K (heat capacity)

1 langley = 4.184 x lO"* J/m^ = 1 cal/cm^ = 3.69 Btu/ft^

iv

TABLE OF CONTENTS

PACK

1.0 Introduction ^•3 2.0 Program Objectives

4 3.0 Performance Evaluation Procedure

3.1 Standard Designations for Sensors and Subsystems ^ 3.2 General Solar Energy System Description and Energy Balance 5 4.0 Active Systems Description and Performance Calculations 11

4.1 Energy Collection. and Storage Subsystem

4.2 Hot Water Subsystem 15

4.3 Space Heating Subsystem 17 4.4 Space Cooling Subsystem 2C

5.0 Passive Systems Description and Performance Calculations 23

5.1 Roof Water Pond 25

5.2 Wall Collector 27

5.3 Performance Evaluation 27

6.0 Systems Performance Evaluation Summary (Active Systems) 30

6.1 Performance Factors - General 30

6.2 Energy Saved - General 32

6.3 Climatic Primary Performance Factors 33

6.4 Energy Collection and Storage Subsystem (ECCS) Primary 34

Performance Factors

6.5 Hot Water Subsystem (HWS) Primary Performance Factors 36

6.6 Space Heating Subsystem (SHS) Primary Performance Factors 38

6.7 Space Cooling Subsystem (SCS) Primary Performance Factors 40

6.8 Solar Energy System/Building Summary 42

6.9 Secondai"y Performance Factors and Measurements 45

7.0 Uncertainty Analysis of Solar Performance Factors 52

7.1 Sensitivity Analysis Methods 52

7.2 Derivation of the Overall Instrumentation Accuracies 55

7 . 3 Summary 64

8.0 Application of Performance Factors 66

8.1 Solar Energy System Thermal Performance 66

8.2 Solar Energy System Thermal Effectiveness 66

8.3 Analytical Predictions 69

8.4 Solar Collector Array 69

8.5 Component Predicted Performance

8.6 Climatic Data 71

8.7'' Recommendations 74

9.0 Conclusions 76

10.0 References 77 V

TABLES AND FIGURES

TABLES PAGE

1. Primary Performance Evaluation Factors 6

2 a&b. CSU Sampled Data Using Different Sampling Intervals 60

3. Range of Measured Daily Variance with Data Extrapolated for 61

Weekly, Monthly and Yearly Periods

4. Sampling Rate as a Function of Time Interval for Several 62

Data Requirement Types

5. Instrumentation Range, Accuracy and Measurement Frequency 65

6. Comparison of Collector Performance Coefficients Derived 72

from Testing and Analysis

7. Application of Specific Performance Factors to Evaluation Areas 75

FIGURES

1. Flow Chart of Elements Comprising Monitoring of System

Performance and Operation

2. Energy Flow Diagram for a General Solar Heating, Cooling

Hot Water System

3. Energy Collection and Storage Subsystem Flow Schematic,

Sensors and Performance Calculations

4. Hot Water Subsystem Flow Schematic, Sensors and Performance

Calculations

5. Space Heating Subsystem Flow Schematic, Sensors and Performance

Calculations

6. Space Cooling Subsystem Flow Schematic, Sensors and Peformance

Calculations

7. Passive Solar Energy Systems Schematics and Sensors 24

8. Calculation Sequence for Building Load Program 29

9. Accuracy in Calculated Solar Energy Collected (QlOO) 57

10. Accuracy in Calculated Solar Used for Hot Water (Q300) 58

11. Monthly Heating and Cooling Loads and Auxiliary Energy 67

Requirement

12. Cummulative Energy Use for the MIT Solar House IV During 68 Two Winter Heating Seasons

13. Comparison of Collector Panel and System Collector Array 70

Performance

14. Illustration of Detecting Collector Degradation from Thermal 73 Performance Measurements

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21

DATA REQUIREMENTS AND THERMAL PERFORMANCE EVALUATION PROCEDURES FOR T}1E

NATIONAL SOLAR HEATING AND COOLING DEMONSTRATION PROGRAM

1.0 INTRODUCTION ;

A major objective of the Solar Heating and Cooling Demonstration Program, described ! in ERDA-23A [1], is to provide data on the technical performance of solar heating

and cooling systems.* This data, following its collection, analysis, and evaluation

will be used to provide the information and data base needed to evaluate subsystem

and system performance, to develop definitive performance criteria and to formulate

analytical models yor use as design guidelines for solar heating and cooling systems. | This report is intended to provide a description and rationale for the instrumentation

selection and resultant data required to monitor and evaluate the thermal effective - ness and reliability of solar heating, cooling and hot water systems in meeting

building thermal loads and in conserving conventional fuels or energy. :

A basic assumption utilized in the preparation of this report concerns the purpose

of the data to be acquired by the described instrumentation. Because of the demonj stration nature of the program, the data acquired must be sufficient to allow for I;

I the evaluation of the thermal effectiveness of the solar components and system, but

j is not intended to be utilized directly in the development of specific components. ji

Because nationally accepted test procedures for building heating and cooling systems

do not exist at the present time and because of the relatively large number of combina- ! tions possible for solar and conventional HVAC systems, the data requirements,

measurement procedures and equations used to determine the performance factors

dicussed in this report will require modifications dictated by the characteristics |t of the specific system being evaluated. ji

ij

The approach and methodology employed to obtain, evaluate and compare thermal

performance data is shown in Figure 1. Measurements from the on-site sensors are used to determine the solar system energy contribution, the auxiliary energy requirements, the building heating or cooling load, the climatic conditions and the comfort |I level maintained by the system. Selected buildings and certain type solar systems will

I be analytically modeled to predict system performance and building thermal response jj as a function of the measured climatic conditions. The resulting predictions will ll then be compared with the experimental data and the analytical modeling procedures

validated. Validated analytical models will be used to predict performance on similar solar system/building types having either reduced levels of instrumentation

or none at all. i

*Solar heating and cooling systems are referred to as Solar Energy Systems in this

report.

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Additional laboratory or field test data on critical components as a function of time

and operating conditions should also be made to the extent necessary to characterize

their performance and resolve differences between predicted and measured system

performance

.

2.0 PROGRAM OBJECTIVES

Technical performance evaluation of each solar energy system/building/climatic region

demonstration will be based upon the following factors:

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

temperature 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 nparameters 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 domestic hot

water (DHW) and conmiercial service hot water (SHW) . The commercial service hot water

may either Jse potable or nonpotable depending on its intended use.

I 3
1.
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 a 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 6.0.

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

second category data can be determined by appropriate calculations or approximations using category one measurements however in some cases the data can only be

direct 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. Wind direction and velocity are examples of such measurements.

The building load, particularly infiltration, and collector losses are related to wind effects. However, most analyses to data have not incorporated corrections

or used detailed calculations to correlate performance with wind data.

3.1 Standard Designations for Sensors and Subsystems

In order to standardize the performance calculations and identify sensors according to type and location, an alpha-numeric name is provided for each performance factor and sensor. A five character name is used consisting of one or two letters which desigiiate either the sensor type or the measured or calculated

quantity and a three digit number which identifies the subsystem or data group as follows

:

4

Letter Designations

C = Specific Heat

D = Direction or Position

EE = Electric Energy

EP = Electric Power

F = Fuel Flow Rate

I = Incident Solar Flux (Insolat

N = Performance Parameter

P = Pressure

PD = Differential Pressure

Q = Thermal Energy

T = Temperature

TD = Differential Temperature

V = Velocity

W = Heat Transport Medium Mass

TI = Time

Subsystem Designations

Number Sequence

001 to 099

100 to 199

200 to 299

300 to 399

400 to 499

500 to 599

600 to 699

ow Rate

Subsystem/Data Group

Climatologlcal

Collector and Heat Transport

Thermal Storage

Hot Water

Space Heating

Space Cooling

Building /Load

Thus the sensor designation TlOl defines an absolute temperature measurement

in the collector subsystem and the variable name Q600 defines a heat flow

measurement or calculation for a building load grouping.

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 subsystems 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 2, 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.

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.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 for 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 accomplish 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

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. In the context of this report, hot

water is also treated as a building thermal load in that the HW subsystem capability

to provide the thermal energy required at the desired temperature must be balanced

against the actual rate of hot water consumption.

.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 within the component.

8

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 2, 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 2 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 energy load.

3.2.2.1 Subsystem Heat Loss

Examination of Figure 2 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 jerf ormance 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 2 as a miscellaneous heat loss/heat gain for the building. The

entire subsystem heat loss for those components located within a temperature

9

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 losr. to reduce the building heating requirements.

Examination of each subsystem element in Figure 2 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 instrumentation 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

priir;ary evaluation factors as energy saved, heating and cooling load, and the

solar fraction of the heating and cooling load. Hoxjever, 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.

10
4
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 3, 4, 5 and 6 were 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 by the government 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

Figure- 3 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 elements 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 thte

11
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SYSTEM A (Liquid Medium, Series Storage)

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LIQUID TO

AUXILIARY AND

LOADS

SOLAR ENERGY STORAGE

Return

EPioi n COLLECTOR

CIRCULATING

PUMP

SYSTEM B (Air Medium, Parallel Storage) ^ ]_ g BUILDING FAN

1001 1002

SOLAR HEATED

AIR TO

AUXILIARY AND

LOADS

VOOl,

DOOl

MEASUREMENTS

SOLAR RADIATION • TEMPERATURE • FLOW

/ WIND VEL. DIRECTION

Q ELEC. POWER

0= OPEN

MD POSITION C= CLOSED

l€) NO. MODE 1 MODE 2 MODE 3

1 0 0 C

2 C C 0

3 0 c C

4 C 0 0

5 C 0 0

FIGURE 3 SPACE HEATING SUBSYSTEM FLOW SCHEMATICS AND SENSORS

12

CATEGORY VARIABLE DESCRIPTION DETININC EQUATION

P QOOl Total Solar Incident /lOOldT

SM Direct Solar Incident /(1001-I002)dT

P qioo Solar Energy Collected (1/Ac ) /WlOO • ClOO • TDlOOdT

S QlOl Collector Heat Loss /1 1001- a/Ac) (WlOO • ClOO • TBIOO) dT , WlOOjIO

ECSS Operating Energy

j

'3413/EPlOldT, SYSTEM A

s qi02

3413/0 -EPAOldT, SYSTEM B

A^-'q10OI-NPUMP-Q102-Q200, SYSTEM A

s Q103 Collector Transp. Heat Loss ^"'^

^ A^-Q10(>«)FAN-Q102-Q200, SYSTEM B/MODE 1

A^-Q10O+NFAN-Q102-Q203, SYSTEM B/MODE 2

Q201+NT'AN-Q102-Q203 , SYSTEM B/MODE 3

'/WlOO-ClOl-TDlOldt , SYSTEM A

Energy to Storage /MlOO-ClOl-TDlOldT , SYSTEM B/MODE 1

Q , SYSTEM B /MODES 2 & 3

q300+Q400+<)500 , SYSTEM A

s Q200

s Q201 Energy from Storage " 0 , SYSTEM B/MODES 14 2

/W400-C101-TD101dT , SYSTEM B/MODE 3

s Q202 Hourly Increase In Stored Energy (lie ) [T200(t)-T200(t-1) 1 P

s 'Q300+Q40OHQ500 , SYSTEM A

p Q203 Total Solar Energy Utilized 0 , SYSTEM B/MODE 1

, A)400-C401-TD401dT , SYSTEM B/MODES 2 & 3

s Q204 Storage Heat Loss Q200-(Q201+Q202)

s Q205 ECSS Total Heat Loss qiQltqi03+q2Q4

s NIQQ Dally Integrated Collector Efficiency /QlOOdT/ZQaOldT

s NlOl Instant. Collector Efficiency WlOO-ClOO-TDlOO/Ac-IOOl, QUASI-STEADY CONBITIONS

s :U02 Collector Panel Efficlencv Factor (l/T]lf[(T100-T001/I001]dT, QUASI-STEADY CONDITIONS

s N103 Collector Panel Factor (t«)

(4) COMPUTER SUBFOUTINE, QUASI-STEADY CONDITONS^ '

s NlO'i Collector Panel Factor Fj^D^^ COMPUTER SUBROUTINE, QUASI-STEADY CONDITIONS

s N105 Collector Hx Effectiveness (l/TI/[TD101/(T101-T200)]dT, HlOOiiQ, SYSTEM A

s N106 DHW Hx Effectiveness (l/TI)/[TB30O/(T2OO-T3OO)]dT, SYSTEM A

s N107 Collector Transp. Efficiency (1/TI) J- [ (Q100-Q103) /Q-lOO ]dT , WlOOyO

s N108 Storage Efficiency /(Q201+<!202)dT/;Q200dT

SM N109 Storage Heat Loss Parameter a/Tl)/(T2OO-T201)dT

s NllO ECSS Coefficient of Performance /(i203dT/ Q102dT

p mil ECSS Conversion Efficiency /Q203dT/Ac-/Q001dT

s N112 ECSS Utilization Efficiency /Q203dT/Ac-/Q100dT

p N113 Avg. Ambient DB Temperature (i/Ti)rrooidT

SM N114 Avg. Wind Velocity a/Ti;/vooidT

SM iTiis Avg. Wind Direction a/TI)..T)001dT

SM N116 Avg. Collector Pressure Differential Cl/TI)/PD100dT, WlOOiiO

SM N117 Avg. Storage Pressure Differential a/TI)/PD101dT, SYSTEM B/MODES 1 i 3

(1) Provided for concentrating collectors 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

(4) QUASI-STEADY Conditions occur when IQOl, TOOl, TlOO, WlOO are essentially constant for 15 minutes.

FIGURE 3 PRIMARY AND SECONDARY PERFORMANCE FACTORS FOR SPACE HEATING SUBSYSTEMS

13

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 rhe

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 evaluaHon of all performance factors, the sensor types and

locations shown in Figure 3 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.

14

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 required. 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. Operating 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 equations are appropriate for both

system types and where different equations are required, the particular system is

noted. However, not all active solar system types to be considered for the

demonstration program can be described by the listed equations. In that case, the

equations must be rewritten 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 have 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

water is 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

15
•

i
16

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 6.

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 liquid-to-air heat exchanger is located in the air duct as the primary

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

solar-heating component and an electric resistance heating coil 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 cotiventional 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

17

Supply Air

r

SYSTEM A

(Heat Pump and Electric Auxiliary)

W400

• ^

Two-way ePAOO

Valve — —r :

r

Mode 1 TD401

Solar

Storage TD402

TD400

I

Cond

EP403 "T^ HT PUMP " COMPRESSOR

Modes 2 & 3

W600

ELECTRIC

AUXILIARY ^ Modes 3 & 4 HEATING

'

I LOOP LOAD

TD601 ' ^

I

>

T6?0 HEAT PUMP Re tun.

• HT PUMP

il

I COND. HX

TD600

}

ni^Bldg. Fan

\uj I EP402 n

I

HEATING LOOP

CIRCULATION PUMP

EP401 Q

SYSTEM B

UNIT Air

F400

(Fossil Fuel Auxiliary)

AUX.HX

.p^n:

SOLAR

STORAGE

1 \

WACO

MEASUREMENTS

# TEMPERATURE

FLOW

n ELECTRIC POWER

r TD401 '

I

I

I

TD400

I TD402

\

I

t

'*

I T400 t,

.TING LOOP

FAN COIL UNIT.

J600l Heating Loop

Load HX

U!

"*

Bidg.

^

\Zy

Heated Air

to Bldg.

TD600

Return Air

T600

EP402 n

HEATING

CIRC. PUMP EP401

FIGURE 5 SPACE HEATING SUBSYSTEM FLOW SCHEMATICS AND SENSORS

18

. ARIABLK PFSCRirtlON DEFINING EOrATinM

060

1

Q402

Q404

Qi.05

Q406

Q407

Q408

q409

QilO

Q411

Q412

Q414

Q415

Q416

Q417

M400

N401

S402

:J403

M404

N405

:I406

W407

Solar L'sed for Space lieaclng

Auxiliary for Space Heating

Space Heating Load

Operating Energy

Heat Pump Compressor Energy

Solar CO Heat Pump

Solar to Building Air

Heat Pump Load

Heating Loop Load

Electric Energy for Aux.

Fossil Energy For Aux.^^^

Total Energy Consumed

SHS Fraction of ECSS Elec. Energy

Elec. Engy. for Solar Space Htg.

SYSTEM B

;'W400-C400-TD400dT

{W600-C60;(TD600-TD601)d-, SYSTEM A/MODES 3 4 4

^W400-C401.TD401d-

/M600-C600-TD600d3413.''(EP401+EP402)dT

3413;EP403dT

/W400-C400-TD402dT

/W400-C401-TD401dT

/^rt00-C601-TD601dT

/W400-C402-TD402dT

3413/EP400dT

HVF/F400dT r Q400+Q403

j Q400+Q403+<)404 J Q40O+Q403-H5404-H3409 ^ Q403-K3409 t Q400+Q403+Q410

Q400/N110

{q403+Q412

Q403-K!404+Q412 Q403+Q404+Q409+Q412

Q403+Q409

Q403+Q412 ,

Elec. Engy. for Conv. Space Hcg

Elec. Energy Saved

Fossil Engy. for Conv. Space Htg.

Fossil Engy. Saved

Solar Fraction of Heating Load

Solar Fraction of Energy Consumed

SHS Coefficient of Performance

Heat Pump Coefficient of Perf.

Elec. Aux. Thermal Efficiency

Fossil Aux. Thermal Efficiency

Avg. Bldg. DB Temp.

Avg. Bldg. Supply Air DB Temp.

(3)

{

SYSTEM a/ MODES 2 i 3

SYSTEM A/ MODES 2 i 3

SYSTEM A/MODE 1

SYSTEM A/MODES 2 i 3

SYSTEM B

SYSTEM A/ MODES 3 i 4

SYSTEM B

SYSTEM A/MODE 1 SYSTEM 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

Q402/:OTE

Q414-Q413

Q402/NHTF , SYSTEM B

0416-0410 , SYSTEM B

/(Q405+0406)dT/.'O402 , SYSTEM A

;Q400dT//0402dT , SYSTEM B

/Q400dT//Q411dT

/Q402dT//(Q403-K)404+O409)dT , SYSTEM A

/Q407dT//(Q403-H5404)dT , SYSTEM A/MODES 2 4 3

/Q401dT//Q409dT , SYSTEM A/MODES 3 4 4

/Q401dT//q410dT , SYSTEM B

(l/TI)/T600dT

(l/TI);(T600+TD600)dT

(1) HVF = Keating Value of Fuel

(2) ;IHTE - Thercial Ffflciency of Conventional Electric Heating Unit

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

FIGURE 5 PRIMARY AND SECONDARY PERFORMANCE FACTORS

FOR SPACE HEATING SUBSYSTEMS

19

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 coll. 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 6.

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.

20

21

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 dehumldif icatlon 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 dehumldification. Building air dehumldif icat ion

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 6.

22

5.0 PASSIVE SYSTEMS DESCRIPTION AND PERFORMANCE CALCULATIONS

The influence of the building envelope materials and construction, particularly

the area and location of windows, on building heating and cooling loads are well established. The application of windows, walls, roof sections with sky

lights and roof ponds as part of the architectural design to utilize solar energy

as a significant fraction of the to'sl ^oad is commonly referred to as a passive

solar energy system. Additional requisites for a building design using windows

to qualify and be evaluated as an alternative energy source have been stated

in reference [2] as (1) operable insulating shutters or other devices which,

when drawn or closed, shall cause the window area to keep maximum outward heat

flows below a selected value, and (2) the window areas are shaded to otherwise

protected from the direct solar rays during the cooling season.

Generally the same functional elements such as the collector, storage and energy

conversion subsystems exist in passive systems but physical distinction between these

elements and the building elements Is not always possible. Direct measurement

of the thermal energy flows will probably not be possible because of the

dependence on natural heat transport phenomena such as free convection, radiation

and evaporation. Therefore, the heat balance approach previously described for

active systems will have to be greatly modified for passive system evaluation.

In general, the only direct measurements practical will be with temperature

sensors, heat flow meters, scanning radiometers and pyranometers. The performance

evaluation will rely upon measurements of the auxiliary fuel usage and the interior

comfort level. Determination of the energy saved will be obtained from load

calculations for similar buildings without the solar energy system or, when

possible, measured energy consumption in an adjacent similar structure without

a solar energy system.

The following section describes the energy flow, instrumentation requirements

and performance evaluation for two alternate designs assumed for illustrating

the use of passive solar energy for space heating and cooling. The systems are considered passive because no auxiliary energy is required for the transfer

of tjjermal energy between the collecting and storage elements and the building

load. Figure 7 illustrates conceptually the two passive solar energy systems

and indicates the required instrumentation for performance evaluation.

One design consists of a water pond with a movable insulation cover that is

thermally integrated into the building structure. The other design consists of

a wall solar collector with a movable insulating device and thermal storage

23

o<

24

that is also thermally integrated into the building structure. These two designs are considered representative of current passive technology but niany

other innovative architectural approaches have been built for private use and

their evaluation is in a relatively primitive stage. It is apparent that the

building solar heat gain, thermal resistance, thermal mass and thermal time

constant are the basic parameters governing the building thermal performance.

Roof Water Ponds

Figure 7 shows the daytime position of the movable insulating cover during the

heating season. In operation, the roof pond is uncovered during the heating

season daytime, thereby enabling solar energy to be stored by raising the internal

energy of the water in the roof pond. At night, the pond is covered to reduce heat losses and enable the stored energy to be used for space heating by

free convection and radiation from the ceiling. During the cooling season, at night the roof panel is uncovered and the pond rejects heat by radiation to the night sky and by evaporation. During the daytime, the roof panel is

covered to prevent absorption of solar energy. Space cooling is provided during

the day because the cool water in the roof panel can absorb the heat that is

released in the space and transferred through the walls and fenestrations.

Roof water ponds can be evaluated in the same manner as conventional solar

collectors. In order to do this, the overall heat transfer coefficient (UA) must be known as a function of the temperature difference between the roof

average pond water (T^) and the average building air (T^) . This relationship

can be quantitatively established by heating the roof pond with solar energy

until a maximum temperature for the day is obtained at which time the roof

water pond is covered with the insulated panels. The rate at which the water

temperature decreases times the water mass (m) and specific heat (c^) gives

the rate of heat transfer to the building, assuming that the heat loss through

the insulated panels is either negligible or can be calculated. Once this

quantitative relationship is established, the useful heat delivered by the water

roof pond to the building can be calculated knowing the value of the aforementioned

temperature difference.

The solar energy collected between time t^^ and QlOO is calculated by:

QlOO = m-Cp[T^(T2)-T^(Tj^)] + / UA(T^-T^)dT (5.1)

25

where UA is the overall heat transfer coefficient between the pond and the ceiling,

and T,,(t^)-T (t,) is the increase in the average pond temperature during the

W z w I o r r

selected time intervals when the pond is uncovered. From a practical standpoint,

daily collector efficiency is the minimum time to obtain reasonable accuracy for

performance evaluation. The efficiency can be expressed by:

2 2 NlOO = / QlOO di// QOOl di (5.2)

^1

where the energy collected and the incident solar radiation quantities

are summed each day when the pond is uncovered.

The rate at which heat is removed from a building during the summer can be

determined in a similar manner. Just before sunrise, the roof water pond is

covered with the insulated roof panels. The rate of water temperature increase

times the water mass and specific heat product gives the rate at which heat is

removed from the building (if the heat transfer through the insulated roof

panels is either negligible or can be calculated) as a function of the tem- perature difference between the water and building air.

It is imperative that the internal air temperature be carefully recorded because

performance will depend significantly on the temperature excursions permitted.

In addition, it is extremely important that the roof pond water depth also be

carefully recorded because it will also affect performance.

The fraction of the annual heating and cooling load furnished by a roof water

pond is strongly dependent on the temperature excursions permitted before auxiliary

energy is used. Therefore, internal temperature is required for space heating

and cooling and relative humidity measurements are needed for the evaluation

of space cooling. The electrical power expended for humidity control must

be measured also.

Measurements of the fossil or electrical energy used for auxiliary purposes

(EAOO/FAOO and E500/F500) are used to determine the total auxiliary energy,

Q401 (heating) and Q501 (cooling). The heating or cooling load, Q402 or Q502

respectively, are obtained by adding the solar and auxiliary contributions as follows

^2 Q402 = / [UA(T -T )dT + Q401 (5.3)

^1

26

2 Q502 = / [UA(T -T )dT + Q501 (5.4)

^1

Because of the building modification to accommodate the roof pon(J, energy

saved calculations will require analytical prediction of the building load for

conventional design and construction.

5.2 Wall Collector

The operation of the wal] solar collector is shown in Figure 7 during the heating

season for sunny days; the insulating device is removed thereby exposing

the high thermal capacity wall to solar radiation. At night, the deployed

insulating device and transparent cover reduce heat losses to ambient and the

heat stored in the wall during the day is transferred by convection and radiation

to the space for heating. The wall collector is primarily a heating device

so that the useful output during the cooling season is limited to the ventilation

capability of the system. To limit solar heat gains during the cooling season,

the insulating device must be deployed and the overhanging roof designed to provide shading from direct solar radiation.

i For the generalized system schematic in Figure 7 the possible heat flows are

the solar input, 1001, heat losses from the wall (a function of the wall or window temperatures T119, ambient temperature TOOl, wind characteristic?

VOOl and DOOl, and radiation exchange with the exterior surrounding) and

the heat delivered or removed from the building heated space.

5.3 Performance Evaluation

Figure 7 shows the sensors utilized for performance evaluation of the passive

type solar systems. Although temperature sensors are indicated for the energy

storage elements, heat flow meters would also be appropriate. Because of the

passive nature of the solar system, air flow measurements are probably impractical and energy transfer and storage must be determined from the measured

temperatures and a knowledge of the thermal characteristics of the building.

Thus, performance analysis of the passive solar system must rely primarily on transient thermal analysis of the integrated building and solar system,

considering the outdoor climatic conditions and the energy release within the

building. It should be noted that the exact number and location of the temperature/

heat flow sensors are very dependent on the design of the particular instrumentation

deemed necessary for passive system evaluation.

The heat transfer calculations for room temperature predictions are similar to

27

the building heating/cooling load calculations perforined by available computer

programs. However, the temperature calculations are more complex because they

require exact heat balances considering the room air, surrounding walls and

infiltration of the outdoor air. Since the major variable in passive system

performance is the hourly room temperature, it is necessary to account for the

transient heat conduction and thermal storage of the building and internal mass.

Determination of the temperature and humidity in non-air conditioned rooms responding to randomly fluctuating outdoor climatic conditions can be determined

using hourly simulations of heat gain and storage obtained with standard

algorlthams published by ASHRAE [3].

A computer program employing these algorithms is available [4]. The calculation

sequence as depicted in Figure 8, requires '^^talled data input for the building,

weather and operating schedule. Building data Includes geometric characterization

of the construction and materials used for the exterior envelope, interior

partitions, ceilings and floors and their associated thermophysical properties.

Weather data is provided in the form of a National Weather Service Tape or provided as measured data Including wet and dry bulb temperature, wind, and solar

radiation. The operating schedule is used to determine energy release profiles for

the appliances and lights and metabolic heat release by the occupants.

Normal solar radiation inputs corrected for local cloud cover, collector tilt

angle and shading can be calculated for conventional building construction heat

gain or for solar modified construction using roof ponds and window collectors.

Routines to calculate the transmission, reflection and absorption for direct

and diffuse solar radiation are used to calculate the solar heat gain through

fenestrations. The thermal response of the various building structural

components and furnishings are calculated using conduction, radiation and convection

heat transfer routines to provide the necessary Inputs to the room temperature

calculation (RMTMP) [4]. This subroutine compares the prescribed room temperature

with the calculated temperature, and variances beyond the prescribed limits result

in calculation of the heating or cooling loads to satisfy the temperature.

28

1

6. SYSTEMS PERFORMANCE EVALUATION SUMMARY (ACTIVE-SYSTEMS)

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.

6.1 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".

6.1.1 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 = ^ % ^^out - V-^^ (^•1>

where m is the fluid mass flow rate in LB/HR ,

c is the fluid specific heat at constant pressure in BTU/LB "F,

P

30

^out ~ ^in fluid temperatui^e

in °F and

the subsystem or component

T^, are the initial and final :e integration periodIn gsneral, both T^^^ and T^^ are functions zf rljne , u is a function of both

tiae and temperature and is a function of i^HEE>=ratiiTe : therefore, evaluation

of S33iiation (6.1) usually involves a numeric?" ^tegration procedure in which

the zs^al time interval is broken down into =-:± ^rer^raJs that are sufficiently

gF-g"

' so that during the subinterval each var~ -"-la in the integrand can be

coti^^-^red constant.

Ide^ continuous data measurement is desirei.. however, in the actual data

acc-.:::u^::-tion system the sensors are scanned a.z --er-iodic intervals and the

ins r-scrr-aneous measured values are used to eva-l::a.r£ equation (6.1), Changes

in variables between data scans are not derentinec and errors are introduced

intc "r= calculated results. Section 7 descrli'^^ these errors due to data

saTTf '

' and presents the results of a study rf sanpling errors based on

data, —-on one of the solar demonstration hous« £t the Colorado State

Uni-rsrrity f^] .

In 23 raJ., for all thermal energy quantities t±r= smallest integration period

desii^rsc: vlll be one hour, with additional int=£r-5.tion periods to provide

cumu-l-srrive daily, monthly, and seasonal or a:".^-^ data.

,1.2 Perf — ice Indices

In '—

^ivaltiation of a performance index whicr: fspends on the ratio of

two — ma

"

! quantities such as the energy con—s^rsion efficiency, the index N

is 2^— bv

S =

Q2 dT

(6.2)

In c.-:^ isquation and Q2 are hourly thermal -r-r^-gy quantities calculated by

Equa : '5.1). For meaningful results the ir.z=:gnratio:i times must be sufficiently

long. — oiily to preclude division by zero, zo assure that a true average

value —- obtained. Thus, the performance index calculations involving the ratio

of tha2=^al energy quantities may require eval-^rlon on a daily, monthly, or annua— jsa^is using hourly values of the thennaJL energy quantity.

31

Other performance indices such as average temperature are determined by

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

1 ^2 N-^f-/ dT (6.3)

where is the actual temperature measurement,

and T2 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.

.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 load 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

32

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.

6-3.1 Total Solar Energy Incident (QOOl »Q002*)

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 and 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

component 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:

6.3 Climatic Primary Performance Factors

QOOl = / lOOl dx (6.4)

T

2 Q002* = / (1001- 1002) dT (6.5)

Where lOOl and 1002 are the instantaneous values of incident total

solar radiation and diffuse solar radiation respectively, and t are the integrating time intervals.

1

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.

33

6.3.2 Average Ambient Dry Bulb Temperature (N113)

Average ambient 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:

1 N113 = —=— ^ TOOl dT (6.6) TI

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

integration period ^2~^1"

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

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

The primary performance factors are based on the ECSS shown in Figure 3.

6.4.1 Solar Energy Collected (QlOO)

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

evaluating Equation 6.1 using the appropriate sensors in the ECSS as follows:

1 "^P QlOO = -i- / WlOO-ClOO- TDIOO dx (6-7)

A

^1

Where A is the total collector area defined by the outside dimensions

c 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 for temperature,

concentration, etc.

6.4.2 Total Solar Energy Utilized (Q30Q, Q400, Q500, Q203)

For Che 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.

Proposed Solar collector test procedure [6] rates flat plate collector performance

on transparant frontal area instead of total area, therefore, thermal comparison of

result will require adjustment by appropriate area ratio.

3A

Equation (6.1) is evaluated using the appropriate measurements 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 3)

6.4.2.1 Solar Used for Hot Water

Q300 = / W300-C301-TD301 di (6.8)

6.4.2.2 Solar Used for Space Heating

^2 Q400 = / W400-C400-TD400 dr (6.9)

6.4.2.3 Solar Used for Space Cooling

^2 Q500 = / W400-C400-TD400 dt (6.10)

^1

6.4.2.4 Total Solar Energy Utilized (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 (6.11)

6.4.2.5 Total Solar Energy Utilized (Air Heat Transfer Medium)

For the ECSS using air as the heat transfer medium (SYSTEM B in Figure 3).

the total solar energy utilized is given by:

^2

Q203 = / W400-C401-TD401 dx (6.12)

^1

6.4.3 ECSS Conversion Efficiency (Nlll)

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

incident on the collector array is termed the solar subsystem conversion

35

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:

Nlll = / Q203 dr/A / ^ QOOl di (6-13)

^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

.

6.5 Hot Water Subsystem (HWS) Primary Performance Factors

6.5.1 Hot Water Load (Q302)

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

to delivery temperature is given by:

Q302 = / W301'C301- (TD301 + TD302)dT (6.14)

^1

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

data summary.

6.5.2 Solar Fraction of the HW Load (N300)

The solar fraction of the HW load is calculated by:

= tT ' TD30^ ^ TD302 ' ^^^^^^ ^''^'^

^1 where TD301 and TD302 are the temperature differences across the HW

storage tank and auxiliary heat exchangers, respectively, when

there is a flow to the HW load (W301?^0) . This parameter should be evaluated on a daily, monthly and annual basis.

6.5.3 HW Electrical Energy Saved (Q311)

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

Q309 = Q303 + Q305 + Q308 (6.16)

where Q303 is the energy 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 HWS fraction of the ECSS operating energy.

36

The calculated electrical energy required to operate a conventional hot water

subsystem is given by:

Q310 = Q302/NHWE (6.17)

where Q302 is the hot water load previously described,

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

electricity as an energy 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 energy required to operate the solar energy system as follows;

Q311 = Q310-Q309 (6,18)

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,

6,5,/, HW Fossil Energy Saved (Q313)

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

Q306 = HVF / F300 dt (6.19)

where HVF is the fuel heating value in BTU/LB ^nd F300 is the measured

mass flow rate of fuel to the auxiliary in LB/HR.

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

Q312 = Q302/NHWF (6.20)

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 is the difference between the calculated fossil

energy required to operate a conventional HW system and the measured fossil

energy required to operate a solar energy system as follows:

Q313 = Q312-Q306 (6.21)

37

6.6 Space Heating Subsystem (SHS) Primary Performance Factors

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

ti.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:

Q402 = / W600-C600-TD600 dt (6.22)

^ ^1 where W600 is the building air flow rate,

C600 is the specific heat,

and 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 determined for rhc hourly, monthly

and seasonal data summary.

6.6.2 So lar Fraction of Space Heating Load (NAOO)

The solar fraction of the space heating load for the SHS comprised of a heat

pump and electric auxiliary (SYSTEM A) is given by:

T T N400 = / (QA06 + Q407)dT// Q402 dx (6.23)

^1 ^1

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 space heating load for the SHS comprised of the fossil

fuel auxiliary (SYSTEM B) is given by:

T T N400 = / Q400 dT// Q402 dt (6.24)

^1

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

.

6.6.3 Space Heating Electrical Energy Saved (Q415)

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

38

5 is given by:

Q413 = Q403 + Q404 + Q409 + Q412 (6- 25)

Where i^40j is cne energy consumed by the heating loop circulation

pump, building 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 (6.26)

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 reauired

for defrosting and auxiliary heating and the reduction in performance due to cyclic operation at off design conditions. Reference [ 7] 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 the solar energy system as follows:

Q4I5 - Q414-Q413 (6.27)

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:

^2 Q410 = HVF / F400 dT (6.28)

"l

where HVF is the heating value of the fuel,

and F400 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 (6.29)

39

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 = QA16-Q410 (6.30)

6.7 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.

6.7.1 S^ace Cooling Load (Q502)

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

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

Q502 = / ^ [W600-C600-TD600+W601-h„^] dt (6.31)

^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.

6.7.2 Solar Fraction of Space Cooling Load (N500)

The solar fraction of the space cooling load is given by:

T T N500 = / Q500 dT// Q506 dt (6.32)

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

.

40

6.7 3 Space Cooling Electrical Energy Saved

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

by:

Q510 = Q503 + Q509 (6.33)

where Q50 3 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 (6.34)

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 (6.35)

6.7.4 Space Cooling Fuel Energy Saved (Q514)

The fossil fuel energy used by the solar space cooling subsystem

is given by

Q508 = HVF / F500 dt (6.36)

^1

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:

41

Q513 = Q502/NCLF (6.37)

where Q502 is the measured space cooling load,

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

The fossil 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 (6.38)

6.8 Solar Energy System/Building Summary

The following primary performance factors summarize the performance of the

overall solar energy system and the building.

6.8.1 Average Building Dry Bulb Air Temperature (N407)

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:

N400 =

1 T600 dT (6.39) TI

where T600 is the measured building air dry bulb temperature.

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

data summary.

6.8.2 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.<i.2 for solar energy utilized and is calculated as follows:

6.8.2.1 Auxiliary Used for HW

Q301 = / W301-C302- TD302 di (6.40)

42

6.8.2.2 Auxiliary Used for Space Heating

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

by:

Q401 = ; W600-C602(TD600-TD601)dT (6.41a)

^1

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

by:

Q401 = / W400-C401-TD401 dt (6.41b)

^1

6.8.2.3 Auxiliary Used for Space Cooling

^2 Q501 = / ^ W400-C401- TD401 dt (6.42)

^1

6.8.2.4 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 (6.43)

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

seasonal/annual data summary.

6.6.3 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 (6.44)

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.

43

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

seasonal/annual data summary.

6.3.4 Total Energy Delivered to Building Load (Q602)

The total building energy load is the sura of the IIW load, the space heating load

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

Q602 = Q302 + Q402 +Q502 (6.45)

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

monthly, seasonal/annual data summary.

6.8.5 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 (6.46)

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, daily, monthly and

seasonal/annual data summary.

6.8.6 Total Electric Energy Saved (Q604)

The total electric energy saved is given by:

Q604 = Q311 + Q415 + Q512 (6.47)

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

space heating and space cooling, respectively.

6.3.7 Total Fossil Energy Saved (Q605)

The total fuel energy saved is given by:

Q605 = Q313 + Q417 + Q514 (6.48)

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, daily, monthly and seasonal/

annual data summary.

44

6.S.8 Solar Fraction of Building Load (N601)

The solar fraction of the building load is determined by averaging the solar

fractions of the individual subsystem loads as follows:

N601 = ^1 [N300-Q302 + N400 Q402 + N500 Q502]dT

/ ^ [Q302 + Q402 + Q502]dT

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

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

and cooling load.

6.8.9 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:

T T N602 = / ^ Q602 dr// ^ [Q306 + Q410 + Q508 + (0601 + 0305 + Q4n9)]dT (6.50)

T X 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 daily, monthly and

seasonal /annual data summary.

6.9 Secondary Performance Factors and Measurements

In addition to the primary system performance factors described in Section 6.3

to 6.8, certain secondary performance evaluation factors for the ECSS and ECDS

are of sufficient importance to warrant further discussion.

45

6.9.1 Daily Integrated Collector Efficiency (NlOO)

The ratio of the daily integrated solar energy collected by the array to the daily

integrated total solar energy incident on the array is termed the daily integrated

collector efficiency and is a measure of the ability of the solar collector to convert daily incident solar radiation into thermal energy available either

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

thermal energy load. Daily integrated collector efficiency is calculated by:

T T NlOO = / QlOO di// QOOl dT (6.51)

^1 ^1

where the numerator represents the total thermal energy collected

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

the total solar radiation incident on one square foot of collector

per day.

6.9.2 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:

where = rate of useful energy extraction from the collector

= collector area, aperature

Fj^ = Actual useful energy collect ed

useful energy collected if the entire

collector were at the inlet fluid temperature

1^ = total incident solar radiation

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

= heat transfer loss coefficient for the collector

T, = fluid temperature entering collector

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 (6.52) is

rearranged to give collector efficiency as follows:

T T N101=Fj^ [(t-)^ - ^

] (6.53)

46

A plot of equation (6.53) as a function of (Tf^^ - T^) /l^ for a range of

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

intercept equal to Fj^ (t <^)q and slope equal to FrUlIf 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 F U over the life of the demonstration, degradation of the array

due to changes in the t= 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 inlet temperature)

WlOO (array flow rate)

1001 (total incident solar radiation)

Other constraints for the procedure as obtained from reference (6 ) 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/hrf t ) . If all the above constraints

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

following performance indicles.

6.9.2.1 Instantaneous Collector Array Efficiency (NlOl)

Nioi = ^i^^Q-^^QQ-yp^QQ(6.54) A • iUUl

c

6.9.2.2 Collector Panel Efficiency Factor (N102)

N102 = (TlOO-TOOl)/ 1001 (6.55)

6. 9.2.3 Collector Panel Factors (N103, NIO4)

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

47
I

I

t-

\
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 = (T-) (6.56)

R e and

,

NlOA = F U (6.57)

K L

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, N103 and NlOA 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.

6.9.3 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:

1 ^2 N105 = ^ f (TD101)/(T101-T200)dT (6.58)

^1

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

and annual basis.

6.9.4 ITW Heat Exchanger Effectiveness (N106)

The hot water heat exchanger effectiveness is determined as follows:

1

"^2 N300 = ^ ; ^11)300) /(T200rT300)dT

^1

D^e to the requirement for double walled heat exchangers to prevent any possible

contamination 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.

48

6.9.5 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 = (Q20H- q202)dT

^ ^0

J

/ ^ Q200 dT

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-deliberate

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

to the following parameter:

1

"^2 N109 = ^

/ (T200-T201)dT (6.61)

^1

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.

6.9.6 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

'^') N307 = T^i- / (T301 + TD301 + TD302)dT (6.62)

49

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.

6.9.7 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 gallons is given

by:

^2 N308 = .12 / W301 dx (6.63)

^1

where W301 is the measured flow rate in Ibs/hr.

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

and annual data summary.

6.9,8 Energy Conversion Equipment Coefficient of Performance

Enegry 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.

6.9.8.1 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:

N404 = / Q407 dx// (Q403 + Q404)dT (6.64)

^1 ^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.

50

QA04 is the electrical energy required to operate the heat pump

compressor.

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

data summary.

6.9.8.2 Space Cooling Equipment COP (N503)

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

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

equipment such as solar assisted Rankine Cycle equipment or dessicant

dehumidification systems as appropriate.

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

Performance is calculated as:

N503 = / Q507// Q506 dx (6.65)

^1 "l

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.

51

7.0 UNCERTAINTY ANALYSIS OF SOLAR PERFORMANCE FACTORS

The uncertainty of determining the performance evaluation facto":; lot 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 Instumentation Errors

° Recommended Sampling Rates and Data Requirement Accuracies

7.1 Sensitivity Analysis Methods

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 3o 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 oi neasured units).

7.1.1 Absolute Limits

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

T = f(x,y,z) (7.1)

If the component error-s in x, y, and z are Ax, Ay and Az respectively,

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

52

f (x + Ax. y + Ay, z + Az) = f (x.y.z) + -^^^ + i^^^ +

1^^^=^ ox dy 9z

+1/2

2 2 2 2 2 2 3fAx ^^Ay\_3^Az2|^ ^^^^

3y 3z

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

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

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

the error can be expressed as:

i«l

7.1.2 Statistical Bounds

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 RCX, , X. X ), where R is the desired measurement and AX, AX

are the individual

1 z errornsources, the following equation can be used:in

AR = £ (ir

1/2

(7.5)

L i=l

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.

7.1.3 Error Analysis - Daily Integrated Collector Array Efficiency

An error analysis of the calculations of dally Integrated collector array

efficiency is presented to illustrate using both methods discussed In the

preceding paragraphs.

53

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

NlOO = /QlOOdiZ/QOOldT =

'" WIOO-CIOO-TDIOO di/Ac / lOOldr (7.6)

If the component errors are independent of time than the uncertainty in the

integrated daily efficiency is the same as the uncertainty in the instantaneous

efficiency given by performance factor NlOl as:

xTim WlOO-ClOO-TDlOO ... = A^TlOOi ^^'^^

For purposes of illustration, the following reference conditions and tolerances

in each variable are assumed:

2 2 = 32 ft +1% (assumption) (+.32 ft ), collector area

WlOO = 1 GAL/HR fc^ x 32 ft^ = 269.91 Ib/hr. +2% FS (+5.4 Ib/hr) , collector flo^

ClOO =1.0 BTU/lb °F, specific heat (NO TOLERANCE)

TDIOO = 18 + 1.7% (+ 0.3°?), temperature rise through collector

1001 = 300 BTU/hr f t^ +3% (+9 BTU/hr f t^) , incident solar radiation

The nominal array efficiency is determined from equation (7.7) by substitution

of the assumed variables at the reference point as: LB BTU

Mini - (270)HR (1.0) LB °F (18.0) °F _ NlOl - - .506

(32 )ft (300) hr ft

Equation 7.7 is differentiated with respect to each variable having a non-zero

tolerance and each partial derivative is evaluated at the reference condition

as follows

9N101 ClOl -TDIOO (1.0) (18.) ^ ^. 3W101 " A -1001 ~ (32.) (300.)

c

SNIOI WlOO -ClOO ^ (270.)(1.0) _ --^ 8TD100 " A -1001 (32.) (300.)

~

c

54

3N101 WIOO-CIOO-TDIOO (270) (1.0) (18.0)

3A

c = -0.0158

(32)^ (300.)

3N101

31001

WlOO-ClOO-TDlOO

A -(1001)^

c

(270) (1.0) (18.0)

Z

(32) (300)

0017

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

derivatives and tolerances in equation (7-4) as follows:

ANIOI = |(. 0019) (5. 4:j-t|(. 0281) (.03j4|(-0. 0158) (.32j+|(-. 0017) (9.0)

ANIOI = .0390

NlOl = .506+. 039

Thus the calculated value of instantaneous efficiency based on absolute error limits indicates an uncertainty of + 7.7 percent.

The error by statistical bounds is obtained by substitution of the partial derivatives and tolerances in equation (7.5) as follows:

The statistical or nns method indicates about a + ^-1 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

(LeT, 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.

Derivation 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

1/2

NlOl = ANIOI = .021

NlOl = .506+. 021

55

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.

7.2.1 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 sum of the individual accuracies squared

divided by the temperature difference or.

accuracy " yo^ + / M (7.8)

Thus, a 27o load temperature accuracy requirement and 20°F assumed load temperature

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

sensor and .3°F for individual sensors. Similarly, a 4% accuracy and 10"?

rise across a collector requires a temperature accuracy of .4"? differential

or .3°F for individual sensors.

Other combinations of flow and temperature sensors which fulfill instrumentation

accuracy requirements can be determined from Figures 9 and 10. These two graphs were computed from the two error equations that constrain flow and

temperature sensor errors.

7.2.2 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 Teaslble 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 numbers which governs sample accuracy

(provided correlation effects do not arise)

.

56

57

b"+

CM+bo

Q ^ Z U. < o

- O

O

>-o

<

orB

q:

CO ^ LJ CO

UJ

01

9

o LlJ

-1 ^

<

z

UJq:

UJ

ou.

AOVdnOOV dOSN3S Moid

o

o

cr

u

o

•a

0)

to

«

r-lO

Ti

0)

U

u

cd

1-1 3

O

o

uo

58

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

by some factor k decreases sampling error by 1/ fh.. 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." Errcxr in measuring "ON-OFF"

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

(ON-OFF) (7.9)

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

change of the signal during one sample interval, a:

a < — (slowly varying) (7.10)

yjui-a)

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

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

the varying to steady signal component, b:

o < -pz (rapidly varying) (7.11)

/N (1-b)

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

of approximately 1/k for "ON-OFF", l/kJ^T f or "slowly varying" and l/^Xfor

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

signals might be auxiliary input to load, storage tempexature, 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 [5]. Typical data for insolation valu&s integrated from

measurements made at different intervals are listed in la-bles 2 a and 2 b.

Assuming the 2 minute sampling rate represents the most s-ccurate value obtained,

the actual sampling error results are listed in Table 3 s=i.c scaled to different

sampling intervals and periods. There is wide variatic' in the monitoring interval

required by the different parameters. For example, the ar^sJlvsis indicates

insolation need only be monitored once every 15 minutes " iiaintain a weekly

variance below 1%, but auxiliary sampling with a non-in'ssrating sensor ORist be made

59

Table 2a CSU Sampled Data Using Different Sampling Intervals (Summer 1975)

Parameter Insolation [5]

Minutes

Date 2 J 60

6/21 1132.9 1130 0 1113 Q X117a x^ 0

>

J 1124 2 1160.

7/9 1111.

1119 0 1089 .

1100. 4 1035 5 995 .

7 /i3 1768.1776 2 1772.6 1X 7fi1 / u J . 9 X / J 7 3 1765 .

7/17 1255 .

£ x^19 71/ J . 0 1242 QJ 1227.0

7 /21 12A8.

1271 g 1254 .1241. 1^ 1153 9 1072 .

7/23 1263.4 1246 8 1253.

1204. 3 1259 7 1271.

1315.2 1811 4 1809.0 1799. 1 1792 0 1767.3 nil 1850.4 1846 6 1840.5 1827 7 1815 1 1779.6

111^ 1564.5 1 LjLd 0 1 1

iO J J 1

1 CI T A

7/31 1205.6 1207 8 1245.6 1229 3 1219 8 1233.3

S.D per day 0 8% 1.3% 2 0% 3 3% 5.3

2b Parameter Insolation (Winter 1974-75]

Date 2 5 Minutes

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.

12/25 1478.9 1476. 0 1472.7 1 iS7 1445 9 1396.

Villi 1238.6 1235. 8 1235,1 1228. q 1251 7 1270.

948.0 937. 8 933.3 916

g 896. 7 846.5

12/31 1108.1 1102. 0 1086.0 1034. 4 1045

5 976.0

1/A 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. jer day 0. 7S 1.1% 4. 3% 5. IZ 9.6;

60

TABLE 3

RANGE OF MEASURED DAILY VARIANCE WITH DATA EXTRAPOLATED

FOR WEEKLY, MONTHLY, AND YEARLY PERIODS.

SAMPLING INSOLATION

FREQUENCY (MIN) 5 10 20 30 ou Daily . 7 - .8 X11-1 . X X.J1 2.0-4.3 3.3-5.1 9_Q fi J . Z— 7 .

0

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

SAMPLING

FREQUENCY (MIN) 5 10

COLLECTOR

OUTPUT

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 10 17 1 . 0-4 .

0

5.2-7.5 7.0-8.0 7.5-9.0

^tonthly .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

SAMPLING

FREQUENCY (MIN) 5 10

AUXILIARY TO

LOAD

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

61

Using the CSU data and the suggested sampling accuracies from Section 7.2.2,

sampling rates for various sensors are determined as listed in Table 5.

Data Requirements

load flow

collector flow and

temperature

auxiliary input

insolation

Weekly Summations

(minutes)

<5

5<5

30

Monthly Summations

(minutes)

5

10

5 60

(minutes)

30

60

60

60

Based on insolation at Colorado State University, Fort Collins, Col. 1974-74.

Table 4 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% [8]. A sampling rate of 5 minutes or less is recommended for both

insolation and auxiliary energy related measurements.

7.2.3 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:

where a ando_, are uncertainties in solar-to-load flow and temperature w ID difference sensors, Og is the sampling uncertainty, Q300 and Q400 is

solar energy to hot water and heating respectively, is insolation sensor uncertainty, and a is the insolation sampling uncertainty.

62

Assuming conditions such that Q300»Q400, the instrumentation accuracy is:

°INS 4^ ^ <'tD^ + ^S^ + -I 4oi (^-13)

The sensor accuracy and sampling rate accuracy necessary to achieve a 6%

instrumentation uncertainty is determined as described in the following sections.

7.2.4 Sensor Accuracy

The two worst case RMS instrumentation error equations that determine necessary sensor accuracies for system and collector array efficiencies respectively are

°iNS = %30i ^rasoi ^001 ^S300 ^sooi ^^-^"^^

4ns = "wioo 4dioo ''lOOl ^ 4ioo °sooi ^^-^^^

where

^'wSOl " ^WlOO " sensor accuracies

*^TD301

" temperature sensor accuracy (20°? differential)

TDIOO

'^lOOl ~ sensor accuracy

Og^QQ " sampling error for solar or auxiliary to load

'^SOOl ~ sampling error for insolation

^SlOO

~ ^^P^^'^S 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: ^ 2, 2.7% 21 a„3oi2ia^3Q^ 2 ajQQ^.:ag3QQ 21^7300^ (7.16)

63

Using this term balancing strategy, sensor and sampling accuracies are selected

and -iteratively refined to reasonable values using tradeoff charts shown in

Figures 9 and 10. The results for the projected sensor accuracy and sampling

requirements are as follows

S PTI Clioc:nT*L lj ouiL/ J. J. LI g ux. y

load flow + 2% + 2%

load temp. + 2%

collector flow + 2%(liq)+ 3%(air) + 2%

collector temp. + 4%(liq)+ 3%(air)

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 5.

64

TYPE DESIGN DATA REOUIRIMENT RANGE ACCURACY MEASUREMENT FREQUENCY

1001

1002 TOOl VOOl

DOOl

T002

Total Radiation Diffuse Radiation Outdoor DB Temperature Wind Velocity

Wind Direction Outdoor Wet Bulb Temp

0-350

0-100

-20 to 120

0 to 100

0 to 360

32 to 90

+ 35; Btu/ft2-hr FS + 65; Btu/ft2-hr FS + 2''F + 3 mph

+ 20''F + 2°F

5 mln or less

5 mln

Avg/hr

Avg/hr

Avg/hr

Avg/hr

TlOO TDIOO

TlOl TDlOl

T102 WlOO

PDIOO

Collector Inlet Temp Collector Temp Dlff Storage Inlet Temp Storage Temp Dlff Collector Absorber Temp Collector Flow Rate Collector Press Dlff

40 to 220

-10 to +50

60 to 230

0 to 100

30 to 450 varies

varies

+ 0.5°F (L) + IT (A) + 0.3°F (L) + 1.2°F (A) + 0,5°F (L) + 2°F (A) + 0.3°F (L) + 2.5°F (A) + 3°? + 2% (L) + 35; (A) FS + 2% FS

5 mln

5 mln

5 mln

5 mln

Dally at noon

5 mln Dally at noon

T200

T201

PDlOl

Storage Media Ave Temp Storage Ambient Temp Storage Press Dlff (Air)

60 to 230 -20 to 120

0 to 4"H,0

+ 2''F + 3°F + 2% FShr. hr.

hr.

3 >

m U J3 9 (A

T301 T300 TD300

TD301

TD302 W300

W301

Makeup Water Temp HX Inlet Temp HX Temp Dlff Storage Temp Dlff Auxiliary Temp Diff Circulation Flow Rate Load Flow Rate

30 to 90

40 to 160

0 CO 50 0 to 75

0 to 100 varies

varies

0.5°F

0,5°F

0.3°F

0.3°F 0.3°F

2% FS

3% FS

Avg/hr.

5 mln mln

mln mln or less mln

mln

T400 TD400

TD401 W400

TD402

Load Return Temp Storage Temp Dlff Auxiliary Temp Dlff Circulation Flow Rate HTG Load Temp Diff

70 to 180

0 to 50

0 to 100 varies

0 to 100

+ 0.5°F (L) + 2°F (A) + 0.3"? (L) + 2''F (A) + O.y? (L) + 2°F (A) + 2Z (L) + 3% (A) FS + 0.3°F (L)

5 mln

5 mln

5 mln

5 mln

5 rain

T500 TD500

T501

TD501 W500

W501

Load HX Inlet Temp

Load HX Temp Dlff Cooling Tower Inlet Temp Cooling Tower Temp Dlff

Load HX Flow Rate Cooling Tower Flow Rate

40 to 60

0 to 75 40 to 120

0 to 20 varies

varies

+ 0.5''F + 0.3°F

+ 0.5°F

+ 0.3°F + 2? FS + 21 FS

mln

mln or less mln min or less min or less

4J <

a

O '•C

EPIOI EP301

EP401

EP402

EP403 EP501 EP300

EP400

F300

F400

F500

Collector Clrc Pump Power HW Clrc Pump Power HTG Loop Clrc Pump Power Bldg Fan Power Heat Pump Compress Power Absorp Chiller Oper Power

HW Elec Aux Power HTG Elec Aux Power HW Aux Fuel Flow HTG Aux Fuel Flow Cooling Aux Fuel Flow

AKW varies + 5% FS 4KW varies + 5Z FS 4KW varies + 5Z FS AKW varies + 5Z FS AKW varies + 2% FS iKW varies + 2% FS iKW varies + 2Z FS 4KW varies + 2% FS varies + 2% FS varies + 2% FS varies + 2% FS

5 min

5 mln

5 mln

5 mln

5 mln or less

5 mln or less

5 mln or less

5 mln or less

5 min or less

5 min or less

5 min or less

5 min

5 min

5 mln

5 min

5 mln

5 min

5 min

5 mln

T600 TD600

T6Q1

T602 W600

W601 UF600

TD601

Bldg Return Air DB Temp Supply/return Air Temp Dlff

Bldg Return air WB Temp Bldg Supply Air WB Temp Building Air Flow Rate Condensate Flow Heat Flow Meter HT Pump Cond i Load HX Temp Dlff

50 to 90

0 to 80

20 to 80

20 to 80 varies

varies

0.25 to 30°F AT

0 to 80

2°F

2'Y 2°F

2°F

2X FS 5%

5%2»F

Table 5 INSTRUMENTATION RANGE, ACCURACY AND MEASUREMENT FREQUENCY

65

8.0 APPLICATION OF PERFORMANCE FACTORS

The performance factor data generated during the Demonstration 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 program national 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

8.1 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 11 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

G. Space Cooling and Hot Water

8.2 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 12. Comparison of the effectiveness of similar solar system types

66



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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.

The design of solar systems is currently based on analytical models and calculated

performances. The demonstration 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 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 11 and 12 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.

The greatest 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 13, 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

8.3 Analytical Predictions

8.4 Solar Collector Array

2 Covers

a. Number

b. Material Type

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B. Concentrator

1. Cylindrical

2 . Tubular

3. Trapezoidal

4. Other

8.5 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 6 for the three key heat transfer areas: (a) solar

absorptance-transmittance product ("t)^; (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 14. Tabular values of «t and U, for

similar materials as a function of climatic exposure will reveal the differences

related to environmental conditions.

8.6 Climatic Data

Climatic data measured during the program will be reported for hourly, monthly and

annual data as follows

A. Total solar radiation at aollector 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

These data will be tabulated and plots indicating variations over the continental

United States will be available.

71

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Figure 14 Illustrations of Detecting Collector Degradation From

Thermal Performance Measurements.

73

Recommendations

Table ^ 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 on a timely basis.

74;



9,0 Conclusions

The quantity and type of measurements described reflect a level of instrumentation

that will provide a capability for full evaluation 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, an assessment of the significance of the performance factors should be made for each proposed demonstration unit. The four

factors considered essential for the performance of solar energy systems are:

" conventional energy saved by the solar energy system

** solar fraction of total load

" solar energy system conversion efficiency

" solar energy collected per unit collector 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 percent

for active systems and fifteen percent for passive systems 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 accuracy of about + 5 percent using commercially available sensors.

76

10.0 REFERENCES

1. National Plan for Solar Heating and Cooling (Residential and Commercial Applications)

ERDA-23A, October 1975.

2. 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

3. "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.

4. T. Kusuda, "NBSLD, Computer Program for Heating and Cooling Loads in Buildings", NBS

Report NBSIR 74-574, November 1974.

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 Systems", NBS Purchase Order No. 608692, March 1976,

6. ASHRAE Standard 93-P "Method of Testing for Rating Solar Collectors Based on Thermal

Performance", August 1976 (Available ibid ASHRAE).

7. G. E. Kelly, "Potential of Air-to-Air Heat Pumps for Energy Conservation in

Residential Buildings", NATO Advanced Study Institutes, Series E: Applied Science

No. 15, Noordoff-leyden, 1976 (Available from National Bureau of Standards, Washington,

D C 20234)

8. Personal Communication, Dr. William H. Klein, Radiation Biology Laboratory,

Smithsonian Institution, Rockville, Maryland, January 1976.

9. 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.

10. J. E. Hill, T. E. Richtmyer and J. Jenkins, "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.

11. J. W. Ramsey, J. T. Borzoni and T. H. Holland, "Development of Flat-Plate Solar

Collectors for the Heating and Cooling of Buildings, "NASA CR-134804, June 1975.

77

NBS.n4A (REV 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. FUHLiCATION OR REPORT NO. NBSIR 76-1137

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLF. AND SUBTITI.F. Thermal Data Requirements and Performance Evaluation

Procedures for the National Solar Heating and Cooling

Demonstration Program

5, Publication Date

6. Performing Organization Code

7. AUTHOR(S)

E. Streed, M. McCabe, D. Waksman, J. Hebrank, T. Richtmyer

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4606500 and 4606505

11. Contract/Grant No. ERDA - 49(1) - 3800

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Energy Research & Development Admin. Dept. of Housing and

Division of Solar Energy Urban Development

Washington, DC 20545 Division of Energy

Wa.^hingtnn, DC 70^10

13. Type of Report & Period Covered Interim

14, Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTR.ACT (A 200-word or less tactual summary of most si^ilicant information. If document includes a significant

bibliography or literature survey, mention it here.) This report presents the results of a study to determine the data requirements and

performance evaluation factors to be used in the National Solar Heating and Cooling

Demonstration Program. Solar energy systems used for heating hot water, space heating,

and space cooling have been considered and specific measurements and analytical procedures have been recommended to determine the thermal effectiveness for daily,

monthly, seasonal, or annual operating periods. The sensor accuracy and sampling rate

effects on measurement uncertainty for several performance factors is presented.

Application of the individual performance factors for the comparison of subsystem and

system thermal performance as a function of building type and climatic region is

discussed

17. KEY WORDS Csix to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name: separated v semicolons

)

Data requirements; measurement uncertainty; solar energy systems evaluation; thermal

performance

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