COMPARISON OF MEASURED TO PREDICTED PERFORMANCE OF STORAGE WATER HEATER SYSTEMS. George Bernard Williamson. Thesis submitted to the Faculty of the

COMPARISON OF MEASURED TO PREDICTED PERFORMANCE OF OWNER-BUILT PASSIVE SOLAR INTEGRAL COLLECTOR

STORAGE WATER HEATER SYSTEMS by

George Bernard Williamson

Thesis submitted to the Faculty of the

Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of

Master of Architecture in

Architecture APPROVED:

Robert P. Schubert, Chairman

Benjamin H. Evans

May 15, 1986 Blacksburg, Virginia

Francis T. Ventre

COMPARISON OF MEASURED TO PREDICTED PERFORMANCE OF.

OWNER-BUILT PASSIVE SOLAR INTEGRAL COLLECTOR STORAGE WATER HEATER SYSTEMS

by

George Bernard Williamson Robert P. Schubert, Chairman

Architecture (ABSTRACT)

This study presents a comparison of field measurements of energy delivered by five integral collector storage (ICS) passive solar water heater sys- tems installed at various geographic locations in Virginia to predicted values calculated using Annual Performance Methodology (APM). APM is a prediction method developed by Alan Zollner that offers quick and easy comparisons of design option for ICS systems.

Several different methods exist today that are meant to predict the per- formance of this type of system and that might be used as a design tool to help a designer make appropriate design decisions. Some of these methods are quit complicated and do not lend themselves to quick and easy comparisons of various design options.

This study measured the amount of energy delivered by five !CS systems over a six month period. The amount of water drawn of of these systems daily was also recorded. This data was compared to predicted values cal-

culated using APM to determine if APM could predict the performance of these systems within plus or minus 15 percent of the measured values.

This study demonstrates that APM was able to predict long term performance of ICS systems within plus or minus 15 percent eighty percent of the time.

Short term performance however demonstrated variation that in some cases were quite large and could not be considered reliable predictions.

ACKNOWLEDGEMENTS

The author would like to extend his sincere appreciation to Robert P.

Schubert whose guidance and encouragement in all aspects of this study was indispensable.

The author wishes also to thank Benjamin H. Evans and Francis T. Ventre for their energy in directing these efforts towards a more complete final product and for serving on my committee.

The author also extends his appreciation to Steven Walz of the Virginia Division of Energy for his efforts in coordinating this project and to Kathryn Pearsall and Dianne Killpack of the Virginia Division of Energy for bring this project to life. This study would not have been possible without their hard work and the financial support of the Virginia Division of Energy.

I would like also to thank the entire staff of the Environmental Systems Laboratory at Virginia Polytechnic Institute & State University for their help at various times and a very special thank you to the homeowners for their time and energy in completing the data sheets over the testing pe- riod. Without their cooperation none of this work could have been done.

Finally the author would like acknowledge the financial and emotional support of his wife Patricia Pedigo Williamson and his son Luke Amar

Acknowledgements iv

Williamson who bring meaning and love to my life and without whom I would have never been able to complete this part of my formal education.

TABLE OF CONTENTS

INTRODUCTION Objective Background

Historical Overview 1891 -1985

METHODOLOGY

Instrument Selection Data Logger

Pyranometer

Signal Conditioning Instrument Calibration Data Collection

RESULTS

Measured vs Predicted Results

DISCUSSION

CONCLUSIONS AND RECOMMENDATIO~S

APPENDIX A. BTU METER INFORMATION

APPENDIX B. DATA ACQUISITION SYSTEMS SPECIFICATION.

Table of Contents

1 2

3 10

21 22 24 26 28 29 29

36 36

48

52

54

57

vi

APPENDIX C. PYRANOMETER SPECIFICATIONS 61 APPENDIX D. BTU METER INSTALLATION GUIDELINES 66

APPENDIX E. TABLES ⁷⁵

APPENDIX F. MODIFIED ZOLLNER PROGRAM LISTING 101

APPENDIX G. HOUSEHOLD PROFILE ¹⁰⁷

APPENDIX H. SIMPLE RATE OF RETURN AND PAYBACK PERIOD. 112

APPENDIX I. COVARIANT ANALYSIS 116

BIBLIOGRAPHY 120

VITA 122

LIST OF ILLUSTRATIONS

Figure 1. Virginia Passive Solar Water Heater 5 Figure 2. Net Cost of Materials. (New Shelter Study) 7 Figure 3. Energy Production (New Shelter Study) 7 Figure 4. Cost Per Square Foot of Collector. (New Shelter Study) 8 Figure 5. Cost Per BTU Delivered. (New Shelter Study~ 8 Figure 6. Rate of Return on Investment. (New Shelter Study) 9 Figure 7. Construction and Installation Time. (New Shelter Study) 9

Figure 8. Zomeworks Breadbox Water Heater 13

Figure 9. Inverted and Snail-type pesigns. 14

Figure 10. TRS-100 with Elexor PL-100 DAS 25

Figure 11. Outdoor Ambient Air Sensor Radiation Shield. 27 Figure 12. Hot and Cold Temperature Sensor Wells. 27

Figure 13. Sensor Location 28

Figure 14. Pyranometer Location. 29

Figure 15. Energy Delivered Comparison - Based on Average 39 Figure 16. Energy Delivered Comparison - Based on Average 39 Figure 17. Energy Delivered Comparison - Based on Average 40 Figure 18. Energy Delivered Comparison - Based on Average 40 Figure 19. Energy Delivered Comparison - Based on Average 41 Figure 20. Measured to Predicted Values Summary for Test Period. 41 Figure 21-. Energy Delivered Comparison - Based on 44 Figure 22. Energy Delivered Comparison - Based on 44 Figure 23. Energy Delivered Comparison - Based on 45 Figure 24. Energy Delivered Comparison - Based on 45

List of Illustrations viii

Figure 25. Energy Delivered Comparison - Based on 46 Figure 26. Measured to Predicted Values Summary for Test Period. 46

Figure 27. Solar Fraction vs Daily Draw. 51

Figure 28. Rate of Return on Investment. 114

Figure 29. Payback Period. 115

LIST OF TABLES

Table 1. Measured Performance Data for Unit ffl Danville, Va. 75 Table 2. Measured Performance Date for Unit 112 Danville, Va.

. ^.

Table 3. Measured Performance Data for Unit ff3 Culpeper, ^{Va. 77} Table 4. Measured Performance Data for Unit ff4 Culpeper, Va.

. .

Table 5. Measured Performance Data for Unit If 5 Shipman, Va.

. .

Table 6. Weather Data for Roanoke, Va.

. . . . ^. . . . . ^.

Table 7. Weather Data for Greensboro, North Carolina

. .

Table 8. Measured and Predicted Energy Delivered for Unit ffl

Collector Parameters Unit /fl

. . . . . . . .

Table 9. Measured and Predicted Energy Delivered

Collector Parameters Unit ff2

. . . . . . . ^{. . .}

Table 10. Measured and Predicted Energy Delivered

Collector Parameters Unit fflO

. . . . . . ^{. . .} . ^{. .}

Table 11. Measured and Predicted Energy Delivered

Collector Parameters Unit ff4

. . . . . ^{. . . . . . .}

Table 12. Measured and Predicted Energy Delivered

Collector Parameters Unit ff5

. . . . ^. . . ^. . . ^{. .}

Table 13. Measured and Predicted Energy Delivered

Collector Parameters Unit /fl

. . ^{. . . . . . . .}

Table 140 Measured and Predicted Energy Delivered

Collector Parameters Unit ff2

. . . . . . . . . ^. . ^.

Table 15. Measured and Predicted Energy Delivered

Collector Parameters Unit ff3

. . . . . . . . . ^{. . .}

List of Tables ^X

Table 16. Measured and Predicted Energy Delivered

Collector Parameters Unit #4

. ^{. . . . . . . . .}

Table 17. Measured and Predicted Energy Delivered

Collector Parameters Unit #5

. . . . ^. . . . . . ^{. .}

Table 18. Predicted Energy Delivered for Varied Loss Coefficient

Collector Parameters

. . ^{. . . . . . . . . .}

Table 19. Predicted Energy Delivered for Varied Loss Coefficient

Collector Parameters

. . ^{. . . . . . .} . ^. .

Table 20. Predicted Energy Delivered for Varied Loss Coefficient

Collector Parameters

. . . ^. . . .

. . . ^.

Table 21. Predicted Energy Delivered for Varied Loss Coefficient Collector Parameters

. . . . . . . . ^{. . . .}

Table 22. Predicted Energy Delivered for Varied Loss Coefficient

Collector Parameters

. . . ^{. . . . .} . ^{. . .}

Table 23. Predicted Energy Delivered for Varied Loss Coefficient

Collector Parameters

. . . . . . . . .

Table 24. Predicted Energy Delivered for Varied Tank Volume

Collector Parameters

. . . . . . . . . .

Table 25. Predicted Energy Delivered for Varied Tank Volume

Collector Parameters

. ^{. . .} . ^{. . . . . . .}

INTRODUCTION

Since the OPEC oil embargoes of the early seventies the United States has sought ways to conserve energy and lessen its dependence on oil imports.

Water heating and space conditioning account for more than one third of the nations total energy requirements. Water heating alone accounts for fifteen percent of residential energy consumption in this country.¹ Solar energy has come to the attention of the public as a means of reducing its dependence on oil imports and domestic fossil fuels. While it is unre- alistic to think that solar energy can solve all of this countries energy problems, it is irresponsible to ignore the contribution that it has made in reducing ~nergy consumption in the United States in the last ten years.

One of the Federal Government's long term goal~, under the Department of Energy's Active Heating and Cooling program (AHAC) is to provide infor- mation on reliable systems that can deliver energy at minimal cost. Solar energy is part of this effort and solar water heating in particular has received a great deal of attention. Most of this attention has focused on active solar water heating systems but this study is concerned only with batch type passive systems. A batch type heater is simply a water tank, usually black which is enclosed in an insulated shell covered on one side with a glazing material, the collector is connected in series with the domestic hot water heater. During the day the south facing col-

Solar Energy Applications Laboratory, Colorado State University.Solar Heating and Cooling of Residential Buildings:Design of Systems, Pre- pared for the U.S. Department of Commerce, 1980.

Introduction 1

lector heats water in the tank this water flows into the domestic hot water heater reducing the amount of energy required by the domestic water heater to heat water.

Assuming that twenty million homes were outfitted with passive solar batch water heaters and the average savings in energy delivered for each home was twenty dollars for a operational period of June - October than there would be a total savings of four hundred million dollars per year. While the total savings to the individual might not seem significant the cumu- lative effect is substantial. Four hundred million dollars is free for consumers to put back into the economy. That figure would represent the purchase of thirty three thousand new cars at an average price of twelve thousand dollars each. If this m011ey were to be placed in a savings ac- count at an interest rate of nine percent the total interest earned for one year would be thirty six million dollars. These figures demonstrate the potential impact of energy conservation.

OBJECTIVE

The objective of this study is to compare field measurements of energy delivered by five noncommercial (i.e., home-built) ICS systems to values predicted using Alan Zollner' s Annual Performance ~fethodology to deter- mine if long-term and short-term performance of these five systems could be predicted within plus or minus fifteen percent of the measured values.

Fifteen percent was chosen as the target margin for the following reasons.

• To account for inherent error in measured values.

• To account for the use of averaged weather data.

• To account for variation between the installations.

BACKGROUND

The present study was undertaken at the request of the Commonwealth of Virginia's State Energy Office. The State Energy Office intention was to help educate vocational school students and their instructor's about passive solar batch water heaters as well as to monitor the performance of passive solar batch water heaters to determine the amount of dollar savings contributed by the installation of these units. Since part of the State Energy Office's purpose is to develop energy conservation programs for the State this study is intended to help evaluate the effectiveness of such installations and to determine the cost of energy delivered by these systems.

The passive solar batch water heaters (or integral collectors storage (ICS) systems as they are sometimes called) were chosen for this partic- ular project because:

• They could be built by experienced do-it-yourselfers, or profes- sionals (i.e. homeowners or builders).

Introduction 3

• Their relative low cost of approximately $600.00 dollars before fed- eral and state tax credits which would reduce cost to approximately

$200. 00. (The federal and state tax credits were in effect at the onset of this particular study and are currently pending an extension in the U.S. Congress.

• These systems require no parasitic power to operate them (i.e. no pumps or other external power sources).

The State Energy Office felt that these systems along with other energy conserving steps such as, reducing domestic hot water tank ~emperatures and installing low flow nozzles on showers and faucets, could help state residents reducd the cost of hot water heating by as much as 50 percent.

These system were also considered to be within the economic reach of more people than more expensive and complex active solar systems. ²

Seven vocational classes from schools around the state built fifteen passive solar batch water heaters based on a slight modification of a design that was originally proposed by Total Environmental Action Foun- dation in the mid-seventies. The materials cost for the design was cal- culated to be approximately 570 dollars based on average costs of materials in 1985. The vocational school classes installed the system in private residences in their localities (see Figure 1).

2 Dwyer, Matthew F., The Virginia Passive Solar Water Heater Owner's Manual,Prepared for the Commonwealth of Virginia State Energy Office and the United States Department of Energy, November 1984.

Figure 1. Virginia Passive Solar Water Heater

•

Rodale's New Shelter magazine performed tests on five home-built passive solar water heater designs: a batch-type; drain-back; drain-down;

thermo-siphon and phase change water heater.³ New Shelter looked at net systems cost, cost per BTU based on BTUs delivered by each system, cost per square foot, return on investment, and the amount of time needed to build each system. To compare the simplest and lowest cost energy con- servation methods pipe insulation, water heater insulation, flow restrictors and a water heater timer were applied to a house with no solar components.

Langa, Frederic S.,"And The Winner Is," New Shelter Magazine, 1981.

Introduction 5

Figure 2 reveals the net cost of materials of each of the systems. This category shows that conservation techniques are the least expensive fol- lowed by the batch water heater.

Figure 3 shows the energy production of each system or in the case of conservation the energy saved. Again energy conservation is the most ef- fective followed by the phase change water heater.

Figure 4 documents the cost of each system per square foot of collector.

In this category the thermo-siphon system leads the group.

Figure 5 illustrates the cost per BTU of delivered energy. Again con- servation rises to the top followed by the batch heater.

Figure 6 demonstrates the rate of return on investment for each system.

Conservation was the overwhelming winner in this category followed by the batch heater.

Figure 7 indicates the amount of time required to build and install each of the systems. It is not surprising that conservation heads the list

followed by the phase change collector.

$2,500

$2.098

$2.000

$1.500

S904

S500

Phase Conser - Change valion

Figure 2. Net Cost of ~1aterials. (New Shelter Study)

Figure 3.

Introduction

(Average Total Btu/Day)

Batch

Heater Thermo-

siphon Drain

Down Drain

Back Phase Change

Note n Al 'h'1f1P"'1 ,_Sll!l1 '" 900 0..,N•day ,:t,'""'· w,,,., ^t 170 AltJ/ ftl: C,,lV ,1ve,1qe, tns,)l,llM"'lft

34,246

Conser- vation

21 8,atch P'l(>llfff aM ff\efl'lffl"•C"'"O" OU!l'IIJII '"D'~~, ,. .,,,, •. ,.,ontft oc,.a,a1,ng SC~tl! .,,,., a ,,..,.,.mo,,tfl .,.,,., ^ShutdOwn.

1n •"'"""' c11"'a1e1 ..,, IOf' ,,11-.ms .n..,,,.,..-o ⁱⁿ t,~1P.orrx,f sun,t.1.acn. ~tonnancn _.. be grett,,...

Jl Thto ...C:11,Caf ~OY I.OU,,l!'G 10 OO@'fll!' the aclav• syslttfn1 l'IH deOucled ltom ,~ output ,01.,.

Energy Production (New Shelter Study)

I

I I I I I I I I I I I I I I I I I I I I

7

$30

$25

$2

"':'"' ·' t."" ..

:,~

:: cc:

i; :z:. ^;:

:,~·

I l~ Hi

;_;;

'!!?

. ':>.

- ...

_,- '

i

...

LVI "' ce ^I

"

.... ' ^I

f

t

Batch Thermo- Drain Drain Phase No••· Ta• e,.01

Heater siphon Down Back Change

·-.a-

Figure 4. Cost Per Square Foot of Collector. (New Shelter Study)

1Sr~n-uo 1nv-.11m-,n1 ,.,-.o-c, To P•oauct

o, Sa"'• Qr,'!' Siu ? .. Q.1w1 8¢

7¢

6¢

5¢

4¢

2¢

1¢

iC

ea\e\1Q'rlo1' 00-,.1' ?,'3c¥-~3('.'i!, ,.3\101'

\C°rl ,(\'\0 0131('.

o~

?,3 ~'(\e ?'!'3

co

Figure 5. Cost Per BTU Delivered. (New Shelter Study)

. I

I I

I I

I I

I I

I I

I I

I I

I I I I I

I I I I I I I I

Figure 6.

I

Rate of Return on Investment. (New Shelter Study)

10

"'

0 ~5

Batch Thermo- Drain

·Heater siphon Down Dram Back

(8-Hour Days)

Phase Conser- Change vat ion

Construction and Installation Time. (New Shelter Study)

The New Shelter study suggests that the passive solar batch water heater combined with energy conservation is an economical method of saving both energy and money. The batch heater was non operational during months of freezing weather and was not recommend in climates where average monthly heating degree-days greater than 1000 occur more than four months of the year. In the United States this is more the exception than the rule.

Introduction 9

The New Shelter study concluded that the batch heater was best choice because:

• It is simple to build.

• It is inexpensive to build.

• It has a high rate of return on investment.

• It is architecturally flexible.

The drain-down and thermosiphon heaters were also considered to be rea- sonable choices while they recommended the active drain-back system for cold climates where batch heaters would be non operational for more than four months. The phase change heater was not recommended at all because of the high cost of construction even though it had the greatest water heating capacity and because it uses Freon as the working fluid and its potential to damage the environment.

A simple rate of return and a simple payback period for the !CS systems of the present study have been calculated and the results may be found in Appendix I .

HISTORICAL OVERVIEW 1891 -1985

Passive solar batch water heaters or integral collector storage systems have been in use in this country for many years.⁵ The first patent to be issued in the United States for such a system was to a Mr. Clarence M.

Kemp in 1891. His basic system consisted of four eight gallon galvanized

steel tanks painted fla-t black and enclosed in a five sided wooden box that was glazed with a single layer of glass. These units were either mounted on the roof or along the south side of the building and plumbed in line with the cold water line. This system was sold in California as an alternative to wood and gas stove water heaters that were impractical for summer time use and in the case of gas was expensive.

While the performance of these systems can't be verified, sales literature stated "During the early spring and late fall months, while the temper- ature during the day has been near the freezing point, the water heater has been over 100 degrees, the efficiency shown by the heater is from 60 to 100 degrees greater than the temperature for the day. The water at times almost boils." By the year 1900 more than 1600 of the so called Climax water heaters had been sold.^{4 5 6}

There were eight Climax systems available ranging in capacity from 32 to 700 gallons. The least expensive system cost only twenty five dollars and in those days would pay for itself in just three years. The idea of

4

5

&

Reif, Daniel K. ,Passive Solar Water Heaters: How to Design and Build a Batch System,Brick House Publishing Company, Andover, Massachusetts. 1983.

Butti, K. and J. Perlin, A Golden Thread: 2,500 Years of Solar Ar- chitecture and Technology, Palo Alto, California.: Cheshire Books, 1980.

Butti, K. and J. Perlin, Solar Water Heaters in California, 1891-1930, Sausalito, CA:, Co-Evolution Quarterly, No. 15., Fall 1977.

Introduction 11

passive solar water heaters was gaining popularity particularly in warm sunny climates like Florida and California.

Frank Walker made modifications to the Climax design and in 1898 applied for a patent. Walker called his system the "Walker Combined Solar and Artificial Heat Water Heater" because it could be connected to a gas or wood stove to provide backup hot water on cloudy days or during cold weather. His system was meant to be installed in the roof, with the bulk of the system inside the structure nocturnal and convective loses are reduced which meant warmer early morning water temperatures.^{4 5 6}

In 1905 Charles Haskel owner of the Solar Heater Company, offered the Improved Climax solar water heater. This new design used a thin rectan- gular tank rather than a cylindrical tank. This change provided for a greater collection. surface to volume ratio, intended to increase the charge time and improve cloudy day performance.^{4 5 6}

The 1930s saw abundant new supplies of natural gas and oil at lower prices. The low cost and availability of these fuels caused the decline of interest in solar water heaters.

ICS systems realized a renewed interest in the mid-1970s during the so called energy crisis. In 1978 Steve Baer of Zomeworks introduced the Zomeworks Breadbox system, so named because of its resemblance to the common kitchen breadbox. The Zomeworks Breadbox system consisted of a horizontal tank enclosed in a four sided insulated box that was double

glazed on the top and south face. The systems insulated coyers may be manually closed in the evening to reduce heat loss at night and opened in the morning. The covers inner surfaces are treated to reflect solar radiation onto the black tank when they were open (see Figure 8).⁷⁸

HOT COLD

Figure 8. Zomeworks Breadbox Water Heater

Stickney and Aaboe's

article describes several inverted ICS systems arid three snail-type de- signs.9 The inverted configuration, in which the glazing faces downward

7

8

9

Baer, S., Breadbox Water Heater Plans, Zomeworks, Albuquerque, N.M., 1978.

Lewandowski, Allen, Cecile M. Leboeuf and Charles F. Kutscher, A Cost and Performance Comparison of Drainback and Integral Collector Stor- age Systems for Residential Domestic Hot Water,Solar Energy Research Institute, SERI/RR-253-2594, Golden, Colorado. November 1985.

Stickney, B., and E.H. Aaboe, Comparative Performance Indices for Solar Batch Water Heaters, Proceeding of the Sixth National Passive

Introduction 13

is aimed at reducing radiation losses to the night time sky. Inverted systems are limited by their size and form for residential application

(see Figure 9).

Figure 9. Inverted and Snail-type Designs.

Burton and Zweig carried out side-by-side performance tests on two iden- tical inclined-tank !CS system in Occidental, California. They used dif- ferent glazings, tank surface treatments and interior collector surfaces and reported that a selective surface treatment on the tank did more to enhance efficiency than any other single option.¹⁰

10

Solar Conference, American Section of the International Solar Energy Society, Portland, Oregon, September 8-12, 1981.

Burton, J.W., and P.R. Zweig, Side-by-Side Comparison of Integral Passive Solar Water Heaters, Proceedings of the 6th National Passive Solar Energy Conference, Newark, DE: American Section of the Inter- national Solar Energy Society. Sept. 8-12, Portland, OR., 1981.

Bishop reported on an ICS system that was specifically designed to tol- erate freezing climates.¹¹ His design included high levels of insulation (R-40) for the enclosure, a multiple- glazing system that consisted of one layer of low-iron glass and three layers of high transmission films, and an involute-curved reflector and selective surface on the two 42 gallon tanks. All exterior piping was polybutylene and was wrapped with (R-25)insulation. Bishop reported that under a constant load gene_rated by a family of four that water temperatures were maintained at 120 degrees F during the month of January in a 6000 degree-day climate. Bishop points out that his monitoring was short term because of a lack of capital and that a more rigorous evaluation could not be done with such a small amount of data.

In 1983 David Robison developed for the Oregon Department of Energy a simulation method for ICS systems on the basis of a thermal network ap- proach. His article describes a simplified test procedure for exper- imentally determining ICS model parameters and how to adjust, "Method of Testing to Determine the Thermal Performance of Solar Domestic Water Heating Systems" ASHRAE 95-81 test standard to other locations. ¹² Robison's method is used by the State of Oregon to determine if a par- ticular passive system can qualify for state residential and commercial

1 1

12

Bishop, R.C., Superinsulated Batch Heaters for Freezing Climates, Proceedings of the 8th National Passive Solar Conference, New York:

American Solar Energy Society. Sept. 7-9, Santa Fe, N.M.

Robison, D.,"Comparing Passive Water Heaters", Solar Age, Vol. 9, No.

2, Feb. 1984.

Introduction 15

tax credits. To qualify, the system must contribute a minimum 50% of the energy required to meet the total hot water load. Robison concludes:

• Passive systems tend to be undersized.

• Passive systems can operate when active systems can not, (i.e. under conditions of low solar radiation intensity).

• Passive systems tend to be predictable. They behave with a similar collection efficiency over a range of environmental conditions.

• Passive systems operate with a stratified storage tank. This means that the hottest water is delivered to the user and the coldest water goes to the collector. This encourages greater collector efficiency.

• Passive systems with large night heat losses (batch heaters) do not operate as efficiently in combination. For this reason the rate of decreased energy savings is quite rapid as additional collector are combined.

Charles Fowlkes performed a side-by-side study of three different sys- tems.13 Over a one year period he collected weather data and performance

1 3 Adams, Jennifer A., "Side-by-Side Performance Monitoring," How do active,ICS and batch water heaters compare?, Solar Age, July 1985.

data on a homemade ICS system, a commercial ICS system and an active solar drainback system in Bozeman, Montana. He also collected data on an elec- tric water heater which he used as a control. Each of the four systems were subjected to a Rand load profile (a hot water use pattern meant to match that of an average family of four). When water was drawn from one system an equal amount of water was drawn off each of the other systems.

This was done to normalize the study. The homemade system was operated for seven months, April thru October and the two other systems were op- erated a full year. Despite the fact that December of 1983 was a record breaking cold month in Bozeman, Fowlkes reported that damage to the system never occurred, even though ice sometimes formed in the tank and pipes of the ICS unit.

Fowlkes performed a series of F-Chart runs for the three systems with the weather data that he had collected substituted in place of the standard weather files, CF-Chart is a computer simulation program commercially available). These runs showed.

•

•

Active systems would be slightly more efficient in the winter than in the summer.

F-Chart underpredicted performance by 10~~ in all months except for December which it overpredicted performance by 36%.

He also calculated the cost of the systems per square foot and compared that to the energy that the system delivered. The commercial ICS unit

Introduction 17

was least expensive, ($72.50)/Ft.^{2 •} in these terms, followed by the ac- tive drainback system ($75. 30)/Ft. ² and the homemade ICS system at

($119.40)/Ft.^{2 •} Payback ratios for the systems, based on 7 cents per kilowatt-hour and a domestic water heater efficiency of 80% were, 14 years for the active system, 16.9 years for the commercial ICS and 17.8 years for the homemade ICS system. System efficiency for the active unit was 44% while it met 59% of the annual load, the commercial ICS units effi- ciency was 35% and met 45% of the annual load, the homemade ICS unit had an annual efficiency of 55% and 76.1% efficiency for its seven month op- erational period and met 10% of the annual load. Fowlkes points out that the homemade unit met 20% of the load during the months that it operated and that the high efficiency can be attributed to its low operation tem- peratures.

Cummings reported on a simulation method that models multi-tube ICS sys- tems similar to the Gulf Thermal Progressive Tube design. ¹⁴ This design incorporates several small diameter tubes that are connected in series and enclosed in a glazed box. Cumming' s model assumed that the tubes filled the aperture of the collector. His model performs an hour-by-hour simulation of performance that considers solar gains, conductive heat losses and night sky losses and the internal heat transfer of the system.

His model is flexible enough that it allowed a series of parametric studies to be performed.

14 Cummings, J.B., Thermal and Economic Performance of Integrated Stor- age Passive Water Heaters in U.S. Climat;es, Thesis for M.S. in Applied Solar Energy, Trinity University, San Antonio, TX., 1983.

Cummings evaluated:

• The number and clarity of glazings.

• The number and volume of tubes.

• Performance with night insulation.

• Absorber surface characteristics.

• Draw schedules.

He concluded that the system that he had modeled was only 3% to 15% less efficient than active solar domestic hot water heaters, based on F-Chart runs for the same locations. A system that had a selective surface was always more cost effective than a system with a nonselective surface.

Single glazing was more cost effective except in cold climates that had high solar saving fractions. Freezing was much less of a problem than had been anticipated. A single glazed system with a selective surface would not freeze in Washington DC or milder climates. A combination of double glazing and selective surface would prevent freezing in all climates tested except that of Bismark, North Dakota. Adding R-9 night insulation improved performance at all locations tested and would prevent a single glazed system freezing in all climates tested. Morning draw schedules reduced performance by 10~~ to lS~L Cummings also reported a relatively

Introduction 19

high rate of return on investment for this type of system, between 13%

and 25% when a 40% tax credit was applied.

Lindsay and Thomas investigated alternative test methods for !CS systems.

Their work resulted in a single node model which was based on the Cornell Model 360 !CS design. The researchers developed this model so they could compare measured values and predicted values for both stratified and mixed tank experiments. They found·through experiments that forced circulation made little difference when compared to stratified tanks in daily col- lection efficiency. Their model was limited to no draw and noon time draw schedules only, however they achieved very good agreement with·the single node model. They concluded that it was possible to use a mixed mean temperature in ~he model to analyze that particular !CS system.¹⁵

1 5 Lindsay, R.C. and W.C. Thomas, Investigation of Standard Test Proce- dures for Integral Storage Solar Domestic Hot Water Systems, Prepared for The National Bureau of Standards by Virginia Polytechnic Insti- tute and State University, Blacksburg, Va., 1983.

METHODOLOGY

This study monitored the performance of ICS systems installed in resi- dences under actual family use conditions. BTU meters were selected as the most direct way to measure delivered energy because of their high degree of accuracy, relative ease of installation and simple data display.

It is important to note that delivered energy is the amount of energy that the system delivered to the domestic hot water heater not the total amount of energy that the system collected. Each installation also contained a flow meter in the cold water line leading to the ICS unit. The BTU meters recorded the total number of BTUs collected and the flow meter recorded the total gallons of hot water used at each location. These values could be used as input for Annual Performance Methodology (APM) program to ar- rive at predicted values. The APM program is based on an algorithm de- veloped from a series of simulations runs using A Transient Systems _Simulation Program (TRNSYS). ^{16 17}

16

17

Zollner, A., S.A. Klein and Beckman, A Performance Prediction Meth- odology for Integral Collection-Storage Solar Domestic Hot Water Systems, Journal of Solar Energy Energy Engineering, Volume 107, No- vember, 1985.

Klein, S.A., TRNSYS-A Transient System Simulation Program, Engineer- ing Experiment Station Report 38-12, Madison, WI: University of Wisconsin, December 1983.

Methodology 21

INSTRUMENT SELECTION

When selecting instruments for measurements it is important to choose the appropriate measuring device for each particular measurement required.

Several factors generally control·selection of an instrument:

• Degree of accuracy required.

• Cost of equipment.

• Reliability.

The degree of accuracy for a carpenter building a house can be measured with a ruler graduated in thirty secondths of an inch, but the machinist requires a caliper or micrometer capable of measuring to the thousandths of an inch. Both of the trades require an instrument that is a measuring device but the carpenter would find little value in a micrometer and the machinist would like-wise be limited by the use of a common ruler. It is

· their tools that allow them to reach certain levels of refinement and accuracy. The same holds true for energy measurement.

A range of options from collection of monthly fuel bills to computerized data collection were considered for this project. The overall target ac- curacy level for measured values used in this study is plus or minus 5 percent. All of the equipment used in this study is capable of meeting this criterion with some allowance for variation in the installations (see

Appendixes A-C). This degree of accuracy eliminated certain options and left only cost and reliability as determining factors. On this basis it was determined that the use of BTU meters was the most appropriate meas- uring device available for this study.

Several different types of BTU meters were investigated as potential monitoring equipment. Based on past research where BTU meters had been

·employed it was determined that only those units that were considered revenue meters, (units that had been used to measure energy usage for billing purposes in the past) would be considered. Revenue meters dem- onstrate appropriate levels of accuracy and reliability not found in all BTU meters.

Like all monitoring equipment BTU meters need to be selected to suit the system. BTU meters are subject to error depending on:

• Type of temperature sensor

• Selection of flow meter pulse head

• Location of hot and cold temperature sensors

The BTU meters that were selected are supplied with plat:i,num RTD temper- ature sensors with a time constant of 12 seconds. The flow meter pulse head sensor is accurate at flows as low as . 3 gallons per minute thru 13. 3 gallons per minute (See Appendix A). The BTU meters were supplied with

Methodology 23

ten foot temperature sensor leads that were calibrated at their factory.

Each BTU meter is approved PTB 22.12.79.14 to assure accuracy (See Ap- pendix A). Since these units were to be installed by different people

in various conditions a manual of proper installation procedures was de- veloped and distributed to all of the vocational school instructors (See Appendix D). Several workshops were also held for the instructors to familiarize them with the equipment and appropriate installation proce- dures.

DATA LOGGER

A TRS-Model 100 portable computer and an Elexor PL-100 16 channel data acquisition system was used to collect data (See Figure 10). The combi- nation demonstrates an overall accuracy of 1 LSB over a temperature range of O - 50 degrees Celsius and a resolution of 20 mV/bit (see Appendix C).

This combination was chosen for the following reasons:

• Compactness

• Battery backup ( data collection would not be disrupted in the event of a power outage)

• Built-in modem (potential to down load data over telephone lines)

• Low cost

llfflll ITU

- ^...

(DftMAI.OII CAIITIIINa)

Figure 10. TRS~lOO with Elexor PL-100 DAS

The data logging channels were configured as follows. The First channel recorded instantaneous pyranometer output and the second channel recorded the integrated value. Five channels recorded system and environmental temperature values. Resistive temperature detectors (RTD) were used be- cause of their high degree of accuracy, interchangeability and their

linear response to temperature over the temperature measurement range.

The first temperature sensor recorded outdoor ambient air temperature.

This sensor was placed in a radiation shield to eliminate direct radiation of the sensor. (See Figure 11) The shielded sensor was placed approxi- mately four feet to the side of the collector and approximately three feet above the ground. This placement was chosen to reflect the location of the ICS unit.

~1ethodology 25

A second temperature sensor was placed inside the collector to record the air temperature of the enclosure. A third sensor was placed approximately fifteen feet away from the collector in the cold water line inside a sensor well (See Figure 12). The sensor were coated with a silicon high conduction grease to insure the best possible contact between the tem- perature sensor and the temperature sensor well.

A forth temperature sensor was placed in the hot water line approximately fifteen feet from the collector. The fifth temperature sensor was placed near the domestic hot water tank to record the ambient air temperature of the basement where all the plumbing runs were located.

Two channels performed event counting, and were connected to a BTU meter.

One channel recorded the total number of BTUs delivered by the collector and the other recorded the total gallons of water that were used. Figure 13 shows the location and relationship of all the sensors.

PYRANOMETER

A LI-COR 200SB silicon photodiode pyranometer (cosine and color cor- rected) was used, cosine amd color correction are important features of a pyranometer because ,they allow the sensor to measure long angel solar radiation. This means that it can measure diffuse radiation which is an important component of solar collector performance. The error for this sensor is less than plus or minus 5% for angles less than 80 degrees. The azimuth error is less than 1% over 360 degrees at 45 degrees elevation

LOCATION

Figure 11. Outdoor Ambient Air Sensor Radiation Shield.

(See Appendix C). The sensor was placed at the side of the collecr::ir normal to the plane of incidence (See Figure 14).

---SBNSOR

Figure 12. Hot and Cold Temperature Sensor Wells.

Methodology 27

I I I I I I I I I I I I I I I I I I

I I-

I, f~ld ~1ter "•in ,, Pvranonter

3, o~tdoor Aobient Air Tnper1ture

•• DP~ Cold httr s,~!or

5. BTU "eter Cold Nat tr Sinor 6, Flow ~,t1r

7, DPS Hot Kater s,~,~r 8, ITIJ r.ettr Not Nater Sensor 9, !~door A~bitnt Air Senor IQ, Hot Nate• To ~oust

Sensor

The pyranometer is supplied with a certified calibration sheet (See Ap- pendix C). It was necessary to determine a time constant for the inte- grated solar radiation values. This was accomplished empirically and was applied to the corresponding data channel.

SIGNAL CONDITIONING

Each of the sensors signals were feed through a front end signal condi- tioning cards that were designed and built for each sensor by Computech, These cards amplified the output of the varied sensors to give voltage reading between 1 and ten volts. Each card was built using precision resistors and are accurate to plus or minus 1 tenth of 1 percent over the temperature measurement range.

Figure 14. Pyranometer Location.

•

INSTRUMENT CALIBRATION

Each of the five RTD temperature sensors were calibrated in an ice bath and a boiling water bath. Output voltage readings were taken in each in- stance and recorded. These values were applied to the corresponding data channels in the data tapes to adjust the data values.

DATA COLLECTION

Homeowners recorded the total numb~r of BTUs and gallons of water used each day on a form (See Appendix E). At the end of each week the homeowners totaled the daily readings and at the end of each month the weekly figures were totaled and the forms were returned to Virginia Polytechnic Institute by mail. As a means of verifying the data recorded by the homeowners, representatives from the vocational schools were asked to visit their

Methodology 29

particular installations each month to record readings taken from the instruments and to return the data by mail to Virginia Polytechnic In- stitute.

One system was outfitted with a data acquisition system which monitored solar radiation striking the collectors surface, inlet and outlet water temperatures, outdoor ambient air temperature, the number of BTUs deliv- ered by the system and the number of gallons drawn off the system. The computer automatically recorded the data on C-90 cassette tape every hour.

At the end of each month the homeowner was to return the tapes to Virginia Polytechnic Institute by mail. This particular installation was also equipped with a BTU meter as a means for verifying the data acquisition systems operation.

The data was reduced each month by Virginia Polytechnic Institute as the report sheets were received. Data tapes were also reduced as they were received giving a monthly profile of each unit tested. The reduced data is shown in Tables 1-5 in Appendix F along with comments reported by the the homeowners for each reporting period.

In order to be able to use the Annual Performance Methodology (APM) pro- gram it was necessary to make minor modifications to the program. Zollner used typical meteorological year (TMY) weather data for his study. His program requires input values for monthly solar radiation normal the collectors surface. In Zollner' s study the collector. tilt was always equal to the latitude for the location which was being tested (Madison,

Wis., Phoenix, Arz. and Denver, Co.) In the present study the collector design called for a collector tilt of 25 degrees off horizontal. The program also requires input of, the average monthly ambient air temper- ature and average monthly water main temperature.

Daily average solar radiation values were taken from Insolation Data Manual. ¹⁸ The manual provides data for solar radiation striking a hori- zontal surface daily. A collector tilt modifica~ion factor was applied to these values to approximate the solar radiation normal to the collector surface daily and the resulting value was multiplied by the number of days for that month. The tilt adjustment factors were calculated based on the method developed by Liu and Jordan. ¹⁹ These values are listed in Tables 6 - 7 of Appendix F along with the average monthly ambient air temper- atures and solar radiation values for a horizontal surface (daily), ra- diation normal to the surface (monthly), the tilt adjustment factor and the water main temperature. The Tables also list the night sky Temperature which is calculated by the program.

Weather data was chosen to represent the areas in which the tested col- lectors were monitored. Greensboro, N.C. was chosen to represent the two collectors located near Danville, Virginia because it was the closest station for which TMY data was available. Roanoke, Virginia was chosen

l 8

l 9

Knapp, Connie L., Thomas L. Stoffel and Stephen D. Whitaker Insolation Data Manual,Solar Information Data Bank, Solar Energy Research In- stitute, Golden, Colorado,SERI/SP-755-789, October 1980.

Associates,Determining the Availability of Solar Energy, 1975

Methodology 31

to represent the three other locations. Weather data for Washington D.C.

was first considered to represent the two collectors located in Culpeper, Virginia, however this data comes from Mount Weather and it was felt that Roanoke was more representative of Culpeper and Shipman because of ele- vation and available THY data.

Zollner suggests that values for sky temperatures below the ambient can be corrected by what he calls an effective sink temperature. The effec- tive sink temperature is defined as subtracting one-fourth of the monthly average sky temperature depression from the monthly average ambient tem- perature, this method takes into consideration convective losses, APM calculates this value. ¹⁶ APM uses this value to replace the average monthly ambient temperature when calculating draw temperatures. The source listing for the program and the calculation within are listed in (Appendix G). APM also requires the input of certain collector design parameters as follows:

•

• Aperture Area (Net Area) FT.²

• Loss Coefficient BTUs/HR.-FT.² °F

• Optical Efficiency

• Number of Nodes (Isothermal Nodes)

• Daily Hot Water Draw (Gallons)

These input values are meant to come from either published Solar Ratings and Certification Corporation (SRCC) ratings or from experimental testing based on the American Society of Heating, Refrigeration and Air- Conditioning Engineers (ASHRAE) test 95-1981. ^{20 21} The collectors that were monitored had not been tested to determine the the optical efficiency or the loss coefficient. The loss coefficient value that is applied in this study is an approximation based on (SRCC) test data for collectors similar in design and and capacitance. The loss coefficient is a function of the collector shell insulation and geometry, the optical cover heat loss characteristics, the reflector emittance and geometry and the tank surface and volume characteristics. In order to account for the fact that these units had smaller amounts of insulation than most of the commercial units tested by SRCC and to account for imperfections of the construction process, the loss coefficient value chosen to represent the collector in this study is somewhat higher than most commercially manufactured ICS water heaters (.26 - .78 BTUs/HR.-FT.² °F). Since all of the units tested were built to the same design it was assumed that they all had approxi- mately the same loss coefficient (.78 BTUs/HR.-FT.² .°F).

20

2 l

Solar Ratings and Certification Corporation, Directory of S.R.C.C.

Certified Solar Water Heater Systems Ratings, Washington DC., 1983.

ASHRAE, 1981, Methods of Testing to Determine the Thermal Performance of Solar Collectors, Standard 95-81, N.Y.: American Society of Heating, Refrigeration and Air-Conditioning Engineers.

Methodology 33

Optical efficiency is a function of the clarity of the optical cover, the reflectivity of the reflector and its geometry, and the tank surface absorptance and geometric characteristics. The tested collectors were glazed with a single layer of 3/16 inch tempered glass with an approximate transmission of 85% of the solar radiation striking normal to the surface.

The reflectors were foil faced rigid insulation with a very dull finish.

The tank was covered with an adhesive backed selective surface foil with an absorptance of O :97 and an emittance of O. 09 .. The geometry of the design is optimized for ease of construction and not for enhancing the optical efficiency. The optical efficiency value used in this study (.39) is lower than most commercially manufactured ICS water heaters (.39 to .69) to reflect the imperfection of the construction process and the types of materials used. In the case of unit #5 there was a noticeable film that developed on the inside of the glazing after it was installed and exposed to solar radiation. It is speculated that the film is the by- product of outgasing from the adhesive of the cloth duct tape that was used in the construction of this particular unit. The design specified use of aluminum foil tape not common duct tape.

The number of nodes was set at ten to account for thermal stratification of the tank. The APM program solves the energy balance for each node. It is assumed that the first node receives water at the main water temper- ature and that the last node represents water at the delivery temperature.

There are two differe·nt daily hot water draw values used in this study as input for the program. The overall average daily draw for the test

period and the average daily draw per month. In cases where data was not reported for the full month the total consumption was divided by the number of days during the recording period to arrive at the average daily draw.

The volume of the tank was taken from the manufacture's literature to be thirty gallons and the aperture was calculated to be (16.44 FT.^{2 )} based on the design drawings of the batch heater.

The result of the computer runs using the overall average daily draw are shown in Tables 8 thru 12 in Appendix F. The results of the computer runs using the average daily draw per month are shown in Tables 13 thru 17 in Appendix F. The last column of each table lists thP monthly measured energy that was delivered by the respective batch heater. In cases where the data reported represented only part of the month the predicted values were adjusted by dividing the predicted monthly value by the number of days for that month. The resulting value was then multiplied by the number of days of the month for which data had been reported.

Methodology 35

RESULTS

This section will show the results of the comparison of the measured to the predicted values. In this section two different series of graphs demonstrate the performance of each unit that was tested. The first se- ries of graphs show the performance-of the units when the overall average daily draw is used as input for the APM program. The second series of graphs demonstrate the performance of the units when the average daily draw for each month that data was reported is substituted in place of the overall average daily draw. This was done to accommodate the reporting periods when the units were not in use or when the monitoring equipment was inoperative.

MEASURED VS PREDICTED RESULTS

The following graphs show the results of the comparison of the measured and predicted values for each month that each unit operated. The percent values shown here are expressed as a percentage of the predicted value

(the measured value divided by the predicted value minus 1).

Figure 15 reveals the results of Unit #1 which is located near Danville, Virginia. Three months June, September and November are within the target range while July, August and October are outside the target range. For the month of June the APM program over predicted the performance by 7%.

July represents an over prediction of 45%. August demonstrates an over

prediction of 28%. September shows an under prediction of 12.8%. October again shows an under prediction of 41% while November is over predicted by only 7%.

Figure 16 demonstrates that unit #2, also located near Danville, Virginia is predicted within the imposed limits for June, July, September and Oc- tober while August and November are not. June showed an over prediction of 10% July is over predicted by 13%, August is over predicted by 37% and September is under predicted by 4%. October is over predicted by 8% and November is under predicted by 50%.

Figure 17 shows that Unit #3 located in Culpeper, Virginia fell within the prescribed limits for September only and May, June, July and October all fell outside. May is under predicted by 26,~ while June is under predicted by 30%. July is under predicted by 22% and September and October are under predicted by .5% and 25% respectively.

Figure 18 shows that unit #4 also in Culpeper, Virginia is also within limits for one month only, September. June, July, August and October were all outside the limits. June was over predicted by 48%, July is also over predicted by 48%. August is over predicted by 56%, September and October are also over predicted by 14% and 27% respectively.

Figure 19 shows that unit #5 located in Shipman, Virginia is never within the sugge5ted range. July is over predicted by 29%. The performance for August is over predicted by 69~~. September and October are also over

Results 37

predicted by 61% and 38% respectively while November is under predicted by 54%.

Figure 20 shows the measured to predicted comparison over the test period for each of the units tested using the average daily draw profile for the test period. Units One, Two and Three are all predicted within the pre- scribed range while units Four and Five are over predicted. Unit #1 is over predicted by only 10%. Unit #2 performance is over predicted by only 11%. Unit# 3 is over predicted by 6%. Unit #4 is over predicted by 41%

and unit #5 is over predicted by 53%.

09BltALL 4 VG, Dllo\l' IZZ] IHWIUIIBD CS3J PlllDICffll

Figure 15. Energy Delivered Comparison: Based On Average Daily Draw, Unit {Fl

UNIT Ill 500

400

=

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Figure 16. Energy Delivered Comparison: Based On Average Daily Draw, Unit /12

Results 39

UNIT .a

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IIAY WNI JULY SIPT. OCT.

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Figure 17. Energy Delivered Comparison: Based On Average Daily Draw, Unit t/3

UNIT e4

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JUNE JULY AUC. SEPT. OCT.

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Figure 18. Energy Delivered Comparison: Based On Average Daily Draw, Unit t/4