Studies of solar collector performance at NRC

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Studies of solar collector performance at NRC

STUDIES OF SOLAR COLLECTOR

PERFORMANCE

AT NRC

b y

S . J . Harrison and J . R . Sasaki

ABSTRACT

As part of N R C t s program f o r t h e development o f solar h e a t i n g s t a n d a r d s and t e s t methods, a f a c i l i t y

has been e s t a b l i s h e d at the D i v i s i o n of Building

Research to obtain d a t a on the thermal performance and durability o f solar c o l l e c r o r s . A v a r i e t y of s o l = coXlectors a r e b e i n g t e s t e d t o determine the f a c t o r s t h a t a f f e c t t h e i r performance and l i f e . A review of t e s t i n g procedures is under way to a s s e s s

their s u i t a b i l i t y

f o r

use

in

Canada. This

note

describes t h e solar calorimeter apparatus and t h e in-house activities currently b e i n g pursued at DBR.

STUDIES OF SOLAR COLLECTOR PERFORMANCE AT NRC

by

S . J . H a r r i s o n and J . R . S a s a k i

1 . 0 INTRODUCTIOM

The i n t e r e s t in solar energy f o r space and service-water heating has

r e s u l t e d recently in the introduction of a number o f s o l a r h e a t i n g

components, notably c o l l e c t o r s , to the Canadian m a r k e t . This has increased

t h e need for solar component performance s t a n d a r d s t h a t w i l l provide users

of s o l a r h e a t i n g systems w i t h same assurance

of

functional performance, r e l i a b i l i t y , and d u r a b i l i t y

.

The Canadian Standards Association and t h e O n t a r i o Research Foundation are c u r r e n t l y p r e p a r i n g i n t e r i m t h e r m a l and

durability performance standards f o r s o l a r c o l l e c t o r s s u i t a b l e for Canadian

conditions.

Performance standards f o r s o l a r c o l l e c t o r s can be used o n l y i f there

are s u i t a b l e test methods a v a i l a b l e and t e s t f a c i l i t i e s able to provide reliable and comparable results. T h i s paper describes in-house a c t i v i t i e s

undertaken by t h e National Reseasch Council to i d e n t i f y s u i t a b l e t e s t methods and t e s t i n g agencies. They include:

1) a study o f clallector thermal -performance t e s t methods,

2) a round-rob in collector testing program,

3) c o l l e c t o r exposure s t u d i e s , and

4 ) material durability s t u d i e s .

2 . 0 IlER/NRC COLLECTOR TEST FACILITY

An outdoor test facility has been established at t h e Division o f Building Research c o n s i s t i n g of a solar collector calorimeter and an exposure s t a n d f o r studying t h e r e l i a b i l ity and durability of collectors undcr simulated o p e r a t i n g and non-operating ( i . e . , stagnation] c o n d i t i o n s .

The f a c i l i t y is located on the roof o f one of t h e DBR l a b o r a t o r i e s

(Figure 1 ) .

A schematic drawing of t h e C O ~ ~ ~ C ~ D T calorimeter i s shown in F i g u r e 2 . It c o n s i s t s o f a controlled-temperature l i q u i d flaw loop and calorimetry

(i . e m , heat-flow measurement) l o o p . I t i s capable o f testing t w o

l i q u i d - b a s e collectors simultaneously on a s t a n d facing due south. The

c a p a b i l i t y f o r t e s t i n g air-base collectors and t o provide a s o l a r (azimuth) t r a c k i n g mechanism to extend the a v a i l ah l e t e s t i n g p e r i o d . The equipment and i n s t r u m e n t a t i o n were designed and s e l e c t e d t o conform t o t h e require- ments of t h e ASHRAE 9 3 - 7 7 t e s t i n g procedure (1).

During a t e s t , t h e f a l l o w i n g measurements a r e t a k e n at I-min intervals

b y a d a t a l o g g e r and s t o r e d on magnetic t a p e f o r subsequent pracessing:

(1) c a l o r i m e t r y factors, including c o l l e c t e d s o l a r energy, c o l l e c t o r f l u i d

flow r a t e , inlet and o u t l e t f l u i d temperatures, and c o l l e c t o r absorber

temperature;

(23 s o l a r r a d i a t i o n data, i n c l u d i n g d i r e c t normal, sky diffuse, total

h o r i z o n t a l and t o t a l on c o l l e c t o r p l a n e ; and

(3) weather data, including wind speed and d i r e c t i o n , and outdoor ambient

temperature.

The c o l l e c t o r exposure stand is described in Section 5,O.

3.0 STUDY OF THERMAL -PERFORbEANCE TEST METHODS

The designer of a s o l a r heating system requires c o l l e c t o r tlmermal

performance d a t a for t w o purposes: first, the data are used as major

determinants in selecting a c o l l e c t o r , t h a t is, to ''ranktV t h e worth of

collectors; second, the designer r e q u i r e s thermal performance d a t a in

d e s i g n i n g s o l a r heating systems. M o ~ e s p e c i f i c a l l y , data a r e used to

determine t h e s i z e of the solar collector array r e q u i r e d t o satisfy a

p a r t i c u l a r h e a t i n g demand.

The thermal performance c h a r a c t e r i s t i c of a collector can be d e r i v e d

e i t h e r b y a n a l y s i s ( 2 )

,

u s i n g the known h e a t transfer and optical

p r o p e r t i e s o f t h e c o n s t i t u e n t materials, or b y experimental means. As many

proprietary c a l l ectors are fabricated w i t h mterial s and methods t h a t a r e

i n a d e q u a t e l y d e s c r i b e d in terns of t h e i r o p t i c a l and heat t r a n s f e r

properties, it h a s become commn p r a c t i c e t o determine t h e thermal perfor- mance c h a r a c t e r i s t i c s of c o l l e c t o r s b y t e s t i n g them w i t h n a t u r a l o r

stmulated s o l a r r a d i a t i o n . This study is designed t o determine which o f

thc a v a i l a b l e test methods i s b e s t s u i t e d for p r o v i d i n g data for ranking

purposes; and t h e relevance of this d a t a f o r designing s o l a r heating

s y s tcms

.

To u n d e r s t a n d c o l l e c t o r testing methods it i s f i r s t necessary to

understand t h c significance o f t h e c o l l e c t o r e f f i c i e n c y curve used to

represent t l ~ c thermal performance of c o l l e c t o r s . The e n e r g y gained by the

h e a t t r a n s f c r f l u i d as it passes through a f l a t - p l a t e c o l l e c t o r i s t h e

Jiffcrcnce b e t w e e n t h e solar energy t r a n s m i t t e d through t h e cower and absorbed b y t h c absorber plate and the heat lost by t h e collector to the

s u r r o u n d i n g s . The e f f i c i e n c y of c o l l e c t i o n , q, i s t h e r a t i o o f c o l l e c t e d

u s e f u l cnergy to s o l a r energy incident on t h e c o l l e c t o r . T h e efficiency

expression devcloped by Bliss ( 3 ) i s based on t h e collector heat b a l a n c e

where,

9, = energy gained by t h e heat t r a n s f e r f l u i d a s it passes

t h r o u g h t h e col 1 ector A = a b s o r b e r area

I = t o t a l s o l a r energy incident an collector p e r unit area

(Ta),

= e f f e c t i v e transmittance-absorptance product of cover and

absorber

UL = over-all h e a t l o s s c o e f f i c i e n t of c o l l e c t o r t ~ i = temperature of f l u i d e n t e r i n g the c o l l e c t o r

ta = outdoor ambient a i r temperature FR = collector heat removal f a c t o r

The e f f i c i e n c y o f a c o l l e c t o r i s d e p i c t e d in F i g u r e 3 . The

characteristic is a f t e n a curve r a t h e r t h a n a s t r a i g h t line because the

h e a t l o s s coefficient is generally

n o t

a c o n s t a n t . Thc c a l l e c t o s

characteristics FR,

(Ta)

and UL may t h e r e f o r e be estimated from t h e e f f i c i e n c y curve d e r i v e d from t e s t r e s u l t s .

Deriva t l o n of 3309 l e c t o r performance c h a r a c t e r i s t i c s by t e s t i n g w a s f i r s t farmaZized by t h e National Bureau of Standards in 1974 (5)

.

The NBS method described an outdoor testing procedure and the test facility to b e used. T t

a l s o

prescribed t h e accuracy requirements of t h e measuring

instruments. Steady-state t e s t s are performed o v e r a range of collector

i n l e t f l u i d temperatures under c l e a r and steady r a d i a t i o n c o n d i t i o n s n e a r

solar noon, or when s o l m r a d i a t i o n is n e a r l y normal to t h e c o l l e c t o r face ( i . e . , n e a r zero i n c i d e n t a n g l e where incident angle is the a n g l e between

tIic s u n ' s rays and a normal drawn from the collector surface]

.

It was recognized t h a t a c o l l e c t o r characteris t i c determined with n e a r z e r o incident angle docs not realistically represent the behaviour of a collcctar installed in the field, since incident angle varies with time o f day. I'hc performancc of

a

conventional flat plate collector decreases as t11r incident a n g l e increases. Some evacuated tabular collcctors, on the other hand, perform b e t t e r at incident a n g l e s greater t h a n zero. T h i s

mcans that some c o l l c c t o r s with poor NBS t e s t r e s u l t s may actually collect

more cncrgy o v e r a day- long p e r i o d than other h i g h e r - r a t e d c o l l e c t o r s . To remcdy this d e f i c i e n c y , the American S o c i e t y o f H e a t i n g ,

I l e f s i g e r a t i n g and Air-Conditioning Engineers (ASHRAE) developed the ASIIRAE

the h9S method, b u t does include a t e s t for d e t e r m i n i n g thc variation i n c o l l e c t o r

performance

w i t h i n c i d e n t angle and another f o r determining t h e

thermal response time o f t h e collector.

Both t h e

NBS

and ASHRAE methods are less t h a n ideal as standard t e s t

methods f o r Canada because the conditions required f o r t e s t i n g

-

b r i g h t

clear days w i t h low wind speeds and low ground reflectance

-

occur

i n f r e q u e n t l y i n Canada, especially in winter, There a r e two o t h e r test methods t h a t must be looked at s e r i o u s l y as possible a l t e r n a t i v e s f o r

Canadian u s e . These are the AS€ method (63 and indoor solar simulation.

The A S E methad, developed in Germany, is composed o f an o u t d o o r t e s t

t o determine t h e maximum efficiency of a c o l l e c t o r [ i . e m when

%i

- ta

1 = 0) and an indoor thermal t e s t t o determine t h e heat l o s s c o e f f i c i e n t . The second a l t e r n a t i v e , t h e indoor simulation t e s t , utilizes an artificial

radiation source to conduct t h e b a s i c ASHRAE t e s t . Both methods may s h o r t e n

testing time and produce more reproducible results, b u t they r e q u i r e more

elaborate t e s t i n g f a c i l i t i e s and f u r t h e r work to correlate their results

w i t h outdoor collector performance. The

NRC

is cooperating w i t h the Working

Group on Solar Energy o f the International Energy Agency in r e s o l v i n g some

of these questions.

A primary requirement o f a standard c o l l e c t o r test method f o r ranking purposes is t h e reproducibility o f r e s u l t s ; that is, a t e s t conducted on a collector at different times of the year o r a t different locations should

produce t h e same r e s u l t s . Following are

some

of the environmental factors

that can affect reproducibility : - intensity o f s o l a r r a d i a t i o n ,

-

ratio of direct beam r a d i a t i o n t o diffuse sky r a d i a t i o n ,

- absolute ambient a i r temperature and e f f e c t i v e s k y temperature,

-

wind speed,

-

ground ref1 ectance,

-

c o l l e c t o r mounting during t e s t i n g .

One study ( 7 ) h a s shown that t h e effect of environmental factors can b e

reduced analytically b y r e f e r r i n g the t e s t r e s u l t s back to a s t a n d a r d s e t

of

conditions. The DBR study w i l l i n v e s t i g a t e the effects o f t h e wider range

of environmental c o n d i t i o n s encountered in Canada on the reproducibility o f t e s t resul t s

.

The applicabif i t y of

rhermal

performance data obtained by

idealized standard t e s t s such as ASHRAE 93-77 i n determining the s i z e o f a

s o l a r h e a t i n g system and predicting its performance has not y e t been

demonstrated. This is o f special concern in Canada where the operating

c o n d i t i o n s i n w i n t e r aFe q u i t e different f r o m those used to d e r i v e t h e performance data. For example, solar systems w i l l o f t e n operate under h i g h

wind c o n d i t i o n s and e i t h e r overcast o r intermittent cloud. b r e o v e r , t h e

characteristic o f a whole a r r a y of collectars; and the energy callcctcd [,y

a

solar

system that turns on and

off

frequently w i l l b e less tllan

tE~ar

colLected by a system o p e r a t i n g continuously.

Designers who use standard thermal performance p l o t s to predict t h e performance o f a solar heating system w i l l probably a r r i v e

a t

the wrong

result. The performance of an actual collector a r r a y operating under r e a l i s t i c c o n d i t i o n s may be quite different from an ASHRAE type test

r e s u l t . An example of this may be seen in Figure 4 of Reference ( 8 ) . Curve 1 i n d i c a t e s the t y p i c a l ASHRAE type i n s t a n t a n e o u s e f f i c i e n c y curve, w h i l e Curve 2 is the measured average daily performance curve of t h e total

i n s t a l l e d c o l l e c t o r array d u r i n g real operation. P a r t o f t h e discrepancy

in t h e value of t h e

FR{Ta)

i n t e r c e p t may b e attributed to incidence angle e f f e c t s and, possibly, to flow imbalance in t h e s y s t e m . The variation in

t h e slope, FRUL, could be due to difference

i n

heat l o s s f r o m the array, a s

compared to t h e t e s t madule. The a r r a y in question i s sitting on an i n s u l a t e d maf, which would reduce back heat l o s s e s and r e s u l t in a d i f f e r e n t performance c h a r a c t e r i s t i c . It

is

apparent t h a t furthei- work w i l l have t o b e done to account for the variation in _{array performance f r o m}

typical test r e s u l t s . One o f the aims of the DBR s t u d y is, t h e r e f o r e , to determine how t h e standard thermal e f f i c i e n c y c h a r a c t e r i s t i c can b e

adjusted ta p r o v i d e a b e t t e r i n d i c a t i o n o f in-use performance of solar

c o l l e c t o r s .

4.0

ROUND-ROBIN TESTING

PROGRAM

T h e r e a r e several groups

in

Canada currently a b l e , o r planning to

provide a c a p a b i l i t y , t o perform o u t d o o r thermal e v a l u a t i o n t e s t s on solar collectors, A major concern w i t h having several testing agents is that o f

oh t a i n i n g comparable r e s u l t s . A round-robin program is planned to

e s t a b l i s h the c r e d i b i l i t y of the t e s t i n g agents, t h a t is, to e s t a b l i s h their

t e s t i n g a b i l i t y .

The

NRC

will test collectars in its test facility and t h e n send them

t o other t e s t i n g laboratories to be t e s t e d again on t h e i r a p p a r a t u s . The

r e s u l t s w i l l b e returned to

NRC,

and if they a r e

i n

reasonable agreement the testing l a b o r a t o r y w i l l b e i d e n t i f i e d a s an "acceptable" t e s t i n g agency

for s o l a r collector testing. The d i f f i c u i ties involved

in

a c h i e v i n g

c o m p a r a b i l i t y o f r e s u l t s can b e appreciated from t h e discussions i n Section 3.0 on t h e r m a l t e s t methods. Regardless o f the d i f f i c u l t i e s , an a t t e m p t must be made to control the variability of results obtained by d i f f e r e n t

testing a g e n t s .

DBR

has assumed the r o l e of t h e central agent and is c u r r e n t l y t e s t i n g s e v c r a l s o l a r collectors to be used as the standard round-robin samples.

A somwhat d i f f e r e n t round-robin sample is also b e i n g prepared and

calibrated. It consists of a c a l i b r a t e d e l e c t r i c a l heater enclosed i n a

casing, with accurate transducers for measuring b o t h instantaneous and integrated electric power i n p u t . It can b e installed i n a c o l l e c t o r t e s t

facility in place of she c o l l e c t o r and used to c a l i b r a t e t h e over-all

measurement accuracy of the calorimeter, i n c l u d i n g losses a s s o c i a t e d with the pipes connected to the test specimen.

h o t h e x requirement for a candidate testing a g e n t seeking

acceptability w i l l be t h a t a l l measuring instruments must conform t o t h e a c c u r a c y requirements o f the ASHRAE 93-77 testing procedure. This is s p e c i a l l y important f o r measurement o f i n c i d e n t s o l a r r a d i a t i o n , which h a s b e e n a major factor c o n t r i b u t i n g t o large variations

in

test r e s u l t s .

Two round-robin programs already completed r e v e a l some o f t h e d i f f i c u l t i e s and p o s s i b i l i t i e s o f a c h i e v i n g comparability. One was

conducted by the National Bureau of Standards (USA) t o determine

c o m p a r a b i l i t y among severa 1 U.S

.

1 a b o r a t o r i e s

.

The o t h e r was r e c e n t l y

undertaken b y t h e Working Party on % l a r Energy o f the I n t e r n a t i o n a l Energy

Agency (LEA)

.

I n t h e NBS program ( 7 ) two l i q u i d heating c o l l e c t o r s were d i s t r i b u t e d t o 2 1 testing l a b o r a t o r i e s where they were t e s t e d b y e i t h e r the NBS test method or the ASHRAE test method. The r e s u l t s , upon analysis, showed a v e r y l a r g e spread. Part o f the spread was a t t r i b u t e d to v a r i a t i o n s in environmental c o n d i t i o n s , b u t much of it was due to experimental e r r o r s

in several o f the p a r t i c i p a t i n g l a b o ~ a t o r i e s . The program revealed t h e need

f o r

mare s t r i n g e n t c o n t r o l s on t h e equipment and methods used, and for

f u r t h e r investigation o f t h e f a c t o r s a f f e c t i n g test results. There a l s o appeared t o b e a need for referencing all t e s t r e s u l t s back to a standard

s e t of environmental conditions to achieve better comparability. The preliminary r e s u l t s of the IEA experience, to which NRC

c o n t r i b u t e d , appear much more promising. These show t h a t with c a r e f u l

attention to t e s t procedures and i n s t r u m e n t c a l i b r a t i o n , reasonably

consisrent r e s u l t s may b e o b t a i n e d among l a b o r a t o r i e s . It i s hoped t h a t the DBR/NRC round-robin pmgram w i l l r e s u l t in the designation of several Canadian t e s t i n g l a b o r a t o r i e s capabl e o f p r o v i d i n g reasonab l y cemparab le

t e s t r e s u l t s . By limiting the number of acceptable l a b o r a t o r i e s i t s h o u l d a l s o b e possible t o undertake p e r i o d i c checks of t h e t e s t i n g procedure used

and t h e r e s u l c s obtained.

5.0 COLLECTaR EXPOSURE STUDIES

A l t h o u g h thermal performance i s a major determinant in the selection of a s o l a r c o l l e c t o r , t h e r e l i a b i l i t y and d u r a b i l i t y characteristics w i l l

determine t h e long-term w o r t h of a collector. Because s o l a r systems a r e c a p i t a l i n t e n s i v e , t h e y require a long s e r v i c e l i f e in o r d e r to b e

cconomj c a l

.

P r e d i c t i n g t h e r e l i a b i l i t y and d u r a b i l i t y of a c o l l e c t o r is cxtrcmcly difficult. These factors depend

n o t

only on t h e p r o p e r t i e s and compatibility of materials u s e d , but a l s o on conditions of service.

Committee E44 o f t h e American S o c i e t y for Testing and Materials is

c u r s c n t l y charged w i t h t h e r e s p o n s i b i l i t y for p r e d i c t i o n

of

service l i f e .

'Ilrc Committee is fo2lowing two paths in judging the reliability and

durability o f c o l l e c t o r s : one i s to s u b j e c t t h e whole collector to extreme

scrvicc conditions; and the other is to subject t h e c o n s t i t u e n t m a t e r i a l s to natural and accelerated a g i n g .

The exposure stand at

DBR

is used to subject c o l l e c t o r s t o natural

i n s o l a t i o n and weathering under either simulated o p e r a t i o n [i.e., w i t h h e a t t r a n s f e r f l u i d E l o w and controlled temperature variations) o r stagnation

(i. e., no-f low) conditions. The i n t e n t is to show changes i n t h e p h y s i c a l , o p t i c a l and chemical properties

of

t h e materials as well as the thermal

performance of t h e col Lector under normal and extreme operating conditions

.

Various c o l l e c t o r types using a _{v a r i e t y of m a t e r i a l s will b e studied.}

Exposure samples a r e instrumented to determine the history o f operating c o n d i t i o n s . The following a r e recorded c o n t i n u o u s l y on magnetic tape :

-

temperatures of absorber, c o l l e c t o r h o u s i n g and cover, - total s o l a r and ul tra-violet r a d i a t i o n l e v e l s ,

-

dew-point inside housing and wetness on component surfaces.

One o f the objectives of t h e s t u d y is t o determine t h e e f f e c t i v e n e s s of t h e various methods u s e d t o c g n t r o l moisture i n s i d e collectars, i .e

.,

d e s i c c a n t s , drainage holes, vent h o l e s

.

The h i s t o r y of a p e r a t i n g c o n d i t i o n s

w i l l be of use in e s t a b l i s h i n g condirions for accelerated aging t e s t s . During t h e exposure period, material samples w i l l b e removed periodically

f o r d e t a i l e d analysis, and t h e collector thermal performance will be

evaluated to derermine whether it is changing with time. Visual observa-

tions w i l l also b e made of the absorber, i n s u l a t i o n , g l a z i n g and housing

seals, and cover material.

Stagnation exposure tests are intended to simulate c o n d i t i o n s t h a t may be experienced during a shut-down o f the s o l a r system. Exposure to 30 clear

days of w e a t h e r i n g w i t h no-flow can reveal weaknesses i n t h e d e s i g n and

material s e l e c t i o n r e l a t e d to r e l i a b i l i t y ; e .g

. ,

t h e glazing materials, g l a z i n g seals, absorber coatings and f a s t e n e r s . Although exposure studies

by themselves cannot give a true prediction of the durability of a collector, t h e y can b e a useful metllod of predict in^ reliability o f the

component parts and a r e a necessary complemenr te material d u r a b i l i t y

studies.

6.0

MATERIAL

DURABILITY STUDIES

The second approach to durability p r e d i c t i o n i s t e s t i n g

o f

materials.

This a c t i v i t y is b e i n g addressed b y t h e Building M a t e r i a l s Section o f

DBR.

Primary areas of concern are absorber surface materials and transparent

cover materials.

To

support this e f f o r t t h e Section h a s a c q u i r e d o p t i c a l

instruments f o r measuring s o l a r ab sarptance and t r a n s m i t t a n c e o f materials, as well as long-wave emittance. D u r a b i l i t y studies on materials such a s

insulation, metals and seal

anas

are already a continuing a c t i v i t y w i t h i n t h e Section. The materials durability work w i l l b e c l o s e l y coordinated w i t h t h e a c t i v i t i e s of ASTM Committee €44.

7 . 0 CONCLUSIONS

The ultimate goal of t h e

NRC

studies

on

solar collector testing is to p r o v i d e information and guidance to manufacturers and u s e r s on the thermal and d u r a b i l i t y performance of collectors under Canadian climatic conditions.

It is i n t e n d e d t o i d e n t i f y those materials and material combinations t h a t appear capable of p r o v i d i n g a reasonable service life, a s w e l l as t h e

collector design features that enhance or s h o r t e n t h i s l i f e . The studies on thermal t e s t methods are aimed at easier assessment o f the r e l a t i v e

merits of collectors, and a t presenting collector performance data in a form suitable for use in the design o f solar h e a t i n g systems. It is hoped t h a t t h e round-robin program w i l l r e s u l t i n t h e establishment

of

a few capable and comparab le thermal testing facilities in Canada.

REFERENCES

1. Methods o f T e s t i n g to Determine the Thermal Performance of Solar Collectors, ASHRAE STANDARD 93-77, ASHRAE, 345 East 47th S t r e e t ,

New York, New York, 10017, 1977.

2 . Duffie, J , A , and

W.A.

Beckman, Solar Energy Thermal Processes, John Wiley and Sons, 1974.

3 . Bliss, R.

W.

, The Derivation of Several Plate-Efficiency Factors

Useful in t h e Design o f F l a t Plate Solar Heat Collectors, Solar Energy, Vol. 3, No, 4 , Dec. 1959.

4 . H o t t l e , H.C. and A . Whillier, Evaluation of Flat-Plate S o l a r Collector Performance, Transactions o f the Conference on the Use of S o l a r Energy,

Vol. 111, Thermal Processes, Tucson, A r i z o n a , 1955.

5 . H i l l , J . E , and

T.

Kusuda, M e t h s d o f T e s t i n g f o r Rating Solar C o l l e c t o r s

Based on Thermal Performance, National Bureau o f Standards Report

NBSIR 74-635, Dec. 1974.

6 B i r n b r e i e r , C., e t a l . , E f f i c i e n c y Tests o f S o l a r Collectors, ASE

hrorking Document, S e p t . 1976.

7 . S t r e e d , E.R., et a l . , Results and Analysis of a Round Robin T e s t

Program for Liquid-Iteating Flat-Plats Solar Collectors, National

n u r c a u of S t a n d a r d s , T e c h n i c a l Note 975, August 1 9 7 8 .

8. S i b h i t t , B . F

.

,

H . Jung, and D. Lorriman, P e r f o r m n c e of the Meadowvale S o l a r Home, Presented at Renewable Alternatives, S o l a r Energy Society

' I

I

Solar collmcilon Power Sn P h Starage Tanks C Chlllrd Coolrr 4 Pump Tmmprrmturo Controf loop I F I G U R E 2 S C H E M A T I C OF DBRJNRC

SOLAR

C A L O R I M E T E R A P P A R A T U S c,,= S S Ac EFFICIENCY

= %

1,

3;

""r

\

~ e d u c t l c n due lo

Net G sin

\

1 1

I ,

Eft. =Q.k.e.: Garns =Lassss

Q 0 I 0.02 I 0.04 0.06 0 08 0.10 0.12 0.14 Z ( f f t - T a l / 3 , I O C / W ~ - ~ I

FIGURE 3

" A S H R A E " , G R A P H I C A L

R E P R E S E N T A T I O N OF T H E R M A L

P E R F O R M A N C E

2a

t

' 2- ACtUlll A w r y Performance F I G U R E 4 C O M P A R I S O N B E T W E E N ARRAY

P E R F O R M A N C E

A N D

C O L L E C T O R MODULE T E S T P E R F O R M A N C E