Performance of the Meadowvale Solar System (October 1976 to April 1978)

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Performance of the Meadowvale Solar System (October 1976 to April

1978)

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PERFORMANCE OF THE MEADOWVALE SOLAR SYSTEM (OCTOBER 1976

TO

APRIL 1978)

by

B . E . SZBBITT and H. J U N G

TNTRODUCTION

T h e Meadowvale Solar Experiment i n Mississauga, Ontario, was one o f t h e first houses i n Canada to u s e s o l a r energy f o r space a n d

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scrvFce na'tcr h e a t i n g

.

It was b u i l t in 1975 w i t h financial a s s i s - t a n c c from t h e Federal Government. The s o l a r h e a t i n g system was d c s i g n c d to meet 6 0 to 7 0 per cent of t h e t o t a l space and service

water h e a t i n g demand of a single-family home under Canadian climatic

conditions. F e a t u r e s of t h i s s o l a r h e a t i n g system include a s o l a r -

a s s i s t e d heat pump, semi-seasonal dual h e a t storage tanks, and o f f -

]leak e l e c t r i c a l heating o f storage water. The l a t t e r f e a t u r e was

121

added i n December 1977

.

Thc Division o f Building Research of t h e N a t i o n a l Rcsearch Council of Canada h a s carried out a comprehensive monj.toring program

t o s t u d y t h c performance of t h e s o l a r h e a t i n g system and i t s associated

subsystems from October 1976 to A p r i l 1978 (3,4,5.6,7) T h i s paper constitutes the f i n a l monitoring r e p o r t on this project and d e s c r i b e s

t h e results o b t a i n e d and the problems encountered over t h e f u l l moni-

t o r i n g aeriod. The r e p o r t i n g format employed is based on t h a t recommended

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DESCRIPTION OF THE ENVIRONMENT 1,ocat ion

Mis.;issaupa i s s i t u a t e d at 43' 45'N latitude, 79' 301W I o n p i r u d e ,

a t an altitude of 120 m above sea l e v e l . It i s a suburban town

located approximately 30 km sauthwest of Toronto, O n t a r i o . The

terrain is f l a t , and t h e air is f r e e of industrial pollution.

C l imatc

Rie r e g i o n has a humid continenTal climate with cool summers and e v e n l y distributed precipitation t h r o u g h o u t the year. Trewar-

t h n 1 8 classification f o r Toronro, Ontario, i s DBF. The r e g i o n

r c c c i v c s a mean total precipitation of 790 mmlyear, including a mean

annV31 snowfall of 141 cm/year, The mean annual duration of b r i g h t s u n s h i n e

is 2045 hours; a s a percentage of the maximum possible aver t h e whole year b r i g h t s u n s h i n e hours c o n s t i t u t e 45 per cent.

S o l a r Radiation, Ambient Temperature and Wind

-

Table I l i s t s t h e monthly means of d a i l y meteorological values at Toronto International Airport, about 16 km east of the house.

Includcd are fractions of maximum possible sunshine hours, mean daily

total a n d d i f f u s e insolation values on a horizontal surface, mean

ambient dry-bulb temperature, h e a t i n g degree d a y s p e r month, mean wind velocity and Albedo.

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IIESCRTPTION OF

BUILDING AND

SYSTEMS

B u i l d i n g

F i g u r e 1 shows t h e s o u t h face of t h e single-family detached 2

housc which h a s 135 rn of t o t a l l i v i n g area on two f l o o r s . I t a l s o h a s a heated f u l l basement and an unheated attached garage.

The e n t i r e s o u t h f a c e of the first f l o o r consists of double-glazed windows and an atrium. The house walls are i n s u l a t e d with e i t h e r

7 . h cm of polystyrene insulation or I S cm o f g l a s s fiber insulation; t h e ceiling is i n s u l a t e d w i t h 20 cm of glass f i b e r insulation. I n

thc f i r s t f l o o r l i v i n g room, there i s a fireplace w i t h a double- w a l l c d f i r e b o x d e s i g n e d to p r e h e a t incoming outdoor a i r . The house h e a t l o s s factor in t h e original design was taken as 260 W/K.

Solar Heating System

Figure 2 i s a schematic of the Meadowvale solar h e a t i n g system.

A description o f t h e major s y s t e m components i s given in Table IT.

Thc solar heating system was designed primarily for space h e a t i n g . The service water pre-heating system operates o n l y in t h e

s p r i n g , summer and early f a l l , d u r i n g which time solar energy is a l s o b e i n g stored f o r space h e a t i n g .

The f l a t - p l a t e collector array has a t o t a l s u r f a c e area of 2

6 4 . 4 m , and is mounted a t an a n g l e of 60" from rhe horizontal on

t h e south-facing roof. Water is t h e heat t r a n s p o r t medium in b o t h

t h c collection and heat distribution circuits. The collector pump

circulates w a t e r from s t o r a g e through the collector a r r a y whenever

thc d i f f c r e n t i a l temperature between t h e c o l l e c t o r p l a t e and storage t a n k watcr exceeds ~ O C , and s h u t s off when t h e r e t u r n w a t e r temperature

d r o p s tsclon t h e s t o r a g e t a n k water temperature. TFlc collector a r r a y a u t o m a t i c a l l y d r a i n s down f o r f r e e z e protection whenever i t s circula-

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Thc s o l a r energy collected i s s t o r e d

i n

18 m3 of water divided

between two c o n c r e t e tanks situated in one corner o f t h e basement.

Both t a n k s are i n s u l a t e d on t h e t o p and sides, but are n o t i n s u l a t e d on t h e bottom, which i s about 1 m below the basement f l o o r . The

tl~esmal resistance values are; 8 . 6 f o r t h e covers, 4 . 2 f o r w a l l s cxposcd t o indoor conditions, and 6.9 f o r t h e walls adjacent to t h e c s t e r i o r basement walls ( a l l values are in a 2 - ~ / ~ ) .

The t a n k s are connected so as to operate at two temperature Lcvcls. Selcctor valves permit collector return water t o e n t e r c i t h e r t a n k and h e a t i n g water t o be d r a m from e i t h e r tank. I n

u s e , tank number 2 supplied t h e collection circuit and the heated

watcr was r e t u r n e d to tank number 1. Tank 1 was used to s u p ~ l y

t h e h e a t distribution circuit because it operated at: a h i g h e r tempe- r ; ~ t u r c t h a n tank 2 .

Spacc H e a t i n g Subsystem. - The space h e a t i n g subsystem c o n s i s t s o f

t w o t h e r m a l s t o r a g e tanks, a water-to-air h e a t exchanger, a water-

t o - a i r h e a t pump, an a i r distribution system and pump, valves,

piping and associated controls. Space heating is controlled by

a two-stage t h e r m o s t a t . When t h e r e i s a demand, s o l a r space h e a t i n g

can be a c c o r n p ~ i s h c d i n e i t h e r of two modes; d i r e c t l y or by t h e h e a t pump. Whcn the storage water temperature i s above 4 5 ' ~ , s t o r a g e

water i s r o u t e d directly t o a water-to-air heat exchanger, and heats t h e circulating air i n the hot air d i s t r i b u t i o n circuit. The water

flow is diverted f r o m t h e heat exchanger to a water-to-air heat

0

pump whenever the s t o r a g e water temperature i s below 45 C, on thc

assumption that dircct heating with 4 5 ' ~ water could c r e a t e occupant d i scornfort.

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The h e a t pump extracts heat from the s t o r a g e warer, and discharges

heat at a h i g h e r temperature to t h e hot a i r d i s t r i b u t i o n c i r c u i t . h

mixing valve tempers t h e h o t storage water with t h e cold r e t u r n to

p r o v i d e the heat pump with water w i t h i n i t s required temperature

range of 15't to 3 0 ' ~ . When t h e storage water temperature drops below

1 5 ' ~ , t h e s o l a r space h e a t i n g system is shut o f f and

an

electrical resistance Sackup h e a t e r in t h e air distribution system supplies t h e t o t a l space h e z t i n g load.

I n December 1977, the e l e c t r i c a l backup a i r h e a t e r was replaced

with an e l e c t r i c water h e a t e r t o take advantage of off-peak electric h e a t i n g . Electrical heat is added to storage tank 1 between m i d n i g h t

and 6 a.m. whenever the tank temperature drops below 3 3 ' ~ . T h i s

cnsurcs sufficient space h e a t i n g capacity in t h e h e a t pump mode f o r

t h e following day.

Service Water Heating Subsystem. - The s e r v i c e water heating subsystem

3

c o n s i s t s o f a 0.45 n preheat tank and conventional 0.27 m3 electric 130t water h e a t e r and tank. Hot water from the main solar storage t a n k is pumped t o an immersion heat exchanger in t h e preheat tank whenever t l ~ c preheat tank temperature drops below 4 3 ' ~ . In this way

c o l d feed water is preheated in t h e solar heated tank and piped into t h e e l e c t r j c h o t water h e a t e r which ~ a i s e s the water t o the desired discharge temperature of 4 3 ' ~ .

Monitoring System Description

The m o n i t o r i n g system included a Kaye Data Acquisition System 8 0 0 0 w i t h a magnetic tape r e c o r d i n g unit, a s e t of i n t e g r a t i n g heat

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and power transducers. The measurements taken by t h i s equipment

a r e listed i.n T a b l c I11 and sensor locations a r e shown in Figure 2 .

From O c t o b e r 1976 through March 1977 m o n i t o r i n g of t h e solar

h e a t i n g system was done with t h e electric eneTgy meters and t h e

Siemens i n t e g r a t i n g h e a t meters, which were usually r e a d once a

d:iy. The Siemcns meter i n t e g r a t e d t h e product of electrical signals from a displacement water f l e w meter

and

a thermopile t h a t measured the flow t h r o u g h , and the temperature d i f f e r e n c e across, an energy s o u r c e or an energy consumer.

F r o m A p r i l 1977 t h r o u g h April 1978 t h e Kaye d a t a l o g g e r was

used to automatically r e c o r d d a t a on magnetic tape every f i v e minutes. Shutdown o f t h i s monitoring system occurred frequently due to mornen- t a r y interruptions i n the electrical power service to t h e house.

An Epplcy pyranometer mounted at the same angle as t h e collector a r r a y measured thc t o t a l d i r e c t and d i f f u s e solas r a d i a t i o n . A model LO was originally i n s t a l l e d , b u t was replaced w i t h a model 8-48 on 9 March 1 9 7 8 .

The contribution o f the fireplace to space h e a t i n g was n o r measured directly.

An indication of t h e measurement accuracy estimated for t h e monitoring instrumentation is g i v e n in Appendix A .

SYSTEM THEliMAL PERFORhfAMCE SUMMARY

System thermal performance data a r e presented using t h r e e time s c a l e s ; h o u r l y , d a i l y and monthly. The monthly summary d a t a a r e presented here a l o n g w i t h some examples of hourly d a t a . D a i l y dntn, tabulated by month for t h e period April 1977 to April 1978 a r e

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i n Appcndix A .

The hourly data supply details of system temperature and energy p r o f i l e s while t h e monthly data display seasonal variations i n system b e h a v i o r . The d a i l y tables contain day by day performance infomatierl

and are the b a s i s for the monthly data.

Space Ileating Subsystem [Winter Ope~ation)

Hourly temperature and power p r o f i l e s f o r operation in t h e direct a n d h e a t pump space h e a t i n g modes a r e shown i n F i g u r e 3 and 4

respectively. The average storage water temperature during t h e direct

h c a t i n g mode cxample (23 t o 26 March 1978) was 3 8 . 9 ' ~ ;

ir

was o n l y

2 8 . h O c d u r i n g t h c heat pump mode example (1 to 4 January 1 9 7 8 ) .

With the exception of t h e energy required to r u n t h e pumps and f a n s ,

The s o l a r system was able to supply the t o t a l space h e a t i n g load from storage i n t h e direct heating mode example and 68 p e r cent in t h e heat pump mode example [i. e., a c o e f f i c i e n t o f performarlce of 5.1).

The temperature of tank 1 e x h i b i t e d a characteristic d r o p whcncvcr t h e s o l a r collection circuit p p w a s t u r n e d on in the morning. The drop i n tank 1 temperature was due t o e n t r y o f cooler

water drawn from tank 2 and circulated t h r o u g h t h e collectors. The

temperature r i s e across t h e collectors during the morning h o u r s was

l e s s than the temperature d i f f e r e n c e between t h e two t a n k s and,

consequently, t a n k 1 was cooled. A t t h e same t i m e , tank 2 w a s warmed by t h e water flawing from t a n k 1 to tank 2. During the non-collection

h o u r s , t h e temperature i n tank 2 g ~ a d u a l l y dropped a s warm watcr was

extracted from t a n k 1, passed through the direct h e a t i n g c o i f o r t h e h e a t pump evaporator, and r e t u r n e d t o t a n k 2 a s cooled w a t e r .

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T h c temperature profiles for tank I i n F i g u r e s 3 and 4 d i f f e r e d

s i g n i f i c a n t l l r because t h e o f f - p e a k e l e c t r i c h e a t e r was t u r n e d on

betwccn m i d n i g h t and 6 a . m - whenever tank 1 temperature dropped below

3 3 ' ~ , a n d it continued to operate until i t had raised the tank I

tenpcrature above 3 3 ' ~ . The r e s u l t i n g s h a r p r i s e in tank 1 temperature a f t e r midnight i s only a p p a r e n t in Figure 4 when operating w i t h t h c

h e a t pump.

The increase i n i n d o o r temperature on b r i g h t sunny days due to

passi-ve s o l a r h e a t i n g i s evident in b o t h Figures 3 and 4 . The s o l a r

e n e r g y e n t e r i n g t h e s o u t h f a c i n g windows on b r i g h t sunny days w a s

sufficient to h e a t the e n t i r e house f o r several h o u r s around noon, i n

January as well a s March. Initially, passive solar heat gain caused minor

overheating i n t h e rooms with s o u t h facing windows. The problem was

subsequently c o r r e c t e d by o p e r a t i n g t h e c e n t r a l h e a t i n g f a n to distribute the h o t a i r to Che remainder o f t h e house.

Scrvicc Water Heating Subsystem (Summer Operation)

F i g u r c 5 shows t h e hourly values of storage tank temperatures, s o l a r collection, and s o l a r energy supplied to the s e r v i c e water

h e a t i n g s y s t e m over a seven-day period in July 1977. The t o t a l scrvice water h e a t i n g demand f o r t h i s period was 295 M J , of which

hO p e r c e n t was supplied by s o l a r energy and the r e m a i n i n g 4 0 p e r

c e n t 11y thc e l e c t r i c hot water h e a t e r . Over the same period the

amount of s o l a r energy collected was 1468 MJ, which was 28 p e r c e n t o f t h e total s o l a r energy i n c i d e n t on the collector array. 'fie n c t

increase i n s t o r e d energy i n t h e t w o t a n k s was 105 MJ resulting in

0

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therefore, 80 per c e n t of t h e t o t a l solar energy collected was

lost t o t h e surroundings.

Ovcr-all System

A summary o f t h e system performance from October 1976 t o A p r i l 1978 i n terms of t h e monthly mean d a i l y values for each month of

m o n i t o r i n g i s given i n T a b l e s

TV

a E b ,

F i g u r e 6 shows the heat balance f o r t h e s t o r a g e subsystem from

October 1976 to April 1978 based on monthly mean daily energy values.

T h e energy from storagc contributing to space heating is n o t equivalent t o t h e solar contribution to space heating from December 1977 through

April 1 9 7 8 . During t h i s p e r i o d , t h e storage water w a s h e a t e d by t h e

s o l a r c n e r g y collected and by the aff-peak electrical h e a t e r . The

monitored value of energy supplied to the space h e a t i n g system from s t o r a g e , t h e r e f o r e , c o n s i s t e d o f electrical as well as s o l a r energy.

'Ille end-of-month values o f the average temperature o f t h e two

storage tanks are a l s o plotted on Figure 6 . A control malfunction

t h a t circulated f l u i d continuously through t h e collectors from 26

August 1977 to 5 September 1977, dropped t h e tank temperature from

6z0c t o 50.3°~.

F i g u r c 7 s h o w s t h e total h e a t i n g load profile from October 1976

t o A p r i l 1978. The solar contribution during r h i s period, w a s

a p p r o x i m a t e l y 4 1 p e r c e n t of t h e total spscc and service warcar. h e a t i n g r v r l k l i r r m e r r t which was less than the d e s i g n goal of G O t o 70 I,cr c p j l t .

Ilrc s o l a r contsibution t o t h e space h e a t i n g requirement was 51 p e r c e n t arid t h c s o l a r c o n t s i b u t i o n to t h e service u i l t c r ~ c q u i r c m c n t was 13 pcr cent.

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-

10

-

The low s o l a r c o n t r j - b u t i o n to s e r v i c e water h e a t i n g was partially d u e t o the failure o f t h e pum-p s t a r t e r s w i t c h c i r c u i t which prevented s o l a r s e r v i c e water prcheating from August 1977 to November 1977; and was also d u e t o t h e operational mode t h a t eliminated service water p r c h e a t i n g d u r i n g the winter months

in

favour of space heating. The

solas system provided 55 p e r cent o f the service water heating requirement when it was contributing t o the service water system.

One i m p o r t a n t f a c t o r t h a t adversely a f f e c t e d thc performance o f t h e s o l a r h e a t i n g system was the heat l a s s from t h e storage

t a n k s , e s p e c i a l l y from t h e uninsulated bottoms. From October 1976 to A p r i l 1978, the t o t a l heat Xass from storage was approximately 54 p e r cent of t h e t o t a l energy added to storage.

The minimum average d a i l y s t o r e d temperature w a s 1 2 ' ~ and

o c c u r r e d on 17 January 1977; t h e maximum temperature was BZOC and o c c u r r e d on 2 5 August 1977.

I n F i g u r e 8 t h e average power supplied by t h e space h e a t i n g

system on a d a i l y h a s i s is plotted a g a i n s t t h e d a F l y average temperature

difference between outdoor and indoor a i r f o r t h e 1977-78 heating s e a s o n , The s c a t t e r i n the d a t a is largely due to t h e v a r i a t i o n i n s o l a r radiation and occupancy effects including use o f t h e f i r e p l a c e . TIlc heat l o s s f a c t o r , r e p r e s e n t e d by t h e s l o p e ( 9 ) of the least squares

l i n e fit t o t h e d a t a shown in E i p r e 8a, i s 190 W/K. This indicates t h a t t h e t h e r m a l performance of t h e building envelope was a p p a r e n t l y b c t t e r t h a n t h e performance a n t i c i p a t e d i n t h e original desi.gn (i-e.,

260 W / K ) ,

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- I 1 -

with up to 5 M J / I I I ~ i n c i d e n t s o l a r r a d i a t i o n and anothe-r group

nf days w i t h h i g h e r levels of solar radiation. The l e a s t squares l i n e s fit to both groups of d a t a i n d i c a t e t h a t on average about 1 Kllr

l c s s spacc h e a t i n g power was used

on

those days with moTe than 5 M J J m 2

solar radiation. Since about 7 0 per cent of t h e h e a t i n g season days f c l l i n t o t h i s category, the average d a i l y benefit from passive solar g a i n was very roughly 65 M J .

The average daily energy supplied by t h e space h e a t i n g system

was approximaly 170 M J of which 89 M J was solar e n e r g y . The avcrage

d a i l y electrical consumption f o r lights and appliances w a s 104 M J

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I l u r i n g t h e year May 197'7 to Apsil 1978 approximately 62,900 M.T ($524 at $ . 0 3 J k \ h ) were collected from 240,000 MJ incident on t h e s o l a r collectors. Solar energy d e l i v e r e d to t h e l o a d s amounted to 21,600 MJ

( $ B H O ) and t h a t l o s t from s t o r a g e was approxirnatcly 43 ,000 M.1.

S o l a r e n e r g y supplicd 18,900 M to t h e J n e t space h e a t i n g l o a d of

36,000 HJ. Solar energy provided 2700

MJ

of 18,200 M J supplied to

t h e s e r v i c e wntcr heating subsystem. I t i s estimated t h a t passive

s o l a r g a i n s c o n t r i b u t e d roughly 14,060 MJ ($1151 to the g r o s s space h e a t i ng requirement.

SUBSYSTEM PERFOR11AKCE SUMMARY S o l a r Collection Sub?.-stem -

O v e r t h e 23 y e a r s o f operation, the solar collectors d i d not

experience any major problems related t o leakage, h o t spots, or

b r e a k a g e . 'rhcy d i d , however, experience recurring condensation

o n t h e inncr f a c e o f t h e cover g l a s s , c a u s i n g a r e s i d u e t o be lcft

on t h c i n s i d e of t h e g l a s s a f t e r t h e condensed water had evaporated. 'I71e c f f c c t of c o n d e n s a t j o n on collector performance h a s n o t been fully

d e t c r m i n e d . The moisture i n t h e collector d i d , however, cause c a r r o - s i o n of t h c temperature sensor on t h e absorber p l a t e , resulting in a

control malfunction w h i c h caused the collector pump T O operate continuously f r o m 26 August 1977 to 5 September 1977.

'rhc average collection e f f i c i e n c y between A p r i l 1977 and A p r i l

1 W 8 was 24 p e r c e n t , based on total available r a d i a t i o n . F i g u r e 9 shows two performance curves o f t h e Meadorwale s o l a r collectors.

CurxTc 1 was d c r i v e d from t h e instantaneous efficiency curve supplicd

h y t h e m a n u f a c t u r c r . Curve 2 i s t h e measured average d a i l y performance

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t o determine the collector characteristics, FR ( ~ a ) and FRUL.*

Over the normal working range o f t h e collector parameter

2

T i H . .

,

0.04 to 0.08 m 'K/IV)' the d i f f e r e n c e between the <I

i n s t a n t a n e o u s curve and the measured collector array performance curve was a s much as 12 percentage points. This would s u g g e s t t h a t

an instantaneous e f f i c i e n c y curve should be used with caution when

d c s i g n i n g and sizing a solar h e a t i n g system.

S t o r a g c Subsystem

From March 1977 to March 1978, a period in which the initial and f i n a l average t a n k temperatures were nearly t h e same, t h e h e a t

l o s s from storage was approximately 60 per cent of t h e t o t a l solar

energy collected and off-peak electrical energy added. In the w i n t e r

months, it was estimated that about 4 p e r c e n t of the storage h e a t

loss went i n t o t h e basement from the tanks, t h e r e b y c o n t r i b u t i n g to space h e a t i n g .

*

FR (ra) and F U represent t h e maximum efficien0y;of t h e - c o l l e c t o r R L

and i t s heat l o s s c h a r a c t e r i s t i c r e s p e c t i v e l y .

where

-ra = transmittance-absorptance product

F = h e a t removal f a c t o r

R

U = over-all heae l o s s coefficient

L

T. = collector inlet temperature

1

T = outdoor ambient temperature

a

(16)

Onc of t h e aims of t h c Mississauga s o l a r experiment was to

investigate t h e benefits derived from t h e use of d u a l storage t c ~ n k s . Thc improvements derived depend v e r y much on t h e heat l o s s c11ar;lctcrj s t i c o f t h e s o l a r collector used. A collector w i t h hig11

t t ~ c r m a l losscs would l l c n e f j t most from d u a l s t o r a g e t a n k s t l ~ a t provide xhc coldest possible water to the collector.

~ h c

following example

i s

intended

t o show t h e

improvement in

collection achieved i n the Meadowale experiment with d u a l tanks. Consider t h e performance d a t a for 1 0 J u l y 1977. The avcrage values

oF t : ~ n k Z temperature, ambient temperature, and solar r a d i a t i o n h e a t

2

f l u x d u r i n g t h e collection period were 5 1 . 3 ' ~ , 2 1 . 3 ' ~ ~ and 548 \V/m ,

r e s p e c t i v e l y . The c o r r e s p o n d i n g collector parameter was 0.055 rnZ

.

K/W. :lccording to t h e measured curve i n Figure 9 , the average d n j l y e f f i - cicnc>. o f t h e collector array was 3 2 per cent. A reduction o f 2 ' ~ i n t a n k 2 tcmpcrature would have i n c r e a s e d t h e d a i l y efficiency to 3 3 pcr

c c n t . From Nay 1977 t o April 1978, t h e m o n t h l y mean d a i l y temperature

d i f f e r e n c e between t h e t w o tanks averaged 2 ' ~ and seldom cxceeded 7 ' ~ .

{A temperature difference o f 1 4 . 5 ' ~ occurred on 20 December 1977, b u t

was Largely due to use of t h e off-peak heater.) To determine t h e worth

of t h e dual tanks rclative to a single tank, t h e increase i n collection

cfficjency must h e weighed against the added heat loss due t o a larger

storagc s u r f a c c area and t h e added csslt: of materials, piping and

c o n t r a l s

.

Sr~ace EIcatinr! Subsystem

"The controller f o r changing ovcr f r o m d i r e c t solar h e a t i n g mode

t o h e a t pump modc w e n t o u t o f adjustment d u r i n g the m o n i t o r i n g p e r i o d .

(17)

- J 5 -

of 4 5 ' ~ . By November 1977, however, t h e changeover had n o t o c c u r r e d

even though the storage temperature had f a l l e n to _{3 3 O ~ . T h e}_indoor thermal environment d i d

n o t

s u f f e r at this low source temperature.

As a result o f t h i s experience, the control was later s e t to changeover

3t

~ s ' c ,

permitting l o n g e r operation in t h e d i r e c t s o l a r heating mode. 'ale average coefficient of performance of the heat pump d u r i n g

t h e monitoring p e r i o d was 3 . 1 . Heat pq operation allowed solar cncrgy t o c o n t r i b u t e t o space h e a t i n g as s t o r a g e water temperatures bclow 35'~. Operation o f t h e s y s t e m below this temperature resulted i n reduced storage heat l o s s ( e s p e c i a l l y important with a h i g h s t o r a g e loss system), and increased collected energy.

S e r v i c e Water Heating Subsystem

The subsystem was designed so t h a t h o t water was pumped from s o l a r storage sank 1 to a heat exchanger immersed in t h c preheat t a n k uhencvcr t h e p r e h e a t t a n k temperature dropped below 4 3 ' ~ . T h j s meant t h a t t h e preheat pump would have operated continuously when s o l a r sto-

T a g e t a n k 1 temperature was less t h a n 4 3 ' ~ . The p r e h e a t system was, therefore, p e r m i t t e d to operate only during the months when t h e main storage tank t m p e r a t u r e exceeded 4 3 ' ~ . The solar contribution to t h e scrvice water heating requirement of 55 p e r cent during t h e period

A p r i l t o J u l y 1 9 7 7 was p r o b a b l y limited by standby losses from t h e

s c r v i c e water h e a t i n g tanks and by t h e preheat exchanger performance.

'The a n n u a l s o l a r contribution to service water heating from A p r i l 1977 t o March 1978 was only 1 8 per c e n t . T h i s low annual s o l a r contribution was due to a long shut-down of t h e p r e h e a t i n g

s y s t e m i n l a t e summer and e a r l y fall caused by a control malfunction,

(18)

Off-Peak Electric Heating Subsystem

Off-peak e l e c t r i c hearing o f f e r s the a d v a n t a g e of u s i n g

cluctricity a t t h o s e times when conv~ntional e l e c t r i c a l demands a r e low. Tt h a s t h e potential, t h e r e f o r e , f o r reducing the peak capacity o f t h e electrical utilities. T h e merit o f such a hack-up e l e c t r i c

h e a t i n g s y s t e m may be marginal, however, when used w i t h a high-loss s t o r a g e subsystem.

The Meadowale storage subsystem lost about 20 per cent of t h e c n e r g y added to storage durlng the w i n t e r months. Because o f t h i s

h i g h storage l o s s , it was estimated t h a t t h e off-peak electric h e a t e r

consumed 17 per c e n t more electrical energy than a c o r ~ v e n t i o n a l

clectric back-up system to satisfy t h e same space h e a t i n g demand. Future Designs

Monitoring this solar system h a s made it apparent that a s i g n i f i - c a n t improvement i n t h e r m a l performance should b e p o s s i b l e by making

some relatively minor changes to t h e system d e s i g n .

The mosr significant of t h e s e would be t h e reduction of t h e sto- r a g e subsystem h e a t l ~ s s . It i s estfmated that a n i d e a l i z e d storage t a n k ( a r i g h t circular cylinder with no p i p i n g connections), insulated

2

t o R R . 5 (m * K / M ) , located in a room at 2 0 O ~ and operated a t t h e sane temperature as t h e Meadowvale s t o r a g e tanks, would have an average

Jnily h e a t loss o f l e s s t h a n 1 0 M J . This is approxim:ltely one t p n t h

oi' tirc observed avcrage d a i l y l o s s o f 106 MJ. T'hc rrduced t n n l i Io.-r; 1 1 i llcrease tank temperature. T h i h i g h e r tank temperature would make

II!C?I-C energy avai1;lble to t h e laads b u t it would a l s o reduce c-ullt-cI ion

(19)

- 1 7 -

D u r i n g t h e monitoring p e r i o d the changeover from dlrect s o l a r

h c a t i n g mode to h e a t pump mode was controlled by tank 1 temperature

h c i n g c i t h e r g r e a t e r than o r less t h a n a preset: temperature. Since

t31c set-point temperature must h e chosen f o r peak h e a t i n g l o a d condi-

t i o n s , it will u s u a l l y be higher than necessary. The use of a two-

stage thermostat to control the changeover should allow a larger

l j r a p o r t i o n of t h e h e a t i n g energy to be delivered in t h e d i r e c t mode

t t l e r c l ~ y increasing the solar energy contribution.

S i z i n g the water to a i r heat exchanger to c a r r y the load down

to a 30'~ e n t e r i n g water temperature would eliminate t h e need for the

c o n t r o l s and hardware which are used to temper water e n t e r i n g the

h ~ a t pump t o this temperature. The main b e n e f i t of this change would

be t h e system simplification and associated c o s t r e d u c t i o n .

The a n n u a l s o l a r contribution t o t h e service water hcating r e q u i -

rement could be improved by changing t h e system control to one that

activatres the p r e h e a t pump whenever the preheat tank temperature falls

below t a n k L temperature. A r e d u c t i o n in t h e heat l o s s from t h e main storage tanks would a l s o improve the contribution to service water

heating. Although not i n keeping w i t h t h e original design concept

of t h e Meadowvale solar experiment, preferentially supplying s o l a r

cncrgy to t h e service water heating system should increase t h e over-

a l l utilization of t h e s o l a r h e a t i n g system even though t h e solar

encrgy d e l i v e r e d to space may be reduced slightly.

I d e a l l y , the s e r v i c c water heating system should have sufficient

h e a t exchange capacity to maintain t h e preheat water temperature

c l o s c t o t h e source temperature. It should also be designed to

n ~ i ~ i i i ~ : i ~ . r s t n v d b y losses and allow the solar system to make u p these losses.

(20)

'The bleadowvale Solar Experiment h a s been s u c c e s s f u l in providing much u s e f u l i n f o r m a t i o n on the performance o f a solar system and i t s components i n t h e Canadian climate. Over a period o f 1 9 months, from Octohcr 1876 t h r o u g h April 1978, t h e s o l a r h e a t i n g system performed

s : l t i s f ; i c t o r i l y , but t h e performance could be improved significantly by seducing t h e s t o r a g e h e a t l o s s , and making o t h e r syscern d e s j g n

ch:~ngc*s. T h j s solar h e a t i n g system is considered to h e an e a r l y

prototype, and as such, an economic analysis b a s e d on i t s c o s t and

pcrfol-mance would be inappropriate. Information o b t a i n e d by ~ n o n i t a r i n g

t h i s systcm indicates t h a t f u t u r e designs w i l l deliver more u s c f u l

c n c r g y w h i l e employing significantly l e s s hardware.

T h e authors gratefully acknowledge t h e contributions o f

(21)

REFERENCES

D.P.

Lorriman. Mississauga Solar House Development P r o j e c t . Paper 111-37, Proceedings of t h e SESCI Conference, The Potential of S o l a r Energy f o r Canada, O t t a w a , Ontario, 1975.

. J , M . B e l l , 0. Lorriman. Off-Peak Electrical Backup Experience

.in t h e Meadowvale Solar Experiment. Paper 3 - 1 - 7 , Vol. I ,

P r o c e e d i n g s of t h e SESCI Conference, Renewable Alternatives,

London, O n t a r i o , August 1978.

J . K . S a s a k i . Mississauga Solar House, P r o c e e d i n g s of t h e CCMS/ISES Conference on the Performance of Solar Heating and Cooling Systems, Dusseldorf, West Germany, April 1978.

B . E . Sibbitt, H . Jung and D. Lorriman. Performance of the

Meadowvale Solar Home. Paper 3-1-6, Vol. 1, Proceedings of t h e SESCI Conference, Renewable Alternatives, London, O n t a r i o , August 1978.

I,. Lorsiman. Meadowvale Solar Experiment Performance Kcpert.

Paper CI28Mpm14, Proceedings of t h e SESCI Conference, Solar Energy Updatc ' 7 7 , Edmonton, Alberta, 1977.

D. L ~ r r d m a n . F i r s t Annual Repart, Meadowvale Solar Experiment Monitoring Program. C o n t r a c t No. 932-556J0621, March 3 1 , 1978.

D. Lorsiman. Second Annual Report, Meadowvale Solar Experiment Monitoring Program. C o n t r a c t No. 032-556/0621, February, 1979. C.T. Trewartha. An Introduction to Climate. McGraw-Hill

Book Company, Toronto, 1968.

W.C. Brown. Mark

XI

Energy Research P r o j e c t , Comparison of

S t a n d a r d and Upgraded Houses. National Research Council of Canada, D i v i s i o n o f Building Research, Building Research Note 160, June 1980.

(22)

(23)

T a b l e I 1 S o l a r System S o l a r C o l l e c t o r Total g r o s s a r e a T o t a l a p e r a t u r e a r e a T h e r m a l p e r f o r m a n c e a s s u p p l i e d b y m a n u f a c t u r e r F " T C X ] , F I U L C o v e r A b s o r b e r a n d t u b e s I n s u l a t i o n S t o r a g e B u m b e r o f tanks D i m e n s i o n s o f e a c h t a n k T o t a l volume o f w a t e r in two t a n k s I n s r i l a t i o n 0 . 7 6 , 6 . 3 5 w/~'-K 0 . 7 3 , 6.1 w / r n 2 ~ # S i n g l e s h e e t , law-iron g l a s s C o p p e r , with s e l e c t i v e c u p r i c o x i d e c o a t i n g 6 . 3 em glass f t b e r 2 2 . 7 6 rn x 1 . 3 1 m x 2 . 7 4 m d e e p 18 m 3 1 0 crn p o l y u r e t h a n e a r o u n d a l l s i d e s ( R = 4 . 2 ) , a d d i t i o n a l 7 . 6 c m p o l y s t y r e n e b o a r d s ( R = 2 - 6 ) a d j a c e n t t a e x t e r i o r wall; 2 3 crn g l a s s - f i b e r p l u s 7 . 6 c m p o l y s t y r e n e b o a r d o n t o p ( R ~ 8 . 6 r n 2 * K / w ) B e a t T r a n s f e r S u b - S y s t e m s S p a c e h a t i n g h e a t e x c h a n g e r !Ica t p u m p { w a t e r - t o - a i r ) 4 row w a t e r s o i l with c a p a c i t y t o r a i s e 0 . 5 m 3 / s o f a i r f r o m 2 4 O C to 4 3 . 3 O ~ with 0 . 6 4 l / s o f w a t e r e n t e r i n g a t 4 9 " ~ 15 k w h e a t i n g c a p a c i t y w i t h 0 . 5

m v s

o r a i r e n t e r i n g a t 2 4 O ~ a n d 0 - 6 4

11s

of w a t e r e n t e r i n g at 15 . ~ O C A u x i l i a r y E l e c t r i c Heaters S i d e - a r m h e a t e r (tank I) S e r v i c e - w a t e r h e a t e r 2 0 kW c a p a c i t y 4 . 5 kW c a p a c i t y

(24)

-

bottom

of

tank

#2

-

i n d o o r - outdoes

-

c o l l e c t o r s u p p l y

water

water

- t o t a l s o l a r r a d i a t i o n incident on

plane

o f c o l l e c t o r s

(25)

(26)

m-A -a r o w -d la C sl m - A rd

=

a m u = + a

(27)

(28)

PUMP

"

INSERVlCEFROMQECEMBER1977

*' _REMOVED_{FROM SERVICE}_{I N}_DECEMBER₁₉₇₇

F I G U R E 2

(29)

50LAR COLLECTION SOLAR 6 NC 1 DENT

SOLAR C OPLECTED

SOLAR TO

SPACE

HZAT I NG

IN DIRECT MODE

MAR 2 3

M A R

24 MAR 25 M A R 26 1978

F I G U R E 3

A V E R A G E H O U R L Y V A L U E S OF T E M P E R A T U R E A N D P O W E R I N THE

D I R E C T

S P A C E H E A T I N G M O D E

(30)

SOLAR INCIDENT

SOLAR COLLECTED

TOTAL (STORAGE & HEAT

PUMP)

LOAD MET B Y STORAGE ! SOLAR &

J A N 1 J A N 2 J A N 3

A V E R A G E H O U R L Y V A L U E S O F T E M P E R A T U R E AND

(31)

(32)

(33)

(34)

0

( a ) A L L D A T A

7

h

I

3 I

I

1 I

1

- -0- DAl LY l NCl DENT SOLAR RAD l AT1 ON

c

5 M J / ~ '

-

DAILY I N C I D E N T S O L A R R A D ~ A T ~ O N > ~ M ~ / ~ ~ -

-

I

A V E R A G E D A l L Y l N D O O R TO O U T D O O R T E M P E R A T U R E D I F F E R E N C E , K

I

1 I

1

I b ) EFFECT O F S O L A R R A D I A T I O N I N T E N S I T Y

-

AVERAGE HEAT LOSS FACTOR = SLOPE = 190 W/K

- - - - + - _- 1 1

I

F I G U R E 8 S P A C E H E A T I N G P O W E R , 1977-78 H E A T I N G S E A S O N

(35)

M A N U F A C T U R E R ' S I N S T A W T A N E O U S C O L L E C T O R E F F l C I E N C Y C U R V E 8 0

_---

M E A S U R E D A V E R A G E D A I L Y C O L L E C T O R A R R A Y E F F I C I E N C Y C U R V E

se

DAILY

PERFORMANCE

SUMMARY

A d e s c r i p t i o n and expected error of solar system and environmen-

l a 1 parameters i s contained in Table A l . Tables of mean and integrate^'

d a i l y v a l u e s of t h e s e parameters follow in Table 62 t h r o u g h A14. The

t a b l e s cover t h e period, April 1977 to April 1978, when t h e Kaye d a t a i ~ c q u i s i t i e n system w a s the prime source of recorded d a t a . Monitoring

system shutdown occurred q u i t e f r e q u e n t l y because of momentary e l e c t r i c

3 u w e r i n t e r r u p t i o n s and, consequently, t h e r e were s e v e r a l days w i t h no

monitored data or w i t h incomplete data. Only those d a y s with more thai:

21.5 h o u r s of monitored data a r e

shown

i n

the t a b l e s . The monthly mean

d a i l y q u a n t i t i e s t a b u l a t e d are based on t h e average of o n l y those days shown.

Negative v a l u e s o f s o l a r energy collected were due to operation

of t h e collector pump when t h e collector return water temperature was l e s s than the supply temperature. Such o p e r a t i o n occurred a t the begin- n i n g and cnd o f some d a i l y collection p e r i o d s and r e s u l t e d in dissipa-

t i o n of stored energy to outdoors.

The t a b u l a t e d values o f s o l a r energy collected from 26 A u g u s t

1977 t o 5 September 1977 were

lower than

they should have been due t o a c o n t r o l malfunction caused by corrosion of t h e temperature sensor on t h e absorber p l a t e . Because o f this control malfunction, t h e

collection pump operated continuously over an eleven-day p e r i o d ,

d i s s i p a t i n g energy from storage at night and d u r i n g overcast days. The absence of s o l a r service water p r e h e a t i n g d u r i n g the late summer and fall of 1977 was due t o t h e failure of a starter s w i t c h

(37)

A 2

i n d i c a t o r light for the service water h e a t i n g p m p on 22 July 1977. The f a u l t was not c o r r e c t e d until mid-October when it was decided to leave the service water p r e h e a t i n g system turned off.

The electric kWh meter measuring t h e service water electrical consumption was inoperable for the entire month of April 1978. An estimated v a l u e o f 51.8 MJ/day was, t h e r e f o r e , introduced in t h e

(38)

T a b l e A 1 D e a c r f p t i o n and E x p e c t e d E r r o r of S o l a r S y s t ~ m a n d ~ n v i r o n m e n t a l Parameters L l s t e d i n M o n t h l y S u m m a r y T a b l e s C O L U M N H E A D I N G D E S C R I P T I O N

11 1

DAY Day o f t h e y e a r A M B I E N T C O N D I T I O N E X P E C T E D 5: E R R O R

-

( 2

>

A V G . TAME. D a i l y mean a m b i e n t t e m p e r a t u r e

C

3 S O L A R I N C D . D a i l y t o t a l s o l a r e n e r g y i n c i d e n t o n collector array tilted a t 6 0 ° f r o m h o r i z o n t a l S O L A R C O L L E C T I O N ( 4 C O L L . D a i l y total s o l a r energy c o l l e c t e d

( 5

1

E F F C Y . Daily solar collection efficiency

(column ( 4 ) / c o l u m n (3)xlQO)

E N E R G Y I N P U T S T O S P A C E H E A T I N G SYSTEM

1 6 ) " TOTAL ENGY. D a i l y t o t a l e n e r g y (solar & e l e c t r i c a l )

s a p p l i e d t o s p a c e h e a t i n g s y s t e m 1 7 ) DIR. STOR. D a L l y t o t a l s t o r a g e e n e r g y ( s o l a r a n d o f f - p e a k electrical) s u p p l i e d d i r e c t l y f o r s p a c e h e a t i n g ( 8 1 E . P . S T O R . D a i l y t o t a l s t o r a g e e n e r g y (solar a n d off-peak electrical) s u p p l i e d to h e a t pump f a r space h e a t l n g C S I * H . P . E L E C . D a i l y t o t a l e l e c t r i c a l energy r e q u i r e d b y h e a t pump ( c o m p r e s s o r a n d f a n )

(10) PUMP & F A N S D a i l y t o t a l e l e c t r i c a l energy r e q u i r e d

b y s o l a r a p a c e h e a t i n g c i r c u i t p u m p ,

s p a c e h e a t i n g d i s t r i b u t i o n f a n s w h e n

n o t in solar heat pump m o d e , and

solar c o E l e c t i o n circuit pump ( s e e

n o t e I)

E N E R G Y INPUTS T O DOMESTIC N O T WATER SYSTEM - -

(11)* T O T A L E N G Y . D a i l y t o t a l energy (solar & e l e c t s l c a l ) _{f 2 %}

s u p p l i e d t o s e r v i c e w a t e r system ( 1 2 ) S T O R . D a i l y t o t a l s t o r a g e energy ( s o l a r and off-peak e l e c t r f c a l ) s u p p l i e d 2 0 s e r v i c e - 5 5 X w a t e r s y s t e m (13)* R . H . E L E C . Daily t o t a l e l e c t r i c a l s e r v i c e -water +0.5X r e s i s t a n c e heating e n e r g y ( 1 4 ) P U M P E L E C . D a i l y t o t a l e l e c t r i c a l e n e r g y r e q u i r e d b y s o l a r s e r v i c e water c i r c u i t p u m p a r d kl. 5%: solar c a l l e c t i o n c i r c u i t pump ( s e e n o t e 1)

(39)

Table ( c o n t i n u e d ) _EXPECTED COL!IMN H E A D I N G

DESCRIPTISN

S T O R A G E ( 1 5 ) A V G . T T K l

(161

A V G .

TTK2

117)

OFFPK

HTG.

( 1 8 ) NET STOR.

(19)

TK.

LOSS ELECTRICAL / 2 0 ) * * DOM.

USAGE

*

On a m o n t h l y b a s i s . daily b a s i s

%

E R R O R

Daily mean No. 1 s t o r a g e tank

₊

t e m p e r a t u r e - 0 . 2 O C

D a i l y

mean

No. 2 s t o r a g e tank

4-

t e m p e r a t u r e

- 0 . 2 O C

Daily t o t a l e l e c t r i c a l energy

s u p p l i e d

t o

s t o r a g e by

the

20.5% off-peak heater

Daily total

net

storage energy

in b o t h t a n k s 220%

D a i l y total heat loss f r o m both

S e p t e m b e r .

N o t e 2

T h e d a t a

a r e

t a b u l a t e d w i t h

one

f i g u r e following t h e decimal

p o i n t

although i n most

c a s e s

all

o f t h e f i g u r e s a r e n o t

~ O O O Q O ~ O O m I k a 7 h l Z 4 Q L T S 1 W I C W - V I I - a - U T U h > u m w u s - v

(43)