NRC 14-House Solar Demonstration Program: first-year performance data

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ISSN 0701-5232 A r - 7

NRC 14-HOUSE SOLAR DEMONSTRATION PROGRAM: FIRST-YEAR PERFORMANCE DATA by

W.E. Carscallen and B.E. Sibbitt

During 1976177 the NRC funded t h e d e s i g n and

installation of 14 active solar space-heating systems in single-family homes as part of its solar demonstration

program. Both air- and liquid-based systems were

installed in new and e x i s t i n g dwellings. A description of the houses and systems i s provided in this Note as well as a limited performance summary of s i x of t h e houses. Problems associated with d e s i g n , c o n s t m c t i o n

and operation of the project houses are also discussed.

OBJECTIVES

The proje,ct was designed:

1. to provide quantitative information on t h e performance of solar

h e a t i n g systems in Canada in order to develop a d a t a base f o r the

r a t i o n a l design of solar h e a t i n g systems and the verification of computer simulation techniques;

2. to gather information an the difficulties encountered in integrating solar heating systems in residential construction;

3. t o stimulate interest w i t h i n the construction industry and among the general public i n s o l a r energy.

PROJECT DESCRIPTION

The fact t h a t t h e 14 houses were scattered across Canada exposed them to a very wide range of climatic conditions and demonstrated t h e concept of solar heating t o a large number o f people. It also, however, made the g a t h e r i n g of d a t a more difficult. The systems were designed to provide 30 per cent o r more of the space heating load and, in some cases,

a portion o f the domestic hot water load. Seven were built with liquid-

heating collectors and an equal number with a i r - h e a t i n g collectors. The liquid systems used water as t h e heat storage medium; t h e a i r systems used rock, except for one which used a sodium sulphate decahydrate l a t e n t heat storage system. Nine systems employed factory prefabricated

employed commercially-produced absorber p l a t e s . Heat pumps ware used in

two of the liquid systems in a t t s e r i e s ' ~ c o n f i g u ~ a t i o n to upgrade the energy i n storage when its temperature was t o o law f o r direct solar h e a t i n g . Two o t h e r systems, one l i q u i d and one a i r , employed heat pumps

in a !'parallelt' configuration as auxiliary h e a t i n g systems. Tables I

and IT describe the houses and systems.

Contracts for the i n s t a l l a t i o n o f s o l a r systems were l e t d u r i n g t h e

t h i r d quarter of 1936, and 13 of t h e 14 houses were substantially

complete by December 1977. Installation of monitoring equipment by the

NRC in the first twelve houses completed took place between July and December of 1977, but the house i n White City, Saskatchewan, was

destroyed by f i r e in February 1978, leaving only eleven ( 1 ) .

?he groups and individuals involved in the design, constructkon and

installation o f t h e solar systems included solar system designers,

building engineering consultants, building contractors, university professors and interested non-technical people. In f u l f i l l i n g t h e i r

contractual o b l i g a t i o n s many o f them encountered problems such as

contract negotiation d e l a y s , r a p i d l y increasing m a t e r i a l and labour costs,

delays i n equipment d e l i v e r y , and bad weather. Problems associated with

the s o l a r systems were also numerous. THEEWIAL PERFORMANCE SUMMARY

Data on t h e thermal performance of t h e remaining 11 houses monitored

d u r i n g t h e 1977178 heating season are incomplete owing to various

problems w i t h t h e solar h e a t i n g systems, the monitoring equipment and human error i n t h e recording and transmission of raw data. Some of the

solar h e a t i n g system problems are examined l a t e r in this Note and a

record of the monitoring problems is a l s o available [I).

Data for six of the houses are now presented, b u t caution is

recommended in interpreting them. Table I11 shows t h e integrated values of collected solar energy, solar energy delivered t o space, and auxiliary

energy utilized [ f o r approximately one-month p e r i o d s ) . The l a s t three columns are estimates of Fraction Solar (i.e., t h e proportion of total space and service waxer heating demand s a t i s f i e d by s o l a r energy) based on three assumptions of how heat l o s s from storage contributes to space

heating requirements. Column 4 fs F r a c t i o n S o l a r , assuming t h a t a l l

storage losses go into the ground; hat is, that there i s no space

h e a t i n g c o n t r i b u t i o n from s t o r a g e loss. Column 5 i s Fraction Solar

assuming t h a t a l l storage losses contribute t o space h e a t i n g . C o l m 6

is Fraction Solar assuming that the f r a c t i o n of storage losses

c o n t r i b u t i n g to space h e a t i n g is proportional to t h e ratio of t a ~ k surface area exposed indoors to t h a t exposed outdoors and ta t h e temperature differences across t h e walls of t h e storage unit. It is

clear t h a t t h e apparent worth o f a s o l a r system with high storage losses

The figures in Table 111 i n d i c a t e some o f t h e problems associated with system d e s i g n and operation. House No. I I i n Calgary, f o r

example, was a model home and used approximately 800 kWh/week for lighting and e l e c t r i c a l equipment. The l i g h t s acted as a secondary heat source and reduced the demand on she s o l a r space heating system.

As a result, much af the solar energy collected was e i t h e r dumped or l o s r from s t o r a g e , T h e results in Table TI1 do n o t c o n s i d e r fnternal gains from l i g h x s as part of the auxiliary h e a t i n g . I f 600 klrrhlweek f o r lighting is included as part of the auxiliary heating, the

Fraction Solar (with a l l storage lasses going to outside) would be t h e

values shown in brackets.

House No. 5 in Lava1 had a similar problem. Auxiliary space heating was provided by electrical baseboard heaters controlled by

separate thermostats in each room; that is, a u x i l i a r y h e a t i n g could be

demanded independently of t h e solar space heating system. Many o f the

electric-heater room thermostats were set h i g h e r than the s o l a r h e a t i n g thermostat, thereby reducing the demand on it, so t h a t much of t h e c o l l e c t e d solar energy was l o s t from s t o r a g e without benefit.

Fox systems t h a t incorporated domestic h o t water

(DMW)

the solar fraction of the DWV heating requirement was small and i s n o t

given. The reason for the small c o n t r i b u t i o n was not r e l a t e d to the system performance but t o Its utilization. I n houses No, 1, 8 and 11,

h o t water usage was minimal because these houses were e i t h e r unoccupied f o r most o f t h e monitoring period o r used as model homes,

me

mainly due to the large heat loss from storage. The storage unit was

over-sized and completely outdoors. Significant air leakage was a l s o observed at d i f f e r e n t p o i n t s i n t h e ducting system.

As there are still many problems ta be solved in these s o l a r systems it is i n a p p r o p r i a t e to draw conclusions about their p o t e n t i a l performance from the data presented.

OPERATTOMAL EXPERIENCE

This Note will identify the areas of design, installation, and

operation where greater care must be exercised in o r d e r to avoid t h e problems encountered in t h e 14-house project, a l t h o u g h t h e experience

upon which the observations a r e based is very l i m i t e d . Suggested solutions have not been t e s t e d and may introduce new problems. Design Stage

One area where greater caye is r e q u i r e d is -In the d e s i g n stage.

The f i n a l system design should take i n t o account the l e v e l o f skill

available from local trades and the availability sf materials and

change a design rather than s p e c i f y a material or p a r t t h a t is not available locally. Similarly, the a b i l i t y or willingness of local

trades to work with unfamiliar materials or a new technology should be determined p r i o r to approving a d e s i g n .

Many problems related to instal1z:ion difficulries can be foreseen and eliminated if proper lay-out drawings are prepared. Difficulties to

be avoided include unnecessarily long piping runs, details leading to a i r locks in piping, inadequate space f o r equipment, and t h e necessity

for custom-built ducts because standard d u c t s do n o t fit. Careful

planning and scheduling at the d e s i g n stage i s particularly important i f

a solar system is t o b e r e t r o f i t t e d to an existing building. P o t e n t i a l

problems must be anticipated before the b u i l d i n g structure is modified. It is a l s o necessary to ensure t h a t p a r t s and materials a r r i v e at t h e

site when scheduled, Otherwise a building can be left exposed to the elements without proper covering.

Comwonent Problems

The major area where care is required is in t h e d e s i g n and

installation of subsystems o r components.

Absorber. Site-fabricated collecrors should be designed so t h a t

materials i n t h e sizes available commercially can be used f o r the absorber. This will r e d u ~ e the necessity for cutting and welding

on-site. The following comments relate to both site-fabricated and factory pre- fabricated collectors:

- The use o f d i f f e r e n t materials for the absorber and flow tubes will result i n thermally-induced flexing of t h e absorber assembly unless the centres of movement of t h e tubes and absorber are

common.

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absorber should be kept to a minimum so t h a t the ratio o f

"ef f e c t i v e 7 ' to " g r o s s f h d l l e c t o r area remains h i g h .

- Insecure mounting of the absorber in t h e collector housing can lead to c o n t a c t between the two, resulting in high heat losses to the housing and thus to outdoor air.

- The application o f selective c o a t i n g under f a c t o r y conditions can

b e difficult. Tt should, therefore, n o t _{be amempted on} site-fabricated collectors.

Glazing,. Adequate edge clearance must be provided between the g l a z i n g

clearance will cause the g l a z i n g to bow when it becomes warm. This may reduce the air space between double g l a z i n g and between the

absorber and glazing material. Excessive bowing can cause t h e glazing to touch The absorber, which may then remove some of t h e

absorber coating or melt t h e g l a z i n g (if p l a s t i c ) . Some g l a z i n g materials will crack when subjected to repeated thermal cycling. Even when clearance is provided, thermal movement of the glazing

material can cause t h e edge sealant or g a s k e t to work free of zhe

joint, thereby causing a loss o f s e a l .

Moisture. Resistance to water leakage must be addressed in the

collector design. Glazing stops t h a t t r a p snow and r a i n r a t h e r than

shed them away from the g l a z i n g seal must be avoided. Careful

a t t e n t i o n must be paid to the f l a s h i n g d e t a i l s a t t h e head of the

collector array.

Condensation will occur on t h e i n s i d e of most collectors.

Attention must be paid, t h e r e f o r e , in t h e collector design t o

providing i n t e r n a l paths that will Lead condensate away from the absorber and i n s u l a t i o n and to the d r a i n holes. Vent h o l e s may be

required to dry the inside sf collectors. General Comments.

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need for o n - s i t e r e p a i r and replacement sf faulty c o l l e c t o r s . The collector d e s i g n and installation detail should allow for easy repair o r removal of a particular collector in a collector a r r a y . If n o t , t h e replacement of collectr>rs w i l l be

time-consuming and expensive.

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hoist collectors or their components to a r o o f , c o r r e c t hoisting procedures must be followed t o avoid damage from buckling.

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mounted on t h e roof with s u f f i c i e n t clearance between collectors.

Otherwise, subsequent thermal movement will cause piping joint

failure and leakage.

- For site-fabricated collectors, workmen must be i n s t r u c t e d to clean t h e i n s i d e of the collector b e f o r e the cover is installed.

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collector manifold o f liquid systems must be located above the h i g h e s t p o i n t in t h e piping t o a v o i d a i r l o c k s . V e n t s should a l s o

be accessible and kept free of piping insulation during construction.

- Thenno-siphoning, or flow reversal, through a cool collector can be a problem in bath air and liquid systems. Continuous

thermo-siphoning will dissipate s t o r e d energy and may cause freezing of heat exchangers in t h e system. One-way valves and t i g h t back-draft dampers are required to avoid this problem.

11. Storage

Although n great deal of attention has been given to t h e

collection of solar energy, l e s s has been given to the d e s i g n and installation o f t h e heat storage unit. The literature

12)

recommends that short-term storage units have the following sizes: f o r air, 0.2 m3/m2 of collector; for water, 0.09 m3/m2 of collector.

In the c u r r e n t p r o j e c t the heat storage units, with two

exceptions, were from two to f i v e times oversized, Such

oversizing should be avoided because it represents an unnecessary

expense and reduces t h e usability o f the collected solar energy,

especially for space h e a t i n g . Whenever it becomes necessary to

reduce the area of the c o l l e c t o r array during design ar installation,

t h e storage size must be educed as well.

The h a a t storage unit should be located i n d o o r s and, i f p o s s i b l e , away from e x t e r i o r w a l l s . Adequate insulation must be provided all round, including the bottom. If a storage unit must be placed adjacent t o an exterior wall, additional insulation should be provided at the interface. If it must be located

outdoors, the insulation round the unit should be much greater

than t h a t provided for an indoor unit, and it should a l s o be protected from w e t t i n g by r a i n and condensation.

111. A i r Handlers and Dampers ( A i r Systems Only)

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storagc and space, and space and collectors.

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overloading.

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d u c t i n g should be taped and sealed during installation because

it is very difficult to locate and rectify l e a k i n g components once installation i s completed. A11 dampers should be properly

IV. Controls

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placement o f sensors. On-off controllers were used in a l l b u t one project to control s o l a r collection and space heat

distribution.

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schematic drawings o r instructions f o r testing and r e p a i r i n g

the devices are provided. This will avoid lengthy shut-dorm of

the system while the device is returned to t h e manufacturer for r e p a i r .

- It is necessary t o ensure t h a t t h e control l o g i c i s failsafe;

t h a t is, if the s o l a r controller f a i l s it should not prevent t h e operation of the auxiliary h e a t i n g system.

- A c o ~ l t r a l mode that requires the storage temperature t o reach a minimum before auxiliary h e a t i n g i s a c t i v a t e d should be avoided

as this can lead to uncomfortably low house temperatures or poor

utilization of s t o r e d energy. The use o f separate thermostats to control solar heating and auxiliary heating independently

should be avoided, as this can cause t h e auxiliary to operate at a l l times.

- Care must be exercised i n t h e placement o f c o n t r o l sensors to ensure t h a t the desired temperatures are measured.

CONCLUSIONS

Experience w i t h 14 s o l a r houses has demonstrated many problems

that can b e encountered in executing an operational solar h e a t i n g system

i n a house, especially when the d e s i g n , component supply, and

installation are separate responsibilities. Site-fabricated collectors presented problems quite d i f f e r e n t from those associated with f a c t o r y - fabricated collectors; and retrofit applications of solar h e a t i n g presented problems that were different from those encountered in new

construction, A major shortcoming i n t h e d e s i g n of many of t h e systems

was the sver-sizing and under-insulation of t h e h e a t s t o r a g e unit.

Another major problem was related to poor choice of control mode for the

space heating system. Inadequate installation drawings and inadequate site supervision contributed to installation problems. Finally, one

a u t h o r i t y must assume responsibility f o r ensuring t h a t t h e system is operational initially, and f o r subsequent maintenance.

The solar experimental homes have shown t h a t utilization of solar space heating systems requires well engineered designs incorporating

proven components installed by competent, well-trained tradesmen. It does no': aCpea? to be a f i e l d far the enthusiastic but unqualified individual.

REFERENCES

1. Rasakat, S.A., W.E. Carscallen, and B.E. Sibbitt, NRC Salar Monitoring Program. SESCI Conference, Renewable Alternatives,

London, Ontario, 1978.

2. Hollands, K.G.T., and J.F. Orgill, Potential f o r Solar Heating in Canada. Waterloo Research Institute, University of Waterloo, Report

C m u -U "

1 2 3

Collected Dcl ivered Auxi 1 iary %Tar S l a r Energy Energy Energy

4 5 b

Fraction S o l n r o f Spacc lleating

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Lasses to Losses t o Estimated Outside Inside Ac tua 1 House No. Period (1977/783 Halifax. N . S . TOTAL Fredericton. N.B. Lava1

.

Thunder Bay, ant.

N.A. TOTAL Celgary, h l t a . 17/2 - 3 1 3 4 / 3 - 31/3 1/4 - t 8 / 4 29/4

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