Techniques for estimating the energy consumption of houses

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Techniques for estimating the energy consumption of houses

Sander, D. M.

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Ser

TH1

N21d

no.

1202

c.

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G

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-National Research

Conseil national

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Council Canada

de recherches Canada

TECHNIQUES FOR ESTIMATING THE ENERGY

CONSUMPTION OF HO

by D.M. Sander

Reprinted from

CIB 83

The 9th. CIB Congress, Stockholm, Sweden

Energy Technology and Construction, Vol.

3a

p. 201

-

212 DBR Paper No. 1202

Division of Building Research

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7111

Title of the

peper

TECHNIQUES FOR ESTIMATING

THE ENERGY

CONSUMPTION OF HOUSES

Author

D.U. Sander

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Division of Building Research, National Research Council Canada

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wards

houses; heating energy; calculation methods

Summary

Tht evaluation of a house deaign requfrea a ltthod for cstiauting the effect of various design features on the heating energy requirements. Such a method must account for the following: heat loee, primarily by conduction, through the exterior envelope; heat loss due to exchange of indoor air and outdoor air; heat loee to the earth through basement walls and floor; heat gain from occupants and appliances; solar heat gain through windars; and the performance characteristics of the heating system.

Although a number of computer program have been developed to simulate the thermal behaviour of a house, simpler methods are more appropriate for use as design tools, or for evaluating house designs for building code or labelling applications. Simple methods sacrifice some accuracy. particularly when the effects of heat storage and variations in room temperature become significant, but they are adequate for many practical applications. Recent research st the National Research Council of Canada has resulted in improved methods for calculating below-grade losses and the utilization of solar gains through windars that can be incorporated into such calculation procedures.

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CIB

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L ~ ~ I R T I C N DE

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Auteur

D.M. Sander

Organisation/Entreprise

D i v i e i o n dee r e c h e r c h e s en b l t i m e n t . Conaeil n a t i o n a l de recherche6 Canada

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_{h a b i t a t i o n s ; Energie de chauf f age; mCthodes de c a l c u l}

Sommaire

Une € v a l u a t i o n de l a conception d'une h a b i t a t i o n e x i g e une d t h o d e pour c a l c u l e r l e e e f f e t s dee d i v e r e e e c a r a c t Q r i s t i q u e e e u r 1 ' 6 n e r g i e d c e s s a i r e au chauffage.

Une mEthode de c a l c u l de ce genre d o i t t e n i r compte d e s p o i n t s e u i v a n t e : p e r t e s de c h a l e u r , s u r t o u t p a r conduction.

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t r a v e r a l ' e n v e l o p p e e x t l r i e u r e ; p e r t e e de c h a l e u r e n t r a f n C e s par 1'Lchange d ' a i r i n t 6 r i e u r - e x t 6 r i e u r ; p e r t e s d e c h a l e u r au s o 1 B t r a v e r s l e p l a n c h e r e t l e e mrs du soue-a01 ; g a i n s de c h a l e u r provenant dee occupante e t dee a p p a r e i l s mCnagere a i n e i que du rayonnencnt s o l a i r e B t r a v e r s l e e f e n s t r e 8 ; e n f i n , c a r a c t C r i s t i q u e s d e rendelrent du a y e t h e de chauf fage.

Bien qu'un c e r t a i n nombre de progr-s d ' o r d i n a t e u r a a i e n t 6 t h c o q u s pour eimuler l e comportemeat thermique d'une h a b i t a t i o n , den d t h o d e e plue simplee a o n t p r € f € r a b l e e comm o u t i l s de conception ou c o m e m y e n d'Cvaluation d e 1s conception d o m i c i l i a i r e a p p l i q d B un code du b l t f m e n t ou

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l ' h o w l o g a t i o n . Lee d t h o d e s simplee manquent quelque peu d e prCcision, notaoment l o r s q u e l e e e f f e t e du etockage de l a c h a l e u r e t l e s f l u c t u a t i o n s de t e m p s r a t u r e d'une p i a c e

r e v e t e n t de l ' i m p o r t a n c e , mais e l l e s conviennent nCanmoins B un bon n m b r e d ' e p p l i c a t i o n s p r e t i q u e e . De r 6 c e n t e t r a v a u x du C o n s e i l n a t i o n a l de recherches Canada o n t permis de m t t r e au p o i n t de m e i l l e u r e a vlpethodee de c a l c u l d e s p e r t e e de c h a l e u r s o u s l e niveau du s o l e t de l ' u t i l i s a t i o n d e s g a i n s de c h a l e u r a o l a i r e p a r l e e f e n P t r e e .

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:2,1:

TECHNIQUES FOR ESTIMATING THE ENERGY CONSUMPTION OF HOUSES

D.M. S a n d e r , Canada

I

T h e r e h a s l o n g been c o n s i d e r a b l e i n t e r e s t i n m o d e l l i n g t h e t h e r m a l b e h a v i o u r of h o u s e s and e s t i m a t i n g t h e i r a n n u a l h e a t i n g e n e r g y r e q u i r e m e n t s . 'Phis i n t e r e s t h a s e v o l v e d i n r e c e n t y e a r s from academic s t u d i e s t o methods t h a t a d d r e s s s p e c i f i c p r a c t i c a l needs f o r c a l c u l a t i n g t h e e n e r g y r e q u i r e m e n t s of houses.

1

T h i s p a p e r d i s c u s s e s some of t h e s e needs i n t h e c o n t e x t of c u r r e n t Canadian c o n d i t i o n s . a s w e l l a s a number of a v a i l a b l e c a l c u l a t i o n methodologies. Recent

I Canadian r e s e a r c h t o improve c a l c u l a t i o n methods f o r below-grade h e a t l o s s e s and u t i l i z a t i o n of s o l a r h e a t g a i n s is d e s c r i b e d b r i e f l y .

1

THE NEED FOR AN ENERGY ESTIMATING HETHOD

Thermodynamic s i m u l a t i o n h a s l o n g been used, i n r e s e a r c h i n s t i t u t i o n s , a s a means of i n v e s t i g a t i n g t h e h e a t t r a n s f e r p r o c e s s e s i n a house. Although i n s p i r e d by a d e s i r e t o g a i n a b e t t e r u n d e r s t a n d i n g of t h e problem, t h e s e s t u d i e s have a l s o been v a l u a b l e f o r d e v e l o p i n g recommendations and g u i d e l i n e s f o r c o n s t r u c t i o n p r a c t i c e , i n s u l a t i o n s t a n d a r d s , and o t h e r energy c o n e e r v a t i o n measures. It is o n l y i n t h e l a s t t e n y e a r s t h a t e n e r g y consumption and t h e consequent c o s t of h e a t i n g a house have become a s i g n i f i c a n t c o n c e r n i n Canada. T h i s concern has been e x p r e s s e d i n a number of government programs

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The problem i s twofold

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t o r e d u c e t h e energy consumption of e x i s t i n g houses, and t o improve t h e c o n s t r u c t i o n of nev houses.

For e x i s t i n g h o u s e s , programs have been i n t r o d u c e d t o p r o v i d e f i n a n c i a l i n c e n t i v e s t o homeowners, through g r a n t s and i n t e r e s t - f r e e l o a n s , f o r r e i n s u l a t i o n and r e t r o f i t . I n 1981, a s p a r t of a n a t i o n a l s t r a t e g y t o r e d u c e t h e c o u n t r y ' s dependence on imported o i l ( 2 ) . t h e Canadian government i n i t i a t e d a program t o s u b s i d i z e t h e c o n v e r s i o n from o i l - f i r e d h e a t i n g s y s t e m t o t h o s e u s i n g n a t u r a l g a s , e l e c t r l c i t y , o r renewable energy. T h e r e h a s developed a r e s u l t i n g need f o r a method of a s s e s s i n g t h e energy r e d u c t i o n p o t e n t i a l of a l t e r n a t i v e r e t r o f i t measures. Moreover, s i n c e most homeovners must b e a r a t l e a a t p a r t of t h e c o s t of a n energy r e t r o f i t , t h e y demand some means of e s t i m a t i n g t h e e x p e c t e d r e t u r n on t h e i r i n v e s t m e n t .

To improve nev h o u s e s , work was i n i t i a t e d t o d e v e l o p a n energy c o n s e r v a t i o n s t a n d a r d . A model document ( 3 ) s p e c i f y i n g r e q u i r e m e n t s s u c h a s h i g h e r

i n s u l a t i o n l e v e l s and b e t t e r windows was produced. T h i s document a l s o c o n t a i n s a p r o v i s i o n p e r m i t t i n g c o n s t r u c t i o n of any t y p e of house t h a t can be shown t o u s e no more energy t h a n one b u i l t i n a c c o r d a n c e w i t h t h e s t a n d a r d . T h e r e f o r e ,

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t h e b u i l d i n g o f f i c i a l must have s o r means of e v a l u a t i n g s b u i l d i n g d e s i g n i n o r d e r t o e n s u r e t h a t i t m e e t s t h e s t a n d a r d .

A number of "low-energy" houses have been b u i l t i n Canada r e c e n t l y . Some have v e r y h i g h l e v e l s of i n s u l a t i o n , a i r t i g h t c o n s t r u c t i o n and s m a l l windows, w h i l e o t h e r s f e a t u r e p a s s i v e s o l a r d e s i g n s i n c o r p o r a t i n g l a r g e s o u t h - f a c i n g g l a s s a r e a s and t h e r m a l mass. Such i n n o v a t i v e h o u s e s r e q u i r e d e s i g n d e c i s i o n s q u i t e d i f f e r e n t from t h o s e f o r c o n v e n t i o n a l c o n s t r u c t i o n . Normally a number of f e a t u r e s would be e v a l u a t e d i n terms of t h e i r energy c o n s e r v a t i o n p o t e n t i a l . c o s t e f f e c t i v e n e s s , and p o s s i b l y r e s u l t a n t problems s u c h a s o v e r h e a t i n g ,

e x c e s s i v e m o i s t u r e o r u n a c c e p t a b l e a i r q u a l i t y . T h e r e i s a need f o r a n a n a l y s i s t o o l f o r t h e d e s i g n e r t o e v a l u a t e and compare d e s i g n a l t e r n a t i v e s f o r a s p e c i f i c house. T h e r e a r e new government i n c e n t i v e s ( 4 . 5 ) f o r t h e c o n s t r u c t i o n of "lw- energy" houses and s i n c e t h e e l i g i b i l i t y c r i t e r i a a r e baaed on a maximum a l l o w a b l e h e a t i n g e n e r g y c o n a m p t i o n , t h e r e m e t be a way t o d e t e d n e t h e e l i g i b i l i t y of proposed d e s i g n s .

T h e r e i s a l s o a need t o p r o t e c t b u y e r s c o n s i d e r i n g t h e p u r c h a s e of a "law- energy" house. The Canadian S t a n d a r d s A e s o c i s t i o n is d e v e l o p i n g a l a b e l l i n g p r o c e d u r e ( 6 ) which would e s t a b l i s h a n e n e r g y c o n e m p t i o n r a t i n g f o r e a c h new house. T h i s would p e r m i t t h e buyer t o b a s e h i s d e c i s i o n on t h e comparison o f c o s t s and a n t i c i p a t e d b e n e f i t s .

I t i s e v i d e n t t h e r e f o r e t h a t t h e r e i s a need b o t h f o r s o p h i s t i c a t e d computer m o d e l l i n g t e c h n i q u e s and s i m p l e c a l c u l a t i o n methods s u i t e d f o r t h e designer, b u i l d e r , a p p r o v a l a u t h o r i t y , and t h e homewner.

CALCULATION OF HOUSE HEATING ENERGY

A l l methode f o r c a l c u l a t i n g t h e e n e r g y r e q u i r e d f o r h e a t i n g m e t a c c o u n t f o r h e a t l o s s e s , h e a t g a i n s , and t h e e f f i c i e n c y of t h e h e a t i n g system. Heat l o s s e s c o n s i s t of t r a n s m i s s i o n t h r o u g h components of t h e b u i l d i n g e n v e l o p e ( s u c h a s w a l l s , c e i l i n g , d o o r s and windows), t r a n s m i s s i o n t h r o u g h basement w a l l s and f l o o r t o t h e ground, and h e a t l o s s d u e t o t h e exchange of i n d o o r and o u t d o o r a i r , e i t h e r t h r o u g h i n f i l t r a t i o n o r by c o n t r o l l e d v e n t i l a t i o n . Heat g a i n s c o n s i s t of s o l a r r a d i a t i o n t h r o u g h windawa a s w e l l a s h e a t g e n e r a t e d by o c c u p a n t s , l i g h t s and a p p l i a n c e s .

Energy c a l c u l a t i o n t e c h n i q u e s may be d i v i d e d i n t o two groups: s i u l a t i o n and m o d e l l i n g , which can o n l y be performed u s i n g computers, and s i m p l i f i e d methods, which p e r m i t manual c a l c u l a t i o n ( a l t h o u g h i t may o f t e n be c o n v e n i e n t t o u s e a computer a s w e l l ) .

COMPUTER MODELLING

The most d e t a i l e d and most f l e x i b l e a n a l y s i s t e c h n i q u e i s dynamic s i m u l a t i o n of t h e t h e r m a l performance of t h e house. E i t h e r f i n i t e d i f f e r e n c e o r t h e r m a l

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I

response methods a r e used t o model t h e non-steady-state h e a t t r a n s f e r due t o

I

thermal s t o r a g e i n t h e m a t e r i a l s of t h e house. Heat g a i n s and h e a t l o s s e s a r e c a l c u l a t e d , u s i n g weather and s o l a r d a t a , t y p i c a l l y f o r a n hourly time

I

i n t e r v a l .

/

Heat l o s s e s through w a l l s and r o o f s may t a k e i n t o account t h e r i s e i n e x t e r i o r s u r f a c e temperatures due t o absorbed s o l a r r a d i a t i o n a s w e l l aa t h e d e c r e a s e i n e x t e r i a r s u r f a c e t e m p e r a t u r e s due t o longuave r a d i a t i o n t o t h e sky.

I n f i l t r a t i o n may be modelled a s a f u n c t i o n not only of t h e leakage

c h a r a c t e r i s t i c s of t h e house i t s e l f but a l s o of outdoor a i r temperature, wind speed. wind d i r e c t i o n , and t h e surrounding t e r r a i n . The c a l c u l a t i o n of s o l a r g a i n s a y account f o r t h e e f f e c t of i n s e t windows, shading by roof overhangs. and shading by a d j a c e n t p a r t s of t h e b u i l d i n g o r by o t h e r b u i l d i n g s . The behaviour of t h e occupant may be s i m u l a t e d by time s c h e d u l i n g t h e i n t e r n a l l o a d s , such a s l i g h t s and appliances. and o p e r a t i o n of b l i n d s , drapes and i n s u l a t i n g s h u t t e r s .

The thermal s t o r a g e c h a r a c t e r i s t i c s of t h e room a r e s i m u l a t e d t o p r e d i c t b o t h t h e h e a t i n g r e q u i r e d and t h e v a r i a t i o n s i n apace temperature. When h e a t g a i n s exceed l o s s e s t h e e x c e s s h e a t i s s t o r e d , r e s u l t i n g i n a r i s e i n room

temperature. When h e a t l o s s e s exceed g a i n s , s t o r e d h e a t i s recovered a s t h e room temperature decreases. The h e a t i n g system is c a l l e d on t o provide t h e h e a t i n g necessary t o prevent t h e temperature from f a l l i n g below t h e t h e r m o s t a t s e t t i n g . Heating systems can be s i m u l a t e d i n d e t a i l i n c l u d i n g v a r i a t i o n of system e f f i c i e n c y w i t h load and outdoor a i r temperature.

Many a i m l a t i o n p r o g r a m model i n d i v i d u a l rooms which may be a t d i f f e r e n t temperatures; i n t h i e c a s e , h e a t t r a n s f e r occurs between t h e rooms. T h i s f u r t h e r p e r m i t s modelling of unheated o r p a r t i a l l y heated s p a c e s , such a s a t t i c s . garages, porches and v e s t i b u l e s , a t t a c h e d sunspacea and greenhouses.

Computer modelling i s a powerful t e c h n i q u e p a r t i c u l a r l y s u i t e d t o r e s e a r c h a p p l i c a t i o n s i n which t h e o b j e c t i v e is t o s t u d y a phenomenon i n g r e a t d e t a i l , t o compare a t h e o r e t i c a l model w i t h experimental d a t a , o r t o e x t r a p o l a t e

experimental d a t a t o produce more g e n e r a l i z e d conclusions. The complex c a l c u l a t i o n s , however, r e q u i r e a g r e a t d e a l of i n p u t d a t a such a s t h e

dimensions. geometry and m a t e r i a l p r o p e r t i e s of a l l b u i l d i n g components. A s a r e s u l t . such p r o g r a m a r e g e n e r a l l y d i f f i c u l t a s w e l l a s expensive t o use.

SIWLIFIED METHODS

P r a c t i c a l a p p l i c a t i o n s a r e g e n e r a l l y not concerned w i t h modelling a h e a t t r a n s f e r process, but with o b t a i n i n g anawere t o q u e s t i o n s such a s whether a house design s a t i s f i e s t h e requirements of a b u i l d i n g ( e n e r g y ) code. what energy l a b e l t o a t t a c h t o a house, o r which d e s i g n a l t e r n a t i v e should be chosen. Simple nethods M Y be S u f f i c i e n t l y a c c u r a t e f o r t h i e purpose; t h e important

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c o n s i d e r a t i o n s a r e t h a t such methods be e a s y t o u s e , r e a d i l y a v a i l a b l e , and i n e x p e n s i v e t o a p p l y . S i n c e a c c e s s t o computers c a n n o t a l w a y s be a s s u r e d , t h e r e

is a need f o r methoda t h a t c a n be a p p l i e d manually.

I t is n e c e s s a r y t o compromise some a c c u r a c y and f l e x i b i l i t y t o a c h i e v e t h e n e c e s s a r y l e v e l of s i m p l i c i t y . S i m p l i f i e d methods g e n e r a l l y c o n s i d e r t h e e n t i r e house a s a s i n g l e a p a c e a t a u n i f o r m and c o n s t a n t t e m p e r a t u r e . A t t a c h e d

unheated s p a c e s a r e approximated a s e q u i v a l e n t a d d i t i o n a l i n s u l a t i o n . An i n d o o r s p a c e t e m p e r a t u r e m a t be assumed; v a r i a t i o n s i n t e m p e r a t u r e a r e n o t c a l c u l a t e d . Thus dynamic h e a t t r a n s f e r is n o t modelled; t h e e f f e c t s of t h e r m a l s t o r a g e a r e e i t h e r i g n o r e d o r a c c o u n t e d f o r by c o r r e c t i o n f a c t o r s o r c o r r e l a t i o n s . These c o r r e l a t i o n s a r e u s u a l l y o b t a i n e d from computer s i m u l a t i o n s t u d i e s . E f f e c t s of s o l a r r a d i a t i o n and long-wave r a d i a t i o n o n t h e opaque p o r t i o n s of t h e b u i l d i n g e n v e l o p e a r e u s u a l l y i g n o r e d ( t h e y a r e assumed t o c a n c e l e a c h o t h e r ) . It s h o u l d be n o t e d t h a t t h e l i m i t a t i o n s of energy c a l c u l a t i o n s a r e . o r e o f t e n due t o u n c e r t a i n t y of t h e i n p u t d a t a t h a n t o t h e c a l c u l a t i o n method i t s e l f . T h e r e f o r e , t h e compromises i n h e r e n t i n t h e s i m p l e methods d o n o t n e c e s s a r i l y reduce t h e a c c u r a c y of a n e n e r g y e s t i m a t e . A d e s c r i p t i o n of s e v e r a l s i m p l i f i e d methods f o l l o w s . T h i s c a t e g o r i z a t i o n i a by no meane complete; t h e r e a r e many v a r i a t i o n s and c o m b i n a t i o n s of t h e s e me t h o d s

.

Temperature Bin Methods

The h o u r l y a i m l a t i o n r e q u i r e e 8760 h o u r l y c s l c u l a t i o n s f o r one year. The b i n method r e d u c e s t h i s number t o between LO and 100 by c a l c u l a t i n g o n l y once f o r e a c h range of o u t d o o r t e m p e r a t u r e ( t y p i c a l l y 1.C t o 5'C), m l t i p l y i n g by t h e number of h o u r s d u r i n g which t h e t e m p e r a t u r e is i n t h i e r a n g e , and t o t a l l i n g t h e r e s u l t s of a l l t h e ranges. T h i s p r o c e d u r e c a n a c c o u n t f o r t h e v a r i a t i o n of h e a t i n g system e f f i c i e n c y w i t h o u t d o o r t e m p e r a t u r e . S i m i l a r l y . i n f i l t r a t i o n may be c o n s i d e r e d a s a f u n c t i o n of o u t d o o r t e m p e r a t u r e . However, t h e l r t h o d d o e s r e q u i r e t h a t a l l o t h e r t h e r m a l components s u c h as s o l a r and i n t e r n a l g a i n 6 a l s o be assumed a f u n c t i o n of o u t d o o r t e m p e r a t u r e . T h a t i e , a n a v e r a g e v a l u e of g a i n s is used i n t h e c a l c u l a t i o n f o r e a c h t e m p e r a t u r e range. Heat s t o r a g e e f f e c t s a r e n o t c o n s i d e r e d . The t e m p e r a t u r e b i n method is p a r t i c u l a r l y w e l l s u i t e d t o t h e a n a l y s i s of h e a t pumps ( 7 ) .

Degree-Day Methods

The f o l l o w i n g methods a r e b a s e d on w e a t h e r d a t a which a r e a v e r a g e d o r i n t e g r a t e d o v e r a r e l a t i v e l y l o n g t i = p e r i o d , t y p i c a l l y one month o r t h e e n t i r e h e a t i n g season. With t h e a i d of a computer t h i e c a l c u l a t i o n i s n o r m a l l y done on a

monthly b a s i s , whereae a s e a e o n a l c a l c u l a t i o n may be p r e f e r r e d f o r a u n u g l

(10)

under Canadian c o n d i t i o n s , i t has been found t h a t t h e r e i s no s u b s t a n t i a l l o s s of accuracy i n t h e s e a s o n a l approach.

The degree-day methods d e s c r i b e d below assume a n average h e a t i n g system e f f i c i e n c y over t h e time period.

Simple degree-day method. The simple degree-day method h a s been i n use f o r o v e r 40 years. It i s based on a h i s t o r i c a l c o r r e l a t i o n of house h e a t i n g energy and degree-days t o t h e base 18.3% (65-F). The d i f f e r e n c e between a c t u a l room temperature and 18.3OC i s aseuned t o compensate f o r t h e u s e f u l h e a t g a i n s from occupants, l i g h t s , a p p l i a n c e s , and s o l a r r a d i a t i o n .

Changes i n both c o n s t r u c t i o n and u s e of houses (more i n s u l a t i o n , h i g h e r i n t e r n a l h e a t g a i n s , l a r g e r windows, lower thermostat s e t t i n g s , e t c . ) have made t h e degree-day c o r r e l a t i o n l e s s a p p r o p r i a t e f o r modern houses. Consequently, modified methods which i n c l u d e c o r r e c t i o n f a c t o r s t o improve t h e c o r r e l a t i o n ( 8 ) have been developed.

The degree-day method h a s t h e advantage of being very simple and of u s i n g r e a d i l y a v a i l a b l e d a t a . "Degree-days" has become t h e recognized measure of "coldness" and v a l u e s a r e published f o r a l a r g e number of l o c a t i o n s . The degree-day method, however, i s based on t h e "average" house; t h e b a s i c

l i m i t a t i o n i s t h a t i t does not account f o r h e a t g a i n s s p e c i f i c t o a p a r t i c u l a r house.

Variable-base degree-day method. S t u d i e s have shown t h a t b e t t e r c o r r e l a t i o n s gay be o b t a i n e d by u s i n g degree-days w i t h a base temperature o t h e r than 18'C. An improvement o v e r t h e simple degree-day method can, t h e r e f o r e , be achieved (9)

by determining t h e base temperature which accounts f o r t h e u s e f u l h e a t g a i n s f o r a s p e c i f i c house. T h i s base temperature is a f u n c t i o n of s o l a r gains. i n t e r n a l g a i n s , t h e h e a t l o s s c h a r a c t e r i s t i c s of t h e house, t h e space temperature and, p o s s i b l y , t h e thermal s t o r a g e c h a r a c t e r i s t i c s of t h e house.

Degree-days f o r base t e m p e r a t u r e s o t h e r t h a n 18°C a r e not g e n e r a l l y a v a i l a b l e ; however, c o r r e l a t i o n s have been d e r i v e d (10) t o o b t a i n them from simple degree- days and average monthly temperatures.

Net annual h e a t l o s s f a c t o r method (11). T h i s v a r i a t i o n on t h e degree-day method a p p o r t i o n s t h e h e a t i n g requirement f o r t h e house among t h e v a r i o u s b u i l d i n g components

-

w a l l s , windows, c e i l i n g and indoor-outdoor a i r exchange. F a c t o r s f o r each component (NALF'e), d e r i v e d from computer a i m l a t i o n s t u d i e s of

a "standard house", a r e given a s a f u n c t i o n of degree-days. The annual h e a t i n g requirement is o b t a i n e d by summing t h e p r o d u c t s of a r e a and NALP f o r a l l components.

(11)

The NALP's d o a c c o u n t f o r t h e e f f e c t of s o l a r r a d i a t i o n o n opaque s u r f a c e s and p e r m i t e v a l u a t i o n of d i f f e r e n t w a l l a b a o r p t i v i t i e s , o r i e n t a t i o n , and window type. The lrcthod i a somewhat l i m i t e d by t h e c o n d i t i o n 8 assumed f o r t h e s t a n d a r d house model ( i n s i d e t e m p e r a t u r e . i n t e r n a l g a i n a , t h e r m a l a t o r a g e

c h a r a c t e r i a t i c s , e t c . ) and by t h e a s s u m p t i o n t h a t s o l a r r a d i a t i o n is a f u n c t i o n of degree-daya. It is, however, s i m p l e and r e l a t i v e l y a c c u r a t e f o r h o u s e s t h a t d o n o t d i f f e r much from t h e s t a n d a r d house.

Energy b a l a n c e method. T h i s method is based d i r e c t l y on t h e h e a t b a l a n c e e q u a t i o n f o r a house, a s i l l u s t r a t e d i n F i g u r e 1. S i n c e t h e sum of h e a t g a i n s must e q u a l t h e sum of h e a t l o s s e s , H = Lt

+

La

+

Lb

-

nici

-

naCs where. H = t o t a l h e a t i n g r e q u i r e d , Lt

-

t o t a l of h e a t l o s s e s d u e t o t r a n s m i s s i o n t h r o u g h e x t e r i o r w a l l s . windowa, c e i l i n g e , e t c . .

La = t o t a l of h e a t l o s s e s due t o indoor-outdoor a i r exchange ( i n f i l t r a t i o n and v e n t i l a t i o n ) , Lb

-

t o t a l below-grade h e a t l o s s . Ci

-

t o t a l of h e a t g a i n s from i n t e r n a l s o u r c e s ( l i g h t s , a p p l i a n c e s . o c c u p a n t s . etc. ), Cs

-

t o t a l of s o l a r h e a t g a i n s t h r o u g h windows, ni

-

u t i l i z a t i o n f a c t o r f o r i n t e r n a l g a i n a ,

ns

-

u t i l i z a t i o n f a c t o r f o r s o l a r g a i n a . The u t i l i z a t i o n f a c t o r s

ni

and

na

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

n

_iand

n

_scan be e s t i m a t e d once t h e g a i n a and l o s s e s a r e known.

I n o r d e r t o c a l c u l a t e t h e h e a t i n g e n e r g y from t h e above e q u a t i o n , i t is f i r s t n e c e s s a r y t o d e t e r m i n e e a c h of t h e l o s s and g a i n components. The c a l c u l a t i o n may be performed o n e i t h e r a monthly o r a e a a o n a l b a s i s .

S i n c e above-grade l o s s e s a r e n o r m a l l y assumed t o be d i r e c t l y p r o p o r t i o n a l t o t h e indoor-outdoor t e m p e r a t u r e d i f f e r e n c e , Lt and La c a n be c a l c u l a t e d u s i n g degree-days w i t h a b a s e t e m p e r a t u r e e q u a l t o t h e i n d o o r t e m p e r a t u r e . It i s

o f t e n more c o n v e n i e n t , hcwever. t o c a l c u l a t e above-grade l o s a e a u s i n g t h e d i f f e r e n c e between i n d o o r and a v e r a g e o u t d o o r t e m p e r a t u r e which c a n be r e a d i l y o b t a i n e d from w e a t h e r d a t a . T h i s i s a good a p p r o x i m a t i o n p r o v i d e d t h a t ;he o u t d o o r t e m p e r a t u r e d o e s n o t exceed t h e i n d o o r t e m p e r a t u r e t o o o f t e n d u r i n g t h e t i m e p e r i o d ( i . e . . t h e month o r t h e h e a t i n g s e a s o n ) c o n s i d e r e d .

H i t a l a s ( 1 2 ) h a s developed an improved p r o c e d u r e f o r c a l c u l a t i n g below-grade h e a t l o s s . Lb. T h i a method. which is baaed on b o t h e x p e r i m e n t a l peaaurements and f i n i t e - e l e m e n t computer models, a c c o u n t s f o r t h e t i m e v a r i a t i o n of h e a t l o s s

(12)

through basement w a l l s and f l o o r s during t h e year. A f e a t u r e is t h a t m n y d i f f e r e n t c o n f i g u r a t i o n s of i n s u l a t i o n ( i n s i d e . o u t s i d e , d i f f e r e n t depths, under t h e f l o o r , e t c . ) can be considered.

The basement w a l l and f l o o r a r e d i v i d e d i n t o s e c t i o n s a s shown i n F i g u r e 2. and t h e h e a t l o s s through each s e c t i o n is computed s e p a r a t e l y . Heat l o s s through each s e c t i o n c o n s i s t s of two p a r t s : a s t e a d y - s t a t e component which does n o t v a q w i t h time, and a t i w - v a r y i n g component which is approximted by a s i n e wave having a p e r i o d of one year.

The s t e a d y - s t a t e component is proportional t o t h e d i f f e r e n c e between i n s i d e t e o p e r a t u r e and mean ground t e a p e r a t u r e . The time varying component is a f u n c t i o n of t h e amplitude of t h e v a r i a t i o n 'bf graund s u r f a c e t e q e r a t u t e about t h i s mean; t h i s f u n c t i o n accounts f o r time l a g s due t o t h e e f f e c t of thermal s t o r a g e i n t h e ground.

Reference 12 c o n t a i n s t a b l e s of c o e f f i c i e n t s f o r rany d i f f e r e n t configurations of basement i n s u l a t i o n . Using t h e s e t a b l e s and published v a l u e s of ground temperature, t h e method provides a f l e x i b l e and r e l a t i v e l y simple means of c l l c u l a t i n g basement h e a t l o s s .

The v l g n i t u d e of t h e i n t e r n a l gains. Gi, depends on t h e occupancy of t h e house. While d a t a on t h e r a t e of h e a t r e l e a s e by v a r i o u s a p p l i a n c e s a r e a r m i l a b l e , it

is

always necessary t o r a k e a r b i t r a r y a s s m p t i o n s regarding occupant bahaviour and, t h e r e f o r e , of t h e i n t e r n a l gains. For w e t s i t u a t i o n s i n which Gi is l e s s t h a n 25% of t h e h e a t l o s s e s , a l l of t h e i n t e r n a l g a i n s can be assumed t o be u s e f u l I).

The s e a s o n a l s o l a r g a i n through t h e windows can be c a l c u l a t e d u s i n g t a b u l a t e d v a l u e s of s o l a r r a d i a t i o n i n c i d e n t on s u r f a c e s of d i f f e r e n t o r i e n t a t i o n . I n Canada t h i s information is a v a i l a b l e from t h e Atmospheric Envirolll~cnt Service a s

10-year averages f o r 130 l o c a t i o n s .

The s o l a r u t i l i z a t i o n f a c t o r , ns. is d e f i n e d a s t h e f r a c t i o n of t h e t o t a l

s o l a r g a i n , through a l l windows of a house, t h a t c o n t r i b u t e a t o a r e d u c t i o n of t h e h e a t i n n reauirement: t h a t is.

- .

Useful s o l a r a i n "s

-

~ o t a l s o l a r g t i n

The u s e f u l s o l a r g a i n f o r any hour i n c l u d e s th; s o l a r g a i n used t o o f f s e t h e a t l o s s e s d u r i n g t h a t hour, p l u s t h e p o r t i o n s t o r e d i n t h e thermal mass and used t o

1

o f f s e t l o s s e s a t a l a t e r

t a r .

I t does not i n c l u d e t h e e x c e s s g a i n t h a t must be d i s c a r d e d t o prevent room temperature from exceedtng a p r e s e t maximum, nor does it include any gain u t i l i z e d t o o f f s e t a d d i t i o n a l l o s s e s caused by

a

r i s e i n

I room temperature above t h e thermostat s e t t i n g .

It has been found (13) t h a t t h e s o l a r u t i l i z a t i o n f a c t o r can be expressed a s a f u n c t i o n of two n o r a a l i z e d parameters, namely t h e "gain-load r a t i o " (GLB) and t h e "thermal mas-gain r a t i o " (MGR). The gain-load r a t i o i e defined as:

(13)

The gain-load r a t i o is t h e r a t i o of t h e s o l a r g a l n t h r o u g h windows t o t h d n e t h e a t i n g l o a d , where t h e n e t h e a t i n g l o a d i s t h e amount of h e a t i n g energy r e q u i r e d i n t h e a b s e n c e of s o l a r g a i n s t o m a i n t a i n t h e room t e m p e r a t u r e a t t h e h e a t i n g t h e r m o s t a t s e t t i n g . The mass-gain r a t i o r e f l e c t s t h e t h e r m a l s t o r a g e c h a r a c t e r i s t i c s of t h e b u i l d i n g a s w e l l a s t h e a r e a , t y p e and o r i e n t a t i o n of t h e g l a z i n g . I t i a d e f i n e d a s . W R

-

c/g, where, C = t h e r m a l c a p a c i t y of t h e b u i l d i n g i n t e r i o r ( E U I K ) , gs = a v e r a g e h o u r l y s o l a r g a i n f o r s e a s o n ( W / h ) . (gs Gs/hours i n , h e a t i n g s e a s o n ) . F i g u r e 3 shows t h e s o l a r u t i l i z a t i o n f a c t o r p l o t t e d a g a i n s t t h e CLR f o r v a r i o u s v a l u e s of MGR and a room t e m p e r a t u r e swing of 5.5'C. Curves f o r t h e c a s e s of O°C and 2.75'C t e m p e r a t u r e swings a r e a l s o a v a i l a b l e (13).

SUMMARY

A number of d i f f e r e n t c a l c u l a t i o n methods have been d e v e l o p e d i n r e s p o n s e t o t h e d i f f e r e n t needs f o r e s t i m a t i n g t h e h e a t i n g e n e r g y r e q u i r e m e n t s of houses. While computer s i m u l a t i o n i s t h e most powerful t e c h n i q u e i t t e n d s t o be b e s t s u i t e d f o r r e s e a r c h s t u d i e s . S i m p l e r methods a r e more a p p r o p r i a t e f o r u s e a s d e s i g n t o o l s , o r f o r e v a l u a t i n g house d e s i g n s f o r b u i l d i n g code o r l a b e l l i n g a p p l i c a t i o n s .

The s i m p l e degree-day method d o e s n o t a c c o u n t f o r t h e f e a t u r e s of a s p e c i f i c house such a s t y p e and o r i e n t a t i o n of g l a s s , i n t e r n a l h e a t g a i n s , o r b u i l d i n g t h e r m a l mass. Both t h e v a r i a b l e - b a s e degree-day and t h e e n e r g y b a l a n c e methods can a c c o u n t f o r many of t h e f e a t u r e s of a p a r t i c u l a r house. The a u t h o r f e e l s t h a t t h e energy b a l a n c e method h a s some a d v a n t a g e s o v e r t h e o t h e r s i m p l i f i e d methods. I t i s c o n c e p t u a l l y more d i r e c t i n i t s a c c o u n t i n g of i n t e r n a l g a i n s , s o l a r g a i n s , and below-grade h e a t l o s s e s . It n o t o n l y p e r m i t s i n v e s t i g a t i o n of v a r i o u s b u i l d i n g f e a t u r e s i n c l u d i n g t h e r m a l mass but a l s o a l l o w s i d e n t i f i c a t i o n o f t h e i n d i v i d u a l components of h e a t l o s s and h e a t g a i n . The method may be a p p l i e d manually w i t h t h e a i d of a pocket c a l c u l a t o r and t a b l e s of c l i m a t i c d a t a . I t h a s a l s o been implemented i n t h e form of a microcomputer

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REFERENCES

1. LATTA, J.K.. "Canadian Energy Consumption and Conservation Programs R e l a t e d t o Buildings", Proceedings of Third I n t e r n a t i o n a l CIB Symposium on Energy Conservation i n t h e B u i l t Environment, Dublin, March 1982.

2. Energy, Wines and Resources Canada, "The N a t i o n a l Energy Program", Ottawa. Canada. 1980.

3. Associate Committee on t h e N a t i o n a l B u i l d i n g Code. "Measures f o r Energy Conservation i n New Buildings". NRCC 16574, N a t i o n a l Research Council of Canada, Ottawa, Canada. 1978.

4. Energy, Minea and Resources Canada, "Program Overview

-

The Super Energy E f f i c i e n t Housing Demonstration Program". Ottawa, Canada.

5. Canada Mortgage and Housing Corporation, " I n i t i a t i v e s i n D o e s t i c Energy Conservation", Ottawa, Canada. 1981.

6. Canadian Standards Association. S t e e r i n g Committee on Energy Conservation i n Housing. Rexdale. O n t a r i o , Canada.

7. CANE, R.L.D.. "A t b d i f i e d Bin Method f o r E s t i m a t i n g Annual Heating Energy Requirements of R e s i d e n t i a l A i r Source Heat Pumps". ASHRAE J o u r n a l , Vol. 21, No. 9. pp. 60-63, Sept. 1979.

8. ASHRAE Handbook of Fundamentals, Chapter 28, 1981.

9. RUSUDA, T.. SUD, I., and ALEREZA, T., "Coaparison of WE-2 Generated R e s i d e n t i a l Design Energy Budgets w i t h t h o s e C a l c u l a t e d by t h e ~ e & e e - ~ a y and Bin Methods", ASHRAE T r a n s a c t i o n s , Vol. 87, P a r t 1 , 1981.

10. TFIOH, H.C.S.. "The R a t i o n a l R e l a t i o n s h i p between Heating Degree-Days and Temperature", Monthly Weather Review 82, 1954, pp. 1-6.

11. MITALAS, G.P., "Net Annual Heat Loss F a c t o r Method f o r E s t i m a t i n g Heat R e q u i r e v n t s of B u i l d i n g " . B u i l d i n g Research Note 117, D i v i s i o n of B u i l d i n g Research. N a t i o n a l Research Council of Canada, Ottawa. Canada, 1976.

12. MITALAS, G.P., "Basement Heat Loss S t u d i e s a t DBR/NRC", NRCC 20416, D i v i s i o n of Building Research. N a t i o n a l Research Council of Canada, Ottawa, Canada, 1982.

13. BARAKAT, S.A. and SANDER, D.M.. " U t i l i z a t i o n of S o l a r Gain Through Windows f o r Heating of Houses i n Canada". Building Research Note 184, D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council of Canada, Ottawa. Canada.

1982.

14. DUMONT, R.S.. LUX, M.E. and ORR, R.W. 'HOTCAN: A Computer Program f o r Estimating t h e Space Heating Requirement of Residences", Computer Program NO. 49, D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council of Canada. Ottawa, Canada. 1982.

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1.0 0.9 0.8 0 . 1 0 . 6 F- 0.5 0.4 0.3 H . Ll+ La + L', -ql GI - q s G* 0 . 2 F I G U R E 1 0. I

HOUSE HEAV BALANCE

0 o 0 . 3 0 . 6 0.V 1.2 1.5 GLR F I G U R E 3 SEASONAL SOLAR U I I L I Z A I I O N F A C I O R ( R O O M I E M P E R A I U R E S W I N G 5.5'C) F I G U R E 2 BASEMENT MODEL