Heat balance relations in fuel-heated houses

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Heat balance relations in fuel-heated houses

Sex

THl

N21d

no.

1255

National Research

Conseil national

C. 2 I

r(

Council Canada

de recherches Canada

BLDG

HEAT BALANCE RELATIONS I N FUEL-HEATED HOUSES

by

C.P. Hedlin

Reprinted from

ASHRAE Transactions

Vol.

90, 1984, Part 2A

p.

207 - 2 1 9

DBR Paper No. 1255

Division of Building

Research

Le b i l a n t h e r m i q u e d ' u n e maison d'epend d e s a p p o r t s e t d e s p e r t e s d e c h a l e u r . En combinant

l e s

mesures d e consommation d e c o m b u s t i b l e pour l e c h a u f f a g e e t l ' e a u chaude a v e c

l e s

a p p o r t s t h e r m i q u e s d u s aux o c c u p a n t s , au rayonnement s o l a i r e e t a u x a p p a r e i l s G l e c t r i q u e s , on a pu Gvaluer l ' a p p o r t t h e r m i q u e t o t a l d a n s l ' e s p a c e h a b i t a b l e e n f o n c t i o n d e s t e m p g r a t u r e s e x t ' e r i e u r e s . Les p e r t e s d e c h a l e u r o n t a u s s i E t 6 c a l c u l g e s e n f o n c t i o n d e s t e m p g r a t u r e s e x t g r i e u r e s . On a pu a i n s i

estimer

l e rendement d ' i n s t a l l a t i o n s de c h a u f f a g e 'a p a r t i r d e s r g s u l t a t s p r g s e n t 6 s s o u s forme d e g r a p h i q u e s . Les m o d i f i c a t i o n s d a n s l a r e l a t i o n e n t r e l a consommation d e c o m b u s t i b l e e t l e s t e m p g r a t u r e s e x t ' e r i e u r e s s o n t prSsent'ees p o u r p l u s i e u r s maisons d o n t l ' i s o l a t i o n thermique a 'etE amglior'ee. Dans deux c a s , l a

mise-

e n mlac_e d d ' n i s o l a n t d e

v a l e u r R S I

7

les

murs du

s o u s - s o l ( p r

30

p o u r c e n t

No. 2839

Heat Balance Relations in Fuel-Heated Houses

!

C.P.

Hedlin, Ph.D.

ASHRAE Member

ABSTRACT

The h e a t balance i n a house depends on h e a t i n p u t s and h e a t l o s s e s . By combining measured f u e l consumptions f o r t h e f u r n a c e and h o t w a t e r system w i t h e s t i m a t e d h e a t g a i n s from

I

occupants, s o l a r r a d i a t i o n , and e l e c t r i c a l a p p l i a n c e s , t o t a l u s e f u l s p a c e h e a t i n p u t s were e s t i m a t e d a s a f u n c t i o n of outdoor temperature. Heat l o s s e s were a l s o c a l c u l a t e d a s a f u n c t i o n of outdoor temperature. From t h e r e s u l t i n g g r a p h i c a l r e l a t i o n s h i p s , e s t i m a t e s were made of h e a t i n g system e f f i c i e n c i e s .

Changes i n t h e f u e l consumption-outdoor temperature r e l a t i o n s h i p a r e g i v e n f o r s e v e r a l houses t o which i n s u l a t i o n was added. In two c a s e s , a d d i t i o n of RSI 2 i n s u l a t i o n t o t h e a t t i c and RSI 1.5 t o basement w a l l s (previously u n i n s u l a t e d ) reduced f u e l consumption by about 30%.

INTRODUCTION

I n Canada a l a r g e p a r t of t h e energy s u p p l i e d t o houses i s used f o r space h e a t i n g . As a consequence, t h e r e i s a l o n g h i s t o r y of study of h e a t l o s s and i t s c o n t r o l . Much of t h i s work has involved l a b o r a t o r y i n v e s t i g a t i o n of i n d i v i d u a l components whose performance can be

s t u d i e d i n i s o l a t i o n . Houses can a l s o be s t u d i e d a s systems under f i e l d c o n d i t i o n s , i n which c a s e a wide v a r i e t y of i n t e r a c t i v e e f f e c t s comes i n t o play. Although some i n d i v i d u a l e f f e c t s may be obscured, r e s u l t s a r e based on p r a c t i c a l f i e l d c o n d i t i o n s and c o n s t i t u t e a n i m p o r t a n t complement t o c o n t r o l l e d s t u d i e s .

A comfortable i n t e r i o r environment r e q u i r e s maintenance of proper b a l a n c e between h e a t l o s s and h e a t i n p u t . Houseto-house v a r i a t i o n s i n h e a t l o s s w i l l o c c u r e v e n f o r houses of t h e same s i z e . The type and s t a t e of r e p a i r of t h e h e a t i n g system, t h e management o r occupancy c o n d i t i o n , and t h e c o n d i t i o n of t h e s t r u c t u r e a l l a f f e c t t h e r e s u l t . On t h e o t h e r hand, houses i n t h e same g e o g r a p h i c a l a r e a a r e s u b j e c t t o s u b s t a n t i a l l y t h e same weather c o n d i t i o n s and t h e same b a s i c h e a t l o s s phenomena (e.g.

,

s t a c k e f f e c t ) and t h e r m a l conduction apply t o a l l of them. Consequently, heat-balance r e l a t i o n s t h a t apply t o one w i l l , w i t h i n limits, be a p p l i c a b l e t o o t h e r s .

The h e a t i n p u t t o houses i n c o l d weather normally i n c l u d e s f u e l and e l e c t r i c i t y purchased from (and metered by) u t i l i t y companies f o r s p a c e h e a t i n g and o t h e r purposes, h e a t i n p u t from occupants, and s o l a r r a d i a t i o n . Under c o n d i t i o n s of e q u i l i b r i u m , n e t h e a t i n p u t s a r e balanced by h e a t l o s s from t h e s t r u c t u r e . The house, i n c l u d i n g i t s components (and occupants),

comprises a system t h a t can be s u b j e c t e d t o a n a l y s i s . I n t h i s s t u d y , t h e energy i n p u t s a n d l o s s e s a r e c o n s i d e r e d i n combination w i t h m e t e o r o l o g i c a l d a t a i n t h e development of a

C.P. Hedlin, Head, P r a i r i e Regional S t a t i o n , 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 Canada, Saskatoon, Saskatchewan.

g r a p h i c a l heat-balance r e l a t i o n s h i p f o r housing systems of a t y p e widely used i n Canada (Hedlin and O r r 1977). Such a graph p o r t r a y s t h e r e l a t i o n s h i p between t h e v a r i a b l e s o v e r t h e range of outdoor t e m p e r a t u r e s and p e r m i t s some d e d u c t i o n s about t h e i r i n d i v i d u a l

c h a r a c t e r i s t i c s o r about t h e i r i n t e r a c t i o n s w i t h o t h e r components of t h e graph. For example, t h e r e l a t i o n developed h e r e c a n be used t o e s t i m a t e a thermal e f f i c i e n c y of t h e system a t a given outdoor temperature and f o r a season.

Thus, t h i s r e p o r t e x p l o r e s r e l a t i o n s h i p s t h a t may complement t h o s e developed i n o t h e r s t u d i e s and c o n t r i b u t e t o t h e s o l u t i o n of e x i s t i n g q u e s t i o n s a b o u t h e a t b a l a n c e i n houses.

R e s u l t s f o r t h r e e Saskatoon houses a r e used a s examples. I n t h e s e houses, n a t u r a l g a s i s used f o r s p a c e and domestic w a t e r h e a t i n g and e l e c t r i c i t y i s used f o r o t h e r household needs i n c l u d i n g cooking.

House A i s a f o u r - l e v e l s p l i t d e s i g n w i t h a p l a n a r e a of 110 m2; houses B and C a r e f u l l basement bungalows w i t h p l a n a r e a s of 93 and 100 m2, r e s p e c t i v e l y . The o v e r a l l t h e r m a l r e s i s t a n c e s f o r w a l l s and c e i l i n g s were about RSI 1.8 (2.1 m2*c/w), e x c e p t f o r t h e c e i l i n g of house C , which was RSI 3.8. A l l a r e h e a t e d w i t h n a t u r a l g a s f u r n a c e s h a v i n g p i l o t l i g h t s . None have s t a c k dampers. The combustion e f f i c i e n c y measured w i t h a n e f f i c i e n c y meter was 78% f o r house A and 76% f o r house C. It was n o t measured f o r house B.

Energy v a l u e s a r e given i n megajoules. E l e c t r i c a l q u a n t i t i e s have been converted from kwh by m l t i p l y i n g by 3.6 ( 1 kwh = 3.6 MJ). N a t u r a l g a s q u a n t i t i e s were converted assuming a h e a t e q u i v a l e n t of 37.3 MJ/m3.

The heat-balance r e l a t i o n involved t h e t o t a l h e a t l o s s from t h e s t r u c t u r e on t h e one hand and a l l of t h e h e a t i n p u t s on t h e o t h e r . I n p u t s i n c l u d e c o n t r i b u t i o n s of t h e occupants (Eo), e l e c t r i c a l equipment (EE), and t h e sun (ESr). The major c o n t r i b u t i o n comes from n a t u r a l g a s (EG), most of which goes t o t h e s p a c e h e a t i n g system

(%);

t h e remainder i s used t o h e a t water. The f r a c t i o n of

%

t h a t i s converted i n t o u s e f u l s p a c e h e a t e q u a l s

%.

P a r t of t h e h e a t from t h e w a t e r h e a t i n g system

(k)

a l s o shows up a s u s e f u l s p a c e h e a t . The remainder

(Ern) i s wasted.

The t h r e e main f a c t o r s i n t h e h e a t balance r e l a t i o n s h i p a r e t h e weather v a r i a b l e , h e a t

l o s s e s , and h e a t i n p u t s . ! I

THE WEATHER VARIABLE

1

I n t h i s s t u d y , t h e energy i n p u t s a r e g i v e n a s d a i l y average (MJIday) and p l o t t e d a g a i n s t a temperature (T) d e f i n e d by t h e number of h e a t i n g d e g r e e d a y s ( b a s i s 1 8 C) a s :

T = 18

-

HDD ( 1 )

HDD i s t h e average number of h e a t i n g degree days f o r t h e p e r i o d involved

--

one o r more days.

I n cold weather, T w i l l be t h e same a s t h e average outdoor temperature (T,); however, i f t h e p e r i o d i n c l u d e s days when t h e average temperature exceeds 18 C , T and Ta w i l l d i f f e r . T a s d e f i n e d by e q u a t i o n 1 can never exceed 18 C , w h i l e Ta may exceed 18 C.

Month-long averages of Ta and T f o r Saskatoon a r e p l o t t e d i n f i g u r e 1. This r e l a t i o n s h i p would probably v a r y w i t h c l i m a t e . The d i f f e r e n c e between Ta and T i s a b o u t 2 C f o r T = 1 8 C , but d e c r e a s e s t o approximately 0.5 C when T = 15 C. Since t h e f o l l o w i n g d i s c u s s i o n i s confined t o temperatures g e n e r a l l y lower t h a n 1 5 C , Ta and T c a n be regarded a s

i n t e r c h a n g e a b l e w i t h very l i t t l e e r r o r . The s l o p e - i n t e r c e p t r e l a t i o n s h i p

i s used t o r e l a t e h e a t energy E (MJ/day) and temperature T (C) f o r h e a t i n p u t s . I i s

to: E

,

IG, and SG would apply t o a l l t h e n a t u r a l g a s consumed. Nomenclature i s l i s t e d followfng t h e summary.

STRUCTURAL HEAT LOSS

I n houses A and C, a i r i n f i l t r a t i o n was measured w i t h a t r a c e r g a s (SF6) u n i t , w i t h which continuous monitoring c a n be done (Kumar e t a l . 1979). Decay measurements were a l s o done w i t h N20. With t h e f i r s t method, measurements were made o v e r three-day w i n t e r p e r i o d s . Some v a r i a b i l i t y was found due t o wind, b u t t h e a v e r a g e s of 0.2 and 0.18 a i r changes p e r hour ( a c / h ) ( f o r houses A and C) were judged t o be c l o s e enough f o r t h e purpose of t h i s study. T h i s r e p r e s e n t s a l l of t h e a i r exchange, w i t h o u t d i s t i n g u i s h i n g between e x i t paths. In t h e c a l c u l a t i o n of i n f i l t r a t i o n h e a t l o s s , a i r was assumed t o l e a v e a t house temperature. Furnace wastage a s s o c i a t e d w i t h a i r exchange would be a p p l i e d t o chimney e x f i l t r a t i o n l o s s e s , u s i n g t h e house temperature a s a base.

For houses A and C , t h e average indoor temperature was 19 C , based on measurements t a k e n o n a l l f o u r l e v e l s w i t h a c h a r t recorder. For house B i t was e s t i m a t e d a t 1 9 C , b u t was n o t measured. A computer program was used t o e s t i m a t e house h e a t l o s s e s f o r each month of t h e y e a r (Dumont e t a l . 1982). The c o e f f i c i e n t s I and S of t h e e q u a t i o n

a r e given i n t a b l e 1 f o r each house. HEAT INPUTS

Heat s o u r c e s i n c l u d e occupants, s o l a r g a i n through windows, and by-product h e a t from e l e c t r i c a l equipment and from t h e burning of n a t u r a l gas.

Heat from occupants v a r i e s w i t h t h e s i z e and number of persons and w i t h a c t i v i t y

(ASHRAE 1981). The occupants of houses A and C were e s t i m a t e d t o c o n t r i b u t e 20 MJIday and f o r house B, 30 MJIday.

A l l of t h e h e a t from e l e c t r i c a l equipment (measured by t h e u t i l i t y company's meter) was assumed t o be c o n v e r t e d i n t o u s e f u l s p a c e h e a t . In f a c t , a f r a c t i o n of i t would b e l o s t by t h e use of e x t e r i o r l i g h t s , o c c a s i o n a l u s e of t h e c a r block h e a t e r , and a c l o t h e s d r y e r vented t o t h e o u t s i d e . These l o s s e s were n o t measured b u t were judged t o be n e g l i g i b l e compared t o t h e t o t a l energy use. The c o e f f i c i e n t s f o r

a r e given i n t a b l e 1 f o r t h e t h r e e houses. I n a l l c a s e s SE was p o s i t i v e , r e f l e c t i n g i n c r e a s e d u s e of e l e c t r i c i t y i n w i n t e r time. Values f o r house A a r e shown i n f i g u r e 2 f o r i l l u s t r a t i v e purposes.

I n t h i s s t u d y t h e e f f e c t of s o l a r g a i n on w a l l s and r o o f s was n o t considered. Useful g a i n s through windows were e s t i m a t e d u s i n g a computer program (Dumont e t a l . 1982). Monthly e s t i m a t e s of s o l a r g a i n s a r e given i n f i g u r e 2 f o r house A. Average v a l u e s f o r t h e y e a r , e x c l u d i n g June, J u l y , and August a r e g i v e n i n t a b l e 1.

N a t u r a l g a s was burned i n two s e p a r a t e u n i t s , a domestic w a t e r h e a t e r and a f o r c e d a i r furnace. From g a s meter r e a d i n g s , d a i l y average energy consumptions (EG) were found. Each p o i n t i n f i g u r e 3 ( f o r houses A and B) r e p r e s e n t s a p e r i o d of about two weeks. These a r e p l o t t e d a g a i n s t T. I n t e r c e p t , s l o p e and c o e f f i c i e n t s of c o r r e l a t i o n a r e g i v e n i n t a b l e 1 f o r f o r t h e t h r e e houses.

The above i n p u t s c a n b e combined t o f i n d t h e t o t a l h e a t i n p u t (ET t , t a b l e 1). T h i s combination of i n p u t s and l o s s e s i s shown g r a p h i c a l l y i n f i g u r e 4 f o r gouse A. For convenience, two groupings were used.

1. The h e a t from occupants (Eo), e l e c t r i c a l a p p l i a n c e s (EE), and s o l a r r a d i a t i o n (ESr)

1

were added t o g e t h e r ( t a b l e 1):

j

1 E~ = E~

+

EE

+

E~~ = ID

+

SD (18-T) ( 6 )

I

2. The n a t u r a l gas used f o r w a t e r h e a t i n g i n houses A and C (EW) was e s t i m a t e d by \ r e c o r d i n g t h e on-time of t h e w a t e r h e a t e r s and measuring t h e i r consumption r a t e s .

These were approximately 100 and 120 MJ/day, r e s p e c t i v e l y . For house B t h e e s t i m a t e

was 160 MJ/day. Based on o b s e r v a t i o n s ( p e r s o n a l communication w i t h S. Barakat,

I

N a t i o n a l Research Council Canada), i t was e s t i m a t e d t h a t t h e u s e f u l h e a t from t h e h o t

water system amounted t o 9 MJ/day

+

8% of t h e g r o s s i n p u t t o t h e system. T h i s amount added t o ED c o n s t i t u t e s a l l of t h e m i s c e l l a n e o u s s p a c e h e a t d e r i v e d from s o u r c e s o t h e r t h a n t h e f u r n a c e . It was r e p r e s e n t e d by EM.

EM = ED

+

Em = IM

+

SM (18-T) ₍₇

_i

S c a t t e r and s e a s o n a l v a r i a t i o n i n t h e miscellaneous i n p u t s were n o t t a k e n i n t o account i n t h e a n a l y s i s . T h e i r e f f e c t s s h o u l d r e s u l t i n i n c r e a s e d o r d e c r e a s e d f u e l c o n s m p t i o n . No

a t t e m p t was made t o q u a n t i f y such i n f l u e n c e s ; however, t h e p o i n t s i n f i g u r e 3 d i f f e r e n t i a t e between t h e January-to-June p e r i o d and t h e July-to-December period.

SYSTEM EFFICIENCY

S t u d i e s i n d i c a t e t h a t t h e e f f i c i e n c y w i t h which f u r n a c e f u e l i s c o n v e r t e d t o u s e f u l s p a c e h e a t i s a f f e c t e d by a v a r i e t y of f a c t o r s i n c l u d i n g o v e r s i z i n g ( J a n s s e n and Bonne 1977; Chi and K e l l y 1978; Sonderegger e t a l . 1980; Hise and Holman 1977; Kweller and M u l l i s 1981). The f u r n a c e s i n b o t h h o u s e s A and B were o v e r s i z e d , judged by t h e i n p u t needed t o o f f s e t h e a t l o s s . The f u l l - l o a d balance-point temperatures (TB), e s t i m a t e d u s i n g e q u a t i o n 8 , ;ere -72, -60, and -88 C f o r houses A, B, and C , r e s p e c t i v e l y ,

(TO+

TB = To

-

-

L ( 8 )

where L i s t h e p e r c e n t a g e on-time a t an o u t s i d e temperature T. To i s t h e temperature when

ESt = EM, i.e., when t h e s t r u c t u r a l h e a t l o s s i s balanced by h e a t i n p u t from m i s c e l l a n e o u s I s o u r c e s . Using f i g u r e 5, system e f f i c i e n c y c a n be d e f i n e d a s :

n

= E ~ t

-

E~ ( 9

EF

where ESt

-

EM i s t h e s p a c e h e a t r e q u i r e d from t h e f u r n a c e , and EF i s t h e h e a t e q u i v a l e n t o f t h e f u e l s u p p l i e d t o t h e f u r n a c e . This i s shown i n f i g u r e 6 f o r t h e temperature r a n g e o f +13 t o -60 C. An e s t i m a t e of s e a s o n a l e f f i c i e n c y ( 0 ) can be made u s i n g t h e e q u a t i o n Y N

=

0, E~

-

i - 1 'ly

-

N (10)

=

E~ i= 1

I n t h e p r e s e n t c a s e , a computer was used t o f i n d and EF f o r e a c h of t h e N days of t h e

"r

h e a t i n g season. The t e m p e r a t u r e s , t a k e n from meterolog c a l r e c o r d s , were a v e r g e s of t h e mean d a i l y t e m p e r a t u r e s f o r a 3 0 q e a r period. For h o u s e s A , B , and C , t h e s e a s o n a l e f f i c i e n c i e s were 69, 67, and 58%, r e s p e c t i v e l y . The l e n g t h of t h e h e a t i n g s e a s o n (N) ranged from a b o u t

250 t o 270 days.

The method of computing e f f i c i e n c y i s v e r y s e n s i t i v e t o e r r o r s i n t h e estimates of

m i s c e l l a n e o u s h e a t and s t r u c t u r a l h e a t l o s s and t o e r r o r s i n measurement and r e p r e s e n t a t i o n o f

21 0

f u e l consumption. For example, i f

%

was 50 MJ g r e a t e r t h a n t h e amounts g i v e n h e r e , e s t i m a t e d s e a s o n a l e f f i c i e n c y would b e approximately 10 percentage p o i n t s lower i n e a c h case. If E

were 50 KT lower than i n d i c a t e d , t h e e s t i m a t e d s e a s o n a l e f f i c i e n c i e s would be approximate!i!y 10% higher.

A t f u l l load, s t e a d y - s t a t e c o n d i t i o n s , t h e e f f i c i e n c y

(n,,)

f o r t h e system i s achieved. I f t h i s e f f i c i e n c y were m a i t a i n e d a t a l l l o a d c o n d i t i o n s , t h e f u r n a c e f u e l consumption c o u l d be r e p r e s e n t e d by a l i n e E: p a s s i n g through t h e p o i n t where t h e s t r u c t u r a l h e a t l o s s l i n e (ESt) meets t h e m i s c e l l a n e o u s h e a t l i n e (EM, f i g u r e 6). It would have a s l o p e

I f SM i s z e r o , then

I f extended i n t h e o t h e r d i r e c t i o n , t h i s l i n e would t h e o r e t i c a l l y meet t h e EF

+

EM l i n e a t t h e f u l l - l o a d b a l a n c e - p o i n t temperature (TB).

I f SF = SGs t h e n a simple r e l a t i o n s h i p can be developed between SG and SSt.* I n f i g u r e 6 t h e i n t e r s e c t i o n of ESt and EM i s used a s t h e o r i g i n corresponding t o temperature To. Then

where AG i s t h e a p p a r e n t f u r n a c e consumption a t To.

(Sst

-

SM)(TO-T) (T

-

To) AG

+

SG (TO-T) = 'lo + A~ (To

-

TB) then r I and

I

LINEARITY OF NATURAL GAS CONSUMPTION/HEATING DEGREE-DAY RELATIONSHIPS

I

The i n t e r s e c t i o n of ESt and EM l i n e s ( f i g u r e 6 ) s u g g e s t s t h a t t h e t r a n s i t i o n from t h e h e a t i n g t o nonheating s e a s o n o c c u r s a b r u p t l y a t about 1 3 C. Above 1 3 C , f u e l would b e consumed o n l y by t h e f u r n a c e p i l o t l i g h t and t h e domestic w a t e r h e a t e r . That would be i n c o s i s t e n t w i t h t h e f a c t t h a t t h e EF

+

EM l i n e i n t e r s e c t s t h e EM l i n e a t a h i g h e r temperature (T:). I n p r a c t i c e , t h e r e appears t o be a t r a n s i t i o n period between t h e r e g u l a r h e a t i n g s e a s o n and t h e nonheating s e a s o n t h a t h a s unique h e a t i n g requirements. Some s p a c e h e a t may b e used t o t a k e t h e c h i l l o f f t h e house i n t h e morning d u r i n g t h e t r a n s i t i o n i n t e r v a l (Reeves 1981; Myer and Benjamini

I 1978). The temperature span f o r t h i s t r a n s i t i o n r e g i o n i s s h o r t and t h e r e a r e n o t many p o i n t s i n t h e i n t e r v a l above 10 C ( f i g u r e 3). Though f i n e d e t a i l i s m i s s i n g , p o i n t s i n t h e v i c i n i t y

I

of T = 10 appear t o f a l l somewhat below t h e l i n e of b e s t f i t . The e x i s t e n c e of s u c h a

d e v i a t i o n was demonstrated by a s t a t i s t i c a l t r e a t m e n t of d a t a f o r a l a r g e number of houses

-

s i m i l a r t o t h o s e d e s c r i b e d i n t h i s r e p o r t . In t h a t (unpublished) r e p o r t , t h e d e p a r t u r e from l i n e a r i t y was shown t o begin when t h e temperature exceeded about 8 C.

*In t h i s model S = SG, provided t h a t t h e amount of f u e l consumed by t h e w a t e r h e a t e r i s

In t h e nonheating season, t h e f u r n a c e would n o t colne on; a l l t h e n a t u r a l g a s used would be f o r h o t water and t h e f u r n a c e p i l o t l i g h t . P r o p e r l y speaking, t h e d a t a p o i n t s f o r t h a t p e r i o d s h o u l d n o t be included. However i n t h i s s t u d y , t h e i r i n c l u s i o n d o e s n o t g r e a t l y a f f e c t t h e r e s u l t s . Dropping o f f a l l t h e p o i n t s corresponding t o o u t s i d e temperatures above 10 C f o r e i g h t sets of d a t a , i n c l u d i n g t h e s i x most populous s e t s i n f i g u r e s 3 and 7, produced

d i f f e r e n c e s i n s l o p e of up t o 4%. The a b s o l u t e average was 1.7% and t h e a r i t h m e t i c a v e r a g e w a s +0.2%.

FUEL CONSUMPTION COEFFICIENT AS A MEASURE OF HOUSE THERMAL PERFORMANCE

The f u e l consumption c o e f f i c i e n t (SG) i s approximately e q u a l t o both t h e h e a t i n p u t

c o e f f i c i e n t (STot) and t h e f u r n a c e consumption c o e f f i c i e n t (SF). I f SG i s used t o r e p r e s e n t STot t h e percentage e r r o r i s

r 1

I n t h e c a s e of house A, r e p r e s e n t e d i n f i g u r e 3, t h a t e r r o r would be

-

-

For houses B and C, t h e e r r o r s would be 3.0% and 0.5%, r e s p e c t i v e l y .

SF and STot a r e i n d i c a t o r s of energy u s e f o r s p a c e h e a t i n g i n houses.* A s t h e i r

approximate e q u i v a l e n t , SG can s e r v e a s a measure of house t h e r m a l performance. It should be n e a r l y independent of i n t e r i o r temperature. It might be used f o r comparing one house w i t h another o r t o e s t i m a t e t h e improvement achieved by adding i n s u l a t i o n t o a house. I n t h e former c a s e , i t should be n o t e d t h a t SD w i l l p l a y a p a r t . For example, two houses may have i d e n t i c a l h e a t i n p u t c o e f f i c i e n t s ; however, s i n c e

t h e v a l u e of SG w i l l be a f f e c t e d by SD.

The e f f e c t of adding i n s u l a t i o n t o t h r e e houses i s i l l u s t r a A : e d i n f i g u r e 7. I n house B , i n s u l a t i o n w i t h RSI 1.2 was added t o h a l f of t h e i n t e r i o r basement w a l l , from t h e t o p of t h e w a l l t o approximately 1.2 m below grade. I n s u l a t i o n was a l s o added i n t h e a t t i c . I n house C

(a 100 m2 bungalow), i n s u l a t i o n w i t h RSI 1.5 was added t o t h e previously u n i n s u l a t e d basement w a l l s . Approximately RSI 2 was added t o t h e a t t i c . I n house D ( a 106 m2 bungalow) RSI 2.1 was added t o t h e a t t i c , r e d u c i n g f u e l consumption t o EG2. Then t h e basement was i n s u l a t e d and f u e l consumption was reduced f u r t h e r t o EG3. For house B , SG was reduced by o n l y about 6%. For C and D, i t was reduced by about 30%.

SUMMARY

Heat l o s s from houses is p a r t l y balanced by h e a t i n p u t s from miscellaneous s o u r c e s such a s occupants, s o l a r r a d i a t i o n , e l e c t r i c i t y , and t h e h o t w a t e r h e a t i n g system. The remaining requirement i s met by t h e s p a c e h e a t i n g system. The combination of energy i n p u t s on one hand and h e a t l o s s e s on t h e o t h e r r e p r e s e n t s t h e h e a t b a l a n c e f o r t h e house.

I n t h i s s t u d y , energy i n p u t s and h e a t l o s s e s were e s t i m a t e d a s f u n c t i o n s of h e a t i n g d e g r e e days (18 C base). A temperature s c a l e i s superimposed o n t h e h e a t i n g - d e g r e e d a y s c a l e . That temperature (T = 18 -HDD/day) i s t h e same a s average outdoor temperature (TI u n l e s s t h e average temperature f o r i n d i v i d u a l d a y s exceeds 18 C. Locally. t h i s o c c u r s mainly i n June, J u l y and August. It makes t h e temperature s c a l e t o o low by about 0.5 C a t 15 C akd by a b o i t 2 C a t 18 C.

.

* u l t i p l y i n g SF by t h e a p p r o p r i a t e number, of h e a t i n g d e g r e e d a y s ( c a l c u l a t e d from t h e a p p r o p r i a t e base) s h o u l d g i v e approximately t h e energy consumption c a l c u l a t e d u s i n g t h e r e l a t i o n s h i p i n t h e ASHRAJ?, Handbook-1981 Fundamentals, ( e q u a t i o n 1, p. 28.2).

In many homes on t h e Canadian p r a i r i e s , n a t u r a l g a s i s used f o r space h e a t i n g and domestic h o t water. For space h e a t i n g , t h e year may be d i v i d e d i n t o t h r e e segments, t h e h e a t i n g season, t h e nonheating season, and a t r a n s i t i o n period. In s p i t e of d i s c o n t i n u i t i e s i n t h e demand f o r space h e a t , t h e r e l a t i o n s h i p between n a t u r a l gas consumption and temperature i s n e a r l y l i n e a r f o r t h e houses used i n t h i s study. When t h e outdoor temperature exceeds 10-12 C, space h e a t may be needed only i n t e r m i t t e n t l y o r n o t a t a l l i n warm weather.

A v a r i e t y of c r i t e r i a might be used t o express t h e thermal performance of a house, i n c l u d i n g f u e l consumption by t h e furnace

(%)

and t h e t o t a l h e a t i n p u t t o t h e house (ETot)* I n t h e houses considered i n t h i s s t u d y , f u e l consumed f o r domestic h o t water and space h e a t i n g is designated EG. EF, ETot, and EG can each be expressed i n t e r m of o u t s i d e temperature using t h e s l o p e i n t e r c e p t r e l a t i o n s h i p ,

This r e s u l t s i n s l o p e s SF (furnace consumption c o e f f i c i e n t )

,

STo (heat i n p u t c o e f f i c i e n t )

,

and SG ( f u e l consumption c o e f f i c i e n t ) .

SG i s approximately equal t o both SF and STot and i s r e l a t e d t o t h e s t r u c t u r a l h e a t 108s c o e f f i c i e n t (SSt). Because of c l o s e l i n k s t o t h e s e parameters of energy use and h e a t l o s s , SG i s a u s e f u l measure of house thermal performance. It i s s u b s t a n t i a l l y independent of t h e i n t e r i o r temperature and a l s o of f u e l consumption f o r o t h e r purposes, i f t h e l a t t e r does n o t vary seasonally.

Fuel consumption d a t a were obtained f o r s e v e r a l houses before and a f t e r a d d i t i o n of i n s u l a t i o n . These r e s u l t s showed r e d u c t i o n s i n t h e f u e l consumption c o e f f i c i e n t (SG) of up t o 30%.

The e f f i c i e n c y w i t h which t h e complete system used h e a t supplied t o i t i s a f f e c t e d by t h e combustion e f f i c i e n c y of t h e furnace and "of f-time" s t a c k l o s s e s up t h e h o t chimney. An

approximate expression f o r e f f i c i e n c y of t h e system was developed. Seasonal e f f i c i e n c i e s f o r t h r e e houses c a l c u l a t e d i n t h i s way ranged from 58% t o 69%. This c a l c u l a t i o n i s s u b j e c t t o a number of u n c e r t a i n t i e s and must be regarded a s very approximate.

I

NOMENCLATURE

= I

+

S (18

-

T) g e n e r a l slope-intercept equation r e l a t i n g h e a t energy E (MJIday) and temperature (T)

= i n t e r c e p t (MJlday)

= s l o p e (MJ/day C)

a 18

-

HDDIday, temperature based on t h e heating-degreeday s c a l e (C)

= average h e a t i n g degree dayslday f o r t h e period presented by t h e d a t a p o i n t

= Kilowatt hours

= megajoule

= average outdoor temperature (C)

= indoor temperature (C)

= temperature a t which s t r u c t u r a l h e a t l o s s e q u a l s miscellaneous h e a t supply (C)

= temperature (C) where E = 0 (no f u e l supplied t o f u r n a c e except f o r p i l o t l i g h t ) e f f i c i e n c y of t h e h e a t i n g system

f u l l - l o a d e f f i c i e n c y of t h e h e a t i n g system apparent f u r n a c e f u e l consumption a t To (MJIday)

= t a n

s ' ~

(where S = s l o p e )

= a i r changes p e r hour

= metre ( l e n g t h )

= thermal r e s i s t a n c e ( M ~ * C/W) Subscripts

I

Subscripts a r e used t o i d e n t i f y t h e h e a t component. S t = s t r u c t u r e

Tot = h e a t energy supplied t o house from a l l sources G = a l l n a t u r a l gas

F = furnace E = electricity

0

-

occupants

Sr = solar

D = occupant

+

electrical

+

solar total W = all energy used by domestic hot water HW = hot water heat converted to space heat H W = heat from domestic hot water wasted M = miscellaneous space heat (D

+

HW)

REFERENCES

ASHRAE. 1981. ASHRAE handbook

-

1981 fundamentals, Chapter 22, Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers.

Chi, J., and Kelly, G.E., 1978. "Method for estimating the seasonal performance of residential gas and oil-fired heating systems" ASHRAE Transactions 84, Part 1, pp. 405-21.

Dumont, R.S.; Lux, M.E.; and Orr, H.W., 1982. HOTCAN: A computer program for estimating the space heating requirement of residences, Computer Program 49, Division of Building Research, National Research Council Canada, Ottawa.

Hedlin, C.P., and Orr, H.W., 1977. "A study of the use of natural gas and electricity in Saskatchewan homes" SHELTER, Proceedings of the Technical Program of the 91et Annual EIC Meeting. NRCC 16898, May, pp. 123-131.

Hise, E.C., and Holman, A.S., 1977. "Heat balance and efficiency measurements of central forced-air residential gas furnaces" ASHRAE Transactions 83, Part 1, p. 868.

Janssen, J.E., and Bonne, U., 1977. "Improvement of seasonal efficiency of residential heating systems" Journal of Engineering for Power, July, pp. 329-34.

Kumar, R.; Ireson, A.D.; and Orr, H.W., 1979. "An automated air infiltration measuring system using SF6 tracer gas in constant concentration and decay methods" ASHRAE Transactions 85, Part 2, pp. 385-95.

Kweller, E.R., and Mullis, W.F., 1981. "Determination of annual efficiency of vented heaters equipped with thermally activated dampers" ASHRAE Transactions 87, Part 1, pp. 753-768. Myer, L.S., and Benjamini, Y., 1978. "Modeling residential demand for natural gas as a

function of the coldness of the month." Energy and Buildings, Vol. 2, p. 301.

Reeves, G.A., 1981. "Degree-day correction factors: basis for values" ASHRAE Transactions 87, Part 1, pp. 507-514.

Sonderegger, R.C.; Condon, P.E.; and Modera, M.P., 1980. "In situ measurements of residential energy performance using electric co-heating" ASHRAE Transactions 86, Part 1,

pp. 394-406.

ACKNOWLEDGEMENT

The author wishes to express his appreciation to J.T. Makohon for his assistance, including the provision of data for one of the houses.

This paper is a contribution from the Mvision of Building Research, National Research Council Canada, and is published with the approval of the Director of the Division.

TABLE 1

Estimated Structural Heat Losses and Energy Inputs for Houses A, B and C [Given as intercepts (I) and slopes (S) of E =

I

+

S ( 1 8 q ) or as constant values.]

Energy Components Houae A House B House C

I S r* I S I* I S

r*

ESt (structural)

E~

(occupants)

ESr (solar)

F i g u r e 1 . Outdoor t e m p e r a t u r e Tg v e r s u s T .

T i s b a s e d on m o n t h l y a v e r a g e s

o f HDD/day f o r May t o September 1975-80, S a s k a t o o n 0 JAN. TO JUNE JULY TO DEC.

-

0

-

-

HOUSE A 0 APR MAR

-

MAY 0 0 0 FEB

-

0 SEP 0

-

OCT 0 0 JAN NOV 0

-

DEC

-

F i g u r e 2 . Measured e l e c t r i c i t y consumption and e s t i m a t e d s o l a r g a i n s v e r s u s T , House A 1 I I I

-

o JAN. TO JUNE d- JULY TO DEC.

-

-

-

-

-

PEGS 109+ 21.0 (18-T) MJ/day

a

-

o HOUSE B

F i g u r e

I I I I I

0 10 2 0 30 4 0

H D D / d a v . O C

F i g u r e 4 . Heat i n p u t s and l o s s e s v e r s u s T , House A

T, 'C I 1 I I I I 0 I 10 20 30 4 0 50 60 H D D / d a y , O C E s t i m a t e d s y s t e m t h e r m a l e f f i c i e n c i e s v e r s u s T , Houses A , B , and C

F i g u r e 6 . C o n s t r u c t i o n u s

-7

d i n d e v e l o p i q g

-

e q u a t i o n ( 1 7 1 N o t e : 8 = t a n and 9 = t a n

"

s~ S~ E G = 160 + 2 2 7 ( 1 8 - T ) M J l d a y - BEFORE HOUSE 0

los + 21 0 (18-TI MJldoY A F T E R I I I I 1 EGI = 8 5 2 9 1 (18-T) MJlday EGZ = 64 + 24.4 (18-T)MJ/day . .9;; n I 000 n.. 0 O . , HOUSE C

-

E G ~ = 5 9 + 20.1 (18-T1MJlday

-

I I I I I 18 10 0 -10 - 2 0 - 3 0 I I EG='60 + 29,61(18-T) I

-

BEFORE -

,

2' -

-

HOUSE D -

-

- AFTER I I I I I 1 8 L O 0 -10 - 2 0 - 3 0 T. O C

F i g u r e 7 . Natural gas v e r s u s t e m p e r a t u r e p l o t s f o r h o u s e s B , C , D b e f o r e and a f t e r a d d i n g i n s u l a t i o n

DISCUSSION

R. RUNDQUIST, Ross & Bruzzini, St. Louis, M0: What were furnace heating capacities relative to calculated heating loads in each of the test houses, and how does this relate to apparent seasonal efficiencies?

C.P. HEDLIN: The rated output capacities of the furnaces were approximately 95, 72, and 95 UJ/hr for houses A, B, and C respectively. Following the same order, the estimated space heating loads at a design temperature of -35°C were 1320, 1110, and 1130 HJ/day. Thus the furnace oversizing was most marked for house C which also had the lowest efficiency. J.A. NATION, CAER, Inc., Golden, CO: Did you attribute loss of efficiency with decreasing degree-days to:

a. infiltration?

b. part-load furnace efficiency?

c. Did furnaces have continuous pilot or intermittent? d. Were vent dampers installed?

HEDLIN: Loss of efficiency with decreasing days may have been caused by a combinations of these factors. The furnaces all had pilot lights which consumed energy at the rate of 15-20 UJ/day. An increasing fraction of this would be lost as with decreasing degree days thus, contributing in a small way to reduced efficiency values. None of the furnaces had vent dampers, and heat loss due to furnace-associated exfiltration following firing periods could also be a factor. No direct measurements of chimney loss were made.

HEDLIN: There was a third question asked at the meeting in Kansas City. The inquirer asked if data for retrofitted houses, shown in figure 7, had been investigated to see whether calculated efficiencies changed with increased insulation. The answer is that this was not done though it would be interesting to do so. Also, I said that these houses were not the same as houses A, B, and C discussed earlier in the paper. In fact two of the three (B and

T h i s p a p e r , w h i l e b e i n g d i s t r i b u t e d i n r e p r i n t f o r m by t h e D i v i s i o n of B u i l d i n g R e s e a r c h , r e m a i n s t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It s h o u l d n o t be r e p r o d u c e d i n whole o r i n p a r t w i t h o u t t h e p e r m i s s i o n of t h e p u b l i s h e r . A l i s t of a l l p u b l i c a t i o n s a v a i l a b l e f r o m t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , D i v i s i o n o f B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a , O t t a w a , O n t a r i o ,

KIA

OR6.