Thermal performance of a supply-air window

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Thermal performance of a supply-air window

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Thermal Performance of a

Supply-Air Window

by S.A. Barakat

ANALYZED

Reprinted from

Proceedings

12th Annual Passive Solar Conference, Solar '87

Volume 12, July 12- 16, 1987

p. 152-158

(IRC Paper No. 1482)

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Price $3.00

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T H E W PEWORPUNCE OP A SUPPLY-AIR WINDOW S.A. Barakat

I n s t i t u t e f o r Bsaearch i n C o n r t r u c t i o n N a t i o n a l Barearch Council of Canada

Ortav., Canada, K1A OR6

An e x p e r i w n t a l r t u d y t o asaerm t h e thermal p e r f o m n e e of a r u p p l y - a i r vindau and i t s impact on energy consumption l a described. The supply-air w i n d w u u a f a c t o r y - s e a l e d d o u b l e - g l u e d vindou r e t r o f i t t e d w i t h e x t r a g l a z i n g on t h e outside. It u a e i n s t a l l e d o n t h e r o u t h w a l l of a two-room t e s t u n i t t h a t war c o n t i w o c u l y monitored. V e n t i l a t i o n a i r v u drawn b a t w e n t h e s e a l e d d o u b l e g l u i n g and th. r e t r o f i t pane through i n l e t h o l e s a t th. bottom of t h e frame. Aa a d j a c e n t ,

r i m i l a r r w r o o m u n i t f i t t e d w i t h a n i d e a t i c a l factory-sealed d o u b l e g l a z e d window w u monitored a 8 a c o n t r o l . C a l i b r a t e d fa- exhausted a n a i r flow e q u i v a l e n t of 0.5 Aaf from each u n i t . In t h e c o n t r o l u n i t t h e outdoor rupply war d r a m d i r e c t l y i n t o t h e room. Ihe paper d e s c r i b e r t h e rupply-air window concept and p r e s e n t 8 d e t a i l s of t h e e x p e r i l m t a l procedure and r e r u l t s . The t h e r a v l performance of t h e two t e s t u d t r La a8ae8red, a 8 w e l l a 8 t h e c a l c u l a t e d p r f o r u n c e of a e i d l a r u n i t f i t t e d w i t h a t r i p l c g l u e d -window. I n r e c e n t y e a r s t h e r e h a s been a r t r o n g t r W a u q f r m dependence on u n c o n t r o l l e d , accidmntal a i r change Ln b u i l d i n g r toward8 c o n t r o l l e d v a n t i l a t i o n . T h i s haa g r a m o u t of t h e need t o a e t t h e requirement f o r a d a q u t a f r e r h a i r rupply w h i l e a c h i e v i n g l w energy c o a t s through t h e u s e of h e a t recovary techniques. An a d d i t i o n a l t r e n d h.8 aeon an i n c r e a r e i n t h e a r e a of g l a e s usad f o r t h e e x t e r i o r b u i l d i n g envelope. B.cognizing t h e l a r g e h e a t l o r s / g a i n a88ociated w i t h l a r g a w i n d w r , t h i s has r e p r e r e n t e d a c h a l l e n g e t o e n g i n e e r r and manufacturer8 t o reduce t h e h e a t t r a l u m l 8 r i o n through g l u i n g a r w e l l a r p t o v i d e thermal c o d o r t i n t h e i n t e r i o r apace mar windour.

A Concapt t h a t a d d r e r s e s both v e n t i l a t i o n

and window h a a t l o a s p r o b l e m i r t h e a i r f l o v window. This i r a m l t i p l e - g l a z e d window w i t h v e n t i l a t i o n a i r f l w i n g between

t h e pane8 i n one of t h e a i r spacer. 'Rro type8 of a i r - f l o v window have been conaidered i n r e c e n t y e a r r : exhaust-air windowr m d supply-air window8 (Figure I ) .

k t h e n.oa i m p l i a r , i n a n e x b u n t - a i r window t h e a i r from t h e b u i l d i n g i u f o r c e d through t h e w i n d w a i r r p a c e b e f o r e being exhausted t o t h e o u t d o o r r , r o o r t i u 8 through a h e a t recovery system. In s o m c a r e r b l i n d s a r e enclosed i n t h e a i r r p a c e f o r e o l a r c o n t r o l . During t h e c o o l i n g s e a s o n t h e a i r f l o v remover most of t h e r o l a r g a i n absorbed by t h e g l i u i o g r and t h e b l i n d b e f o r e i t r e a c h e r t h e indoor rpace a r c o o l i n g load. In t h e h e a t i n g r e u o n t h e a i r flow reduces t h e temperature d i f f e r e n c e a c r o r r t h e i n a i d e pane(s), e l i m i n a t i n g l a r g e p a r t 8 of t h e h e a t 1088. The window a l a o a c t s a 8 a r o l a r c o l l e c t o r , and i n t h i n c a a e t h e h e a t c o n t a i n e d i n t h e a i r is recovered b e f o r e t h e a i r i r d i r c h a r g e d t o outdoorr. E x h a u s t - a i r windowr b v e been t e s t e d and ured i n a number of c o u n t r i e r , p a r t i c u l a r l y i n Europe, and a r e r e p o r t e d t o have an e q u i v a l e n t h e a t t r a n s f e r c o e f f i c i e n t a s low

u 0.4 t o 0.6 W / E ~ - K depending on t h e a i r f l o w r a t e (1-4).

In t h e rupply-air window t h e a i r t o t h e r p a c e i r i n t r o d u c e d through t h e a i r rpace between t h e window panes. Iluring t h e h e a t i n g r e u o n t h e outdoor a i r a t r e a m between panes lovers t h e t e q e r a t u r e of t h e a i r rpece, s i g n i f i c a n t l y reducing h e a t 108s through t h e window o u t e r panes t o t h e outdoorr. The a i r n t r e a a is, a t t h e same tios, preheated continuouely by t h e h e a t flow through t h e i n n e r pane8 of t h e window a 8 w e l l a 8 by s o l a r energy absorbed i n t h e g l a r s panes d u r i n g t h e day. Tha magnitude of pre-heating depends on t h e a i r f l a u r a t e and t h e f o r c e d convection p a t t e r n i n t h e a i r apace. Pacovered energy reducer t h e energy r e q u i r e d t o pre-heat t h e v e n t i l a t i o n a i r and r e a u l t r i n a l o v e r s p a c e h e a t i n g

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OUTDOOR INDOOR OUTDOOR

SUPPLY- AIR WINDOW EXHAUST- AIR WINDOW

Figure 1. A i r f l o w windovr

? . I ?

4

DIMENSIONS, a

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t a b o r a t o r y s t u d i s r i n F i n l a n d (5) h a m i n d i c a t e d t h a p o s s i b i l i t y of d e r r l o p i n g v i a t h a t could p r r h e a t v e n t i l a t i o n a i r

t o wet the r e q u i r c r a n t of a s i n g l a f d l y base by recovering moat o f t h a hmat t r a n s f e r through t h e widow. Incoming a i r w a s hoatmd t o about 50 p e r c e n t of t h e temperature d i f f e r e n c e lmtueea t h e Indoor aad outdoor a i r . The e f f e c t of a i r i n c h arrmngewnts on tlurul comfort and

v a n t i l a t i o a a f f i c i e n c y w u a l s o examined, A t h r o r e t i u l study c a r r i e d o u t i n Norway (6) h a s i n d i c a t e d that a double-pa- n u p p l p i r window can have a h e a t l o s s c o e f f i c i e n t u

la u 0.5 u / Q ~ * K . Recent c a l c u l a t i o n 8 w i n g t h a 'VISION' window program (7) f o r a a m b e r of syrtem c o n f i g u r a t i o n 8 i n d i c a t e a s i g n i f i c a n t r e d u c t i o n i n h e a t l o s s w i t h l i t t l e e f f e c t on shading c o e f f i c i e n t . S f f e c t i v e U-values f o r supply-air windows were between 0.42 and 0.68 of t h e v a l u e s without a i r flow.

mile

supply-air windows m y r e p r e s e n t an a t t r a c t i v e and i n e x p e l u i v e a l t e r n a t i v e d u r i n g h w e renovation o r the& upgrading, o t h e r f a c t o r s should be considered: t h e e f f e c t of sir flow on l a u e r i n g t h e i l u i d e - p a o c t e q e r a t u r e , which i n t u r n a f f e c t 8 t h e m 1 comfort a d p o t e n t i a l w i n d w condenoation; t h e i n t e g r a t i o n of t h e w i n d w i n t o t h e v e n t i l a t i o n system; and t h e a d d i t i o n n l r e q u i r c u n t s f o r c l e a n i n g of t h e a i r f l o w space.

T h i s experimental cltudy war undertaken a t t h e I n s t i t u t e f o r Research i n C o n s t r u c t i o n , N a t i o n a l Research Council of Canada

(IRCINRCC) outdoor t e s t f a c i l i t y t o e v a l u a t e the performance of a supply-air window and i t 8 i w a c t on a n e r w coruumption a s c o l p a r e d t o conventional double- and t r i p l e - g l a r e d w i n d a s .

The NRCC outdoor test f a c i l i t y (8) c o r u i s t s of a r i n g l e a t o r a y , i n s u l a t e d vood f r a o c c o r u t r u c t i o n over a basement and i s d i v i d e d i n t o t u o 2 7 0 0 1 u n i t s . An shown i n

Figure 2, u c h u n i t has a south-facing window of 2.6 m2 n e t g l a s s a r e a (mnde of t h r e e s e c t i o n o ) aad a 1-r2 north-f a c i n g windor. Windows a r e double-glazed w i t h 6.4- i n t e r p a n e a i r space. A l l r o o m a r e h e a t e d t o 20.C by means of e l e c t r i c baseboard h e a t e r s c o n t r o l l e d by p r e c i s i o n c o n t r o l l e r s t o w i t h i n 0.1 C deg. The t e s t u n i t s were c o n s t n r c t e d , and measured, t o be a i r t i g h t .

Tha a i r a u p p l y windov was c o n s t r u c t e d on t h e s o u t h s i d e of t h e w e s t u n i t by r e t r o f i t t i n g the e x i s t i n g double-glazed window w i t h a n e x t r a pa- of g l a a s 66 m o u t s i d e t h e o u t e r p.ru (Figure 3). 'Phis d i v i d e d t h e window i n t o t h r e e s e c t i o n s , each of 584- width.

For e a c h s e c t i o n t h r e e 25-Q h o l e s were d r i l l e d a t t h e bottom of t h e frame of t h e r e t r o f i t pane and a t t h e t o p of t h e o r i g i n a l frame t o a l l o w a i r flow. The v e r t i c a l d i s t a a c e between t h e bottom and t o p h o l e s w u 1625 me. The t o p h o l e s v e r e l i n e d w i t h

r i g i d conduiLs through t h e w a l l i n s u l a t i o n .

Two _small_fa- _{were used t o e x t r a c t}_{a i r}

continuously from each u n i t t o t h e c o r r i d o r a t a r a t e of 11.5 L/s, t h e e q u i v a l e n t of about 0.5 a i r changes p e r hour. I n t h e vest u n i t , t h e a i r was drawn through t h e

supply-air window; t h i s t r a n s l a t e s i n t o an a i r f l a u r a t e of 6.1 L/s p e r

d

of windov a r e a , o r a n e q u i v a l e n t v e l o c i t y of 0.1 m / s . I n t h e e a s t c o n t r o l u n i t t h e a i r was a l l a v e d t o e n t e r t h e u n i t d i r e c t l y through a supply i n l e t .

Continuous measurements included t h e average indoor a i r temperature a t mid-height of each room, a i r t e P p e r a t u r e r i n t h e a t t i c and c o r r i d o r , outdoor a i r temperature, and t h e a i r c e q e r a t u r e s a t t h e i n l e t and o u t l e t of t h e s u p p l y - a i r vindow. Other measurements included s o l a r r a d i a t i o n i n c i d e n t on t h e s o u t h and n o r t h s u r f a c e s , and t h e e l e c t r i c energy consumption of each space. A i r f l o w r a t e s through t h e v e n t i l a t i o n f a n s were m n i t o r e d once a week and a d j u s t e d i f necessary. This was done by measuring t h e p r e s s u r e drop a c r o s s a c a l i b r a t e d l e n g t h of d u c t downstream of t h e f a n o u t l e t . A d a t a l o g g e r scanned and recorded t h e d a t a on a magnetic t a p e f o r processing.

AIR OUTLET

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3. DATA ANALYSIS Data v e r e c o l l e c t e d f o r about f o u r # n t h 8 d u r i n g t h e h e a r i n g s e u o n . A number of h e a t - f l w value8 and p e r f o r m n c e p a r a n t a r s have k e n c n l c u l a t e d from t h e c o l l e c t d data. I h e y a r e i n d i c a t e d s c h e m t i c a l l y on Figure 4 and a u v r i t e d i n the f o l l d n g . 3.1 B u t u n i t ( c o n t r o l )

Envelope h a r t l o s s , Qle

-

E(UA), (Tr,-T0)bt South vindow h e a t l o s s .

&.

-

& (UA) (Tre

-

To) A t V e n t i l a t i o n h e a t Poaa. v h e r e V e n t i l a t i o n h e a t 10.8, Qw

-

f VP cp(T,

-

To) A t Envelope loam, Qlv

-

Bv + Qsv + Q, + Qe

-

Q, where

Tout

-

a i r t e a p e r a t u r e a t supply-air windcw o u t l e t , K

v

-

r u b r c r i p t d e n o t i n g v e s t u n i t (rupply-air window).

k envelope l o s s e s ( o t h e r than s o u t h vindov) and v e n t i l a t i o n Loases f o r both t h e t e s t u n i t (Qcv) and t h e c o n t r o l u n i t (Qce) a r e assumed t o be e q u a l , t h e d i f f e r e n c e i n t h e e l e c t r i c energy conaurption f o r t h e two u n i t s represents t h e d i f f e r e n c e i n t h e n e t h e a t g a i n of t h e r e s p e c t i v e v i n d w s . Heat l o s s through t h e supply-air vindov t o o u t e i d e ,

G ,

i s c a l c u l a t e d t h e r e f o r e from t h e r e l a t i o n :

-

o v e r a l l envelope h e a t 10.8 c o e f f i c i e n t , V/K

*

eouth vindov ( i n c l u d i n g frame) h e a t 108s c o e f f i c i e n t , V/K

-

room a i r t a c p e r a t u r e , K

-

outdoor a i r t e a p e r a t u r e , K

-

v e n t i l a t i o n air-flow r a t e , m3/r

-

s p e c i f i c h e a t of a i r , Y s / k g K

-

s o l a r g a i n f a c t o r f o r s o u t h double-glazed v i n d w

-

s o l a r g a i n f a c t o r f o r n o r t h double-glazed v i n d w

-

n e t s o u t h windou gla.8 a r e a , m2

-

n e t n o r t h window g l a a s a r e a ,

d

-

i n c i d e n t r a d i a t i o n on s o u t h vindov, V/ m2 Hns

-

i n c i d e n t r a d i a t i o n on n o r t h vlndav, U/ a2

P

-

energy consumption, kUh

A t = d a t a l o g g e r i n t e g r a t i o n period, h e

-

s u b s c r i p t d e n o t i n g e a s t unit.

For the c o a c r o l u n i t , t h e envelope h e a t 108s c o a f f i c i e n t , UA, obtained d u r i n g a previous r t u d y (8) 18 used f o r t h e c a l c u l a t i a t . In a d d i t i o n , t h e average s o l a r g a i n f a c t o r s t o r south- and north-facing d o u b l e g l u e d window vere obtained using d a t a from Rcfarence 9 (0.74 and 0.72, r e s p e c t i v e l y ) .

The aouth v i n d w tos8 c o e f f i c i e n t ( i n c l u d i n g fr-) i n t h n a s 2.85 ~ l d K; t h i s value w a s o b t a i n e d i n a guarded h o t bar measurement f o r a s i m i l a r v i n d w . 3.2 V e s t u n i t (supply-air vindov) I n a d d i t i o n t o a number of energy f l o w c a l c u l a t e d a 8 f o r t h e c o n t r o l u n i t , o t h e r v a l u e s a r e c a l c u l a t e d unique t o t h e p r e s e n t one:

lieat g a i n by a i r flow through vindov, Qa E

v

Cp(ToUt

-

To) A t

The h e a t l o s e through t h e i n n e r panes of t h e s u p p l y - a i r w i n d w , Qiw, may be c a l c u l a t e d a s :

Q i v

-

Q,

+ Q,

These c a l c u l a t i o n r i n c l u d e a f e v arsumptiona. k _{t h e envelope h e a t l o s s}

c o e f f i c i e n t of t h e u n i t was not known (due t o t h e i n s t a l l a t i o n of t h e supply-air vindov), i t v a s a e e u w d , s i n c e both u n i t s a r e of s i m i l a r c o n s t r u c t i o n , t h a t t h e h e a t l o s s e s through t h e opaque envelope

coaponenta a r e e q u a l f o r both u n i t s . In a d d i t i o n , t h e n e t thermal s t o r a g e of b o t h u n i t r was assumed t o be t h e earn? ( t h i s f a

c a l c u l a t e d a s Qe f o r t h e c o n t r o l u n i t ) . As

v i l l be shown, t h i s assumption has a n i m i g n i f i c a n t e f f e c t on t h e seasonal r e s u l t s and o n l y a s m a l l e f f e c t on t h e t o t a l day o r n i g h t tiu r e a u l c s i f c a l c u l a t e d separately. A t h i r d u s u t u p t i o n i n v o l v e r the c a l c u l a ~ i ~ n of r o l a r gain. through t h e supply-air

vindou. The s o l a r g a i n f a c t o r Lor t r l p l e g l a z i n g i n used f o r c h i s c a l c u l a t i o n (0.67). It r u y i n t r o d u c e some e r r o r s i n c e t h e inward-flowing f r a c t i o n of t h e absorbed s o l a r energy i n t h e o u t e r pane may be smaller due t o added convection t o t h e v e n t i l a t i o n a i r . The e r r o r is, h w e v e r , very s m a l l ( l e e r than 0.5 percent of t h e s o l a r g a i n ) .

Dnta f o r t h e e a r t ( c o n t r o l ) u n i t v e r e a d j u s t e d t o account f o r a s l i g h t d i f f e r e n c e i n a v e r a g e indoor temperature and

(8)

(1 1.4 L/r and 11.6 L/r f o r e u t and v e s t Under t h e t e s t c o n d i t i o n r , t h e f o l l w i n g u n i t s , reopectively). &st u n i t r e s u l t s a r e o b s e r v a t i o n s were made:

I d j u s t a d f o r window h e a t l o s s and s o l a r g a i n

t o o b t a i n a n e q u i v a l e n t c o n t r o l u n i t w i t h a 1. 010 average, t h e a i r t e a p e r a t u r e rise i n t r i p l a - g l u e d v i n d w .

Tha

U-value and r o l a r t h e vindov is a p p r o l d ~ t e l y 50 p e r c e n t of g a i n f a c t o r f o r t r i p l e g l n i n g a r e t a k e n a s t h e t e q e r a t u r e d i f f e r e n c e between indoor 1.85 ~ / m 2 K and 0.68, r e s p e c t i v e l y (9). and outdoor temperatures. This r a t i o 1s

l o r n r a t n i g h t (44 p e r c e n t ) and h i g h e r d u r i n g t h e day (58 p e r c e n t ) oving t o t h e 4. BZSULTS AND DISCUSSION

Results f o r t h e t o t a l m n i t o r i n g p e r i o d a r e 8 t n u r i z . d i n Table 1; 8-18. o f t h e c o a d i t i o l u d u r i n g t h e m n i t o r i n g p e r i o d a r e g i v e n i n T a b l e 2. Of i n t e r e s t is t h e v e n t i l a t i o n a i r t e q e r s t u r e a t t h e s u p p l y v i n d w o u t l e t . To i n d i c a t e 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 t h e r s s u l t s and th. p o t e n t i a l e f f e c t of t h e s u p p l y - a i r v i a d w a t o t h e r o r i e n t a t i o r u , d a t a a r e s p l i t i n t o t o t a l s d u r i n g d a y t i m (6:00 am t o 8:00 pm) and n i g h t t i m (9:OO pa

-

5:00 U ) and presented i n Tables 3 and 4, r e s p e c t i v e l y . These p e r i o d s a r e s e l e c t e d t o minimize t h e e f f e c t of thermal s t o r a g e , from day t o n i g h t , on t h e r e s u l t s .

Over th. monitoring p e r i o d ( a t o t a l of 3000 la) t h e n e t ermrgy b a l a n c s , which r e p r e s e n t s t h e n e t enargy s t o r a g e i n t h e u n i t and should approach z e r o , v a s indeed found t o k i n o i g n i f i c a n t v i t h r e s p e c t t o o t h e r ermrlpr v a l u e s ( o n l y about 6 kUh). T h i s may r e f l e c t t h e accuracy of t h e energy c o . e o w n t s c o r u t i t u t i n g t h e energy balance. Day and n i g h t ti- d a t a shov l a r g e r

(74 and 68 kUh, r e s p e c t i v e l y ) t h e n u l s t o r a g s components, an expected r e s u l t of t h e s o l a r energy e f f e c t . I d d i t l o ~ l r o i a r h e k i n g e f f a c t . Under t h e latest outdoor t e q e r a t u r e c o n d i t i o n g i v e n i n Table 2, t h i s r a t i o i s a l s o 45 percent. Thew result8 a g r e e v i t h p r e v i o u s l y r e p o r t e d l a b o r a t o r y s t u d i e s . C o r r u p o n d i n g l y , t h e h e a t g a i n by t h e v e n t i - l a t i o n a i r i n t h e supply-air vindov amounts t o about 50 p e r c e n t of t h e t o t a l ' energy r e q u i r e d t o h e a t i t t o room temperature. k

noted i n T a b l e 2, a s w e l l , under r o w runny c o n d i t i o n s t h e v e n t i l a t i o n a i r h e a t g a i n may c o n t r i b u t e t o o v e r h e a t i n g of t h e rpace. 2. Coaparad t o a t r i p l e - g l a z e d window, t h e h e a t 1088 through t h e i n n e r g l a z i n g of t h e supply-sir vlndow f n c r e u e d , but i t d i d n o t reach t h e magnitude of t h e l o u r through a double%lazed vindov. I n a d d i t i o n , most of t h i s h e a t l o a s is recovered by t h e a i r f l o v , r e s u l t i n g i n a very small o v e r a l l h a t l o s s through t h e o u t e r pane t o o u t r i d e . k i n d i c a t e d i n Tables 1 and 3, d u r i n g t h e monitoring p e r i o d less than 20 p e r c e n t of t h e h e a t flow through t h e i n n e r penes v a s a c t u a l l y l o s t t o outside. This r e p r e r e n t s l e s s than 20 percent of t h e h e a t l o r e through a t r i p l e g l a z e d window and only 15 percent of t h a t through a double-glazed window.

ENVELOPE LOSS

V€NTlUTlON LOSS ~ X C W D I N G S O V T ~ WINDOW

5. SOW GAIN S. WINDOW HEAT LOSS, a,

k

RJRCMED ENERGY CONTROL U N I T _E. \ . 3. k an i n d i c a t i o n of t h e t h e n u l p e r f o n m a c e of t h e rupply-air window, an e q u i v a l e n t h e a t l o s s c o m f f i c i e n t (U-value) c a n be bared on t h e n e t h e a t l o s s through t h e o u t e r pane o v e r a l l n i g h t ti= hours. The average c a l c u l a t e d h e a t l o s e c o e f f i c i e n t is about 0.45 w/m2 K, v h i c h a g r e e s v i t h p r e v i o u s t h e o r e t i c a l v a l u e s (6). 4. Gvsr t h e monitoring pariod energy conrumption of t h e u n i t with t h e r u p p l y r i r v i n d a r w u 25 p e r c s n t l e s s than t h a t of t h e c o n t r o l u n i t f o r a d o u b l c g l a z s d window and 20 p e r e s n t l e s s than t h a t of a n e q u i v a l e n t c o n t r o l u n i t f o r a t r i p l e - g l u s d vindov. A t n i g h t t h e s e r a t i o s ware about 22 and 17 p e r c s n t , b ) SUPPLY-AIR W I N D O W U N I T

.'

L Figure 4. Erurgy b e l u ~ c e r e s p e c t i v e l y , a n i n d i c a t i o n of t h e ~ e r f o n u n c e a t t a i n a b l e f o r s i i l a r windows o r i e n t e d o t h e r than routh.

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TABU 1. Seaaorul eturgy.balance (3000 h) bit

S u p p l y a i r Double-glued Triple-gluad

b u u r e n n t rindor Winda Window

Av outdoor a i r t a w , 'C -5.3 -5.3 -5.3

A r indoor a i r t a w , 'C ' 20.5 20.2 20.5

Av vane a i r o u t l e t t a w , 'C 8.2

-

Vent a i r heat gain, kUh 567.0

-

Vent haat l o a s , kUh 1081.0 1081.0 1081.0

8UVOlope heat 10.8

( e x e l rout h windw)

,

kUh 1286.0 1286.0 1286.0

South windw molar gain, kYh 543.0 590.0 543.0

k r t h vindar molar gain, kUh 71.0 71.0 71.0

Total p u t c h u d e n e r a , kUh 1870.0 2506.0 2352.0

Energy from storage, kUh -6.0 -6. 0 -6.0

South windw heat loor,* kYh 117.0 794.0 593.0

Heat 10.8 though inner

panma of aouth v i n d w , kUh 684.0 794.0 593.0

*Includes f r . u loma and molar energy contribution

TABLE 2. Supply window o u t l e t t e q e r a t u r e under d i f f e r e n t conditions

D.1

16 20 56 16

T i m 06:OO 00:OO 13:15 12:OO

Outdoor tamparacure, 'C -25.0 -10.0 1.9 -20.0

South molar radiation, id/& 0.9 0.0 880.0 950.0

Wind opead, m/r calm 1.4 calm 2.8

lbom t e q e r a t u r a , 'C 20.2 20.2 27.3 21.5

Supply-air vindou o u t l e t temperature, 'C -4.6 5.0 32.8 17.1

TABLE 3. Nlght energy balance (1219 h) U n i t

S ~ ~ p p l ~ l i t Double-glared Triple-glared

!haauramot window Windw Window

Av outdoor a i r tecp, 'C -6.0 -6.0 -6.0

k indoor a i r tecp, 'C 20.1 20.0 20.1

Av vane a i r o u t l e t t e q , 'C 5.6

-

Vent a i r heat pain, kYh 198,O

-

Vantilation heat 1008, kUh 446.0 446.0 446.0

Envelop. heat l o r e

(excluding mouth windor), kYh 53010 530.0 530.0

South r i n d w molar gain, kUh 0.0 0.0

North window molar gain, kUh 0.0 0.0

Total purchued energy, kYh 958.0 1234.0 1152.0

Enarm from rtoraga, kYh 68. 0 68.0 68.0

South windav hear lor@,* kYh 50. 0 326.0 244.0

h a t lo88 though

inner

pa-8, kwh 248.0 326.0 244.0

Window e f f o c t i r e hoar

loaa c o e f f i c t e n t , V / ~ K 0.44 2.85 2.13

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TABLE 4. Daytipc energy balance (1781 h)

-- - --

hit

Supply-air Double-glazed Triple-glazed

vindov Window Uindov

Av outdoor a i r t e q , 'C -4.8 -4.8 -4.8 Av indoor a i r temp, 'C 20.7 20.3 20.7 Av vent a i r o u t l e t temp, 'C 10.0

-

Vent a i r h e a t g a i n , kUh 370.0

-

V e n t i l a t i o n h e a t l o s s , kUh 636.0 636.0 636.0 Envelope h e a t l o s s

(excluding s o u t h vindow), kUh 787.0 1224.0 1106.0 South window s o l a r g a i n , kUh 543.0 590.0 543.0 North window s o l a r g a i n , kUh 71.0 71.0 71.0 T o t a l purchamed energy, kUh 913.0 1273.0 1202.0 Energy from s t o r a g e , ' kUh -74.0 -74.0 -74.0 *Negative i n d i c a t e s energy i n t o s t o r a g e

An experimental study h a s k e n performed a t a n outdoor t e s t f a c i l i t y t o a s s e s s t h e p o t e n t i a l performance of a supply-air vindov and its i a p a c t on energy consumption. The v i n d w was a factory-sealed double-glazed v i n d w r e t r o f i t t e d v i t h a n a d d i t i o n a l pane on t h e outside. Air f l w through t h e vindov recovered a l a r g e f r a c t i o n of t h e h e a t l o s s ; t h i s represented about 50 percent of t h e energy r e q u i r e d t o h e a t v e n t i l a t i o n a i r . The e f f e c t i v e U-value of t h e v i n d w v a s found t o be i n t h e o r d e r of 0.5 W/mZ K. The o v e r a l l reduction i n purchased energy of t h e aupply-air vindov u n i t r e l a t i v e t o a s i m i l a r double-glazed vindow u n i t o r t o a

t r i p l e g l u e d v i n d w u n i t is about 25 and 20 percent, i e s p e c t i v e l y . This i n d i c a t e s a good p o t e n t i q l f o r supply-air v i n d w s ; more work is needed t o optimize any d e s i g n based on t h i s concept and on t h e i n t e g r a t i o n of t h e vindov v i t h t h e b u i l d i n g system.

(1) Sodergren, D. and Bostroo, T.

' V e n t i l a t i n g v i t h t h e Exhaust A i r Window,' ASHRAE J o u r n a l ( A p r i l 1971).

( 2 ) Cabrielason. J. 'Extract-air Windov. A b y t o B e t t e r Heat Economy i n Buildings,' Proc. 10th World Energy Conference, I s t a n b u l , Turkey (September 1977). ( 3 ) Wiart, L.B. and S u v a c h i t t a n o n t , S.

'Performance and E c o n o d c Analysis of Air P l w Windove i n A T r o p i c a l Climate." Energy Research,

2,

441-447 (1985).

( 4 ) Chapman, W.F. 'Less Ref r i g e r a t i o n : More c l a s s , A Compatible I d e a ? , " ASHRAE J o u r n a l (February 1979).

( 5 ) Korkala, T., Saarnio. P., and S i i tonen, V. 'Air I n t a k e Arrangements of t h e Supply-Air Windov from t h e View of Comfort and V e n t i l a t i o n E f f i c i e n c y , ' Proc. Windws i n Buildings, Sweden (June 1984).

( 6 ) T j e l f l a a t , P.O., and Bergensen, 8. 'Improved Thermal I n s u l a t i o n i n Uindws by Laminar Air Plovs,' Proc. Thermal

Performance of t h e E x t e r i o r Envelopes of Buildings 111 (December 1985).

( 7 ) Wright, J.L. ' E f f e c t i v e U-values and Shading Coef f i c i e n t s of Prebeat/Supply Air Glazing Systems,' Proc. S o l a r

Energy Society of Canada Conference ( J u l y 1986).

( 8 ) Barakat, S.A. lRCC Passive S o l a r Test F a c i l i t y , D e s c r i p t i o n and Data Reduction,' National Research Council of Canada, Division of Building Research, BR Note 214 (1984).

( 9 ) Barakat, S.A. "Solar Heat Gains through Uindovs i n Canada,' National Research Council of Canada, Division of Building Research, NRCC 18674 (1980).