Experimental studies on exterior wall venting for smoke control in tall office buildings

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Experimental studies on exterior wall venting for smoke control in tall

office buildings

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National R e s e a r c h Council of Canada

Q , ,J

Conseil national d e r e c h e r c h e s du Canada

EXPERIMENTAL STUDIES ON EXTERIOR WALL VENTING FOR

SMOKE CONTROL IN T A L L O F F I C E BUILDINGS

by

George T. T a m u r a

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R e p r i n t e d f r o m

ASHRAE T r a n s actions

Vol. 84, P a r t 2, 1978

p. 204

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215

DBR P a p e r No. 833

Division of Building R e s e a r c h

8

APR

1s

1979

P r i c e 25 cents

OTTAWA

NRCC 17279

S

OMMAI

RE

/

Des gtudes ont ete menges sur la ventilation des murs extgrieurs dans

le contexte de la pressurisation des bitiments destin6e 5 contrsler

la fumge. I1 a

6t6

dgmontr; que le degrg de ventilation dgpend du taux

de pressurisation dans le bgtiment, de la surface de ventilation et de

la surface de fuite dans l'enveloppe de l'gtage. Des essais effectugs

sur deux b2timents de grande hauteur ont rgvglg que la ventilation

d'une surface qui est ggale

5

_{un pour cent de la surface extzrieure}

totale du mur de l1;tage ventilg se rapprochait du taux de ventilation

maximal. ~'aprGs

ce taux, les diffgrences de pression favorable sur

l'enveloppe coupe-feu de l'gtage atteignent leurs plus hautes valeurs

et sont

5

_{peine infgrieures 5 la moitige de la pressurisation du}

batiment

,

sans ventilation. Les essais ont 6galement dgmontr; que

le vent n'a pas tendance

h

inf

luer sgrieusement sur le rendement

de la ventilation sauf dans le cas oii les tuyaux de ventilation

des murs ne donnent que sur le mur expose/

au vent.

No.

2504

EXPERIMENTAL STUDIES ON EXTERIOR

WALL VENTING FOR SMOKE CONTROL

IN TALL OFFICE BUILDINGS

GEORGE T. TAMURA, P.E.

Member ASHRA E ABSTRACT

S t u d i e s were c o n d u c t e d on e x t e r i o r w a l l v e n t i n g i n t h e c o n t e x t of t h e b u i l d i n g p r e s s u r i z a t i o n a p p r o a c h t o smoke c o n t r o l . I t was shown t h a t t h e v e n t i n g r a t e d e p e n d s on t h e amount o f b u i l d i n g p r e s s u r i z a t i o n , v e n t a r e a and t h e l e a k a g e a r e a o f t h e f l o o r e n c l o s u r e . T e s t s on two m u l t i - s t o r y b u i l d i n g s i n d i c a t e d t h a t a v e n t a r e a e q u a l t o one p e r c e n t of t h e t o t a l e x t e r i o r w a l l a r e a of t h e v e n t e d f l o o r a p p r o x i m a t e d t h e maximum v e n t i n g r a t e . A t t h i s r a t e , t h e f a v o r a b l e p r e s s u r e d i f f e r e n c e s a c r o s s t h e f i r e f l o o r e n c l o s u r e a r e a t t h e i r h i g h e s t v a l u e s a n d a r e j u s t a l i t t l e l e s s t h a n o n e - h a l f of t h e b u i l d i n g p r e s s u r i z a t i o n w i t h no v e n t i n g . T e s t s a l s o i n d i c a t e d t h a t wind i s u n l i k e l y t o s e r i o u s l y a f f e c t t h e v e n t i n g p e r f o r m a n c e e x c e p t f o r t h e c a s e w i t h t h e w a l l v e n t s opened o n l y on t h e windward w a l l . INTRODUCTION Venting o f h e a t a n d smoke g e n e r a t e d b y a f i r e i s r e c o g n i z e d a s a n a i d t o f i r e f i g h t e r s a n d t o o c c u p a n t s i n g a i n i n g a c c e s s t o r e f u g e a r e a s o r o u t d o o r s . One means of v e n t i n g t h e f i r e r e g i o n i s t o p r o v i d e o p e n a b l e p a n e l s o r windows i n t h e e x t e r i o r w a l l s ; o t h e r s a r e smoke s h a f t s 1 a n d m e c h a n i c a l v e n t i n g 2 . The f o r m e r method, which i s t h e s u b j e c t o f t h i s p a p e r , p e r m i t s d i r e c t v e n t i n g o f smoke from t h e f i r e f l o o r t o t h e e x t e r i o r ; t h e l a t t e r methods a l l o w smoke from t h e f i r e f l o o r t o f l o w i n t o a n d o u t o f t h e e x h a u s t s h a f t e x t e n d i n g a b o v e t h e r o o f o f a b u i l d i n g .

T h i s p a p e r d i s c u s s e s t h e c o n d i t i o n s u n d e r which e x t e r i o r w a l l v e n t i n g c a n b e a p p l i e d

e f f e c t i v e l y t o m u l t i - s t o r y b u i l d i n g s a n d gj.ves a g u i d e l i n e f o r d e t e r n i n i n g t h e r e q u i r e d s i z e of v e n t o p e n i n g s f o r c o n t r o l l i n g smoke movement. The r e s u l t s of e x t e r i o r w a l l v e n t i n g t e s t s c o n d u c t e d on two m u l t i - s t o r y o f f i c e b u i l d i n g s a r e a l s o r e p o r t e d .

EXTERIOR WALL VENTING

F i g . 1 i l l u s t r a t e s t h e smoke movement w i t h e x t e r i o r w a l l v e n t i n g f o r v a r i o u s f i r e c o n d i t i o n s . For a l l b u t t h e l a s t two c a s e s , i t i s assumed t h a t t h e b u i l d i n g a i r h a n d l i n g s y s t e m s a r e s h u t down.

A . V e n t i n g (summer)

-

With t h e i n s i d e t e m p e r a t u r e e q u a l t o o u t s i d e t e m p e r a t u r e , t h e i n s i d e and o u t s i d e p r e s s u r e s a r e t h e same a s shown on t h e p r e s s u r e d i a g r a m t o t h e r i g h t of a s i m p l e model b u i l d i n g . Under t h i s s i t u a t i o n t h e r e i s l i t t l e a i r movement w i t h i n a b u i l d i n g

.

With a f i r e on one f l o o r , t h e a i r t e m p e r a t u r e s on t h a t f l o o r a r e h i g h e r t h a n t h o s e of t h e s u r r o u n d i n g s p a c e s r e s u l t i n g i n l o c a l s t a c k a c t i o n . T h i s c a u s e s a i r t o flow i n t o t h e f i r e f l o o r t h r o u g h t h e lower l e a k a g e o p e n i n g s o f t h e w a l l s of v e r t i c a l s h a f t s

( e l e v a t o r , s t a i r , s e r v i c e ) and o u t s i d e w a l l s , and c a u s e s smoke and h o t g a s e s t o f l o w o u t from t h e f i r e f l o o r t h r o u g h t h e u p p e r l e a k a g e o p e n i n g s i n t h e s e w a l l s . Venting o f t h e

G.T. Tamura i s a R e s e a r c h O f f i c e r i n t h e Energy and S e r v i c e s S e c t i o n , 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 , Nationa 1 R e s e a r c h C o u n c i l of Canada, Ottawa, O n t a r i o . KIA OR6

f i r e f l o o r c a n g r e a t l y i n c r e a s e t h e r a t e of r e l e a s e o f h e a t a n d smoke t o t h e e x t e r i o r , b u t some smoke w i l l p r o b a b l y m i g r a t e i n t o t h e e l e v a t o r and s t a i r s h a f t s .

When wind p r e s s u r e s a r e a c t i n g on t h e w a l l s of a b u i l d i n g , opening t h e v e n t s o n l y on t h e windward w a l l w i l l r a i s e t h e p r e s s u r e s o f t h e f i r e f l o o r above t h o s e o f o t h e r f l o o r s a n d , h e n c e , i n c r e a s e t h e r a t e of smoke f l o w i n t o t h e e l e v a t o r and s t a i r s h a f t s . I f t h e v e n t s on t h e l e e w a r d a n d s i d e w a l l s a r e a l s o open, t h e f l o w o f smoke i n t o t h e s h a f t s may b e r e d u c e d depending on t h e l o c a t i o n o f t h e f i r e r e g i o n w i t h r e s p e c t t o t h e w a l l v e n t s . Opening t h e v e n t s o n l y on t h e leeward and s i d e w a l l s c a n lower t h e p r e s s u r e s on t h e f i r e f l o o r below t h o s e o f o t h e r f l o o r s , which w i l l a s s i s t i n p r e v e n t i n g smoke from f l o w i n g i n t o t h e v e r t i c a l s h a f t s .

B. Venting o f l o w e r f l o o r ( w i n t e r ) - B u i l d i n g s t a c k a c t i o n u n d e r w i n t e r c o n d i t i o n s c a u s e s a n upward f l o w o f a i r w i t h i n a b u i l d i n g . Thus, w i t h a f i r e on a lower f l o o r , smoke m i g r a t e s i n t o and up t h e v e r t i c a l s h a f t s t o c o n t a m i n a t e t h e u p p e r f l o o r s a t a much more r a p i d r a t e t h a n u n d e r t h e summer c o n d i t i o n 3 . The p r e s s u r e d i a g r a m shows t h a t on t h e lower f l o o r s o u t s i d e p r e s s u r e s a r e h i g h e r t h a n i n s i d e p r e s s u r e s s o t h a t when t h e v e n t s a r e opened, a i r f l o w s from o u t s i d e i n t o t h e f i r e f l o o r . F i r e f l o o r p r e s s u r e s a r e r a i s e d and a p p r o a c h o u t s i d e p r e s s u r e s w i t h a c o r r e s p o n d i n g i n c r e a s e i n t h e u n f a v o r a b l e p r e s s u r e d i f f e r e n c e s a c r o s s t h e w a l l s o f t h e v e r t i c a l s h a f t s , r e s u l t i n g i n a s u b s t a n t i a l i n c r e a s e i n t h e r a t e o f smoke c o n t a m i n a t i o n o f t h e v e r t i c a l s h a f t s a n d u p p e r f l o o r s . C . V e n t i n g o f u p p e r f l o o r ( w i n t e r ) - A s t h e i n s i d e p r e s s u r e s a r e g r e a t e r t h a n t h e o u t s i d e p r e s s u r e s , v e n t i n g t h e f i r e f l o o r on t h e u p p e r f l o o r s c a u s e s a n o u t f l o w of a i r from t h e f i r e f l o o r t o o u t s i d e , c a u s i n g a r e d u c t i o n i n t h e f i r e f l o o r p r e s s u r e s below t h o s e of a d j a c e n t f l o o r s a n d v e r t i c a l s h a f t s . Hence, u n d e r t h i s c o n d i t i o n , smoke i s p r e v e n t e d from s p r e a d i n g i n t o a d j a c e n t s p a c e s w i t h i n a b u i l d i n g . D . V e n t i n g w i t h b u i l d i n g p r e s s u r i z a t i o n (summer)

-

V e n t i n g t h e f i r e f l o o r e i t h e r i n t e n t i o n a l l y o r u n i n t e n t i o n a l l y ( a s b y window b r e a k a g e s c a u s e d by t h e h e a t o f t h e f i r e ) c a n a g g r a v a t e problems a s s o c i a t e d w i t h smoke m i g r a t i o n . The p r e s s u r e s i n s i d e a b u i l d i n g must b e r a i s e d , t h e r e f o r e , above o u t s i d e p r e s s u r e s a t a l l l e v e l s , t o e n s u r e t h a t t h e f i r e f l o o r p r e s s u r e d e c r e a s e s when t h e v e n t s a r e o p e n e d . T h i s c a n be a c c o m p l i s h e d b y p r e s s u r i z i n g a l l f l o o r s w i t h a l l o r some o f t h e s u p p l y a i r s y s t e m s o f a b u i l d i n g o p e r a t i n g a t 100 p e r c e n t o u t s i d e a i r and t h e r e t u r n and e x h a u s t s y s t e m s s h u t down.

Under summer c o n d i t i o n , w i t h e q u a l r a t e s o f s u p p l y o f o u t s i d e a i r t o a l l f l o o r s , t h e amount of b u i l d i n g p r e s s u r i z a t i o n i s u n i f o r m a t a l l h e i g h t s o f a b u i l d i n g . Opening t h e w a l l v e n t s on a n y f l o o r w i l l r e s u l t i n t h e same amount o f r e d u c t i o n i n t h e f l o o r s p a c e p r e s s u r e s f o r v e n t s o f e q u a l s i z e on a l l f l o o r s .

E . V e n t i n g w i t h b u i l d i n g p r e s s u r i z a t i o n ( w i n t e r )

-

I n w i n t e r w i t h t h e b u i l d i n g p r e s s u r i z e d i n t h e same manner a s f o r t h e p r e v i o u s c a s e , t h e amount o f b u i l d i n g p r e s s u r i z a t i o n r e l a t i v e t o o u t s i d e p r e s s u r e i s l e a s t on t h e ground f l o o r and g r e a t e s t on t h e t o p f l o o r . T h i s i s due t o s t a c k a c t i o n which c a u s e s t h e o u t s i d e a i r s u p p l i e d t o t h e lower f l o o r s t o f l o w up t h r o u g h t h e v e r t i c a l s h a f t s t o u p p e r f l o o r s . C o n s e q u e n t l y , t h e p r e s s u r e s o f a v e n t e d f l o o r l o c a t e d a t u p p e r l e v e l s a r e r e d u c e d more t h a n t h o s e l o c a t e d a t lower l e v e l s . Hence, t h e v e n t i n g r a t e s and t h e p r e s s u r e d i f f e r e n c e s a c r o s s s t a i r and e l e v a t o r d o o r s on t h e v e n t e d f l o o r o f t h e upper f l o o r s a r e g r e a t e r t h a n t h o s e o f t h e lower f l o o r s . Except f o r t h e c a s e when t h e v e n t s a r e opened o n l y on t h e windward w a l l , wind a c t i o n i s

u n l i k e l y t o a f f e c t s e r i o u s l y t h e p e r f o r m a n c e o f t h i s method o f smoke c o n t r o l f o r o f f i c e b u i l d i n g s i n which t h e o c c u p a n t s a r e e x p e c t e d t o v a c a t e t h e f i r e f l o o r soon a f t e r t h e s t a r t o f a f i r e . VENT SIZES With t h e b u i l d i n g p r e s s u r i z e d , o p e n i n g t h e w a l l v e n t s c a u s e s a i r t o f l o w from t h e a d j a c e n t f l o o r s i n t o t h e v e n t e d f i r e f l o o r and o u t t h r o u g h t h e v e n t s ( F i g . 2 ) . Assuming t h a t t h e s u p p l y a i r t o t h e v e n t e d f l o o r i s s t o p p e d , i t f o l l o w s t h a t t h e t o t a l a i r f l o w r a t e t h r o u g h t h e w a l l v e n t s e q u a l s t h e a i r f l o w r a t e i n t o t h e v e n t e d f l o o r from t h e s u r r o u n d i n g s p a c e s , 1 i . e . , AV(Pf

-

P ~= )Ae(Pi ~ - Pf)

4

where, A = l e a k a g e a r e a i n terms o f e q u i v a l e n t o r i f i c e a r e a P = p r e s s u r e s u b s c r i p t s v = w a l l v e n t f = f i r e f l o o r o = o u t s i d e e = e n c l o s u r e o f f i r e f l o o r i = non-vented f l o o r

The l e a k a g e a r e a o f t h e f i r e f l o o r e n c l o s u r e (Ae) i s t h e sum o f t h e l e a k a g e a r e a s o f t h e w a l l s o f t h e v e r t i c a l s h a f t s , t h e f l o o r c o n s t r u c t i o n s a n d t h e a i r d u c t o p e n i n g s ( r e t u r n , e x h a u s t ) o f t h e v e n t e d f l o o r . Eq 1 assumes t h a t t h e p r e s s u r e s i n s i d e t h e v e r t i c a l s h a f t s a n d a i r d u c t s a r e e q u a l t o Pi. I n f a c t , t h e y a r e l e s s t h a n Pi b u t w i l l p r o b a b l y be c l o s e t o i t a s a i r f l o w s i n t o t h e s h a f t s and d u c t s from a l l f l o o r s e x c e p t t h e v e n t e d f l o o r (where i t f l o w s o u t ) .

T r a n s p o s i n g t e r m s i n Eq 1 , But L e t t h e n I (P. - P ) = (Pi - Pf) + (Pf

-

Po) 1 0

(Pi

-

Po) = AP (amount o f b u i l d i n g p r e s s u r i z a t i o n ) b

( P . - P ) = AP ( p r e s s u r e d i f f e r e n c e a c r o s s t h e f l o o r e n c l o s u r e )

1 f e

(Pf

-

Po) ' = APv ( p r e s s u r e d i f f e r e n c e a c r o s s t h e w a l l v e n t )

S u b s t i t u t i n g t h e above i n Eq 2 ,

The p l o t of E q 3 ( F i g . 3) shows t h a t a s t h e vent s i z e i s i n c r e a s e d f o r a g i v e n amount of b u i l d i n g p r e s s u r i z a t i o n (APb) a n d l e a k a g e a r e a o f t h e f i r e f l o o r e n c l o s u r e (Ae), t h e p r e s s u r e d i f f e r e n c e s a c r o s s t h e v e n t e d f l o o r e n c l o s u r e a r e i n c r e a s e d a s y m p t o t i c a l l y t o a maximum v a l u e (APb). A s t h e f l o w r a t e v a r i e s d i r e c t l y a s t h e s q u a r e r o o t of t h e p r e s s u r e d i f f e r e n c e , t a k i n g t h e s q u a r e r o o t of APe/APb g i v e s t h e r a t i o o f t h e flow r a t e t h r o u g h t h e v e n t o v e r t h e maximum f l o w r a t e (Qv/Qmx). These were a l s o p l o t t e d i n F i g . 3 .

When t h e v e n t a r e a i s e q u a l t o t h e l e a k a g e a r e a of t h e f l o o r e n c l o s u r e (AV/Ae = l ) , t h e n t h e p r e s s u r e d i f f e r e n c e s a c r o s s t h e f l o o r e n c l o s u r e a r e o n e - h a l f o f t h e b u i l d i n g p r e s s u r i z a t i o n

(APe/APb = 0 . 5 0 ) , and t h e flow r a t e through t h e v e n t i s 70 p e r c e n t o f t h e maximum v e n t i n g r a t e (Qv/Qllax = 0 . 7 0 ) . Also, when Av/Ae = 3 . 0 , APe/APb = 0.90 and Qv/Qmax = 0 . 9 5 . I n c r e a s i n g t h e v e n t s i z e f u r t h e r w i l l n o t s i g n i f i c a n t l y i n c r e a s e t h e v e n t i n g r a t e .

I n t h e f o r e g o i n g simple a n a l y s i s , i t was assumed t h a t t h e supply a i r f o r p r e s s u r i z a t i o n was stopped on t h e f i r e f l o o r . I f n o t , i t would be e x p e c t e d t h a t t h e v e n t s i z e r e q u i r e d t o o b t a i n a g i v e n v a l u e of A P e / A 4 , would be g r e a t e r t h a n t h a t shown i n F i g . 3. Information on t h e measured v a l u e s of A, o f a few o f f i c e b u i l d i n g s i s g i v e n i n Ref 2.

FIELD TESTS

Venting t e s t s were conducted on two m u l t i - s t o r y o f f i c e b u i l d i n g s u s i n g t h e windows a s a means of p r o v i d i n g v e n t openings. These t e s t s were conducted t o d e t e r m i n e t h e e f f e c t of v e n t s i z e on t h e v e n t i n g r a t e and t h e p r e s s u r e and a i r flow p a t t e r n s a c r o s s t h e d e s i g n a t e d f i r e f l o o r e n c l o s u r e . They were a l s o checked f o r c a s e s w i t h t h e s t a i r doors open on t h e v e n t e d f l o o r and o t h e r f l o o r s .

Venting T e s t s On Building A

Building A i s a 1 7 - s t o r y government o f f i c e b u i l d i n g w i t h a p l a n dimension of 26.8 m by 42.7 m and a f l o o r h e i g h t o f 3 . 3 5 m g i v i n g an o u t s i d e w a l l a r e a p e r f l o o r o f 466 m 2 . The windows a r e openable casement-type which a r e normally key l o c k e d . When f u l l y open, each window provided a f r e e a r e a of 1 . 6 5 m 2 . The t y p i c a l f l o o r l a y o u t i s given i n F i g . 4 .

Venting t e s t s were conducted on t h e 4 t h f l o o r o f t h i s b u i l d i n g w i t h a n o u t s i d e t e m p e r a t u r e of 18OC and low wind v e l o c i t y . The b u i l d i n g was p r e s s u r i z e d b y s h u t t i n g down a l l r e t u r n and

e x h a u s t f a n s and o p e r a t i n g a l l s u p p l y f a n s a t 100 p e r c e n t o u t s i d e a i r . The t e s t s involved opening t h e windows on t h e s o u t h w a l l of t h e 4 t h f l o o r t o o b t a i n t h e r e q u i r e d v e n t a r e a , and measuring t h e a i r v e l o c i t i e s a t t h e window opening t o d e t e r m i n e t h e t o t a l a i r flow r a t e through t h e s e windows. The a i r v e l o c i t i e s were measured w i t h a h o t - w i r e anemometer a t 1 2 l o c a t i o n s f o r each window and t h e r e a d i n g s were averaged f o r c a l c u l a t i o n s of a i r flow r a t e . The p r e s s u r e d i f f e r e n c e s a c r o s s t h e e l e v a t o r door, s t a i r door and a c r o s s t h e 4 t h and 5 t h f l o o r c o n s t r u c t i o n s were measured a s w e l l a s t h o s e a c r o s s t h e e x t e r i o r w a l l s o f s e v e r a l f l o o r s . A diaphragm-type p r e s s u r e t r a n s d u c e r w i t h a s i l i c o n p i e z o - r e s i s t i v e gauge w i t h a s t a t i c e r r o r band o f 5 p e r c e n t of f u l l - s c a l e o u t p u t was u s e d .

With a t o t a l v e n t a r e a of a b o u t 1 p e r c e n t of t h e w a l l a r e a (4.94 m2), t h e s t a i r d o o r on t h e 4 t h f l o o r was opened and t h e flow v e l o c i t i e s a t t h i s opening were measured. T h i s was r e p e a t e d w i t h t h e 4 t h and t h e 2nd f l o o r doors of t h e same s t a i r s h a f t open and, i n a d d i t i o n , a t e s t was conducted w i t h t h e 5 t h f l o o r s t a i r d o o r a l s o open.

Tho summary of t h e t e s t r e s u l t s i s given i n Table 1. T e s t s Nos. 1 through 5 were conducted w i t h v a r i o u s v e n t s i z e openings. I n c r e a s i n g t h e v e n t s i z e r e s u l t e d i n a c o r r e s p o n d i n g i n c r e a s e i n t h e v e n t i n g r a t e and a l s o a f a v o r a b l e p r e s s u r e d i f f e r e n c e a c r o s s t h e e n c l o s u r e o f t h e v e n t e d f l o o r . F i g . 5, which g i v e s t h e v e n t i n r a t e vs v e n t s i z e , shows t h a t t h e maximum v e n t i n g r a t e i s o b t a i n e d w i t h a v e n t a r e a of 4.94 mq ( s l i g h t l y g r e a t e r t h a n 1 p e r c e n t of t h e w a l l a r e a ) . The t o t a l l e a k a g e opening of t h e f l o o r e n c l o s u r e of t h i s b u i l d i n g was measured and r e p o r t e d i n Ref 2 a s 1 . 3 0 m2, g i v i n g t h e v a l u e of Av/Ae a s 3 . 8 . F i g . 3 , d e r i v e d from t h e o r e t i c a l c o n s i d e r a t i o n s , shows t h a t f o r p r a c t i c a l purposes t h e maximum v e n t i n g r a t e i s r e a c h e d a t about t h i s v a l u e . During t h e t e s t s , t h e o u t s i d e s u p p l y a i r t o each f l o o r f o r b u i l d i n g p r e s s u r i z a t i o n was about

1 . 2 0 m 3 / s .

The v e n t a r e a t h a t was r e l a t e d t o t h e leakage a r e a of t h e f l o o r e n c l o s u r e (Ae) i n t h e

p r e v i o u s s e c t i o n i s e x p r e s s e d i n p e r c e n t o f w a l l a r e a . The v a l u e s of Ae c a n v a r y from b u i l d i n g t o b u i l d i n g depending on t h e i n t e r i o r d e s i g n and c o n s t r u c t i o n ; i t is l i k e l y , however, t h e y a r e g r e a t e r f o r b u i l d i n g s w i t h l a r g e r f l o o r a r e a s , which a r e r e l a t e d t o t h e o u t s i d e w a l l a r e a and, hence, t h e o u t s i d e w a l l a r e a might b e used t o s p e c i f y t h e r e q u i r e d v e n t s i z e . I f t h r e e t i m e s t h e v a l u e of A, i s t h e r e q u i r e d v e n t s i z e , a check on t h e f o u r b u i l d i n g s 2 measured f o r t h e i r v a l u e s of A, gave t h e r e q u i r e d v e n t s i z e s a s 0.84, 0.76, 0.76 and 1 . 3 0 p e r c e n t of t h e w a l l a r e a .

I t would seem t h a t t h e r e i s some v a l i d i t y i n b a s i n g t h e v e n t i n g r e q u i r e m e n t s on t h e o u t s i d e w a l l a r e a .

B u i l d i n g p r e s s u r i z a t i o n w i t h t h e v e n t s c l o s e d was a b o u t 50 Pa ( F i g . 6 ) . With vent a r e a s of 1.64 m2 and 4.94 m2 i t was reduced t o a b o u t 27 and 23 Pa f o r a l l t y p i c a l f l o o r s o t h e r t h a n t h e v e n t e d f l o o r . The maximum p r e s s u r e d i f f e r e n c e s measured a c r o s s t h e f i r e f l o o r e n c l o s u r e were about 20 Pa (Table 1) o b t a i n e d w i t h a v e n t a r e a o f 4.94 m2 (1.06 p e r c e n t of w a l l a r e a ) . These

were s l i g h t l y lower t h a n t h e amount o f b u i l d i n g p r e s s u r i z a t i o n o f 23 Pa o b t a i n e d w i t h t h i s v e n t a r e a , o r l e s s t h a n h a l f o f t h e o r i g i n a l b u i l d i n g p r e s s u r i z a t i o n w i t h no v e n t i n g s .

The r e s u l t s o f t h e t e s t s c o n d u c t e d w i t h a 1 . 0 6 p e r c e n t v e n t a r e a and w i t h some s t a i r d o o r s open a r e a l s o g i v e n i n T a b l e 1 ( T e s t s Nos. 6, 7 and 8)

.

When one s t a i r d o o r on t h e 4 t h f l o o r

( v e n t e d ) was opened, t h e r a t e o f a i r flow i n t o t h e v e n t e d f l o o r t h r o u g h t h e open s t a i r d o o r was 1 . 6 0 m 3 / s ( a v e r a g e v e l o c i t y o f 0.82 m/s) accompanied by a r e d u c t i o n i n t h e p r e s s u r e d i f f e r e n c e s a c r o s s t h e f l o o r e n c l o s u r e t o a b o u t 1 5 Pa. When t h e 5 t h f l o o r d o o r o f t h e same s t a i r s h a f t was a l s o opened, t h e flow r a t e i n c r e a s e d t o 3 . 3 3 m 3 / s and, i n a d d i t i o n , when t h e 2nd f l o o r s t a i r door was opened, t h e flow r a t e i n c r e a s e d t o 4 . 2 3 m 3 / s . I n c r e a s i n g t h e number o f open s t a i r d o o r s r e s u l t e d i n a c o r r e s p o n d i n g r e d u c t i o n i n t h e p r e s s u r e d i f f e r e n c e s a c r o s s t h e f l o o r e n c l o s u r e . Opening t h e s t a i r d o o r on t h e v e n t e d f l o o r and o t h e r f l o o r s , i n e f f e c t , i n c r e a s e d t h e l e a k a g e a r e a o f t h e f l o o r e n c l o s u r e , A,. The s t a i r door t e s t s showed t h a t a i r f l o w s from t h e s t a i r s h a f t t o t h e v e n t e d f l o o r t h r o u g h t h e open s t a i r d o o r s o t h a t d u r i n g a f i r e smoke i s i n h i b i t e d from e n t e r i n g t h e s t a i r s h a f t . I f t h e v e n t i n g o f t h e f i r e f l o o r i s i n a d e q u a t e , smoke c a n e n t e r t h e s t a i r s h a f t i f a n o t h e r f l o o r i s n o t s u f f i c i e n t l y p r e s s u r i z e d and i f t h e d o o r s o f t h e same s t a i r s h a f t o f b o t h f l o o r s were o p e n . T h i s was d e m o n s t r a t e d by p r o v i d i n g a w a l l v e n t a r e a o f 1.64 m 2 , (0.35 p e r c e n t o f w a l l a r e a ) on t h e 4 t h and 2nd f l o o r s and o p e n i n g t h e s t a i r d o o r s on b o t h f l o o r s , t h u s

c o n n e c t i n g t h e two f l o o r s . P l a c i n g a v e n t opening i n t h e w a l l o f t h e 2nd f l o o r reduced t h e amount o f p r e s s u r i z a t i o n on t h i s f l o o r r e l a t i v e t o o t h e r f l o o r s . The d i r e c t i o n o f f l o w t h r o u g h t h e open s t a i r d o o r o f t h e 4 t h f l o o r was from t h e f l o o r i n t o t h e s t a i r s h a f t a t a r a t e o f 0.47 m 3 / s . T h i s emphasizes t h e need f o r a d e q u a t e v e n t i n g and e q u a l p r e s s u r i z a t i o n o f a l l t h e f l o o r s . S p e c i a l a t t e n t i o n s h o u l d b e g i v e n t o t h e p r e s s u r i z a t i o n o f t h e ground f l o o r a s t h i s f l o o r u s u a l l y h a s a h i g h e r e x t e r i o r w a l l l e a k a g e a r e a t h a n t h o s e of o t h e r f l o o r s , and i t may a l s o h a v e e s c a l a t o r a n d open s t a i r c o n n e c t i o n s t o f l o o r s below f o r o f f i c e s and shops s e r v e d by s e p a r a t e a i r h a n d l i n g s y s t e m s .

V e n t i n g T e s t s On B u i l d i n g B

B u i l d i n g B i s a 5 7 - s t o r y commercial o f f i c e b u i l d i n g w i t h a p l a n dimension o f 3 4 . 1 m by 6 8 . 3 m and a f l o o r h e i g h t o f 4 . 0 m g i v i n g a n o u t s i d e w a l l a r e a p e r f l o o r o f 811 m 2 . The f l o o r p l a n o f t h e 22nd f l o o r on which t h e w a l l v e n t i n g t e s t s were c o n d u c t e d i s g i v e n i n F i g . 7 . T h r e e f i x e d windows, each l o a c t e d a t t h e m i d - f a c e of e a s t , s o u t h and w e s t w a l l s o f t h e 22nd f l o o r , were removed and r e l a c e d by 2 plywood p a n e l d o o r s o f e q u a l s i z e f o r each window. The a r e a of e a c h

8

door was 1 . 2 m

.

T e s t s w e r e c o n d u c t e d w i t h t h e a i r h a n d l i n g s y s t e m s i n normal o p e r a t i o n which p r e s s u r i z e d t h e b u i l d i n g s u f f i c i e n t l y f o r t h e v e n t i n g t e s t s . The p r e s s u r e d i f f e r e n c e s a c r o s s t h e o u t s i d e w a l l s o f t h e s o u t h , e a s t and w e s t w a l l s on t h e 22nd f l o o r were, r e s p e c t i v e l y , -62, -65 a n d - 2 5 Pa ( r e f . p r e s s u r e

-

f l o o r s p a c e ) . The w e a t h e r r e p o r t e d b y t h e l o c a l m e t e o r o l o g i c a l s t a t i o n a t t h e t i m e o f t h e t e s t was -7'C and a w e s t wind o f 9 m / s . The l o w e r p r e s s u r e d i f f e r e n c e r e a d i n g a c r o s s t h e w e s t w a l l was c a u s e d b y t h e wind a c t i n g on t h e west f a c e o f t h e b u i l d i n g which was p a r t i a l l y s h i e l d e d by n e a r b y t a l l b u i l d i n g s . R e s u l t s o f t h e v e n t i n g t e s t s a r e g i v e n i n T a b l e 2. T e s t s Nos. 1 t h r o u g h 4 were c o n d u c t e d w i t h v a r i o u s v e n t s i z e o p e n i n g s i n t h e e a s t w a l l ( l e e w a r d w a l l ) a n d t h e s o u t h w a l l ( s i d e w a l l ) . A s shown i n F i g . 8 , t h e v e n t i n g r a t e i n c r e a s e d w i t h i n c r e a s i n g v e n t a r e a and a p p r o a c h e d a maximum v e n t i n g r a t e w i t h a n a r e a o f a b o u t 0 . 5 p e r c e n t o f t h e t o t a l w a l l a r e a o f t h e 22nd f l o o r . The p r e s s u r e d i f f e r e n c e a c r o s s t h e v e n t o p e n i n g s d e c r e a s e d w i t h i n c r e a s i n g v e n t a r e a , and a t n e a r t h e maximum v e n t i n g r a t e i t approached t h e z e r o v a l u e ( a l s o shown i n F i g . 8 ) . The r e q u i r e d v e n t a r e a i n t e r m s o f p e r c e n t a g e o f w a l l a r e a a t maximum v e n t i n g f o r B u i l d i n g B i s a b o u t o n e - h a l f of t h a t o f B u i l d i n g A . T h i s i s p a r t l y due t o t h e way i n which t h e b u i l d i n g s were p r e s s u r i z e d . B u i l d i n g A was p r e s s u r i z e d w i t h t h e s u p p l y a i r s y s t e m s o p e r a t i n g and t h e r e t u r n and e x h a u s t s y s t e m s s h u t down; B u i l d i n g B was p r e s s u r i z e d w i t h t h e b u i l d i n g a i r h a n d l i n g s y s t e m s o p e r a t i n g i n t h e normal mode. For t h e l a t t e r c a s e , t h e f l o o r s p a c e was v e n t e d b y t h e r e t u r n and e x h a u s t s y s t e m s a s w e l l a s b y t h e e x t e r i o r w a l l v e n t s a n d , hence, t h e r e q u i r e d v e n t a r e a f o r B u i l d i n g B

was c o n s i d e r a b l y l o w e r t h a n t h a t f o r B u i l d i n g A .

A s shown i n T a b l e 2 , t h e p r e s s u r e d i f f e r e n c e s a c r o s s t h e f l o o r e n c l o s u r e s i n c r e a s e d w i t h i n c r e a s i n g w a l l v e n t a r e a . The maximum p r e s s u r e d i f f e r e n c e s measured (27 Pa between a d j a c e n t f l o o r s and t h e 22nd f l o o r ) were l e s s t h a n o n e - h a l f o f t h e b u i l d i n g p r e s s u r i z a t i o n a s measured a c r o s s t h e e a s t w a l l (65 Pa) w i t h a l l v e n t s c l o s e d . T h i s was a l s o t h e c a s e f o r B u i l d i n g A .

opened. The measured flow r a t e a c r o s s t h e door opening was 4 . 3 0 m 3 / s i n t o t h e f l o o r from t h e s t a i r s h a f t . When t h e s t a i r d o o r on t h e ground f l o o r was a l s o opened, t h e f l o w r a t e i n c r e a s e d t o 6 . 5 0 m3/s.

T e s t s Nos. 2 t h r o u g h 5 were conducted b y opening t h e v e n t s on t h e leeward and s i d e w a l l s . T e s t No. 6 was c o n d u c t e d by opening t h e v e n t s on t h e windward w a l l (west) and t h e leeward w a l l

( e a s t ) w i t h v e n t o p e n i n g s of e q u a l a r e a (0.30 p e r c e n t o f t h e t o t a l w a l l a r e a ) . A i r flowed i n t o t h e f l o o r s p a c e t h r o u g h t h e west w a l l v e n t a t a r a t e of 3.10 m 3 / s and o u t through t h e e a s t w a l l v e n t a t 1 0 . 5 7 m 3 / s . The f l o w r a t e i n t o t h e f l o o r s p a c e t h r o u g h t h e open door of t h e n o r t h s t a i r s h a f t was 3.04 m 3 / s . T e s t No. 7 was c o n d u c t e d w i t h o n l y t h e west w a l l v e n t open. The d i r e c t i o n of a i r f l o w t h r o u g h t h i s v e n t r e v e r s e d w i t h a i r f l o w i n g o u t t o t h e e x t e r i o r a t a r a t e of 6 . 6 0 m 3 / s , which was a b o u t t w o - t h i r d s of t h a t w i t h t h e v e n t of e q u a l a r e a l o c a t e d i n t h e o p p o s i t e w a l l ( T e s t No. 3 ) . Venting t h r o u g h t h e windward w a l l was p o s s i b l e a s t h e i n s i d e p r e s s u r e s were h i g h e r t h a n t h e o u t s i d e p r e s s u r e s by 25 Pa w i t h a l l v e n t s c l o s e d . However, it

c a n b e e x p e c t e d t h a t u n d e r h i g h wind, e f f e c t i v e v e n t i n g may n o t b e p o s s i b l e w i t h v e n t s open o n l y on t h e windward w a l l .

CONCLUSIONS

V e n t i n g s t u d i e s were conducted t o d e t e r m i n e t h e r e q u i r e d v e n t s i z e s i n c o n j u n c t i o n w i t h b u i l d i n g p r e s s u r i z a t i o n f o r smoke c o n t r o l i n m u l t i - s t o r y b u i l d i n g s .

The f o l l o w i n g s t a t e m e n t s c a n be made from t h e t h e o r e t i c a l s t u d i e s :

1 ) Maximum v e n t i n g r a t e i s o b t a i n e d w i t h v e n t a r e a e q u a l t o a b o u t 3 t i m e s t h e l e a k a g e a r e a of t h e f l o o r e n c l o s u r e ( F i g . 3 ) .

2) The r a t i o o f p r e s s u r e d i f f e r e n c e a c r o s s t h e f l o o r e n c l o s u r e and b u i l d i n g p r e s s u r i z a t i o n (APe/APb) depends on t h e r a t i o of t h e v e n t a r e a and t h e l e a k a g e a r e a of t h e f l o o r e n c l o s u r e (Av/Ae) (Eq 3)

.

3) Under summer c o n d i t i o n , a s t h e b u i l d i n g p r e s s u r i z a t i o n i s c o n s t a n t w i t h b u i l d i n g h e i g h t , v e n t i n g performance c a n b e e x p e c t e d t o b e t h e same f o r a f i r e on a n y f l o o r . Under

w i n t e r c o n d i t i o n , however, b u i l d i n g p r e s s u r i z a t i o n i n c r e a s e s w i t h h e i g h t b e c a u s e of s t a c k a c t i o n . From s t a t e m e n t 2, t h i s would r e s u l t i n g r e a t e r v e n t i n g r a t e s and p r e s s u r e

d i f f e r e n c e s a c r o s s t h e f l o o r e n c l o s u r e s of u p p e r f l o o r s compared w i t h t h o s e o f lower f l o o r s . Hence, e x c e s s i v e p r e s s u r e d i f f e r e n c e s c a n d e v e l o p a c r o s s t h e s t a i r and e l e v a t o r d o o r s of t h e v e n t e d upper f l o o r of a t a l l b u i l d i n g , which may r e q u i r e some l i m i t on t h e amount o f v e n t i n g . From t h e r e s u l t s of t e s t s on two m u l t i - s t o r y o f f i c e b u i l d i n g s , t h e c o n c l u s i o n s a r e a s f o l l o w s : 4) Maximum v e n t i n g r a t e i s o b t a i n e d w i t h w a l l v e n t a r e a e q u a l t o a b o u t 1 p e r c e n t of t h e t o t a l o u t s i d e w a l l a r e a of t h e v e n t e d f l o o r . 5) A t maximum v e n t i n g , t h e p r e s s u r e d i f f e r e n c e s a c r o s s t h e f l o o r e n c l o s u r e a r e j u s t u n d e r o n e - h a l f o f t h e amount of b u i l d i n g p r e s s u r i z a t i o n w i t h t h e v e n t s c l o s e d . 6) Opening t h e s t a i r d o o r on t h e v e n t e d f l o o r c a u s e s a s u b s t a n t i a l f l o w of a i r from t h e I s t a i r s h a f t i n t o t h e v e n t e d f l o o r accompanied b y a r e d u c t i o n i n t h e p r e s s u r e d i f f e r e n c e s a c r o s s t h e f l o o r e n c l o s u r e .

I

7) Except f o r t h e c a s e w i t h t h e w a l l v e n t s opened o n l y on t h e windward w a l l , wind a c t i o n i s u n l i k e l y t o a f f e c t s e r i o u s l y t h e v e n t i n g performance f o r smoke c o n t r o l .

8) A s t h e flow of h o t g a s e s t h r o u g h t h e w a l l v e n t s c a n be s u b s t a n t i a l , p r e c a u t i o n must b e t a k e n i n t h e d e s i g n of t h e w a l l c o n s t r u c t i o n above t h e w a l l v e n t s t o minimize t h e p o s s i b i l i t y o f t h e e x t e r i o r s p r e a d o f f i r e t o u p p e r f l o o r s .

REFERENCES

1. Tamura, G.T. and Shaw, C . Y . , "Basis f o r t h e Design of Smoke S h a f t s , " F i r e Technology, Vol. 9 , NO. 3, pp. 209-222, August 1973

2 . Tamura, G.T. and Shaw, C . Y . , "Experimental S t u d i e s on Mechanical Venting f o r Smoke C o n t r o l

3. ASHRAE Handbook and Product Directory, 1976 Systems Volume, Ch 41, "Fire and Smoke Control"

ACKNOWLEDGEMENTS

The author is indebted to the Department of Public Works and the Canadian Imperial Bank of Com- merce for granting us permission to conduct tests in their building and for their assistance during the tests. He also wishes to acknowledge the assistance of C.Y. Shaw and

R.G

Evans during discussions and conduct of the field tests. This paper is a contribution from the Division of Building Research, National Research Council of Canada and is published with the approval of the Director of the Division.

TABLE 1. R e s u l t s o f V e n t i n g T e s t s o n t h e 4 t h F l o o r o f B u i l d i n g A

P r e s s u r e D i f f e r e n c e s A c r o s s F l o o r E n c l o s u r e

Vent Area Flow R a t e ( R e f . P r e s s u r e - 4 t h F l o o r ) , Pa No. o f V e n t i n g 4 t h F l o o r

T e s t % w a l l Open S t a i r R a t e , S t a i r Door, 5 t h 3 r d S t a i r E l e v a t o r No. m2 a r e a Doors m3/s m 3 / s F l o o r F l o o r Door Door

4 t h F l o o r 4 t h , 2nd F l o o r 4 t h , 2nd 5 t h F l o o r 1 m 2 = 10.764 f t 2 1 m 3 / s = 2119 cfm 1 Pa = 0.004016 i n c h o f w a t e r TABLE 2 . R e s u l t s o f V e n t i n g T e s t s on t h e 22nd F l o o r o f B u i l d i n g B Vent Area P r e s s u r e D i f f e r e n c e s A c r o s s F l o o r E n c l o s u r e ( R e f . P r e s s u r e - 21?rld F l o o r ) , Pa % V e n t i n g T e s t Wall R a t e , 23rd 2 1 s t P a s s e n g e r S e r v i c e North S o u t h No m2 Area m 3 / s F l o o r F l o o r E l e v a t o r E l e v a t o r S t a i r S t a i r 3 E . Wall

-

2.4 0 . 3 0 4 E. Wall - 2.4 0 . 4 5 S . Wall

-

1 . 2 5 E . Wall - 2.4 0 . 4 5 S . Wall

-

1 . 2 6 E . Wall - 2 . 4

-

W . Wall - 2 . 4 7 W . Wall - 2 . 4 - 28 28 d o o r s open 4 . 3 m3/s* 2 2 24 d o o r s open 3.04 m3/s*

*

Flow from s t a i r s h a f t i n t o 22nd f l o o r

* *

Flow from o u t s i d e i n t o 22nd f l o o r

PRESSURE A. SUMMER

VENTING

SPACE FLOOR SPACE

PRESSURE PRESSURE

B. WINTER C. WINTER

VENT l NG OF LOWE? FLOOR VENTING OF UPPER FLOOR

SPACE SPACE

PRESSURE PRESSURE

D. SUMMER E. WINTER

VENTING WITH BUILDING VENTING WITH BUILDING PRESSURIZATION PRESSURIZATION F i g . 1 P r e s s u r e a n d f l o w p a t t e r n s w i t h e x t e r i o r w a l l v e n t i n g V E N T O P E N I N G

+-

3 'i

+

'

_f C - 'i -. FIRE FLOOR /

_-

-L

FIRE FLOOR ENCLOSURE F i g . 2 F l o w p a t t e r n w i t h v e n t i n g o f f i r e f l o o r

-

-

-

Q, = F L O W RATE T H R O U G H V E N T

-

Q,,, = M A X I M U M F L O W RATE T H R O U G H V E N T FREIOIIT ELEVITOR

T

1

WOMEN 5HAf 7 t L O C A T I O N OF P R E S S U R E M E A S U R E M E N T S F i g . 3 V a r i a t i o n o f f l o o r s p a c e p r e s s u r e s a n d v e n t i n g r a t e s w i t h v e n t s i z e F i g . 4 _{F l o o r p l a n o f B u i l d i n g A} I I I 1 I /

i

-

_/

-

/ /

I

/-*-:

I

-

_I

-

I

I

A

OUTSIDE TEMPERATURE 1 8 ° C

1

LOW W l N D

-

I

I I I I 1 I & 0 VENTS CLOSED VENT AREA

-

0.35% A O A VENT AREA - 1.06% A 0 (% OF OUTSIDE WALL AREA) LOW WlND OUTSIDE TEMPERATURE 8 . 0 _18°C B U I L D I N G P R E S S U R I Z A T I O N , Pa

1

I I I I I

1

0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 1 . 2 F i g . 6 B u i l d i n g p r e s s u r i z a t i o n f o r v a r i o u s s i z e s o f v e n t o p e n i n g ,

AREA OF WALL V E N T , PERCENT OF B u i l d i n g A TOTAL WALL AREA OF 4TH FLOOR

F i g . 5 V e n t i n g r a t e vs v e n t s i z e

N O R T H S T A I R S S E R V I C E E L E V A T O R S

I

D U C T S H A F T

1

E L E V . S H A F T

I

E L E V . S H A F T

1

I

E L E V S H A F T

I

S O U T H S T A I R S

I

E L E V . S H A F T

I

P A S S E N G E R E L E V A T O R S I I I I I O U T S I D E T E M P E R A T U R E - 7 O C W E S T W I N D O F 9 m / s

-

-

_.-

-

V E N T I N G R A T E

./

-

-

P R E S S U R E D I F F E R E N C E

-

S S V E N T O P E N I N G

-

I 1 . O 2 . 0 3 . 0 4 . 0 5 . O A R E A O F W A L L V E N T , m 2 A R E A O F W A L L V E N T , P E R C E N T O F T O T A L W A L L A R E A O F 2 2 N D F L O O R t L O C A T I O N O F P R E S S U R E M E A S U R E M E N T S F i g . 8 V e n t i n g e f f e c t vs v e n t s i z e o p e n i n g , B u i l d i n g B F i g . 7 _{C e n t e r c o r e l a y o u t} o f B u i l d i n g B ( 2 2 n d f l o o r )

DISCUSSION

DR.

GIDEON SHAVIT, Chairman o f Adv. Engg.

,

H o n e y w e l l , I n c .

,

A r l i n g t o n H e i g h t s ,

I L :

F o r v a r i o u s w e a t h e r c o n d i t i o n s , w o u l d

i t

b e u s e f u l t o m e a s u r e t h e p r e s s u r e

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

v e n t , a n d / o r t o m a i n t a i n c e r t a i n p r e s s u r e d i s t r i b u t i o n t o i n s u r e v e n t i n g t h r o u g h

t h e e x t e r i o r w a l l ?

G.T. TAMURA:

W i t h v e n t o p e n i n g s o f e q u a l s i z e f o r e a c h f l o o r , t h e v e n t i n g r a t e

u n d e r t h e summer c o n d i t i o n s f o r any v e n t e d f l o o r i s t h e same.

The v e n t i n g r a t e

u n d e r t h e w i n t e r c o n d i t i o n s , h o w e v e r , due t o t h e i n f l u e n c e o f s t a c k a c t i o n

i s

v a r i a b l e f r o m f l o o r t o f l o o r w i t h t h e r a t e l e a s t o n t h e g r o u n d f l o o r a n d g r e a t e s t

on t h e t o p f l o o r .

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

a c r o s s t h e e l e v a t o r a n d s t a i r d o o r s o f t h e v e n t e d f l o o r l o c a t e d a t t h e u p p e r l e v -

e l o f a b u i l d i n g , i n some i n s t a n c e s , c a n b e e x c e s s i v e .

A s

s u g g e s t e d , t h e s e p r e s -

s u r e d i f f e r e n c e s c a n be l i m i t e d by c o n t r o l l i n g t h e a r e a o f t h e v e n t o p e n i n g .

Reprinted from ASHRAE TRANSACTIONS 1978, Volume 84, Part 1, pages 204-215, by permission of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Copyright 1978. Technical publications by the Society do not purport to reflect the

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