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Solar & Wind Technology ee l . 6 , No . 5 , pp . 557-567 , 1989 0741-983X/89 $3 .00+ .00Pr in ted in Gre at Br i ta in . Pergam on Press p lc

A R E V I E W O F P A SS IV E S Y S T E M S F O R N A T U R A LH E A T I N G A N D C O O L IN G O F B U IL D I N G S

P . C . A G R A W A LDep artm ent o f Mechanical and Prod uct ion Engineering, Bright Star Univers i ty o f Technology,P.O. Box 58158, Ajadab ia , Libya

(Received 1 Novem ber 1988; accepted 9 January 1989)A b~ 'ac t - - In the present e ra o f energy c ri si s, ene rgy requ ired for hea t ing and cool ing of bu ild ings i s 6 .7%of the to tal world energy. U ti l izat ion of na tural heat ing an d co ol ing sys tems which essent ia l ly cons ist o fcol lect ion, s torage, dis t r ibu t ion, and co ntrol o f therm al energy f low can save 2.35% of the wo rld energyrequirement . The bas ic methods of heat ing and cool ing of bui ldings are: solar radiat ion, out-goinglongwave rad ia t ion , wa te r evap ora t ion , and noc tu rna l rad ia t ion cool ing . Tro mb e-Miche l wal l consi st s oflarge concrete mass , exposed to sunl ight through large, south facing windows, is used for heat ing thebui ldings . Solar absorp t ion cool ing and solar dehumidification a nd ev apora t ive cool ing are two app roach eswhich ut il izes solar energy for generat ion of working f luid and cool ing the dwel l ings . Longwave r adiat io nsemit ted by the surface o f the ear th to the atmosphere and oute r space is very s t rong in a d esert cl imate andi s e ff ect ive f rom a roo f sur face . W ate r evapo ra t ion by dese r t coole rs is the m ethod of cool ing in a r idregions. No cturn al radia t ion both heats in winter an d coo ls in summer, in sui table c l imates , and does sowith no no n-renewable energy other than a negl igible am oun t required to mo ve the insulation twice a day .The diff icul ty encountered in th e ut i l izat ion of na tural energies is the large area exposed w ith sui tableorien tat ion for col lection o f energy and large space requirement for the s torage of therm al energy. Thispap er reviews these pass ive sys tems for natu ral heat ing an d cool ing o f buildings.

I N T R O D U C T I O NT h e u t i l iz a t i o n o f s o l a r e n e r g y b y m a n f o r b u i l d in g si s n o t n e w . H o u s e s h a v e b e e n b u i l t to c o l l e c t a s m u c hs o l a r e n e r g y a s p o s s i b l e - - - d u r in g t h e w i n t e r d a y s a n ds t o r e t h i s e n e r g y w i t h i n t h e b u i l d i n g m a t e r i a l , f o r n i g h tu s e s , t o r e s t r i c t t h e i n c i d e n t a l s o l a r r a d i a t i o n i n s u m -m e r b y p r o p e r s h a d i n g d e v ic e s a n d r a d i a t e o u t a t n i g h tf o r n i g h t c o o l i n g .

I n f a c t , th e r e i s n o b u i l d i n g w h i c h d o e s n o t m a k eu s e o f s o l a r e n e r g y i n a p a s s i v e w a y . T h i s w a s o n l yw h e n l i q u i d fu e ls b e c a m e a b u n d a n t a n d r e a d i l y a v a i l-a b l e , m a n i g n o r e d t h e s i g n i fi c a n c e o f s u c h p a s s i v es y s te m s t o m a k e a d w e l l in g c o m f o r t a b l e a n d r e s o r t e dt o a c t i v e d e v i c e s .

T h e a m o u n t o f o il r e s er v e s o f t h e A r a b w o r l d ( u pto 1 /1 /85) i s 405 .2 l 0 9 b a r r e l s [ 1 ]. I f w e c o n s i d e r t h ep r e s e n t o i l r e s e r v e t o b e u s e d f o r i n t e r n a l u s e w i t h i nt h e A r a b w o r l d a n d i f w e a s su m e a 2 % p o p u l a t i o ng r o w t h p e r a n n u m , t h e n i n t h e y e a r 2 00 0 , t he p o p u -l a t io n o f t h e A r a b w o r l d w i ll r e a c h a p p r o x i m a t e l y 2 9 0m i l l i o n , w h i c h i n t u r n d o u b l e s i t s e l f e v e r y 3 5 y e a r s t or e a c h 1 1 60 m i l l i o n i n t h e y e a r 2 0 7 0. I f w e c o n s i d e r t h ea n n u a l a v e r a g e e n e rg y c o n s u m p t i o n p e r c a p i t a in t h eA r a b w o r l d f r o m 1 9 8 5 u n t i l 2 0 7 0 i s 5 0 G J / p / y r , t h e nt h e o i l re s e r ve o f t h e A r a b w o r l d w i ll b e j u s t e n o u g h

t o c o v e r t h is l o c a l c o n s u m p t i o n . T h e r e f o r e , i t is q u i tec l e a r t h a t b y t h e e n d o f t h e 2 1 s t c e n t u r y t h e A r a bw o r l d w i l l a l s o r u n d r y o f o i l a n d i n o r d e r t o m a i n t a i nt h e s a m e l iv i n g s t a n d a r d w e m u s t t h i n k n o w o f c o n -s e r v i n g e n e r g y .

A t p r e s e n t , r e q u i r e m e n t o f e n e r g y fo r h e a t i n g a n dc o o l i n g o f b u i ld i n g s is 6 . 7 % o f t h e t o t a l w o r l d e n e r g yo u t p u t ( f o r th e A r a b w o r l d e x a c t d a t a i s n o t a v a i l a b l e ,b u t i t c a n n o t b e l e s s t h a n t h i s f i g u r e ) . I t h a s b e e ne s t i m a t e d in a U . S . r e p o r t t h a t a t l e a s t 3 5 % o f th et o t a l e n e r g y r e q u i re d f o r h e a t i n g a n d c o o l i n g o f b u i ld -i n g s c a n b e s u p p l i e d b y n a t u r a l e n e r g y s o u r c e s ( s u c h a ss o l a r , e tc . ). B y p r o p e r p a s s i v e d e s i g n c o n c e p t s , e n e r g ys a v in g o f 2 .3 5 % c a n b e o b t a i n e d ; i t r e d u c e s a ir p o l -l u t io n p r o b l e m s c a u s e d b y t h e c o m b u s t i o n o f f u el .

. ~ F I V E A N D P A S S I V EB a s i c al ly , t h e r e a r e t w o a p p r o a c h e s o f a p p l i c a t i o no f s o l a r e n e r g y t o b u i l d i n g s v i z . a c t i v e s y s t e m s a n d

p a s s i v e s y s t e m s . T h e a c t i v e s y s t e m u s e s s o l a r c o l -l e c t i n g p a n e l s , s t o r a g e u n i t , e n e r g y t r a n s f e r m e c h -a n i s m a n d e n e r g y d i s t r i b u t i o n s y s t e m . T h i s t y p e o fs y s te m a l w a y s u s e s o n e o r m o r e w o r k i n g f l u id s w h ic hc o l l e c t , t r a n s f e r , s t o r e a n d d i s t r i b u t e t h e c o l l e c t e d

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Fig. 1. Act ive solar system for space heat ing and hot-w ater heating.

s o l a r e n e r g y . T h e w o r k i n g f l u i d s a r e c i r c u l a t e d b ym e a n s o f f a n s a n d p u m p s . F i g u r e 1 sh o w s a n a c t i v es y s te m f o r s p a c e h e a t i n g a n d h o t w a t e r s u p p l y .

T h e t e r m " p a s s i v e " r e fe r s to s o l a r - r e l a te d a r c h i-t e c t u r a l c o n c e p t s a n d t e r m " p a s s i v e s o l a r e n e r g y "d e s c r i b e s t h e m e t h o d s o f u t i li z i n g s o l a r h e a t a v a i l a b l et o b u i l d i n g s . P a s s i v e d e s i g n i s a n a t t i t u d e t o w a r d sb u i l d i n g s a n d r e p r e s e n t s s o p h i s t i c a t e d r e s p o n s e s t oe n v i r o n m e n t a n d d y n a m i c in t e r a c t i o n s t h a t c a n a l lo wa b u i l d i n g t o c o l l e c t a n d s e c ur e e n e r g y in o r d e r t o c o o la n d h e a t i t s e l f . P a s s i v e s y s t e m s s e e k t o r e d u c e t h eh o u s e e n e r g y b i l l b y c l o se a t t e n t i o n t o o r i e n t a t i o n ,i n s u l a ti o n , w i n d o w p l a c e m e n t a n d d e s i g n . P a ss i v e sy s -t e m s c o n t a i n f iv e b a s i c c o m p o n e n t s : c o l l e c t o r ( w in -d o w s , w a t e r p o n d s , d a r k w a l l s ) ; s u n l i g h t i n w i n t e r ,w a t e r p o n d s ) ; d i s t r i b u t i o n ( r a d i a t i o n , f r e e c o n v e c -t i o n , s i m p l e c i r c u l a t i o n f a n s ) ; c o n t r o l s ( m o v i n g i n s u -l a t i o n p a n e l s t o c o n t r o l b u i l d i n g o r c o l l e c t o r h e a t l o ss ,v e n t s, a n d w i n d o w s - - g e n e r a l l y , t h e se a r e m a n u a l l yo p e r a t e d ) a n d b a c k u p s y s te m s ( a n y n o n - s o l a r h e a t in go r c o o l i n g s y s te m ) .I n a p a s s i v e s y s t e m a l l t h e f u n c t i o n s o f c o l l e c t io n ,s t o r a g e a n d d i s t r i b u t i o n a r e c a r r ie d o u t b y t h e b u i l d -i n g m a t e r i a l s t h e m s e l v e s . M o s t o f t h e p a s s i v e s o l a rh e a t e d b u i l d i n g u s e e x t e n s i v e s o u t h - f a c i n g g l a z i n ga r e a t o a d m i t l o w - a n g l e w i n t e r s u n sh i n e i n t o t h eb u i l d i n g s , a n d e x t e n s i v e m a s s h e a t c a p a c i t y i n s i d e th e

t h e r m a l e n v e l o p e o f t he b u i l d i n g t o s t o r e t h e a d m i t t e de n e r g y . T h o u g h t h e c o s t o f h e a ti n g a n d c o o l i n g inp a s s i v e s y s t e m is i n c r e a s e d b e c a u s e o f t h e e x t r a c o s t o ft h e m a t e r i a l s r e q u i r e d a b o v e t h a t o f t h e c o n v e n t i o n a lb u i l d i n g m a t e r i a l s t h e y r e p l a c e ; b u t t h is a p p r o a c hp r o d u c e s b e t t e r r e s u lt s in t e r m s o f e n e r g y c o n s e r -v a t i o n . S u c h a t y p e o f s y s t e m r e q u i r e s l e s s m a i n -t e n a n c e, n o r e p l a c e m e n t , d u r a b l e a n d w i ll l a s t fo r al o n g l i f e t i m e . A l l t h e s e f a c t o r s i n c r e a s e th e e c o n o m yo f t h e p a s s i v e s y s t e m . I n c a s e o f o v e r c a s t s k i e s o ri n t e r m i t t e n t s u n s h in e a n a c t iv e s ys t e m m a y s h u t d o w nb u t a p a s s i v e s y s t e m c o n t i n u e s c o l l e c t i n g . F i g u r e 2s h o w s c l a s s e s o f p a s s i v e a n d a c t i v e s y s t e m s u s i n gw a t e r o r a i r a s w o r k i n g f l u i d . G e n e r a l l y , a c o m -b i n a t i o n o f a c ti v e a n d p a s s i ve s y s te m i s o f t e n s o u g h ti f a p a s s i v e d e s i g n d o e s n o t m e e t a l a r g e e n o u g h p o r -t i o n o f t h e t o t a l h e a t i n g a n d c o o l i n g r e q u i re m e n t s .

T h e p r o b l e m s e n c o u n t e r e d i n u t il i z in g th e s o l a re n e r g y f o r h e a t i n g a n d c o o l i n g o f b u i l d i n g s is t h a t t h i si s i n t e r m i t t e n t o n a d i u r n a l s c al e. F o r e x a m p l e , s o l a rr a d i a t i o n i s a v a i la b l e d u r i n g t h e d a y t i m e a n d c o o l i n gb y c o n v e c t io n a n d o u t g o i n g l o n g w a v e r a d i a t i o n o c c u ra t n i g h t. T h e r e q u i r e m e n t f o r w i n t e r h e a ti n g a n d s u m -m e r c o o l i n g i s c o n t i n u o u s b u t t h e r e a r e d a y t o d a yv a r i a t i o n s in a v a i l a b l e e n e r g y a n d i n t h e n e e d f o r i t.T h e r e m a y b e fr e q u e n t p e r i o d s w h e n t h e d e m a n d i st h e g r e a t e s t w h i l e t h e s u p p l y is n il . A s a c o n s e q u e n c e


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Wa t e r tank Sky-lw rm lfstaaFig. 2 . Classes of pass ive an d act ive sys tems us ing water o r a i r as w orking f luid.

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a l l t h e s y s t e m s r e l y i n g t o a s i g n i f ic a n t d e g r e e o n s o l a re n e r g y , h a v e t o b e i n c o r p o r a t e d a s a n i n t e g r a l p a r t o ft h e o v e r a l l s y s t e m c a p a c i t y f o r s t o r i n g t h e t h e r m a le n e r g y .S o l a r r a d i a t i o n , o u t - g o i n g l o n g w a v e r a d i a t i o n ,w a t e r e v a p o r a t i o n a n d n o c t u r n a l r a d i a t io n c o o l i n ga r e t h e b a s i c m e t h o d s o f h e a t i n g a n d c o o l i n g o f b n il d -i n g s. S o l a r r a d i a t i o n a n d n o c t u r n a l r a d i a t i o n c o o l i n gc a n b e u s e d f o r b o t h h e a t i n g a n d c o o l i n g o f a b u i l d i n gw h i le t h e o t h e r n a t u r a l e n e r g y r e s o u r c e s c a n b e u s e df o r c o o l i n g o f t h e b u i l d i n g o n l y .1. So lar radiation

I n s o l a r r a d i a t io n h e a t i n g t h e T r o m b e - M i c h e l w a l li s u s e d f o r h e a t i n g t h e b u i l d i n g . I n s o l a r r a d i a -t i o n c o o l i n g s o l a r a b s o r p t i o n c o o l i n g a n d s o l a r d e -h u m i d i f i c a t i o n a n d e v a p o r a t i v e c o o l i n g a r e t h e t w om e t h o d s o f c o o l i n g t h e b u i ld i n g .

( a ) Trombe-Michel wal l . I t w a s f i r s t d e v e l o p e d b yE . S . M o r s e i n t h e 1 9 t h c. ~ xt u ry a n d r e c e n t l y r e v i v e db y T r o m b e et al . I t c o n s i s ts o f a l a r g e c o n q m t e m a s s 4 0

c m o r m o r e i n t h i c k n es s , e x p o s e d t o s u n l i g h t t h r o u g hl a r g e , s o u t h f a c i n g w i n d o w s . S u n l i g h t a b s o r b e d o nt h e s u r f a c e o f a t h e r m a l m a s s i s t r a n s f e r r e d t o t h ei n t e r i o r o f t h e s t o r a g e m a s s b y c o n d u c t i o n o r c o n v e c -t io n . T h e a i r h e a t e d b y c o n v e c t i o n r i se s a n d p a s s e si n t o t h e h e a t e d s p a c e . D u r i n g t h e p e r i o d o f n o s u n l ig h tt h e s o u t h - f a c i n g w a l l m a y b e i n s u l a t e d t o r e d u c ep o t e n t i a l l y la r g e h e a t l o ss e s t h r o u g h t h e g l a s s. H e a ts t o r e d in t h e t h e r m a l m a s s w a l l i s r a d i a t e d a n d c o n -v e c t e d i n t o t h e s p a c e t o b e h e a t e d .D u r i n g t h e s u m m e r , v e n t s a t t h e t o p o f s o u t h - fa c i n gw a l l a n a r e o p e n e d t o c r e a t e a c h i m n e y e f fe c t t oe n h a n c e v e n t i l a t i o n . F i g u r e 3 s h o w s a s c h e m a t i c d i a -g r a m o f a T r o m b e - t y p e p a s s i v e s o l a r - h e a t in g s y st e m .S u c h k i n d s o f h o us e s h a v e b e e n b u i lt in t h e P y r t n t e s -O r i e n t a l e s d i s t r i c t o f F r a n c e a n d i n t h e U . S . s o u t h w e s t .I n t h e A r a b w o r M , a s o l a r h o u s e w o r k i n g o n t h i sp r i n c i p le h as b e e n m a d e i n J o r d a n i n 1 9 8 3 - 1 9 8 4 w i t ht w o s e c t i o n s i n t h e l i v i n g s p a c e ( h e a t e d p a r t o f t h eh o u s e w i t h a t o t a l a r e a o f 6 4 . 8 4 m 2 ) a n d m e c h a n i c a lr o o m ( n o t h e a t e d p a r t w i t h a t o t a l a r e a o f 4 3. 3 m 2) .T h i s s y s t e m h a v i n g a c o l l e c t o r l o o p , a s p a c e h e a t i n g


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l o a d l o o p a n d a d o m e s t i c h o t w a t e r l o o p h a s s o l a rc o l l e c t o r a r e a o f 4 0 m 2 o f t u b e - - i n p l a t e ty p e w i t h as i n g le g la s s c o v e r w i t h a s t o r a g e t a n k c a p a c i t y o f 2 .5m 3. I t h a s b e e n r e p o r t e d b y T a ' a n i e t aL [2 ] tha t w i thp r o p e r r e t r o f i tt i n g s to t h e h o u s e i t w a s p o s s i b l e tom e e t t h e 5 4 % o f th e t h e r m a l l o a d o n t h e h o u s e b ys o l a r e n e r g y w i t h a c o l l e c t o r a r r a y e f f ic i e n cy o f 2 2 % .

T h e p e r f o r m a n c e o f p a s s iv e s o l a r h e a t i n g s y s t e mh a s b e e n c a r ri e d o u t b y B a l c o m b a n d H e d s t r o m [3 ]. I th a s b e e n f o u n d t h a t a s i n g l e - g l a z e d s o u t h - w a l l sy s t e mw i t h n o i n s u l a t i o n i s a n e t e n e r g y lo s s m e c h a n i s m f o rn e g l i g i b l y s m a l l s t o r a g e a n d e v e n f o r v e r y l a r g e s t o r -a g e i t i s a n i n e f f e c t i v e s y s t e m . I t c a n b e s e e n f r o mF i g . 4 t h a t d o u b l e - g l a z i n g w i th n i g h t i n s u l a t i o n , f o r ar e a s o n a b l y s t o r a g e m a s s h e a t c a p a c i t y c a n a l m o s t

m e e t t h e c o m p l e t e h e a t i n g r e q u i r e m e n t o f th e b u i l d i n gb y p a s s i v e s o l a r e n e r g y o n l y . F i g u r e 5 s h o w s t h e e f f e cto f a r e a o f g l a s s /a r e a o f h o u s e v s p e r c e n t a g e o f a n n u a ls o l a r h e a t i n g . I t c a n b e s e e n f r o m t h e f i g u r e t h a t a w e l l-d e s i g n e d p a s s i v e s y s t em ( d o u b l e - g l a z in g w i t h n i g h ti n s u l a t i o n ) c a n p e r f o r m n e a r l y a s w e l l a s a n a c t i v es y s te m t i l te d n e a r t h e o p t i m u m a n g l e .

(b ) Solar absorp t ion cool ing . S u i t a b l e c h e m i c a ls o lu t io n s f o r s o l a r a b s o r p t io n c o o l in g a r e N H 3 - H 2 0 ,a n d L i B r - H 2 0 . I n N H 3 - H 2 0 s o l ut io n , N H 3 i s u s eda s w o r k i n g f lu i d a n d i n L i B r - H 2 0 s o l u t io n , H 2 0 i su s e d a s w o r k i n g f l u i d .

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O 200 400 600 800 1000Storage m osshe at capociL'y kJ/m gC)Fig. 4. Effect of s torag e mass on the ann ual energy del ivery

of a pass ively heated bui lding.

Active system / / ~

~ gl.oIintl; __

02 0.4 0.6Area of gloss 0~8 1 OArea of houseFig. 5. Area o f glass /area of house vs percentage of annu alsolar heat ing.


5/11

Passive systems in buildings for heating and cooling\ \ \R e c l r c u t o t o dw o t e r

P u m p

A i r o r w a t e rc o o t a n t

t 1~ ~ n ~ ~ ! i L i q u i d 1

e r a n t ' v ~ ? C o o l=

, IK , _ . / - I , , I = v o p o rP u m p

N r o r r a t e rc o o l a n tFig. 6. Solar absorption cooling system.

561

v a p o r i z e N H 3 v a p o u r f r o m N H 3 - H 2 0 s o l u t i o n i nt h e g e n e r a t o r , w h i le a l l t h e o p e r a t i o n s r e m a i n s a m e a st h a t i n t h e o r d i n a r y v a p o u r a b s o r p t i o n s y s t e m . T h i ss y s t e m o f c o o l i n g i s e x pe n s iv e a s w a t e r a t h i g h t e m -p e r a t u r e a t 9 5 C i s re q u i r ed t o o p e r a t e t h e a b s o r p t i o nc o o l i n g m a c h i n e . F i g u r e 6 s h o w s t h e s c h e m a t i c d i a -g r a m o f s o l a r a b s o r p t i o n c o o l in g s y s te m .

(c ) Solar dehumidification and evaporate cooling.D e s ic c a n t ma te r i a l s h a v e h ig h a f f i n i ty f o r w a te rv a p o u r w h i c h c a n b e u s e d t o d e h u m i d i f y m o i s tu r e . T h ema te r i a l s g e n e r a l ly u s e d i n s o l a r s y s t e ms a r e s il ic a g e la n d mo le c u la r s i e v e . M o le c u la r s i e v e h a s t h e h ig h e s tc a p a c i t y u p t o 3 0 % r e la t iv e h u m i d i t y ( R H ) a n d s il ic ag e l b e tw e e n 3 0 - 7 4 % R H .F i g u r e 7 s h o w s a s c h e m a t i c d i a g r a m o f s o l a r d e h u -m i d i f i c at i o n a n d e v a p o r a t i v e c o o l i n g u s i n g t r i e t hy l e n eg l y c o l ( T E G ) a s t h e d e s i c c a n t m a t e ri a l. T h e T E G i sa t o m i z e d i n o r d e r t o c a u s e r a p i d a b s o r p t i o n o f w a t e rv a p o u r i n th e a b s o r p t i o n c h a m b e r . T h e d e h u m i d i f ie da i r c a n b e f u r t h e r c o o l e d i n a n e v a p o r a t i v e c o o l e r .T E G i s r e g e n e r a t e d i n a s t r i p p i n g c h a m b e r b y t h eu s e o f h o t a i r f r o m a s o l a r c o l le c t o r. T h e h o t a i r d r iv e sm o i s t u r e f r o m t h e a t o m i z e d T E G i n t h e s tr ip p e r a n dt h e s t r o n g T E G i s c o l le c te d . H e a t e x c h a n g e r s c a n b ei n s e r t e d a t s e v e r a l p o i n t s b e t w e e n w e a k a n d s t r o n gs t r e am s t o i m p r o v e t h e t h e r m o d y n a m i c e ff ic i en c y o ft h e c y c le . T h is s y s t e m o f c o o l i n g i n w h i c h w a t e r i sa d d e d o r s u b t r a c t e d f r o m t h e a t m o s p h e r e r e q u ir e s th eh e a t i n g o f a g r e a t m a s s o f a i r, a b s o r b e n t m a t e r i a l a n d

t h e w a t e r v a p o u r r e s u lt i n g in a l a r g e a m o u n t o f h e a tr e q u ir e m e n t . T h e C O P o f t hi s s y s t e m is o f t h e o r d e ro f 0 . 1 0 -0 . 1 5 . F i g u r e 8 s h o w s t h e p r o c e s se s o f s o l a rd e h u m i d i f i c a t i o n a n d e v a p o r a t i v e c o o l i n g o n a p s y -c h r o m e t r i c c h a r t.

2. Out-going longw ave radiationL o n g w a v e r a d i a t i o n s a r e e m i t t e d f r o m t h e s u r fa c eo f th e e a r t h t o t h e a tm o s p h e r e a n d s p a c e . A c c o r d i n gt o t h e S t e f a n - B o l t z m a n l a w , t h e i n te n s i ty o f e m i t t e dr a d i a t i o n i s d i r e c t ly p r o p o r t i o n a l t o t h e d i f f e r e n c eb e t w e e n f o u r t h p o w e r o f a b s o l u te t e m p e r a t u r e s ( k )o f th e e mi t t i n g a n d a b s o r b in g s u r f a c es . I t , t h e r e f o r e ,d e p e n d s u p o n t h e t e m p e r a t u r e o f t h e e a r th ' s s u r fa c ea n d t h a t o f th e m e d i u m a b s o r b i n g t h e r a d i a ti o n .T h e n e t r a d i a t iv e h e a t l o s s ( R ) f r o m a g iv e n s u r f a c ec a n b e c a l c u la t e d f r o m G e i g e r ' s e q u a t io n ,

R = 0. 26 x 1 0 - " ~ ( 0 . 2 3 + 0 . 2 8 x 1 0 - ' ' 4 p ) ( 1)w h e r e T s = a b s o l u t e t e m p e r a t u r e o f e a r t h ' s s u r f a c e(K )

p = w a t e r v a p o u r p re s s u r e ( m e a s u r e d c l o se t ot h e g r o u n d ) ( r a m o f H g ) .T h i s e q u a t io n i s o n ly a p p l i c a b l e t o a c lo u d le s s s k y .T h e n e t r a d i a t i v e h e a t l o s s i s m a x i m u m w h e n t h ea t m o s p h e r e i s c l e a r a n d d r y . T h e n e t r a d i a t i v e h e a tl os s de c re a se s a s t h e a m o u n t o f w a t e r v a p o u r a n d

c lo u d s i n t h e s k y in c r ea s e s .


6/11


7/11

- 5 0 o 5 t0o t5 9 2 0 o25 3 0 3 5 o 4 0 4 5

Dr, / ~ tm~rature *C

Passive systems in buildings for heating and cooling

o

Fig. 8. Psychrometric chart.

563~r kg of ~ry air

order ofg -15 C, which is sufficient o cause heat trans-fer. Air or water can be cooled as they circulate pasta surface exposed to the night sky. Several empiricalrelations have been proposed to relate the black bodysky temperature (T~) and ambient air temperature(To), such as

Ta, = To(E~)0.25 (2)T~ = 0.0552T,1.5 (3)

T , k = To--6 (4)

T~ = (0.55 + 1.66p)0.25T~ (5)where Ea = appa rent emissivity of the sky.

Measurement of the radiat ion characteristics of thesky is complex and no precise data are available. Sloane t a l . made measureme nt of the sky radiation and hisresult suggested that outside the 8-13/~m wavelengthband, the sky radiation characteristics approximatethose from a black body at about ambient tem-perature and that within 8-13 #In band, on nights oflow humidity an d clear sky, there is little sky radiation.

Table 1. Effect of water vapour on outgoing longwave radiation at various surfacetemperaturesSurfacetemperature(C)

Transmitted radiation ( v . 4 ~ t ] / c m 2 / c m 2 / m i n )at vapour pressures (mm of Hg)4 6 8 10 15 20 3010 0.197 0.175 0.160 . . . .20 0.225 0.200 0.183 0.160 0.153 - - - -30 0.260 0.230 0.210 0.195 0.163 0.155 0.150


8/11

564Table 2. Effect of clouds on outgoing long wave radiation

Cloudiness in tenths Per cent of outgoing radiation0 I001 982 953 904 855 796 737 648 529 35I0 15

The net radiation loss for a terrestial surface in asteady state ( q i r ) is the algebraic sum of outgoingradiation and incoming radiation from the atmo-sphere and is given by the empirical equationq i r = a T ~ E ~ ( 0 . 3 9 - 0.0096p)(1 - a 3 c c )

+ 4 E , a T 3 ( T ~ - T , ~ ) (6)where tr = Stefa n-Bol tzman 's consta nt (118 1 0 - 9

cal/cm 2 day K 4 = 5.71 10 -5 ergs/cm 2sec K 4)

E, = emissivity of the surfacea3 = empirical constan t function of latitude of

a placec c = cloud covers expressed in tenths.

Table 3 shows the values of a3 for different latitudeangles. A passive system which can bot h heat in winterand cool in summer, in suitable climates, and doesso with no non- renewable energy other than a smallamount of energy required to move the insulationpanels twice a day (invented by Harold's Hay)involves space heating with solar radia tion in winterand cooling by radiation to the night sky and waterevaporat ion in summer, was accomplished with a ceil-ing pond movable insu lation. This system is reportedto be capable of meeting different weather types withvarious means of m odulating ambient conditions.

The salient feature of this "Sky Th erm" system insummer is that water enclosed or filled in plastic bags

Table 3. a3 at different latitude angles.Latitude (degrees) a 3 Latitude (degrees) a3

5 0.50 5010 0.52 6015 0.55 7020 0.59 8030 0.63 9040 0.68

P. C. AGKAWALcalled "Thermoponds" and is exposed to the nightsky. Three effects opera te to dissipate heat :

(i) convection. When the average ambient air tem-perature is cooler than the water in the ponds. Con-vective cooling is effective when the night tem-peratures are appreciably below the comfo rt zone, i.e.below 19C and when the wind speeds during thenight are above 5 km/hr.

(ii) Radiation. When the atmospheric dew pointtemperature is low.

(iii) Evaporat ion. When the pon ds are flooded toprovide an exposed water surface.

Duri ng day time, insulations are moved to positionsover the roof ponds, an d prevent the heating of pondsfrom above. The bottom of the pond is a metallicplate, which is also the ceiling of a room. Thus, thereis heat transfer from the roof to the pond. The pondis maint ained at temperature below the ambien t tem-perature during the day. With ambient temperatureof the order 37C and dew point 15-20C, forcedevaporat ion of water using blower becomes necessaryto mai ntai n a temperature of 27C in the room.

In winter the ponds are covered with transparentplastic to prevent evaporation of water. The pondsare heated by exposure to sunlight in the day time.During the night the insulation is moved in positionso that there is no heat flow from the roof pond tothe atmosphere. Room temperature above 22C couldbe maintained with outdoor temperature as low as5C.

Duri ng the change of season from winter to summerand vice versa, when slight heating is desired dur-ing the night and slight cooling during the day time,the insulation need not be moved from its over-head position. Heat capacity of the po nd is sufficientenough to modulate the ambient air temperature.There is heat transfer from the room to the pond inthe day time and from the pond to the room at night.

Movable horizontal insulation, generally made of5 cm urethane panel, is rolled back and forth to con-trol the rate of heat flow into the thermoponds onwinter days and ou t of the pon d to air and the sky insummer nights. Figure 9 shows the oper ating principleof the ther mopon d system.

The first 'Sky Therm ' buildi ng was a one-r oomprototype which was tested extensively in Phoenix,Arizona, during an 18 month period in 1967-1968.

0.72 The data take n every 12 min showed that the well-0. 76 insulated concrete block buildin g could be kept within0.80 the comfort zone durin g the Arizon a winter when the0. 84 outside temperature was as low as -4 C , and during0.86 the Arizona summers, when the atmospheric tem-

peratu re rose to 46C. Test results showed that during


9/11

M o v o l ) ( ei m m t o t i o n

, ' . ' 5I I4 i

r ft l ,f 6 ' ,i : !

Passive systems in buildings for heating and coolingEvaporat ion andr a d i a t i o n t o s k y

RefLec ted so lar Absorbe d so(orr tx lio tio n ~ r o dio tio n I ~- , , , .= ~ . \ ] [ I I , . ~ . . d , = , , tCorr/ugos t e e l d e c k I I ~ g s , ,

Fig. 9. Operating pr inciple o f the 'Therm o-pon d' system.

565

s e v er a l m o n t h s o f t h e y ea r , n o m o v e m e n t s o f p a n e l sw a s n e e d e d s i n c e th e n o c t u r n a l l o s s o f h e a t f r o m t h eb u i ld in g s u r f a c e i s j u s t b a l a n c e d b y h e a t g a in s f r o ms o la r r a d i a t i o n a n d in t e r n a l h e a t s o u r c e s .A f u l l s i z e h o u s e u t i l i z in g a h e a t i n g a n d c o o l in gs y s t e m c o m p o s e d o f r o o f w a t e r b a g s i n t e r m i t t e n t l yc o v e r e d w i th i n s u l a t i o n w a s d e s ig n e d a n d t e s t e d i nA ta s c a d e r o , C a l i f o r n i a ( 3 5 N l a t it u d e ) , h a v in g a c o m -p le t e a r e a o f 1 0 2 m 2. T h e e n e r g y f l o w t a k e s p l a c e f r o m

v a r io u s s o u r c e s o n a t y p i c a l d a y a s s h o w n in F ig . 1 0.T a b le 4 s h o w s th e h e a t b a l a n c e o f a t y p i c a l c o o l in gd a y i n A t a s c a d e r o .S o m e t h e o r e t i c a l a n d t e c h n i c a l p r o b l e m s w h i c hr e q u i r e f u r th e r r e s e a r c h a n d d e v e lo p me n t a r e :( i ) T h e o r e t i c a l mo d e l f o r p r e d i c t i n g q u a n t i t i v e lyt h e t h er m a l p e r f o r m a n c e o f r o o f p o n d s w i th m o v a b l einsu la t ion .

/ ~ 1~ : ' ~ ' ' ~ "" I I

A - - ' ' - - ' "

2 2 . 1 1 J ~ s i ~ b

Fig. 10. Energy flow on a typical cooling d ay.


10/11

56 6 P. C. AGRAWALTable 4 . He a t ba lance of a typ ica l cool ing day in A tascadero

He at sourcesH e a trejected to OutgoingIncoming night sky heatheat (M J) (%) (M J)

Sun throug h glass 80.20 36.70Co nduc ted throu gh glass 06.75 03.09Sun on walls 14.80 06.77Co nduc ted throug h wal ls 08.65 03.96Co nduc ted throu gh s labs 02.20 01.01Inf i l t ra t ion 01.90 00.87Thro ugh peop le 16.20 07.42By appliances 25.30 11.58Sun through shut panels 156.00 71.4062.50 28.60

218.50 100.00

Hea t rejectedto n igh t sky218.50

218.50

( ii ) O p t i m u m d e p t h o f w a t e r .( ii i) T h e n e e d f o r , a n d d e t a i l s o f , t h e s t o r a g e o f h e a t

i n w in t e r a n d s u m m e r .( iv ) M a i n t e n a n c e o f t h e p o n d .

E C O N O M I C S A N D A P P L I C A T I O NT h e c o m p e t i t i v e p o s i t i o n o f n a t u r a l h e a t i n g a n d

c o o l i n g s y st e m i n r e l a ti o n t o h e a t p u m p o r r e f r ig e r -a t i o n a n d h e a t i n g d e p e n d s u p o n i t s m a s s a c c e p t a n c ea f t e r th e e c o n o m i c s a r e p r e c i s e l y p r o v e d . T h e m a i nf e a t u r e o f a n a t u r a l h e a t i n g a n d c o o l i n g s y st e m m a y b ei n it s l o w o p e r a t i n g c o s t . O n e a p p r o a c h o f r e d u c t i o n i nc o s t m a y b e i n u t i li z a t i o n o f e l e m e n t s o f t h e b u i l d i n g ,e . g . t h e r o o f o r t h e s o u t h e r n w a l l , a s a n i n t e g r a l p a r t o ft h e e n e r g y c o l l e c t i o n sy s t e m . E l e m e n t s o f t h e b u i l d i n gs u c h a s t h e c e i l i n g a n d t h e f l o o r c a n a l s o b e u t i l i z e da s t h e h e a t ( o r c o l d ) d i s t r i b u t i o n s y s t e m s t a k i n ga d v a n t a g e s o f t h e ir l a r g e a r e a s w h ic h e n a b l e o p e r a t i o na t v e r y s m a l l t e m p e r a t u r e s .

A s i g n if ic a n t a p p l i c a t i o n o f n a t u r a l h e a t i n g a n dc o o l i n g s y s t e m i s i n a g r i c u l t u r a l f o r d u a l c o n t r o l o ft e m p e r a t u r e s t o h e a t o n e b u i l d i n g w i t h s o l a r e n e r g ya n d t o c o o l a n o t h e r i m p a r t i n g t h i s e n e r g y to t h e n i g h ts k y . T h e d e s i r e d t e m p e r a t u r e s i n b o t h s i t u a ti o n s c a nb e m a i n t a i n e d w i t h t h e s a m e i n s u l a ti o n . A g r e e n h o u s em a y b e k e p t w a r m a t n i g h t a n d a s t o r a g e s h e d c o o lt h r o u g h t h e d a y , o r a f a r m e r ' s h o u s e m a y b e w a r m e da n d p o t a t o e s a n d o t h e r c r o p s h e d s c o o l ed .A m o d e r n d u a l f u n c t io n u n i t m a y b e d e s i g n e d w i t ha s o l a r s t il l p r o d u c i n g w a t e r i n t h e d a y t i m e f o r d r i n k -i n g p u r p o s e s a n d f o r c o n v e r s i o n t o i c e a t n i g h t b yr a d i a t i o n t o t h e c o l d s k y .

C O N C L U S I O N SB y p r o p e r p a s s i v e s o l a r d e s i g n c o n c e p t s , a t l e a s t

2 . 3 5 % o f t h e w o r l d e n e r g y o u t p u t c a n b e s a v ed . P a s -s i v e d e s i g n c o n c e p t s i n v o l v e m e t h o d s o f c o l l e c t i n g ,s t o r i n g , d i s t r i b u t i n g a n d c o n t r o l l i n g t h e t h e r m a le n e r g y f lo w b y v a r i o u s c o n c e p t u a l a n d p h y s i c a l p r i n -c i p le s o f th e r m o d y n a m i c s a p p l i c a b l e t o t h e b u i l d i n gm a t e r i a l s. T h e s e p r i n c i p l e s c a n b e t r a n s l a t e d t h r o u g ha r a n g e o f b u i ld i n g v o c a b u l a r i e s a n d b e c o m e q u a l i ti e si n h e r e n t to t h e b u i l d i n g c o n s t r u c t i o n a n d o p e r a t i o nm e t h o d o l o g y . I t p r o d u c e s a b u i l d i n g t h a t is m o r e i n t e -g r a t e d i n i t s p h y s i c a l c o n t e x t , a n d o f fe r s d e s i g n p o t e n -t i a l t o t h e a r c h i t e c t u r a l a n d b u i l d i n g p r o f e s s i o n .I t a p p e a r s t h a t a g e n e r a l e v a l u a t i o n o f d if fe r e n ta p p r o a c h e s i s n o w n e c e s s ar y f o r t h e d e v e l o p m e n t o fc o m p o n e n t s a n d s y s te m w h i c h c a n b e i n t e g r a t e d in t h ed e s i g n o f m a s s - p r o d u c e d h o u s e s . T h e n e w b u i l d i n g ss h o u l d b e d e s ig n e d b y a p p l y i n g n e w a p p r o a c h e s a n dt e c h n i q u e s o n a r e l a t i v e l y l a r g e s c a l e , t h u s e n a b l i n gs i g n if ic a n t e n e r g y s a v i n g i m p r o v e m e n t o f t h e q u a l i tyo f t h e e n v i ro n m e n t .A m a j o r d i f fi c u l ty i n p a s s i v e s y s t e m d e s i g n i s t h el a r g e sp a c e r e q u i r e m e n t f o r t h e s t o r a g e o f t h e r m a le n e r g y . T h e s t r u c tu r e o f th e b u i l d i n g c a n s t o r e a b o u t0 .2 3 k W h / C / t o n o f i ts m a s s. T h e m a s s o f t h e s tr u c -t u r e , t h e r e f o r e , c a n p r o v i d e a p a r t i a l s o l u t i o n o f t h es t o r a g e p r o b l e m . F o r e ff ec ti v e h e a t s t o r a g e , t h e m a s so f t h e b u i l d i n g sh o u l d b e c o n c e n t r a t e d m a i n l y w i t hi nt h e i n t e r i o r o f b u i l d i n g , s u c h a s i n t h e i n t e r n a l p a r -t i t i o n s a n d f l o o r s , w h i l e t h e e x t e r n a l w a l l s s h o u l d b eo f h i g h i n s u l a t io n c a p a c i t y . I n o t h e r w o r d s , t h e h e a ts t o r a g e w i t h i n t h e s t r u c t u r e r e q u i r e s sp e c i fi c a p p r o a c ht o t h e d e s i g n o f b u il d i n g s .


11/11

Passive systems in bu i ld in gs for hea t ing a nd cool ing 567R E F E R E N C E S

11 M . M . L abab id i , Oi l explor a t ion and i t s p r esen t p r ospec ti n t h e A r a b - c o u n t r i e s. 4 t h T r a i n i n g P r o g r a m i n t h e F u n -d a r a e n t a ls o f th e O i l a n d G a s I n d u s t r y , O A P E C , K u w a i t ,30.10.85 to 12.11.85 ( in Arab ic) .2 . R . Ta ' an i , H. E1- M ulk i and S . Ba tor seh , Jor dan so la rh o n s e - - s e c o n d t e s ti n g y e a r. Proc. Second Arab Int. SolarEnergy Conf. Bah r a in , 15- 21 Febr ua r y 1986, p . 160 .3 . J . D. Ba lcom b an d J . C . Hed s t r om, S im ula t ion ana lys i sof pas s ive so la r - hea ted bu i ld ings . Los Alamos Repor t ,LA- U R- 76- 8 9 (1976).

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