1996-monitoring hfc leakage from ac in buildings

8/12/2019 1996-Monitoring HFC Leakage From AC in Buildings

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ELSEVIER

pplied Energy53 (1996) 341 347Copyr ight 1996 Elsevier Science Limited

Printed in Great Britain. All rights reserved0306-2619/96/ 15.00

0 3 0 6 - 2 6 1 9 ( 9 5 ) 0 0 0 2 7 - 5

M onitoring Hydrofluorocarbon Refrigerant Leak age fromAir Conditioning Sy stem s in B uildings

K . W. Cheong

School of Building and Estate Management, National University of Singapore,10 Kent Ridge Crescent, Singapore, 0511

S . B . Riffat

Building Technology Group, School of Architecture, University of Nottingham,Nottingham, UK, NG7 2RD

B S T R C T

Hydrof luorocarbons H FC s) a re now wide ly used in re f rigera tion and a ir-condi t ioning systems. These systems lose refr igerants through leaks andduring servicing. This pap er discusses the pos sibi l i ty o f determ ining theemission rate of HF C s in bui ldings by applying t racer-gas techniques. Themeasu remen t o f t he emi ss ion r a te o f an HF C r e f ri ger an t R1 34a ) u s ingthe concentrat ion-de cay technique wa s carr ied out in a s ingle-zone cha m-ber. The resu l t s were compared wi th measurements made us ing an SF6t racer and the P i to t - tube t raverse method .

NOTATION

C t C o n c e n t r a t i o n o f t r a ce r g a s a t t im e t p p m )C o C o n c e n t r a t i o n a t t i m e t = 0 p p m )E E m i s s io n r a te m g / h )I A i r e x c h a n g e r a te p e r h )M C o n v e r s i o n f a c t o r f r o m p p m t o m g / m 3 f o r R 1 3 4 a - - 4 - 17 )t P e r i o d o f m e a s u r e m e n t h )V V o l u m e o f a ir in r o o m m 3)

341


2/7

342 K. W. Cheong S. B. Riffat

I N T R O D U C T I O N

C h l o r o f l u o r o c a r b o n s (C F C s ) a n d h y d r o c h l o r o f l u o r o c a r b o n s ( H C F C s )

a r e u s e d i n r e f r i g e r a t i o n a n d a i r - c o n d i t i o n i n g s y s t e m s . H o w e v e r, t h el os se s o f C F C s a n d H C F C s t h r o u g h l e a k s a n d d u r i n g s e rv i ci n g c a n c a u s ed a m a g e t o t h e o z o n e la y e r a n d c o n t r i b u t e t o g lo b a l w a r m i n g . T h e M o n -t r ea l P r o t o c o l c a ll s fo r a n i n t e r n a t i o n a l f r e e zi n g o f p r o d u c t i o n a n d c o n -s u m p t i o n o f C F C s a n d H C F C s a n d h a s t h e u lt im a t e o b je c ti ve o f p h a s in go u t t h e s e c o m p o u n d s b y A D 2 00 0. H y d r o f l u o r o c a r b o n s ( se e Ta b l e 1)ha ve r ecen t l y been emp loy ed i n r e f r i ge r a t i on and a i r - cond i t i on ing sy s -t e m s . The se r e f r i ge r an t s ha ve no po t en t i a l t o dep l e t e t he ozone l aye r bu ta r e s t i l l r e cogn i s ed a s g r eenh o use ga se s because t hey con t r i bu t e t o g lob a lw a r m i n g .

The cause s o f r e f r i ge r an t l e akage have r ecen t l y been r ev i ewed by Bu t -l er. ~ Re f r i ge r a n t l o s se s t end t o b e g r a du a l w hen l e ak a ge o ccu r s ow ing t oa de f ec t ive sea l o r j o in t . O the r t ypes o f l e ak a ge a r e c au sed by m echa n i ca lfa i lu re (e.g . a ru p tu re d p ipe) , se rv ice ven t ing , o r loss f rom a i r purgers .Le aka g e c an a l so be caus ed b y t he r e t ro f i t t in g o f ch i ll e rs w i th new r e fr ig -e r a n t s . F o r e x a m p le , le a kag e can occu r whe n a ch i ll e r u s ing R12 i s co n -ve r t ed t o R134a , because t he R134a mo lec u l e is sma l l e r a nd ca np e r m e a t e t h r o u g h s ea ls m o r e e a s il y. S o m e n e w r e f ri g e r a n ts h a v e p o w e r f u lso l ven t p rope r t i e s and can r eac t w i th ma t e r i a l s i n s ea l s and ga ske t s t o

ca use l e akage .To m in i mi s e r e f r i ge r an t em i s s ions , i t i s nece s sa ry t o mon i to r t he r a t e

o f r e f r ig e r a n t r e le a s e in t o t h e a t m o s p h e r e . T h e B u i l d in g R e s e a r c h E s t a b -l i s hmen t h a s c a r r i e d o u t i n i ti a l w ork on t he p os s ib il i ty o f de t ec t i ng t hel os s o f r e f r ig e r a n t b y m e a s u r i n g c h a n g e s i n t h e m a c h i n e o p e r a t i n g p e r f o r -ma nc e . Th i s pap e r de sc r i b e s an a l t e rna t i ve t e chn ique o f e s t ima t i ng t hee m i s s io n r a te o f a n H F C r e f ri g e ra n t . H y d r o f l u o r o c a r b o n s a r e t r e a te d a st r a c e r s a n d t h e i r c o n c e n t r a t i o n s i n b u i l d i n g s a r e m o n i t o r e d u s i n g a nac t i ve t e chn iq ue ( e . g . pu mp s a mp l ing u s ing ga s ana ly se r s ) o r a pa s s ive

t e chn ique ( e . g . s amp l ing t ubes packed w i th adso rben t ) . Re f r i ge r an t - l e a k -ag e de t ec t i on dev i ce s su ch a s pe rmanen t l y f i xed r e f r i ge r an t s enso r s con -n e c te d t o a n a l a r m c o u l d b e us e d in c o n j u n c t io n w i th H F C m o n i t o r in ge q u i p m e n t .

T H E O R Y

T h e c o n c e n t r a t i o n - d e c a y t e c h n i q u e w a s u s e d t o d e t e r m i n e t h e a i rexch ange r a t e i n a r oom . The me thod i s ba sed on an i n i t i a l i n j e c t i on o ft r a ce r g a s ( t o s imu la t e l e aka g e o f HFCs caused by s e rv i ce ven t i ng i n a


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344 K. W. Cheong, S. B. Riffa t

p l a n t r o o m ) i n t o a r o o m , f o l lo w e d b y m o n i t o r i n g t h e d e c a y o f itsc o n c e n t r a t i o n o v e r a g i v e n t i m e in t e rv a l . A s s u m i n g th a t t h e c o n c e n t r a -t i o n o f tr a c e r g a s i n t h e o u t d o o r a i r is n e g li g ib l e a n d t h a t t h e r e i s n o

s o u r c e o f tr a c e r g a s w i t h in t h e r o o m , t h e f o l lo w i n g e q u a t i o n c a n b e u s e dt o d e t e r m i n e t h e a i r e x c h a n g e r a te :

Ct = Co e -1 (1)

I f t h e n a t u r a l l o g a r i t h m o f t h e t r a c e r -g a s c o n c e n t r a t i o n i s p l o t t e d a g a i n s tt i m e , a s t r a i g h t l in e is o b t a i n e d a n d t h e g r a d i e n t o f t h e l in e is t h e a i r e x -c h a n g e r a t e i n t h e r o o m . E q u a t i o n ( 1 ) c a n b e w r i t t e n a s

I = I n C o - I nC t (2)t

T h e e m i s s i o n r a te f o r R 1 3 4a c a n b e c a l c u l a t e d u s i n g

E = I x M V (3)

E X P E R I M E N T A L W O R K

E x p e r i m e n t a l w o r k w a s c a r ri e d o u t in a ti g h t ly s e a le d c h a m b e r, a s s h o w ni n F i g . 1 . A v a r i a b l e - s p e e d a x i a l f a n s u p p l i e s fr e s h a ir i n t o t h e c h a m b e r

v i a t h e 0 .3 m d i a m e t e r d u c t w o r k a n d 2 m x 0 . 5 m d i f fu s e r s i n t h e c e il in g .A i r i s r e m o v e d f r o m t h e c h a m b e r v i a t h e d i f f u s e r s a n d e x t r a c t d u c t u s i n ga f a n w i t h v a r i a b le s p e e d c o n t r o l .

I n o r d e r t o s i m u l a t e r e f ri g e r a n t l e a ka g e , R 1 3 4 a w a s i n j e c t e d i n t o t h ec h a m b e r w i t h a l l t h e d a m p e r s c l o s e d a n d f a n s o f f .S F 6 w a s a l s o r e l e a s e din t h e c h a m b e r in o r d e r t o c o m p a r e t h e a c c u r a c y o f R 1 34 a m e a s u r e m e n to f a ir e x c h a n g e r a te s . A d e s k f a n w a s u s e d t o a s s is t t h e m i x i n g o f t r a c e rg a s e s a n d a i r i n t h e c h a m b e r o v e r a p e r i o d o f 1 0 m i n . O n c e a u n i f o r mc o n c e n t r a t i o n o f tr a c e r g a s es w a s a c h ie v e d , d a m p e r s a t t h e s u p p l y a n de x t ra c t d u c t s w e re o p e n e d a n d t h e f a n s w e re s w i tc h e d o n . M o n i t o r i n g o ft h e c o n c e n t r a t i o n s o f R 1 3 4a a n d S F 6 t r a c e r g a s t h e n c o m m e n c e d s i m u l t a -n e o u s l y a t th e c e n t r e o f t h e c h a m b e r, u s i n g a m u l t i g a s a n a l y se r , t y p e1 30 2 ( B r u e l & K j a e r , D e n m a r k ) .

I n a d d i t i o n , t h e ; i r f l o w s u p p l i e d t o t h e r o o m i s m e a s u r e d a t t h e d u c tu s i n g t h e P i t o t - s t a t i c t r a v e r s e m e t h o d .

R E S U LT S A N D D I S C U S S IO N

A s e ri es o f m e a s u r e m e n t s w e r e c a r r ie d o u t i n t h e c h a m b e r t o d e t e r m i n e


5/7

H y d r o f l u o r o c a r b o n r e f r ig e r a n t l e a k a g e 345

R134a

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a ir e x c h a n g e r a te s . T h e s e m e a s u r e m e n t s w e r e c o n d u c t e d s i m u l t a n e o u s l yu s i n g R 13 4 a a n d S F 6 t r a c e r g a s e s. F i g u r e 2 s h o w s t h e v a r i a t i o n w i t h t i m eo f th e c o n c e n t r a t io n o f R 1 3 4 a a n dS F 6 f o r a n a i r e x c h a n g e r a t e o f 4-7p e r h . T h e r e s u l t s i n d i c a t e t h a t t h e d e c a y c u r v e f o r R 1 3 4 a i s s i m i l a r t ot h a t f o r S F 6 . Ta b l e 2 s h o w s t h e e x p e r i m e n t a l r e s u lt s f o r t h r e e d i f f e re n t a ir

e x c h a n g e r a te s .T h e d i f fe r e n c e s i n t h e e s t i m a t e d a i r e x c h a n g e r a te s u s i n g t h eP i t o t - s t a t i c t r a v e r s e t e c h n i q u e a n d c o n c e n t r a t i o n - d e c a y tr a c e r - g a s t e c h -n i q u e w i t h S F 6 a n d R 1 3 4 ( i . e . I t , - I S F 6 / I pa n d ( / p - I R 1 3 4 a ) / i p )w e r e f o u n dt o b e i n th e r a n g e 0 - 3 . 6 % a n d 1 4 . 3- 1 6 .5 % , r e s pe c t iv e l y. T h i s s h o w s t h a tv a l u e s o b t a i n e d f r o mS F 6 m e a s u r e m e n t s a r e g e n e r a l l y c l o s e r t o t h e P i t o t -t u b e m e a s u r e m e n t s th a n t h o s e o b t a i n e d u s in g R 1 3 4a . H o w e v e r , t h er e s u l t s a r e w i t h i n a c c e p t a b l e e x p e r i m e n t a l e r r o r a s c o n c e n t r a t i o n m e a -s u r e m e n t s w e r e c a r ri e d o u t a t a s i n gl e p o i n t i n t h e c h a m b e r. T h e e m i s-s i o n r a t e f o r R 1 3 4 a w a s f o u n d t o b e i n t h e r a n g e 2 7 0 . 2 - 8 7 0 . 7 m g / h ,d e p e n d i n g o n t h e a i r e x c h a n g e r a te .


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346 K . W. C h e o n g , S . B . R i f f a t

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F i g . 2 . Va r i a t i o n o f th e c o n c e n t r a t i o n o f R 1 3 4 a a n dS F 6 w i t h t i m e f o r a n a i r e x c h a n g era t e o f 4 .7 p e r h .

C O N C L U S I O N S

T h e a i r e x c h a n g e r a t e i n t h e c h a m b e r h a s b e e n m o n i t o r e d u s i n g t h e c o n -

c e n t r a t i o n - d e c a y t e c h n i q u e w i t h R 1 3 4 a a n dS F 6 . Va l u e s o f a i r e x c h a n g er a te s d e r i v e d f r o m R 1 34 a w e r e f o u n d t o b e g e n e r a ll y i n g o o d a g r e e m e n tw i t h m e a s u r e m e n t s m a d e u s i n gS F 6 a n d t h e P i t o t - t u b e m e t h o d . T h eemis s i on r a t e o f R1 34a wa s f ound t o be i n t he r ange 270 -2 -870 .7 mg /h .A d d i t i o n a l w o r k w o u l d b e r e q u i r e d t o d e t e r m i n e e m i s s i o n r a t e s f r o mre f r i ge r a t i on p l an t s i n b u i ld in gs . I n t he f i e l d t e st , a p r e s su r i s a t i on r ig c anb e u sed t o va l i da t e t he r e su l t s o f t he l e akage r a t e measu red u s ing t hec o n c e n t r a t i o n - d e c a y te c h n i q u e . R e s e a r c h o n t h e d e v e l o p m e n t o f a n e w

TA B L E 2

E x p e r i m e n t a l r e s u l ts

Te c h n i q u e A i r e x c h a n g e r a t e in t h e c h a m b e rp e r h )

Pi t o t - s t a t i c t r ave r s e ( Ip )A i r excha nge r a t e ( pe r h ) ,SF 6 ( I a )A i r ex c h an g e r a t e ( pe r h ) , R134a f ib )E m i s s i on r a t e o f R 134a (mg /h )% Di ff e r e n ce

Ip - la) / Ip) 100

lp - Ib ) / lp ) 100

4.2 5 5 13.94.2 5.3 13.63.6 4.7 11.6

270.2 352.8 870.7

0 3.6 2.2

14.3 14.5 16.5


7/7

Hydrofluorocarbon refrigerant leakage 347

p a s s i v e t e c h n i q u e f o r m o n i t o r i n g r e f r i g e r a n t l e a k a g e i n b u i l d i n g s w o u l da l s o b e n e c e s s a r y.

R E F E R E N C E S

1. But ler, D. J . G. , M inimis ing ref r igerant emiss ions f rom a i r cond i t ioning sys-tems in. bui ld ings . BR E Info rm at ion Paper, IP 1 /94 , 1994.

2. V ineyard , E. A. , Sand , J . R. & Stat t , T. G. , Select ion o f ozon e-safe, non -azeot ropic ref r igerant mixtures for capaci ty modula t ion in res ident ia l hea tpumps . A S H R A E Tr a n s . 9 5Pa rt 1 (1989) 34 46.

3. Stat t , T. G. , A n overview of ozon e-safe refr igera nts for centr ifu gal chil lers .A S H R A E Tr a n s . 9 6Pa rt 1 (1990) 1424-8.

4 . Sand, J . R. , Viney ard , E . A. & No wa k, R. J . , Exp er imen ta l per fo rm ance ofozone-safe a l te rna t ive ref r igerants .A S H R A E T r a n s .96, Part 2 (1990)173-82.

1996-monitoring hfc leakage from ac in buildings

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