RESEARCH ON THE RADIANT CEILING COOLING SYSTEM

Transcription

1 RESEARCH ON THE RADIANT CEILING COOLING SYSTEM Y Ya,*, ZX 2 a W Wag 3 Departmet o Urba Costructo Egeerg, Bejg Isttute o Cvl Egeerg a Archtecture Bejg 00044, Cha 2 Cha Natoal Real Developmet Group Ne Techology Ceter, Bejg 00036, Cha 3 The Sxth Grauate School o Iormato Iustral Mstry, Bejg 00084, Cha ABSTRACT The raat celg coolg s a e techology th hgher comortable egree the el o ar-cotog. Physcal a umercal moels o the raat celg coolg system ere bult a umercally smulate. The results shoe that the loer the temperature o the coolg ater s, the loer the surace o the celg, a the bgger the coolg capacty. Raat heat s more tha covectve heat traserre rom the celg to oor evromet, so the comortable egree s hgh. By testg the expermetal room, the oor temperature strbutos, the all temperature a the surace temperature o the celg the eret coolg ater temperature ere gve. Raat heat traser a covectve heat traser ere aalyze. Expermetal results are coorme to calculatg results by comparso. It s coclue that the room th the raat celg coolg has ell-strbute temperature a hgher comortable egree. The raat celg coolg s a applcable a eal ar-cotog moe th a goo oor qualty. INDEX TERMS Raat celg coolg, Comortable egree, Ioor evromet, Numercal smulato, Temperature strbuto INTRODUCTION Bulg eergy cosumpto s ma the eergy cosumpto, so eergy-savg o the bulg system has become a tre the orl. It s more a more mportat a mperatve to mprove oor ar qualty, rase comortable egree a ecrease evrometal polluto. Some e ar-cotog a heatg moes are rsg. They are ely use the bulg because they have hgh comortable egree a goo oor ar qualty, less eergy cosumpto a evrometal polluto. The raat loor heatg as rstly rse Germa, Korea a Japa. Ths techology ca be use the heatg system ter but ot the coolg system summer. I 980s, the raat loor coolg bega to be evelope Frace a as use the comortable ar-cotog. Subsequetly, the raat loor heatg a coolg as rse Europe. Hoever, ths ar-cotog moe, oor ar temperature s hgher tha the loor temperature summer a the cool s here to traser rom coolg ater to the room. The raat celg coolg has more avatages compare th the raat loor coolg. The raat celg coolg a heatg has gae * Correspog author goo results some coutres Europe (Staley 0). The raat celg coolg a heatg system s a eal a e ar-cotog moe. At preset, there are may stues a reports o the techology, applcato a acaemc research o the raat loor heatg a coolg system(bjare 00, Mchel 994, Olese 997). Hoever, the stues o the raat celg heatg a coolg system especally o thermal propertes a basc las are very lmte(wag Xaotog 0, Zhou Peg 998). Ths paper bult a aalyze physcal a umercal moels o heat traser the raat celg. Las o heat traser a the relatoshps amog luece uctos ere umercally smulate. Expermetal tests ere mae the expermetal room th a raat celg coolg system. PHYSICAL AND NUMERICAL MODELS The room, th mesos m, have a outer all a three er alls. The structure o the celg th heat preservato layer s sho Fgure. The heat traser betee coolg ater the tubes o the celg a * Correspog author emal: yaquayg@sc.com 97

2 oor ar clue these processes as ollos: CONVECTIVE HEAT TRANSFER BETWEEN COOLING WATER AND THE TUBE WALL Covectve heat lux ca be calculate by equato. π L b here ( t t ) α ( ) s α s covectve heat exchage coecet, s the er ameter o the tube, L s the tube legth, t b s the mea temperature o the tube er all, a t s s the mea temperature o coolg ater the tube. CONDUCT HEAT BETWEEN THE INNER WALL AND OUTER WALL OF THE TUBE Couct heat lux ca be rtte as 2 tb2 tb I 2πλ L ( 2 ) here t b 2 s the mea temperature o the outer all o the tube, λ s couctvty o the tube, a s the outer ameter o the tube. HEAT TRANSFER BETWEEN THE OUTER WALL OF THE TUBE AND THE CEILING SURFACE Heat traser process as smple as to-meso couct heat. Calculatg ut s sho Fgure 2. Goverg equato s 2 2 t t + 0 ( 3 ) 2 2 x y bouary cotos are 0 y h + y 2 (4) 0 x x y a be (5) t t b2 x y ce (6) λ α ( ) t t y y 0 (7) y c e a b x Fgure. Structure o the celg Fgure 2. Calculatg ut 972

3 HEAT TRANSFER BETWEEN THE CEILING SURFACE AND INDOOR ENVIRONMENT Covectve heat exchage coecet ca be calculate by ( Pr)3 Nu 0.5 Gr (8) Raat heat exchage coecet ca be rtte as 4 4 ( T T ) εδ α (9) T T tb A T (0) A t b t0 t t + K () 8.72 here ε s emttace o the celg surace,0.95, δ s Stea-Boltzma costat, , T s the mea raat temperature o the surroug, T s the celg surace temperature, t, b A a K are the temperature, the area a heat traser coecet o the other surace thout coolg respectvely, a s ar temperature the ajacet room. Total heat exchage coecet ca be rtte as α α + α (2) Total heat traser betee the celg surace a oor evromet s equal to the sum o covectve heat lux a raat heat lux. α a b ( t t ) 4 (3) EXPERIMENTAL TESTS I a laboratory test space th a celg coolg system, surace temperatures at several eret locatos o the celg, the outer all temperature, the er all temperature a ar temperature ere measure. I the expermet, sx testg postos ere selecte alog the heght o the expermetal room a the all respectvely. Temperatures ere measure these postos. Expermets ere perorme uer these cotos: outoor temperature as 33, oor esgg temperature as 24 a coolg ater temperature the tubes o the celg as 6. The results are sho Fgure 3. I aother expermet, te testg pots ere evely arrage the celg. The temperatures o all testg pots ere measure. The mea temperature o these values as thought as the celg surace temperature. Expermets ere perorme uer eret coolg ater temperature. The results are cate Fgure 4. RESULTS AND DISCUSSION The testg results o oor temperature, er all surace temperature a teral surace temperature o the outer all eret postos are sho Fgure 3. Fgure 3 shos that the chage o oor temperature s small alog vertcal recto, hch s less tha oe cetgrae. The temperature strbuto s eve. So comortable egree the room s hgh. The erece betee er all surace temperature a oor temperature s small. The erece betee teral surace temperature o the outer all a oor temperature s evet. The surace temperature strbutos o the outer a er all are stll ell-strbute alog vertcal recto. From the above results, e ca ko that the raat celg coolg system has a hgh comortable egree. The comparso betee calculatg a testg values o the celg surace temperature eret coolg ater s sho Fgure 4. Results sho ther ereces are small. 973

4 30 23 tempeature( ) oor ar temperature surace temperature o the outer all surace temperature o the er all the celg surace temperature, t calculatg results testg results stace rom the loor(m) Fgure 3. Ioor temperature a the all temperature eret posto 5 the coolg ater temperature, t s Fgure 4. Surace temperature o the cel By calculatg, the relatoshps betee the surace temperature, the coolg capacty a the coolg ater temperature are sho Fgure 5 a t q(/m 2 ) t s t s Fgure 5. Relatoshp betee the temperature o coolg ater a the celg surace Fgure 6. Relatoshp betee the celg coolg capacty a the coolg ater temperature Results sho that the loer the coolg ater temperature s, the loer the celg surace temperature, a the larger the coolg capacty o the celg. The erece betee the coolg ater temperature a the celg surace temperature ecreases th the creasg o the coolg ater temperature. Celg surace temperature shoul be to cetgrae more tha oor ar e pot, so coolg ater temperature assumes 6 to. Raat heat lux betee the celg surace a oor space s more tha covectve heat lux. Raat heat lux occupes 59 percet to 69 percet the total heat lux. The hgher the oor temperature s, the hgher the celg surace temperature, a the loer the coolg capacty. The hgher the outoor temperature s, the loer the coolg ater temperature, the loer the celg surace temperature, a the larger the coolg capacty. But the chages are small. Wth the creasg o the tube epth, celg surace temperature creases a coolg capacty o the celg ecreases, but the chages are very small. So t s ot ecessary to excessvely ecrease the celg thckess or coolg. The larger the tube space s, the larger the celg surace temperature, a the smaller the celg coolg capacty. So the tube space shoul ot be too large. CONCLUSIONS I the room th the raat celg coolg system, the chage o oor temperature s small alog vertcal recto, hch s less tha oe cetgrae. The temperature strbuto the er all a the teral surace o the outer all s ell-strbute alog vertcal recto. So the room s more comortable. The loer the cool 974

5 ater temperature s, the loer the celg surace temperature, a the larger the coolg capacty o the celg. It s sutable the cool ater temperature s 6 to. Raat heat lux betee the celg surace a oor space s more tha covectve heat lux. The luece o tube epth o coolg system s small, so t s ot ecessary to excessvely ecrease the celg thckess or coolg. The tube space shoul ot be large. The results the paper ca prove the bass or the esg a operato o the real project. ACKNOWLEDGEMENTS Ths project as supporte by Bejg mucpalty key lab o heatg, gas supply, vetlato a ar-cotog egeerg. REFERENCES Bjare WO. a Mchel E. 00. Heat exchage coecet betee loor surace a space by loor coolg-theory or a questo o eto, ASHRAE Trasactos:Symposa. 8: Mchel E. a.isoar JP Coolg loor, Proceegs o clma 00. Loo. Olese BW Possbltes a lmtatos o raat loor coolg, ASGRAE Trasacros. 03(): Staley AM. 0. Celg pael coolg systems, ASHRAE Joural. : Wag XT. a Guo. 0. The relato o ppe structure measuremets a temperature eveess the loor surace to loor pael heatg systems, HV&AC. 3():40-4 Zhou P. a L M vetlato a coolg celg, HV&AC. 28(5):