CONTROL OF THE HUMIDITY AND TEMPERATURE IN AN ATRIUM BY COOLING THE SURFACE OF A POND IN THE ATRIUM

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1 CONTROL OF THE HUMIDITY AND TEMPERATURE IN AN ATRIUM BY COOLING THE SURFACE OF A POND IN THE ATRIUM Masamch Ena, Yasufum Kaaguch, Shge Nshzaa, and Hdeho Maeda Graduate School of Engneerng, Hoado Unversty Address: N-1 W-8, Ktau, Saoro Jaan ABSTRACT Ths aer resents a method for dynamc numercal analyss of the thermal envronment n an atrum. In ths study, the quantty of condensaton on and the quantty of evaoraton from the surface of ater n a small ool (ater surface area, 1m 2 ) ere exermentally measured, and changes n the vertcal dstrbutons of humdty and temerature n an atrum ere numercally calculated by usng the Successve Integraton Method. The analyss as carred out usng BASIC language softare. The atrum used as the model for ths study as 6 m 2 n floor area, m n heght, and had a ond th a surface area of 5 m 2. The arflo beteen the atrum and outdoor s naturally ventlated n summer. If the temerature of the surface of the ond s mantaned at less than degrees Celsus, the estmated rate of vaor condensaton n summer s 6 g/h. Ths ould allo the cool and lo humdty ar to be crculated to other arts of the buldng. A cooled surface of a ond n an atrum ould therefore functon as a tye of dehumdfer, le an ar-condtonng system. and such a ventlated envronment ould be benefcal for the health of aged eole. Moreover, cold fresh ar nfltratng nto the atrum n nter can be heated by solar radaton enetratng through the glazed roof, and ths armed ar can be crculated to other arts such as the ards. On the other hand, one dsadvantage of an atrum s that the temerature of the ar heated by solar radaton enetratng through the glazed roof n summer s too hgh for the ar to be used as ventlaton for other arts of the buldng. There s, hoever, one relatvely easy ay to solve ths roblem. Snce many atrums have artfcal onds bult nsde them, the ater n the ond could be revented from evaoratng by eeng the ater surface temerature loer than de-ont temerature, and ths ould lead to vaor condensaton, hch ould cool the fresh ar comng nto the atrum from outsde. Ths dea 4) ould enable both the humdty and temerature n an atrum to be controlled. It ould also reduce the coolng load of the buldng n summer and the roblem of condensaton on the glazed roof n nter. INTRODUCTION Many nsttutons for the elderly have recently been bult n Jaan due to the agng socety. In Hoado, the northernmost sland of Jaan, aroxmately ten ne nsttutons for the aged are currently beng constructed every year. In nter, t s dffcult for the resdents of nsttutons for the aged n Hoado to go outdoors because of the large amount of sno and the frozen sdeals. In such cold and snoy regons, a glasscovered sace le atrums could rovde deal laces for aged eole to exercse n nter ). For examle, such a sace n a buldng can rovde several benefts for the occuants of the buldng, esecally f the buldng s a resdental faclty for aged eole. For one, a hgh level of ventlaton s requred to elmnate the unleasant odor caused by ards annexed for aged eole, summer nter Fg. 1 System of ventlaton for the buldng 1

2 Secfcaton for numercal smulaton: EConvectve heat transfer coeffcent Celng : C=.495Hc+4.74 (uard) Wall : C=.411Hc+2.51 Floor : C=.11Hc+4.2 (uard) : C=.1Hc+1.4 (donard) C: convectve heat transfer coeffcent [W/m 2 K] HC: convectve heat flux [W/m 2 ] EIn ths smulaton, nd effect and ar leaage of the atrum s neglgble. EConsttutons of each all as follos Heat balance equatons: () Imagnary zones dθ c γ V + dt () Wall surfaces A Mosture balance equatons: Imagnary zones dx γ = α A cl l SW NS ( x j x ) Y V = Q j + dt γ NS ( θ ) ( ) l θ + cγq W j θ j θ ( H H ) + α A ( θ θ ) + ε β α ( θ θ ) + W = m () Pond c j l r l dθ c γ V c q = γ dt + α A c SW ( θ θ ) + A ( H H ) c ( θ j θ ) + ε βlα r( θ l θ ) A rz W + SW m Secton of glass covered sace Fg. 2 Consttutons of each all n the Atrum T2<T<T1 T<T<T2 T<T a) exchanged ventlaton of oen ar c :secfc γ : densty [g/m ] V α Q W Y Z : : volume of a room, zone, : radatve heat transfer : quantty : heat gan (solar radaton, human body, etc.) [W] : mosture gan (human body) [g/h] quantty of condensaton or of A :area H H : loss of heat [Wh/gK] of all surface, :nflo of heat flux from the all surface [W/ u] ε : absorbtvty of q heat flux through the surroundng alls : ncdent factor to of ventlaton from sace j to [m /h] x : humdty rato of ar [g/g'] β r l j m ond [ u] all surface coeffcen t [W/ uk] radaton ond [m ] θ : temerature of ar, all surface, ater [ Ž] : quantty of crculated through the ater ond r : latent heat of vaorzaton [Wh/g] evaoraton [g/ uh] [W/ u] [m /h] Ta<T2 T<Ta<T1 T1<Ta b) sutable ventlaton beteen one sace and another j : neghborng@ sace number of sace, sace l : to hch all surface number of all surface faced and all surface : ond : ater NS : neghborng saces faces, outdoor to sace c : coolng ater SW : surroundng alls T<T2<T1 T<T2 T2<T1 c) recrocal ventlaton beteen one sace and another Fg. Modelng of arflo aths beteen magnary dvsons n the atrum 2

3 In ths study, the thermal envronment of an atrum n an nsttuton for the aged as numercally calculated ). These results ere used to determne the best ays (1) to mrove the thermal envronment of an atrum hen the roof s oened for buoyant convecton and to cool the atrum sace by natural ventlaton n summer, and (2) to crculate ar that has been cooled and dehumdfed by a ond n an atrum to other arts of the buldng and thereby reduce energy costs. ANALSIS METHOD The Successve Integraton Method 1) as used for the analyss, BASIC language softare as used for the numercal calculaton. An llustraton of the ventlaton system used n the nsttuton s shon n Fgure 1, and the modelng arflo aths n the atrum s shon n Fgure. Dry-bulb temerature s horzontally contoured n some actual measurements n a sace th a hgh celng, such as an atrum, and the sace s dvded nto the magnary dvsons of uer zone, mddle zone and loer zones (.e., occued sace) such as Bloc Model 2). The heat transfer th resect to the consttuent alls n the sace s dvded nto convecton and radaton comonents 2). The magnary alls beteen three zones are transarent to the radaton comonent, each zone has heat and arflo balances, resectvely. The all surfaces do not emt or absorb vaor. The temerature n each ard s mantaned at 27 degrees Celsus, eeng RH 6 %. Fresh ar nto each ard s ventlated through the atrum by the forced ventlaton system (2 ac/h) throughout the year. The olluted ar s alays exhausted from the ards to outsde. Fgure 4 shos the floor lan and a cross secton of the subject buldng used as the model for ths study. The buldng s a resdental nsttuton for elderly eole (current number of resdents, 9 n both the East and West ards). There s an artfcal ond contanng cooled ater on the floor level of the atrum. The roof of the atrum has oenngs (.e., exhaust oenngs for fre smoe) to allo arm ar near the roof level to be exhausted and fresh ar from outsde to enter the atrum by the buoyant ventlaton 2). When usng the eather data n Saoro (.e., outdoor ar temerature, de ont temerature, solar radaton [ncludng the beamed comonent on a normal face and the dffuse comonent] of HASP standard data), hourly data n summer as shon Degree Celsus Fg. 4 Floor lan and a cross secton of the buldng Elased tme Outdoor temerature Relatve humdty Fg. 5 Fluctuatons n outdoor temerature and relatve humdty n summer n Saoro n Fgure 5 s made u an average value of the same tme durng 2-ee of the hottest erod. Anng cloths under the glazed roof absorb about 5 % of solar radaton enetratng through the glazed roof, and the ar armed by the absorbed heat of the cloths accelerates the buoyant ventlaton through the exhaust oenng n the roof. Changes n the area of sunshne on each all ere calculated before the dynamc numercal analyss of the thermal envronments n the atrum s started, the solar radaton on each all surface s estmated by the above changes n the area of sunshne. The quantty of condensaton on and quantty of evaoraton from the ater surface ere exermentally measured by usng a small ool contanng ater th a surface area of 1 m 2. The vaor transfer on the surface of a ond as calculated from the measurement results by usng the follong aroxmated equatons 4).

4 Condensaton: Z=(14.8*v+45.5){df+.68(1-RH)} Maeda-Ena C=.6*v+4.1 Evaoraton: Z=(169.4*v+41.){df+.54(1-RH)} Kaaguch-Ena C=5.4*v+7.4 here Z: quantty of condensaton or of evaoraton [g/(m 2 h)] v: ar velocty on the ater surface [m/s] df: dfference beteen vaor ressure n room ar and on the ater surface [Pa] RH: relatve humdty [%] Changes n the dstrbutons of temerature and humdty n the atrum sace and changes n the thermal load for the ards can easly be calculated by the above BASIC language softare. SETTING CONDITIONS We examned 17 cases n hch the enetraton coeffcent, ater surface area, ar velocty and ater temerature ere vared ( Table 1). In case, the ards are drectly ventlated from outdoor. Effect of ater surface temerature: The effect of mantanng ater surface temerature at beteen 1 and degrees Celsus, of exhaustng arm ar by buoyant convecton and on energy costs and amenty erformance n the occued zone of the atrum and n the ards ere examned. Effect of sheld cloths: If the anng cloths are not used, the enetraton coeffcent of the glazed roof s. One mert of an atrum s to mae the occuants feel as f they are n an outdoor sace, hch ould not be ossble f the anng cloths shelded too much of the glazed roof. The enetraton coeffcent as therefore controlled at the value of.5. Effect of ar velocty: Ar velocty strongly affects the quantty of condensaton on and the quantty of evaoraton from the ater surface. The ar velocty at the ater surface level as mantaned n the range of.25 to 1. m/s. RESULTS & DISCUSSION Table 1 Settng condtons Penetraton Water surface area Ar velocty Water temerature coeffcent [u] [m/s] [Degree Celsus] Case.5 Case1 Case2.2 Case no control Case no control Temerature [Degree Celsus] Temerature[Degree Celsus] CASE CASE 1 CASE 2 CASE CASE 4 CASE 5 CASE 6 CASE 7 CASE 8 CASE 9 CASE 1 CASE 11 CASE 12 CASE 1 CASE 14 CASE 15 CASE 16 Max. OT Average OT Mn. OT Max. ar tem. Average. ar tem. Mn. ar tem. Fg. 6 Thermal envronments n the occuant zones Elased tme OT Uer Mddle Lo er Outdoor Fg. 7 Fluctuatons n temerature n each of the three zones of the atrum Fgure 6 shos the thermal envronment of the occuant zone n each of the 17 cases lsted n Table 1. The results for cases 1 to case, hch are thout onds, are bases for dscussng the effect of a cooled surface of a ond n an atrum. In case 1, the oeratve temerature (OT) n the occuant zone rose as hgh as.6 degrees, a temerature hch s not comfortable for occuants. When the enetraton coeffcent of anng cloths to solar radaton as set to.5, the temerature of the loer zone as less than 29 degree Celsus. Even n case 7, here there s a ond n the atrum, the ater surface temerature rose to more than degrees Celsus due to the ar temerature n the atrum. On the other hand, n case 8, here anng cloths ere used, thermal amenty could be mantaned due to the decrease 4

5 8 Quantty of condensaton [g/h] Humdty rato [g/g'] Quantty of condensaton daly[g/day] Elased tme Case1 Fg. 9 Fluctuatons n humdty rato n the loer zone Elased tme Case1 Fg. 8 Fluctuatons n quantty of condensaton Fg. 1 Comarson of the quanttes of condensaton n the ar temerature of the loer zone, as shon n Fgure 7. Fgure 8 shos the quantty of vaor condensaton on the ater surface, Negatve values ndcate the quantty of vaor evaoraton. Fgure 9 shos the changes n humdty rato n the loer zone. The humdty rato n the loer zone decreases th decrease n the ater surface temerature. Thus, ater surface temerature affects the humdty n the loer zone. Fgure 1 shos the quantty of vaor condensaton throughout the day under varous condtons. If the ater n the onds s not cooled, t constantly evaorates. Condensaton s greatly affected by the ater surface area and ar velocty at ater surface level. Fgure 11 and Fgure 12 sho the sum of radaton heat, convecton heat and latent heat absorbed on the ater surface f the ond as cooled. Each s llustrated as the value er the floor area. The ater temerature af- Case1 Amount of thermal load [W/u] Case1 Radaton Convecton Latent heat Fg.11 Thermal load reduced th cool ater surface at ea tme Amount of thermal load [Wh/u ] Case1 Radaton Convecton Latent heat Fg. 12 Integral thermal load reduced daly th cool ater surface Amount of thermal load [W/u] Case Case1 Case2 Case Case1 Frst floor Second floor Fg. 1 Sensble thermal load rovded by ventlaton through atrum sace at ea tme Amount of thermal load [W/u] Case Case1 Case2 Case Case1 Frst floor Second floor Fg. 14 Latent thermal load rovded by ventlaton through atrum sace at ea tme 5

6 fects the amount of condensaton or evaoraton. If the ater temerature ll not be et loer than the de ont temerature n the loer zone, the latent heat to evaorate from the ater surface becomes the thermal load to the ards hch are ar-condtoned. The maxmum thermal load n case 8 s 1-tmes greater than that n case 11. Fgure 1 and Fgure 14 sho the thermal loads n each case hen ventlatng nto the ards through the atrum. The thermal loads ere exressed as the values er the floor area of ards. If anng cloths are not used, the ea load rses to about 4 W/m 2 as the total heat. The thermal load s greatly affected by solar radaton enetratng through the glazed roof. In comarson th case hch s the atrum thout a ond and case 8 hch s the atrum th a ond, the effects of a ond can be dscussed, and also n the same ay from case 9 to case 16, the effects of the ond can be evaluated. The cooled ond can decrease the total heat of 6.4 W/m 2 to the maxmum of thermal load. Artfcal onds, hch are often bult n atrums for esthetc urose, can become a source of hgh humdty f there s no control of the ater temerature. On the other hand, f the ater temerature s et loer than the de ont temerature, the cool ater surface can act as a tye of dehumdfer by causng vaor to condense. REFERENCE 1) N. Aratan, N. Sasa, M. Ena: A Successve Integraton Method for the Analyss of the Thermal Envronment of Buldng, Buldng Scence Seres 9 of NBS,.5-16,1971 2) M. Ena, N. Aratan, K. Kubota, H. Matsumura: Modelng of a Hgh Celng Sace for Numercal Analyss of Thermal Envronment Wth Inhomogeneous Temerature Dstrbuton, and Alcaton of Three Zones Model to Glass-Covered Saces by Usng Successve Integraton Method, Journal of Archt. Plann. Envron. Engng, AIJ, No.419,.21-29, 1991 ) S. Yamamoto, M. Ena, N. Aratan: Thermal Envronment n an Atrum Sace as an Insttuton for the Elderly n a Wnter Cty, Proceedngs of PLEA1997 KUSHIRO Smulaton & Montorng,.91-96, ) M. Ena, H. Maeda, T. Mor, N. Aratan, Y. Kaaguch: Control of Humd Condton n a Large Well by the Cool Runnng Water, Transactons of the Heatng, Ar-Condtonng and Santary Engneers of Jaan No.72,.47-56, 1999 CONCLUSIONS In ths study, e nvestgated the effect on amenty and energy conservaton n an atrum of (1) sheldng solar radaton by the use of anng cloths under the glazed roof of an atrum, (2) usng oenngs n the roof of an atrum as a mean to rovde fresh ar to other arts of the buldng and to exhaust arm ar from the atrum n summer, () coolng the surface of a ond n an atrum. The merts of an atrum as art of a buldng used for elderly eole are as follos: (1) the hgh level of ventlaton needed to elmnate the unleasant odor caused by ards s benefcal for the health of aged eole, and (2) ar that cool and of lo humdty can be crculated throughout the buldng f the surface of a ond n the atrum s cooled. 6