Journal of Engineering Science and Technology Review 6 (3) (2013) Research Article. Zhi-yong ZHOU 1,* and Ye-cong HE 2

Transcription

1 Jestr Journal of Engineering iene and Tehnology Review 6 (3) (013) Researh Artile JOURNA OF Engineering iene and Tehnology Review The feasibility analysis of the performane of the phase hange material wallboard used in outhwest China Zhi-yong ZHOU 1,* and Ye-ong HE 1 Faulty of Civil Engineering and Mehanis, Kunming University of iene and Tehnology, Kunming, Yunnan provine, , China Faulty of Urban Constrution and Environmental Engineering, Chongqing University, Chongqing, , China Reeived 10 June 013; Aepted 3 November 013 Abstrat In order to study the feasibility that PCM wallboard use in the building of outhwest China, based on the enthalpy model of the PCM wallboard, with a analysis of the fators effeting the heat transfer performane of PCM, taking Chongqing as an example to hoose one suitable type of PCM wallboard for outhwest China, simulating the heat transfer performane of a PCM wallboard room and a ommon room in Chongqing, testing the indoor air temperatures of the PCM room and a ommon room in summer and winter for validating the simulation through field experiments and ounting with a peak load shifting eonomy poliy the analysis shows that suh a PCM room is not only energy effiient, thermal omfort, and it also has a short investment period (only 1.4 months). Keywords: Phase Change Material Wallboard Room, Building Energy aving, Enthalpy Model, Heat Transfer 1. Introdution Adopting the "Peak load shifting" poliy ontributes to a wide development prospets of the tehnology of thermal energy storage with phase hange material. The researh about the tehnology was started at the last entury 80'. The Building tudy Center of the Conordia University of Canada and the Florida Institute of Tehnology of Ameria have researhed the performane of fatty aid phase hange material wallboard and how to reah the neessary heat storage by ontrolling the uptake and melting amount of PCM [1], []. The Kanagawa University and Tokyo University of Japan have researh on the performane of organi phase hange material wallboard and the thermal property of the PCM room. The researh data shows PCM an make the heat load be more gentle, people feel more omfortable in the radiation region, the eletriity onsumption be redued and it is helpful to ut down peak load [3]. Jiang Yi analyzed the present researh situation of phase hange and hemial energy storage applied to building heating and their study also point out the right researh diretion of this field [4]. Yu Dan has researhed the performane of the phase hange material omposed of HR-35, HR-50 and lauri aid [5]. Feng Guohui put forward getting phase hange wallboard surfae heat transfer oeffiient with geneti algorithm by studying the heat transfer performane of omposite phase hange material wallboard through experiments [6]. in Kun studied the heating performane of eletro-thermal phase hange material wallboard and analyzes the appliation effet of this system in winter in several limati regions of China [7]. * address: zhiy_zhou@163.om IN: Kavala Institute of Tehnology. All rights reserved. Zhang Yinping researhed the PCM wallboard applied in Yiling in summer and the effet of the position of wallboard and insulation layer on whole room's heat omfortable [8]. Though simulating and analyzing some situations here this paper aim to determine the oeffiient of the PCM wallboard suitable for Chongqing, researh the performane of PCM wallboard room in winter and summer and get the eonomy analysis.. The mathematial model of PCM wallboard.1 Analysis of the heat transfer of PCM wallboard The heat transfer proess inludes heat aumulation and release. In order to study the effet of the parameters of PCM wallboard on its heat transfer performane, it is heating by a homogeneous heat soure (aq 0 ) provided by eletro-thermal film in the heat storage proess. Then the temperature, thikness and radius for phase hange were determined. If a=1, the wallboard is aumulating. The energy was absorbed from aq 0. Meanwhile the heat is exhanging in the medial wall. The rate of heat through radiation heat transfer is defined as q inf and through the onvetive heat transfer as q ind Aording to the energy onservation priniple, while aq 0 >q inf +q ind, the heat storage rate of the PCM wallboard an be shown as: q =aq 0 -q ind -q inf q : heat storage rate (W) q 0 : power in unit area (W/m ) aq 0 : homogeneous heat soure (W)

2 Zhi-yong ZHOU and Ye-ong HE/Journal of Engineering iene and Tehnology Review 6 (3) (013) q ind : onvetive heat transfer (W) q inf : radiative heat transfer (W) when a=0, the heat was released and the rate of it an be alulated as: q F = q ind -q inf q F : heat release rate (W). Establishing mathematial model of the PCM wallboard In order to simplify the model, study the heat storage unit more deeply and stand out its physial essene, before the following step it is neessary to make some assumption, simplifiation and some essential premises. (1) Ignore the natural onvetion as PCM melting and the under ooled effet as solidifying. () Taking heat ondution as the main way of the heat transfer in PCM. Heat only transfers in thikness diretion and the onvetive heat transfer of liquid phase will be overlooked. (3) PCM is regarded as being pure and isotropi. (4) The initial temperature was lower than the other phase hange temperature. Assume that the volume of the wallboard wouldn't hange. (5) Aording to the one-dimensional heat transfer assumption, set up Axes ox from the medial side to the outside of the wallboard. The enthalpy model [9] of the heat transfer of PCM wallboard is shown in Fig.1. q T qi T 4 f = 5.67 ( ) ( inf ) 4 T qi : temperature of interior wall surfae ( ) T f : average temperature of the non-radiative struture surfae( ) The q ind is alulated as: q ind = ( tqi tin) t in : indoor temperature (6 ) Relation between the temperature (T) and enthalpy (H) as: H T = ps Qpm H + ( Tm ε ) = ε H Qpm ps + ε H H T = Tm + ε + T pl H < H H H H < H H s : enthalpy of solid PCM (J/kg) H : enthalpy of liquid PCM (J/kg) T m : average phase hange temperature (K) Q pm : phase hange latent heat of PCM (kj/kg) H an ben expressed as: H = ( T + ε ) + Q Ps m pm Then, q 0 an be alulated: q 0 =0/( )=145(W/m ). It an be ontrolled by low temperature radiation eletrothermal film (DYMCO, made in Korea) with power 0w/piee and size (mm 3 ). Phase hange latent heat Q pm is displayed as follow. The Q was as listed below, it is alulated as: f s Qpm = Q τ Fig. 1 One-dimensional phase hange heat transfer panel diagram Therefore, the related alulation an be expressed as: H T ρi = λi τ x The boundary ondition is shown as: T qind q + inf = λ X x = T q0 = λ x x=0 The radiation heat transfer rate in unit area q inf as: f s : phase hange rate The phase hange rate,taking the heating proess as an example, is as follow. In addition when the PCM is solidifying to release heat, the desription of f s is just the opposite as: 0 T < T f = f( T) T T T 1 T < T Phase hange rate have relations with pre and post temperature at an interval. In the formulae as follow, the supersript 1 and 0 stand for the previous time and the next time respetively. Utilizing two temperature values to judge 19

3 Zhi-yong ZHOU and Ye-ong HE/Journal of Engineering iene and Tehnology Review 6 (3) (013) the phase hange rate, it an be simplified by iterative omputation as: 0 0 T < T s = ( ) 0 1 T < T f f T T T T or 1 0 T < T = ( ) 1 1 T < T f f T T T T o the above equations an be alulated as: Q pm = Q f f Δτ Heat transfer model of phase hange wall room There are four equations the heat transfer of the room satisfied. (1) The Outer surfae of exterior wall: Condutive heat + onvetive heat exhange with the air outdoor + solar radiation heat exhange + surfae radiation heat exhange + diffuse sky radiation heat = 0. () The inner surfae of the exterior wall: Condutive heat transfer + onvetive heat exhange + radiation heat transfer = 0. (3) Windows: Q C =ondutive heat transfer from the window into the room + solar radiation heat transfer from the window into the room + the heat onvetive heat exhange of the surfae of the window + the radiation heat transfer of the window's surfae. (4)The heat balane formula of the room is alulated as: dt pρv = Qd + QR + Q dτ C Q d : onvetive heat transfer rate of the inner surfae of enlosure struture (W) Q r : radiative heat transfer rate of the inner surfae of enlosure struture (W) Q : heat transfer rate through the windows into the interior inluding the ventilation heat transfer at night (W) 3. Numerial solution for the temperature field of PCM wallborad Based on the differential equations and the relative boundary onditions stated above, adopting finite differene method to disrete the partial differential equation of phase hange heat transfer and full impliit method for time, enter differene for x-oordinate, it an be drawn to approximate numbers of the temperature and heat flux of eah speifi part of eah speifi time of PCM wallboard. Net divided for PCM wallboard alulation as Fig. Fig. The numerations of the PCM wallboard Time-step is 0 minutes. pae-step is determined by dimensionless number. For obtaining a relative stable solution, the two numbers must be limited. o assume that F 0 0.5, B i 0.1. For simplifying and keeping preision when dealing with the model [10]: kδτ Fo = ρ p ( Δx) and hδx Bi = k F o : Fourier number B i : Biot number The limate information was obtained from "China building thermal environment analysis speial purpose limate date",inluding sky temperature, the diret sunlight radiation intensity, sky sattering intensity, land surfae temperature, wind speed [11]. olving the equations above with the software Matlab the value of the room's temperature time by time. For verifying the orretness of the program, the enthalpy model [1] should be solving firstly. If the result is in 6% of the allowable date error range, the program is right. 4. Analysis of the simulation results The PCM wallboard is made up by paraffin and high density polyethylene in ertain proportions. Meanwhile, for improving the heat ondution oeffiient, it was added some graphite in proper proportion. The physis parameters is as listed: density 950kg/m 3, speifi heat.85kj/ (kg K), enthalpy 00kJ/kg, heat ondution oeffiient 0.40W/ (m C). The heat transfer proess was simulated on ondition of different thikness of PCM wallboard, phase hange radius, phase hange temperature and dimensionless number. The law of the effet from parameters hange on the temperature of PCM wallboard was analyzed to hoose a suitable type of PCM wallboard. 4.1 Influene from phase hange temperature on the performane of wallboard's heat transfer Varying average phase hange temperature T m, the heat transfer model testing data are listed in Table 1. (ε=, t in =4, = 0.06m, Fo = 0.4,Bi = 0.1) Table 1 Data of the PCM wallboard with different T m Parameters( T m) Endothermi time h Delay time h Outer surfae temperature Minimum Outer surfae temperature Maximum Inner surfae temperature Minimum Inner surfae temperature Maximum As was shown in Table 1, as average phase hange temperature beome higher, the endothermi time was ut down slightly, beside that the temperature of inner and outer fae are higher, but the delay time was ut down substantially. Therefore it is onluded that the average phase hange temperature mainly effet the delay time. 4. Influene from the thikness of phase hange wallboard on the performane of heat transfer 130

4 Zhi-yong ZHOU and Ye-ong HE/Journal of Engineering iene and Tehnology Review 6 (3) (013) Varying the thikness of PCM wallboard, the data is listed in Table. (T m = 3, ε =, t in = 4, Fo = 0.4, Bi = 0.1) The data of Table shows while the wallboard is thiker, the endothermi time inreases but slightly, even as the inreases almost twie, the endothermi time just inreases less than 1.5 hours, but the delay time beome more longer. It is very good at the time eletriity peak value an be dropped down well in summer. However the delay time inrement will make the exothermi time longer during the day. But it an be done by venting at night to release the heat. The reason why the wallboard is thiker the outer surfae's temperature is higher is that when the heat storage apaity of PCM wallboard beome stronger, it spend more time to heat, so the temperature relative to the outer surfae of wallboard inrease substantially. Meanwhile the temperature of inner surfae hange slightly and the limited temperature hange less than 1 beause the and thermal resistane beome lager. o it mostly effets on delay time and improves the heat storage performane but does nothing to the omfort of the room. Table Data of the PCM wallboard with different Parameters() Endothermi time h Delay time h Outer surfae temperature Minimum Outer surfae temperature Maximum Inner surfae temperature Minimum Inner surfae temperature Maximum Influene from phase hange radius on the performane of heat transfer The heat transfer model was simulated with varying ε with 1.5, and.5. The results were shown in Table 3. Table 3 Data of the PCM wallboard with different ε Parameters(ε) Endothermi time h Delay time h Outer surfae temperature Minimum Outer surfae temperature Maximum Inner surfae temperature Minimum Inner surfae temperature Maximum Table 3 shows that with ε inreases, the endothermi time and delay time inreases. But the hange rage of delay time is slight. Besides, the maximum of inner and outer surfae temperature is higher and the minimum is lower ontrarily. o the hange rage of the temperature is bigger. The reason of stated above is that when the radius ε was hanged, in other word the temperature of phase hange was hanged, the apaity of the wallboard's heat storage was hanged, that means the endothermi time was hanged. Therefore the main hanging objet is the endothermi time and the influene on inner and outer surfae temperature an be negleted. 4.4 The determination of the PCM wallboard Aording the atual situation, the PCM wallboard must meet onditions: the max temperature an be not over 60, the surfae radiation intensity is between 30~60W/m, make sure that the heating time in winter must be during the low valley eletriity prie time(3:00~7:00), in other words, between 8 hours. o the delay time is just over at the heating time start. A perfet period of the endothermi and exothermi time should be not over 4 hours. On the other hand the phase hange temperature must be in an appropriate range as it was used in summer to adjust the peak of eletriity. The requirement of delay time is different aording to the type of the room. This one stated is an offie, the working hours is 8:00~17:00, by reason of the top temperature of outdoor air omes at 1:00~14:00, the delay time should be in 6~8 hours. At last, the parameters are fixed aording to loal limate. The required and T m are determined aording to the hanging rule of phase hange radius, average phase hange temperature, the thikness of PCM wallboard, endothermi time, delay time and the surfae temperature analyzed above. Where parameters of Chongqing is as: ε = 1, T m = 30, = 0.04m, Fo = 0.4,Bi = 0.1. o endothermi time is 6.5 hours, the delay time is 6.3 hours, the minimum of inner surfae temperature is 5.96, and the maximum is 6.64, the minimum of inner surfae heat flux is 5.00 W/m and the maximum is W/ m. The requirement is satisfied. 5. Analysis of PCM wallboard simulation Taking Chongqing as the example, the eletriity through period starts at 3:00 was analyzed. The indoor air hourly temperature of PCM and the ommons in two days standing for winter and summer was hosen to be simulated respetively, to researh the dynami heat transfer property of the two rooms and to evaluate the feasibility and eonomi effiieny of the plan. The limate data ame from "China onstrution thermal environment analysis speial limate data". 5.1 PCM wallboard room's heat transfer simulation and analysis For researh the room's indoor temperature hanges in summer, the parameters equal whih stated above. The simulation time was 5 th August. The same limate situation was hosen for the ontrast between the PCM room and the ommons' hourly temperature. Parameters to be test in the simulation are PCM indoor temperature t p and ommon room indoor temperature t n. The result was shown in Fig.3. Fig. 3 Temperature of PCM room and ommon room on 5 th August The two temperature lines in Fig.3 go with a similar tendeny. The t n is about 4 higher than t p. But there is 5 hours delay time of t p whih an delay the highest temperature well. As shown in Fig.3, the ommon room's temperature was hanging between 9 ~33 and the amplitude is about 4. The temperature t p stayed between 6 ~8 and just has a amplitude. o it is better to people. While thinking about the heat storage property of PCM, the simulation proess was assumed that a onstant hilling input in non-offie time to remove the heat released at night. 131

5 Zhi-yong ZHOU and Ye-ong HE/Journal of Engineering iene and Tehnology Review 6 (3) (013) Heat transfer simulation of PCM wallboard room in winter Based on the same parameters above, the PCM heat transfer proess was simulated for winter situation at 1 th January. The parameters to be tested are t n, PCM wallboard's heating side temperature t p1 and inner side temperature t p. (hown in Fig.4) As is shown in Fig.6, t n is between 3~35, t nm is between 31~33, t p is between 7~30 and t pm is between 6~8. All of them inrease during 10:00 and 14:00 beause from 10:00 the solar radiation intensity begins to inrease gradually. o the room gets more thermal. Until 14:00 the temperature reahes the highest value and the heat exhange between indoor and outdoor inrease. o there are two times low-amplitude inrements. The testing temperature is higher than the simulating temperature due to the limate data from "China onstrution thermal environment analysis speial limate data" based on the limate in Considering the highest temperature of a hundred year in 007 and it's about 3 higher than the same time in history, the simulation is orret. Fig. 4 Temperatures of PCM wallboard and the room on 19 th January As shown in Fig.4, the heating side of the wallboard's highest temperature was less than 40 and in the safe range. The heating time is 6.5 hours. When it was the eletriity through time, the inner temperature of the wallboard was hanging between 3~5 and the indoor temperature of is between 0~ Contrast between PCM wallboard room and ommon room in winter limate With the same limate situation simulating the heat transfer proess of PCM wallboard room and the ommons both at 19th January, the temperature hanging lines are shown in Fig.5. Fig. 6. Temperature of PCM room and ommon room on 5 th August (The letter n represents for ommon room, p represents for PCM wallboard room and is test value and m represents for simulating value) Above all, under the no air onditioning situation, the indoor temperature an reahes 6 ~8 in summer. On the other hand, at the low eletriity through taking 6.5 hours heating to eletro-thermal film in winter, the indoor temperature an reah 0~3. It an both meet the omfort requirement in summer and winter. As it was shown above the testing temperature is in aord with simulating temperature Fig. 5 Temperature of PCM room and ommon room on 19 th January As shown is Fig.5, the temperature of the two types room has a large disparity. o taking advantage of PCM has a little higher indoor temperature than the standard but more suitable for living. It is no reason to redue the thikness of the wallboard beause the tehnology was mostly used to shave peak in hot summer and old winter. Therefore the indoor temperature was only ontrolled by heating time. Besides, the internal disturbane of the simulation was assumed 300W. o the heating time an be ontrolled aording to the indoor devises' working ondition flexibly. 6. Analysis of the experiments To prove the orretness of the alulation, under the same ondition as the simulation, the ommon room was tested every other hour for 7 hours uninterruptedly at 4 th, 5 th and 6 th August. Considering the hill input in simulation at night, so there is only the temperature situation at daytime. The result is shown as Fig Eonomial effiieny analysis Assuming the air onditioning of ommon room is Green (KFR-3GW/K(3516)E-HN5), the eletro-thermal film is DYMCO (made in Korea) and the PCM's working time is both three month in summer and winter, the eonomi effiieny analysis is shown as Table 4. Table 4 Prie of the PCM and eletriity Material or Period of use power HDPE Paraffin Prie 8360 (Yuan/t) 590 (Yuan/t) Eletrothermal film 158 (Yuan/m ) Air onditioning Flat eletriity prie in the dry season Valley eletriity prie in the dry season Peak eletriity prie in the dry season Valley eletriity prie in the wet season Peak eletriity prie in the wet season Flat eletriity prie in the wet season (Yuan) 0.97 (Yuan/kWh) (Yuan/kWh) (Yuan/kWh) (Yuan/(kWh) (Yuan/kWh) (Yuan/kWh) The ommerial eletriity prie of Chongqing is (Yuan/kWh) if below 1kV. The wet season is from June to 13

6 Zhi-yong ZHOU and Ye-ong HE/Journal of Engineering iene and Tehnology Review 6 (3) (013) Otober, the dry season is from Deember to January of next year and the normal season is May and November. PCM wallboard's prie estimation: the material of the wallboard is made up with HDPE and paraffin (prie of Fushun Petrohemial Corporation, January 009) at some rate. Element graphite was added for improving thermal ondutivity [13]. o the osts of 0.04 mm thik wallboard are alulated as: ( ) 4=38.998(Yuan/m ) Assuming the proessing harge is 10 Yuan/h, the wallboard osts about The primary investment equals = Besides that the eletrothermal film osts =370. o the total osts is Eletriity prie was alulated as: Y = y h p t m φ The eletriity osts for PCM wallboard heating in winter an be alulated from the above formulae: /0.9 = The eletriity osts for ommon room in summer and winter: ( ) = o the investment reovery period n= ( ) 1. / ( )=1.4. Aording to the stated above, it only osts about one year to reover the investment. More than that, it ould largely relieve the stress of the eletri network. o it is feasible and will bring huge eonomi benefits to the hot summer and old winter area. 8. Eonomial effiieny analysis Aording to the seond law of thermodynamis, eletri heating is not a sientifi heating way. But the power annot storage diretly and the generated energy will not be hange in peak or trough period. o it would be huge waste if the trough eletriity is not used. As was stated above, trough energy storage to supply energy for the next day in winter will be a good way of peak load shifting. On the other hand, diretly take advantage of the heat storage property delay time to avoid the eletriity peak in summer. There are huge eonomi benefits with supplying a omfortable environment and higher trough eletrial energy effiieny. 9. Aknowledgements This work was finanially supported by: (1) National Natural iene Foundation of China, under Grant No () Applied Basi Researh Program Foundation of Yunnan Provine, under Grant No. 011FZ04. Referenes 1. Feldman, D., Banu, D., Hawers, D., Obtaining an energy storing building material by diret inorporation of an organi phase hange material in gypsum wallboard, olar Energy Materials, (), 1991, pp Rudd, A. F., Phase hange material wallboard for distributed thermal storage in building, AHRAE Transations 99(), 1993, pp Takeshi, Kondo., Tadahiko, Ibamoto., Tsubota, Yuuji., Researh on the thermal storage of PCM wallboard, Japan Arhitetural planning environment engineering, 540, 001, pp Zhang, Y.-P., Kang, Y.-B., Jiang, Y., Researh of phase hange and hemial energy storage using in building heating field, Heating Ventilation & Air Conditioning, 9(5), 1999, pp Yu, D., Cao Y., Mei, F.-M., Combined PCM heat interhanger energy storage rate experiment and researh, Heating Ventilation & Air Conditioning, 38(5), 008, pp Feng, G.-H., Gao F.-., Fu, Y.-H, Complex PCM wall thermal property experiment and parameters distinguishing methods, Journal of hengyang Arhiteture and Civil Engineering University (natural sienes), 0(3), 004, pp in, K.-P., Zhang Y.-P., Eletrothermal PCM heat storage floor thermal performane simulation, Ata Energiae olaris inia, 5, 003, pp in, K.-P., Zhang Y.-P., Eletrothermal PCM heat storage floor thermal performane simulation, Ata Energiae olaris inia, 4(5), 003, pp in, K.-P., Zhang Y.-P., Jiang, Y., ummer air onditioning PCM wall design. Ata Energiae olaris inia, 4(), 003, pp Voller, V., Cross, M., Aurate solutions of moving boundary problems using the enthalpy method, Int J Heat Mass Transfer, 4(3), 1981, pp Yan, Q.-., Zhao Q.-Z., Building heating proess analysis. China Arhiteture & Building Press, Beijing, National Meteorologial Information Centre Referene Room., China building thermal environment analysis speial limate data, China Arhiteture & Building Press, Beijing, hamsundar, N., parrow E. M., Analysis of Multidimensional Condution Phase Change Via the Enthalpy Model, Journal of Heat Transfer, 97(3), 1975, pp Zhang, Y.-P., Ding J.-H., Influene of additives on the thermal ondutivity of shape-stabilized phase hange material, olar energy materials and solar ells, 90(11), 006, pp