Numerical simulation and experimental study on thermal properties of trailer house composite envelope with vacuum insulation panels

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1 Bulgara Chemcal Commucatos, Volume 48, pecal Issue D (pp. 6) 6 Numercal smulato ad permetal study o thermal propertes of traler house composte evelope wth vacuum sulato paels Haju Lou, Akag Ka *, Zhpeg Guo Merchat Mare College, hagha Martme Uversty, hagha, 6, P.R.Cha Receved Jue 5, 6, Revsed eptember 6, 6 Due to dstgushed thermal performace of vacuum sulato paels (VIPs),.e. the thermal coductvty s approxmately 5- tmes lower tha that of tradtoal thermal sulato materal, t has bee wdely appled for eergy coservato purpose, especally as buldg evelope. To research the thermal characterstc of VIPs composte evelope for traler house, the VIPs are employed, based o the clmate characterstcs of the cold zoe, ad three typcal models, amely, the teror adabatc, sadwch ad teror adabatc models are costructed. The physcal ad mathematc models are developed ad the umercal comparatve aalyss of the thermal performace s made uder the lager temperature dfferece codto. Compared amog those costructos wth the same cotuous temperature waves, the dampg factor, the delay tme, the temperature vbrato of teror wall surface, heat trasfer flux ad the thermal brdge are theoretcally aalyzed. The results of the smulato mply that, teror adabatc model of the VIPs composte evelope s the best for the eergy coservato, especally thermal brdge rego, reducto the rage of the teror temperature fluctuato, radato thermal cool sesato ad mprovemet thermal comfort d. The work provdes the theoretcal foudato for the VIPs developmet ad applcato buldg cotracture. Key words: Vacuum sulato paels, Traler house, Composte evelope costructo, Thermal performace, Eergy coservato. INTRODUCTION The developmet of cold regos s mportat for regoal ecoomc, mltary sgfcace ad research value. The traler house ca be the temporary workg ad lvg place for researchers or staff. As the specal outdoor clmate wter, that s, the temperature dfferece betwee teror ad teror ca be up to 6, thermal performace of the buldg evelope s vtal for eergy coservato ad persoal thermal comfort. Excellet adabatc performace of evelope costructo, ot oly ca reduce eergy cosumpto, mprove door thermal comfort, but also ca avod mosture codesato problems of er wall surface []. Due to the dstgushed low thermal coductvty,.e. approxmately 5- tmes lower tha tradtoal thermal sulato materals [--4], Vacuum sulato paels (VIPs), has sgfcat advatages as the adabatc compoet for traler house evelope. The VIPs are already troduced to the market large-scale producto, such as reefer cotaers, cvl buldg evelopes, refrgerato storage room, ce boxes ad so o[5]. ome theoretcal calculatos have bee proposed ad amout of study has bee carred out o the possbltes of VIPs sulated systems. But the To whom all correspodece should be set: E-mal: akag57@6.com reports for the VIPs stallato ad thermal operato system are rare. The objectve of ths paper was to aalyse theoretcally the thermal sulato models, the teral terface temperature, delay tme, thermal erta d, etc., model the traler houses wall structure wth VIPs ad compare the models combed wth the teror temperature varato cold regos [5]. THERMAL PERFORMANCE OF TRAILER HOUE ENVELOPE The evelopes of traler house, cludg oe door pael, three sde paels, oe roof pael, ad oe floor pael, maly used to reduce the heat leakage ad mata the room temperature. Accordg to the thermal comfort d, teror wall surface temperature closed to the door evromet temperature meas the comfortable feelg [6]. However, the teror surface wall temperature maly depeds o the door ar temperature ad the thermal resstace of the wall. Accordg to some relevat provsos, heat trasfer coeffcet of traler house evelope cold rego must be: k.4 W/(m.K), ad temperature dfferece betwee teror surface ad desg ambet temperature must be: t 4.K [7-9]. Too thck wall meas hgh tal vestmet 6 Bulgara Academy of ceces, Uo of Chemsts Bulgara

2 H.J. Lou, et al. : Numercal smulato ad permetal study o thermal propertes... ad trasportato costs, whle too th wall meas eergy cosumpto ad eve mosture codesato. Optmal costructo of the traler house evelope ca ot oly provde comfortable lvg evromet, but ca also reduce eergy cosumpto. I addto, traler house belogs to reusable buldg, whch s beefcal to evrometal protecto, ecoomc. Mmum thckess of traler house evelope costructo The mmum heat trasfer resstace of buldg evelope cold rego should meet the requremets of the GB576-99, Ca be calculated by Eq.(): ( t t ) R m R () [ t] where: R,m s mmum heat trasfer resstace of the evelope, m K/W; t s door desg temperature of the traler house wter, K; t s outdoor desg temperature of the traler house wter, K ; s temperature dfferece correcto factor, =.; s teral surface heat trasfer resstace; R =. m K/W; Δt meas allow error betwee door ar ad teror wall surface, Δt =.5 K. o, R,m =.99 m K/W. Accordg to the desg Code [8], ts heat trasfer resstace should be: R 7.4m K/W.4 () k VIPs ad polyurethae (PU) as traler house evelope costructo of fllg materals, ad the thckess of PU layer ca be calculated by Eq. (): 4 f vp R R R R () R Where: R s the desg teror surface heat trasfer resstace, R =.4 m K/W; f s thermal coductvty of PU, f =. W/(m K); vp s thermal coductvty of VIPs, vp =.7 W/(m K); vp s thckess of VIPs, vp =. m. The teror protectve layers of the traler house evelope are made of steel plate ad galvazed sheet ad the teror protectve layer s made of staless steel plate. All the protectve layers are very th ad the cellet thermal coductors. R ad R are gored the calculato. Combed wth the Eqs. () ad (), the PU layer thckess s mm. I fact, PU layer thckess s 5 mm ths research. f vp The thermal characterstc parameters of traler house evelope costructo VIPs caot be used aloe as the evelope of the traler house, but form of composte paels wth other thermal sulatg materals. The followg parameters should be cofed before the study. () The dampg factor. The dampg factor refers to the teror ar temperature stablty of the traler house evelope, the teror evelope effect by outdoor tegrated temperature or outdoor ar temperature harmoc. The dampg factor s the rato of outdoor tegrated temperature or outdoor ar temperature harmoc ampltude to teror surface temperature harmoc ampltude. For the multlayer evelope, the dampg factor ca be calculated by the Eq. (4) [8]: D Y Y Y v.9e (4) Y Y Y where: ν s the dampg factor of the multlayer evelope; D s thermal erta d of the layer ; h s teror surface thermal covectve coeffcet of the traler house, W/(m K); h s teror surface thermal covectve coeffcet, W/(m K);,,, are heat storage coeffcets of each layer materals from sde to outsde, W/(m K); Y, Y,,Y s surface heat storage coeffcet of each layer materals from sde to outsde, W/(m K). ()The delay tme. The delay tme s the tme dfferece betwee the momet that hghest (or lowest) teror surface temperature harmoc appears ad the momet that the hghest (or lowest) outdoor tegrated temperature or the hghest (or lowest) outdoor ar temperature harmoc appears. It ca be calculated by Eq. (5) (GB576-99): Y (4.5 D arcta arcta ) 5 Y Y (5) where: s the delay tme, h; Y s the heat storage coeffcet of teror surface evelope, W/(m K); Y s heat storage coeffcet of outer surface evelope, W/(m K). () Thermal erta d. Thermal erta d D s a dmesoless d to characterze ts resstace ablty of temperature fluctuatos ad thermal flux fluctuatos. The greater the D value s, the better thermal stablty of evelope s. The D of a sgle materal layer evelope ca be calculated by Eq. (6)[8] : C p D R (6) T

3 H.J. Lou, et al. : Numercal smulato ad permetal study o thermal propertes... Where: R s thermal resstace, m /W; s thermal storage coeffcet, W/(m K); δ s thckess, m; C p s specfc heat at costat pressure, J/(kg.K); ρ s desty, ; s heat coductvty coeffcet, ; T s perod of fluctuatos, s. For multlayer composte layers evelope, the D value ca be calculated by Eq. (7) [8]: W/(mK) kg/m D R (7) (4)The thermal storage coeffcet. The thermal storage coeffcet s the rato of the heat flux ampltude through the layer surface to the surface temperature ampltude. It ca characterze the merts of the materal thermal stablty. The greater the thermal storage coeffcet s, the better thermal stablty s. It's ca be calculated by the Eq. (8)[8]. Aq C p (8) At T where: A q s heat flux wave-ampltude of layer surface; A t s temperature wave-ampltude of layer surface. The types of composte evelope As the thermal coductvty of VIPs s much less tha that of tradtoal thermal sulated materals, the composte evelope of traler house, accordg to VIPs layer locato posto, ca be dvded to three types, that s, teror adabatc (Fgure a), sadwch (Fgure b) ad teror adabatc (Fgure c ). (a) (b) (c) Fg.. The adabatc types of the composte evelope: (a) teror adabatc, (b) sadwch ad(c) teror adabatc. ()- teral staless steel plate; () - VIPs layer; () - H-shaped fxed pece; (4) - PU layer; (5) - teral steel plate. VIPs COMPOITE ENVELOPE CONTRUCTION MODEL Heat trasfer through traler house evelope uder large temperature dfferece cold rego s a complcated usteady process, whch s ot oly affected by the outdoor ar temperature, solar radato, wd speed ad so o, but also relates to thermal coductvty, thermal storage coeffcet, specfc heat at costat pressure, desty ad thermal performace of evelope materal. As the drect calculato for the heat trasfer process traler house evelope s very complcated, the followg ecessary assumptos should be made advace. ()No clearace st betwee each layer; () Physcal parameters of each layer materal does ot chage wth temperature;()igore the fluece of ''H-shape coectg pece" ad heat trasfers oe dmeso way;(4) No teral heat source ad mass trasfer. Physcal model Iteral staless steel plate ad teral steel plate are gored to smplfy the models ad the physcal models are llumated Fgure. The types of composte evelope maly deped o the locato of the VIPs layer. I ths physcal model, the thckess δ vp of VIPs layer s a costat value, ad total thckess δ + δ for polyurethae layer s also a costat value. Whe δ =, the type s teror adabatc. Whle δ =, the type s teror adabatc. Whle δ = δ, the type s sadwch. Fg.. The sketch of traler house VIPs composte evelope. Outdoor temperature The outdoor temperature s a key varable to calculate the heat flux that trasfers from teror to teror. However, the outdoor temperature chages wth tme. I a perod of tme (for ample wth a

4 H.J. Lou, et al. : Numercal smulato ad permetal study o thermal propertes... moth), the dural varato of the temperature ca be thought as a cyclcal fluctuato 4 hours. e (or cose) fucto seres are always take to smplfy temperature fluctuato for calculato practce. The real outdoor temperature fluctuato a certa Chese cold rego oe day of the coldest moth s collected by the atoal meteorologcal stato, ad the fttg curve s show Fgure. Fg.. Actual temperature ad fttg curve the cold rego. Outdoor comprehesve temperature fttg fucto s: T, 47 6.cos( ( 5)) (9) 4 where: T, s the correspodg outdoor temperatures at the momet, K. Mathematcal model As the dmeso of heght ad wdth s much larger tha that of thckess of traler house evelope, o heat source sts ad materals of every layer s uform dvdually, the thermal coducto of the evelope ca be cosdered as oe dmesoal way. Based o Fourer's law, a correspodg usteady dfferetal equato () ca be establshed. T T () C x Where, s tme; x s fte-thckess. Accordg to the cold rego clmate characterstcs, h = 8.7 W/(m K), h = 9. W/(m K). The desg door temperature wter s o C, relatve humdty %. That boudary codto s: T x T x x xl h ( T T ) p T T T 47 6.cos( ( 5)) 4 () Lear fte elemet equato of usteady thermal coducto fucto ca be derved by varable separato method. upposed that door ar temperature s costat, the heat flux, trasferrg through the teror surface s maly used for heat storage at the begg. A perod later, the heat trasfers from the teror surface to the teror surface. Whle the thermal equlbrum s establshed, the teror surface temperature reaches ts maxmum value. For the usteady-state heat trasfer of the evelope, t's teror surface thermal trasfer stregth s: q h( T T( )) () Where: s thermal flux desty through q evelope teral surface, ; s temperature of evelope teror surface, K. the thermal flux desty s made up of two parts, that s, thermal coducto stregth of evelope materal q evelope materal. T ( ) T5 ( ) q q / W/m T ( ) ad thermal storage stregth of q h ( T ( ) T 5 Where: ( )) () dt( ) q Cp (4) d ( ) s average temperature chage dt d K / s amout per ut tme of the materal, Accordg to q q q, Eq.(5) ca be obtaed. h h hh R h R ht ht hht R ( h RD ) T () ( e ) h h hh R h R Where: D D ; R /. (5) Types ad thermal parameters of VIPs composte evelope The three evelopes are costructed accordg to the Fgure. As the thermal resstaces of staless steel plate ad steel plate are much smaller tha that of thermal sulated materals, the staless steel plate ad steel plate are gored the smplfed models ad the followg smulato. The core materal of VIPs s super-fe glass fbre. Ad thermal propertes parameters of thermal sulated materals are show Table.

5 Bulgara Chemcal Commucatos, Volume 48, pecal Issue D (pp. 6) 6 Table. VIPs composte evelope structure. NO. Models Composto (from sde to outsde) Iteror taless steel plate ad teral decorato +CUFF pael + VIPsmm+ PU5mm+steel adabatc plate, galvazed plate ad outer decorato taless steel plate ad teral decorato + PU 75mm+ VIPsmm+ PU 75mm+ steel plate, adwch galvazed plate ad outer decorato Exteror taless steel plate ad teral decorato + PU5mm+ VIPs mm +CUFF pael+ steel adabatc plate, galvazed plate ad outer decorato Table. Thermal propertes parameters of sulated materals. Materals Heat coductvty coeffcet/ W/(mK) Desty/ kg/m pecfc heat capacty / J/(kgK) Heat storage coeffcet 4h / W/(m K) PU / VIPs REULT AND DICUION Comparso of the dampg factor ad the delay tme As metoed above, the dampg factor ad the delay tme of a buldg evelope are all mportat parameters to characterze the teror surface temperature stablty. The dampg factor ad the delay tme of the three kd traler house evelopes are collected Table. Table. The dampg factor ad the delay tme of three traler house evelopes. Thermal The dampg The delay NO. Models erta d factor tme / h D Iteror adabatc adwch Exteror adabatc The cocluso ca be easly made from Table that, the dampg factor of model s the largest oe, followed by that of model, ad that of model s the smallest oe. The chage treds of delay tme are the same wth that of the dampg factor. Uder the same outdoor evromet wave fluctuato codto, the bgger the dampg factor s, the loger the delay tme s, ad the smaller the teral surface temperature fluctuato s, that meas the cellet at terferece ablty of outdoor evromet temperature ad good thermal stablty. o the teror adabatc model, amely Thermal erta d/ the VIPs layer s closed to the teror the evelope structure, s good for the teral surface temperature stablty. Iteror surface temperature fluctuato The teror surface temperature of traler house evelope s oe of the mportat factors of door thermal comfort study. It s also a vtal factor of the mosture codesato o the surface of buldg teral wall surface, especally cold rego. The teral wall surface temperature fluctuatos of three models uder the same codto were umercally aalyzed, ad the smulato curves are posed Fgure 4. Fg. 4. mulato curves of three teral wall surface temperatures. All the teral wall surface temperatures kept pace wth the teral evromet chage ad 6 Bulgara Academy of ceces, Uo of Chemsts Bulgara D

6 H.J. Lou, et al. : Numercal smulato ad permetal study o thermal propertes... appeared maer of se waves, whle the teror temperature was costat. As the thermal erta d s the bggest of the three, the model has the logest delay tme ad the smallest wave ampltude. The wave trough of the model, that s, 9.5K, appeared at about 4: Bejg tme. The wave troughs of models ad are all a lttle lower that that of model, respectvely 9.89K ad 9.5K, eve the dfferece wth teror ar temperature s ot over 4K. Obvously, the teral wall surface of model wll easly mosture codese whle the relatve humdty s up to the dew pot. Takg the door thermal comfort for cosderato, the mea teral wall surface temperature of model, a lttle hgh tha that of models ad, s much closer to the teror costat temperature ad ca reduce the cold feelg of wall radato. Heat trasfer capacty For the usteady thermal process of the traler house evelopes, the tal put heat capacty Q L Q R s always ot equal to the output heat capacty. As the heat storage capacty of the evelopes, resultg the delay trasfer of heat, ad the fluctuato effect of teral temperature, ad Q R Q R > Q L caot be equal to each other all the tme, eve Q L at some momet. But for a cycle terval, the total put heat capacty should be approxmate equal to the output oe, that s, 4 Q d 4 QRd.The relate fucto ca be L pressed as: 4 4 T 4 QL d h h T T d ( ( )) (6) x Total heat trasfer capactes 4 hours of three evelopes are summarzed Table 4. Table 4. Heat trasfer capacty of three evelopes. NO.Models Heat trasfer quatty /4h / kj/m Iteror adabatc adwch 9.6 Exteror adabatc 44. The cocluso ca be made from Table 4 that, eergy trasmsso, that s, output heat capacty of model s the smallest, followed by that of model, ad the last s that of model. o, teror adabatc structure s the best oe for eergy coservato. Local thermal brdge effect I order to ehace the traler house evelopes stregth, the steel compoets, such as beams, reforcg rbs, crutches, etc. are always volved. But they ca chage the temperature dstrbuto at ther locato, causg so called local thermal brdge. Uder the cold rego codto, the local teral surface temperature s much lower tha that of ma teral surface temperature, resultg mosture codesato, eve frost at the local space, reducg thermal comfort ad causg potetal dager. Although the area of the thermal brdge space s small, the heat loss s huge. As thermal brdge spots ad types are varous, the typcal thermal brdge at the beam s selected ths research to smulato ad dscusso. Three dfferet cofguratos dagrams are show Fg. 5a, whch sold le meas model, dotted le, model, dash le dot, model, ad upper left corer area meas door room boudary. Combed wth the thrd boudary codto, smulatos for three models were posed the temperature dstrbuto ad thermal brdge effect. Ad the results were show Fgure 5b,c,d. Wth the posto of VIPs evelopes shftg from the sde to the outsde, the thermal brdge of the beam s becomg more ad more sgfcat. Isothermal treds of model Fgure 5 (b) s getle, ad the local teral surface temperature, the mmum value 9.5K, eve a lttle lower tha the ma teral surface temperature, s ot beyod 4K dfferece wth the teror temperature, that the code requres. Isothermal treds of model (show Fgure 5(c)) ad model (show Fgure 5 (d)) are dstorted, mplyg the thermal brdge effects are obvously. The lowest temperatures of model ad model, respectvely, are 9.6K ad 9.86K, all beyod 4K dfferece. o, uder the large temperature dfferece codto, the teror adabatc type of VIPs traler house evelope s deal for the reducto of eergy loss ad mprovemet of the teror thermal comfort. Takg the temperature dstrbuto charts for cosderato, the mea temperatures of the VIPs layers are also dfferet. For a cycle perod, the mea temperature of model s 87K, s hgher tha that of model, 75K, also hgher tha that of model, 55K. However, VIPs' servce lfe s flueced by ambet temperature. It s helpful to ted the servce lfe f the surroudg temperature s close to the room temperature. o, the model s deal for the traler house evelope. 5

7 H.J. Lou, et al. : Numercal smulato ad permetal study o thermal propertes... (a) Three dfferet evelopes cofguratos. (b) Temperature dstrbuto of model. CONCLUION Three typcal composte evelopes models for traler house, by usg VIPs, that s, teror adabatc, sadwch, teror adabatc, are structured. Ad the thermal characterstcs of the evelopes are theoretcally compared uder the cold rego temperature codto. () Combg wth the three types ad thermal performace cold rego, the dampg factor, the delay tme, the teral wall surface temperature vbrato, ad heat trasfer flux are theoretcally aalyzed. Iteror adabatc model s superor to the others eergy coservato ad door thermal comfort. () The thermal brdge effects of three VIPs composte evelopes are smulated ad theoretcally aalyzed uder the usteady codto. The cocluso ca be gaed that, the teror adabatc type s cellet for eergy coservato o thermal brdge regos ad temperature dfferece decreasg betwee the teral wall surface temperature ad door ar temperature. Meawhle, the teror adabatc evelope ca reduce radato cold feelg, avod local mosture codesato ad mprove thermal comfort d. Ackowledgemet: Ths research s facally supported by the Natural ceces Foudato of hagha, Cha (5ZR499). The authors would also lke to reder thakfuless to Mr. Yag Baotog from Yagzhou Toglee Reefer Cotaer Co., Ltd. for the kd help. (c) Temperature dstrbuto of model. (d) Temperature dstrbuto of model. Fg. 5. Three dfferet evelopes cofgurato ad temperature dstrbuto dagram. REFERENCE. H.H. Wag, Y.Y. Zhua, Togj Uversty(Natural ceces), 8, 64 ().. R. Baetes, B.P. Jelle, J.V. Thue, Eergy ad Buldgs, 4, 47 ().. M. Alam, H. gh, Appled Eergy, 88, 59 ( ) 4. J. Frcke, U. Heema, H.P. Ebert, Vacuum, 8, 68 (8). 5. J. Zhag, Z.L. Huag, Harb Egeerg Uversty,, 56 (9). 6. H.M. L, W.L. J, J. Buldg truct., 5, 9 (4). 7. GB589-5, Desg stadard for eergy effcecy of publc buldgs, Cha Buldg Idustry Press, Bejg, GB576-99, Code for thermal desg of cvl buldgs, Cha Buldg Idustry Press, Bejg, CAN/CA-Z4..-99, Caada tadards Assocato tadards, tructure Requremets for Moble Homes, Caada ( press), 99. 6