Available online at ScienceDirect. Energy Procedia 78 (2015 )

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1 Avalable onlne at ScenceDrect Energy Proceda 78 (2015 ) th Internatonal Buldng Physcs Conference, IBPC 2015 Combned thermal effect of cool roof and cool façade on a prototype buldng Anna Laura Psello a, *, Veronca Luca Castaldo b, Crstna Psell b, Glora Pgnatta b, Franco Cotana a a Department of Engneerng Unversty of Peruga, Va Durant 63, Peruga, Italy b CIRIAF Interunversty Research Center on Polluton and Envronment Mauro Fell, Va Durant 67, Peruga, Italy Abstract Recently, huge efforts were made to develop new passve solutons for optmzng buldng summer thermal-energy behavor. Whle cool roofs are well nvestgated, a lack of knowledge s detected about the benefts dervng from the combnaton of cool roofs and cool façades. Ths work ams at determnng the thermal performance of nnovatve cool roofng membrane and cool façade pantng when appled on a prototype buldng, through contnuous montorng. Addtonally, senstvty analyss s performed to nvestgate the thermal benefts of the coupled solutons. Results showed that the combned solutons generate sgnfcant passve coolng n terms of ndoor operatve temperature reducton Publshed The Authors. by Elsever Publshed Ltd. by Ths Elsever s an open Ltd. access artcle under the CC BY-NC-ND lcense Peer-revew ( under responsblty of the CENTRO CONGRESSI INTERNAZIONALE SRL. Peer-revew under responsblty of the CENTRO CONGRESSI INTERNAZIONALE SRL Keywords: Cool roof; Cool façade; Contnuous montorng; Buldng thermal-energy performance; Senstvty analyss. 1. Introducton Urban Heat Island (UHI) s a well acknowledged urban mcroclmate phenomenon [1] characterzed by hgher temperatures n urban areas compared to the surroundng suburban and rural areas [2]. It s due to varous factors, such as solar radaton trappng and wnd shelters caused by urban street canyon geometry, urban greenhouse effect, dmnuton of evaporaton surfaces and storage of sensble heat n the cty fabrc, and anthropogenc heat released [3]. Although mtgatng the heatng energy requrement n wnter, UHI ncreases the coolng energy demand n * Correspondng author. Tel.: ; fax: E-mal address: anna.psello@unpg.t, psello@crbnet.t Publshed by Elsever Ltd. Ths s an open access artcle under the CC BY-NC-ND lcense ( Peer-revew under responsblty of the CENTRO CONGRESSI INTERNAZIONALE SRL do: /j.egypro

2 Anna Laura Psello et al. / Energy Proceda 78 ( 2015 ) summer. Therefore, n last decades the contrbuton of ar condtonng n buldngs energy consumpton has been growng [4]. Several studes focused on the development of technques for mtgatng the UHI phenomenon, such as smart materals wth hgh optc-thermal performances [5], ncreased urban green areas [6], solar shadng of urban surfaces [7], cool buldng envelope materals [8]. The potental of such cool materals has been wdely nvestgated n roof applcatons, whle ther capablty n mtgatng UHI when appled n buldng façades s stll not well acknowledged [2; 9-10]. Fndngs confrmed the potental of ths technque n southern European clmatc condtons. Consderng cool roof applcablty n cold clmates, Mastrapostol et al. [11] observed a decrease of 73% for coolng, wth neglgble heatng penaltes, as a result of the applcaton of a cool roof fluorocarbon coatng for an ndustral buldng n Oss, Netherlands. In order to compare the performance of such nnovatve materals under dfferent boundary condtons, dedcated buldng prototypes have been often used [12-13]. For nstance, Doya et al. [13] employed reduced-scale buldng prototypes n a typcal urban canyon confguraton to assess the thermal effects of cool façade pants on both buldng and outdoor envronment. Usng fve dedcated test cells, Revel et al. [14] montored the thermal performance of cool colored ceramc tles, acrylc pants and btumnous membranes for both roof and walls [13]. In ths panorama, the purpose of ths work s to evaluate the thermal effect of two nnovatve cool solutons for buldng envelopes,.e. a cool roof membrane and a façade reflectve pantng. To ths am, such cool materals were prevously expermentally characterzed and optmzed n-laboratory. Therefore, ther performance n terms of achevable ndoor comfort condtons was assessed when appled on () the roof and () the South-facng façade of a dedcated test-room located n Peruga, Italy. The n-feld contnuous montorng of the man thermal and optcal parameters was performed. The fnal objectve s to determne the enhancement of the testroom thermal performance assocated to the applcaton of the proposed cool coatngs compared to tradtonal testroom buldng materals,.e. btumen membrane and red colored pantng. In fact, whle cool roof technologes are well nvestgated f compared to cool façades, a lack of knowledge and research effort s detected about the expermental measurement of benefts dervng from couplng the two solutons. Therefore, the senstvty analyss of the two envelope strateges was carred out to compare the effects of the combned solutons,.e. cool roof and cool façade. Fnally, frst results of the n-feld measured albedo of the cool roof membrane were analyzed. Nomenclature T out Outdoor dry bulb Temperature [ C] T op Indoor Operatve Temperature [ C] T op, max Maxmum hourly value of ndoor Operatve Temperature [ C] R * Equvalent Reflectance of the buldng envelope [-] R solar Solar Reflectance [%] A Sze of envelope surfaces,.e. roof and façade [m 2 ] VF Vew Factor of the envelope surface to the sky [-] OP, IP Output and Input Parameters of senstvty analyss [-] OP max, OP mn, IP max, IP mn Output Parameter and Input Parameter extremes [-] SC Senstvty Coeffcent [-] 2. Materals and methods The am of ths study s to compare the thermal behavor of the two nnovatve cool envelope solutons,.e. cool roof membrane and cool façade pantng. Therefore, the two solutons have been appled on a dedcated prototype case study buldng,.e. test-room, located nsde the unversty campus n Peruga, Italy. The n-stu contnuous montorng of the thermal-energy performance of the proposed solutons has been carred out under real dynamc boundary condtons durng summer Both the ndoor/outdoor thermal characterstcs and the roof albedo have been montored. Frstly, the case study buldng wth non-cool envelope materals,.e. btumen membrane and red colored pantng, has been montored as base case scenaro. Secondly, the cool membrane has been appled on the test-room roof n order to assess the specfc contrbuton of the cool roof to the thermal performance of the testroom n summer condtons. Thereafter, the cool pantng has been appled n the South-facng façade of the same

3 1558 Anna Laura Psello et al. / Energy Proceda 78 ( 2015 ) case study buldng. In ths way, the performance of the coupled solutons has been analyzed. Montored data have been subsequently post-processed n order to compare the thermal effect of the two cool solutons. In partcular, the senstvty analyss has been performed to understand the coupled coolng contrbuton of the cool roof and the cool South-façade. Three dfferent scenaros for the case study buldng envelope have been dentfed: Standard scenaro (S): the materals mplemented n the buldng envelope are constructon technques commonly used n recent buldngs n Italy. In partcular, the roof s covered wth a btumnous black membrane and the walls wth a red colored tradtonal pantng; Cool Roof scenaro (CR): the nnovatve cool roof membrane s appled over the exstng membrane of the case study buldng Standard scenaro; Cool Roof and Façade scenaro (CR+F): the further nnovatve cool façade pantng s appled on the Southfacng façade of the case study buldng Standard scenaro Cool roof membrane and cool façade pantng The nnovatve cool roofng membrane s a polyurethane-based waterproof lqud whte membrane wth hgh elastcty. The coolng potental of such membrane was optmzed through teratve laboratory and n-feld tests by ncreasng specfc components such as the ttanum doxde (TO 2) and hollow ceramc mcrospheres percentage. Therefore, the fnal optmzed membrane presents almost 12% of TO 2 and 4% of hollow ceramc mcrospheres. The proposed cool pantng for buldng façade applcatons s an almost whte non-organc pantng, manly composed by potassum slcate wth small percentage of resn. It s characterzed by hgh vapor permeablty. Also the pantng was optmzed through an teratve procedure by ncreasng TO 2 and hollow ceramc mcrospheres percentage. The most performng combnaton s agan wth 12% of TO 2 and 4% of hollow ceramc mcrospheres Senstvty analyss The senstvty analyss has been performed to defne the mpact of each proposed soluton on the buldng thermal performance. In fact, senstvty analyss allows the dentfcaton of the more sgnfcant varables (hgh senstvty) and strateges from both techncal and economcal pont of vew [15]. Therefore, the reflectance propertes of the roof and the walls represent the nput parameters (IP) of the thermal analyss mult-varable problem. The output parameter (OP) chosen for defnng the senstvty coeffcent (SC) s the maxmum hourly value of ndoor operatve temperature (T op). T op results are stated as a functon (1) of the equvalent reflectance of the buldng envelope (R * ) that represents the sole IP varable. R * for the envelope s expressed as the combnaton of the equvalent reflectance of the dfferent envelope components. The varable R * s a functon (2) of the Solar Reflectance (R solar), the surface area (A), and the vew factor of surface to the sky (VF) of the -th materal. The consdered VF for roof and wall are equal to 1 and 0.5, respectvely. Such VF values have been defned assumng free feld condtons to the sky, even f small obstacles are present. Therefore, the R * value s slghtly overestmated. T * ( x ; x x ) f ( R ) op, max = f 1 2;...; n = * = ( R ; A VF ) R f ; solar, The dfferental of the OP s calculated through the equatons reported n [15] consderng that each IP varable s ndependent from every other one. The SC expressng the IP role s obtaned wth (3), consderng the maxmum OP stuaton as the base case. SC ( OP OP )/ OP max mn max = [-] (3) ( IPmax IPmn)/ IPmax (1) (2)

4 Anna Laura Psello et al. / Energy Proceda 78 ( 2015 ) Case study and montorng setup The case study buldng conssts of a fully nstrumented test-room (12 m 2 ) located n Peruga (Italy), and bult followng recent constructon technques [16]. Fg. 1 reports the pctures of the roof and the South-facng façade of the case study buldng before (Fg. 1a,c) and after (Fg. 1b,d) the applcaton of the cool membrane and pantng. The expermental setup [16] s composed by () an outdoor meteorologcal staton located over the roof of the unversty buldng close to the test-room faclty (Fg. 1e) and () an ndoor staton postoned nsde the same testroom (Fg. 1f). The meteorologcal staton allows the contnuous montorng of the clmate boundary condtons n terms of temperature, relatve humdty, wnd velocty and drecton, ran fall, and solar radaton. The ndoor staton s meant to measure the man thermal-energy parameters nsde the prototype buldng,.e. walls and celng surface temperatures, ar temperature, mean radant temperature, relatve humdty, energy consumpton, etc., and the reflected roof radaton for the n-feld measurements of albedo. Detaled nformaton s reported n [16]. Fg. 1. Case study buldng: (a, b) roof confguratons; (c, d) façade confguratons; (e) outdoor and (f) ndoor mcroclmate montorng setup. 4. Results and dscusson 4.1. Albedo The analyss of the optcal propertes of the two roof coatng solutons has been carred out by comparng the nfeld md-day albedo measured durng summer The comparson between the black btumnous membrane and the cool membrane hghlghts the hgher solar reflectance of the nnovatve cool membrane. Although the average albedo measured durng the montorng perod for the proposed membrane s equal to 51%, the albedo ncreases by about 80% f compared to the btumen membrane (11%). Such ncreased albedo results n an mproved sheld to the heat gans through the roof, as thoroughly expressed n the followng analyses. Addtonally, the n-feld montorng over tme showed a slght reducton (4%) of the cool roofng membrane albedo due to weatherng and agng effects. Further analyses of such phenomenon are stll on gong Thermal performance of the prototype case study buldng Further analyses have been performed on the nfluence of the mplemented cool solutons on the ndoor/outdoor thermal propertes of the test-room. The results show that wth equvalent outdoor ar temperature condtons the cool roofng membrane s able to decrease the ndoor operatve temperature of the prototype buldng by a maxmum of 2.6 C (11%) n the hottest day. Whereas, the further applcaton of the cool pantng on the South-facng façade of the test-room generates a lower reducton n the ndoor operatve temperature,.e. 0.5 C (2%). Consstent and slghtly lower dfferences have been obtaned n terms of mean radant temperature decrease n the CR scenaro and the CR+F scenaro, compared to the S scenaro. Therefore, the passve coolng potental of the cool roof membrane s sgnfcant. Whereas, the effect due to the cool façade pantng s reduced, when appled together wth an already effectve soluton,.e. cool roof. The results are depcted n Fg. 2, whch shows the dstrbuton of ndoor operatve temperature wth respect to the outdoor dry bulb temperature for the three scenaros. Fnally, the combned effect of the cool pantng and cool roofng membrane generates a maxmum ndoor passve coolng effect of 3.1 C (13%) n terms of ndoor operatve temperature. Addtonally, the cool roofng membrane s able to cool the external roof

5 1560 Anna Laura Psello et al. / Energy Proceda 78 ( 2015 ) surface up to 19.8 C (55%), and the nternal celng up to 3.4 C. Non-neglgble results are detected for the cool pantng n terms of surface temperatures. It s, ndeed, able to reduce both the external and nternal surface temperature of the South-facng wall up to 9.9 C (25%) and 4.4 C, respectvely. Fg. 2. Dstrbuton of ndoor operatve temperature vs. outdoor dry bulb temperature for the three scenaros durng the montorng perod Senstvty analyss The senstvty analyss has been carred out to compare the effect of the two cool envelope solutons and of ther couplng on the ndoor thermal condtons of the case study buldng. To ths am, the equvalent reflectance of the buldng envelope has been assumed as the only IP. The S scenaro corresponds to the lower solar reflectance value, the CR scenaro to the medum one, whle the CR+F scenaro presents the hgher reflectance. Fg. 3 reports the results n terms of maxmum hourly value of ndoor operatve temperature, the OP, durng the montorng perod. Fg. 3. Senstvty analyss results for the maxmum hourly value of ndoor operatve temperature durng summer perod. Fndngs are consstent wth the above mentoned results of ndoor thermal behavor. The graph ndcates the effectveness of the cool roof membrane n reducng the maxmum ndoor operatve temperature, stressed by the hgh slope of the lne between the S and the CR scenaro. Moreover, the lower lne slope between the CR and the CR+F scenaro confrms the mnor contrbuton of the cool façade pantng n the ndoor passve coolng. In partcular, the two coupled solutons optmze the thermal performance of the case study buldng. Nonetheless, the comparson among CR and CR+F results shows lmted dscrepances n terms of ndoor thermal comfort. 5. Concluson In ths paper, the benefts dervng from the applcatons of two passve coolng strateges for buldng envelope,.e. cool roof membrane and cool façade pantng, were evaluated and compared. To ths am, a contnuous montorng of the thermal performance of a prototype buldng,.e. test-room, was performed, after the applcaton

6 Anna Laura Psello et al. / Energy Proceda 78 ( 2015 ) of both the proposed solutons on () the roof and () the South-facng façade of the buldng. Fnally, a senstvty analyss was carred out n order to quantfy the effectveness of the two solutons n mprovng the ndoor thermal condtons of the case study buldng by consderng both the separate and combned contrbutons. The results showed that the only cool roof membrane s able to decrease up to 2.6 C (11%) the ndoor operatve temperature. The combnaton of the two cool solutons leads to an overall temperature reducton of 3.1 C (13%). Addtonally, the applcaton of the only cool membrane s able to guarantee a 19.8 C (55%) decrease of the external roof surface temperature, whle the further surface temperature reducton generated by the cool façade pantng s equal to 9.9 C (25%). Therefore, ths study demonstrates how the passve coolng contrbuton of the proposed façade pantng to the enhancement of the ndoor thermal performance of the test-room s relatvely lmted wth respect to the cool roof effect n terms of operatve temperature decrease. However, the contrbuton of the cool façade s not neglgble n terms of surface temperature of the case study buldng. Moreover, fndngs of ths study stress how ths soluton,.e. the cool façade, deserves much more nvestgaton as future developments of ths research. The possble effect n reducng buldng façade temperatures n urban areas, and ts role n mtgatng urban heat sland phenomenon should be assessed more n detal. The combnaton of the two nnovatve solutons, ndeed, best optmzes the thermal behavor of the test-room. Acknowledgements The authors would lke to thank the CVR s.r.l. company for provdng the samples for the laboratory measurements and assstng the expermental set up. The frst author acknowledgments are due to the CIRIAF program for UNESCO n the framework of the UNESCO Char Water Resources Management and Culture for supportng her research. References [1] Santamours M. Coolng the ctes A revew of reflectve and green roof mtgaton technologes to fght heat sland and mprove comfort n urban envronments. Sol Energy 2014;103: [2] Santamours M, Gatan N, Spanou A, Salar M, Gannopoulou K, Vaslakopoulou K, Kardomateas T. Usng cool pavng materals to mprove mcroclmate of urban areas Desgn realzaton and results of the flsvos project. Buld Envron 2012;53: [3] Gros A, Bozonnet E, Inard C. Cool materals mpact at dstrct scale Couplng buldng energy and mcroclmate models. Sustanable Ctes and Socety 2014;13: [4] Hernández-Pérez I, Álvarez G, Xamán J, Zavala-Gullén I, Arce J, Smá E. Thermal performance of reflectve materals appled to exteror buldng components A revew. Energ Buldngs 2014;80: [5] Ma Y, Zhu B, Wu K. Preparaton and solar reflectance spectra of chameleon-type buldng coatngs. Journal of Solar Energy 2001;70: [6] Yu C, Hen WN. Thermal mpact of strategc landscapng n ctes: a revew. Advances n Buldng Energy Research 2009;3(1): [7] Akbar H. Shade trees reduce buldng energy use and CO 2 emssons from power plants. Envron Pollut 2002;116(1): [8] Santamours M. Usng cool pavements as a mtgaton strategy to fght urban heat sland A revew of the actual developments. Renew Sust Energ Rev 2013;26: [9] Kolokotron M, Gowreesunker BL, Grdharan R. Cool roof technology n London: An expermental and modellng study. Energ Buldngs 2013;67: [10] Romeo C, Znz M. Impact of a cool roof applcaton on the energy and comfort performance n an exstng non-resdental buldng. A Sclan case study. Energ Buldngs 2013;67: [11] Mastrapostol E, Karless T, Pantazaras A, Kolokotsa D, Gobaks K, Santamours M. On the coolng potental of cool roofs n cold clmates: Use of cool fluorocarbon coatngs to enhance the optcal propertes and the energy performance of ndustral buldngs. Energ Buldngs 2014;69: [12] Doya M, Bozonnet, Allard F. Expermental measurement of cool facades performance n a dense urban envronment. Energ Buldngs 2012;55: [13] Revel GM, Martarell M, Emlan M, Gozalbo A, Orts MJ, Bengochea MA, Delgado LG, Gak A, Katsap A, Taxarchou M, Arabatzs I, Fasak I, Hermanns S. Cool products for buldng envelope Part I: Development and lab scale testng. Sol Energy 2014;105: [14] Revel GM, Martarell M, Emlan M, Celott L, Nadaln R, De Ferrar A, Hermanns S, Beckers E. Cool products for buldng envelope Part II: Expermental and numercal evaluaton of thermal performances. Sol Energy 2014;105: [15] Psello AL, Gorett M, Cotana F. Buldng energy effcency assessment by ntegrated strateges: dynamc smulaton, senstvty analyss and expermental actvty. ICAE 2011 Internatonal Conference on Appled Energy, Peruga (Italy), [16] Psello AL, Cotana F, Ncoln A, Buratt C. Effect of dynamc characterstcs of buldng envelope on thermal-energy performance n wnter condtons: n feld experment. Energ Buldngs 2014;80: