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An approach to the simulation of PCMsin building applications using TRNSYSManuel Iba ´n ˜eza,1,Ana La ´zaro b ,Bele ´n Zalba b,2,Luisa F.Cabeza c,*a Dept.de Medi Ambient i Cie`ncies del So `l,Universitat de Lleida,Rovira Roure 191,25198Lleida,Spain b Dept.de Ingenierı´a Meca ´nica,Universidad de Zaragoza,Marı´a de Luna s/n,50018Zaragoza,Spain c Dept.d’Informa`tica i Enginyeria Industrial,Universitat de Lleida,Jaume II 69,25001Lleida,Spain Received 12February 2004Available online 16December 2004AbstractThe use of phase change materials (PCMs)for thermal storage in buildings was one of the first applica-tions studied,together with typical storage tanks.An interesting possibility in building application is the impregnation of PCMs into porous construction materials,such as plasterboard or concrete,to increase thermal mass.The thermal improvements in a building due to the inclusion of PCMs depend on the cli-mate,design and orientation of the construction,but also to the amount and type of PCM.Therefore,these projects require a complete simulation of the thermal behaviour of the designed space in the conditions of use established a priori.In this paper a simple methodology for the energetic simulation of buildings including elements with PCMs using the program TRNSYS is presented and validated.This procedure does not aim a simulation of the real transfer processes inside the materials with PCM,but to evaluate the influence of walls/ceiling/floor with PCM in the whole energy balance of a building.The key parameter in the simulations is the equivalent heat transfer coefficient which has to be determined for each material.Experimental evaluation1359-4311/$-see front matter Ó2004Elsevier Ltd.All rights reserved.doi:10.1016/j.applthermaleng.2004.11.001*Corresponding author.Tel.:+34973702742;fax:+34973702702.E-mail addresses:m.ibanez@macs.udl.es (M.Iba ´n ˜ez),bzalba@unizar.es (B.Zalba),lcabeza@diei.udl.es (L.F.Cabeza).1Tel.:+34973702538;fax:+34973702613.2Tel.:+34976762566;fax:+34976762189./locate/apthermengApplied Thermal Engineering 25(2005)1796–1807M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–18071797 of the coefficient is presented.The methodology is applied in a building such as a prototype room built with concrete panels with PCM.Ó2004Elsevier Ltd.All rights reserved.Keywords:Simulation;Phase change material(PCM);Thermal energy storage(TES);TRNSYS1.IntroductionThe use of phase change materials(PCMs)for thermal storage in buildings was one of thefirst applications studied,together with typical storage tanks[1].The former application of PCMs de-scribed in the literature was their use for heating and cooling in buildings,by Telkes in1975[2] and Lane in1986[3].The use of building material for thermal storage was pointed out already in 1975by Barkmann and Westtling[4]and later by other authors.An interesting possibility in building application is the impregnation of PCMs into porous con-struction materials,such as plasterboard or concrete,to increase thermal mass.The use of PCMs to store coolness have been developed for air conditioning applications,where cold is collected and stored from ambient air during night,and its relieved to the indoor ambient during the hottest hours of the day.This concept is known as free cooling(Zalba[5],Vakilaltojjar and Saman[6,7], Bruno and Saman[8]).In the last decade the integration of PCMs in building walls has regained interest and several projects are going on at the moment(Mehling et al.[9]).For each application,before the con-struction phase,the most adequate melting temperature of the PCM,the percentage of PCM to mix in the mortar with conventional materials,or the position of panels with PCM in the build-ing depending on its use and architectonic characteristics of the buildings,must be considered. The optimization of these parameters is fundamental to demonstrate the possibilities of success of the PCMs in building materials.Like in many other technologies,the success of the product depends more in the way of use than in the product itself.The thermal improvements in a building due to the inclusion of PCMs depend on the climate,design and orientation of the construction and operation of the building,but also to the amount and type of PCM.Therefore,these projects require a complete simulation of the thermal behaviour of the designed space in the conditions of use established a priori.Nowadays,there are different commercial programs for the thermal simulation of buildings: EnergyPlus,TRNSYS15,ESP-r,RADCOOL,DOE-2,I DA-I CE3,HVACSim,CLI M2000,and many others.Some studies done with these programs,like the one presented by Natural Re-sources Canada(NCR[10])outline the threefirst ones for their versatility and reliability. Although all the possibilities of these programs,none of them have modules that allow direct simulation of the effect of adding a PCM in a wall or window.However,they include algorithms to simulate active walls with tubes including a circulatingfluid.The temperature of the liquid compared to the internal ambient drives the surfaces to radiative heating or cooling of the indoor spaces.At the same time,while analytical models of several PCM building elements are available, very few authors have worked on the simulation of the effect of PCMs in buildings using whole thermal building simulation programs(Peippo et al.[11],Feustel and Stetiu[12],Jokisalo et al.1798M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–1807[13],Schossig et al.[14]).Peippo et al.[11]were one of thefirst to discuss the use of PCMs walls for short-term heat storage in a building simulation environment.In their proposal all surfaces of the south-facing direct-gain room excluding thefloor were covered by PCM panels.The PCM considered was fatty acid impregnated into conventional13mm-thick plasterboard.The energy simulation balances were analyzed by the code FHOUSE(Aro-Heinila¨and Sunanen[15]).Owing to computational limitations,the effect of latent heat of the PCM was accounted for by defining an effective specific heat capacity.The project from Feustel and Stetiu[12]studied the use of PCM imbedded in gypsum wallboards.A functional description of the specific heat was implemented into some of the wall modules available for the program RADCOOL(Stetiu et al.[16]).The paper by Jokisalo et al.[13]include the model of a concrete wall that contains macroencapsulated PCM, that is,tubesfilled with a hydrated salt.The mathematical model of this wall is included to the component of TRNSYS14.2(Beckman et al.[17])that simulates the behaviour of a single room. These algorithms cannot be easily included in simulations of more complex buildings with different zones.The project from Schossig et al.[14]is about microencapsulated PCM mixed with gypsum for interior wall application.The authors implemented the possibility to calculate non-linear thermal properties of construction materials in the simulation environment ESP-r(Clarke [18]).Therefore,the aim of this work is to present and compare a methodology that allows to easily simulating using a standard program the effect of the inclusion PCMs in the elements of a build-ing.The objective is not to develop a strict model of the wall to explain its thermal behaviour.The construction materials have to be characterized previously in a laboratory.The goal is to have a tool that allowed the analysis of the thermal effect of these materials in the building as a whole. Within this general objective,it is interesting for the methodology to allow:•The inclusion of materials with PCM in walls,ceiling and/orfloor.•The possibility of an easy definition of the thermal behaviour of these materials,once they are well characterized.•The characteristics of the materials with PCM located in different parts of the building can vary with the inclusion of different PCMs and in different percentages.Due to its versatility for the complete simulation of a building,to the analysis done by the I EA (2003)[19]for radiative construction elements,and to the possibilities of connection of the sim-ulation module of a building with other installations,solar or HVAC,the program TRNSYS15is selected as base tool for the purpose.TRNSYS is an acronym for aÔtransient simulation programÕand is a quasi-steady simulation model.This program was developed at the University of Wiscon-sin by the members of the Solar Energy Laboratory(Beckman et al.[17]).2.MethodologyOne of the components to simulate building thermal behaviour in TRNSYS is Type56ÔMulti-Zone buildingÕ.This component model deals with the thermal balances of a building having up to 25thermal zones.The building model in Type56is a non-geometrical balance model with one air node per zone,representing the thermal capacity of the zone air volume and capacities that areM.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–18071799 closely connected like furniture with the air node.Separate equipment components can be coupled to the zones as either internal convective gains or ventilation gains.In order to use Type56a separate pre-processing program PREBID is executed.The PREBID program reads in and processes afile containing the building description and generates twofiles that are used by the Type56component during a TRNSYS simulation.The inputs and outputs of Type56depend upon the building description and options within the PREBID program. Thermally active building elements are used to condition buildings by integrating afluid system into massive parts of the building itself.Examples are radiantfloor heating or cooling systems, radiant ceilings or wall heating or cooling systems,all well known.To take into account the behaviour of radiant heating and cooling in dynamic simulation programs specific models or modelling methods have been proposed in TRNSYS15.Koschenz and Lehmann[20]developed a powerful method for modelling thermo-active construction element systems and integrated it in the multi-zone building model TYPE56of TRNSYS15.In the integrated model the heat con-duction through the element is reduced to a one-dimensional form by applying resistance models. Thereby,the existing transfer function method of the building model TYPE56for walls can be used for solving the one dimensional heat conduction problem.The developed theory can be ap-plied for dynamic simulation.The model is defined easily within the building description as a wall with a so-called active layer.As input data for the active layer geometric data andfluid data are required.But an expert mode is available in which an equivalent heat transfer coefficient is defined by the user.Due to the thermal behaviour and applications analogies(free cooling,free heating)between the radiative active walls and those including PCM,it seems adequate to simulate walls including PCM as a differentiate type of active system.The methodology here presented consists in giving to the TRNSYS program the characteristics of a wall with PCM to a standard active wall. Essentially,the wall with PCM keeps its temperature approximately constant in the central part during the phase change of the PCM,and the thermal conductivity of the wall can be a function of the temperature.These behaviours are easily simulated in TRNSYS using walls with active layers with the proper external control.Only ultra-pure paraffins melt and freeze sharply at a given temperature but mixtures of PCM show a region of temperatures where melting takes place,if desired the functions for specific enthalpy can also be introduced to Type56active layers [12].To simulate that the storage and release of energy,the control of thefluidflow and temperature of the active layer in Type56is suggested.When the active layer reaches the PCM phase change temperatures,the circulation of thefluid at the phase change temperature is imposed in the simulation:•for the energy storage in the active layer with PCM,with an ambient with higher temperature, the circulatingfluid will release thermal energy of the wall giving an analogue thermal effect to the melting of PCM in a solid–liquid phase change and the storage in the PCM,until the given maximum storage capacity is reached,•for the energy release from the active layer with PCM,with an ambient with lower temperature, the circulatingfluid will store energy in the wall at the phase change temperature,in a similar way to the solidification of the PCM,until all the previously stored energy is released and all the PCM is solid,and1800M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–1807•usually,partial charge and discharge processes of the PCM occur without reaching the maxi-mum storage capacity or complete discharge;then,the liquidflux at the PCM phase change temperature do not stop.Together with the circulating waterflow and temperature in the active layer,a third fundamen-tal element in the simulation is the equivalent heat transfer coefficient.This parameter,that can be defined by the user and introduced in each step of the simulation,is the one that really character-izes the operative way of the thermal behaviour of the wall with PCM,because it allows to give to the simulation the rate at which the thermal energy transfer processes due to the storage material occur.TRNSYS15allows controlling the Type56in the simulation through modules connected to it. Standard TRNSYS modules can be used to control Type56introducing the necessary active wall temperature functions.For simplicity of the whole project,in the presented method one of the controllers included in the standard package of TRNSYS was modified generating a new one, from now on called Type222.This subprogram will determine in each step of the simulation the enthalpy of the PCM,its temperature and the variations with the previous simulation step. Depending on these parameters,with Type222theflow and temperature of thefluid inside the tubes of the active wall,and the equivalent heat transfer coefficient are calculated and Type 222acts on Type3and Type56.Once all the components on a TRNSYS system have been identified and a mathematical description of each component is available,it is interesting to construct theflow diagram system.A simplified informationflow diagram for the building with PCM is shown in Fig.1.As it can be seen in Fig.1,the main component of the TRNSYS deckfile constructed for this purpose are Type56and Type222.Additional components required are a Type9data reader,Type16radi-M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–18071801 ation processor,Type3pump,Type33psychometrics,Type69sky temperature,Type93input value recall,and Type55and Type5for treatment of the output data.The working way of Type56in the diagram of Fig.1is not different from those corresponding to other building simulations with active layers.There are three inlets,related to the active layer, for each wall/ceiling/floor containing PCMs:inlet temperature offluid in the active layer,inlet massflow rate in the active layer and user-defined equivalent heat transfer coefficient.The outlets are stored in Type93and simultaneously introduced in Type222.Four outlets,to evaluate element temperature and enthalpy,are given for each wall/ceiling/floor with PCM:node temperature of active layer,inside surface temperature,outside surface temperature and energy input byfluid of active layer to zone.3.Experimental validationUsing the operative methodology proposed in the previous section it is possible to evaluate the PCM behaviour in a wall without simulating the real heat transfer processes.An empirical justi-fication is given in this section.The validation has been planned using a concrete block with5%kg PCM/kg concrete.The ther-mophysical properties of the PCM microencapsulated used MICRONALÒcan be obtained from the manufacturer BASF.The dimensions of the sample block are8cm·8cm·15cm.To perform the experimental tests,an energy storage test rig built in the University of Zaragoza was used(Fig.2)[5].This test rig is an air closed loop that goes inside a chamber where the mate-rial to be tested islocated.1802M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–1807The laboratory test is conducted in the following way.The sample temperature is initially homogeneous,around18°C.Just one side of the block is not thermally insulated,therefore the heat transfer in the block is unidimensional.This side(8cm·8cm)is placed in the space with air at constant temperature(above30°C).Then energy transfer from the surface in contact with the air to the opposite side of the block is related to the thermal properties of the sample.The opposite surface,15cm far away,is defined hereafter as the control surface.This control surface temperature and the air temperature are measured ter,1min time averages are studied.According to the methodology proposed in this paper,the laboratory test is simulated using the Type56of TRNSYS15under the proper control.Thefirst step is to define the material for the wall in Type56using the thermophysical parameters previously determined of the concrete block PCM5%.This amount of PCM is estimated from previously published data in other applications [14].The density of the concrete with PCM5%was estimated as2050kg mÀ3,the thermal conduc-tivity1.0W mÀ1KÀ1and the heat capacity800J kgÀ1KÀ1.The second step is to simulate the PCM effect;therefore an active layer has to be introduced to model the heat storage capacity of the wall.The active layer control is done using three inputs defined in Type56:circulating waterflow and temperature in the active layer,and the equivalent heat transfer coefficient.A high waterflow is selected to avoid the influence of this parameter.The circulatingfluid temperature is determined according to MICRONALÒcharacteristics.Waterflow is turned on or offto simulate the maximum heat storage capacity defined according to the PCM content and its phase change enthalpy.The equivalent heat transfer coefficient is the key parameter unknown.It has to be determined for each new composite material.The simulation of the test has been done using different values of the key parameter.Simulated temperatures in the control surface have been compared to measured parison has been done computing the RMSE of measured and simulated data for thefirst3h of test.Table1is a summary of the results.The minimum RMSE,0.39,is obtained using an equivalent heat transfer coefficient of10W mÀ2KÀ1.Hereafter,10W mÀ2KÀ1is chosen as the reliable value to simulat-ing concrete block MICRONALÒ5%using the methodology developed.Fig.2shows the temperatures of control surface measured and simulated using the equivalent heat transfer coefficient of10W mÀ2KÀ1.Agreement between experimental and simulated data is really good.In the same graph the air heated temperature is plotted.It is also drawn the temper-ature of control surface simulated without using the active layer approach,assuming a wall with-out latent heat storage.Simulated and measured control surface temperatures tend to the air temperature.The simulated temperatures without PCM demonstrate the lower thermal inertia of this wall.It is proven that it is possible tofind an equivalent heat transfer coefficient that makes suitable the simulation using TRNSYS of building components incorporating PCM.Though in this test a constant equivalent heat transfer coefficient has given accurate results it is not discarded that for Table1Comparison of measured and modelled temperature values for different equivalent heat transfer coefficients Equiv.heat transfer coefficient(WmÀ2KÀ1)5102550100 RMSE(°C)0.500.39 1.03 1.54 2.17M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–18071803 different materials or in different temperature ranges a temperature dependent coefficient could be needed.4.ApplicationThe presented methodology has been applied to the discussion of the characteristics of a pro-totype of a room developed within the MOPCON project.This construction is done with concrete panels that include PCM(Fig.3).The presented results cannot be generalized and are only an example of application.Ultimately,the effect of PCM storage must be evaluated in each case application,taking into account the climate,the construction,and the operation of the building. Here,the simulations done were located in Lleida,using hourly data of temperature,humidity and solar radiation for the average year during June,July and August[21].Within the project MOPCON,the goal of the analysis was an economical optimization of the use of the PCM,therefore the following three variables were considered:•the panels including PCM can be installed in one or more walls,ceiling andfloor,•the thermal storage capacity by volume unit in the panels varies as function of the percentage of PCM included,and•the phase change temperature of the PCM was also discussed.I n this work,also the different possible dimensions of the prototype room were studied,with the same structure of Fig.3.The results of this fourth variable are not presented here.The combina-tion of the considered variables,shown in Fig.4,gives200alternatives that needed comparison by simulation.Due to the application within the considered project,free cooling,for the evaluation of the ef-fect of the panels with PCM,the selected parameter of interest is the indoor air temperature in the prototype room.The difference of the maximum temperature with and without PCM is calculated daily.The average of these differences during the studied period of three months is considered a good indicator of the answer of the prototype room to the inclusion of PCM.As example,some of the results are presented here.Fig.5shows the maximum temperature of the prototype room during July for some configurations.The PCM was considered to be included only in the ceiling,and two phase change temperatures were compared (25and 30°C),combined with two thermal storage densities (15,000kJ m À3and 60,000kJ m À3).The graphical result al-ready shows that a phase change temperature around 25°C would be the most interesting.Table 2presents the results of the most interesting alternatives of the average of the difference between daily maximum temperatures in the (Fig.6)prototype room with PCM and a prototype room withoutPCM.Fig.4.Prototype room sketch.1804M.Iba ´n ˜ez et al./Applied Thermal Engineering 25(2005)1796–1807M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–18071805Table2Average of the difference between maximum daily temperatures for several alternatives(°C)Ceiling West wall Ceiling+south wall Ceiling+west wall 25°C—5000kJ mÀ30.770.300.84 2.5725°C—37,500kJ mÀ3 1.59 1.03 2.13 2.9225°C—60,000kJ mÀ3 1.98 1.11 2.68 3.5830°C—15,000kJ mÀ30.780.500.62 1.6330°C—37,500kJ mÀ3 1.130.81 1.78 2.6430°C—60,000kJ mÀ3 1.53 1.18 2.35 3.021806M.Iba´n˜ez et al./Applied Thermal Engineering25(2005)1796–1807The study of the prototype room using the simulation program TRNSYS allows to obtain information for future designs and applications.To minimize the quantity of used PCM and, therefore the production costs of the panel,but to get an interesting effect of reduction of maxi-mum temperatures,the following recommendations should be followed:1.The PCM should be included in the ceiling and west wall of the prototype room.2.The needed storage capacity of the panels for the maximum air temperature to be reducedenough to be measured is around15,000kJ mÀ3and37,500kJ mÀ3.3.The used PCM for the climatic conditions and the design of this application should have aphase change temperature between25°C and27.5°C.With these considerations,an average maximum ambient temperature decrease up to3°C would be obtained.5.ConclusionA simple methodology for the energetic simulation of buildings including elements with PCMs with the program TRNSYS is presented.The method uses the simulation possibilities of active layers for radiative heating and cooling of the Type56of TRNSYS15.The control of the behaviour of the active layer must be done from the exterior of Type56.This proce-dure does not aim a simulation of the real transfer processes inside the materials with PCM, but to evaluate the influence of walls/ceiling/floor with PCM in the whole energy balance of a building.The method is validated in a laboratory experience using concrete that incorporates PCMs.The equivalent heat transfer coefficient is a key parameter which has to be evaluated for each material. The coefficient is related to the heat transfer rate between the PCM microencapsulated and the concrete.The suitability of the methodology has been proven when the proper equivalent heat transfer coefficient is used.The methodology was used in a building such as a prototype room built with concrete panels with PCM.The simulations showed interesting results for the determination of the PCM in walls/ceiling/floor,storage capacity of the panels with PCM,and the optimum phase change temperature used.Although the methodology requires more experimental validation,it can already be concluded that it is a good tool for discussion of the application of PCMs in buildings.AcknowledgmentsThe present work was developed under MOPCON EU CRAFT Project G5ST-2002-50331.The authors would like to acknowledge ASPICA Constructora S.A.(Spain)and B.S.A.Arquitectura y Gestio´n S.L.(Spain)for the design of the cubicle,and all the other partners in the project for their help and contributions:PROKEL S.A.(Greece),MEDYSYS(France),I NTRON B.V.(Nether-lands)and Fundacio´n INASMET(Spain).References[1]B.Zalba,J.M.Marı´n,L.F.Cabeza,H.Mehling,Review on thermal energy storage with phase change:materials,heat transfer analysis and applications,Appl.Thermal Eng.23(2003)251–283.[2]M.Telkes,Thermal storage for solar heating and cooling,in:Proceedings of the Workshop on Solar Energy Storage Subsystems for the Heating and Cooling of Buildings,Charlottesville,VA,USA,1975.[3]ne,Solar Heat Storage:Latent Heat Material,Technology,vol.,CRC Press,Florida,1986.[4]H.G.Barkmann,F.C.Wessling,Use of buildings structural components for thermal storage,in:Proceedings of the Workshop on Solar Energy Storage Subsystems for the Heating and Cooling of Buildings,Charlottesville,VA,USA,1975.[5]B.Zalba,Almacenamiento te´rmico de energı´a mediante cambio de fase,Procedimiento experimental,Ph.D.Thesis,University of Zaragoza,Spain,2002.[6]S.M.Vakilaltojjar,W.Saman,Analysis and modelling of a phase change storage system for air conditioning applications,Appl.Thermal Eng.21(2001)249–263.[7]S.M.Vakilaltojjar,W.Saman,Domestic heating and cooling with thermal storage,in:Proceedings of Terrastock 2000,Stuttgart,Germany,2000,pp.381–386.[8]F.Bruno,W.Saman,Testing of a PCM energy storage system for space heating,in:Proceedings of the World Renewable Energy Congress WI ,Cologne,Germany,2002.[9]H.Mehling,S.Hiebler,L.F.Cabeza,News on the application of PCMs for heating and cooling of buildings,I EA,ECES I A,Annex 17,Advanced Thermal Energy Storage Through Phase Change Materials and Chemical Reactions—Feasibility Studies and Demonstration Projects,3rd Workshop,Tokyo,Japan,2002.[10]NRC,Defining the methodology for the next-generation HOT2000simulator.Available at www.buildings-group.nrcan.gc.ca/docs/pdf/final_report_survey.pdf ,1998.[11]K.Peippo,P.Kauranen,P.D.Lund,A multicomponent PCM wall optimised for passive solar heating,EnergyBuildings 17(1991)259–270.[12]H.E.Feustel,C.Stetiu,Thermal performance of phase change wallboard for residential cooling application,Report LBL-38320,Lawrence Berkeley National Laboratory,1997.[13]J.Jokisalo,mberg,K.Sire´n,Thermal simulation of PCM structures with TRNSYS,in:8th nternational Conference on Thermal Energy Storage,Stuttgart,Germany,2000.[14]P.Schossig,H.-M.Henning,T.Haussman,A.Raicu,Encapsulated phase-change materials integrated intoconstruction materials,in:Proceedings of the 9th I nternational Conference on Thermal Energy Storage—Futurestock Õ2003,Warsaw,Poland,2003.[15]V.Aro-Heinila ¨,M.Suvanen,Simulation program for energy analysis of multiroom houses for solar energy studies,Report TKK-F-A436,Helsinki University of Technology,1980.[16]C.Stetiu,H.E.Feustel,F.C.Winkelmann,Development of a model to simulate the performance of hydronicradiant cooling ceilings,ASHRAE Trans.101(1995)730–743.[17]W.A.Beckman et al.,TRNSYS,Reference manual,vol.2,Solar energy Laboratory,Madison,USA,2001.[18]J.A.Clarke,Energy simulation in building design,Adam Hilger Ltd.,1985.[19]I EA,RADTest—Radiant heating and cooling test cases,A Report of Task 22,subtask C,Building EnergyAnalysis Tools Comparative Evaluation Tests,I nternational Energy Agency,2003.[20]M.Koschenz,B.Lehmann,Handbuch thermoaktive Bauteilsysteme TABS,EMPA Abteilung Energiesysteme/Haustechnik,CH-8600Du ¨bendorf,2000.[21]M.Iba ´n ˜ez,L.F.Cabeza,An approach to the simulation of PCMs in building applications using TRNSYS,in:Proceedings of the III International TRNSYS Users Õday,Barcelona,Spain,2004.M.Iba ´n ˜ez et al./Applied Thermal Engineering 25(2005)1796–18071807。