Effect of microencapsulatednext term phase change material in sandwich panels

Technical NoteEffect of microencapsulated phase change material in sandwich panelsCecilia Castellón a ,Marc Medrano a ,Joan Roca a ,Luisa F.Cabeza a ,*,Maria E.Navarro b ,1,Ana I.Fernández b ,Ana Lázaro c ,2,Belen Zalba c ,2aGREA InnovacióConcurrent,Edi fici CREA,Universitat de Lleida,Pere de Cabrera s/n,25001Lleida,Spainb Departamento de Ciencias de los Materiales e Ingeniería Metalúrgica,Universitat de Barcelona,Martíi Franqués 1,08028Barcelona,Spain cInstituto de Investigación en Ingeniería de Aragón,I3A,Grupo de Ingeniería Térmica y Sistemas Energéticos (GITSE),Dpto.Ingeniería Mecánica,Área de Máquinas y Motores Térmicos,Universidad de Zaragoza,Campus Politécnico Río Ebro,Edi ficio “Agustín de Betancourt,”María de Luna s/n,50018Zaragoza,Spaina r t i c l e i n f oArticle history:Received 10December 2008Accepted 23March 2010Available online 24April 2010Keywords:Sandwich panelPhase change material (PCM)Thermal energy storage (TES)Microencapsulationa b s t r a c tSandwich panels are a good option as building materials,as they offer excellent characteristics in a modular system.The goal of this study was to demonstrate the feasibility of using the micro-encapsulated PCM (Micronal BASF)in sandwich panels to increase their thermal inertia and to reduce the energy demand of the final buildings.In this paper,to manufacture the sandwich panel with microencapsulated PCM three different methods were tested.In case 1,the PCM was added mixing the microencapsulated PCM with one of the components of the polyurethane.In the other two cases,the PCM was added either a step before (case 2)or a step after (case 3)to the addition of the polyurethane to the metal sheets.The results show that in case 1the effect of PCM was overlapped by a possible increase in thermal conductivity,but an increase of thermal inertia was found in case 3.In case 2,different results were obtained due to the poor distribution of the PCM.Some samples showed the effect of the PCM (higher thermal inertia),and other samples results were similar to the conventional sandwich panel.In both cases (2and 3),it is required to industrialize the process to improve the results.Ó2010Elsevier Ltd.All rights reserved.1.IntroductionNowadays,reduction of energy consumption is an important factor for existing buildings as well as for new buildings.Several extensive reviews and practical studies about this topic can be found in the literature [1e 5].These technical efforts concluded that it is necessary to develop materials and techniques to minimize the use of non-renewable energy for air conditioning purposes in buildings.Phase Change Materials (PCM)have been considered for thermal energy storage in buildings since 1980.Implementing the PCM in gypsum boards,plaster,concrete or other wall covering materials,thermal energy storage becomes a part of the building structure,useful even for light-weight buildings.In the literature,development and testing were conducted for prototypes of PCM wallboard and PCM concrete systems,with particular interest in peak load shifting and solar energy utilization.During the last 20years,new PCM products to be used in buildings appeared in the market.In these products,PCM ismacroencapsulated,having dif ficulties to be melted by direct solar radiation because of the poor heat conductivity of the PCM.On the other hand,the walls and ceilings of a building offer large areas for passive heat transfer within every zone of the building [5].Several researchers have investigated methods for impregnating gypsum wallboard and other architectural materials with PCM [1,6e 9].In these papers,different types of PCM and their characteristics are described.Other references discuss manufacturing techniques,thermal performance and applications of gypsum wallboard and concrete block,which have been impregnated with PCM [10e 12].Commercial buildings use sandwich panels as wall systems due to their excellent modular characteristics (Fig.1).These panels are mainly used in buildings,sport halls,and industrial buildings,giving them insulation properties not reached with other construction techniques.Sandwich panels integrate characteristics such as cladding,thermal insulation,water tightness,mechanical strength,and aesthetic appeal.It is a product composed of a ribbed sandwich panel formed by two metal sheets and insulating poly-urethane foam core injected in between.Some kinds of sandwich panel prototypes were studied,including air layer between the PCM (macroencapsulated in rigid containers)and the metal sheet.Results of the energetic behaviour were similar to high thermal mass walls [13].*Corresponding author.Tel.:þ34973003576;fax:þ34973003575.E-mail address:lcabeza@diei.udl.cat (L.F.Cabeza).1Tel.:þ34934021298;fax:þ349340335438.2Tel.:þ976762567;fax:þ976762616.Contents lists available at ScienceDirectRenewable Energyjournal ho me page:www.elsevier.co m/locate/renene0960-1481/$e see front matter Ó2010Elsevier Ltd.All rights reserved.doi:10.1016/j.renene.2010.03.030Renewable Energy 35(2010)2370e 2374The goal of this study was to demonstrate the feasibility of using a microencapsulated PCM (Micronal BASF)in sandwich panels to increase their thermal inertia and to reduce the energy demand of the final building.2.Experimental methodology with the sandwich panel The experimental methodology of this study was developed with the idea of including the PCM in sandwich panels,as well as,ful filling some technical requirements (standards)of the conven-tional sandwich panel that may be affected by the inclusion of PCM.Therefore,the speci fic objectives of this study are:to study different methods to include microencapsulated PCM;to demon-strate a higher thermal inertia in the sandwich panel by the inclusion of microencapsulated PCM without reducing its insu-lating properties.Other objectives are to obtain an homogeneous distribution of the microcapsules of PCM in the sandwich panel and to achieve the standard of adhesion for sandwich panels (such as UNE 41950).The conventional process of manufacturing sandwich panel is a continuous injection of an insulating polyurethane foam core between two metal sheets of galvanized pre-lacquered steel.For the addition of PCM,two manufacturing options were studied:Without modifying the standard manufacturing process,add-ing a mix of polyurethane and PCM (case 1).Modifying the manufacturing process,with the addition of a new step to include microencapsulated PCM.This new step may be done in two different ways (case 2or case 3).Case 1consists of mixing the microencapsulated PCM with one of the liquid components of the polyurethane.This process was tested with collaboration of PLASFI,and was studied only with the insulating polyurethane (without including the metal sheet).In case 2,the PCM was added at the beginning of the manufacturing process,just before the injection of the poly-urethane (Fig.2)and,in case 3,the PCM was added after the polyurethane (Fig.3).These experiments were performed in Europer fil.In these two last options,an 8%in weight of PCM with respect to the weight of the PUR was added manually,and samples from resulting PCM-sandwich panels were taken to evaluate how the microencapsulated PCM was distributed in the sandwich panel.For each case,a reference sample without PCM was also produced.Table 1shows the properties of the microencapsulated PCM used.The reference samples and samples with PCM were cut in smaller subsamples and the following tests were carried out: Distribution of the PCM:with the help of a stereoscope,the distribution of the PCM in the samples was analyzed.Adhesion test:the adhesion between the metal sheets and the polyurethane foam was measured following the UNE 41950procedure,in order to validate if the values were within the limits.Thermal performance test:the measurements were performed in two experimental installations,at the University of Zaragoza [14](Fig.4)and at the University of Barcelona.In these experiments,the evolution of the temperature with time was measured,against an air flow (Fig.4)[15].Fig.1.View of the sandwichpanel.Fig.2.Manufacture of the sandwich panel with PCM (case2).Fig.3.Manufacture of the sandwich panel with PCM (case 3).C.Castellón et al./Renewable Energy 35(2010)2370e 237423713.Results3.1.Results for case 1Fig.5shows the distribution of the PCM through the foam (case 1).A homogeneous distribution of the PCM microcapsules can be observed;this uniformity was expected because the PCM was included in the polyurethane formulation.Fig.6shows thermal performance results for case 1(reference sample and sample with PCM).The figure shows the air flow temperature (around 34.5 C)at which the samples were tested.The temperature behaviour of the insulated surface shows a faster heating of the sample with PCM.For example,to reach 32 C,the sample with PCM needs about 400s more than the reference sample.This result is in contradiction with the expected effect of increased thermal inertia and can be explained by an increase of the effective thermal conductivity of the insulation due to the presence of solid particles.The adhesion test results can be seen in Table 2.In this case,the reference sample and the sample with PCM are within the limits for strength established by the standard UNE 41950(L.MAX >0.10MPa).3.2.Results for case 2Fig.7(a)shows the PCM distribution through the foam for case 2.In general,the distribution of the PCM was not homogeneous;the microcapsules are concentrated close to the metal sheet (free surface)and in some areas in the middle of the foam (foam with a whitish colour).Small cracks in the polyurethane can be observed,and microcapsules of PCM were observed within these cracks (Fig.7(b)).Fig.7(c)shows an image of the reference sample.Small cracks that do not contain PCM can be observed (Fig.7(d)).Fig.8shows the results of the thermal performance test for case paring the insulated surfaces,the sample with PCM does not show the expected effect (higher thermal inertia).A faster heating,with a time delay to reach 32 C in about 100s,between the sample with PCM and the reference sample can be seen.The same proce-dure was followed with two different samples and the results were one similar to the previous sample,and the second one with the expected effect (it shows a delay in the temperature evolutionofFig.5.Case 1:(a)sandwich panel with PCM;and (b)zoom of the sample withPCM.Fig.4.Experimental installation to measure the temperature evolution in a solid sample (University of Zaragoza).X 1¼free surface (external surface);X 2¼insulated surface (internal surface).Table 1Properties of Micronal BASF as given by the manufacturer.Micronal BASF PCM Melting temperature w 26 C Phase change enthalpy 100kJ/kg Microcapsules size5mmFig.6.Thermal performance test of the reference sandwich panel and sandwich panel with PCM (case 1).C.Castellón et al./Renewable Energy 35(2010)2370e 23742372the PCM sample).These results may be attributed to the poor distribution of the PCM or even to the possibility that the sample tested does not contain PCM,because of the inhomogeneous distribution previously observed.Even though,the results obtained in the third sample reveal that the possibility of increasing thermal inertia due to the inclusion of PCM was demonstrated.3.3.Results for case 3Case 3shows a different distribution of the PCM microcapsules that are concentrated close to the metal sheet,and also small areas with PCM at the middle of the foam (whitish cracks)were found;see Fig.9(a)and (b).As seen in these figures,it seems that in this case there were fewer cracks than previously.Fig.10shows the results of the thermal performance test for case 3.The sample with PCM achieved the same temperature of the reference sample (32 C)about 450s later.Due to an increase of thermal inertia,this effect is expected when the PCM is used.Table 2shows the adhesion results of case 1,case 2and case 3.In all cases,the reference samples are within or close to the limits (0.1MPa is the minimum load for adhesion test in sandwich panels).Adhesion results of the sandwich panel with PCM are out of the limits.During the performance of the adhesion test,the failure of the reference sample is always between the metal sheet and the foam,but for the sample with PCM (case 2)the failurewas in the middle of the foam and at a much lower stress,revealing that PCM microcapsules are acting as stress concen-trators within the foam.For the results with PCM (case 3)these are far below the limit.4.DiscussionThe objective of this work was to demonstrate the feasibility of using microencapsulated PCM in sandwich panels to increase their thermal inertia.The main problem lies on how to include the micro-encapsulated PCM ful filling standards of the conventional sand-wich panel.Therefore,different manufacturing cases to implement the PCM were tested.For every case three different analyses were realized:the distribution of the PCM through the foam,an adhesion test,and a thermal performance test comparing samples with and without PCM.In case 1,the distribution of the microcapsules is homogeneous throughout the foam,but it seems as the effect of the PCM is overlapped by a possible increase in thermal conductivity of the polyurethane (due to the increase of solids in the formulation).A faster heating of the sample with PCM can be observed.Results of adhesion test were not a problem because they are within the limits,the distribution of the microcapsules helped to get an acceptable result.In case 2,the distribution of the PCM was concentrated close to the metal sheet (external surface)and in some areas in the middle of the foam.For thermal performance test,three samples were analyzed.Two of them presented an unexpected faster heating of the sample with PCM and a third sample showed the expected increase of thermal inertia in the sample with PCM,giving a time delay of 450s to reach 32 C.Such a variety of results may be explained due to the poor distribution of the PCM in the foam.Results of adhesion test are out of the limits because the failure of sample with PCM occurs within the foam.In case 3,the distribution of the PCM was concentrated close to the metal sheet (internal surface)and in some areas of the foam.A higher thermal inertia in the sample with PCM can be observed.Problems were found in the adhesion test,similar to case 2.A possible solution of this process could be a located dosage of the PCM during the process that could concentrate the microcapsules close to the metal sheet even aided by anadhesive.Fig.7.Case 2:(a)sandwich panel with PCM;(b)zoom of the sample with PCM;(c)reference sample;and (d)zoom of the referencesample.Table 2Fig.8.Thermal performance test of the reference sandwich panel and sandwich panel with PCM (case 2).C.Castellón et al./Renewable Energy 35(2010)2370e 237423735.Concluding remarksThe goal of this study was to demonstrate the feasibility of using a microencapsulated PCM (Micronal BASF)in sandwich panels to increase its thermal inertia,and to reduce the energy demand of the final buildings.The results shown above include different manufacturing processes and the results obtained with case 1was the expected,the PCM effect is overlapped by a possible increase in thermal conductivity,case 2and case 3show the feasibility of using a microencapsulated PCM in panel sandwich increasing its thermal inertia and without substantial increase of the weight of the sandwich panel with the inclusion of PCM.In both cases (2and 3),the industrialisation of the process to improve the results is required.The possibility of adapting this technology to manufac-ture panels allows their installation on ceilings and walls.AcknowledgmentsThe work was partially funded by the Spanish government (project ENE2008-06687-C02-01/CON)and the European Union (COST Action COST TU0802),in collaboration with the companiesEuroper fil and PLASFI.The authors 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