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Energy and Buildings 65 (2013) 464–476

Contents lists available at ScienceDirect

Energy and Buildings

j ourna l ho me pa g e: www.elsev ier .com/ locate /enbui ld

nfluence of the use of PCM drywall and the fenestration inuilding retrofitting

. Rodriguez-Ubinasa,∗, B. Arranz Arranza, S. Vega Sáncheza, F.J. Neila Gonzálezb

TISE Research Group, “Técnicas Innovadoras y Sostenibles en la Edificación”, Department of Construction and Technology in Architecture (DCTA), School ofrchitecture, Technical University of Madrid (UPM), Av. Juan de Herrera 4, 28040 Madrid, SpainABIO Research Group, “Arquitectura Bioclimática en un Entorno Sostenible”, Department of Construction and Technology in Architecture (DCTA), School ofrchitecture, Technical University of Madrid (UPM), Av. Juan de Herrera 4, 28040 Madrid, Spain

r t i c l e i n f o

rticle history:eceived 1 August 2012eceived in revised form 1 December 2012ccepted 9 June 2013

eywords:rywallnergy storage

a b s t r a c t

Building retrofitting is one of actions promoted by the European Union in order to reduce the energydependence, the consumption of fossil fuels and the CO2 emissions. In climates with high thermal vari-ability, thermal mass can increase the hours of thermal comfort and reduce the need for mechanicalconditioning systems, helping to reduce the energy consumption in both new and existing buildings.However, it is not always feasible to use traditional materials to increase thermal energy storage inbuilding retrofitting. The use of Phase Change Materials (PCM) can be an alternative to provide highthermal storage capacity to rehabilitated buildings as their applications have relatively low weight and

lazingCMhase changeehabilitationetrofittinghading Factor

need little or no additional space. Different ways in which PCM can be used in building rehabilitationhave been analyzed, and the influence of PCM drywall panels and fenestration was evaluated in differentSpanish cities. The results reflect the importance of the Window to Wall ratio and the Shading Factor inthe thermal behavior of buildings. Also, they show that, with proper selection of these parameters, theuse of PCM drywall can contribute to increase the thermal comfort, reducing the peaks and temperaturefluctuations in existing buildings, particularly under overheating conditions.

hermal mass

. Introduction

The European Union has been taking steps to reduce energyonsumption in buildings, ensuring comfort conditions. Directive010/31/CE hardens the energy efficiency requirements for bothew and existing buildings [1], moving toward nearly zero energyuildings by 2020. This directive emphasizes that the consumptionf fossil energy must be reduced, increasing both the energy effi-iency and the use renewable energy. Its goals include reducing CO2missions, securing of energy supplies and minimizing the energyependency in EU countries. The energy dependence, in Spain, isreater than the EU average, reaching almost 75% [2]. Therefore inhis country is more urgent to strengthen energy measures in theuilding sector.

In Spain, most of the energy consumption in buildings is relatedo external climate protection and the need for mechanical sys-

ems to maintain indoor comfort [2]. This situation is aggravatedy the growing demand for air conditioning. Buildings constructedsing the 2006 Building Code (CTE) will have better energy

∗ Corresponding author. Tel.: +34 626876673.E-mail addresses: edwin.rodriguez@upm.es,

dwin rodriguez@bioclimaticos.com (E. Rodriguez-Ubinas).

378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.enbuild.2013.06.023

© 2013 Elsevier B.V. All rights reserved.

performance, but the existing buildings are the main consumersof energy. In Spain, there are currently 2262 million m2 of housingand 476 million m2 of commercial buildings constructed before thenew energy requirements [1]. It is necessary to implement correc-tive design strategies, and use materials and equipment that helpimprove the energy performance of the existing building stock.

Improving the envelope is a fundamental action to increasethe energy efficiency of existing buildings. The retrofitting build-ing process usually includes increasing the insulation level andthe improvement of glazing. The Spanish climatic zones in gen-eral have significant daily temperature swings. This variability indaily temperature enables the use of other strategies that couldfurther increase the efficiency of existing buildings. Some of thesestrategies are related to thermal mass, Window to Wall ratio (WWratio) and Shading Factor (fs). Thermal mass has a significant influ-ence on the heat transfer inside building spaces, providing themThermal Energy Storage capacity. This capacity helps to reducethermal peaks and smooth thermal variations within buildings,contributing to increased thermal comfort, and reducing the neces-sity of mechanical conditioning equipment. In heating periods, the

heat that penetrates the interior of the buildings is storage andreleased hours later when there is no solar contribution. In coolingperiods, the thermal mass can eliminate or reduce the overheating.The proper selection of the glazing characteristics, its size and its

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hading devices, has also a significant impact in the interior com-ort, reducing the need of mechanical equipment for heating orooling the buildings [3]. The thermal mass and the fenestrationsre related, the optimal amount of thermal mass required dependsn, among other things, the area of glazing [4]. The “Mass to glassatio” defines the relationship between the areas of thermal massnd the glazing. Proper planning of fenestrations and thermal massould increase the benefits of solar radiation during heating periodsnd avoid overheating during cooling periods, thus improving ther-al conditions and also helping to reduce energy consumption.Usually, heavy building materials, such as stone, brick or con-

rete, are used to provide thermal mass in buildings. Thermalnergy Storage capacity of these materials is linked to their weightmass), the heavier the material the higher the thermal energytored. However, in building retrofitting, when it is necessary toncrease thermal mass, is not always feasible to use heavy materials,ue to the excess weight added to the structure, or due the reduc-ion of interior space. An alternative is the Latent Heat Thermalnergy Storage using Phase Change Materials (PCM). These materi-ls are substances of relatively low weight and high heat of fusion,apable of storing and releasing a large amount of heat in latentorm. The temperature of these materials is kept almost constanturing its phase change. These characteristics make them suitableo be used for thermal conditioning in buildings. PCMs work differ-ntly to heavy materials; however, they are also able to improve thenterior thermal conditions and help to reduce energy consumptionn buildings [5,6].

This study was based on the need to determine the potential ofmproving thermal performance in existing buildings, in Spain, byhe use of Latent Heat Thermal Energy Storage (LHTES). At the sameime, the influence of the correct selection of the size of the glazingWW ratio) and Shading Factor (fs) was analyzed. It was decided tose PCM drywall after studying the potential applications of Phasehange Materials in building retrofitting. This material is suitableor building rehabilitation due it has relatively low weight, requiresittle or no extra space, and it can replace or be placed on the existingnishing material. The influence of this application of PCM drywallanels in the operative temperature was evaluated in five citiesith the most representative climates on the Spanish mainland.

he evaluation was done comparing the influence of the use, orot, of PCM drywall with different WW ratios and fs.

. Phase change materials: possibilities on the buildingetrofitting

In recent years, there has been great interest in PCM, and itsotential applications for space heating or cooling [7], proposinghe use of these materials as an alternative to traditional solutionsf thermal mass. In climates with large daily temperature swings,he correct use of PCM in building retrofitting can help to increasehe interior thermal comfort. The PCM help to reduce the peak tem-erature, smooth the daily temperature fluctuations, maintain theemperature of the interior surfaces in the range of thermal comfort,nd reduce the negative effects of air temperature stratification [8].

The viability of using Phase Change Materials in the rehabilita-ion of buildings depends on the local climate, and in the possibilityf guaranteeing that the thermal energy can be charged and dis-harged in daily cycles. Therefore, to achieve the desired results,t is necessary to select the switch temperature correctly, takingnto account the local climate, the orientation of the room and theize of glazing, and implement appropriate strategies of ventila-

ion and sun screening. The use of PCM in building retrofits may beeasonable in:

a. Lightweight construction buildings.

d Buildings 65 (2013) 464–476 465

b. Heavyweight construction, when interior insulations need to beadded.

c. Heavyweight construction, in which their mass cannot be usedas a thermal storage medium.

d. Buildings where is aimed to improve the energy efficiency of theHVAC or the renewable Energy Systems with the use of ThermalEnergy Storage.

Adding thermal energy storage capacity to existing lightweightbuildings could significantly improve their thermal behavior. Mostheavyweight buildings have sufficient thermal mass. However, insome cases the building mass is not usable for stabilizing theirinterior temperature. Increase the insulation level on the exte-rior is probably the best solution to improve the existing buildingenvelopes in Spain. This solution prevents heat loss in winter andreduces unwanted heat gain in the hot season; and also mini-mizes thermal bridges and enables the use of thermal mass inheavyweight buildings. However, sometimes, either because oflimitations of the regulations, or because the building facades areprotected by cultural or historical interest, it is not possible toadd insulation on the exterior of the buildings. In such cases, therequired additional insulation must be applied to the interior, pre-cluding the utilization of the buildings’ mass. The use of PCMcould return thermal energy storage capacity to these buildings.Similarly, the use of PCM could help improve the thermal per-formance of heavyweight buildings, in which their mass elementsare separated from inhabited areas by materials with low thermalconductivity.

Phase Change Materials can be used in building retrofitting inboth passive and active applications. The PCM can be used as acomponent, integrated into construction materials or in thermalstorage units [9]. PCM components are applications in which a PCMlayer or element is added to the construction section. In most ofthe cases, the PCM components are placed behind the interior fin-ishing materials. Integrated PCM solutions are those in which thePCM is mixed with, impregnated or incorporated, into a construc-tion material such as drywall panels. In Integrated PCM solutions,no additional layers are needed as they replace conventional con-struction materials. The PCM components and the PCM integratedinto construction materials may be used in active and passive sys-tems. Finally, the PCM storage units are linked to HVAC or othermechanical systems. Storage units are part of an active system,and they are usually thermally separated from the building inte-rior by insulation. The functioning of the storage units and otheractive PCM systems is not dependent on meteorological changesas their thermal energy is transferred through the circulation ofa fluid, usually water or air. This functional independence pro-vides them with flexibility in terms of where the PCM applicationshould be located. However, the location of passive PCM applica-tions is related to how they will work, the way in which the energywill be charged and discharged, and its primary purpose, cooling,heating or both [10]. Zhang et al. suggest that the best locationfor passive PCM applications is within the living spaces, in wallsand partitions [11]. In addition to vertical surfaces, place the PCMat ceilings offer three significant advantages: large areas for heattransfer, the heat exchange surface is not reduced by the place-ment of furniture, paintings, curtains or carpets, and in the caseof macro-encapsulated PCM there is less risk of material leakageby drilling or punctures. However, being horizontal surfaces withdown-draught heat flow, the thermal resistance is greater than thevertical or other horizontal surfaces, like floors [12].

This study is centered on passive PCM applications, specifically

those that can be used in the interior of rehabilitated buildings. Pas-sive PCM applications are easy to implement, no additional energyis required for their use, and thermal energy is stored or releasedautomatically when the temperature rises or falls beyond the

466 E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476

M: ap

mramsaLrPFrF[

Fig. 1. Building retrofit with the use of PC

aterial switch point. The PCM can be placed in the interior of theetrofitted building in different ways, replacing the interior finishes,s part or connected to building elements, or included in comple-entary elements, such as sunscreens and blinds [6,7]. Fig. 1 shows

ome ways to use the PCM in interior spaces: in walls, partitionsnd ceilings [13–17]. In the market there are materials based onatent Heat Thermal Storage that can be easily used in buildingehabilitation, such as PCM drywall panels, PCM composite panels,CM pouched mats. PCM gypsum blocks and PCM plaster solutions.

ig. 2a shows a PCM application integrated in the finishing mate-ial. The PCM components can be macro-encapsulated as shown inig. 2b [18], or included in a composite panel as shown in Fig. 2c8,19]. Additionally, a PCM can also be integrated in the insulation

Fig. 2. PCM at buildings’ interior: walls and partitions (si

plications in walls, partitions and ceiling.

layer in both ways macro and microencapsulated [20,21], see Fig. 2dand f.

The performance of PCM in building interiors has been studiedby many researchers. As a reference to these studies, only those thatanalyzed the reduction of interior thermal peaks and the smooth-ing of the diurnal temperature swings using experimentation infull size cell or rooms were selected. Table 1 presents the stud-ied works and includes information on the test cells or rooms thathave been used in each case. Table 2 shows the characteristics of

the PCM applications, the locations and main results. Organic PCMshave been used in all cases: fatty acid or paraffin. Different forms ofPCM containment are presented: adsorbed by the gypsum boards,integrated in composite panels and macro or micro encapsulated

milar PCM applications can be used also at ceiling).

E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476 467

Table 1Studies of PCM at buildings’ interior: rooms or experimental cells.

Researchers Experimental cell quantity (dimensions) Window quantity (dimensions) Cell location PCM location WW ratio

Shilei et al. [14] 2 (5.00 × 3.30 × 2.80) 1 (1.50 × 1.50) Exterior Walls 24.35Athienitis et al. [13] 1 (2.82 × 2.22 × 2.24) 1 (1.80 × 1.80) Exterior 4 walls 51.29Scalat et al. [15] 2 (2.29 × 2.27 × 2.45) 0 Laboratorya 4 walls and ceiling 0.00Voelker et al. [23] 2 (4.43 × 2.95 x h) 1 (4.43 × h) Exterior 3 walls and ceiling –Schossig et al. [16] 2 rooms without solar protection (ND) 1 In real a building 3 walls –

2 rooms with solar protection (ND) 1 In real a building 3 walls – 3.10) a

0.60)

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Kuznik et al. [8,19] 1 (3.10 × 3.10 × 2.50) 1 (3.10 ×Konuklu et al. [24] 1 (2.70 × 1.50 × 2.00) 2 (1.87 ×a Controlled test cell in a laboratory where summer, winter or mid-season condit

pplications. The operating temperature range of Latent Heat Sys-ems can be quite narrow, and the transition zone of the PCM muste entirely within this range [22]. Therefore, the switch tempera-ure is one of the most relevant criteria for PCM selection [10]. Thewitch temperature must be selected taking account the climatend the main purpose of the application, help in heating or coolingeriods [16]. The PCM with a switch temperature that performsell in heating periods has a marginal effect in cooling periods

nd vice versa [6]. As shown in Table 2, most of the applicationsesigned for heating periods have switch temperatures between7 ◦C and 21 ◦C, and most designed for cooling periods have switchemperatures between 25 ◦C and 28 ◦C.

Shilei et al., Athienitis et al. and Scalat et al. worked with PCMoaked drywall for heating periods, using switch temperaturesetween 16 ◦C and 21 ◦C, finding a reduction of the interior swingemperature between 1.7 ◦C and 4.0 ◦C [13–15]. Scalat et al. also,ested their 17–21 ◦C PCM drywall in summer conditions and found

low reduction of overheating due to the low switch temperature.oelker et al. carried out their research on PCM gypsum plasterith a switch temperature between 25 and 28 ◦C [23]. They found

hat it was possible reduce the cell temperature by up to 4 ◦C. Theylso found that the effectiveness of the PCM may be significantlyeduced after several consecutive hot days. Schossig at al. carriedut an experiment with 15 mm gypsum plaster with 20% PCM inhe interior of the test cell, and found a temperature reduction ofp to 4 ◦C and a significant reduction in the number of hours withemperatures above 28 ◦C. Kuznik et al. studied the efficacy of aomposite material, a mix of a copolymer and microencapsulatedaraffin with a switch temperature of 21.7 ◦C [8,19]. They found thathe air temperature fluctuated between 18.9 ◦C and 36.9 ◦C in theeference room and 19.8 ◦C and 32.8 ◦C in the PCM room, achieving

temperature swing reduction of 4.7 ◦C. Konuklu et al. packagedicroencapsulated PCM with two different switch temperatures

26 ◦C and 23 ◦C) in aluminum foil, and placed these packages inhe interior of the test cell. In summer conditions, they found aemperature reduction of 2.5 ◦C and a cooling load reduction of 7%.n winter, an increase of 2.2 ◦C in temperature and a heating loadeduction of 17% were achieved [24].

. Influence of the use of PCM drywall and the fenestrationn the building retrofit: methodology

.1. Starting premises

The study was based on three premises:

. In Spain, the thermal Energy Storage can help increase thermalcomfort in rehabilitated buildings.

. Thermal comfort can be significantly improved by selecting

an appropriate fenestration size (WW ratio) and an adequateShadow Factor (fs), whether using PCM or not.

. The high capacity of Thermal Energy Storage of PCM drywall pan-els could smooth out indoor temperature fluctuations, reducing

Laboratory 3 walls 100.00 2 (0.72 × 0.60) Exterior 4 walls 76.74

re simulated.

the thermal peaks and helping to get more hours with tempera-tures within the thermal comfort range.

3.2. Study variables

From the starting premises of the study, it was selected the fol-lowings variables: Climatic Zones (Cities), Window to Wall ratio(WW ratio), Shading Factor (fs) and the possibility of using PCMdrywall panels or not.

3.2.1. Climate zonesSpain has diverse climate conditions throughout its territory.

Five cities were chosen to corroborate the starting premises; thesecities represent the different climate zones in continental Spain.This selection was made using the classification established by theSpanish Building Code (CTE) in the document HE. This documentestablishes twelve climate zones based on the climatic severitiesof winter (SCI) and summer (SCV). The climatic severities weredefined taking account the Degree Days and the Solar Radiationin each city. The Code identifies four climatic severities of summerrepresented by numbers from 1 to 4, and five severities of sum-mer represented by the letters A, B, C, D and E [25]. Table 3 showsthe five cities selected, their climate zone, and other informationrelevant to the study, like the global radiation [26].

3.2.2. Window to Wall ratio and Shading FactorIn each of the cities, five different Window to Wall ratios (WW

ratio) were evaluated: 10%, 20%, 30%, 40% and 60%. Similarly, fiveShading Factors (fs) were evaluated: 0.1, 0.3, 0.5, 0.7 and 0.9. Thefs value equal to one means that there is no shading in the glazing,and the fs value equal to zero means that the glazing is entirelyshade. The experimental rooms were identified using the followingnomenclature: the first two letters identify the city (see Table 3),followed by two numbers with a “w” to specify the WW ratio andtwo numbers with an “s” to specify the fs. For example, MA20w50s,refers to a room located in Madrid with a WW ratio equal to 20%and a fs equal to 50%.

3.3. Preliminary study: influence of thermal mass in the studiedclimatic zones

Initially, a preliminary study was conducted to get a firstapproximation of the influence of the use of thermal mass in therehabilitation of buildings in the five selected cities. The calcu-lations were made with Climate Consultant 5.0 [27], using thecomfort model defined in the ASHRAE Handbook of Fundamen-tals 2005 [28]. This model establishes two zones of comfort interms of clothing, heavy in the colder months and lightweight forthe warmer months. The results provide a preliminary idea about

the potential numbers of hours that could be added to the com-fort periods by the implementation of different design strategies.Since the main objective of this preliminary work was to determinethe influence of thermal mass, only three strategies were analyzed;

468 E. Rodriguez-Ubinas et al. / Energy an

Tab

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14]

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ster

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8,19

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ter)

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Kon

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24]

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ffin

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ter)

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Dry

wal

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bD

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PCM

d Buildings 65 (2013) 464–476

one for heating periods, direct solar gain with high thermal mass,and the other two, high thermal mass and the combination of highthermal mass and night ventilation, for the cooling periods.

3.4. Main study: influence of PCM drywall and fenestration in theclimate zones studied

3.4.1. IntroductionOnce the potential benefits of using thermal mass (sensible heat

storage) in the cities studied were verified, a study to determine theinfluence of the use of PCM (latent heat storage) and the fenestra-tions in building retrofitting was carried out. The starting premisescorroboration was made using a comparative method aided bythermal simulations. The air temperature is not a sufficient indi-cator to determine the thermal comfort. It is necessary take intoaccount other factors as the influence of radiant energy of the sur-round surfaces. Since the PCM add thermal energy storage capacityto the rooms, it is expected that the temperature of the room’s sur-faces were a significant factor in the thermal comfort. Therefore inthe analysis of this work the operative temperature was used. Theoperative temperature is a weighted value that representing bothdry bulb air temperature and the mean radiant temperature of therooms [29].

3.4.2. PCM applicationThe use of microencapsulated PCM drywall panels was decided.

Drywall panels are one of the most common interior finishing mate-rials and the microencapsulated PCM have the advantages of easyapplication, proper heat transfer and no need for protection againstencapsulation destruction [16]. Spain’s climatic conditions, withmany hours of temperatures exceeding 26 ◦C, have considerablepotential to reduce overheating. As shown in Table 2, the PCMgypsum applications with switch temperature between 25 ◦C and28 ◦C have performed effectively in cooling periods. In the mar-ket, there are microencapsulated PCM with switch temperaturesof 21 ◦C, 23 ◦C and 26 ◦C, and PCM drywall with a switch temper-ature of 23 ◦C and 26 ◦C. The latter was the switch temperatureselected in the present study. Regarding the thickness of the panels,as shown in Table 2, in works with PCM drywall panels, a thicknessof 10 and 13 mm was used, and in those with PCM gypsum plaster,a thickness of 15–30 mm was used. 15 mm panels were chosen asthe best results were achieved using these as shown in Table 2. Itis possible to find PCM drywall with that thickness. The maximumweight ratio of microencapsulated PCM that can be incorporatedin drywall panels is 30% [19]. Taking into account the climate inSpain, the need to reduce overheating, the findings of the literatureand the availability of PCM products in the market, 15 mm 26 ◦Cdrywall panels with 30% of microencapsulated PCM were selected.These panels have 3 kg of PCM per m2, and their thermal propertiesare: Thermal Conductivity 0.18 W/mK (PCM in solid state), LatentHeat DH: 330 kJ/m and Specific Heat 1.20 kJ/kgK.

3.4.3. Test roomsTwo similar study rooms were used: ones identified as “Refer-

ence Rooms” finished with standard drywall panels and the othersidentified as “Experimental Rooms” finished with PCM drywall pan-els. The floor area of the study rooms was 18 m2 (3 m × 3 m × 6height, width and depth), and their length was oriented to theeast–west axis. The boundary conditions used in the study werethe same as those used in the validation process of the simula-tion software as explained in Section 3.4.5; the side facing southwas the only one in contact with the outside, the other sides,

interior walls, floor and ceiling, were considered to have an adi-abatic relationship with the interior of the building. The roomshad a window in the south wall. These windows had insulateddouble-glazing mounted in a thermal break aluminum frame. The

E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476 469

Table 3Selected cities: general information.

City (ID) Barcelona (BA) Bilbao (BI) Madrid (MA) Seville (SE) Soria (SO)

Climate Humid mediterranean Atlantic (humid maritime) Continental Warm mediterranean MountainLatitude (◦) 41.23 N 43.15 N 40.24 N 37.23 N 41.46 NAltitude (m) 12.00 19.00 667.00 10.00 1063.00CTE classification C2 C1 D3 B4 E1Winter climatic severity (degree days) 0.60 < SCI ≤ 0.95 0.60 < SCI ≤ 0.95 0.95 < SCI ≤ 1.30 0.30 < SCI ≤ 0.60 SCI > 1.30

.60

wtTsTrc

3

wiAodt

1

2

34

3

wslfspaP“mfialP

-

-

-

-

-

-

Summer climatic severity (degree days) 0.60 < SCV ≤ 0.90 SCV ≤ 0Global Radiation (kWh/m2 day) 4.56 3.54

indows’ Thermal Transmittance (U-value) were 1.2 W/2 mK andheir Solar Heat Gain (G-value) coefficient was 0.62. As shown inable 2, the researchers who studied PCM drywall and PCM gyp-um plaster used a PCM area/Floor area ratio between 2.56 and 5.30.he Experimental Rooms of this study have a PCM area/Floor areaatio of 3.00, a total of 54 m2 of PCM drywall panels covering theeiling and the interior faces of the north, east and west walls.

.4.4. SimulationsThe simulations were performed in pairs, analyzing both rooms

ith and without PCM drywall, and evaluating 25 different casesn each city resulting from the combination of WW ratio and fs.

total of 125 double simulations were carried out. The purposef these simulations was to determine the influence of the PCMrywall panels and the fenestrations in the thermal behavior of theest rooms, quantifying the following four indicators:

. Total number of hours within the range of thermal comfort (21◦ Cand 26 ◦C).

. Number of hours within the range of thermal comfort that poten-tially can be added.

. Reduction of daily thermal peaks.

. Reduction of daily thermal swings.

.4.5. Simulation softwareThe final report of the IEA ECES Annex 20, sustainable cooling

ith thermal energy storage, includes the results of a comparativetudy on the design and analysis tools that can be used to simu-ate thermal energy storage systems, including the ones suitableor the use of PCM in buildings [30]. From those, PCMexpress waselected to carry out the thermal simulations in this work. PCMex-ress is a simplified planning and simulation tool designed to get

quick approximation of the thermal behavior of buildings usingCM. This software was developed within the framework programActive thermal storage systems in buildings using phase changeaterials”. It was conceived for support in the initial design phase,

acilitating a reliable decision-making process [30]. The mathemat-cal models and calculation engine of the software were developedt the Fraunhofer Institute for Solar Energy (ISE) working in col-aboration with industrial partners [30,31]. The decision to useCMexpress was based on the following:

Was designed to simulate the thermal and energy performanceof buildings with PCM.

Makes it possible to use the variables of this study and evaluatethe four selected indicators (see Sections 3.1 and 3.4.4).

Calculates the operative temperature of the rooms. (This param-eter was used for the analysis of the present study.)

Performs fast double simulations, shows the behavior of the

buildings with and without PCM.

PCM simulation based on a simplified Enthalpy Method. (TheEnthalpy Method is used by ESP-r and EnergyPlus).

Results were validated using the ESP-r results as a reference [31].

0.90 < SCV ≤ 1.25 SCV > 1.25 SCV ≤ 0.604.88 5.23 4.48

PCMexpress has a comprehensive database of material (withemphasis on PCM materials), construction systems and Europeanweather files. Materials and construction system can be createdand added to the software libraries. In PCMexpress, generic HVACsolutions can be defined using predefined systems. The software isstructured to work with Room Combinations, and it can simulateup to ten Room Combinations, each one of them may be made upof three zones [30].

PCMexpress has a component-oriented calculation core anduses the Node-Edges model. In this model, the layers of the wallconstructions, the air and the partitions were represented as heatcapacity and temperature-prone nodes. The edges represent theflow of energy (heat transfer) between the nodes. Energy sourcesand sinks, such as the radiation through the window and onto theouter wall, heating and cooling surfaces, air exchange and internalheat loads act as “external sources” of the corresponding node. Theenergy flows are tracked, and the overall energy balance is mon-itored in the external edges. The PCM effect is calculated usinga simplified enthalpy method. The thermal behavior of the PCMapplications is defined using enthalpy–temperature characteristiccurves. The curves of the materials included in the software weredefined according the German Institute for quality Assurance andCertification (RAL) [30].

The results are presented in reports and explanatory graphics,always making a comparison of the two systems, one with and otherwithout PCM. By default, three types of results are obtained: therooms operative temperature in relation to the Outdoor Runningmean temperature according to EN 15251, the frequency distribu-tion of the room temperatures and the daily progress charts withthe highest PCM effects [30,31]. Also, changing the default sett-ings, the software generates a text file with the calculated data ofeach room on an hourly basis. The file includes, among other infor-mation, the air temperature, the temperature of the surfaces andthe operative temperature. There are other software capabilitiesthat have not been used in this study such as the possibility ofsimulating active surfaces with water circulation, or carrying outeconomic analysis, comparative amortization studies based on theguide VDI 2067, developed by the Association of German Engineers[31]. Researchers at the Fraunhofer Institute conducted a validationstudy, comparing the PCMexpress results with those obtained withESP-r software. The model selected for the validation process waschosen from the DIN 4108-2:2003-07, and consisted of rooms of3.9 m × 5.2 m × 3.0 m, with only one exterior wall with a window,and with their interior walls, ceilings and floors related adiabat-ically with the interior of the building. The results of this studyindicate that the validation was successful, despite the simplifica-tions of the program in relation to the glazing, and they found asatisfactory correlation between the results of ESP-r and PCMex-press [31].

Some of the software limitations are: it only analyses rectan-gular spaces, it uses few parameters to define the glazing elements

and HVAC systems, and like the most building simulation software,only gives one value for the interior temperature, thus possible airtemperature stratification can not be registered. Furthermore, forthe simplified Enthalpy simulation process, it only uses the heating

470 E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476

s in Sp

pifia

4

4m

itmhavott

4f

icnWitt

Fig. 3. Influence of the use of thermal mas

ortion of the PCM enthalpy curve, so possible supercooling effects not considered [30,31]. This study was not affected by this simpli-cation due the microencapsulated paraffin is a stable substance,nd the supercooling is unusual in this material [23].

. Results

.1. Preliminary study results: influence of the use of thermalass in Spain

Results of this preliminary study are shown in Fig. 3; the barsndicate the number of hours that could potentially be added tohe thermal comfort range as a result of the correct use of thermal

ass strategies. The cities with the largest potential to increase inours of comfort in both cold and hot periods are Seville, Madridnd Barcelona (see Fig. 4). The results also show that summer nightentilation is useful in Seville and Madrid. In Soria, many hoursf comfort in the heating periods could be added, and in Bilbaohe lowest potential for increasing the number of hours within thehermal comfort range was found.

.2. Main study results: influence of PCM drywall andenestration in the climate zones studied

The improvement of thermal conditions in buildings rehabil-tated using PCM drywall, varies day-to-day depending on thehanging weather conditions of each city studied. Also, there areotable differences in the results of the cases due to the values of the

W ratio and the glazing Shading Factor. For a better understand-

ng of the influence of the use of PCM drywall and the fenestration,he results were organized by cities taking into account the indica-ors defined in Section 3.4 – Simulations.

Fig. 4. Annual comfort hours that potentially could b

anish cities: results of preliminary study.

4.2.1. Barcelona (BA): additional hours in comfort andpercentage of annual hours in comfort

It was found that cases BA40w50s and BA20w90s showed thehighest improvement in indoor thermal conditions due to theincorporation of PCM drywall. Comparing those cases with theirrespective reference rooms, an increment up to 1568 h per year inthe number of hours within the thermal comfort range was found,representing an improvement of 30.8% (Fig. 5a). However, in caseBA50w10s with PCM drywall, the highest number of hours per yearwithin the range of thermal comfort was found, 88.5% (see Fig. 5b).In Barcelona, the influence of the PCM drywall used had lowerinfluence in rooms with small glazing area (WW ratio = 10) and inrooms with low value Shading Factor (fs = 10). In rooms where WWratio = 10, when the Shadow Factor increases, both the additionalhours within thermal comfort range and the annual percentage ofhours in comfort increase. In cases with WW ratio above 20%, thegreatest reduction of hours above 26 ◦C is achieved when the fsvalue is between 0.30 and 0.50.

4.2.2. Bilbao (BI): additional hours in comfort and percentage ofannual hours in comfort

In case BI30w70s, the greatest improvement of indoor thermalconditions due to the incorporation of PCM drywall was achieved.Comparing this case with its reference room resulted in 1699additional hours within thermal comfort range, which means animprovement of 31.1% (Fig. 6a). However, in case BI50w10s withPCM was where the highest number of hours per year withinthe range of thermal comfort was registered, 88.5% (as shown inFig. 6b). In Bilbao, rooms with small glazing area (WW ratio = 10)

and in rooms with low value Shading Factor (fs = 10) the effectof PCM drywall was low. Less than 300 h of comfort were addedduring the cooling periods in rooms BI10w10s, BI10w30s andBI20w10s. In rooms where WW ratio = 10, when the value of

e added by the use of thermal mass strategies.

E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476 471

ywall

frca0

4o

iiwoaco(rSri

Fig. 5. Barcelona: annual results of the influence of the usage of PCM dr

s increases, both the additional hours within thermal comfortange and the annual percentage of hours in comfort increase. Inases with WW ratio above 20%, the greatest reduction of hoursbove 26 ◦C is achieved when the fs value is between 0.50 and.70.

.2.3. Madrid (MA): additional hours in comfort and percentagef annual hours in comfort

In this city, case MA20w90s had the highest improvement inndoor thermal conditions by the addition of PCM drywall, compar-ng this case with the reference one, an annual increment of 1533 h

ithin the range of thermal comfort was found, an improvementf 29.0% (Fig. 7a). It was also found that the highest percent-ge of hours within the range of thermal comfort was 88.5% inase MA50w10s with PCM (as shown in Fig. 7b). The influencef PCM drywall used was low in cases with small glazing areaWW ratio = 10) and cases with low Shading Factor (fs = 10). In

ooms where WW ratio = 10, when increasing the value of thehadow Factor, both the additional hours within thermal comfortange and the annual percentage of hours in comfort were in turnncreased.

Fig. 6. Bilbao: annual results of the influence of the usage of PCM drywall a

and the annual percentage of hours within the thermal comfort range.

4.2.4. Seville (SE): additional hours in comfort and percentage ofannual hours in comfort

In case SE10w90s, the greatest improvement of indoor thermalconditions by incorporating PCM drywall was found. In this case,31.1% of the annual hours were added to the thermal comfort range;1086 h more than its reference room (Fig. 8b). However, it was inroom SE10w30s with PCM in which the highest number of hoursper year within the range of thermal comfort was registered, equiv-alent to 74.9% (as shown in Fig. 8b). Comparing the cases in all citieswhere WW ratio = 10, Seville cases achieved the highest numberof additional hours within the comfort range due the use of PCMdrywall.

4.2.5. Soria (SO): additional hours in comfort and percentage ofannual hours in comfort

In this city, the rooms SO50w50s and SO40w70s showed thehighest improvement in indoor thermal conditions by the addition

of PCM drywall. Comparing these cases with their reference rooms,an increment of 1559 h per year within the range of thermal com-fort was found, an increment of 26.5% (Fig. 9a). However, it wasin case SO40w30s with PCM drywall in which the highest number

nd the annual percentage of hours within the thermal comfort range.

472 E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476

Fig. 7. Madrid: annual results of the influence of the usage of PCM drywall and the annual percentage of hours within the thermal comfort range.

Fig. 8. Seville: annual results of the influence of the usage of PCM drywall and the annual percentage of hours within the thermal comfort range.

Fig. 9. Soria: annual results of the influence of the usage of PCM drywall and the annual percentage of hours within the thermal comfort range.

E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476 473

f peak

o9rthtrhii

4

tictSwptwctt

Fig. 10. Reduction o

f annual hours within the range of thermal comfort was found,0.8% (as shown in Fig. 9b). In cases with small glazing area (WWatio = 10) as well as in cases with low value Shading Factor (fs = 10),he effect of the PCM drywall were less significant than in cases withigh WW ratio and fs values. In many of cases with WW ratio = 10,he additional annual hours in the thermal comfort range did noteach 300 h, in case SO10w10s, it did not even reach 100 additionalours. In this city where WW ratio = 30, when the Shadow Factor

ncreases, the additional hours within thermal comfort range aren turn increased.

.2.6. Thermal peak and daily temperature swing reductionsThermal Energy Storage in buildings helps to reduce the indoor

hermal peaks of both the high and the low temperatures, smooth-ng the daily thermal swings. These effects were analyzed using theases in which the greatest increase in the number of hours with thehermal comfort was achieved: BA20w90s, BI30w70s, MA20w90s,E10w90s and SO50w50s. As shown in Fig. 10, the cases in citiesith the coolest temperatures, Soria and Bilbao show a similarattern in terms of the reduction of thermal peaks. In Seville, inhe months of July and August, the reduction of the thermal peaks

ere small, in most of the days did not reach 1 ◦C. All the studied

ases achieved the largest peak temperature reductions betweenhe last weeks of September and the end of October. In those weeks,he results vary considerably from day to day as shown in Fig. 10,

temperatures in ◦C.

October was the month in which the cases BA20w90s, MA20w90sand SE10w90s achieved the greatest monthly average of high tem-perature peak reduction as shown in Table 4. However, in the case ofSoria the greatest reduction were achieved in July and August. Thecase BI30w70s show a reduction between 2.3 ◦C and 2.4 ◦C from Julyto October. Also in October, in four of the five analyzed cases therewere reduction close to 5 ◦C, the exception was the case SE10w90swhere maximal peak thermal reduction in this month was 4.4 ◦C.The influence of the 26 ◦C PCM drywall in the reductions of hourswith temperatures below 21 ◦C are not as significant as the reduc-tion of high temperature peaks. Therefore, in most of the casesthe reductions of the daily temperature swings are similar to thedecrement of high temperature thermal peaks as shown in Fig. 11.

4.2.7. Influence of the study variables on the thermal comfortIn order to determine the influence of each study variable, the

thermal performance of the rooms was studied changing only onevariable at a time. For example, to determine the influence of theWW ratio in the thermal comfort of rooms, the cases with thesame Shading Factor (fs) and different WW ratio were compared.The influence of the fs on the thermal comfort of rooms without

PCM was determined comparing the cases with same WW ratioand different fs. Additionally, the influence of the combination ofboth factors was verified, comparing the results in rooms with andwithout PCM drywall panels. Table 5 summarizes the findings of

474 E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476

Table 4Cases with more hours added to the thermal comfort and theirs high temperature peak reduction.

Cases Additional hours of comfort High temperature peak reduction in ◦C (average/maximum)

Quantity Percentage June July August September October

BA20w90s 1568 30.8 1.6/2.9 1.4/2.8 1.3/3.0 1.8/4.6 2.5/5.1BI30w70s 1699 31.1 1.9/3.5 2.4/4.2 2.3/4.8 2.3/4.9 2.3/5.4MA20w90s 1533 29.0 2.3/3.9 1.6/4.2 1.7/3.8 2.0/4.8 2.5/5.3SE10w90s 1086 31.1 1.5/2.8 0.5/0.8 0.6/2.0 1.1/2.6 1.8/4.4SO50w50s 1559 26.5 2.6/3.9 3.1/4.5 3.1/4.8 2.5/4.9 2.5/5.3

Table 5Influence of the variables of study: annual results.

City Additional hours incomfort (%)Changing the WW ratio

Additional hours incomfort (%)Changing the ShadingFactor

Rooms without PCMAdditional hours incomfort (%)Between worth and thebest case

Comparative betweenthe worth case withoutPCM and the best withPCMAdditional hours incomfort (%)

Barcelona From 2.2% (fs = 0.1) to 28.0% (fs = 0.9) From 6.0% (WW = 10%) to 33.7% (WW = 50%) 34.6% (50w90s–30w10s) 44.2% (50w90s–50w10s PCM)Bilbao From 2.8% (fs = 0.3) to 13.6% (fs = 0.9) From 3.3% (WW = 10%) to 23.9% (WW = 50%) 23.9% (50w90s–50w10s) 35.3% (50w90s–50w90s PCM)

to 29.7to 24.2to 23.6

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combination of WW ratio and fs in which the use of PCM drywallcould help to maintain a comfortable temperature in the rooms forabout 90% of hours of the year. The exception was Seville where a

Madrid From 6.8% (fs = 0.3) to 18.7% (fs = 0.9) From 4.2% (WW = 10%)

Seville From 7.4% (fs = 0.1) to 20.9% (fs = 0.9) From 8.9% (WW = 10%)

Soria From 8.7% (fs = 0.7) to 20.9% (fs = 0.9) From 6.6% (WW = 20%)

he thermal simulation in relation to the influence on the thermalomfort of the variables of this study, first the effect of each oneeparately and them the combined effects.

. Discussion

In an effort to determine the influence of PCM drywall and theenestration in building retrofitting in Spain, a comparative simu-ation works of rooms with and without PCM drywall panels wasarried out. These works were preceded by a preliminary study.his preliminary study provided an initial idea of the increment inhe number of hours within the thermal comfort range due the cor-ect use of the thermal mass. The results of the preliminary studynd the results of the simulations are similar only in the cases withow WW ratio and low fs values, see Figs. 4b and 12a. The results ofhe simulations in Madrid, Barcelona and Bilbao with 10w10s areimilar to the results of the preliminary study. In Seville, the casesith 10w10s present the greatest increase in the hours of thermal

omfort in both studies. However, the simulation results were lessromising than the preliminary study results.

The results of thermal simulations, shown in Table 5, corrobo-ate that, in building rehabilitations, it is first necessary to studyassive design strategies, such as the size of windows and theirhading systems, whether if new materials such as PCM drywallanels will be used or not. In Barcelona, for example, analyzinghe number of hours where the range of thermal comfort in roomsithout PCM and with fs = 90, it was found that depending on theW ratio used, the difference in results may vary by up to 28%.

n this city, in rooms without PCM and a WW ratio of 50%, theumber of hours of thermal comfort may vary by up to 33.7%,epending on the Shading Factor of glazing. The results in roomsithout PCM with different combinations of WW ratio and fs show

hat the number of hours in comfort could be increased by morehan 20%. In Barcelona, it could rise to 34.6%. The results also showhat the thermal comfort conditions of existing rooms could be fur-her enhanced with the use of PCM drywall. Comparing the worstombination of WW ratio and fs without PCM drywall, with anppropriate combination of these variables with PCM drywall, was

ound that the number of hours in the range of thermal comfortn all the cities could be increased by over 30%, and in Madrid thencrement could be up to 49% comparing the cases MA50w90s and

A50w10s.

% (WW = 50%) 30.4% (50w90s–40w10s) 49.0% (50w90s–50w10s PCM)% (WW = 50%) 31.6% (50w90s–10w10s) 37.8% (50w90s–10w30s PCM)% (WW = 50%) 24.8% (10w10s–40w10s) 31.5% (10w10s–40w30s PCM)

The thermal simulation results show that the use of 26 ◦C PCMdrywall cold reduce both the high and low temperature peaks.However, the reduction of high temperature peaks was more sig-nificant: in some cases a reduction of 5 ◦C was achieved. PCMdrywall panels also show greater effectiveness in reducing thenumber of annual hours with temperatures above 26 ◦C, more sothan reducing the number of hours with temperatures below 21 ◦C.The reduction in hours with temperatures below 21 ◦C was not themost beneficial effect of the PCM drywall panels. However, in somecases in Bilbao, more than 500 h were added to the thermal com-fort range. Similarly, in Soria there were cases in which over 400 hwere added. In Seville, with warmer weather, the annual reductionof hours below 21 ◦C is negligible.

In relation to the enhancement of thermal comfort by the use of26 ◦C PCM drywall panels in the Spanish territory, there is at leastone case in all the analyzed cities in which more than 1000 h couldbe added to the thermal comfort range, see Table 4. The results var-ied depending on the climate zone and combinations of variables,but all of them show at least a slight improvement in comfort condi-tions due to the use of PCM drywall (see Fig. 12a). In three out of the25 cases of Soria were found that the number of hours with temper-atures below 21 ◦C increased: 53 h in SO10w10s, 18 h in SO3010sand 79 h in SO20w30s. However, in these cases there was a largerreduction in hours with temperatures above 26 ◦C, resulting in apositive annual balance (as shown in Fig. 12a).

In four of the five cities studied, it was found that at least one

Fig. 11. Reduction of daily temperature swings in ◦C.

E. Rodriguez-Ubinas et al. / Energy and Buildings 65 (2013) 464–476 475

M dry

mw

dtHcrt1iwt

nFaut1tshh

tndtotbphi

oT

Fig. 12. Influence of the use of PC

aximum of 74.9% of the hours within the range of thermal comfortas achieved (case SE10w10s with PCM).

There were no cases where the maximum benefit of the PCMrywall was achieved and, where in turn, a maximum reduction inhe number of hours out of the thermal comfort range was reached.owever, there were some cases in Soria and Bilbao with resultslosed to this possibility. In the case SO50w40s, when the room isetrofitted using PCM drywall, 87.1% of the annual hours are withinhe thermal comfort range and in turn a potential increment of559 h within the range of thermal comfort was registered. Sim-

larly in the case BI50w30s with PCM drywall, 87.9% of the hoursere in thermal comfort, and there was potential to increase the

hermal comfort range to 1629 h.In the other hand, there cases were the use of PCM drywall can-

ot be justified, due to the small benefits that could be obtained.or example, in all the cities studied the rooms with WW ratio = 10nd F = 10 the results shown a low level of improvement by these of PCM drywall, being SO10w10s the worst case. In this case,he reduction of hours with temperature above 26 ◦C did not reach00 h per year, and as explained before, the number of hours withemperatures below 21 ◦C was increased. However, in Seville themallest benefits were obtained in a room with high WW ratio andigh fs values. For example, in case SE50w90s, the reduction ofours with temperatures above 26 ◦C did not reach 300 h per year.

In building retrofitting is not common to change the sizes ofhe openings. However, in some cases due the change of use, theecessity of increased daylight or views to the outdoors, new win-ows are added, or the existing ones are enlarged. In these cases,he proper sizing of PCM surface can also help to absorb the excessf heat gains due to the increased glazing area, and even be ableo achieve more hours of comfort than those obtained before reha-ilitation. This possibility was corroborated with the results of theresent study; in many cases, it was found a greater number ofours with temperatures above 26 ◦C in rooms without PCM than

n the rooms with PCM even with larger glazing.The results presented in this paper have the typical limitations

f studies based on numerical analysis or building simulations.hese limitations as usual are related to simplifications in the

wall in the studied Spanish cities.

method of calculation. So it is necessary to continue the exper-imental phase of the research, to validate or adjust the resultsobtained so far. The simulation results show the effect of the PCMon the air temperature, in the surface temperatures and also in theoperative temperature of the rooms on an hourly basis. However,there are other effects that could influence indoor thermal comfortthat cannot be observed with the simulations, such as the possiblereduction in air thermal stratification since the software providesonly one temperature value per room. Kuznik et al. observed forthe first time that the PCM wallboard panels enhance the natu-ral convection mixing in the air, avoiding uncomfortable thermalstratifications [19].

6. Conclusions

The influence of the use of PCM drywall and the fenestration inbuilding retrofitting, in Spain, has been studied. The PCM drywallpanels are designed to improve thermal performance of build-ings with low thermal mass, especially those located in areas withhigh diurnal temperature range. PCM drywall panels are relativelylightweight, have low thickness, are easy to install, can replace theexisting interior finishing or be placed over them; these characteris-tics make these panels particularly suitable for building retrofitting.A comparative study on the influence of the study variables in fiveSpanish cities was carried out. The influence of the fenestrationswas evaluated using the WW ratio and the Shading Factor as vari-ables.

In all studied cases, it was found that the PCM drywall couldhelp to increase the number of hours within the thermal comfortrange, reducing thermal peaks, smoothing the daily temperatureswing and increasing the number of hours within the range of ther-mal comfort. However, the influence of the 26 ◦C PCM drywall onthe thermal comfort was not the same in all cities. Cases in Sevilleshowed better performance with low WW ratio. In Bilbao and Soria

the best results were obtained with a high WW ratio. In Madrid andBarcelona was found high potential of increment of hours withinthe range of thermal comfort and a significant reduction in hourswith temperatures above 26 ◦C. Regarding the reduction of hours

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76 E. Rodriguez-Ubinas et al. / Ene

elow 21 ◦C, cases in Soria and Bilbao obtained the best results, fol-owed by others in Madrid and Barcelona. The effect of reducing thehermal peaks by the use of 26 ◦C PCM drywall in some cases wasp to 6 ◦C. Likewise, the reduction of internal temperature swing

n some cases reached 60%. In all the cities, there were cases inhich the number of hours in thermal comfort may be potentially

ncreased in more than 1000 h. In one of the Bilbao cases, it wasound that the potential increase of hours in thermal comfort mayeach 1600 h. However in some of the cases, the use of PCM drywallannot be justified, due the negligible results obtained.

In rehabilitation projects, in which it is necessary to increase theize of the windows, the use of PCM drywall could also be useful.he results of this study show that with the proper sizing of PCMrywall surfaces, the excess heat due to the increased glazing areaay be absorbed by the PCM, getting in some cases even more hours

f thermal comfort than those achieved before the rehabilitation.It is necessary to keep in mind that the viability of the passive uti-

ization of PCM drywall depends on the diurnal thermal variability,s well as the appropriated thermal energy charge and discharge.herefore, the orientation of the rooms and their ventilation pos-ibilities, as well as glazing types, sizes and solar protection areundamental elements to take into account in the planning of these PCM drywall. The results of the simulations bring a preliminary

dea of the influence of the PCM drywall and fenestrations on thehermal comfort in retrofitted buildings. However, further research,ith full scale cells or in real buildings is necessary to quantify the

mprovements in the thermal comfort conditions and determinehe energy savings due the use of PCM drywall panels.

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