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Experimental and Computational Study of the Implementation of mPCM-Modified Gypsum Boards in a Test Enclosure

Experimental and Computational Study of the Implementation of mPCM-Modified Gypsum Boards in a... buildings Article Experimental and Computational Study of the Implementation of mPCM-Modified Gypsum Boards in a Test Enclosure 1 1 1 1 Juan Pablo Bravo , Tomás Venegas , Elizabeth Correa , Alejandro Álamos , 1 1 , 2 Francisco Sepúlveda , Diego A. Vasco * and Camila Barreneche Departamento de Ingeniería Mecánica, Universidad de Santiago de Chile, Av. Lib. Bernardo O’Higgins 3363, Santiago 9170002, Chile; jpbravod@gmail.com (J.P.B.); tomasvenegast@gmail.com (T.V.); elizabeth.correag@usach.cl (E.C.); alejandro.alamos@usach.cl (A.Á.); francisco.sepulveda.p@usach.cl (F.S) Departament de Ciència del Materials i Enginyeria Metallúrgica, Universitat de Barcelona, Martí i Franquès 1–22, 08028 Barcelona, Spain; c.barreneche@ub.edu * Correspondence: diego.vascoc@usach.cl; Tel.: +56-(0)2-2718-3120 Received: 7 November 2019; Accepted: 13 January 2020; Published: 19 January 2020 Abstract: The application of phase change materials (PCM) in the thermal envelope of buildings has proven to be an alternative to reduce energy consumption and to improve thermal comfort conditions. The present work evaluates the thermal behavior of gypsum boards modified with a microencapsulated PCM (mPCM) in a cubic test enclosure, considering the climatic conditions of Santiago de Chile in the September–November period of 2017. The design of the test enclosure was performed considering the minimization of parameters that a ect the variation of its inner temperature and favoring the heat flow through the gypsum boards. Experimentally, the results reflect the main e ects of the implementation of a mPCM, among which the displacement of the maximum heat load and the decrease in the daily oscillation of the internal temperature of the test enclosure (up to 2 C) stand out. In addition, the mPCM modified gypsum board was thermally characterized to carry out a thermal simulation of the enclosures using EnergyPlus—. The obtained numerical results agree with those obtained experimentally, including the behavior of the transient heat flux through the gypsum boards. Moreover, it was found that considering a null infiltration rate gives place to unrealistic results, suggesting that this parameter should be controlled. Keywords: microencapsulated PCM; gypsum board; test enclosure; thermal simulation 1. Introduction Among the commitments of the energy policy of Chile for 2035 are to reduce CO emissions by 30% regarding to 2007, and the ensuring of continuous and quality access to energy for dwellings of vulnerable families [1]. Energy may be stored as chemical, electric, kinetic, potential, or thermal [2]. Among the many existing technological options to increase energy eciency in buildings, it has been recommended to put attention to Thermal Energy Storage (TES) [3]. Thermal energy storage systems use energy density of materials or latent heat associated with a phase transition to provide a heating or cooling source [4]. Phase change materials (PCMs) have been used increasingly as Latent Heat Thermal Energy Storage (LHTES) systems for heating and cooling applications. LHTES is considered a passive method of heat modulation, where PCMs can absorb heat from the environment and release it indoors when required [5,6]. The integration of LHTES in buildings can be done using their floor, walls, ceilings, and external solar facades [7]. The process of charging and discharging thermal energy from and to a PCM depends on the thermal oscillations of the environment. Thus, the phase change temperature is the main characteristic Buildings 2020, 10, 15; doi:10.3390/buildings10010015 www.mdpi.com/journal/buildings Buildings 2020, 10, 15 2 of 18 that allows to di erentiate each PCM and therefore to choose the most appropriate for an application. PCMs are commonly classified as inorganic, eutectic mixtures, and organic (O-PCMs) [8]. Among O-PCMs, there are di erent substances such as parans, fatty acids, fatty acid esters, long-chain alcohols, polyglycols, and their mixtures [9,10]. Thanks to their properties, O-PCMs can be used in applications near human comfort temperature, moreover, O-PCMs are chemically and physically stable, and they are less prone to subcooling than inorganic PCMs [11]. One of the main applications of O-PCMs is the increase of thermal inertia of building materials, which gives place to decreasing inner temperature fluctuations, shifting heat load peaks, and reducing the energy consumption of buildings associated with air conditioning [12–15]. Therefore, O-PCMs work exceptionally well on buildings of low thermal mass [16], where temperatures change abruptly, giving place to high energy consumption associated with thermally conditioning the building. The results of several investigations have proven that a proper design is necessary to take advantage of the capabilities of PCMs like the reduction of energy consumption, and the improvement of thermal comfort in buildings [17]. In a passive strategy, the integration of PCMs into building materials allows releasing of heat during the colder hours, beginning the solidification process. During the warmer hours, the melting process of PCM gives place to heat absorption. The integration of O-PCMs into lightweight building materials increases their energy density or volumetric heat capacity. Typical building materials such as gypsum plaster store up to 1 kJ/(kg K) as sensible heat, whereas average paran materials store energy as latent heat of approximately 100 kJ/kg [18]. There are some reported limitations in using PCMs in building materials [19]: (i) PCMs may interact with the building structure; (ii) leakage of PCMs; (iii) PCMs have low thermal conductivities. In order to overcome these issues, microencapsulated phase change materials (mPCM) have been integrated into building materials such as gypsum plaster, concrete, and mortar [20]. There are currently several forms of PCM encapsulation. Generally, the PCM is incorporated into a polymer matrix and depending on the final size of the encapsulated material is classified as nano-encapsulated (p < 1 m), micro-encapsulated (1 m < p < 1 mm) for particles, and macro-encapsulation (p > 1 mm) [21]. There are several processes to micro-encapsulate PCMs, A. Jamekhorshid et al. [22] propose to classify encapsulation methods in physical, physicochemical, and chemical procedures. Barreneche et al. [23] characterized the e ective thermal conductivity and the thermal inertia of gypsum and Portland cement modified with a mPCM (5 wt% and 15 wt%) by using two di erent apparatuses. The authors found that the addition of mPCM causes a reduction (25–35%) of the thermal conductivity of both building materials. Moreover, a 15 wt% load of mPCM causes a higher increase of the thermal inertia of gypsum boards. Zhou et al. [24] performed numerical simulations of the thermal performance of shape-stabilized PCM (melting point of 21 C) plates integrated into the inner surfaces of walls and the ceiling of a passive house located in Beijing, China, during winter. The results showed that shape-stabilized PCM gypsum plates can diminish the indoor temperature variation by up to 56%. Lachheb et al. [25] experimentally characterized a plaster composite incorporating 10% of microencapsulated paran (Micronal , BASF Company, Dayton, USA) by the guarded hot plate method. Moreover, the authors made a parametric study to analyze the e ect of the wallboard thickness (1–3 cm), and the mass fraction (0–30%) of mPCM. The obtained results show that there are no essential di erences in the inner surface temperature variation for mPCM mass fractions of 20% and 30%. Li et al. [26] characterized the thermal properties (thermal conductivity, apparent heat capacity and enthalpy) as function of temperature of a mPCM-gypsum wall board composite (20%). The authors found that thermal conductivity increases linearly with temperature, the apparent specific heat capacity of the composite is 2.71 times larger than that of gypsum wallboard. Regarding the enthalpy, the authors found that an appropriate heating rate, according to the application, is necessary. In 2007, Cabeza et al. [27] performed experiments with concrete cubicles (2 m 2 m 3 m) located in Lleida (Spain) with and without windows to analyze the e ect of the incorporation (5 wt%) of a commercial mPCM (melting point of 26.8 C) into the south, west, and roof walls. The measured temperature values during spring days showed that the south wall of the cubicle without mPCM at Buildings 2020, 10, 15 3 of 18 midday is 2 C higher than that of the cubicle with PCM. Arce et al. [28] mention that a PCM should complete the phase change cycle to work correctly. Then, it is a problem that during the colder winter days and warmer summer day, the PCM might not reach its melting and solidification temperature, respectively. In 2018, Zhu et al. [29] made a review about experimental and numerical applications with shape stabilized PCMs into building envelope components. This review work identified several factors that a ect the performance of a PCM, including its melting temperature, location and orientation of the building, and weather conditions. There is a trend of using hybrid composites with di erent melting points to be used during the colder and warmer seasons of the year. Kheradmand et al. [30] experimentally and numerically (Ansys-Fluent) evaluated a hybrid PCM plastering mortar in a test cell of reduced dimensions submitted to simulated weather conditions. The authors found that the use of three PCMs of di erent suitable melting points reduces heating and cooling temperature demands. Berardi and Soudian [31] implemented a composite of two macroencapsulated PCMs with melting temperatures of 21.7 C (Energain) and 25 C (BioPCM—) in the walls and the ceiling of a test cell, which resembles apartments with 80% window to wall ratio located in Toronto (Canada). The studies performed during one-year show that the hybrid PCM system reduce the temperature fluctuations during fall and summer. Previously, the same authors [32] made a parametric analysis of an apartment with the same hybrid composite and window to wall ratio by using Energyplus— showing promising results in two di erent climates (Toronto and Vancouver). In the review of Kalnæs and Jelle [33] about PCMs and their application in buildings, the authors mentioned that there are few studies on the e ects of PCMs in roofing. Moreover, the authors claimed that the use of PCMs on the roof would absorb the incoming solar radiation and heat from the surroundings reducing the inner temperature fluctuations. Piselli et al. [34] found that the inclusion of PCM in waterproof membranes improves the thermal performance of roofs under climatic conditions in the cities of Rome (Italy) and Abu Dhabi (UAE). Pasupathy and Velraj [35] made a study about the thermal performance of double layer PCM in the roof of a building located in Chennai (India). In order to reduce the inner temperature fluctuation, the authors recommended a double layer PCM with di erent melting points of 27 C and 32 C. Bamonte et al. [36] performed a numerical study, using the finite volume method, of concrete panels with aggregates containing PCMs (capric acid and glycerine) under temperature conditions of Bucharest (Romania) and Seville (Spain). The authors claimed that the implementation of these PCMs may reduce the energy consumption for cooling and heating by up to 20% and 10%, respectively. Jaworski [37] studied the thermal performance of mPCM-plaster ceiling panels with air ducts that works as a heat exchanger. The system was used in an oce building to improve the free cooling strategy. Sa ari et al. [38] studied the cool roof strategy to mitigate the e ect of urban heat island. Their results showed that PCMs with higher melting point are more suitable for reducing thermal loads in summer. Cornaro et al. [39] implemented a commercial PCM panel (RUBITHERM ) on the floor of a test enclosure under the weather conditions of Rome (Italy). The authors used the experimental results to validate a tool implemented in Indoor Climate and Energy software. The numerical results obtained for three di erent locations showed that only the energy savings using PCM and implementing night ventilation meet the Italian energy performance regulation. Ramakrishnan et al. [40] implemented a PCM stabilized cement mortar (FS-PCM) in the envelopes of a test box, comparing its thermal behavior with similar test boxes built on cement plasterboard (OCB) and gypsum plasterboard (GPB). The experimental results showed that the implementation of FS-PCM reduced the peak temperature by up to 2.4 C, compared to GPB and OCB test boxes. In the present work, the temperature variation inside a cubic test enclosure containing gypsum boards modified with a mPCM in the roof is recorded experimentally (September–November 2017). In addition, the behavior of the heat flux across the gypsum boards with and without mPCM is determined, being able to observe more clearly the displacement of the heat load. Gypsum boards modified with mPCM are thermally characterized, determining thermal conductivity, heat capacity, Buildings 2020, 10, 15 4 of 18 determined, being able to observe more clearly the displacement of the heat load. Gypsum boards modified with mPCM are thermally characterized, determining thermal conductivity, heat capacity, Buildings 2020, 10, 15 4 of 18 and enthalpy according to the temperature. These properties were incorporated into a thermally simulated physical model with EnergyPlus™. Numerical results also include the variation of the and enthalpy according to the temperature. These properties were incorporated into a thermally inner temperature of the enclosure in a period of moderate and warm temperatures in Santiago de simulated physical model with EnergyPlus—. Numerical results also include the variation of the inner Chile, as well as heat fluxes through the plates. In general, the numerical results show a behavior like temperature of the enclosure in a period of moderate and warm temperatures in Santiago de Chile, those recorded experimentally. as well as heat fluxes through the plates. In general, the numerical results show a behavior like those r 2. ecor Ma ded terials experimentally and Methods . This section describes the experimental procedures for the preparation of gypsum samples 2. Materials and Methods modified with mPCM, the determination of their thermophysical properties, and the experimental This section describes the experimental procedures for the preparation of gypsum samples assembly performed to study the behavior of gypsum boards modified with mPCM in a test modified with mPCM, the determination of their thermophysical properties, and the experimental enclosure. To manufacture the modified gypsum boards, the gypsum plaster (TOPEX ) and mPCM assembly performed to study the behavior of gypsum boards modified with mPCM in a test enclosure. (MikroCaps 28), whose properties are shown in Table 1, are poured into a container according to the To manufacture the modified gypsum boards, the gypsum plaster (TOPEX ) and mPCM (MikroCaps analyzed mass concentration (20 wt%). Initially, a lower mass concentration of 10 wt% was 28), whose properties are shown in Table 1, are poured into a container according to the analyzed considered but given its low enthalpy its use was discarded. Moreover, the obtained gypsum boards mass concentration (20 wt%). Initially, a lower mass concentration of 10 wt% was considered but of higher mass concentration (30 wt%) presented a poor mechanical stability, which prevented its given its low enthalpy its use was discarded. Moreover, the obtained gypsum boards of higher mass use in the test enclosure. Subsequently, this dry mixture is homogenized to then, add the amount of concentration (30 wt%) presented a poor mechanical stability, which prevented its use in the test distilled water required and obtain the mass proportion Plaster/water = 0.7. Finally, the wet mixture enclosure. Subsequently, this dry mixture is homogenized to then, add the amount of distilled water is blended until it acquires a slightly viscous consistency and is poured into melamine molds of 35 required and obtain the mass proportion Plaster/water = 0.7. Finally, the wet mixture is blended until [cm ] and 1 [cm] thick. The wet mixture is dried for one day at ambient temperature, then the it acquires a slightly viscous consistency and is poured into melamine molds of 35 [cm ] and 1 [cm] wooden mold is removed, and the plates are placed in an oven (Heraeus T 6120) at 30 °C for four thick. The wet mixture is dried for one day at ambient temperature, then the wooden mold is removed, days. and the plates are placed in an oven (Heraeus T 6120) at 30 C for four days. The gypsum samples for the characterization of the thermophysical properties are of different The gypsum samples for the characterization of the thermophysical properties are of di erent geometry and dimensions due to the requirements of the equipment used, so these were obtained by geometry and dimensions due to the requirements of the equipment used, so these were obtained pouring the wet mixtures into PVC molds of 3.6 mm in diameter and 8 cm high. Figure 1 shows SEM by pouring the wet mixtures into PVC molds of 3.6 mm in diameter and 8 cm high. Figure 1 shows images (Jeol, JSM 5410) of the gypsum samples modified with mPCM can be seen, where the SEM images (Jeol, JSM 5410) of the gypsum samples modified with mPCM can be seen, where the formation of microcapsule agglomerates between the plaster crystals is evident, therefore the final formation of microcapsule agglomerates between the plaster crystals is evident, therefore the final modified gypsum boards are not homogenous. The measurement of the thermal conductivity and modified gypsum boards are not homogenous. The measurement of the thermal conductivity and the the thermal diffusivity of the samples has been made by the thermal properties analyzer KD2-Pro thermal di usivity of the samples has been made by the thermal properties analyzer KD2-Pro (Decagon (Decagon devices) using the dual needle probe (sh1). The measurements were made in triplicate devices) using the dual needle probe (sh1). The measurements were made in triplicate controlling the controlling the temperature (±0.1 °C) in the range from 0 °C to 40 °C. In addition, a differential temperature (0.1 C) in the range from 0 C to 40 C. In addition, a di erential scanning calorimeter scanning calorimeter DSC 4000 (PerkinElmer) has been used to obtain the enthalpy (2% error) DSC 4000 (PerkinElmer) has been used to obtain the enthalpy (2% error) according to the temperature according to the temperature (±0.1 °C), which is fundamental to model the thermal behavior of (0.1 C), which is fundamental to model the thermal behavior of phase change materials correctly. phase change materials correctly. One collected three different samples from the modified gypsum One collected three di erent samples from the modified gypsum boards, and the obtained DSC results boards, and the obtained DSC results were quite similar between samples with percentage were quite similar between samples with percentage di erences lower than 0.2%. differences lower than 0.2%. a b Figure 1. Microstructure of the fracture surface of gypsum plaster samples modified with Figure 1. Microstructure of the fracture surface of gypsum plaster samples modified with microencapsulated phase change materials (mPCM): (a) ×100 and (b) ×500. microencapsulated phase change materials (mPCM): (a)100 and (b)500. Buildings 2020, 10, 15 5 of 18 Figure 2 shows the obtained results of thermal conductivity and thermal diffusivity. These results show a decreasing tendency of both properties with temperature when the PCM is in solid state (<25 °C). The enthalpy as a function of temperature was estimated from the DSC measurements according to equations available in the literature [41]. The enthalpy of mPCM-modified plaster with the implemented weight fraction is shown in Figure 3. Table 1. mPCM (MicroKaps 28) technical information supplied by the manufacturer [42]. PCM content in dry capsule 75–80% Heat storage capacity 184–196 [J/kg] Melting range 25–29 [°C] Bulk Density 200–350 [g/l] Average particles size 70–150 [μm] Wall thickness ~200 [nm] Type of membrane Melamine-formaldehyde Type pf PCM Paraffin wax Experimental Set-Up The experimental set-up consists of two cubicles of 0.512 m in volume, one with three gypsum boards modified with mPCM and the other with three not modified gypsum boards as control (Figure 4). The walls and base of the enclosures are composed of 1 m sandwich-type refrigeration panels, made of expanded polystyrene (100 mm thick) coated by galvanized steel on both sides. This material has a U value of 0.364 W/m K, as obtained by the calculation procedure according to NCh 853. Of.91. Pre-painted metallic profiles of the same type of steel were used to assemble the enclosures, as wells as sanitary profiles finished in PVC, and as fasteners, Philips stainless steel self-drilling screws and countersunk screws were used. The roofing is made of a zinc plate, structural plywood, calcium silicate board as a thermal insulator, and three gypsum boards with and without mPCM according to the different study configurations. A metal grid is used to affix the gypsum boards. In addition, synthetic rubber bands are employed to reduce air infiltration (Figure 5). Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of the modified boards, a fraction of 20 wt% of mPCM. In Figure 6, a diagram of both test enclosures indoors can be observed; these were installed on Buildings 2020, 10, 15 5 of 18 the roof of the Department of Mechanical Engineering of the University of Santiago, where they were subjected to the same weather, atmospheric conditions and were kept at a reasonable distance Figure 2 shows the obtained results of thermal conductivity and thermal di usivity. These results so they would not affect each other. Another important feature of the installation is that test show a decreasing tendency of both properties with temperature when the PCM is in solid state enclosures were separated from the “floor” using platforms of approximately 30 cm high, to avoid (<25 C). The enthalpy as a function of temperature was estimated from the DSC measurements any effect of the enclosure on which the experimental installation was performed (Figure 4b). The according to equations available in the literature [41]. The enthalpy of mPCM-modified plaster with design of the test enclosures points to the minimization of heat gains or losses through walls and the implemented weight fraction is shown in Figure 3. floor, favoring the heat flow through the ceiling where the plaster boards are located. Figure 2. Figure 2. Thermal conductivity and th Thermal conductivity and thermal ermal diffusiv di usivity ity of of mPCM-modified pla mPCM-modified plaster ster (20 (20 wt%). wt%). Table 1. mPCM (MicroKaps 28) technical information supplied by the manufacturer [42]. PCM content in dry capsule 75–80% Heat storage capacity 184–196 [J/kg] Melting range 25–29 [ C] Bulk Density 200–350 [g/l] Average particles size 70–150 [m] Wall thickness ~200 [nm] Type of membrane Melamine-formaldehyde Type pf PCM Paran wax Buildings 2020, 10, 15 6 of 18 Figure 3. Heat flux (segmented line) and obtained from di erential scanning calorimeter (DSC) Figure 3. Heat flux (segmented line) and obtained from differential scanning calorimeter (DSC) measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). Experimental Set-Up The experimental set-up consists of two cubicles of 0.512 m in volume, one with three gypsum boards modified with mPCM and the other with three not modified gypsum boards as control (Figure 4). The walls and base of the enclosures are composed of 1 m sandwich-type refrigeration panels, made of Figure 4. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Figure 5. Support structure of the gypsum boards. Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of modified plates, a fraction of 20 wt% of mPCM. The temperatures were recorded in four positions in each test enclosure: on the lower internal base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, and the temperature of the air just below of the gypsum board. The measurements were made during the spring season (September–November) of 2017 in the premises of the Department of Mechanical Engineering of the University of Santiago de Chile (33° 26 ʹ47.401 “S, 70° 40ʹ 53.311” W). The data acquisition system is a seven-channel temperature measurement system prototype whose main features are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim Integrated Products), (iii) processing and communication through Arduino UNO (Arduino), (iv) Buildings 2020, 10, 15 6 of 18 Buildings 2020, 10, 15 6 of 18 Buildings 2020, 10, 15 6 of 18 expanded polystyrene (100 mm thick) coated by galvanized steel on both sides. This material has a U Figure 3. Heat flux (segmented line) and obtained from differential scanning calorimeter (DSC) value of 0.364 W/m K, as obtained by the calculation procedure according to NCh 853. Of.91. measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). Figure 3. Heat flux (segmented line) and obtained from differential scanning calorimeter (DSC) measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). Figure 4. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Figure 4. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Pre-painted metallic profiles of the same type of steel were used to assemble the enclosures, as wells as sanitary profiles finished in PVC, and as fasteners, Philips stainless steel self-drilling screws and countersunk screws were used. The roofing is made of a zinc plate, structural plywood, calcium silicate board as a thermal insulator, and three gypsum boards with and without mPCM according to the di erent study configurations. A metal grid is used to ax the gypsum boards. In addition, synthetic rubber bands are employed to reduce air infiltration (Figure 5). Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of the modified boards, a fraction of 20 wt% ofFigure 4. mPCM. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Figure 5. Support structure of the gypsum boards. Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of modified plates, a fraction of 20 wt% of mPCM. The temperatures were recorded in four positions in each test enclosure: on the lower internal base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, and the temperature of the air just below of the gypsum board. The measurements were made during the spring season (September–November) of 2017 in the premises of the Department of Mechanical Engineering of the University of Santiago de Chile (33° 26 ʹ47.401 “S, 70° 40ʹ 53.311” W). The data acquisition system is a seven-channel temperature measurement system prototype whose main features are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim Figure 5. Figure 5. Su Support pport stru structur cture of the g e of the gypsum ypsum boards. boards. Each of Each of the three gypsum boards has a the three gypsum boards has an n area of 35 area of 35 Integrat cm ed Pr , a thickness oductsof ), (i 1 cm, ii) processin and, in thegcase and ofcommun modifiediplates, cation atfraction hrough ofArd 20 wt% uinoof U mPCM. NO (Arduino), (iv) cm , a thickness of 1 cm, and, in the case of modified plates, a fraction of 20 wt% of mPCM. In Figure 6, a diagram of both test enclosures indoors can be observed; these were installed on The temperatures were recorded in four positions in each test enclosure: on the lower internal the roof of the Department of Mechanical Engineering of the University of Santiago, where they were base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, subjected to the same weather, atmospheric conditions and were kept at a reasonable distance so they and the temperature of the air just below of the gypsum board. The measurements were made would not a ect each other. Another important feature of the installation is that test enclosures were during the spring season (September–November) of 2017 in the premises of the Department of separated from the “floor” using platforms of approximately 30 cm high, to avoid any e ect of the Mechanical Engineering of the University of Santiago de Chile (33° 26 ʹ47.401 “S, 70° 40ʹ 53.311” W). enclosure on which the experimental installation was performed (Figure 4b). The design of the test The data acquisition system is a seven-channel temperature measurement system prototype whose enclosures points to the minimization of heat gains or losses through walls and floor, favoring the heat main features are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim flow through the ceiling where the plaster boards are located. Integrated Products), (iii) processing and communication through Arduino UNO (Arduino), (iv) The temperatures were recorded in four positions in each test enclosure: on the lower internal base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, and the temperature of the air just below of the gypsum board. The measurements were made during the spring season (September–November) of 2017 in the premises of the Department of Mechanical 0  0 Engineering of the University of Santiago de Chile (33 26 47.401 “S, 70 40 53.311” W). The data acquisition system is a seven-channel temperature measurement system prototype whose main features Buildings 2020, 10, 15 7 of 18 are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim Integrated Products), Buildings 2020, 10, 15 7 of 18 (iii) processing and communication through Arduino UNO (Arduino), (iv) user control interface by Buildings 2020, 10, 15 7 of 18 LabVIEW (National Instruments). The sampling ratio was every 10 min, and the sensitivity of the user control interface by LabVIEW (National Instruments). The sampling ratio was every 10 min, temperatures reading was0.1 C. and the sensitivity of the temperatures reading was ±0.1 °C. user control interface by LabVIEW (National Instruments). The sampling ratio was every 10 min, and the sensitivity of the temperatures reading was ±0.1 °C. Figure 6. Diagram of the test enclosures. 1. Galvanized steel plate, 2. Plywood, 3. Internal air volume, Figure 6. Diagram of the test enclosures. 1. Galvanized steel plate, 2. Plywood, 3. Internal air volume, Figure 4. Pla 6.ster Diagram boards, of 5.the Calciu testm enclosur silicate board es. 1. s Galvanized , 6. Cold room steel board plate, s, 7 2. . G Plywood, rillage, 8. 3. Synthetic Internal ru air bber volume, 4. Plaster boards, 5. Calcium silicate boards, 6. Cold room boards, 7. Grillage, 8. Synthetic rubber 4. Plaster tapes. boards, 5. Calcium silicate boards, 6. Cold room boards, 7. Grillage, 8. Synthetic rubber tapes. tapes. 3. Results 3. Results 3. Results 3.1. 3.Experimental 1. Experimental Measur Measure ements ments 3.1. Experimental Measurements An experimental analysis is carried out to study the behavior of the temperatures inside both An experimental analysis is carried out to study the behavior of the temperatures inside both experimental set-up during three periods corresponding to the southern spring in Santiago de Chile experimental set-up during three periods corresponding to the southern spring in Santiago de Chile An experimental analysis is carried out to study the behavior of the temperatures inside both (Csb): (a) 16–30 September, (b) 12–26 October, and (c) 29 October–12 November. The average (Csb): (a) 16–30 September, (b) 12–26 October, and (c) 29 October–12 November. The average outdoor experimental set-up during three periods corresponding to the southern spring in Santiago de Chile outdoor temperature and the mode in each analyzed period are (a) 16.3 °C and 13.7 °C, (b) 17.6 °C temperature and the mode in each analyzed period are (a) 16.3 C and 13.7 C, (b) 17.6 C and 16.5 C, (Csb): (a) 16–30 September, (b) 12–26 October, and (c) 29 October–12 November. The average and 16.5 °C, and (c) 18.3 °C and 15.8 °C, respectively. Figures 7–9 show the behavior of the internal and (c) 18.3 C and 15.8 C, respectively. Figures 7–9 show the behavior of the internal and external outdoor temperature and the mode in each analyzed period are (a) 16.3 °C and 13.7 °C, (b) 17.6 °C and external temperature of the test enclosure without and with gypsum boards modified with temperature of the test enclosure without and with gypsum boards modified with mPCM for periods and mPCM for pe 16.5 °C, and (c riods ) 18 (a .3 ), ° (b), C and and (c 15 ). .8 More °C, resp over, it ect can b ively. e seen det Figuresa 7 il– s about 9 show t the ef he b fect eha of mPCM vior of ton t he h int e ernal (a), (b), and (c). Moreover, it can be seen details about the e ect of mPCM on the peak temperatures. peak temperatures. and external temperature of the test enclosure without and with gypsum boards modified with mPCM for periods (a), (b), and (c). Moreover, it can be seen details about the effect of mPCM on the Date peak temperatures. 16/09 17/09 18/09 19/09 20/09 21/09 22/09 23/09 24/09 25/09 26/09 27/09 28/09 29/09 30/09 01/10 Plaster Date MePCM-Plas ter 16/09 17/09 18/09 19/09 20/09 21/09 22/09 23/09 24/09 25/09 26/09 27/09 28/09 29/09 30/09 01/10 Ambient Plaster MePCM-Plas ter Ambient 30 20 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 0 Time (h) Figure 7. Cont. 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 0 Time (h) Temperature (°C) Temperature (°C) Buildings 2020, 10, 15 8 of 18 Buildings 2020, 10, 15 8 of 18 Buildings 2020, 10, 15 8 of 18 bb Figure 7. (a) Average temperatures of the test enclosures during the first period and (b) detail of days Figure 7. (a) Average temperatures of the test enclosures during the first period and (b) detail of days Figure 7. (a) Average temperatures of the test enclosures during the first period and (b) detail of days when there is a decrease in the maximum internal temperature in the enclosure with gypsum boards when there is a decrease in the maximum internal temperature in the enclosure with gypsum boards when there is a decrease in the maximum internal temperature in the enclosure with gypsum boards modified with mPCM. modified with mPCM. modified with mPCM. Date Date 12/10 13/10 14/10 15/10 16/10 17 /10 18 /10 19 /10 20/10 21/10 22/10 23/10 24/10 25/10 26/10 27 /10 12/10 13/10 14/10 15/10 16/10 17 /10 18 /10 19 /10 20/10 21/10 22/10 23/10 24/10 25/10 26/10 27 /10 Plaster Plaster 35 MePCM-Plaster 35 MePCM-Plaster Ambient Ambient 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 Time (h) 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 Time (h) Figure Figure 8. 8. (a( )aA ) verage Average temperatures of temperatures of the te the test st en en closures d closures u during ring the secon the second d perio period d (b,c( ) a b,n cd deta ) and il detail at the end of the period when there is a decrease in the temperature oscillation of the enclosure with at the end of the period when there is a decrease in the temperature oscillation of the enclosure with gypsum boards modified with mPCM. Figure 8. gypsum(a boar ) Av ds erage temperatures of modified with mPCM. the test enclosures during the second period (b,c) and detail at the end of the period when there is a decrease in the temperature oscillation of the enclosure with In the second period of analyzed tests (Figure 8), the effect of the mPCM incorporated in the gypsum boards modified with mPCM. gypsum board is evident for a greater number of days (7). In this period, it is also observed that during the same amount of days the micro-encapsulated phase change material influences the In the second period of analyzed tests (Figure 8), the effect of the mPCM incorporated in the variation of the minimum temperature, finding that, in the case of the enclosure with plates gypsum board is evident for a greater number of days (7). In this period, it is also observed that modified with mPCM, these are lower than in the reference room. It is also interesting to note that at during the same amount of days the micro-encapsulated phase change material influences the the end of this period, the effect of the phase change material is evident in the decrease in the variation of the minimum temperature, finding that, in the case of the enclosure with plates oscillation of the internal temperature of the enclosure. modified with mPCM, these are lower than in the reference room. It is also interesting to note that at the end of this period, the effect of the phase change material is evident in the decrease in the oscillation of the internal temperature of the enclosure. Temperature (°C) Temperature (°C) Buildings 2020, 10, 15 9 of 18 Figure 9 shows the behavior of temperatures during the third period of tests, from 29 October to 12 November. In this period, only three days are observed in which the incorporation of mPCM to the gypsum board is evident. However, the most interesting thing during this period is that there are two days (8 and 11 November) where the average internal temperature in both enclosures is much higher than the outside temperature. This increase can be explained from the rise in the minimum temperature during the previous days, which causes the mPCM not to be able to discharge during the hours of low temperatures. As in the previous period, the effect of the phase change material is more evident in the decrease of the oscillation of the enclosure’s internal temperature. In Figures 10 and 11, the maximum and minimum daily temperatures in both test enclosures are observed, measured in the lower internal base and in the air just below the gypsum board, respectively. In Figure 10, no significant effect of the incorporation of the phase change material is observed due to the condition of the ventilated floor, which is also a common characteristic that can be seen repeatedly in constructions in the Chilean coast. However, the effect of the mPCM is observed in the decrease of the maximum temperature measured in the adjacent air on the gypsum board during the analyzed period (Figure 11), approximately between 1 °C and 4 °C. Regarding the minimum temperature, it is noted that the effect of the mPCM is evidenced only in some days, Buildings 2020, 10, 15 9 of 18 which reflects in a higher minimum temperature, between 1.5 °C and 3.0 °C, specifically at the end of the analyzed period. Date 29/10 30/10 31/10 01/11 02/11 03/11 04/11 05 /11 06/11 07/11 08/11 09/11 10 /11 11/11 12/11 13/11 MePCM-Plaster Plaster Ambient 0 a 08 16 08 16 08 16 08 16 0 8 16 08 16 08 16 08 16 08 16 0 8 16 08 16 08 16 08 16 08 16 0 8 16 0 Time (h) b c Figure 9. (a) Average temperatures of the test enclosures during the third period (b,c) and detail at the Figure 9. (a) Average temperatures of the test enclosures during the third period (b,c) and detail at end of the period when there is a decrease in the temperature oscillation of the enclosure with gypsum the end of the period when there is a decrease in the temperature oscillation of the enclosure with boards modified with mPCM. gypsum boards modified with mPCM. In the second period of analyzed tests (Figure 8), the e ect of the mPCM incorporated in the gypsum board is evident for a greater number of days (7). In this period, it is also observed that during the same amount of days the micro-encapsulated phase change material influences the variation of the minimum temperature, finding that, in the case of the enclosure with plates modified with mPCM, these are lower than in the reference room. It is also interesting to note that at the end of this period, the e ect of the phase change material is evident in the decrease in the oscillation of the internal temperature of the enclosure. Figure 9 shows the behavior of temperatures during the third period of tests, from 29 October to 12 November. In this period, only three days are observed in which the incorporation of mPCM to the gypsum board is evident. However, the most interesting thing during this period is that there are two days (8 and 11 November) where the average internal temperature in both enclosures is much higher than the outside temperature. This increase can be explained from the rise in the minimum temperature during the previous days, which causes the mPCM not to be able to discharge during the hours of low temperatures. As in the previous period, the e ect of the phase change material is more evident in the decrease of the oscillation of the enclosure’s internal temperature. In Figures 10 and 11, the maximum and minimum daily temperatures in both test enclosures are observed, measured in the lower internal base and in the air just below the gypsum board, respectively. In Figure 10, no significant e ect of the incorporation of the phase change material is observed due to Temperature (°C) Buildings 2020, 10, 15 10 of 18 the condition of the ventilated floor, which is also a common characteristic that can be seen repeatedly in constructions in the Chilean coast. However, the e ect of the mPCM is observed in the decrease of the maximum temperature measured in the adjacent air on the gypsum board during the analyzed period (Figure 11), approximately between 1 C and 4 C. Regarding the minimum temperature, it is noted that the e ect of the mPCM is evidenced only in some days, which reflects in a higher minimum Buildings 2020, 10, 15 10 of 18 temperature, between 1.5 C and 3.0 C, specifically at the end of the analyzed period. Buildings 2020, 10, 15 10 of 18 Figure 10. Maximum and minimum daily temperatures of the lower surface of the test enclosure Figure 10. Maximum and minimum daily temperatures of the lower surface of the test enclosure with Figure 10. Maximum and minimum daily temperatures of the lower surface of the test enclosure with gypsum boards with (filling) and without (empty) mPCM. gypsum boards with (filling) and without (empty) mPCM. with gypsum boards with (filling) and without (empty) mPCM. Figure 11. Maximum and minimum daily temperatures of the air adjacent to the gypsum board with Figure 11. Maximum and minimum daily temperatures of the air adjacent to the gypsum board with Figure 11. Maximum and minimum daily temperatures of the air adjacent to the gypsum board with (fill) and without (empty) mPCM. (fill) and without (empty) mPCM. (fill) and without (empty) mPCM. 3.2. Heat Flow Calculation 3.2. Heat Flow Calculation 3.2. Heat Flow Calculation According to the configuration of the experimental set-up, the heat flow to (or from) the test According to the configuration of the experimental set-up, the heat flow to (or from) the test According to the configuration of the experimental set-up, the heat flow to (or from) the test enclosure is mainly by conduction, through the layer of structural plywood and the three gypsum enclosure is mainly by conduction, through the layer of structural plywood and the three gypsum enclosure is mainly by conduction, through the layer of structural plywood and the three gypsum boards layers (Figure 12). In the case of the test enclosure with non-modified gypsum boards, boards layers (Figure 12). In the case of the test enclosure with non-modified gypsum boards, the boards layers (Figure 12). In the case of the test enclosure with non-modified gypsum boards, the the physical situation can be modeled as a pair of conductive thermal resistance series associated with physical situation can be modeled as a pair of conductive thermal resistance series associated with physical situation can be modeled as a pair of conductive thermal resistance series associated with structural plywood L = 18 mm, k = 0.130 W/mK and gypsum board layers without mPCM L = 30 mm, t t p structural plywood Lt = 18 mm, kt = 0.130 W/mK and gypsum board layers without mPCM Lp = 30 structural plywood Lt = 18 mm, kt = 0.130 W/mK and gypsum board layers without mPCM Lp = 30 k = 0.422 W/mK. In this way, the overall transfer coecient is calculated from the equation: mm, kp = 0.422 W/mK. In this way, the overall transfer coefficient is calculated from the equation: mm, kp = 0.422 W/mK. In this way, the overall transfer coefficient is calculated from the equation: L p  L p [ ] U = + W/m K 2, (1)  U = L + [W/m K], k k (1)  p t t p 2  U = + [W/m K],  (1) kk tp  kk tp  Then, the heat flux per unit area is calculated through the equation: Then, the heat flux per unit area is calculated through the equation:  Qk=− U Tso Tsi W/m , () (2)  Qk=− U Tso Tsi  W/m , () (2)  where the temperatures Tso and Tsi correspond to the external surface temperature of the structural where the temperatures Tso and Tsi correspond to the external surface temperature of the structural plywood (x = 0) and the internal temperature of the third gypsum board (x = L). In the case of the plywood (x = 0) and the internal temperature of the third gypsum board (x = L). In the case of the enclosure with gypsum boards modified with mPCM (Lp = 30 mm, kp = 0.306 W/mK) a capacitor is enclosure with gypsum boards modified with mPCM (Lp = 30 mm, kp = 0.306 W/mK) a capacitor is added to the thermal circuit parallel to the conductive thermal resistance of the gypsum boards. This added to the thermal circuit parallel to the conductive thermal resistance of the gypsum boards. This capacitor models the thermal inertia of the gypsum boards with mPCM, counting the heat absorbed capacitor models the thermal inertia of the gypsum boards with mPCM, counting the heat absorbed or released depending on the environmental conditions. In this way, using Equations (1) and (2), it is or released depending on the environmental conditions. In this way, using Equations (1) and (2), it is possible to obtain approximately the heat flows by conduction during the test periods in the possible to obtain approximately the heat flows by conduction during the test periods in the enclosures with gypsum boards not modified and modified with mPCM (Figure 13). According to enclosures with gypsum boards not modified and modified with mPCM (Figure 13). According to Buildings 2020, 10, 15 11 of 18 this analysis, the heat accumulated on gypsum boards modified with mPCM can be estimated approximately as the difference of heat fluxes through the thermal model of the test enclosure with Buildings 2020, 10, 15 11 of 18 gypsum boards modified with PCM and that with non-modified gypsum boards (Figure 12). (a) (b) Figure 12. Roofing model of the test enclosures (a) and equivalent thermal circuit for the Figure 12. Roofing model of the test enclosures (a) and equivalent thermal circuit for the approximate calculation approximate calculation of heat fluxes (of he b). at fluxes (b). Then, the heat flux per unit area is calculated through the equation: Figure 13 shows the result of the behavior of instantaneous heat fluxes through the roofing of the test enclosures during the second and third studied periods. These figures allow to better h i ( ) Qk = U T T W/m , (2) so si observe the displacement in time of the peak of thermal loads due to the incorporation of mPCM, evidenced by the difference between the times at which the heat flux peaks manifest in each case. where the temperatures T and T correspond to the external surface temperature of the structural so si plywood (x = 0) and the internal temperature of the third gypsum board (x = L). In the case of the 3.3. Computational Simulation enclosure with gypsum boards modified with mPCM (L = 30 mm, k = 0.306 W/mK) a capacitor p p EnergyPlus™ is a thermal simulation software for developed by collaborations between the is added to the thermal circuit parallel to the conductive thermal resistance of the gypsum boards. United States Renewable Energy Laboratory (NREL), United States Department of Energy (DOE), This capacitor models the thermal inertia of the gypsum boards with mPCM, counting the heat academic institutions, and private companies. It consists of a tool that interrelates the performance of absorbed or released depending on the environmental conditions. In this way, using Equations (1) active energy systems, geometric dimensions, envelope characteristics, geographical location, and and (2), it is possible to obtain approximately the heat flows by conduction during the test periods in weather data to perform a computer simulation and subsequently deliver reports of energy the enclosures with gypsum boards not modified and modified with mPCM (Figure 13). According consumption by air conditioning of spaces, lighting, temperatures, and other values required by the to this analysis, the heat accumulated on gypsum boards modified with mPCM can be estimated user. For this simulation, the software required the following fundamental information: approximately as the di erence of heat fluxes through the thermal model of the test enclosure with gypsum boards modified with PCM and that with non-modified gypsum boards (Figure 12). (i.) Climatic data, including solar radiation and cloudiness of the geographical location, dry bulb Figure 13 shows the result of the behavior of instantaneous heat fluxes through the roofing of the temperature, relative humidity, and wind speed. This information was obtained for Santiago de test enclosures during the second and third studied periods. These figures allow to better observe the Chile from the EnergyPlus ™ website [43]. displacement in time of the peak of thermal loads due to the incorporation of mPCM, evidenced by the (ii.) Geometric information of the necessary enclosures to create a 3-D model, considering di erence between the times at which the heat flux peaks manifest in each case. dimensions, materials, and the orientation of the enclosures. (iii.) The thermophysical properties of the enclosure’s envelope materials obtained experimentally 3.3. Computational Simulation and from information available in Chilean regulations. (iv.) Ener The external floors o gyPlus— is a therm f ea alch simulation enclosure we softwar re consid e for developed ered ventilated surfac by collaborations es, not ex between posed to dir the United ect Statessun r Renewable adiation Ener . gy Laboratory (NREL), United States Department of Energy (DOE), academic (v.) institutions, Air renew and als private per hour companies. on the enclo It consists sure. A pa of ra a meter tool that thainterr t was set elates at fthe ive renewa performance ls/hour. of active energy systems, geometric dimensions, envelope characteristics, geographical location, and weather data to perform a computer simulation and subsequently deliver reports of energy consumption by air conditioning of spaces, lighting, temperatures, and other values required by the user. For this simulation, the software required the following fundamental information: Buildings 2020, 10, 15 12 of 18 (i.) Climatic data, including solar radiation and cloudiness of the geographical location, dry bulb temperature, relative humidity, and wind speed. This information was obtained for Santiago de Chile from the EnergyPlus — website [43]. (ii.) Geometric information of the necessary enclosures to create a 3-D model, considering dimensions, materials, and the orientation of the enclosures. (iii.) The thermophysical properties of the enclosure’s envelope materials obtained experimentally and from information available in Chilean regulations. (iv.) The external floors of each enclosure were considered ventilated surfaces, not exposed to direct sun radiation. Buildings 2020, 10, 15 12 of 18 (v.) Air renewals per hour on the enclosure. A parameter that was set at five renewals/hour. Date 12/10 13/10 14/10 15/10 16/10 17/10 18/10 19/10 20/10 21/10 22/10 23/10 24/10 25/10 26/10 27/10 -10 -20 -30 -40 -50 -60 Plaster MePCM-Plas ter Subtraction -70 0 8 16 0 8 16 08 16 08 16 08 16 08 16 08 16 0 8 16 08 16 08 16 08 16 08 16 08 16 0 8 16 0 8 16 0 Time (h) Date 29/10 30/10 31/10 01/11 02/11 03/11 04 /11 05/11 06/11 07/11 08/11 09/11 10/11 11/11 12/11 13/11 Plaster MePCM-Plas ter Subtraction -10 -20 -30 -40 -50 Figure 13. Estimated heat flux through the gypsum boards in the test enclosures with and without Figure 13. Estimated heat flux through the gypsum boards in the test enclosures with and without gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. Figur Figure 14a shows the num e 14a shows the numerical erical resu results lts of of tempera temperat tur ure beha e behavior vior duri during ng the the f first irst peri period od of test of tests. s. As As in in the exp the experimental erimental study, the study, the simulation simulation predi predicts cts tha thatt the temper the temperatur ature e inside inside the test en the test enclosur closures es is is hi higher gher than the outsi than the outside de temper temperatur ature. e. H However owever,, t this his d dii ffer erence ence i is s m much uch m mor ore e e evident vident t than han i in n t the he experimental experimental case (F case (Figur igure 7a). e 7a). The The simulation simulation re results sults pr predict edict t that hat t the he ef e fect ect of of incorporating incorporating g gypsum ypsum boar boards modified ds modified with with mPCM mPCM is notis not important important during du this ring this stage; thissta isgbecause e; this ithe s because the outer outer temperature temperature does not exceed the PCM melting temperature. It is for this reason that the simulation results for the other two experimentally analyzed periods are not shown. Figure 14b shows the results of the variation of the temperature inside the test enclosures during a warmer period than those analyzed experimentally. During this period, it is observed that the difference between the internal temperature of the enclosures and the outdoor temperature is further accentuated. It is also possible to identify the effect of the incorporation of the modified gypsum boards, visualized in the behavior of the temperature inside the enclosure, specifically in the reduction of the maximum temperature (Figure 14c). However, said reduction does not exceed 2 °C. q (W/m ) q (W/m ) Buildings 2020, 10, 15 13 of 18 does not exceed the PCM melting temperature. It is for this reason that the simulation results for the other two experimentally analyzed periods are not shown. Figure 14b shows the results of the variation of the temperature inside the test enclosures during a warmer period than those analyzed experimentally. During this period, it is observed that the di erence between the internal temperature of the enclosures and the outdoor temperature is further accentuated. It is also possible to identify the e ect of the incorporation of the modified gypsum boards, visualized in the behavior of the temperature inside the enclosure, specifically in the reduction of the maximum temperature (Figure 14c). However, Buildings 2020, 10, 15 13 of 18 said reduction does not exceed 2 C. Date 16/09 17/09 18/09 19/09 20/09 21/09 22/09 23/09 24/09 25/09 26/09 27/09 28/09 29/09 30/09 01/10 Plaster MePCM-Plas ter Ambient -5 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 0 8 16 0 Time (h) Figure 14. Simulated average temperatures of the test enclosures during two periods of spring (a) Figure 14. Simulated average temperatures of the test enclosures during two periods of spring (a) and southern and southern summer summer ( (b). The b). Th detail e detail shows shows the decr the de ease crease in tem in peratur temperature o e oscillation scillation of the of enclosur the enclosure e with gypsum with gyps boar um board ds withsmPCM with mPCM ( (c). c). Figure 15 shows the predicted behavior of the net heat flux by conduction through the roofing of the test enclosures. As with the heat flux values estimated from the experimental measurements, a heat flux is considered positive when it flows into the test enclosure and it is negative when it flows to the outside. The results obtained for the first period (Figure 15a) do not allow to observe an apparent difference between the net heat fluxes by conduction through the roofing of both enclosures. However, in the warmest period analyzed (Figure 15b), it shows a more significant difference between the two enclosures. The difference in heat fluxes by conduction through the roofing of both enclosures corresponds, as in the experimental case (Figure 13), to the heat flux stored in the gypsum boards with mPCM. Temperature (°C) Buildings 2020, 10, 15 14 of 18 Figure 15 shows the predicted behavior of the net heat flux by conduction through the roofing of the test enclosures. As with the heat flux values estimated from the experimental measurements, a heat flux is considered positive when it flows into the test enclosure and it is negative when it flows to the outside. The results obtained for the first period (Figure 15a) do not allow to observe an apparent di erence between the net heat fluxes by conduction through the roofing of both enclosures. However, in the warmest period analyzed (Figure 15b), it shows a more significant di erence between the two enclosures. The di erence in heat fluxes by conduction through the roofing of both enclosures corresponds, as in the experimental case (Figure 13), to the heat flux stored in the gypsum boards Buildings 2020, 10, 15 14 of 18 with mPCM. Figure 15. Predicted heat flux through the gypsum boards in the test enclosures with and without Figure 15. Predicted heat flux through the gypsum boards in the test enclosures with and without gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. 4. Discussion 4. Discussion The The dimensions of the test enclosure dimensions of the test enclosure (Figur(Figure es 4 ands 64 ) ar an ed 6) no suit are no able to suit extrapolate able to ext therap obtained olate the results to a real scale building. Nevertheless, the used enclosure does not pretend to be a physical obtained results to a real scale building. Nevertheless, the used enclosure does not pretend to be a model physic ofal m an actual odel of building; an actuinstead, al buildin the g; goal instis ead, t to assess he gothe al is t mPCM-modified o assess the mgypsum PCM-modi boar fie ds d gyp under sum actual weather conditions minimizing the parameters that a ect the variation of the enclosure’s inner boards under actual weather conditions minimizing the parameters that affect the variation of the temperatur enclosure’s in e and ner favoring temperat theure and favor heat flux through ing the the he gypsum at flux th boar rough d surfaces. the gypsum board surfaces. One characterized the thermal properties of the gypsum boards modified with a paranic mPCM One characterized the thermal properties of the gypsum boards modified with a paraffinic (20mPCM (20 wt%) by the wt%) transient by the tra line heat nsient li sourne ce method. heat source The method. results showed The resul thatts showed both thermal that conductivit both therma y l and thermal di usivity depend on temperature, and these properties are higher when the PCM is conductivity and thermal diffusivity depend on temperature, and these properties are higher when solid. the PCM is solid The measured . The measured ph phase change enthalpy ase change enth of 28.79 J/kg alpy of is lower 28.79 J/ thankg is expected lower t due han expected to the formation due to of agglomerates of mPCM. It can be observed, in all the experimental and numerical analyzed cases, the formation of agglomerates of mPCM. It can be observed, in all the experimental and numerical how anatemperatur lyzed cases, how t es describe eman perat oscillatory ures describ behavior e an os typical cillatory beh of passive avior t systems. ypical Another of passive common systems. feature is that, for most days, the internal temperature of the enclosure is higher than the ambient Another common feature is that, for most days, the internal temperature of the enclosure is higher than the ambient temperature, reaching even a difference of 3 °C. Similar behavior was observed in previous works using test enclosures of different dimensions, and mPCMs concentrations [27,30]. It is believed that this effect is a consequence of the design used in the construction of the enclosure, since it seeks to reduce as much as possible infiltrations and losses and gains of heat by the surfaces of the walls and the floor, favoring heat transfer by the roofing of the enclosure, where the gypsum boards are located. According to Kalnæsa and Jelle [33], there are few studies on the effects of PCMs in passive roof systems. Our experimental results agree to the hypothesis of the authors who claimed that PCMs placed on the roof would absorb the incoming thermal energy from the sun and surroundings to reduce temperature fluctuations on the inside. The effect of the incorporation of the mPCM in the test enclosure during the first analyzed period indicates three days (16, 22, and 23 September) in which the maximum temperature exceeds 30 °C. During these days, the maximum temperature of the test enclosure with gypsum boards Buildings 2020, 10, 15 15 of 18 temperature, reaching even a di erence of 3 C. Similar behavior was observed in previous works using test enclosures of di erent dimensions, and mPCMs concentrations [27,30]. It is believed that this e ect is a consequence of the design used in the construction of the enclosure, since it seeks to reduce as much as possible infiltrations and losses and gains of heat by the surfaces of the walls and the floor, favoring heat transfer by the roofing of the enclosure, where the gypsum boards are located. According to Kalnæsa and Jelle [33], there are few studies on the e ects of PCMs in passive roof systems. Our experimental results agree to the hypothesis of the authors who claimed that PCMs placed on the roof would absorb the incoming thermal energy from the sun and surroundings to reduce temperature fluctuations on the inside. The e ect of the incorporation of the mPCM in the test enclosure during the first analyzed period indicates three days (16, 22, and 23 September) in which the maximum temperature exceeds 30 C. During these days, the maximum temperature of the test enclosure with gypsum boards modified with mPCM is lower than that of the enclosure of reference by approximately 2 [ C]. The other e ect of the incorporation of the mPCM that can be observed is the slight shifting in time between the external and internal maximum temperatures of the enclosure caused by the thermal storage capacity of the roofing of the test enclosure. The experimental results show that the internal temperature of the enclosure is influenced by the mPCM, with a maximum di erence between both enclosures of 6.5 C observed on October 21, being able to better observe, such a day, the e ect of the displacement of the thermal load from 16:57 h until 18:17 h. The maximum temperature di erence observed during the nighttime was 2.75 C on November 11, when a minimum of 14.25 C is reached at 7:17 h in the enclosure without mPCM, while in the enclosure with mPCM a minimum temperature of 17 C is reached at 8:17 h. There are periods during the afternoon, where heat flux to the interior of the test enclosure with gypsum boards modified with mPCM is higher than in the reference enclosure, while in the mornings, the heat flux to the outside is more significant in the latter. In general, it is observed that the heat flux into the interior of the test enclosures increases during the early hours of the morning until reaching a maximum peak around noon. Then, the heat flux decreases during the afternoon until the first hours of the next day. The computer simulations carried out employing EnergyPlus— allowed to predict the thermal behavior of the test enclosure approximately. However, the numerical results were not contrasted with the experimental ones, given the moderate behavior of the environmental temperatures of the climate archive available for Santiago de Chile compared to the temperatures measured in situ during the experiments carried out between September and November 2017. Moreover, the numerical results fail to predict the observed shifting of the behavior of the heat flux resulting from the modification of the gypsum boards with mPCM. Maybe for enclosures of low dimensions, it is more precise to use computational tools based on the finite volume method, as other authors performed it [29,31]. When comparing the experimental and numerical results, it is observed that the numerically predicted heat fluxes are of the same order than those experimentally estimated, but the software predicts a smaller di erence between the heat fluxes in both enclosures. The computer simulation carried out in a warmer period (2–15 February) predicts that the incorporation of the mPCM in the gypsum boards reduces the maximum average temperature reached in the enclosure by no more than 1.5 C, which is approximately 1 C lower than that reported by Ramakrishnan et al. [40]. However, they implemented a PCM composite in the walls and floor of a test enclosure with a comparable inner volume of 1130  725  690 mm , and a double-glazed window. The thermal simulations showed to be very sensitive to the air renewal rate, keeping this value equal to 5 renewals/h, since lower values gave rise to very high average temperatures inside the enclosure, and higher renovations diminish the e ect of the mPCM incorporated in gypsum boards. In general, the proposed experiment can be used to evaluate materials modified with PCMs under current climatic conditions, but the numerical results suggest infiltration rate should be a parameter to be measured or controlled in future experiments. Buildings 2020, 10, 15 16 of 18 5. Conclusions In the present work, gypsum boards modified with a paranic mPCM (20 wt%) were prepared, producing construction elements with higher thermal storage capacity that were implemented in a test enclosure in the period between 16 September and 12 November. In general, the obtained results of the thermal characterization are coherent, and allow capturing the behavior and e ect of latent heat storage of the components analyzed in a computer simulation using EnergyPlus—. Two test enclosures with an interior volume of 0.512 m are built using sandwich-type refrigeration panels to construct the walls and base of the enclosures. The envelope of the walls and floor of the enclosures provide high thermal resistance, thus achieving that the heat flux during the experiments flows mainly through the roofing of the test enclosures. This feature was sought, given the need to use this assembly to characterize the thermal behavior of materials modified with PCMs under actual weather conditions. However, the increase of the interior temperature above the outside can be considered an unwished situation during warmer days. In general, the experimental results show that using a mPCM with melting temperature range of 26.5 C to 29.2 C in a climate such as that of Santiago de Chile, allows to decrease and increase the maximum and minimum temperatures respectively, this if the material manages to charge and discharge thermally during the day. In addition, the e ect of the displacement of thermal loads becomes more noticeable as the days get hotter. The proposed thermal model with a capacitor element to estimate the heat fluxes through the placed gypsum boards allows obtaining values and a behavior coherent with that predicted by computer simulations, which enable this methodology to be used to determine the heat flux through and stored on the surface of interest. The computer simulations carried out employing the EnergyPlus— allowed to predict the thermal behavior of the test enclosure approximately. However, the numerical results were not contrasted with the experimental ones, given the moderate behavior of the environmental temperatures of the weather file available for Santiago de Chile compared to the temperatures measured in situ during the experiments carried out between September and November. The numerical results fail to capture this behavior during the same period experimentally analyzed since the temperatures of the weather archive used in the simulations are more moderate. The computer simulation carried out in a warmer period (2–15 February) predicts that the incorporation of the mPCM in the gypsum boards reduces the maximum average temperature reached in the enclosure by no more than 1.5 C. The simulations showed to be very sensitive to the air renewal rate, keeping this value equal to 5 renewals/h, since lower values generated interior temperature values significantly higher than the measured ones, and higher renovations diminish the e ect of the mPCM incorporated in gypsum boards. In general, the proposed experiment can be used to evaluate materials modified with PCMs under current climatic conditions, but the numerical results suggest that the enclosure should not be manufactured by minimizing infiltrations, but the infiltration rate should be a parameter to be measured or controlled in future experiments. Author Contributions: Conceptualization, D.A.V. and F.S.; methodology, E.C., A.Á., and J.P.B.; software, T.V.; validation, T.V. and D.A.V.; formal analysis, D.A.V. and T.V.; data curation, D.A.V.; writing—original draft preparation, D.A.V.; writing—review and editing, F.S., T.V., and C.B.; supervision, D.A.V., F.S., and C.B.; project administration, D.A.V. and F.S.; funding acquisition, D.A.V. and F.S. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Conicyt/Fondecyt, grant number 11130168 and by Usach/Dicyt, grant number 091816SP. Conflicts of Interest: The authors declare no conflict of interest. References 1. LIBRO-ENERGIA-2050-WEB. Available online: http://www.minenergia.cl/archivos_bajar/LIBRO-ENERGIA- 2050-WEB.pdf (accessed on 1 November 2019). Buildings 2020, 10, 15 17 of 18 2. Dincer, I. On thermal energy storage systems and applications in buildings. Energy Build. 2002, 34, 377–388. [CrossRef] 3. EMIRI. 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A study of wind and buoyancy driven flows through commercial wind towers. Energy Build. 2011, 43, 1784–1791. [CrossRef] 15. Hughes, B.R.; Calautit, J.K.; Ghani, S.A. The development of commercial wind towers for natural ventilation: A review. Appl. Energy 2012, 92, 606–627. [CrossRef] 16. Marin, P.; Sa ari, M.; de Gracia, A.; Zhu, X.; Farid, M.M.; Cabeza, L.F.; Ushak, S. Energy savings due to the use of PCM for relocatable lightweight buildings passive heating and cooling in di erent weather conditions. Energy Build. 2016, 129, 274–283. [CrossRef] 17. Madad, A.; Mouhib, T.; Mouhsen, A. Phase Change Materials for Building Applications. Buildings 2018, 42, 1361–1368. 18. Pomianowski, M.; Heiselberg, P.; Zhang, Y. Review of thermal energy storage technologies based on PCM application in buildings. Energy Build. 2013, 67, 56–69. [CrossRef] 19. Bland, A.; Khzouz, M.; Statheros, T.; Gkanas, E.I. PCMs for residential building applications: A short review focused on disadvantages and proposals for future development. Buildings 2017, 7, 78. [CrossRef] 20. Zhao, C.Y.; Zhang, G.H. Review on microencapsulated phase change materials (MEPCMs): Fabrication, characterization and applications. Renew. Sustain. Energy Rev. 2011, 15, 3813–3832. [CrossRef] 21. Li, W.; Zhang, X.; Wang, X.; Tang, G.; Shi, H. Fabrication and morphological characterization of microencapsulated phase change materials (MicroPCMs) and macrocapsules containing MicroPCMs for thermal energy storage. Energy 2012, 38, 249–254. [CrossRef] 22. Jamekhorshid, A.; Sadrameli, S.M.; Farid, M. A review of microencapsulation methods of phase change materials (PCMs) as a thermal energy storage (TES) medium. Renew. Sustain. Energy Rev. 2014, 31, 531–542. [CrossRef] 23. Barreneche, C.; Navarro, M.E.; Fernández, A.I.; Cabeza, L.F. Improvement of the thermal inertia of building materials incorporating PCM. Evaluation in the macroscale. Appl. Energy 2013, 109, 428–432. [CrossRef] 24. Zhou, G.; Zhang, Y.; Wang, X.; Lin, K.; Xiao, W. An assessment of mixed type PCM-gypsum and shape-stabilized PCM plates in a building for passive solar heating. Sol. Energy 2007, 81, 1351–1360. [CrossRef] 25. Lachheb, M.; Younsi, Z.; Naji, H.; Karkri, M.; Nasrallah, S. Thermal behavior of a hybrid PCM/plaster: A numerical and experimental investigation. Appl. Therm. Eng. 2017, 111, 49–59. [CrossRef] Buildings 2020, 10, 15 18 of 18 26. Li, C.; Hang, Y.; Song, Y. Experimental investigation of thermal performance of microencapsulate d PCM-containe d wallboard by two measurement modes. Energy Build. 2019, 184, 34–43. [CrossRef] 27. Cabeza, L.F.; Castellón, C.; Nogués, M.; Medrano, M.; Leppers, R.; Zubillaga, O. Use of microencapsulated PCM in concrete walls for energy savings. Energy Build. 2007, 39, 113–119. [CrossRef] 28. Arce, P.; Castellón, C.; Castell, A.; Cabeza, L.F. Use of microencapsulated PCM in buildings and the e ect of adding awnings. Energy Build. 2012, 44, 88–93. [CrossRef] 29. Zhu, N.; Li, S.; Hu, P.; Wei, S.; Deng, R.; Lei, F. A review on applications of shape-stabilized phase change materials embedded in building enclosure in recent ten years. Sustain. Cities Soc. 2018, 43, 251–264. [CrossRef] 30. Kheradmand, M.; Azenha, M.; de Aguiar, J.L.B.; Castro-Gomes, J. Experimental and numerical studies of hybrid PCM embedded in plastering mortar for enhanced thermal behaviour of buildings. Energy 2016, 94, 250–261. [CrossRef] 31. Berardi, U.; Soudian, S. Experimental investigation of latent heat thermal energy storage using PCMs with di erent melting temperatures for building retrofit. Energy Build. 2019, 185, 180–195. [CrossRef] 32. Berardi, U.; Soudian, S. Benefits of latent thermal energy storage in the retrofit of Canadian high-rise residential buildings. Build. Simul. 2018, 11, 709–723. [CrossRef] 33. Kalnæs, S.E.; Jelle, B.P. Phase change materials and products for building applications: A state-of-the-art review and future research opportunities. Energy Build. 2015, 94, 150–176. [CrossRef] 34. Piselli, C.; Castaldo, V.L.; Pisello, A.L. How to enhance thermal energy storage e ect of PCM in roofs with varying solar reflectance: Experimental and numerical assessment of a new roof system for passive cooling in di erent climate conditions. Sol. Energy 2018, 192, 106–119. [CrossRef] 35. Pasupathy, A.; Velraj, R. E ect of double layer phase change material in building roof for year round thermal management. Energy Build. 2008, 40, 193–203. [CrossRef] 36. Bamonte, P.; Caverzan, A.; Kalaba, N.; Lamperti Tornaghi, M. Lightweight concrete containing phase change materials (PCMs): A numerical investigation on the thermal behaviour of cladding panels. Buildings 2017, 7, 35. [CrossRef] 37. Jaworski, M. Thermal performance of building element containing phase change material (PCM) integrated with ventilation system—An experimental study. Appl. Therm. Eng. 2014, 70, 665–674. [CrossRef] 38. Sa ari, M.; Piselli, C.; de Gracia, A.; Pisello, A.L.; Cotana, F.; Cabeza, L.F. Thermal stress reduction in cool roof membranes using phase change materials (PCM). Energy Build. 2018, 158, 1097–1105. [CrossRef] 39. Cornaro, C.; Pierro, M.; Puggioni, V.A.; Roncarati, D. Outdoor characterization of phase change materials and Assessment of their energy saving potential to reach NZEB. Buildings 2017, 7, 55. [CrossRef] 40. Ramakrishnan, S.; Sanjayan, J.; Wang, X. Experimental research on using form-stable PCM-integrated cementitious composite for reducing overheating in buildings. Buildings 2019, 9, 57. [CrossRef] 41. Del Barrio, E.P.; Dauvergne, J.L. A non-parametric method for estimating enthalpy-temperature functions of shape-stabilized phase change materials. Int. J. Heat Mass Transf. 2011, 54, 1268–1277. [CrossRef] 42. Mikrocaps. Available online: https://www.mikrocaps.com/ (accessed on 20 December 2019). 43. Weather Data by Location: Santiago de Chile. Available online: https://energyplus.net/weather-location/ south_america_wmo_region_3/CHL//CHL_Santiago.855740_IWEC (accessed on 20 December 2019). © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Buildings Multidisciplinary Digital Publishing Institute

Experimental and Computational Study of the Implementation of mPCM-Modified Gypsum Boards in a Test Enclosure

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buildings Article Experimental and Computational Study of the Implementation of mPCM-Modified Gypsum Boards in a Test Enclosure 1 1 1 1 Juan Pablo Bravo , Tomás Venegas , Elizabeth Correa , Alejandro Álamos , 1 1 , 2 Francisco Sepúlveda , Diego A. Vasco * and Camila Barreneche Departamento de Ingeniería Mecánica, Universidad de Santiago de Chile, Av. Lib. Bernardo O’Higgins 3363, Santiago 9170002, Chile; jpbravod@gmail.com (J.P.B.); tomasvenegast@gmail.com (T.V.); elizabeth.correag@usach.cl (E.C.); alejandro.alamos@usach.cl (A.Á.); francisco.sepulveda.p@usach.cl (F.S) Departament de Ciència del Materials i Enginyeria Metallúrgica, Universitat de Barcelona, Martí i Franquès 1–22, 08028 Barcelona, Spain; c.barreneche@ub.edu * Correspondence: diego.vascoc@usach.cl; Tel.: +56-(0)2-2718-3120 Received: 7 November 2019; Accepted: 13 January 2020; Published: 19 January 2020 Abstract: The application of phase change materials (PCM) in the thermal envelope of buildings has proven to be an alternative to reduce energy consumption and to improve thermal comfort conditions. The present work evaluates the thermal behavior of gypsum boards modified with a microencapsulated PCM (mPCM) in a cubic test enclosure, considering the climatic conditions of Santiago de Chile in the September–November period of 2017. The design of the test enclosure was performed considering the minimization of parameters that a ect the variation of its inner temperature and favoring the heat flow through the gypsum boards. Experimentally, the results reflect the main e ects of the implementation of a mPCM, among which the displacement of the maximum heat load and the decrease in the daily oscillation of the internal temperature of the test enclosure (up to 2 C) stand out. In addition, the mPCM modified gypsum board was thermally characterized to carry out a thermal simulation of the enclosures using EnergyPlus—. The obtained numerical results agree with those obtained experimentally, including the behavior of the transient heat flux through the gypsum boards. Moreover, it was found that considering a null infiltration rate gives place to unrealistic results, suggesting that this parameter should be controlled. Keywords: microencapsulated PCM; gypsum board; test enclosure; thermal simulation 1. Introduction Among the commitments of the energy policy of Chile for 2035 are to reduce CO emissions by 30% regarding to 2007, and the ensuring of continuous and quality access to energy for dwellings of vulnerable families [1]. Energy may be stored as chemical, electric, kinetic, potential, or thermal [2]. Among the many existing technological options to increase energy eciency in buildings, it has been recommended to put attention to Thermal Energy Storage (TES) [3]. Thermal energy storage systems use energy density of materials or latent heat associated with a phase transition to provide a heating or cooling source [4]. Phase change materials (PCMs) have been used increasingly as Latent Heat Thermal Energy Storage (LHTES) systems for heating and cooling applications. LHTES is considered a passive method of heat modulation, where PCMs can absorb heat from the environment and release it indoors when required [5,6]. The integration of LHTES in buildings can be done using their floor, walls, ceilings, and external solar facades [7]. The process of charging and discharging thermal energy from and to a PCM depends on the thermal oscillations of the environment. Thus, the phase change temperature is the main characteristic Buildings 2020, 10, 15; doi:10.3390/buildings10010015 www.mdpi.com/journal/buildings Buildings 2020, 10, 15 2 of 18 that allows to di erentiate each PCM and therefore to choose the most appropriate for an application. PCMs are commonly classified as inorganic, eutectic mixtures, and organic (O-PCMs) [8]. Among O-PCMs, there are di erent substances such as parans, fatty acids, fatty acid esters, long-chain alcohols, polyglycols, and their mixtures [9,10]. Thanks to their properties, O-PCMs can be used in applications near human comfort temperature, moreover, O-PCMs are chemically and physically stable, and they are less prone to subcooling than inorganic PCMs [11]. One of the main applications of O-PCMs is the increase of thermal inertia of building materials, which gives place to decreasing inner temperature fluctuations, shifting heat load peaks, and reducing the energy consumption of buildings associated with air conditioning [12–15]. Therefore, O-PCMs work exceptionally well on buildings of low thermal mass [16], where temperatures change abruptly, giving place to high energy consumption associated with thermally conditioning the building. The results of several investigations have proven that a proper design is necessary to take advantage of the capabilities of PCMs like the reduction of energy consumption, and the improvement of thermal comfort in buildings [17]. In a passive strategy, the integration of PCMs into building materials allows releasing of heat during the colder hours, beginning the solidification process. During the warmer hours, the melting process of PCM gives place to heat absorption. The integration of O-PCMs into lightweight building materials increases their energy density or volumetric heat capacity. Typical building materials such as gypsum plaster store up to 1 kJ/(kg K) as sensible heat, whereas average paran materials store energy as latent heat of approximately 100 kJ/kg [18]. There are some reported limitations in using PCMs in building materials [19]: (i) PCMs may interact with the building structure; (ii) leakage of PCMs; (iii) PCMs have low thermal conductivities. In order to overcome these issues, microencapsulated phase change materials (mPCM) have been integrated into building materials such as gypsum plaster, concrete, and mortar [20]. There are currently several forms of PCM encapsulation. Generally, the PCM is incorporated into a polymer matrix and depending on the final size of the encapsulated material is classified as nano-encapsulated (p < 1 m), micro-encapsulated (1 m < p < 1 mm) for particles, and macro-encapsulation (p > 1 mm) [21]. There are several processes to micro-encapsulate PCMs, A. Jamekhorshid et al. [22] propose to classify encapsulation methods in physical, physicochemical, and chemical procedures. Barreneche et al. [23] characterized the e ective thermal conductivity and the thermal inertia of gypsum and Portland cement modified with a mPCM (5 wt% and 15 wt%) by using two di erent apparatuses. The authors found that the addition of mPCM causes a reduction (25–35%) of the thermal conductivity of both building materials. Moreover, a 15 wt% load of mPCM causes a higher increase of the thermal inertia of gypsum boards. Zhou et al. [24] performed numerical simulations of the thermal performance of shape-stabilized PCM (melting point of 21 C) plates integrated into the inner surfaces of walls and the ceiling of a passive house located in Beijing, China, during winter. The results showed that shape-stabilized PCM gypsum plates can diminish the indoor temperature variation by up to 56%. Lachheb et al. [25] experimentally characterized a plaster composite incorporating 10% of microencapsulated paran (Micronal , BASF Company, Dayton, USA) by the guarded hot plate method. Moreover, the authors made a parametric study to analyze the e ect of the wallboard thickness (1–3 cm), and the mass fraction (0–30%) of mPCM. The obtained results show that there are no essential di erences in the inner surface temperature variation for mPCM mass fractions of 20% and 30%. Li et al. [26] characterized the thermal properties (thermal conductivity, apparent heat capacity and enthalpy) as function of temperature of a mPCM-gypsum wall board composite (20%). The authors found that thermal conductivity increases linearly with temperature, the apparent specific heat capacity of the composite is 2.71 times larger than that of gypsum wallboard. Regarding the enthalpy, the authors found that an appropriate heating rate, according to the application, is necessary. In 2007, Cabeza et al. [27] performed experiments with concrete cubicles (2 m 2 m 3 m) located in Lleida (Spain) with and without windows to analyze the e ect of the incorporation (5 wt%) of a commercial mPCM (melting point of 26.8 C) into the south, west, and roof walls. The measured temperature values during spring days showed that the south wall of the cubicle without mPCM at Buildings 2020, 10, 15 3 of 18 midday is 2 C higher than that of the cubicle with PCM. Arce et al. [28] mention that a PCM should complete the phase change cycle to work correctly. Then, it is a problem that during the colder winter days and warmer summer day, the PCM might not reach its melting and solidification temperature, respectively. In 2018, Zhu et al. [29] made a review about experimental and numerical applications with shape stabilized PCMs into building envelope components. This review work identified several factors that a ect the performance of a PCM, including its melting temperature, location and orientation of the building, and weather conditions. There is a trend of using hybrid composites with di erent melting points to be used during the colder and warmer seasons of the year. Kheradmand et al. [30] experimentally and numerically (Ansys-Fluent) evaluated a hybrid PCM plastering mortar in a test cell of reduced dimensions submitted to simulated weather conditions. The authors found that the use of three PCMs of di erent suitable melting points reduces heating and cooling temperature demands. Berardi and Soudian [31] implemented a composite of two macroencapsulated PCMs with melting temperatures of 21.7 C (Energain) and 25 C (BioPCM—) in the walls and the ceiling of a test cell, which resembles apartments with 80% window to wall ratio located in Toronto (Canada). The studies performed during one-year show that the hybrid PCM system reduce the temperature fluctuations during fall and summer. Previously, the same authors [32] made a parametric analysis of an apartment with the same hybrid composite and window to wall ratio by using Energyplus— showing promising results in two di erent climates (Toronto and Vancouver). In the review of Kalnæs and Jelle [33] about PCMs and their application in buildings, the authors mentioned that there are few studies on the e ects of PCMs in roofing. Moreover, the authors claimed that the use of PCMs on the roof would absorb the incoming solar radiation and heat from the surroundings reducing the inner temperature fluctuations. Piselli et al. [34] found that the inclusion of PCM in waterproof membranes improves the thermal performance of roofs under climatic conditions in the cities of Rome (Italy) and Abu Dhabi (UAE). Pasupathy and Velraj [35] made a study about the thermal performance of double layer PCM in the roof of a building located in Chennai (India). In order to reduce the inner temperature fluctuation, the authors recommended a double layer PCM with di erent melting points of 27 C and 32 C. Bamonte et al. [36] performed a numerical study, using the finite volume method, of concrete panels with aggregates containing PCMs (capric acid and glycerine) under temperature conditions of Bucharest (Romania) and Seville (Spain). The authors claimed that the implementation of these PCMs may reduce the energy consumption for cooling and heating by up to 20% and 10%, respectively. Jaworski [37] studied the thermal performance of mPCM-plaster ceiling panels with air ducts that works as a heat exchanger. The system was used in an oce building to improve the free cooling strategy. Sa ari et al. [38] studied the cool roof strategy to mitigate the e ect of urban heat island. Their results showed that PCMs with higher melting point are more suitable for reducing thermal loads in summer. Cornaro et al. [39] implemented a commercial PCM panel (RUBITHERM ) on the floor of a test enclosure under the weather conditions of Rome (Italy). The authors used the experimental results to validate a tool implemented in Indoor Climate and Energy software. The numerical results obtained for three di erent locations showed that only the energy savings using PCM and implementing night ventilation meet the Italian energy performance regulation. Ramakrishnan et al. [40] implemented a PCM stabilized cement mortar (FS-PCM) in the envelopes of a test box, comparing its thermal behavior with similar test boxes built on cement plasterboard (OCB) and gypsum plasterboard (GPB). The experimental results showed that the implementation of FS-PCM reduced the peak temperature by up to 2.4 C, compared to GPB and OCB test boxes. In the present work, the temperature variation inside a cubic test enclosure containing gypsum boards modified with a mPCM in the roof is recorded experimentally (September–November 2017). In addition, the behavior of the heat flux across the gypsum boards with and without mPCM is determined, being able to observe more clearly the displacement of the heat load. Gypsum boards modified with mPCM are thermally characterized, determining thermal conductivity, heat capacity, Buildings 2020, 10, 15 4 of 18 determined, being able to observe more clearly the displacement of the heat load. Gypsum boards modified with mPCM are thermally characterized, determining thermal conductivity, heat capacity, Buildings 2020, 10, 15 4 of 18 and enthalpy according to the temperature. These properties were incorporated into a thermally simulated physical model with EnergyPlus™. Numerical results also include the variation of the and enthalpy according to the temperature. These properties were incorporated into a thermally inner temperature of the enclosure in a period of moderate and warm temperatures in Santiago de simulated physical model with EnergyPlus—. Numerical results also include the variation of the inner Chile, as well as heat fluxes through the plates. In general, the numerical results show a behavior like temperature of the enclosure in a period of moderate and warm temperatures in Santiago de Chile, those recorded experimentally. as well as heat fluxes through the plates. In general, the numerical results show a behavior like those r 2. ecor Ma ded terials experimentally and Methods . This section describes the experimental procedures for the preparation of gypsum samples 2. Materials and Methods modified with mPCM, the determination of their thermophysical properties, and the experimental This section describes the experimental procedures for the preparation of gypsum samples assembly performed to study the behavior of gypsum boards modified with mPCM in a test modified with mPCM, the determination of their thermophysical properties, and the experimental enclosure. To manufacture the modified gypsum boards, the gypsum plaster (TOPEX ) and mPCM assembly performed to study the behavior of gypsum boards modified with mPCM in a test enclosure. (MikroCaps 28), whose properties are shown in Table 1, are poured into a container according to the To manufacture the modified gypsum boards, the gypsum plaster (TOPEX ) and mPCM (MikroCaps analyzed mass concentration (20 wt%). Initially, a lower mass concentration of 10 wt% was 28), whose properties are shown in Table 1, are poured into a container according to the analyzed considered but given its low enthalpy its use was discarded. Moreover, the obtained gypsum boards mass concentration (20 wt%). Initially, a lower mass concentration of 10 wt% was considered but of higher mass concentration (30 wt%) presented a poor mechanical stability, which prevented its given its low enthalpy its use was discarded. Moreover, the obtained gypsum boards of higher mass use in the test enclosure. Subsequently, this dry mixture is homogenized to then, add the amount of concentration (30 wt%) presented a poor mechanical stability, which prevented its use in the test distilled water required and obtain the mass proportion Plaster/water = 0.7. Finally, the wet mixture enclosure. Subsequently, this dry mixture is homogenized to then, add the amount of distilled water is blended until it acquires a slightly viscous consistency and is poured into melamine molds of 35 required and obtain the mass proportion Plaster/water = 0.7. Finally, the wet mixture is blended until [cm ] and 1 [cm] thick. The wet mixture is dried for one day at ambient temperature, then the it acquires a slightly viscous consistency and is poured into melamine molds of 35 [cm ] and 1 [cm] wooden mold is removed, and the plates are placed in an oven (Heraeus T 6120) at 30 °C for four thick. The wet mixture is dried for one day at ambient temperature, then the wooden mold is removed, days. and the plates are placed in an oven (Heraeus T 6120) at 30 C for four days. The gypsum samples for the characterization of the thermophysical properties are of different The gypsum samples for the characterization of the thermophysical properties are of di erent geometry and dimensions due to the requirements of the equipment used, so these were obtained by geometry and dimensions due to the requirements of the equipment used, so these were obtained pouring the wet mixtures into PVC molds of 3.6 mm in diameter and 8 cm high. Figure 1 shows SEM by pouring the wet mixtures into PVC molds of 3.6 mm in diameter and 8 cm high. Figure 1 shows images (Jeol, JSM 5410) of the gypsum samples modified with mPCM can be seen, where the SEM images (Jeol, JSM 5410) of the gypsum samples modified with mPCM can be seen, where the formation of microcapsule agglomerates between the plaster crystals is evident, therefore the final formation of microcapsule agglomerates between the plaster crystals is evident, therefore the final modified gypsum boards are not homogenous. The measurement of the thermal conductivity and modified gypsum boards are not homogenous. The measurement of the thermal conductivity and the the thermal diffusivity of the samples has been made by the thermal properties analyzer KD2-Pro thermal di usivity of the samples has been made by the thermal properties analyzer KD2-Pro (Decagon (Decagon devices) using the dual needle probe (sh1). The measurements were made in triplicate devices) using the dual needle probe (sh1). The measurements were made in triplicate controlling the controlling the temperature (±0.1 °C) in the range from 0 °C to 40 °C. In addition, a differential temperature (0.1 C) in the range from 0 C to 40 C. In addition, a di erential scanning calorimeter scanning calorimeter DSC 4000 (PerkinElmer) has been used to obtain the enthalpy (2% error) DSC 4000 (PerkinElmer) has been used to obtain the enthalpy (2% error) according to the temperature according to the temperature (±0.1 °C), which is fundamental to model the thermal behavior of (0.1 C), which is fundamental to model the thermal behavior of phase change materials correctly. phase change materials correctly. One collected three different samples from the modified gypsum One collected three di erent samples from the modified gypsum boards, and the obtained DSC results boards, and the obtained DSC results were quite similar between samples with percentage were quite similar between samples with percentage di erences lower than 0.2%. differences lower than 0.2%. a b Figure 1. Microstructure of the fracture surface of gypsum plaster samples modified with Figure 1. Microstructure of the fracture surface of gypsum plaster samples modified with microencapsulated phase change materials (mPCM): (a) ×100 and (b) ×500. microencapsulated phase change materials (mPCM): (a)100 and (b)500. Buildings 2020, 10, 15 5 of 18 Figure 2 shows the obtained results of thermal conductivity and thermal diffusivity. These results show a decreasing tendency of both properties with temperature when the PCM is in solid state (<25 °C). The enthalpy as a function of temperature was estimated from the DSC measurements according to equations available in the literature [41]. The enthalpy of mPCM-modified plaster with the implemented weight fraction is shown in Figure 3. Table 1. mPCM (MicroKaps 28) technical information supplied by the manufacturer [42]. PCM content in dry capsule 75–80% Heat storage capacity 184–196 [J/kg] Melting range 25–29 [°C] Bulk Density 200–350 [g/l] Average particles size 70–150 [μm] Wall thickness ~200 [nm] Type of membrane Melamine-formaldehyde Type pf PCM Paraffin wax Experimental Set-Up The experimental set-up consists of two cubicles of 0.512 m in volume, one with three gypsum boards modified with mPCM and the other with three not modified gypsum boards as control (Figure 4). The walls and base of the enclosures are composed of 1 m sandwich-type refrigeration panels, made of expanded polystyrene (100 mm thick) coated by galvanized steel on both sides. This material has a U value of 0.364 W/m K, as obtained by the calculation procedure according to NCh 853. Of.91. Pre-painted metallic profiles of the same type of steel were used to assemble the enclosures, as wells as sanitary profiles finished in PVC, and as fasteners, Philips stainless steel self-drilling screws and countersunk screws were used. The roofing is made of a zinc plate, structural plywood, calcium silicate board as a thermal insulator, and three gypsum boards with and without mPCM according to the different study configurations. A metal grid is used to affix the gypsum boards. In addition, synthetic rubber bands are employed to reduce air infiltration (Figure 5). Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of the modified boards, a fraction of 20 wt% of mPCM. In Figure 6, a diagram of both test enclosures indoors can be observed; these were installed on Buildings 2020, 10, 15 5 of 18 the roof of the Department of Mechanical Engineering of the University of Santiago, where they were subjected to the same weather, atmospheric conditions and were kept at a reasonable distance Figure 2 shows the obtained results of thermal conductivity and thermal di usivity. These results so they would not affect each other. Another important feature of the installation is that test show a decreasing tendency of both properties with temperature when the PCM is in solid state enclosures were separated from the “floor” using platforms of approximately 30 cm high, to avoid (<25 C). The enthalpy as a function of temperature was estimated from the DSC measurements any effect of the enclosure on which the experimental installation was performed (Figure 4b). The according to equations available in the literature [41]. The enthalpy of mPCM-modified plaster with design of the test enclosures points to the minimization of heat gains or losses through walls and the implemented weight fraction is shown in Figure 3. floor, favoring the heat flow through the ceiling where the plaster boards are located. Figure 2. Figure 2. Thermal conductivity and th Thermal conductivity and thermal ermal diffusiv di usivity ity of of mPCM-modified pla mPCM-modified plaster ster (20 (20 wt%). wt%). Table 1. mPCM (MicroKaps 28) technical information supplied by the manufacturer [42]. PCM content in dry capsule 75–80% Heat storage capacity 184–196 [J/kg] Melting range 25–29 [ C] Bulk Density 200–350 [g/l] Average particles size 70–150 [m] Wall thickness ~200 [nm] Type of membrane Melamine-formaldehyde Type pf PCM Paran wax Buildings 2020, 10, 15 6 of 18 Figure 3. Heat flux (segmented line) and obtained from di erential scanning calorimeter (DSC) Figure 3. Heat flux (segmented line) and obtained from differential scanning calorimeter (DSC) measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). Experimental Set-Up The experimental set-up consists of two cubicles of 0.512 m in volume, one with three gypsum boards modified with mPCM and the other with three not modified gypsum boards as control (Figure 4). The walls and base of the enclosures are composed of 1 m sandwich-type refrigeration panels, made of Figure 4. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Figure 5. Support structure of the gypsum boards. Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of modified plates, a fraction of 20 wt% of mPCM. The temperatures were recorded in four positions in each test enclosure: on the lower internal base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, and the temperature of the air just below of the gypsum board. The measurements were made during the spring season (September–November) of 2017 in the premises of the Department of Mechanical Engineering of the University of Santiago de Chile (33° 26 ʹ47.401 “S, 70° 40ʹ 53.311” W). The data acquisition system is a seven-channel temperature measurement system prototype whose main features are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim Integrated Products), (iii) processing and communication through Arduino UNO (Arduino), (iv) Buildings 2020, 10, 15 6 of 18 Buildings 2020, 10, 15 6 of 18 Buildings 2020, 10, 15 6 of 18 expanded polystyrene (100 mm thick) coated by galvanized steel on both sides. This material has a U Figure 3. Heat flux (segmented line) and obtained from differential scanning calorimeter (DSC) value of 0.364 W/m K, as obtained by the calculation procedure according to NCh 853. Of.91. measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). Figure 3. Heat flux (segmented line) and obtained from differential scanning calorimeter (DSC) measurement calculated enthalpy (continuous line) [41] of mPCM-modified plaster (20%). Figure 4. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Figure 4. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Pre-painted metallic profiles of the same type of steel were used to assemble the enclosures, as wells as sanitary profiles finished in PVC, and as fasteners, Philips stainless steel self-drilling screws and countersunk screws were used. The roofing is made of a zinc plate, structural plywood, calcium silicate board as a thermal insulator, and three gypsum boards with and without mPCM according to the di erent study configurations. A metal grid is used to ax the gypsum boards. In addition, synthetic rubber bands are employed to reduce air infiltration (Figure 5). Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of the modified boards, a fraction of 20 wt% ofFigure 4. mPCM. (a) Test enclosures of refrigeration panels (b) and installation of test enclosures. Figure 5. Support structure of the gypsum boards. Each of the three gypsum boards has an area of 35 cm , a thickness of 1 cm, and, in the case of modified plates, a fraction of 20 wt% of mPCM. The temperatures were recorded in four positions in each test enclosure: on the lower internal base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, and the temperature of the air just below of the gypsum board. The measurements were made during the spring season (September–November) of 2017 in the premises of the Department of Mechanical Engineering of the University of Santiago de Chile (33° 26 ʹ47.401 “S, 70° 40ʹ 53.311” W). The data acquisition system is a seven-channel temperature measurement system prototype whose main features are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim Figure 5. Figure 5. Su Support pport stru structur cture of the g e of the gypsum ypsum boards. boards. Each of Each of the three gypsum boards has a the three gypsum boards has an n area of 35 area of 35 Integrat cm ed Pr , a thickness oductsof ), (i 1 cm, ii) processin and, in thegcase and ofcommun modifiediplates, cation atfraction hrough ofArd 20 wt% uinoof U mPCM. NO (Arduino), (iv) cm , a thickness of 1 cm, and, in the case of modified plates, a fraction of 20 wt% of mPCM. In Figure 6, a diagram of both test enclosures indoors can be observed; these were installed on The temperatures were recorded in four positions in each test enclosure: on the lower internal the roof of the Department of Mechanical Engineering of the University of Santiago, where they were base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, subjected to the same weather, atmospheric conditions and were kept at a reasonable distance so they and the temperature of the air just below of the gypsum board. The measurements were made would not a ect each other. Another important feature of the installation is that test enclosures were during the spring season (September–November) of 2017 in the premises of the Department of separated from the “floor” using platforms of approximately 30 cm high, to avoid any e ect of the Mechanical Engineering of the University of Santiago de Chile (33° 26 ʹ47.401 “S, 70° 40ʹ 53.311” W). enclosure on which the experimental installation was performed (Figure 4b). The design of the test The data acquisition system is a seven-channel temperature measurement system prototype whose enclosures points to the minimization of heat gains or losses through walls and floor, favoring the heat main features are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim flow through the ceiling where the plaster boards are located. Integrated Products), (iii) processing and communication through Arduino UNO (Arduino), (iv) The temperatures were recorded in four positions in each test enclosure: on the lower internal base, on the surface of the gypsum board in contact with the air, on the outer surface of the roofing, and the temperature of the air just below of the gypsum board. The measurements were made during the spring season (September–November) of 2017 in the premises of the Department of Mechanical 0  0 Engineering of the University of Santiago de Chile (33 26 47.401 “S, 70 40 53.311” W). The data acquisition system is a seven-channel temperature measurement system prototype whose main features Buildings 2020, 10, 15 7 of 18 are: (i) K-type thermocouples, (ii) MAX31855 analog signal converter (Maxim Integrated Products), Buildings 2020, 10, 15 7 of 18 (iii) processing and communication through Arduino UNO (Arduino), (iv) user control interface by Buildings 2020, 10, 15 7 of 18 LabVIEW (National Instruments). The sampling ratio was every 10 min, and the sensitivity of the user control interface by LabVIEW (National Instruments). The sampling ratio was every 10 min, temperatures reading was0.1 C. and the sensitivity of the temperatures reading was ±0.1 °C. user control interface by LabVIEW (National Instruments). The sampling ratio was every 10 min, and the sensitivity of the temperatures reading was ±0.1 °C. Figure 6. Diagram of the test enclosures. 1. Galvanized steel plate, 2. Plywood, 3. Internal air volume, Figure 6. Diagram of the test enclosures. 1. Galvanized steel plate, 2. Plywood, 3. Internal air volume, Figure 4. Pla 6.ster Diagram boards, of 5.the Calciu testm enclosur silicate board es. 1. s Galvanized , 6. Cold room steel board plate, s, 7 2. . G Plywood, rillage, 8. 3. Synthetic Internal ru air bber volume, 4. Plaster boards, 5. Calcium silicate boards, 6. Cold room boards, 7. Grillage, 8. Synthetic rubber 4. Plaster tapes. boards, 5. Calcium silicate boards, 6. Cold room boards, 7. Grillage, 8. Synthetic rubber tapes. tapes. 3. Results 3. Results 3. Results 3.1. 3.Experimental 1. Experimental Measur Measure ements ments 3.1. Experimental Measurements An experimental analysis is carried out to study the behavior of the temperatures inside both An experimental analysis is carried out to study the behavior of the temperatures inside both experimental set-up during three periods corresponding to the southern spring in Santiago de Chile experimental set-up during three periods corresponding to the southern spring in Santiago de Chile An experimental analysis is carried out to study the behavior of the temperatures inside both (Csb): (a) 16–30 September, (b) 12–26 October, and (c) 29 October–12 November. The average (Csb): (a) 16–30 September, (b) 12–26 October, and (c) 29 October–12 November. The average outdoor experimental set-up during three periods corresponding to the southern spring in Santiago de Chile outdoor temperature and the mode in each analyzed period are (a) 16.3 °C and 13.7 °C, (b) 17.6 °C temperature and the mode in each analyzed period are (a) 16.3 C and 13.7 C, (b) 17.6 C and 16.5 C, (Csb): (a) 16–30 September, (b) 12–26 October, and (c) 29 October–12 November. The average and 16.5 °C, and (c) 18.3 °C and 15.8 °C, respectively. Figures 7–9 show the behavior of the internal and (c) 18.3 C and 15.8 C, respectively. Figures 7–9 show the behavior of the internal and external outdoor temperature and the mode in each analyzed period are (a) 16.3 °C and 13.7 °C, (b) 17.6 °C and external temperature of the test enclosure without and with gypsum boards modified with temperature of the test enclosure without and with gypsum boards modified with mPCM for periods and mPCM for pe 16.5 °C, and (c riods ) 18 (a .3 ), ° (b), C and and (c 15 ). .8 More °C, resp over, it ect can b ively. e seen det Figuresa 7 il– s about 9 show t the ef he b fect eha of mPCM vior of ton t he h int e ernal (a), (b), and (c). Moreover, it can be seen details about the e ect of mPCM on the peak temperatures. peak temperatures. and external temperature of the test enclosure without and with gypsum boards modified with mPCM for periods (a), (b), and (c). Moreover, it can be seen details about the effect of mPCM on the Date peak temperatures. 16/09 17/09 18/09 19/09 20/09 21/09 22/09 23/09 24/09 25/09 26/09 27/09 28/09 29/09 30/09 01/10 Plaster Date MePCM-Plas ter 16/09 17/09 18/09 19/09 20/09 21/09 22/09 23/09 24/09 25/09 26/09 27/09 28/09 29/09 30/09 01/10 Ambient Plaster MePCM-Plas ter Ambient 30 20 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 0 Time (h) Figure 7. Cont. 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 0 Time (h) Temperature (°C) Temperature (°C) Buildings 2020, 10, 15 8 of 18 Buildings 2020, 10, 15 8 of 18 Buildings 2020, 10, 15 8 of 18 bb Figure 7. (a) Average temperatures of the test enclosures during the first period and (b) detail of days Figure 7. (a) Average temperatures of the test enclosures during the first period and (b) detail of days Figure 7. (a) Average temperatures of the test enclosures during the first period and (b) detail of days when there is a decrease in the maximum internal temperature in the enclosure with gypsum boards when there is a decrease in the maximum internal temperature in the enclosure with gypsum boards when there is a decrease in the maximum internal temperature in the enclosure with gypsum boards modified with mPCM. modified with mPCM. modified with mPCM. Date Date 12/10 13/10 14/10 15/10 16/10 17 /10 18 /10 19 /10 20/10 21/10 22/10 23/10 24/10 25/10 26/10 27 /10 12/10 13/10 14/10 15/10 16/10 17 /10 18 /10 19 /10 20/10 21/10 22/10 23/10 24/10 25/10 26/10 27 /10 Plaster Plaster 35 MePCM-Plaster 35 MePCM-Plaster Ambient Ambient 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 Time (h) 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 8 16 0 Time (h) Figure Figure 8. 8. (a( )aA ) verage Average temperatures of temperatures of the te the test st en en closures d closures u during ring the secon the second d perio period d (b,c( ) a b,n cd deta ) and il detail at the end of the period when there is a decrease in the temperature oscillation of the enclosure with at the end of the period when there is a decrease in the temperature oscillation of the enclosure with gypsum boards modified with mPCM. Figure 8. gypsum(a boar ) Av ds erage temperatures of modified with mPCM. the test enclosures during the second period (b,c) and detail at the end of the period when there is a decrease in the temperature oscillation of the enclosure with In the second period of analyzed tests (Figure 8), the effect of the mPCM incorporated in the gypsum boards modified with mPCM. gypsum board is evident for a greater number of days (7). In this period, it is also observed that during the same amount of days the micro-encapsulated phase change material influences the In the second period of analyzed tests (Figure 8), the effect of the mPCM incorporated in the variation of the minimum temperature, finding that, in the case of the enclosure with plates gypsum board is evident for a greater number of days (7). In this period, it is also observed that modified with mPCM, these are lower than in the reference room. It is also interesting to note that at during the same amount of days the micro-encapsulated phase change material influences the the end of this period, the effect of the phase change material is evident in the decrease in the variation of the minimum temperature, finding that, in the case of the enclosure with plates oscillation of the internal temperature of the enclosure. modified with mPCM, these are lower than in the reference room. It is also interesting to note that at the end of this period, the effect of the phase change material is evident in the decrease in the oscillation of the internal temperature of the enclosure. Temperature (°C) Temperature (°C) Buildings 2020, 10, 15 9 of 18 Figure 9 shows the behavior of temperatures during the third period of tests, from 29 October to 12 November. In this period, only three days are observed in which the incorporation of mPCM to the gypsum board is evident. However, the most interesting thing during this period is that there are two days (8 and 11 November) where the average internal temperature in both enclosures is much higher than the outside temperature. This increase can be explained from the rise in the minimum temperature during the previous days, which causes the mPCM not to be able to discharge during the hours of low temperatures. As in the previous period, the effect of the phase change material is more evident in the decrease of the oscillation of the enclosure’s internal temperature. In Figures 10 and 11, the maximum and minimum daily temperatures in both test enclosures are observed, measured in the lower internal base and in the air just below the gypsum board, respectively. In Figure 10, no significant effect of the incorporation of the phase change material is observed due to the condition of the ventilated floor, which is also a common characteristic that can be seen repeatedly in constructions in the Chilean coast. However, the effect of the mPCM is observed in the decrease of the maximum temperature measured in the adjacent air on the gypsum board during the analyzed period (Figure 11), approximately between 1 °C and 4 °C. Regarding the minimum temperature, it is noted that the effect of the mPCM is evidenced only in some days, Buildings 2020, 10, 15 9 of 18 which reflects in a higher minimum temperature, between 1.5 °C and 3.0 °C, specifically at the end of the analyzed period. Date 29/10 30/10 31/10 01/11 02/11 03/11 04/11 05 /11 06/11 07/11 08/11 09/11 10 /11 11/11 12/11 13/11 MePCM-Plaster Plaster Ambient 0 a 08 16 08 16 08 16 08 16 0 8 16 08 16 08 16 08 16 08 16 0 8 16 08 16 08 16 08 16 08 16 0 8 16 0 Time (h) b c Figure 9. (a) Average temperatures of the test enclosures during the third period (b,c) and detail at the Figure 9. (a) Average temperatures of the test enclosures during the third period (b,c) and detail at end of the period when there is a decrease in the temperature oscillation of the enclosure with gypsum the end of the period when there is a decrease in the temperature oscillation of the enclosure with boards modified with mPCM. gypsum boards modified with mPCM. In the second period of analyzed tests (Figure 8), the e ect of the mPCM incorporated in the gypsum board is evident for a greater number of days (7). In this period, it is also observed that during the same amount of days the micro-encapsulated phase change material influences the variation of the minimum temperature, finding that, in the case of the enclosure with plates modified with mPCM, these are lower than in the reference room. It is also interesting to note that at the end of this period, the e ect of the phase change material is evident in the decrease in the oscillation of the internal temperature of the enclosure. Figure 9 shows the behavior of temperatures during the third period of tests, from 29 October to 12 November. In this period, only three days are observed in which the incorporation of mPCM to the gypsum board is evident. However, the most interesting thing during this period is that there are two days (8 and 11 November) where the average internal temperature in both enclosures is much higher than the outside temperature. This increase can be explained from the rise in the minimum temperature during the previous days, which causes the mPCM not to be able to discharge during the hours of low temperatures. As in the previous period, the e ect of the phase change material is more evident in the decrease of the oscillation of the enclosure’s internal temperature. In Figures 10 and 11, the maximum and minimum daily temperatures in both test enclosures are observed, measured in the lower internal base and in the air just below the gypsum board, respectively. In Figure 10, no significant e ect of the incorporation of the phase change material is observed due to Temperature (°C) Buildings 2020, 10, 15 10 of 18 the condition of the ventilated floor, which is also a common characteristic that can be seen repeatedly in constructions in the Chilean coast. However, the e ect of the mPCM is observed in the decrease of the maximum temperature measured in the adjacent air on the gypsum board during the analyzed period (Figure 11), approximately between 1 C and 4 C. Regarding the minimum temperature, it is noted that the e ect of the mPCM is evidenced only in some days, which reflects in a higher minimum Buildings 2020, 10, 15 10 of 18 temperature, between 1.5 C and 3.0 C, specifically at the end of the analyzed period. Buildings 2020, 10, 15 10 of 18 Figure 10. Maximum and minimum daily temperatures of the lower surface of the test enclosure Figure 10. Maximum and minimum daily temperatures of the lower surface of the test enclosure with Figure 10. Maximum and minimum daily temperatures of the lower surface of the test enclosure with gypsum boards with (filling) and without (empty) mPCM. gypsum boards with (filling) and without (empty) mPCM. with gypsum boards with (filling) and without (empty) mPCM. Figure 11. Maximum and minimum daily temperatures of the air adjacent to the gypsum board with Figure 11. Maximum and minimum daily temperatures of the air adjacent to the gypsum board with Figure 11. Maximum and minimum daily temperatures of the air adjacent to the gypsum board with (fill) and without (empty) mPCM. (fill) and without (empty) mPCM. (fill) and without (empty) mPCM. 3.2. Heat Flow Calculation 3.2. Heat Flow Calculation 3.2. Heat Flow Calculation According to the configuration of the experimental set-up, the heat flow to (or from) the test According to the configuration of the experimental set-up, the heat flow to (or from) the test According to the configuration of the experimental set-up, the heat flow to (or from) the test enclosure is mainly by conduction, through the layer of structural plywood and the three gypsum enclosure is mainly by conduction, through the layer of structural plywood and the three gypsum enclosure is mainly by conduction, through the layer of structural plywood and the three gypsum boards layers (Figure 12). In the case of the test enclosure with non-modified gypsum boards, boards layers (Figure 12). In the case of the test enclosure with non-modified gypsum boards, the boards layers (Figure 12). In the case of the test enclosure with non-modified gypsum boards, the the physical situation can be modeled as a pair of conductive thermal resistance series associated with physical situation can be modeled as a pair of conductive thermal resistance series associated with physical situation can be modeled as a pair of conductive thermal resistance series associated with structural plywood L = 18 mm, k = 0.130 W/mK and gypsum board layers without mPCM L = 30 mm, t t p structural plywood Lt = 18 mm, kt = 0.130 W/mK and gypsum board layers without mPCM Lp = 30 structural plywood Lt = 18 mm, kt = 0.130 W/mK and gypsum board layers without mPCM Lp = 30 k = 0.422 W/mK. In this way, the overall transfer coecient is calculated from the equation: mm, kp = 0.422 W/mK. In this way, the overall transfer coefficient is calculated from the equation: mm, kp = 0.422 W/mK. In this way, the overall transfer coefficient is calculated from the equation: L p  L p [ ] U = + W/m K 2, (1)  U = L + [W/m K], k k (1)  p t t p 2  U = + [W/m K],  (1) kk tp  kk tp  Then, the heat flux per unit area is calculated through the equation: Then, the heat flux per unit area is calculated through the equation:  Qk=− U Tso Tsi W/m , () (2)  Qk=− U Tso Tsi  W/m , () (2)  where the temperatures Tso and Tsi correspond to the external surface temperature of the structural where the temperatures Tso and Tsi correspond to the external surface temperature of the structural plywood (x = 0) and the internal temperature of the third gypsum board (x = L). In the case of the plywood (x = 0) and the internal temperature of the third gypsum board (x = L). In the case of the enclosure with gypsum boards modified with mPCM (Lp = 30 mm, kp = 0.306 W/mK) a capacitor is enclosure with gypsum boards modified with mPCM (Lp = 30 mm, kp = 0.306 W/mK) a capacitor is added to the thermal circuit parallel to the conductive thermal resistance of the gypsum boards. This added to the thermal circuit parallel to the conductive thermal resistance of the gypsum boards. This capacitor models the thermal inertia of the gypsum boards with mPCM, counting the heat absorbed capacitor models the thermal inertia of the gypsum boards with mPCM, counting the heat absorbed or released depending on the environmental conditions. In this way, using Equations (1) and (2), it is or released depending on the environmental conditions. In this way, using Equations (1) and (2), it is possible to obtain approximately the heat flows by conduction during the test periods in the possible to obtain approximately the heat flows by conduction during the test periods in the enclosures with gypsum boards not modified and modified with mPCM (Figure 13). According to enclosures with gypsum boards not modified and modified with mPCM (Figure 13). According to Buildings 2020, 10, 15 11 of 18 this analysis, the heat accumulated on gypsum boards modified with mPCM can be estimated approximately as the difference of heat fluxes through the thermal model of the test enclosure with Buildings 2020, 10, 15 11 of 18 gypsum boards modified with PCM and that with non-modified gypsum boards (Figure 12). (a) (b) Figure 12. Roofing model of the test enclosures (a) and equivalent thermal circuit for the Figure 12. Roofing model of the test enclosures (a) and equivalent thermal circuit for the approximate calculation approximate calculation of heat fluxes (of he b). at fluxes (b). Then, the heat flux per unit area is calculated through the equation: Figure 13 shows the result of the behavior of instantaneous heat fluxes through the roofing of the test enclosures during the second and third studied periods. These figures allow to better h i ( ) Qk = U T T W/m , (2) so si observe the displacement in time of the peak of thermal loads due to the incorporation of mPCM, evidenced by the difference between the times at which the heat flux peaks manifest in each case. where the temperatures T and T correspond to the external surface temperature of the structural so si plywood (x = 0) and the internal temperature of the third gypsum board (x = L). In the case of the 3.3. Computational Simulation enclosure with gypsum boards modified with mPCM (L = 30 mm, k = 0.306 W/mK) a capacitor p p EnergyPlus™ is a thermal simulation software for developed by collaborations between the is added to the thermal circuit parallel to the conductive thermal resistance of the gypsum boards. United States Renewable Energy Laboratory (NREL), United States Department of Energy (DOE), This capacitor models the thermal inertia of the gypsum boards with mPCM, counting the heat academic institutions, and private companies. It consists of a tool that interrelates the performance of absorbed or released depending on the environmental conditions. In this way, using Equations (1) active energy systems, geometric dimensions, envelope characteristics, geographical location, and and (2), it is possible to obtain approximately the heat flows by conduction during the test periods in weather data to perform a computer simulation and subsequently deliver reports of energy the enclosures with gypsum boards not modified and modified with mPCM (Figure 13). According consumption by air conditioning of spaces, lighting, temperatures, and other values required by the to this analysis, the heat accumulated on gypsum boards modified with mPCM can be estimated user. For this simulation, the software required the following fundamental information: approximately as the di erence of heat fluxes through the thermal model of the test enclosure with gypsum boards modified with PCM and that with non-modified gypsum boards (Figure 12). (i.) Climatic data, including solar radiation and cloudiness of the geographical location, dry bulb Figure 13 shows the result of the behavior of instantaneous heat fluxes through the roofing of the temperature, relative humidity, and wind speed. This information was obtained for Santiago de test enclosures during the second and third studied periods. These figures allow to better observe the Chile from the EnergyPlus ™ website [43]. displacement in time of the peak of thermal loads due to the incorporation of mPCM, evidenced by the (ii.) Geometric information of the necessary enclosures to create a 3-D model, considering di erence between the times at which the heat flux peaks manifest in each case. dimensions, materials, and the orientation of the enclosures. (iii.) The thermophysical properties of the enclosure’s envelope materials obtained experimentally 3.3. Computational Simulation and from information available in Chilean regulations. (iv.) Ener The external floors o gyPlus— is a therm f ea alch simulation enclosure we softwar re consid e for developed ered ventilated surfac by collaborations es, not ex between posed to dir the United ect Statessun r Renewable adiation Ener . gy Laboratory (NREL), United States Department of Energy (DOE), academic (v.) institutions, Air renew and als private per hour companies. on the enclo It consists sure. A pa of ra a meter tool that thainterr t was set elates at fthe ive renewa performance ls/hour. of active energy systems, geometric dimensions, envelope characteristics, geographical location, and weather data to perform a computer simulation and subsequently deliver reports of energy consumption by air conditioning of spaces, lighting, temperatures, and other values required by the user. For this simulation, the software required the following fundamental information: Buildings 2020, 10, 15 12 of 18 (i.) Climatic data, including solar radiation and cloudiness of the geographical location, dry bulb temperature, relative humidity, and wind speed. This information was obtained for Santiago de Chile from the EnergyPlus — website [43]. (ii.) Geometric information of the necessary enclosures to create a 3-D model, considering dimensions, materials, and the orientation of the enclosures. (iii.) The thermophysical properties of the enclosure’s envelope materials obtained experimentally and from information available in Chilean regulations. (iv.) The external floors of each enclosure were considered ventilated surfaces, not exposed to direct sun radiation. Buildings 2020, 10, 15 12 of 18 (v.) Air renewals per hour on the enclosure. A parameter that was set at five renewals/hour. Date 12/10 13/10 14/10 15/10 16/10 17/10 18/10 19/10 20/10 21/10 22/10 23/10 24/10 25/10 26/10 27/10 -10 -20 -30 -40 -50 -60 Plaster MePCM-Plas ter Subtraction -70 0 8 16 0 8 16 08 16 08 16 08 16 08 16 08 16 0 8 16 08 16 08 16 08 16 08 16 08 16 0 8 16 0 8 16 0 Time (h) Date 29/10 30/10 31/10 01/11 02/11 03/11 04 /11 05/11 06/11 07/11 08/11 09/11 10/11 11/11 12/11 13/11 Plaster MePCM-Plas ter Subtraction -10 -20 -30 -40 -50 Figure 13. Estimated heat flux through the gypsum boards in the test enclosures with and without Figure 13. Estimated heat flux through the gypsum boards in the test enclosures with and without gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. Figur Figure 14a shows the num e 14a shows the numerical erical resu results lts of of tempera temperat tur ure beha e behavior vior duri during ng the the f first irst peri period od of test of tests. s. As As in in the exp the experimental erimental study, the study, the simulation simulation predi predicts cts tha thatt the temper the temperatur ature e inside inside the test en the test enclosur closures es is is hi higher gher than the outsi than the outside de temper temperatur ature. e. H However owever,, t this his d dii ffer erence ence i is s m much uch m mor ore e e evident vident t than han i in n t the he experimental experimental case (F case (Figur igure 7a). e 7a). The The simulation simulation re results sults pr predict edict t that hat t the he ef e fect ect of of incorporating incorporating g gypsum ypsum boar boards modified ds modified with with mPCM mPCM is notis not important important during du this ring this stage; thissta isgbecause e; this ithe s because the outer outer temperature temperature does not exceed the PCM melting temperature. It is for this reason that the simulation results for the other two experimentally analyzed periods are not shown. Figure 14b shows the results of the variation of the temperature inside the test enclosures during a warmer period than those analyzed experimentally. During this period, it is observed that the difference between the internal temperature of the enclosures and the outdoor temperature is further accentuated. It is also possible to identify the effect of the incorporation of the modified gypsum boards, visualized in the behavior of the temperature inside the enclosure, specifically in the reduction of the maximum temperature (Figure 14c). However, said reduction does not exceed 2 °C. q (W/m ) q (W/m ) Buildings 2020, 10, 15 13 of 18 does not exceed the PCM melting temperature. It is for this reason that the simulation results for the other two experimentally analyzed periods are not shown. Figure 14b shows the results of the variation of the temperature inside the test enclosures during a warmer period than those analyzed experimentally. During this period, it is observed that the di erence between the internal temperature of the enclosures and the outdoor temperature is further accentuated. It is also possible to identify the e ect of the incorporation of the modified gypsum boards, visualized in the behavior of the temperature inside the enclosure, specifically in the reduction of the maximum temperature (Figure 14c). However, Buildings 2020, 10, 15 13 of 18 said reduction does not exceed 2 C. Date 16/09 17/09 18/09 19/09 20/09 21/09 22/09 23/09 24/09 25/09 26/09 27/09 28/09 29/09 30/09 01/10 Plaster MePCM-Plas ter Ambient -5 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 08 16 0 8 16 0 Time (h) Figure 14. Simulated average temperatures of the test enclosures during two periods of spring (a) Figure 14. Simulated average temperatures of the test enclosures during two periods of spring (a) and southern and southern summer summer ( (b). The b). Th detail e detail shows shows the decr the de ease crease in tem in peratur temperature o e oscillation scillation of the of enclosur the enclosure e with gypsum with gyps boar um board ds withsmPCM with mPCM ( (c). c). Figure 15 shows the predicted behavior of the net heat flux by conduction through the roofing of the test enclosures. As with the heat flux values estimated from the experimental measurements, a heat flux is considered positive when it flows into the test enclosure and it is negative when it flows to the outside. The results obtained for the first period (Figure 15a) do not allow to observe an apparent difference between the net heat fluxes by conduction through the roofing of both enclosures. However, in the warmest period analyzed (Figure 15b), it shows a more significant difference between the two enclosures. The difference in heat fluxes by conduction through the roofing of both enclosures corresponds, as in the experimental case (Figure 13), to the heat flux stored in the gypsum boards with mPCM. Temperature (°C) Buildings 2020, 10, 15 14 of 18 Figure 15 shows the predicted behavior of the net heat flux by conduction through the roofing of the test enclosures. As with the heat flux values estimated from the experimental measurements, a heat flux is considered positive when it flows into the test enclosure and it is negative when it flows to the outside. The results obtained for the first period (Figure 15a) do not allow to observe an apparent di erence between the net heat fluxes by conduction through the roofing of both enclosures. However, in the warmest period analyzed (Figure 15b), it shows a more significant di erence between the two enclosures. The di erence in heat fluxes by conduction through the roofing of both enclosures corresponds, as in the experimental case (Figure 13), to the heat flux stored in the gypsum boards Buildings 2020, 10, 15 14 of 18 with mPCM. Figure 15. Predicted heat flux through the gypsum boards in the test enclosures with and without Figure 15. Predicted heat flux through the gypsum boards in the test enclosures with and without gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. gypsum boards modified with mPCM for the second (a) and third (b) analyzed periods. 4. Discussion 4. Discussion The The dimensions of the test enclosure dimensions of the test enclosure (Figur(Figure es 4 ands 64 ) ar an ed 6) no suit are no able to suit extrapolate able to ext therap obtained olate the results to a real scale building. Nevertheless, the used enclosure does not pretend to be a physical obtained results to a real scale building. Nevertheless, the used enclosure does not pretend to be a model physic ofal m an actual odel of building; an actuinstead, al buildin the g; goal instis ead, t to assess he gothe al is t mPCM-modified o assess the mgypsum PCM-modi boar fie ds d gyp under sum actual weather conditions minimizing the parameters that a ect the variation of the enclosure’s inner boards under actual weather conditions minimizing the parameters that affect the variation of the temperatur enclosure’s in e and ner favoring temperat theure and favor heat flux through ing the the he gypsum at flux th boar rough d surfaces. the gypsum board surfaces. One characterized the thermal properties of the gypsum boards modified with a paranic mPCM One characterized the thermal properties of the gypsum boards modified with a paraffinic (20mPCM (20 wt%) by the wt%) transient by the tra line heat nsient li sourne ce method. heat source The method. results showed The resul thatts showed both thermal that conductivit both therma y l and thermal di usivity depend on temperature, and these properties are higher when the PCM is conductivity and thermal diffusivity depend on temperature, and these properties are higher when solid. the PCM is solid The measured . The measured ph phase change enthalpy ase change enth of 28.79 J/kg alpy of is lower 28.79 J/ thankg is expected lower t due han expected to the formation due to of agglomerates of mPCM. It can be observed, in all the experimental and numerical analyzed cases, the formation of agglomerates of mPCM. It can be observed, in all the experimental and numerical how anatemperatur lyzed cases, how t es describe eman perat oscillatory ures describ behavior e an os typical cillatory beh of passive avior t systems. ypical Another of passive common systems. feature is that, for most days, the internal temperature of the enclosure is higher than the ambient Another common feature is that, for most days, the internal temperature of the enclosure is higher than the ambient temperature, reaching even a difference of 3 °C. Similar behavior was observed in previous works using test enclosures of different dimensions, and mPCMs concentrations [27,30]. It is believed that this effect is a consequence of the design used in the construction of the enclosure, since it seeks to reduce as much as possible infiltrations and losses and gains of heat by the surfaces of the walls and the floor, favoring heat transfer by the roofing of the enclosure, where the gypsum boards are located. According to Kalnæsa and Jelle [33], there are few studies on the effects of PCMs in passive roof systems. Our experimental results agree to the hypothesis of the authors who claimed that PCMs placed on the roof would absorb the incoming thermal energy from the sun and surroundings to reduce temperature fluctuations on the inside. The effect of the incorporation of the mPCM in the test enclosure during the first analyzed period indicates three days (16, 22, and 23 September) in which the maximum temperature exceeds 30 °C. During these days, the maximum temperature of the test enclosure with gypsum boards Buildings 2020, 10, 15 15 of 18 temperature, reaching even a di erence of 3 C. Similar behavior was observed in previous works using test enclosures of di erent dimensions, and mPCMs concentrations [27,30]. It is believed that this e ect is a consequence of the design used in the construction of the enclosure, since it seeks to reduce as much as possible infiltrations and losses and gains of heat by the surfaces of the walls and the floor, favoring heat transfer by the roofing of the enclosure, where the gypsum boards are located. According to Kalnæsa and Jelle [33], there are few studies on the e ects of PCMs in passive roof systems. Our experimental results agree to the hypothesis of the authors who claimed that PCMs placed on the roof would absorb the incoming thermal energy from the sun and surroundings to reduce temperature fluctuations on the inside. The e ect of the incorporation of the mPCM in the test enclosure during the first analyzed period indicates three days (16, 22, and 23 September) in which the maximum temperature exceeds 30 C. During these days, the maximum temperature of the test enclosure with gypsum boards modified with mPCM is lower than that of the enclosure of reference by approximately 2 [ C]. The other e ect of the incorporation of the mPCM that can be observed is the slight shifting in time between the external and internal maximum temperatures of the enclosure caused by the thermal storage capacity of the roofing of the test enclosure. The experimental results show that the internal temperature of the enclosure is influenced by the mPCM, with a maximum di erence between both enclosures of 6.5 C observed on October 21, being able to better observe, such a day, the e ect of the displacement of the thermal load from 16:57 h until 18:17 h. The maximum temperature di erence observed during the nighttime was 2.75 C on November 11, when a minimum of 14.25 C is reached at 7:17 h in the enclosure without mPCM, while in the enclosure with mPCM a minimum temperature of 17 C is reached at 8:17 h. There are periods during the afternoon, where heat flux to the interior of the test enclosure with gypsum boards modified with mPCM is higher than in the reference enclosure, while in the mornings, the heat flux to the outside is more significant in the latter. In general, it is observed that the heat flux into the interior of the test enclosures increases during the early hours of the morning until reaching a maximum peak around noon. Then, the heat flux decreases during the afternoon until the first hours of the next day. The computer simulations carried out employing EnergyPlus— allowed to predict the thermal behavior of the test enclosure approximately. However, the numerical results were not contrasted with the experimental ones, given the moderate behavior of the environmental temperatures of the climate archive available for Santiago de Chile compared to the temperatures measured in situ during the experiments carried out between September and November 2017. Moreover, the numerical results fail to predict the observed shifting of the behavior of the heat flux resulting from the modification of the gypsum boards with mPCM. Maybe for enclosures of low dimensions, it is more precise to use computational tools based on the finite volume method, as other authors performed it [29,31]. When comparing the experimental and numerical results, it is observed that the numerically predicted heat fluxes are of the same order than those experimentally estimated, but the software predicts a smaller di erence between the heat fluxes in both enclosures. The computer simulation carried out in a warmer period (2–15 February) predicts that the incorporation of the mPCM in the gypsum boards reduces the maximum average temperature reached in the enclosure by no more than 1.5 C, which is approximately 1 C lower than that reported by Ramakrishnan et al. [40]. However, they implemented a PCM composite in the walls and floor of a test enclosure with a comparable inner volume of 1130  725  690 mm , and a double-glazed window. The thermal simulations showed to be very sensitive to the air renewal rate, keeping this value equal to 5 renewals/h, since lower values gave rise to very high average temperatures inside the enclosure, and higher renovations diminish the e ect of the mPCM incorporated in gypsum boards. In general, the proposed experiment can be used to evaluate materials modified with PCMs under current climatic conditions, but the numerical results suggest infiltration rate should be a parameter to be measured or controlled in future experiments. Buildings 2020, 10, 15 16 of 18 5. Conclusions In the present work, gypsum boards modified with a paranic mPCM (20 wt%) were prepared, producing construction elements with higher thermal storage capacity that were implemented in a test enclosure in the period between 16 September and 12 November. In general, the obtained results of the thermal characterization are coherent, and allow capturing the behavior and e ect of latent heat storage of the components analyzed in a computer simulation using EnergyPlus—. Two test enclosures with an interior volume of 0.512 m are built using sandwich-type refrigeration panels to construct the walls and base of the enclosures. The envelope of the walls and floor of the enclosures provide high thermal resistance, thus achieving that the heat flux during the experiments flows mainly through the roofing of the test enclosures. This feature was sought, given the need to use this assembly to characterize the thermal behavior of materials modified with PCMs under actual weather conditions. However, the increase of the interior temperature above the outside can be considered an unwished situation during warmer days. In general, the experimental results show that using a mPCM with melting temperature range of 26.5 C to 29.2 C in a climate such as that of Santiago de Chile, allows to decrease and increase the maximum and minimum temperatures respectively, this if the material manages to charge and discharge thermally during the day. In addition, the e ect of the displacement of thermal loads becomes more noticeable as the days get hotter. The proposed thermal model with a capacitor element to estimate the heat fluxes through the placed gypsum boards allows obtaining values and a behavior coherent with that predicted by computer simulations, which enable this methodology to be used to determine the heat flux through and stored on the surface of interest. The computer simulations carried out employing the EnergyPlus— allowed to predict the thermal behavior of the test enclosure approximately. However, the numerical results were not contrasted with the experimental ones, given the moderate behavior of the environmental temperatures of the weather file available for Santiago de Chile compared to the temperatures measured in situ during the experiments carried out between September and November. The numerical results fail to capture this behavior during the same period experimentally analyzed since the temperatures of the weather archive used in the simulations are more moderate. The computer simulation carried out in a warmer period (2–15 February) predicts that the incorporation of the mPCM in the gypsum boards reduces the maximum average temperature reached in the enclosure by no more than 1.5 C. The simulations showed to be very sensitive to the air renewal rate, keeping this value equal to 5 renewals/h, since lower values generated interior temperature values significantly higher than the measured ones, and higher renovations diminish the e ect of the mPCM incorporated in gypsum boards. In general, the proposed experiment can be used to evaluate materials modified with PCMs under current climatic conditions, but the numerical results suggest that the enclosure should not be manufactured by minimizing infiltrations, but the infiltration rate should be a parameter to be measured or controlled in future experiments. 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BuildingsMultidisciplinary Digital Publishing Institute

Published: Jan 19, 2020

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