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USE OF PHASE CHANGE MATERIALS IN CONSTRUCTION OF BUILDINGS: A REVIEW
The paper on the use of Phase change materials in building construction has been a recent development and a keen interest of the researchers have been demonstrated in this regards. Furthermore, there is ongoing research regarding the various applications of PCM. It may be stated in this context that this research project focuses on the types of PCMs used in the building construction industry. In addition to that, this paper provides a significant insight into the methods or techniques employed for integrating or mixing thee PCM with the concrete or other building material. Moreover, the advantages and the limitations of using PCM as a significant building construction material have been evaluated through this paper. Additionally, Arizona Public Service or APS in the Solar Testing and Research (STAR) center or APS STAR center is taken into consideration for their role in conducting relevant, consequential and noteworthy research on the applications of PCM. Furthermore, the applicability of PCM as an alternative to solar power has been considered through the research conducted by the organisation.
The survey and interviews conducted for performing the quantitative and qualitative analysis of the data, illustrates the knowledge of the researchers and junior research fellows at APS STAR center with regards to the particular subject of discussion. It may be mentioned in this context that the thermal storage capacity of PCMs are exploited through this research and the research at the aforementioned organisation. The methodology chosen for the purpose of execution of this research project has been identified to have a positivism philosophy, and a deductive approach for carrying out these research studies.
Table of Contents
Substances exhibiting thermodynamic properties as a result of the presence of high heat of fusion or latent heat are termed as Phase Change materials. The outcome of the latent heat presents the opportunity for storing and releasing large amounts of energy. The PCMs are capable of demonstrating such thermodynamic properties during the phase change, generally solid to liquid transition, resulting in the heat storage in accordance with the per unit volume of the substance. The PCMs can be classified as organic, inorganic, hygroscopic or even Solid-Solid PCMs. The implementation of the various kinds of PCMs in building construction is dependent on the advantages and the disadvantages that the materials pose in different environment conditions. The thermophysical properties of the PCMs are taken into consideration as selection criteria for the type of PCM for the materials for building construction (Qiu et al. 2017). It may be stated in this regards that the concept of implementation of PCMs for improving the insulation of building materials had been taken into account after the World War II. This research provides an insight into the classification of the PCMs based on their thermophysical properties, along with the techniques implemented for improving the insulation of building materials. In addition to that, this research investigates the various applications of PCMs, including the involvement in building construction.
Often issues with leakage of insulation are noted due to the implementation of high temperatures. However, the encapsulation of paraffin into small spheres, and thereafter mixing with concrete, aids in the building construction purposes. The techniques used in this regard and their efficiency are studied for the purpose of this research paper. Impregnation, immersion and direct mixing are techniques which are emphasized in this paper. Furthermore, the applications of PCM are studied and an evaluation is made regarding which of the techniques may be suited for the construction industry.
The objectives and sub-goals of the research are detailed below:
- Discussions of the utilization of PCM in construction
- Assessing the advantages and disadvantages of PCM in construction
- Evaluating the issues that get associated with Phase Change Material
The following questions have been formulated to detail the issue that this paper discusses in a better way:
- How can you define and understand Phase Change Material?
- How do you assess Phase Change Material in the manufacturing units of construction?
- Explain the utilization of Phase Change Management and its advantages when related to the construction industries.
- Explain the disadvantages of the application of PCM in the industry of construction (Paksoy, 2007, p. 67).
- Identify and discuss the technologies that can be applied for the better utilization of PCM in the industry of construction.
The study of phase change materials provides a concept regarding the efficiency of the materials, and it has been evident that the use of PCMs results in more energetically efficient buildings. A literature review of the PCM stated by several scholars has been discussed in this regards. The productivity and advantages offered by a variety of PCMs in the building construction industry have been illustrated in this research. In addition to that, the multiple techniques for enhanced PCM integration into building construction work have been mentioned and studied.
Phase Change Material can be described as a substance that has a heat of fusion, which is high. As it possesses this quality it can be melted or solidified at a specific temperature and then it can store as well as release huge amounts of energy. Phase Change Materials can be called as the units of latent heat storage or LHS too, as the substance while turning from solid to liquid or from liquid to solid releases or absorbs a lot of heat. The storage of latent heat can be done in a few ways and through the following changes in the phase of a material:
- Solid to liquid
- Liquid to solid
- Liquid to gas
- Solid to gas
While all these phases are present, PCM involves only the two initial phases, which are the solid to liquid and the liquid to solid phase. The phase change from liquid to gas has a higher degree of the transformation of heat than the solid to liquid or the liquid to solid transitions, the first phase change involves the utilization of high pressures or large volumes in order to store the materials in the gas phase and have been concluded as being impractical for the purpose of thermal storage. On the other hand the solid to solid phase transition is a very slow process that produces low heat. The solid to liquid transitions of PCM initially behave like the sensible heat storage or SHS where the temperature increases constantly log with the absorption of heat. However, the PCMs reach a certain temperature when they melt and then they can absorb huge amounts of heat without rising radically in the temperature. The PCMs are available at a diverse range of temperature, which starts from -5 degree C to 190 degree C. some PCMs are also available at the comfort range of the human beings, which is between 20-30 degree C and are quite effective as well because they are able to store heat 5 to 14 times more per unit volume than the conventional materials of storage like masonry, rock or water.
The classification of PCMs can be classified as depicted in Figure 1.
Figure 1: Classification of PCM
(Source: Mishra, Shukla and Sharma, 2015)
The first category can be cites as eutectics, which are commonly called eutectic mixtures. Eutectic mixtures can be considered as PCMs, which are mixtures of two or more substances having low melting points (de Gracia and Cabeza, 2015). The characteristic feature of this mixture is that the mixture melts at the freezing point of one of the two mixtures, which is the lowest among the two. The temperature at which the mixture freezes is termed as its eutectic point. The binary systems of the eutectics have demonstrated freezing points between 16℃ and 51℃, while the melting point has been noted to be between 18℃ and 51℃ (Mishra, Shukla and Sharma, 2015). The latent heat of fusion of this range of melting and freezing points have been noted to be around 120 and 160 kJ/kg. A mixture of Lauric acid (LA) and Capric acid (CA) is often used as an efficient PCM in building construction (de Gracia and Cabeza, 2015). Figure 2 illustrates the melting points of the binary systems of each of the components of the eutectic mixture, namely, Capric acid and Lauric acid (Qiu et al. 2017).
Figure 2: Melting points of the binary systems of Capric acid and Lauric acid
(Source: Bland et al. 2017)
Using the Schroder’s equation to calculate the transition temperatures of the eutectic mixture of LA and CA have been found to be at 19.6℃. Figure 3 depicts the DSC curve of the binary systems of CA and LA. This had been derived through a DSC analysis of the eutectic mixture, when the proportion of the mixture of LA to CA was 34.88% to 65.12% (Bland et al. 2017).
Figure 3: DSC curve of the eutectic mixture of CA and LA
(Source: Bland et al. 2017)
2.2.2 Organic phase change materials
Organic phase change materials are known to have lower thermal conductivity. The increase in the technology of microencapsulation has enhanced the use of organic PCMs. Furthermore, the use of bio-based PCMs may serve as an alternative to the prevalent petroleum-based PCM. for instance, paraffin (CnH2n+2)is one of the most examples of bio-based PCMs which offer numerous advantages (Bland et al. 2017). The chemical inertia of paraffins, along with the extensive range of melting temperatures from 200℃ to 700℃ makes it a suitable PCM in building construction (Bland et al. 2017). The advantages include the ability to freeze without much undercooling, non-reactive and safe. In addition to that, the organic PCMs are chemically stable and offer a high heat of fusion. Moreover, the lipid and carbohydrate based PCMs are generally produced from renewable substances, which does not harm the environment. Additionally, it is to be noted that the compatibility of the organic PCMs with the traditional materials of construction are an interesting feature for the purpose of building construction. Regardless, there are certain disadvantages as well, such as the low thermal conductivity offered by the PCMs in their respective solid states, which may be addressed through the high heat transfer rates for the freezing cycles. Furthermore, organic PCMs are flammable in nature and have a low volumetric latent heat storage capacity (Bland et al. 2017). Examples of organic PCMs include phenol, glycerin, formic acid, methyl palmitate, and Paraffin n-Carbons.
2.2.3 Inorganic phase change materials
Inorganic PCMs are generally salt hydrates in nature with the chemical formula (MnH2O). As opposed to the organic PCMs, the inorganic PCMs have a high latent heat of fusion and are non-inflammable, which provides better scopes of application for the same. The other advantages offered by inorganic PCMs include low cost and abundant availability, high thermal conductivity, high rates of volumetric storage capacity of latent heat of fusion and a sharp melting point. However, there are a number of drawbacks identified with respect to inorganic PCMs, such as a high volume change, phase separation and incongruous melting on cycling, which may potentially pose a threat to the latent heat enthalpy (Fokaides, Kylili and Kalogirou, 2015). In addition to that, inorganic PCMs are noted to be corrosive to other substances such as metals, and the requirement of nucleating agents is essential as the PCMs are likely to become inactive after repeated cycles. Furthermore, the solid to liquid transition require supercooling which may become potentially problematic to the PCMs. Sodium sulfate (Na2SO4·10H2O), Sodium hydroxide/ sodium carbonate NaOH / Na2CO3 (7.2%) and more can be considered common examples of inorganic PCMs. Since, inorganic PCMs are subject to undergo phase decomposition, the cross-linking enhances the stability of the compound, which may prove beneficial. For instance, HDPE or high density polyethylene is cross-linked when 98% of the heat of fusion is utilised through transition. However, the temperature range for organic PCMs is quite favourable as they offer a wide range, but the inorganic PCMs are active at a temperature range of 30℃ to 600℃ (Kalnæs and Jelle, 2015).
Incorporation of the PCMs into the building materials proves beneficial as it may aid in the storage of thermal energy. However, it may be mentioned in this regards that the additional of the PCMs into the building material, such as concrete allows the increment of efficiency through providing a higher thermal mass, which aids in the provision of a higher energy efficiency. The process of impregnation is one of the many techniques through which PCMs are incorporated into concrete or other building and construction materials (Fokaides, Kylili and Kalogirou, 2015). Impregnation requires three fundamental steps, namely, the evacuation of activities that result to physical healthiness. For example, proper diet, ensuring that all meals are balanced and taking a lot of water and air from the light-weight aggregates. This is performed with the help of a vacuum pump. Figure 4 illustrates a diagram depicting the process of incorporation of PCMs into concrete. The second step entails the absorption of the porous materials or aggregates into the liquid PCM. Finally, the previously soaked PCM aggregates are mixed with the concrete. The formerly soaked PCM aggregates act as a ‘carrier for the PCM’ (Fokaides, Kylili and Kalogirou, 2015). For instance, taking butyl stearate as a PCM, the aggregates expanded shale aggregate (S), normal clay aggregate (C2) and expanded clay aggregate (C1) had been used for a comparative study of porosity of the materials and as a ‘carrier for the PCM’. It was identified that the porosity of the materials had been found to be 0.081, 0.176 and 0.876 ml/g of the aggregates, S, C2 and C1 respectively. The net outcome of the experiments can be illustrated as the capability of the PCM to occupy about 75% of the porous aggregate (Kalnæs and Jelle, 2015).
Figure 4: Incorporation of PCM into concrete
(Source: Fokaides, Kylili and Kalogirou, 2015)
The primary principle acting behind this technique has been identified as the capillary action. As opposed to the impregnation technique, wherein the liquid PCM is incorporated into the concrete, this technique entails the building materials such as concrete or bricks and more, to be dipped within the PCM. The liquid PCM is absorbed by the construction material through capillary action. Figure 5 illustrates the procedure of heat absorption of the PCM and the state transition.
Figure 5: PCM transition
(Source: Fokaides, Kylili and Kalogirou, 2015)
It may be mentioned in this regards that the effectiveness of this particular technique implemented is primarily dependent on the capacity of absorption of the concrete or other building materials used for the building purposes. Furthermore, it is also to be noted in this context that the incorporation or integration of the PCM into the concrete results in the negative impact on the properties of the concrete. However, this may be corrected through the selection of the appropriate and the most suitable technique of PCM integration. Investigation by scientists have demonstrated that the absorption of porous materials or PCM into concrete take a few hours in general. The investigation further highlighted that the liquid PCM required at temperature of approximately 80°C±5 in order to soak through concrete blocks (Kalnæs and Jelle, 2015). Furthermore, it was identified that autoclaved concrete blocks have increased porosity, therefore, it has resulted in an increased rate of absorption of the liquid PCM.
2.3.3 Direct mixings
The process of encapsulation has been previously mentioned in the literature. The physically and chemically stable form of the PCM is directly added into the constituents of the building materials. The common processes identified in this regards are namely, emulsion polymerization, interfacial polymerization, spray drying and more. The use of Zeocarbon or Zeolite is implemented in this regards, in order to avoid the breakage of the capsule during the process of direct mixings. The principle behind this has been identified as the surface reinforcement in order to withstand impact or high impact (Stritih et al. 2018).
2.4.1 Building applications
The role of PCM integrated into concrete is known to have multiple applications in several components of building construction. Major components have been identified as:
- Glass windows filled with PCM: The windows in this aspect have double sheets, filled with air-filled gaps between them. Two holes at the bottom of the window are connected to PCM tank and a pump. Furthermore, the pump is connected to the tank containing the PCM in the liquid state. Temperature sensors are enabled, which enables a pre-set temperature and the pump is activated and the air-filled gaps are replaced with the PCM from the tank (Lee et al. 2015). Hence, the PCM starts freezing as a result of the low outside temperature, thereby maintaining the internal temperature.
Figure 6: PCM embedded in a wall system of a building
(Source: Derradji, Errebai and Amara, 2017)
- Under-Floor Electric Heating System: The thermal floor performance of the building may be evaluated through the implementation of PCM for undertaking the under-floor electric heating systems (Karaipekli, Sarı and Biçer, 2016). The components of the heating system include electric heater, wooden floors, air layer, polystyrene insulation, some wooden supporters and PCM.
- Roof integrated with PCM: A thermal PCM storage unit is installed in the iron roof sheets acting as a solar radiation collection in order to heat up the air. The operations may be performed depending on the requirements. For instance, the PCM is melted by pumping air into the thermal storage facility. However, in the absence of heat, an auxiliary gas heater is implemented for heating.
- PCM assisted ceilings: In this case, a ceiling-mounted fan is used for pumping the air out through the heat pipes, while the other end of the storage pipes is considered as a PCM storage module. The phase transition property of PCM is utilised in this regards, during the day, the PCM absorbs the heat, which cools the warm air generated within the room, while the shutters are opened and the fans are reversed at night, thereby facilitating the heating from the PCM when the cooler air passes over the pipes (Akeiber et al. 2016).
2.4.2 PCM enhanced concrete
Thermo-concrete, which is commonly known as PCM enhanced concrete, implements EPS or Expanded Polystyrene that is embedded in Thermo-concrete panels. This technique implements the use of thermal mass technology. PCM is mixed with the concrete is enhance its durability as well as the properties of heat retention and absorption. Furthermore, a series of experiments performed on PCM in SCC or Self Compacting Concrete have been performed taking 1%, 3% and 5% of PCM in the experiments (Kylili and Fokaides, 2016). It has been established that an increase in 1.7, 3.0 and 3.5 times in the samples, with a consistent increase in the levels of PCM. Additionally, the melting temperatures have been in the range of 23℃ to 26℃, which have been identified to play a vital role in influencing the specific heat capacity of the experimental samples (Souayfane, Fardoun and Biwole, 2016).
2.4.3 Thermal Energy Storage and Cooling Power Potential
It has been found upon conducting several experiments that upon incorporating PCM into the walls of an office space, the indoor ambient temperature had been reduced by about 7℃ in the summer, while the ambient indoor temperatures rose by 4℃ in the winter (Kenisarin and Mahkamov, 2016). Furthermore, it had been established that upon integrating PCM into the walls of the office had resulted in reduced energy consumption as well. It may be stated that it had been demonstrated through a series of experiments that the energy consumption of the office had been found to be 33 kWh without the integration of PCM, while upon integration with PCM, the energy consumption had been reduced to 18 kWh (de Gracia and Cabeza, 2015). Furthermore, as an efficient thermal storage system, PCM has a major role to play in the building construction industry. The PCM embedded in the concrete primarily absorbs the surplus heat during the day, and melts. On the contrary, it solidifies on cooler nights and the the heat absorbed is released into the environment. The principle behind the efficiency can be demonstrated in connection with the heat transfer steam/ water that take place in two phases.
Efficient energy performance of building is becoming an increasing concern with the rise in global warming and other negative environmental effects. Recent works in this field have primarily contributed to a better understanding of the management of the energy flow within and out of the buildings. The paper by Fokaides, Kylili and Kalogirou (2015), investigates the incorporation of PCM for the transparent glazing development of a building. The paper draws inspiration from the series of experiments con.............
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