بررسی تجربی و تجزیه و تحلیل های شبیه سازی عددی بر عملکرد حرارتی تغییر فاز مواد که شامل ساختمان سقف (پی سی ام) برای مدیریت گرمایی

Thermal storage plays a major role in a wide variety of industrial, commercial and residential application when there is a mismatch between the supply and demand of energy. Latent heat storage in a phase change material (PCM) is very attractive, because of its high-energy storage density and its isothermal behavior during the phase change process. Several promising developments are taking place in the field of thermal storage using phase change materials (PCM) in buildings. It has been demonstrated that for the development of a latent heat storage system (LHTS) in a building fabric, the choice of the PCM plays an important role in addition to heat transfer mechanism in the PCM. Increasing the thermal storage capacity of a building can enhance human comfort by decreasing the frequency of internal air temperature swings, so that the indoor air temperature is closer to the desired temperature for a longer period of time. This paper attempts to study the thermal performance of an inorganic eutectic PCM based thermal storage system for thermal management in a residential building. The system has been analyzed by theoretical and experimental investigation. Experiments are also conducted by circulating water through the tubes kept inside the PCM panel to test its suitability for the summer months. In order to achieve the optimum design for the selected location, several simulation runs are made for the average ambient conditions for all the months in a year and for the various other parameters of interest.

Scientists all over the world are in search of new and renewable energy sources. One of the options is to develop energy storage devices, which are as important as developing new sources of energy. Thermal energy storage systems provide the potential to attain energy savings, which in turn reduce the environment impact related to non-renewable energy use. In fact, these systems provide a valuable solution for correcting the mismatch that is often found between the supply and demand of energy. Latent heat storage is a relatively new area of study although it previously received much attention during the energy crisis of late 1970’s and early 1980’s where it was extensively researched for use in solar heating systems. When the energy crisis subsided, much less emphasis was put on latent heat storage. Although research into latent heat storage for solar heating systems continues, recently it is increasingly being considered for waste heat recovery, load leveling for power generation, building energy conservation and air conditioning applications. As demand for air conditioning increased greatly during the last decade, large demands of electric power and limited reserves of fossil fuels have led to a surge in interest with regard to energy efficiency. Electrical energy consumption varies significantly during the day and night according to the demand by industrial, commercial and residential activities. In hot and cold climate countries, the major part of the load variation is due to air conditioning and domestic space heating, respectively. This variation leads to a differential pricing system for peak and off peak periods of energy use. Better power generation/distribution management and significant economic benefit can be achieved if some of the peak load could be shifted to the off peak load period. This can be achieved by thermal energy storage for heating and cooling in residential and commercial building establishments. There are several promising developments going on in the field of application of PCMs for heating and cooling of building. Zalba et al. [1] performed a detailed review on thermal energy storage that dealt with phase change materials, heat transfer studies and applications. Farid et al. [2] also presented a review on the analysis of phase change materials, hermetic encapsulation and application of PCMs. Mehling and Hiebler [3] summarized the investigations and developments on using PCMs in buildings. Murat Kenisarin1and Khamid Mahkamov [4] presented a review of investigations and developments carried out during the last 10–15 years in the field of phase change materials, enhancing heat conductivity, available fields of using PCM, and clarifying typical questions. Arkar and Medved [5], Stritih and Novak [6] designed and tested a latent heat storage system used to provide ventilation of a building. The results of their work, according to the authors, were very promising. Phase change dry wall or wallboard is an exciting type of building integrated heat storage material. Several authors investigated the various methods of impregnating gypsum and other PCMs [7], [8], [9], [10], [11] and [12] in wallboards. Limited analytical studies of PCM wallboard have been conducted, but few general rules pertaining to the thermal dynamics of PCM wallboard are available. Lee et al. [13] and Hawes et al. [14] presented the thermal performance of PCM’s in different types of concrete blocks. They studied and presented the effects of concrete alkalinity, temperature, immersion time and PCM dilution on PCM absorption during the impregnation process. Wood lightweight concrete is a mixture of cement, wood chips or saw dust, which should not exceed 15% by weight, water and additives. This mixture can be applied for building interior and outer wall construction. For integration in wood lightweight concrete, two PCM materials Rubitherm GR40, 1–3 mm and GR 50, 0.2–0.6 mm were investigated by Mehling et al. [15]. Meng Zhang et al. [16] presented the development of a thermally enhanced frame wall that reduces peak air conditioning demand in residential buildings. Ismail et al. [17] proposed a different concept for thermally effective windows using a PCM moving curtain. UniSA (University of South Australia) [18] developed a roof-integrated solar air heating/storage system, which uses existing corrugated iron roof sheets as a solar collector for heating air. Kunping Lina et al. [19] put forward a new kind of under-floor electric heating system with shape-stabilized phase change material (PCM) plates. Hed [20] investigated PCM integrated cooling systems for building types where there is an over production of heat during the daytime such as offices, schools and shopping centers. Free cooling was investigated at the University of Zaragoza/Spain by Zalba [21]. The objective of the work was to design and construct an experimental installation to study PCMs with a melting temperature between 20 and 25 °C. The approach at the University of Nottingham [22] is a replacement of a full air conditioning system by the new system, called a nighttime cooling system, which is easy to retrofit. To reduce the air conditioning load of airtight and insulated apartment building, Kuroki et al. [23] proposed a ventilation system that makes use of both thermal storage and outdoor conditions. The sustainable energy centre (SEC) at University of South Australia [24] started work with PCMs in the mid 1990’s with the development of a storage unit that can be used for both space heating and cooling. The night time charging and day time utilization process during both heating and cooling seasons for a storage system comprising of two different PCMs integrated into a reverse cycle refrigerative heat pump system utilizing off peak power. In order to achieve thermal storage capacity approximately equal to the heat gains within the space during the daily cycle, a new concept for the ceiling panel was developed by Markus Koschenz and Beat Lehmann [25] to incorporate this system in a light weight building that can be retrofitted. Velraj et al. [26] presented a detailed study on PCM based cool thermal energy storage (CTES) integrated with building air conditioning system in Tidel Park, Chennai, India which is an active system where the storage tank is kept separately away from the building. Stetiu and Feustel [27] used a thermal building simulation program based on the finite difference approach to numerically evaluate the latent heat storage performance of PCM wallboard in a building environment. Fraunhofer Institute [Germany] [28] simulated the thermal behavior of building components in order to compare the dynamic performance of different types of wall constructions incorporating different amounts of PCMs. Athienitis et al. [29] conducted an extensive experimental and one-dimensional non-linear numerical simulation study in a full scale outdoor test room with PCM gypsum board as inside wall lining. Bransier [30] was the first to analyze cyclic melting/freezing of a phase change material (PCM). He used a one-dimensional conduction model to analyze conductive cyclic phase change of a slab and a concentric PCM module and found that a maximum of two interfaces could coexist during cyclic melting/freezing. Hasan et al. [31] developed a one-dimensional cyclic phase change heat conduction model for a plane slab and carried out a detailed parametric study on the effects of various parameters on the energy charge/discharge. Brousseau and Lacroix [32] carried out a numerical analysis for the cyclic behavior of alternate melting and freezing in a multi-plate latent heat energy storage exchanger. In the present paper, a detailed study on the thermal performance of a phase change material based thermal storage for energy conservation in building is analyzed and discussed. An experimental set up consisting of two identical test rooms has been constructed to study the effect of having PCM panel on the roof for thermal management of a residential building. One room is constructed without PCM on the roof to compare the thermal performance of an in-organic eutectic PCM (48% CaCl2 + 4.3% NaCl + 0.4% KCl + 47.3% H2O), which has melting temperature in the range of 26–28 °C. A mathematical model has been developed and the finite volume method is employed for the computation of thermal behavior of the roof incorporating PCMs. A comparison with the experimental results is made and several simulation runs are conducted for the average ambient conditions for all the months in a year and for the various other parameters of interest. During the summer months, as the PCM does not change to the solid state during the night hours, experiments are conducted to test the possibility of removing the heat from the PCM slab and the ceiling by circulating water through the PCM panel.

Several promising developments are taking place in the field of thermal storage using PCMs in buildings. A literature review on PCM incorporation in building material, PCMs integration with building architecture for space heating, space cooling and in combination of heating and cooling has been carried out. It is quite evident from the preceding studies that the thermal improvements in a building due to the inclusion of PCMs depend on the melting temperature of the PCM, the type of PCM, the climate, design and orientation of the construction of the building. The optimization of these parameters is fundamental to demonstrate the possibilities of success of the PCMs in building materials. Being site specific, a detailed study is required for the selection of material and to implement the PCM based thermal storage in buildings at a particular location. The selection of PCM, based on phase transition temperature for one climatic region will not be appropriate for another. In the present research, a detailed investigation has been carried out to analyze the thermal performance of the roof of a building incorporating PCM suitable for Chennai City, India. A mathematical model has been developed and finite volume method is used to predict thermal behavior of roof incorporating PCMs. In order to achieve the optimum design for the selected location, several simulation runs are made for various parameters of interest. The effect of variation in the ambient condition for all the months, variation in heat transfer coefficient on the outer surface of the roof and the PCM panel thickness are studied in detail. In addition the effect of water circulation through the PCM panel is also attempted for the thermal management during summer months. It is observed from the study that the quantity of water required is very large which is not easily available during the summer months.