Thermal analysis of macro-encapsulated phase change material coupled with domestic gas heater for building heating

Rising concerns of environmental degradation and energy security particularly in developing countries like Pakistan has exhilarated the need for energy storage systems for efficient source utilization. Phase Change Material (PCM) based Thermal Energy Storage (TES) systems are used with air conditioning systems for thermal load management in buildings. The TES system discussed in this paper consists of a macro-encapsulated PCM Magnesium chloride hexahydrate (MCHH) in aluminum cylinders. The system is integrated with a domestic gas heater to capture extra energy dissipated by the gas heater, used to raise the room temperature to the thermal comfort level. A numerical model is developed in MATLAB based on the enthalpy method for the performance analysis and investigating the phase transition phenomenon of MCHH, followed by experimental validation. Different thermal performance indices of TES are investigated such as liquid fraction, energy, and exergy stored during the charging/discharging process. The model has predicted 42 kJ and 9 kJ of energy and exergy stored, respectively during the charging cycle, while experimentations showed 39.6 kJ and 6 kJ energy and exergy stored in the material, respectively. The deviation of 15% in energy and 33.33% in exergy from experimental results indicated that the actual phase transition is non-isothermal and the mathematical model does not include the factor to accommodate the actual melting phenomenon with changing thermophysical properties of PCM. This performance analysis is significant to design and optimize the PCM-based TES coupled with conventional heating sources.