Research On Thermal Performance Of Phase Change Thermal Energy Storage Unit For Solar Energy Heat Pump Heating System

With the development of society, the proportion of the building energy consumptionin the total energy consumption is growing. Building energy efficiency can be carried outby reducing the winter heating energy consumption. As a kind of green and energy savingheating system, solar heat pump heating system is more and more popular in our country.Solar energy has some imperfections, such as instability, low energy density and so on. Soa reliable and efficient heat storage device is needed in solar energy system, which canincreas the efficiency of solar energy and reduce the consumption of conventional forheating in winter.In this paper, a phase-change thermal storage equipment which uses spherical heatstorage unit in the solar energy heat pump heating system is designed. And the thermalperformance of phase-change thermal storage equipment was studied using numericalsimulation method. First, parameters related to solar heat pump system, such as the solarradiation intensity, the heating load and the solar collector area were. Second, the paraffinadded the expanded graphite was chosen as Phase Change Material (PCM), and thequantity of PCMs was calculated. Then, the structure and size of the phase change heatstorage tank was determined. Third, Gambit and Fluent, two kind of softwares, were usedto establish the physical and mathematical model of phase change heat storage tank, andnumerical simulations were made by these softwares. Finally, the data is processed, then,the influences of spherical capsules diameter and the supply-return water temperaturediffer on thermal performance of phase change heat storage tank were analysed. Thetemperature field and liquid fraction in spherical capsules were obtained. The heat transferprocess in the presence of natural convection was analysed. The results showed that heattransfer efficiency is enhanced when reducing the spherical capsules diameter, and phasechange time is cut down, the maximum value of the outlet water temperature is increased,but the effective heating time is reduced. The processes of PCMs melting and freezing arealmost not impacted by the change of the supply-return water temperature differ, but theoutlet water temperature is influenced. The phase change process in spherical capsules isoutside-in step by step, and due to the impact of natural convection, phase change processis no longer symmetrical movement. Direction of the overall phase change and thermalbody flow is consistent in the heat storage tank.In this paper, a phase change heat storage device for the solar energy heat pump heating system with spherical heat storage unit was simulated. The results are helpful foroptimization and application of the heat storage devices in solar heating engineering.