The Numerical Analysis Of The Soil Heat Transfer Based On Ground-coupled Heat Pump With Seasonal Heat Storage

In recent years, ground-coupled heat pump systems are rapidly applied in construction projects. One of the applicable conditions of the ground-coupled heat pump is the heating load in winter and the cooling load in summer basic balance throughout the year. It is to a certain extend limited to promote in cold regions in North China. When the heating load in winter is greater than the cooling load in summer, the soil temperature field is difficult to renew which leads to the efficiency of ground-coupled heat pumps decrease or even stop running. In order to solve this problem, the paper does preliminary research on the seasonal heat storage of the solar energy based on ground-coupled heat pump systems. The seasonal heat storage of the solar energy based on the geothermal heat exchanger can make up the limitations of the ground-coupled heat pump system and solar energy can be utilized fully. Besides, it can overcome the disadvantages of daily and seasonal variation, intermittence, unreliability of solar energy.First, the study object is the heat transfer and storage of the geothermal heat exchanger and the soil. Three-dimensional numerical model of the heat transfer of the geothermal heat exchanger and the soil is established. Based on the numerical simulation, the properties of the heat storage are analyzed.First, analyze the necessity of the heat storage. The solar energy storage is not only to supplement energy to make the balance of heat absorption and release in the soil but also to increase the temperature difference between the inlet and outlet water in the pipe in winter, the heat transfer is also enhanced.Second, the heat storage of single U-type heat exchanger is simulated. Analyze soil temperature field variation and resumption after two years running and the heat obtained in soil in summer, heat extraction from the soil and thermal utilization factor in winter are given. The relationship between thermal influencing radius and the duration of time of thermal storage is simulated. Third, the heat storage of muti U-type heat exchangers is simulated. Based on the simulation, the factors which influence on the heat storage of pipe, such as pipe distance, temperature of inlet water, velocity of inlet water, the thermal properties of soil etc are analyzed. The soil temperature field of these factors is analyzed mostly. The heat obtained in soil in summer and heat extraction from soil in winter is also involved with. Compare heat transfer ability of single U-type heat exchanger with muti U-type heat exchangers from two factors:heat storage per unit of heat exchangers in summer and heat extraction per unit of heat exchangers in winter. The thermal utilization factor of muti U-type heat exchangers is greater than that of single U-type heat exchangerFinally, Research the intermittent operation influence on the soil temperature field distribution and heat storage performance in summer operation condition. Moreover, discuss the differences between heat storage in summer and autumn. Analyze thermal utilization factor in summer and autumn. Meantime, research the possibility of part of geothermal heat exchangers which are used to storage the heat to recover the whole soil temperature.The results show that the seasonal heat storage of the solar energy based on the exiting geothermal heat exchangers is feasible. It is very necessary in the cold regions. The results and conclusions provide guidance and references for seasonal heat storage of the solar energy.