Comparison of Influencing Factors on Heat Transfer Efficiency for Borehole Heat Exchangers Based on Thermal Response Test in Linqu County, Shandong Province, China

Developing shallow geothermal energy with a borehole exchanger helps energy supply and CO 2 emission reduction . This paper comprehensively compares the influencing factors on heat transfer efficiency based on the field investigations in Linqu County, Shandong Province, China. We built a three-dimensional conceptual model and simulated the heat transfer efficiency of the borehole heat exchanger. We systemically compare the influence of groundwater seepage, circulating water flow rate, pipes spacing and length, the operation interval, and the annual operation mode on the heat transfer efficiency. The results show that the heat transfer efficiency decreases with long-term operation due to the accumulation of cold/heat of surrounding soil. The existence of groundwater seepage increases the heat transfer efficiency. The heat transfer efficiency of the borehole heat exchanger increases with the pipe length, inlet and outlet pipes spacing, and operation interval. It decreases with the circulating water flow rate. The annual operation mode, i.e., both in heating and cooling periods, is of greatest importance in the heat transfer efficiency compared to other influencing factors. The results provide a reference for the practical installation and optimization of the borehole heat exchanger for sustainable utilization of shallow geothermal energy