Experimental study on geotechnical thermal response test of coaxial borehole heat exchanger

Geotechnical thermophysical properties are the key factors affecting the design and operation of ground source heat pump(GSHP) system. Two thermal response tests lasted 48 h were performed in two experimental coaxial borehole heat exchangers with different depths located in Hongshan District of Wuhan City, and the average fluid temperature in the annular space between inner tube and outer tube of coaxial borehole heat exchangers was measured. A simple in-situ method to obtain ground thermal properties was presented, which combines the analytical solution of borehole thermal resistance with the infinite line source model (ILSM), according to the geometric characteristics of coaxial borehole heat exchanger. Compared with the laboratory test results, the thermal physical properties of rock and soil obtained by this method are in good agreement, which indicates that the proposed method is feasible. © 2022, Solar Energy Periodical Office Co., Ltd. All right reserved.