In-situ thermal response test of the ground thermal properties for a ground source heat pump project located in the Inner Mongolia district

Ground thermal properties are important parameters for the design of ground heat exchangers (GHE) used in ground source heat pump (GSHP). In order to estimate the ground thermal properties of site, an experimental apparatus of in-situ thermal response test (TRT) was designed and built to measure the temperature response of ground, the experimental apparatus, test methodology and data analysis method were presented in detail. Based on the apparatus and data analysis model, a test project of GSHP located in the Hohhot of Inner Mongolia has been performed to determine the site ground thermal properties. The test results indicate that for the test borehole, the ground initial temperature is about 8.9~9.2°C, the effective thermal conductivity and volumetric specific heat are 2.25 W/(m·K) and 2045 kJ/(m³·K) respectively, and the borehole thermal resistance is about 0.133 (m·K)/W. At the same time, the voltage stabilizer and thermal insulation for exposed pipe should be used to improve test accuracy. The test data after 10 h should be selected to proceed for obtaining the results. The experimental validation shows that the thermal response experimental apparatus and analysis model proposed in this paper is feasible and can be used for the determination of ground thermal properties in the practical GSHP project.