Determination and analysis of parameters for an in-situ thermal response test

An in-situ thermal response test (TRT) is important for ground source heat pump (GSHP) systems. To obtain precise ground thermal properties, determining and controlling the TRT parameters are important. In this study, the determine principle of heating power was discussed for an in-situ TRT. The influence of test time and flow velocity on the test results was analysed. The results showed that the heating power has large influence on the heat transfer capacity and time to reach a quasi-stable state and little influence on the soil thermal conductivity. The suitable heating power is to ensure that when the water temperature is stable, the inlet temperature of the buried pipe meets the outlet temperature of the heat pump unit, usually 35 °C. When the heating power was increased by 15.70% and decreased by 16.18%, the heat transfer capacity increased by 17.10% and decreased by 14.64%, the time to reach a quasi-stable state increased by 29.16% and decreased by 8.33%, and the soil thermal conductivity had relative errors of 4.17% and 2.98%, respectively. If a heating power is selected accurately, the quasi-stable state can be reached within a test time of 24 h; extending the test time had no significant effect on the test accuracy. A flow velocity of 0.4-0.6 m/s in pipe is recommended for in-situ TRT.