Analysis of Influencing Factors of Thermal Response Test of Deep Borehole Heat Exchanger

As a new kind of ground heat exchanger (GHE), deep borehole heat exchanger (DBHE) has a great potential to exploit medium-deep geothermal energy. Soil thermal properties are very important parameters for designing GHE, and they are normally measured by thermal response test (TRT). TRT of shallow GHE has been studied widely, however, there are only a few researches to study the TRT of DBHE. In this paper, TRT of DBHE is simulated based on a 3D numerical model, and the simulated TRT data are used to estimate the thermal conductivity and volumetric heat capacity of soil based on a parameter estimation method, and then the influences of different factors (including test time, geothermal gradient, soil thermal conductivity, volumetric heat capacity of soil, mass flow rate and heat output rate) on the estimated soil thermal properties of TRT are studied. The results are follows: for longer test time or lower mass flow rate, the estimated results of TRT have higher precision, and the test time of 80 hours is recommended; for higher thermal conductivity or volumetric heat capacity of soil, the TRT results have higher precision; geothermal gradient and heat output rate have little influences on the TRT results. The results of this paper offer important guidelines for TRT of DBHE.