Use of temperature derivative to analyze thermal response tests on borehole heat exchangers

Thermal response tests (TRTs) are often performed on vertical borehole heat exchangers, which are used in ground-source heat pump systems. Conventional analysis methods for TRTs provide estimates of the ground thermal conductivity and the effective borehole resistance. Both parameters are required in the design of GSHP systems. A parameter estimation method is proposed to analyze the TRT data using the temperature derivative in addition to the usual transient temperature curve. The method provides an estimate for the ground volumetric heat capacity in addition to the ground thermal conductivity and effective borehole resistance. Without the derivative curve parameter estimation gives unrealistic values of ground volumetric heat capacity, if the three unknown parameters are to be determined. The proposed method is demonstrated on TRT data sets from three boreholes.