Effect of vertical ground temperature distribution on parameter estimation of in-situ thermal response test with unstable heat rate

Abstract

This paper proposed a parameter estimation method for identifying ground thermal conductivity and volumetric heat capacity using the Nelder-Mead Simplex search algorithm (NMSA) in in-situ thermal response test (TRT) with unstable heat rate, the duct storage system (DST) model for borehole heat exchanger (BHE) was applied to do with variable heat rate and the vertical ground temperature distribution in initial soil temperature. The parameter estimation was carried out using the in-situ TRT data in Qingdao, and the effect of vertical ground temperature distribution on estimated results was compared and analyzed. The relative error of estimated ground thermal conductivity using the regression temperature fitted by the test temperatures from the 5th m depth to the 120th m depth decreased by about 9.1% than that corresponding to the integral mean temperature calculated by test temperatures from the 5th m depth to the 120th m depth. However, the estimated volumetric heat capacity is hardly sensitive to initial soil temperature, and the relative errors are not higher than 2% no matter how to do with initial soil temperature.