A numerical investigation to analyze the effect of changing ambient conditions on accurate and stable identification of thermal conductivity of ground source heat pump system using thermal response test

摘要

This study aimed to investigate the effect of changing ambient conditions on the accuracy and stability of ground thermal conductivity, lambda(s), using the thermal response test (TRT). First, a detailed numerical model considering the heat fluxes on the field surface of TRT was developed. Then, the numerical model was compared with that with the adiabatic surface boundary in two representative test seasons. After that, the impacts of three parameters associated with the surface heat fluxes, including the surface absorptivity, evaporation coefficient, and surface infrared emissivity on the lambda(s) were analyzed. Lastly, statistical analyses with various ambient conditions were employed to evaluate the degree of estimated lambda(s) deviating from its actual value in different specifications of TRT and actual ground thermal conductivities. Results show that the surface absorptivity can be generally seen as the most significant contributory factor to the uncertainty of lambda(s). The lambda(s) is overestimated and the uncertainty of TRT is aggravated by considering the changing ambient conditions, especially when the depth of drilling test well is short and the actual lambda(s) is high. For such conditions, the heat insulation on the test site surface is highly recommended considering the acceptable accuracy of lambda(s) with the adiabatic boundary.