The performance of the backfills of the borehole heat exchanger of the ground source heat pump system in cooling dominated region of China

The ground temperature increase is the crucial problem that influences the longterm performance of Ground Source Heat Pump (GSHP) system in cooling dominated region of China. In this report, the numerical simulation model based on the heat rejection model of an insitu Thermal Response Test (TRT) is created using TRNSYS simulation tool. Seven different thermal conductivity backfills are simulated for 1, 5, 10, 15 and 20 years. The result illustrates that the higher conductivity backfills improves the heat exchange performance between BHE and surrounding ground but it also increases the ground temperature in cooling dominated regions for long terms operation. In the case of Chuzhou city of this study, when the conductivity of backfill is higher than 1.9 W/(m center dot K) which is closest to the thermal conductivity of the surround ground, there are little growth in ground temperature as well as the heat exchange performance.