Thermal interference and heat transfer performance of vertical U-tube ground heat exchangers

For analysing the main factors (thermal conductivity of backfill materials and operating modes of heat pump) affecting thermal interference and heat transfer performance of ground heat exchangers, establishes a three-dimensional unsteady numerical model of U-tube ground heat exchanger, and verifies the model by a thermal response test. Based on the simulation and analysis with FLUENT software, obtains the variation laws of the loss coefficient of thermal interference and heat transfer rate per linear meter with the thermal conductivity of backfill materials on the conditions of the soil with different thermal conductivities, and recommends the backfill material whose thermal conductivity is slightly higher than that of surrounding soil. By comparing the continuous operation mode with the intermittent operation mode, concludes that when the thermal conductivity of backfill materials is less than or equal to that of surrounding soil, intermittent operation has almost no effect on thermal interference. When the thermal conductivity of backfill materials is greater than that of surrounding soil, the loss coefficient of thermal interference could be reduced by 51.6 percent to 74.5 percent, and the heat transfer rate per linear meter could be increased by 32.6 percent to 34.0 percent in intermittent operation mode.