Thermal performances of vertical ground heat exchangers in different conditions

This study investigates thermal performance of vertical ground heat exchangers (GHEs) with different inlet water temperatures and borehole depths. The performances of three types of GHEs namely U-tube, double-tube and multi-tube GHEs are evaluated by numerical method using a CFD code. The simulation results show that heat exchange rates per unit borehole depth increase in the cooling mode and decrease in the heating mode of 3.4 W/m for U-tube, 5.7 W/m for double-tube, and 3.3 W/m for multi-tube with increasing of 1 ?C of the temperature difference between inlet water and ground. In addition, increasing the depth of vertical GHE lowers the heat exchange with the ground. By comparing with 20 m depth, the heat exchange rates per unit borehole depth lower of 32.5 % in 60 m depth, 47.9 % in 100 m depth for U-tube GHE and 29 % in 60 m depth, 42.7 % in 100 m depth for multi-tube GHE, respectively