Abstract
Numerical analysis of heat exchange rate of several types of vertical ground heat exchangers (GHEs) with different condition of inlet water temperatures, borehole depths, and tube configurations have been carried out. The GHE models were built and simulated by using a commercial CFD code, FLUENT. Heat exchange rates per unit borehole depth of the GHEs 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 ℃ of the temperature difference between inlet water and ground. Also, increasing the borehole depth lowers temperature difference between circulated water and surrounding ground and then lowers the heat exchange with the ground. Furthermore, thermal interference between inlet and outlet tubes due to the tube configuration affects significantly to the heat exchange rate of the GHEs. Insulating the outlet tube and increasing the inlet tube diameter in the multi-tube GHE contributes to the increasing the GHE performance.
