In this paper, the authors define the heat extraction or injection rate of ground heat exchanger (GHEX) per length and temperature difference as the coefficient of heat extraction or injection. Applying the definition, the heat extraction or injection performances of GHEXs are quantified corresponding to the conditions such as ground properties and GHEXs' specifications are changed.
In addition, the authors compared to the quantified heat extraction or injection performances. When the flow condition of heat transfer medium in GHEX turns from laminar flow to turbulent flow, the heat extraction or injection performances of GHEXs increase 5-12%. On the other hand, the increase of heat extraction or injection performances of GHEXs in the range of turbulent flow is only less than 2% even in the where the flow rate is up to more than thrice. When the number of U-tubes is two and flow rate per the one U-tube is set at 6 L/min, the ratios of heat extraction performance of GHEXs using pre-casting concrete pile and steel pile compared to the borehole GHEX are 1.35-1.58 and 1.29-1.40, respectively.