Investigating the effective parameters and various methods of computing the borehole depth of vertical ground heat exchanger of geothermal heat pump

In geothermal heat pumps, the heat exchange with ground is performed by the ground heat exchanger. In fact, the ground heat exchanger is installed to extract or inject the thermal energy from/to the earth. The borehole depth of this heat exchanger has a major effect on the system investment cost and operation; thus, this parameter must be computed with a high accuracy. There are various methods to compute the borehole depth of ground heat exchanger. The geothermal heat pump capacity and the regional soil characteristics are the main parameters which affect the borehole depth and size of the ground heat exchanger. In this paper, the important soil characteristics are first introduced. Then, the main five methods for computing the borehole depth of ground heat exchanger are investigated with their effective parameters. Finally, these methods are compared and their application priority is determined.