The results of the heat transfer processes studies in the heat exchange borehole (BHE), equipped with coaxial collector in order to establish the influence of its design parameters, the properties of the rock mass, mode and duration of the coolant flow to the effective temperature difference. The resulting analytical equation for the effective temperature difference in the conditions of unsteady heat transfer experimentally verified in a lab BHE and can be used in the design of these BHE systems in specific geological and technical conditions. Use the resulting equation for the inverse calculation can be counted the diameter and the depth of the BHE, as well as the duration of the coolant circulation in the coaxial collector. The advantage of such approach is the consideration of the main factors that influence the of the effective temperature difference.

Keywords: borehole heat exchanger (BHE), effective temperature difference, coaxial collector, heat pump, low-potential energy