Energy analysis of geothermal heat pumps with U-tube installations

Heat pumps can be used for different purposes for building services, including the heating, cooling and domestic hot water production. Heat pumps play the following role with regard to energy: they obtain heat from the environment of lower temperature (e.g. air, water, earth) and transfer it into the building at a higher temperature. In this paper we demonstrate a calculation method to obtain the amount of extractable heat from the earth in the function of time, mass flow and the spacing of U-tube legs. We constructed differential equations for the modelling of U-tube. In these equations the calculation of overall thermal resistance is complex. Much research has been done on this topic so far. In our paper we put forward a method to obtain overall thermal resistance in the function of time and the spacing of U-tube legs. Furthermore, we graphically show the change of the extractable temperature and the value of COP for boreholes with separate diameters.