Modelling of a borehole heat exchanger using a finite element with multiple degrees of freedom

An increasing number of installations with underground heat storage have determined the development of new, more accurate and quicker calculation techniques. Therefore, this article shows a numerical model for a single vertical borehole heat exchanger working with underground heat storage. Emphasis has been put on developing a finite element which describes the process of heat exchange. A one-dimensional element with multiple degrees of freedom was used in this work. The changes of grout temperature affect the temperature of the circulating fluid, thus it is necessary to apply a suitable model. The grout area has been divided into three zones, and each one corresponds to a different temperature. Such an attempt allows to determine a more accurate temperature of the fluid. The results obtained for temperature distribution were compared to a model created with the use of Ansys commercial numerical software.