Two-dimensions finite-difference heat transfer study for a single borehole heat storage system during a seasonal charge-discharge cycle

Borehole heat exchangers are used to remove and/or add heat from/into the ground in different applications involving low-temperature heat usage, such as residential or social buildings heating by means of heat pumps. In such types of applications, seasonal heat storage is necessary since during the warm season an additional solar system is used to charge heat into the ground via the borehole system in order to regenerate the heat source for usage during the cold season. Heat transfer in the ground by means of the borehole results in both radial and axial propagations of the perturbation (ground heating/cooling). The magnitude of this perturbation and the added/removed heat are important parameters of the process that must be evaluated. The theoretical model presented in the paper uses the decomposition finite difference technique to determine the temperature distribution in the ground at different moments (1, 2, 4, and 6 months) during a charge/discharge cycle of the heat storage. The numerical results are necessary in order to evaluate the penetration depth of the thermal perturbation along the radial and longitudinal axes and the amount of stored/extracted heat. (paper)