Process Simulation of a Borehole Thermal Energy Storage combined with a Reverse Brayton Cycle Rotation Heat Pump for use in District Heating

Heat pumps and seasonal thermal energy storage are key technologies for decarbonizing district heating networks. If both are combined, excess heat stored during summer can be very efficiently reused in winter time, even at a raised temperature level. This paper compares two borehole thermal energy storage (BTES) models and introduces a model of an innovative high-temperature heat pump, all of them designed for seamless integration into process simulators. The BTES models are based on an analytical and a numerical simulation approach. They rely on calculating heat transfer rates and temperatures within the borehole depending on the effective borehole resistance and the properties of the surrounding ground. The results of both modeling approaches are compared and validated using long-term operational data from a real ground heat exchanger system. For the heat pump, a reverse Brayton cycle rotation heat pump is modeled, which operates without phase changes and is suitable for temperatures above 100 °C. Pressure and temperature increase are achieved through centrifugal forces. The paper elaborates on the theoretical basis and thermodynamic modeling of this novel heat pump technology. It is demonstrated that the high potential of this heat pump could be effectively utilized in combination with seasonal storage in district heating systems using BTES.