This paper presents a linearized control-oriented model of a borehole thermal energy storage (BTES), describing the storage temperature dynamics under varying operating conditions, i.e., varying inlet temperatures, mass-flow rates, and borehole connection layouts (e.g., in-series, in-parallel or mixed). An optimization framework was employed to determine the best operating conditions for a heat pump-driven BTES, subject to different CO2 intensity profiles of the electricity.
It was demonstrated that this boundary condition, due to its seasonal variation, is critical for the optimal operation of the system. Increasing heat pump efficiency in winter while accepting a lower efficiency in summer is found to be beneficial.
Results show that a lower relative CO2 intensity in summer compared to the one in winter leads to an overall higher optimal operating temperature of the storage than typically encountered in low temperature BTES operated close to the undisturbed soil temperature. This highlights that there is untapped potential for CO2 reduction in implementing high-temperature BTES systems, particularly for those with access to energy sources featuring low summer CO2 intensities (e.g., solar thermal or PV electricity).
Fiorentini, Massimo, and Baldini, Luca: Control-oriented modelling and operational optimization of a borehole thermal energy storage. Applied Thermal Engineering, Volume 199, 117518, November 2021, https://doi.org/10.1016/j.applthermaleng.2021.117518
