Modelling and Simulation of Groundwater Influence on Borehole Thermal Energy Stores

Borehole thermal energy stores used for seasonal heat storage in solar assisted district heating systems are very sensitive to groundwater flow. A heat and mass transport model has been developed by the authors in order to simulate the influence of moving groundwater on borehole thermal energy stores. This was done by combining an advanced numerical strategy, where the borehole heat exchangers are modeled by one-dimensional finite-element representations with three-dimensional finite element modeling of the surrounding ground. Thus, the computation time is significantly reduced compared to fully discretized computations while precise results are still achieved. The model is used to investigate the efficiency of a borehole thermal energy store consisting of 80 borehole heat exchangers similar to the one that is currently built in Crailsheim, Germany.