Modelling of the thermal performance of a borehole field containing a large buried tank

Seasonal storage of solar thermal energy for space heating of multiple dwellings in cold climates can be accomplished through the use of borehole fields in conjunction with large buffer tanks. The buffer tank is used to account for the difference between the time over which solar energy can be collected and the time required to deposit the collected energy into the borehole field. There is motivation to bury the tanks in order to save space on ground level, as well as to improve the overall efficiency of the system by reducing heat losses from the tank. The current paper uses computational fluid dynamics (CFD) to explore the impact of a buried tank on the performance of a borehole thermal energy storage (BTES), as well as the thermal interactions between the tank and boreholes.The long-term performance was assessed in detail by simulating a 20-year period. The first 5 years of performance were then compared to results for a series of other cases including: a typical BTES layout, a tank with the bottom wall insulated as well as tanks with varying aspect ratios. It was found that the presence of the tank did not significantly reduce the BTES performance. Moreover, performance was relatively insensitive to the tank aspect ratio. Insulating the bottom of the tank also had negligible difference.