Numerical modeling of borehole thermal energy storage in unsaturated soils

Abstract

Abstract Borehole Thermal Energy Storage (BTES) in unsaturated soils offers advantages such as enhanced heat storage efficiency and widespread accessibility. However, the complex heat and mass transfer mechanisms and their impact on BTES performance necessitate further investigation. In this study, a componential two-phase heat transfer and fluid flow model was employed to examine the key mechanisms impacting the heat storage performance of a soil BTES system. Simulated results reveal that changes in soil thermal and hydraulic properties due to heat injection may significantly affect the heat transfer mechanisms and heat storage performance of the system. In particular, strong convective heat transfer may cause a reduction in heat storage efficiency. Comparison with results from the heat conduction model demonstrates the effectiveness of the modeling approach, especially when drying out occurs. The findings of this study can inform the design of soil BTES systems.