Simplified Analytical Solutions Based on Finite Line Source Theory for Borehole Thermal Energy Storage Systems

BTES is an important seasonal thermal energy storage technology that effectively addresses the uneven temporal and spatial distribution of energy. However, the complex and time-consuming thermal analysis of BTES poses challenges to its development. This paper presents a simplified analytical algorithm based on the FLS model, integrating convective heat transfer within the borehole fluid and transient thermal conductivity of the surrounding soil to establish an analytical model. The model is simplified based on its geometric symmetry, and a numerical model is established for validation. The results show that the relative errors between 0.54% and 5.76% were associated with temperature variations ranging from 0.21°C to 0.58°C.