Long-term borehole energy storage by the inlet position control for low temperature heat source application

Abstract

Borehole thermal energy storage (BTES) systems are gaining attention due to their potential to efficiently store and release thermal energy. However, the conventional BTES systems often suffer from reduced efficiency under low heat source temperature conditions. This study aims to address this issue by introducing and evaluating the inlet position control method, a novel approach to enhance the BTES performance for low-temperature heat source applications. A single-cycle 3D simulation model, substantiated by experimental data from a BTES system installed in the YeonCheon region, Korea, is developed using the ANSYS Fluent program. The model investigates the heat transfer from the water heat source to the soil and compares the performance of the conventional method with the inlet position control method in terms of heat gradient contours and average temperature difference in the soil. The inlet position control method is found to improve the BTES storage efficiency by 11.90% during the early winter season of the thermal release period in the third year, compared to the conventional method. The standard deviation for simulation data is ± 1.787 with a peak error of 2.4%, indicating the effectiveness of the simulation model. Furthermore, the inlet control method enhances the BTES storage efficiency under low heat source temperature conditions and promotes faster thermal equalization, resulting in a 4.2% improvement in thermal energy release efficiency. We demonstrated the novelty of the inlet position control method in improving BTES performance and its applicability to low-temperature heat source applications. The findings have significant implications for the design and operation of future BTES systems, with the potential to expand their application in various industries and climates.