Research on the Short-Term Borehole Thermal Energy Storage Characteristics of Ground Heat Exchangers

To mitigate the subsurface temperature attenuation caused by long-Term heat extraction from ground heat exchangers (GHEs) and enhance the sustainability of geothermal energy systems, this study investigates the optimization mechanisms for storage duration and temperature in borehole thermal storage technology. Numerical models of coaxial-cased geothermal wells at depths of 500 m and 2000 m were established based on the geological conditions of Xi'an, Shaanxi Province. Using OpenGeoSys software, the impacts of short-Term storage duration and inlet temperature on thermal storage performance were simulated and analyzed. The results demonstrate that both thermal storage capacity and heat extraction increase linearly with longer storage duration and higher temperatures. In the shallow system, thermal storage capacity can reach 1.85 times the heat extraction during extended storage periods, whereas heat extraction consistently exceeds storage capacity in the deep system. The heat extraction enhancement rate peaks at a 2 4-hour storage duration in the shallow system. In contrast, it decays exponentially with storage duration in the deep system; however, increasing the storage temperature effectively improves this enhancement rate. The thermal recovery ratio peaks at approximately 45% after 8 hours in the shallow system and is temperature-insensitive. In the deep system, short-Term storage is temperature-sensitive, while the recovery ratio stabilizes after prolonged storage, with thermal insulation properties becoming the dominant factor. This study elucidates the optimization principles for short-Term thermal storage parameters, providing a theoretical basis for the design of borehole thermal storage systems.