Thermal analysis of underground thermal energy storage systems

The energy efficiency of underground thermal energy storage (UTES) system has been analysed from the fundamental laws of thermodynamics and heat transfer theory, in comparison with similar technology of ground-source heat pump (GSHP) system. The main characteristic of UTES is a passive cooling or heating system, which has high energy efficiency. The storage of high quality thermal energy could improve its application level of passive cooling or heating. While the suitable terminal system could relax the requirement of thermal energy quality from demand side, thus high thermal energy storage and utilization efficiency could be reached. The storage system with thermal stratification or different temperature zone design could maintain thermal energy quality at large extent and at the same time enhance the heat transfer.