Thermal performance analysis of ground source heat pump system for low-temperature waste heat recovery storage

This study investigated the thermal performance of a ground source heat pump (GSHP) system for low-temperature waste heat storage. Considering the large amount of low-temperature heat from industrial effluents wasted to the environment, this study intends to store this low-temperature waste heat in the ground. A GSHP system for low-temperature waste heat storage was established, which could simultaneously achieve heat storage and extraction. In this system, the borehole cluster comprises two parts: inner and outer layers of ground heat exchangers (GHEs). The inner layer was used for space heating as a common GHE, which extracts heat from the ground, whereas the outer layer connected to the industry was designed for injecting low-temperature waste heat to the ground seasonally. The heat fluxes of the GHEs for heat injection and extraction were set differently and were taken as two different strengths of heat sources in this study. A heat and moisture transfer model was established and experimentally validated. Subsequently, the waste heat storage and heat extraction processes are modelled numerically. The results show that the average soil temperature increases by at least 2.63 and 6% when the heat flux of the outer layer GHEs are 40 and 50 Km(-1), respectively. It reveals that the injection of low temperature waste heat into the soil is not only beneficial to waste heat recovery, but can also alleviate soil thermal imbalance, providing significant support in heating dominated area, especially in cold regions. This study complements the thermal analysis between two different strength of heat sources, providing a reference for practical engineering design.