Annual Operation Optimization of Ground Source Heat Pump Systems Under Hybrid Short- and Long-Cycle Heat Exchange

Abstract

To address the soil thermal imbalance and energy performance degradation caused by long-term operation of ground source heat pump (GSHP) systems in hot-summer/cold-winter regions such as Chongqing, this study proposes a hybrid heat exchange strategy that coordinates short- and long-cycle thermal regulation. On the long-cycle scale, cooling towers are employed during spring or transitional seasons to extract ambient cold energy and store it seasonally in the soil, thereby achieving cross-seasonal cold storage and temporal redistribution of cooling capacity. On the daily scale during summer, the seasonal cold storage and cooling tower heat rejection jointly regulate the ground temperature. A dynamic simulation model of the GSHP system was established to evaluate and optimize its long-term operational performance under cooling, heating and cold storage modes. Annual simulation results show that cold storage efficiency is positively correlated with the temperature difference between the outdoor wet-bulb temperature and the soil, and that cross-seasonal cold storage exerts only a minor impact on the heating COP in spring, which decreases by merely 0.16–0.29 compared with the wet-bulb temperature-controlled GSHP (WBT-GSHP) strategy. During summer operation, cooling towers preferentially handle the cooling load when the outdoor wet-bulb temperature is low; once the cooling load increases significantly, the heat pump units are activated and the soil-stored cold energy is utilized, effectively suppressing the rise in ground temperature. Compared with the WBT-GSHP strategy, the proposed approach improves the summer cooling COP by 0.79–1.41, substantially enhancing the operational efficiency of the cooling mode while maintaining the long-term soil temperature within a predefined range. This strategy can provide a novel solution and theoretical basis for mitigating the thermal imbalance problem in GSHP systems in Chongqing and similar hot-summer/cold-winter climate zones.