A new solution for underground thermal imbalance of ground-coupled heat pump systems in cold regions: Heat compensation unit with thermosyphon

Ground-coupled heat pump systems (GCHPs) are environmentally friendly and energy-saving heating and cooling sources that are widely applied in recent years. However, for heating-dominant buildings in cold regions, more heat is extracted from the ground than is rejected, which leads to yearly decrease in soil temperature and degradation of the GCHPʹs heating performance and even results in GCHP failure after long-term operation. To solve this problem, a novel heat compensation unit with thermosyphon (HCUT) is proposed. The HCUT combines an air-source thermosyphon and an air-source heat pump to transfer heat from ambient air into the ground during the non-heating season as seasonal thermal storage and to recover the soil temperature. To investigate its long-term operation performance, a multi-year simulation was conducted in Harbin (one of the coldest cities in China) by TRNSYS, and the performance of the novel system is compared with the traditional “boiler + split air-conditioner” system. The results indicate that HCUT can effectively eliminate the underground thermal imbalance in cold regions, while ensuring that the GCHP system continues to work efficiently without performance deterioration and strengthening the heating reliability. Additionally, the novel system can save approximately 15% in energy compared with the traditional system. Thus, the HCUT is a potential solution for the underground thermal imbalance of GCHP systems in cold regions.