This study presents long-term performance predictions for ground source heat pump (GSHP) systems in various climatic regions of Japan. The research calculates the dynamic heat load of a typical Japanese building in various cities using their meteorological data and considers different schedules for heating and cooling seasons. The performance degradation of the GSHP system after 15 years of operation is analyzed due to imbalanced heating and cooling loads. The study also compares the changes in ground temperature and variations in the coefficient of performance (COP). Ground temperatures were observed to increase by a maximum of up to 4 °C in cooling-dominated regions due to higher accumulative loads of thermal imbalance. Conversely, in heating-dominated regions, ground temperatures decreased to around 1 °C. The model also indicated that the coefficient of performance (COP) decreased in the dominant operation for each case study due to induced thermal imbalance and changes in soil temperature. The system's cooling COP decreased by 0.015/year in Okinawa City and 0.006/year on average due to thermal imbalance.

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