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This study predicts the long-term performance of ground source heat pump (GSHP) systems in different climatic regions of Japan. The research model calculates the dynamic heat load of a typical Japanese building in various cities using their meteorological data, considering different schedules for heating and cooling seasons. The model aims to analyze the performance degradation of the GSHP system after 15 years of operation due to the imbalanced heating and cooling loads. Additionally, it compares ground temperature changes, coefficient of performance (COP) variations, and annual operation times based on different thermal imbalance ratios (TIR) for the case studies. The results demonstrate that TIR serves as an appropriate factor for comprehensively evaluating system aspects, including GHE length, ground temperature, and COP degradation, across various climates. It was found that ground temperatures increased by a maximum of up to 4 °C in cooling-dominated regions due to higher thermal imbalance accumulative loads, while it decreased to around 1 °C in heating-dominated regions. The model also revealed that the COP decreased in the dominant operation for each case study due to induced thermal imbalance and soil temperature change. The thermal imbalance caused the system cooling COP decreased by 0.015/year in the worst case (Okinawa City) and 0.006/year in average for other cases. (1) The climatic regions of japan and the color-coded average hourly temperature for the different cities. (2) This variety causes different cooling and heating season schedules, imbalance load, and (3) Changes the ground temperature in long-term operation. [Display omitted] [ABSTRACT FROM AUTHOR]

• The horizontal directional drilling technology is used for GSHP systems. • Horizontal Directional Drilling technology can reduce capital cost of GSHPs. • Larger Diameter of directional GHE enhances heat exchange rates, significantly. • The depth and length of the directional GHE are critical parameters. • Groundwater flow presence causes significant enhancement in heat exchange rate. The drilling cost of Ground Heat Exchangers (GHEs), which increases the capital cost, is one of the main obstacles to their widespread development. Horizontal Directional Drilling (HDD) is a lower cost no-dig drilling technology commonly used for drilling tunnels or for the installation of urban infrastructure such as pipes, cables, etc., using the prescribed underground path. Thus, using HDD technology for horizontal GHE (HGHE) is expected to improve the competitiveness of ground source heat pump (GSHP) systems, since its drilling cost and the requirement of surface land area are significantly smaller than those of conventional excavation. In this research, a horizontal U-shaped hole was drilled as an experimental GHE in Saga City, western Japan. This hole with diameter of 230 mm, length 63 m, and a maximum depth of 8 m was used to place a polyethylene pipe with a 52 mm ID as GHE, inside. The thermal response test (TRT) with a heat load of 35−45 W/m effectively demonstrated the good heat exchange ability of the HGHE due to the larger heat exchange surface and the lack of thermal interference between pipes. The developed numerical model in FEFLOW and based on GHE design as well as the field's geological condition were validated through the history matching of the heat medium temperatures measured during the TRT. This model was then used to carry out a sensitivity analysis under different design conditions. The results showed that the heat exchange rates were significantly enhanced in larger diameter of GHEs, while the unit heat exchange rates declined in longer lengths of GHE. The deeper installation of GHE was found to be insignificant due to the delayed seasonal change of the ground temperature, not to mention the consequent higher drilling cost. In addition, the effect of groundwater flow indicated that faster groundwater velocities, and in perpendicular direction, show the maximum system improvement. Finally, an economic and comparative study was performed to calculate and compare the merits of HDD with equivalent conventional GSHPs including single and double U-tube, coaxial and slinky GHE. The results of economic analysis showed that HDD technology can reduce GHSP cost up to a maximum of 78 %. [ABSTRACT FROM AUTHOR]