Evaluating the performance of a large borehole ground source heat pump for greenhouses in northern Japan

The objective of this study was to use both field data and a numerical simulation to examine the long-term performance and environmental effects of a large GSHP (ground source heat pump) system that heats and cools industrial greenhouses in a cold region. A large vertical GSHP system was installed in the city of Akabira in the north of Hokkaido, Japan to provide heating and cooling for 12 greenhouses. The system has a maximum capacity of 640 and 648 kW for heating and cooling, respectively. The system was monitored and analyzed from Oct. 2010 through May 2011. The system had a COP (coefficient of performance) of 3.0 and SCOP (system coefficient of performance) of 2.7. The average heat extraction rate of the system was approximately 27.7 W/m. In addition, the ground temperature at a depth of 40 m decreased from approximately 7.8 °C to 0 °C after 8 months of operation. A numerical model of the system was developed in FEFLOW to predict its future behavior under conditions where the demand for heating surpasses the demand for cooling. The simulation results suggest that the system could maintain the heat exchange rate for several years without significantly compromising its performance. The risk of operating the system under unbalanced heating and cooling loads was addressed via case studies. Groundwater flow decreases the risk of operating the system when the heat extraction was much higher or lower than the heat injection. •Large borehole system performance in very cold region and its influence to the soil temperature variation were discussed.•The system performance in the future was predicted by a numerical model in FEFLOW.•The risk of system operation in which the heating load is larger than the cooling load was examined.•Advantages of the groundwater flow to the system performance and soil temperature variation were discussed.