COOLING DEMONSTRATION EXPERIMENT OF A FLOW-RATE CONTROLLED GROUND SOURCE HEAT PUMP SYSTEM USING A LINING BOREHOLE GROUND HEAT EXCHANGER

This study aims to examine the operation status of a flow-rate controlled ground source heat pump system using a lining borehole ground heat exchanger (LBHE). The system was installed in an office in Kato city, Hyogo prefecture, and the construction tests of the LBHE were conducted in 2019. The construction test results confirmed that the improved construction method reduced the construction time and number of workers as compared to conventional construction methods. Then, we performed cooling demonstration experiments to examine the flow and temperature conditions in the system by controlling the flow rate taken from LBHEs (the circulation flow rate) on extremely hot days in August and September. In these experiments, the ambient air temperature, outlet and inlet water temperatures of the heat pump on the primary side, the circulation flow rate, heat pump power consumption, and room air temperature were measured. The outlet water temperature was maintained almost at the setting temperature (32°C) under experimental conditions, and the circulation flow rate was varied depending on the heat required for the heat pump. However, the output of the heat pump became unstable when the flow rate was close to the minimum flow rate and started fluctuating significantly. Overall, the measured sum of power consumption of the heat pump and auxiliary equipment of the system was 28.4–45.5% lower than the estimated power consumption of the air source heat pump.