Performance Evaluation of Ground Source Heat Pump Using Direct Expansion Method

‐Performance of Hot Water Supply System‐

Abstract

The purpose of this study is to investigate the performance of a ground source heat pump (hereafter, GSHP) using direct expansion method in case of hot water supply system. The underground temperature beneath about 10m maintains almost constant throughout a year. The GSHP utilizes this constant temperature. The GSHP using direct expansion method has higher performance than the GSHP using indirect heat exchange method. The GSHP using direct expansion method can also be reduced the number of parts and initial cost. However, the GSHP using direct expansion method is difficult to obtain an amount of heat removed in a refrigerant side because the refrigerant becomes two phase flow and it reduces the measurement accuracy of flow rate. Therefore, we tried to evaluate the performance of the GSHP using direct expansion method as hot water supplying system. The amount of heat removed was evaluated by measuring the temperature difference and flow rate of supplying hot water. We used the closed loop vertical borehole whose depth was 30m. In the case that the setting temperature of hot water was 45°C, the heating time was 7 hour 46 minutes and time averaged COP was 3.29.