Performance evaluation under the actual operating condition of a vertical ground source heat pump system in a school building

This study is to evaluate the performance of a ground source heat pump (GSHP) system installed in the Pusan National University, Korea. The GSHP system consists of ground heat exchanger (GHE), measuring devices and heat pumps which have 2 compressors (inverter type and fixed type). The closed vertical type GHE is constructed with 24 boreholes of 175 m in depth. The outdoor temperature, the indoor temperature and relative humidity, the inlet and outlet temperature of circulating water are obtained. Also, the electricity consumption of compressor and cooling (heating) load are measured in order to analyze the COP of heat pump. From the measuring data, the variation of ground temperature at 2.5 m, 5.0 m in depth are affected by outdoor air temperature. But it is proved that the ground temperature is almost constant below 10 m in depth. In cooling period, the COP of the heat pump is 6.0–10.9 at partial load condition, while the overall system COP is 4.3–7.4. In heating period, the COP of the heat pump is 4.3–8.3 at partial load condition, while the overall system COP is 3.0–6.2.

► We install thermocouples under the ground to analyze thermal diffusion property of the GHE.
► The variation of ground temperature is stable below 10 m in depth.
► We estimate the performances of GSHP.
► The COP of GSHP system in cooling period is 6.0–10.9, while the COP of overall GSHP system is 4.3–7.4.
► The COP of GSHP system in heating period is 4.3–8.3, while the COP of overall GSHP system is 3.0–6.2.
► The GSHP system can reduce electricity consumption to average 44.1 kWh per day.