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 175m 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. (c) 2012 Elsevier B.V. All rights reserved.