The ground source heat pump system is installed at Pamukkale University in Denizli, Turkey. The U-bend ground heat exchanger pipe length of 225 m was buried in soil at 110 m depth. In the 2007-2008 heating season, performance coefficients of the heat pump and the system were determined in the range of 2.5-4.2 and 2.03-2.66, respectively. The values of solar radiation, external temperature, relative humidity, and wind speed were measured continuously. The relations of performance coefficients of ground source heat pump according to the meteorological data including solar radiation, wind speed, relative humidity, and external temperature with this experiment was revealed exactly. The results of this study fulfill the lack in the literature.