Ground water source heat pump system is the oldest one of the ground source heat pump systems. Despite of this, little formal design information has been available until recently. The important design parameters for open system are the identification of optimum ground water flow, heat exchanger selection and well pump. In this study, the capacity of 50 RT system of two well type ground water heat pump system was used. As a result, static water level was -7 m and the level during the heating operation was -32 m, cooling operation was -40 m. The initial static water level recovered within 48 hrs. The temperature of ground water is $15.6^{circ}C$ for heating season and $16.2^{circ}C$ for cooling season and does not depend on the outdoor temperature. Operation efficiency of the system shows that, COP 3.1 for heating and COP 4.2 for cooling.