Field test of the Ground Source Heat Pump (GSHP) system applying variable water volume (VWV) control and multi-split heat pump has been carried out in order to demonstrate the effect of reduction of circulation pumps' electric power consumption. It was confirmed that the constant differential temperature control is practicable method as the VWV control method. As the result of field test, the GSHP system applying VWV control could reduce approximately 80 % of circulation pumps' electric power consumption compared to the GSHP system applying constant water volume. Seasonal performance factor of the GSHP system was 4.51 and this result achieved the target value of more than 4.5. During the heating operation, seasonal performance factor of the GSHP system was 3.61 and the value was higher than the one of conventional system. In addition, it was shown that the decrease of system COP of GSHP system using antifreeze solution as heat carrier fluid is less than 15 % compared to the one of GSHP system using water.