In this study, the effect of the process parameters and levels of the coefficient of performance (COPWS) of a ground-source heat pump (GSHP) system with a double U-tube heat exchanger is studied. The experiments were performed under various space air inlet/outlet temperatures and soil inlet/outlet temperatures in the GSHP system. The optimization of the process parameters in the GSHP system was carried out by the Taguchi method. In this study, the process parameters were considered as air inlet/outlet temperatures and soil inlet/outlet temperatures. The experimental design was evaluated as an L-16 orthogonal array. To evaluate experimental results, the most significant process parameter, COPWS, was determined by using analysis of variance (ANOVA) and signal/noise (S/N) ratio. The optimum parameters and levels of COPWS for GSHP were obtained as A(1)B(4)C(1)D(3) by the Taguchi method. The optimum levels were computed as T-i(,sa) at Level 1 (7.5 degrees C), T-o,T-sa, at Level 2 (21 degrees C), T-i(,)wa at Level 2 (25.5 degrees C), and T-o,T-wa at Level 1 (24 degrees C). As a result, the most significant factor of COPWS in the GSHP system was obtained as the space air inlet temperature, which is the most significant parameter with 66.50 percent contribution ratio.