A hybrid ground-source heat pump (HGSHP) is proposed to overcome the decrease in the performance of a ground-source heat pump (GSHP) at the degraded ground thermal condition. In this study, a performance comparison between the GSHP and the HGSHP with parallel and serial configurations was conducted by varying the leaving fluid temperature (LFT) of the ground heat exchanger (GHEX), the fluid flow rate of the supplemental loop, the mean outdoor bin temperature, and the switching temperature of the hybrid operation. At the LFT of the GHEX of 40 degrees C, the coefficient of performances (COPS) for the HGSHP with the parallel and serial configurations were 18% and 6% higher than that of the GSHP, respectively. The cooling seasonal performance factors (CSPFs) of the HGSHPs with the parallel and the serial configurations were 6.5% and 2.0% higher, respectively, than that of the GSHP for Daegu city in South Korea. (c) 2012 Elsevier Ltd. All rights reserved.