A HGSHP (hybrid ground-source heat pump) is proposed to solve the performance degradation of the GSHP (ground-source heat pump) under imbalanced load conditions. The HGSHP is composed of three flow loops: a refrigerant flow loop, a GEL (ground flow loop), and a SFL (supplemental flow loop). In this study, the transient performance characteristics of the HGSHP were measured and analyzed in the cooling mode at various flow loop configurations, including the HGSHP(S) (HGSHP with the serial configuration) and HGSHP(P) (HGSHP with the parallel configuration), and GSHP. During the hybrid operation, the HGSHP(S) showed relatively higher COP (coefficient of performance) than the HGSHP(P) due to the lower heat accumulation in the ground under the degraded ground thermal condition. In addition, under the steady state condition, the COPs in the HGSHP(S) and HGSHP(P) were 15% and 7% higher, respectively, than that in the GSHP. (C) 2015 Elsevier Ltd. All rights reserved.