This paper presents a novel model for a refrigerant-based photovoltaic/thermal assisted heat pump water heater (PVTA-HPWH) system, in which PVT evaporator simultaneously provides solar electricity and thermal energy to assist HPWH system. The thermodynamics model for a refrigerant-based PVT device features the direct interaction of PV and thermal energy with environment and HPWH system. Considering the interactive effect of surrounding conditions on PV characteristics, the proposed model can well simulate the reciprocal energy exchange of PVTA-HPWH system with better precision. The model accuracy is validated through experimental measurement with a test rig of integrated PVTA-HPWH system under real climate conditions. The dynamic behaviors of the PVTA-HPWH system are studied by theoretical and experimental analysis. The results reveal good agreements between model simulation and experiment measurement with sufficient confidence. (C) 2015 Elsevier Ltd. All rights reserved.