Operational performance study on a photovoltaic loop heat pipe/solar assisted heat pump water heating system

A new photovoltaic loop heat pipe/solar assisted heat pump (PV-LHP/SAHP) water heating system was introduced in this paper. With the combination of solar energy, LHP and heat pump technology, the composite system could operate in the PV-LHP mode, the solar/air source heat pump (SASHP) mode and the air source heat pump (ASHP) mode. The mathematical model of the system was constructed to simulate operating performances in typical working conditions and in long-term run. The influence of main structure and operating parameters were also analyzed. To validate the accuracy of the built model, an outdoor test rig of the PV-LHP mode was established in Qinhuangdao City. Investigation results showed that the overall photothermal efficiency of the system is comparable to traditional photovoltaic/thermal (PV/T) water heating systems. The monthly average power consumption per liter hot water is 0.009 kW h/L, and the monthly average COP of heat pump modes is about 3.10. Besides, the annual solar heating ratio of the system is up to 57.8%. Compared with the traditional ASHP system, the life cycle cost of the PV-LHP/SAHP system could be reduced by 29.6%.