Experimental investigation of a solar driven direct-expansion heat pump system employing the novel PV/micro-channels-evaporator modules

This paper aims to investigate a solar driven direct-expansion heat pump system employing the novel PV/micro-channels-evaporator modules, in terms of its solar thermal, electrical and overall efficiency, as well as coefficient of performance (COP), at the real-time operational condition. This work was undertaken through a dedicated system design, construction, field-testing and performance analysis. It was found that the novel PV/micro-channel-evaporator modules could achieve an average thermal, electrical and overall efficiency of 56.6%, 15.4% and 69.7% respectively at the specified operational condition, while average COP of the system reached 4.7. The innovative feature of the system lied in the structure of the evaporator that was made of the parallel-laid micro-channels. Such a structure created the reduced interior cross-sectional area and thus increased vapor flow velocity within the channels, while the high vapor velocity generated a higher shear stress exerted upon the liquid-vapor interface, leading to the reduced liquid film thickness, increased refrigerant evaporation rate, and increased electrical and heat outputs. The research has provided the fundamental data and experience for developing a highly efficient and practically feasible solar heat pump system applicable to the cold climatic conditions, thus contributing to significant fossil fuel saving and carbon reduction in the global extent.