Numerical investigation on the factors influencing the temperature distribution of photovoltaic/thermal (PVT) evaporator/condenser for heat pump systems

Abstract

Due to a high solar energy utilizing efficiency, Direct-expansion Solar-Assisted Heat Pump (DX SAHP) system has been a research hotspot for many years, especially for the system using PV/T module as the evaporator. The heat transfer throughout the PVT evaporator is an important factor for either electrical or thermal performance. We have developed and analyzed numerically the temperature distribution of a multi-source PVT heat exchanger of serpentine shape to fit a function as evaporator/condenser for Direct-expansion Photovoltaic/Thermal-Heat Pump (DX PVTHP) system. The suitability of the developed model was based on the calculated results of the efficiency factor and simulated results of temperatures of heat exchanger and working fluid as well the working fluid pressure drop. During the numerical simulations, we have considered different temperature influencing factors such as the refrigerant and refrigerant flow rate, spacing between the adjacent tubes of the heat exchanger, backside convection and radiation effect and finned heat exchanger. Simulated results showed that the serpentine PVT heat exchanger with fins and small space between tubes (62.5 mm) at 0.02 kg/s flow rate could achieve better results in terms of uniform temperature distribution, smaller fluid pressure drop (0.078 bar) and the highest efficiency factor (0.9873) which make it recommended as the best option for suitable evaporator/condenser. The average PV temperature reached by cooled and uncooled PVT evaporator at 0.02 kg/s flow rate was 47.81 °C and 71.11 °C, respectively. It was 40.99 °C and 37.07 °C at the flow rate of 0.035 kg/s and 0.05 kg/s, respectively, and 44.44 °C for PVT evaporator with smaller space between tubes at 0.02 kg/s. The average PV temperature reached by the PVT evaporator with fins was 40.734 °C at the flow rate of 0.02 kg/s while it was 53.956 °C when the unit is insulated.