| Well known as a non-polluting, inexhaustible, and clean energy source, solar energy has received considerable attention due to the shortage of the normal fossil energy and the pollution of the environment. As two different means of utilization of solar energy, the photovoltaic technology and solar-assisted heat pump technology have received great development in recent decades.The electrical efficiency of a commercial PV module is about 6-15%. More than 85% of the incident solar energy is either reflected or absorbed as heat energy. Therefore, the electrical efficiency will drop due to the considerable increase of the working temperature of the PV cells. A photovoltaic/thermal (PV/T) system, which applies a coolant onto the solar cells, can override such a limitation by bringing down its working temperature and re-utilizing the captured heat energy. The researches mainly focus on PV/T systems with water or air as the coolant. The previous researches showed that the cooling effect of water is much better than air due to its thermo-physical properties. Nevertheless, for resident use, the hot water temperature has to reach at least 40℃, which unavoidably lowers down the cooling effect of the PV system. The working temperature of the refrigerant in a direct expansion evaporator is much lower and steadier. Therefore, if the refrigerant works as the coolant of the PV cells, better cooling effect can be achieved. Based on the principle, a novel photovoltaic solar assisted heat pump (PV-SAHP) has been presented. A specially designed direct expansion PV/T solar collector with PV cells laminated on the front surface is employed in the system to act as the evaporator (PV evaporator) for dual production of electricity and heat energy. This improves the electrical yield and the overall efficiency of the system.A mathematical model based on the distributed parameter technique has been introduced for predicting the dynamic behavior of the evaporator. The pressure drop due to the friction is considered in the model. The influence of the pressure drop on the physical properties of the liquid and vapor refrigerant, such as temperature, density and enthalpy, has also been taken into account. Numerical simulation was performed with instantaneous solar irradiance, ambient temperature and inlet parameters of the evaporator. Corresponding experiments were conducted to verify the model. The results show that the photovoltaic and thermal performance, pressure and temperature are mainly decided by the solar irradiance. The ambient temperature also has some influence on the thermal performance of the evaporator. Simulation results, such as output electricity, heat gain and temperature distribution of the PV cells and evaporator show satisfactory agreement with the experimental data. Notwithstanding these, the model underestimates the refrigerant pressure drop at the PV evaporator.A distributed dynamic model for the PV-SAHP system is then established based on the theoretical study of the PV evaporator. To improve the predicting accuracy of frictional pressure loss, a simple modification factor is introduced in the model. Theoretical and experimental studies were then conducted under two different working conditions of constant and rising condensing water temperature. The results show that high photovoltaic and thermal performance can be obtained by the system. The average electrical efficiency, output electricity and coefficient of performance are around 13.11%, 371.82W and 4.3 respectively under the working condition of constant condensing water temperature. While their values are about 13.02%, 455W and 3.41 under the working condition of rising condensing water temperature. The output electricity is about 88.1% and 85.5% of the power consumption under the two different working conditions, which means that the system can offer most of the power consumed by itself. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions.Furthermore, the numerical simulations are conducted on the PV-SAHP system, commercial PV module, DX-SAHP system and "PV+SAHP" system which is a simple combination of commercial PV module and DX-SAHP system. The energy efficiency and exergy efficiency, which are based on the 1 st and 2nd thermodynamic law respectively, are presented to evaluate the overall performance of the above four systems. The results show that both the energy efficiency and exergy efficiency of the PV-SAHP system are higher than the other three systems, which means that the overall efficiency of the system can be improved with the refrigerant as the coolant.The influence of the PV cell coverage ratio and the glass cover of the evaporator on the overall performance of the PV-SAHP system was also studied theoretically. The results show that the increase of the PV cell coverage ratio can improve both the energy efficiency and exergy efficiency. While the adoption of the glass cover can improve the energy efficiency, but will bring down the exergy efficiency of the PV-SAHP system.To describe the dynamic performance of the air-source evaporator and immersed condenser, the models for the two components based on the distributed parameter technique have been introduced. An air-source heat pump system (ASHP), which employs an air-source evaporator and immersed condenser, was built. Numerical simulation and experimental study were carried out under dynamic temperature and humidity of the environment. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions of instantaneous variables of the system, including the condensing water temperature, temperature and pressure of the refrigerant, condenser power, power consumption and COP. The predicted spatial temperature distributions of evaporator and condenser also show good agreement with the experimental data. The research provides a solid theoretical and experimental foundation for the PV-SAHP system working with the air-source evaporator.
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