Experimental Study On The Operating Characteristics Of Direct Expansion Photovoltaic Solar Heat Pum

Environmentally friendly energy has become the main energy source for economic development.Solar energy has become one of the first choices for clean energy because it is clean,pollution-free,renewable and has no geographical restrictions.Photovoltaic heat pump system can convert solar energy into heat and electricity at the same time,and improve the utilization rate of solar energy.The direct expansion solar photovoltaic heat pump system uses refrigerant to take away the heat of the photovoltaic panel and provide it to the heat pump system,which can maximize the energy conversion efficiency.In-depth understanding of the operating characteristics of the photovoltaic heat pump system can provide the necessary theoretical basis for improving the performance of the system.This thesis conducts experimental research on the operating characteristics of the solar photovoltaic heat pump system with direct expansion collector/evaporator.The following work has been carried out:1.Determine the flow channel of the collector/evaporator.The flow and phase change heat transfer process of refrigerant in quadrilateral and hexagonal channels are mathematically modeled,and the temperature,velocity and gas phase rate of refrigerant in the channel are compared and analyzed respectively.The results show that the gas phase rate of refrigerant in hexagonal channel is higher than that in quadrilateral channel under the same flow rate and pipe diameter.The increase of the tube diameter helps to reduce the average temperature of the refrigerant,but also reduces the gas phase rate during evaporation.2.The PV/T heat pump system test bench was built,and the iodine tungsten lamp was used as the constant heat source of the experiment to test the PV/T heat pump system.The test results show that the heat gain and COP increase with the increase of irradiance.When the irradiance is 545W/m~2,the maximum heat gain of the system is 1204.67 k J,which is 45.84%higher than that of the non-radiation stage.The maximum instantaneous COP is 6.93,and the maximum instantaneous COP_ris 7.83.The refrigerant evaporation temperature varies from-6°C to 20°C.3.With the increase of irradiance,the photovoltaic output current,photovoltaic output power and photoelectric conversion efficiency all show an increasing trend,and the photoelectric conversion efficiency can reach 14.72%.The cooling effect of refrigerant effectively improves the photoelectric conversion efficiency,which is 65.35%higher than that without refrigerant.4.The multiple linear regression method is used to analyze the influencing factors of heat gain and coefficient of performance.The correlation analysis of different factors shows that the main factors affecting the heat gain,COP and COP_rof the system are refrigerant compression ratio and evaporation temperature.The multivariate fitting formulas of heat gain,COP and COP_rare proposed by linear regression analysis,which can provide theoretical support for the performance prediction of the system under constant heat source.