| The process of urbanization and social and economic development have accelerated the rapid consumption of traditional fossil fuels,resulting in a large number of greenhouse gas emissions and aggravating environmental pollution.In the field of energy consumption,the energy consumption of the whole process of China’s buildings accounts for 45% of the total energy consumption and 50.6% of the carbon emissions,of which the operation stage accounts for 21.6%.Hot water supply is an important link in the construction operation stage.In order to reduce its energy consumption and carbon emissions in the construction field,the application of renewable energy technology become the major alternative based on traditional fossil fuel technologies.Solar energy is an important component of renewable energy.The efficient development and utilization of solar energy is an important means to solve the problems of energy consumption and environmental pollution in the construction sector.At present,various solar energy utilization technologies are developing rapidly.Among them,photovoltaic/thermal(PV/T)technology,which can realize electrothermal cogeneration,has become the research hotspot of academia and the focus attention of solar energy industry,and has important social significance and broad application prospects.This paper proposes a solar PV/T photovoltaic energy storage direct drive heat pump water heater system.The PV/T collector can remarkably reduce the temperature of photovoltaic panel,improve power generation efficiency and comprehensive utilization efficiency of solar energy.In order to deeply explore the operation performance of the system and provide scientific basis and practical guidance for the promotion and application of the system,the main research contents of this paper are as follows:(1)An experimental platform for the solar PV/T photovoltaic energy storage direct drive heat pump water heater system has been built.With R134 a as the heat transfer medium,the system is equipped with energy storage batteries,and direct current(DC)variable frequency compressor is used.The DC power system can reduce the energy loss during the system operation,and consider the compactness of the system to maximize the space utilization rate,as well as realize the electrothermal cogeneration to promote the building energy conservation and electrification level.(2)The start-up characteristics of solar PV/T photovoltaic energy storage direct drive heat pump water heater system were tested experimentally.The refrigerant migration characteristics of the system at the start-up stage,as well as the start-up characteristics at different ambient temperatures and compressor speeds were studied.The experimental results show that the refrigerant migrates significantly at the initial stage,mainly from the low-pressure side to the high-pressure side,and the dimensionless pressure loss in the evaporator increases,and the refrigerant distribution tends to be stable with the system operation.At different ambient temperatures,the increase of ambient temperature is conducive to the improvement of working medium cycle status,increasing the coefficient of performance(COP)and reducing the pressure ratio,and shortening the system startup time.At different compressor speeds,the increase of compressor speed will increase the pressure ratio and reduce COP,and the system performance will be reduced,so low speed is conducive to system start-up.(3)When the water temperature in the water tank reaches 50 ℃,the operation performance of the solar PV/T photovoltaic energy storage direct drive heat pump water heater system is tested in a single heating cycle,and the influence of compressor speed on the system performance is compared.The research shows that the system performance in sunny days is better than that in cloudy days.With the increase of compressor speed,the heating duration will be shortened and the heat collection efficiency will be improved,but the COP will be reduced,which has little impact on the system power generation and power generation efficiency.The total system power generation is mainly determined by the solar radiation intensity and the system operation duration.In addition,selecting the appropriate compressor speed can make the power generation of the system meet the power consumption and improve the system performance.(4)The whole day operation performance of solar PV/T photovoltaic energy storage direct drive heat pump water heater system is tested.The results show that the power generation performance of PV/T system is higher than that of conventional PV system in summer climate,no matter in sunny or cloudy conditions.The refrigerant circulation in the PV/T collector has a remarkable cooling effect on the PV panel,compared with traditional PV panel,the average temperature can be reduced by 12.2℃～13.6℃.The average COP of the system is 5.47 in sunny day and 3.73 in cloudy day.The power generated by the system is in direct proportion to the change of the solar radiation intensity,and the power generation efficiency is comprehensively affected by the solar radiation intensity and the photovoltaic panel temperature.In sunny days,the average power generation efficiency of PV/T system and PV system is 13.67% and 12.64% respectively,with a relative increase of 8.1%.The power generation of PV/T system and PV system is 3.33 k Wh and 3.15 k Wh respectively,and the power consumption is 1.69 k Wh.The remaining power can be used by other DC equipment.The average heat collection efficiency of the system is 37.30%,and the average comprehensive efficiency is 71.24%.The system has excellent electrothermal cogeneration performance,which can provide reference for the promotion of PV/T heat pump system in the construction field. |
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