Research On Performance Of Photovoltaic Loop Heat Pipe Water Heating System

A new solar photovoltaic loop heat pipe(PV-LHP)water heating system was designed in this paper,which combines loop heat pipe and photovoltaic/thermal(PV/T)technology.The system has high solar overall efficiency,and can provide domestic hot water for users in cold regions.It can solve some of its own power consumption problems,which is conducive to achieve building energy conservation and emission reduction targets.In this paper,the energy and exergy performance of the system were studied by the combination of experiment and numerical simulation.The research content of this paper includes the following aspects:First of all,according to the meteorological situation in the cold regions of China,we had designed the target system.An outdoor testing rig was set up in Qinhuangdao City to measure the system performance.Based on the first and second laws of thermodynamics,the energy and exergy performance evaluation indicators and methods were proposed to analyze the system performance.Based on the testing rig,the performance of typical working conditions in winter,summer,spring and autumn were tested,and the influence of main structure and operating parameters on system performance was analyzed.The results showed that the operating performance of the system shows obvious seasonal characteristics.The average solar thermal efficiency and overall energy efficiency in summer conditions were 62.5% and68.47%,respectively.While the largest daily average photoelectric efficiency and overall exergy efficiency appeared in winter were 13.31% and 12.11% respectively.Thus the PV-LHP water heating system has the potential to promote applications in cold regions.The refrigerant charge and the height difference between the collector and the condenser have a significant impact on the system performance.In addition,based on the law of conservation of energy,a numerical model of the target system was established.The simulation program of the system was written with Visual Basic 6.0 as the platform,and the difference between the simulation and the experimental results was compared and analyzed to verify the accuracy of the numerical model.Finally,the transient simulation software TRNSYS was used to establish a common flat-panel solar water heating system and a common single-crystal silicon photovoltaic power generation system model,and the performance comparison between the target system and the single solar energy utilization system was carried out.The results showed that compared with the single solar energy utilization system,the overall energy efficiency and overall exergy efficiency of the system were increased by at least 6.77% and 36.68%,respectively,and the solar energy utilization efficiency advantage is obvious.