Study On The Comprehensive Performance Of An Air-cooling PV/T Wall System In Cold Climate Regions

Building integrated photovoltaic thermal technology is integrated to building envelope to achieve PV/T system,contributing to reducing cooling and heating load of building as well as electricity generation so as to reduce the comprehensive energy consumption of the building.However,most studies on building integrated photovoltaic thermal technology is now centered on areas with hot summer and warm winter and areas with hot summer and cold winter.There are relatively a fewer such studies in cold areas and freezing areas and also few applicable and efficient building integrated photovoltaic thermal systems for freezing areas are available.In this study,high-performance vacuum glass is used as the cover plate to design an air-cooling PV/T walling system suitable for freezing areas.Combined methods of theoretical analysis and numerical simulation,it studies the thermoelectric comprehensive performance of PV/T walling system,characteristics of the flow and heat transfer in the air channel and the influence factors.Firstly,this paper designed the air-cooling PV/T walling system suitable for freezing areas and the corresponding operation model,built theoretical analysis model and thermoelectric performance evaluation indicators for this walling system and then simulated its continuous operational states in Harbin in winter.The result shows that the temperature variation trend of each surface of PV/T walling system is in line with that of local solar radiation intensity and outdoor air temperature as time changes.When the system runs continuously,all of the temperature rises of air outlet and inlet in the channel,its instantaneous thermal efficiency and Instantaneous output power reach the maximum at noon,while the variation of instantaneous electrical efficiency of PV module goes the opposite way.Secondly,the mathematical model for turbulent flow heat transfer in the channel is built and the numerical solution is completed through simplifying the physical model of air channel in the PV/T Walling System.By comparing the calculation results of the model in this paper with the experimental results in literature,it is found that the variation trend of the two models is consistent and the error is less than 8%,which verifies the reliability of the model.Thirdly,the paper simulated and analyzed the development process of the flow field in the air channel of PV/T system with the model build above,and analyzed the heat transfer characteristic of air flow in the channel.The simulation result shows that the high and narrow channel is more favorable to the development of temperature field,velocity field and pressure field.For the temperature field,the development of temperature in the direction of height is close to the exponential distribution,the development of temperature in the direction of width decreases sharply from the two sides of walls to the middle and the temperature gradient near the walls is the biggest.It appears correlations in development of both velocity field and pressure field in the direction of height and width.The negative pressure absolute value and velocity magnitude of the flow field in the channel increase with the increase of height and decrease with the increase of width.When the ratio of height to width is bigger than 30,heat transfer of air flow in the channel perform better.Finally,this paper simulated and analyzed the variation trends of air temperature,velocity and flow in the channel of PV/T Walling System under different channel heights,widths and heat fluxes.With the increase of height,width and heat density of the channel,the air flows through the channel increase.But temperature rise will decrease as the width of channel increases.The increase of height and heat flux in the channel will increase the temperature and flow velocity at every position in the air channel to various degrees;while the increase of width in the channel will lead to the decrease of temperature and flow velocity at every position in the air channel.As a certain temperature rise shall be guaranteed for the air in the channel,the height of channel should be designed as tall as possible,while the width of channel should no more than 70 mm.The study in this paper will provide new ideas for design and application of air-cooling PV/T walling system in Freezing Area and provide theoretical basis and technical support for the implementation of Building integrated photovoltaic thermal technology in freezing areas.