Optimization Of Solar Fresh Air Preheating And Heating Wall With External Glass Cover

There is a significant contradiction between building insulation to reduce air penetration load and the indoor fresh air demand in winter.In order to overcome this contradiction,the predecessors and the research group studied the transpired fresh air preheating solar wall in the early stage.The problem of extra load caused by fresh air is preheated.However,its low solar energy efficiency results in low fresh air temperature,which does not meet the requirements of heating design temperature.In addition,the heat loss is great in high crosswind and extremely cold area.On this basis,in this study,the original fresh air preheating solar wall is added with external glass cover plate,and the original heat collecting metal plate is upgraded to corrugated plate.Furthermore,a novel type of solar air preheating and heating wall with glass cover is formed by adopting the downward air supply mode.Based on this,a heat transfer process of the new solar wall is analyzed and a corresponding heat transfer mathematical model is establishes in this paper,and then some evaluation index of the thermal performance of the device is put forward.Further,the thermal performance of the new solar wall is tested and simulated,and the variation law of the thermal performance of the new solar wall under different structural and environmental factors is analyzed.Next,a new simplified calculation method for thermal efficiency of solar wall is proposed for popularize engineering application.Finally,dynamic simulation and field test are carried out for the actual indoor thermal environment construction effect of the new solar wall,and its regional and architectural adaptability are analyzed.The specific research process and conclusions are as follows:（1）.Theoretical model and evaluation index of solar fresh air preheating and heating wall:The relationship between the novel type of solar wall structure and energy conservation is analyzed and the dynamic heat transfer model of this solar wall is established through theoretical analysis.The heat transfer links and thermal performance were analyzed,and the thermal performance evaluation indexes including temperature rise,heat exchange efficiency,heat collection efficiency,heat loss efficiency,equivalent thermal efficiency and exergic efficiency in the whole operation cycle of the device are given.At the same time,the evaluation indexes of instantaneous application including application efficiency,heat loss coefficient and heat load elimination rate are given.（2）.Heat transfer characteristics and structure optimization of solar fresh air preheating and heating wall:At first,the thermal balance stability time and the corresponding heat collection efficiency of the new solar wall are obtained through the experimental test of the control variables.The results show that the enhancement of secondary heat transfer in cavity 2 is an important factor to improve the efficiency.Compared with the traditional solar wall,the heat collection efficiency and heat exchange efficiency of the new solar wall are both improved by 18%～20%.Secondly,in order to expand the influence of structural factors and environmental factors on the thermal efficiency,CFD numerical simulation is carried out according to the experimental verification results.It is found that exergic efficiency increase by 1.3 times than traditional solar wall,and heat loss rate decreased by 40%in the area with high crosswind and extremely cold.The above results indicate that the energy harvesting ability of the new solar wall is improved,and the application range is wider.（3）.Simplified engineering calculation of thermal efficiency of solar fresh air preheating and heating wall:The convective heat transfer intensity,outlet heat transfer and system resistance are evaluated by Nu number,heat exchange coefficient H_εand pressure difference P_dropfor engineering extension.The coupling effects of structural parameters（height ratio H^*,characteristic thicknessδ^*,porosityσ,corrugation convexity L_w,corrugation w^*）and operating parameters（wall Reynolds number Re）on the system performance were studied by CFD simulation and the simplified expression is finally obtained.The maximum deviation of this formula is less than 6.85%.Compared with the traditional calculation method,the accuracy of the simplified calculation formula can be improved by more than 10%,indicating that the result is true and reliable.（4）.Indoor thermal environment characteristics of solar fresh air preheating and heating wall:Field test on the new solar wall shows that the temperature difference between indoor and outdoor can reach 15℃～22℃,and the temperature difference between different locations in the room is not more than 1.5℃.When the wind speed is less than 0.2m/s,both temperature and blowing sense can be met.The novel solar wall can not only provide 2～5 times as much heat as the heat load,but also reduce the heat load of the enclosure.In addition,CFD numerical simulation results show that the introduction of fresh air reduces the indoor CO₂concentration by 75%compared with natural convection.Finally,through the simulation calculation of different areas and buildings with different functions,it is found that the adaptability of the new solar wall in Xigaze is the best,and the adaptability of residential houses and offices is better than other building types.To sum up,the solar fresh air preheating and heating wall with glass cover can not only effectively improve the utilization rate of solar energy and create a good indoor environment,but also be less affected by the cold and high crosswind outdoor environment,thus solving the problems of low efficiency of the traditional solar wall and limited application in extreme areas.In addition,the structure is optimized to provide reference for engineering applications,and the designers can also evaluate the thermal efficiency according to the simplified calculation method.Finally,the dynamic elimination and adaptability of the thermal load are analyzed,which provides a basis for the operation setting.