| The heating energy consumption in north China is an important part of building energy consumption,and the cold wind infiltration heat load is the main component of the heating load in winter.This often requires the building to have good tightness,winter indoor lack of fresh air,air quality deterioration phenomenon is widespread.If the outdoor fresh air can be preheated by natural energy in winter and then passed into the room,the problem of insufficient fresh air and high energy consumption of heating can be alleviated to a certain extent.Therefore,in the western plateau heating area with rich solar energy resources in China,unglazed transpired solar collectors is an efficient and reliable passive solar energy utilization technology,which can organically combine fresh air and heat demand,and alleviate the dual problems of indoor fresh air demand in winter and reduce cold air infiltration load.This paper firstly introduces the structure and working principle of unglazed transpired solar collectors,analyzes the air flow and heat transfer process inside the wall through the network diagram of heat transfer resistance of the wall,and establishes the heat transfer mathematical model of unglazed transpired solar collectors.The heat performance evaluation indexes such as heat collection efficiency,heat exchange efficiency and fresh air preheating effect are put forward.The geometric design parameters and thermal performance evaluation indexes of unglazed transpired solar collectors are analyzed by the combination of experimental research and numerical simulation.The research process and main conclusions are as follows:(1)The effects of infiltration hole diameter,solar radiation intensity and fan suction speed on the thermal performance of unglazed transpired solar collectors in steady state meteorological environment were studied.The results show that the solar radiation intensity has a significant effect on the efficiency of unglazed transpired solar collectors and the preheating effect of fresh air.Fan suction speed can improve the overall heat transfer of the system,increase the amount of new air into the room,and can improve the heat collection efficiency of the system,but can not effectively improve the outlet temperature and reduce the heat exchange efficiency;The infiltration hole diameter can effectively improve the heat collection efficiency,but is not conducive to the air preheating effect.(2)Through the three-dimensional unsteady dynamic environment simulation,the order of influence of the key factors on the thermal performance of unglazed transpired solar collectors is obtained:the infiltration hole diameter D<non-uniformity of heat collecting plate opening H*<air interlayer thickness<fan suction speed Vs;when the infiltration hole diameter is larger than 6mm,the temperature of the outlet suddenly drops nearly 8℃.Therefore,the reasonable selection of the infiltration hole diameter range is one of the keys to system performance.Non-uniformity of heat collecting plate opening is closely related to the convective heat transfer performance.And the maximum convective heat transfer is when the non-uniformity of heat collecting plate opening is0.45.A small thickness of air interlayer is beneficial to heat collection of the system,but too small thickness of air interlayer may lead to obvious overheating problem.When the thickness of air interlayer is kept at 50mm,the suitable air supply temperature can be satisfied.Increasing the fan suction speed can improve heat transfer and increase the fresh air volume,but it will reduce the temperature of the outlet.A balance should be found between the demand for fresh air volume and the air supply temperature.It is recommended that the air supply volume should be 46m~3/h～56m~3/h.It can be seen from the comprehensive analysis of the temperature field and velocity field distribution at different locations in the room,and it is found that the temperature and velocity distribution basically meet the requirements of thermal comfort of human body and the uniformity of blowing.By analyzing the matching relationship between the fresh air load and the fresh air volume in different periods throughout the day,it is found that the average load at noon can completely meet the requirement of zero load of indoor fresh air.When the fresh air load is maintained at the daily average level,the new air volume is kept below 56m~3/h,which can fully meet the indoor heat demand.The applicability of unglazed transpired solar collectors in each functional building is ranked as:school building>office building>hotel entertainment and other residential buildings.More suitable for school buildings,office buildings such as promotion in this kind of buildings due to their characteristics of heating day and night. |
