The Influence Of The Ventilation Mode Of Shopping Mall Buildings On The Diffusion Of Indoor Pollutants

In recent years,China’s economy continues to grow and develop,more and more commercial buildings towering in the city,shopping malls and buildings have good airtightness,indoor functional areas(catering,cosmetics,department stores,etc.)are diverse,and indoor pollution sources are becoming more and more complex,making indoor air quality worse.Therefore,it is particularly important for shoppers and staff to establish a good thermal and comfortable environment and hygienic environment in the mall.Due to the large flow of people in commercial buildings,relatively speaking,the fresh air volume and exhaust air volume required for their air conditioning systems are also very large,and the energy consumption is multiplied.This paper mainly studies the impact of exhaust air exhaust mode and exhaust air volume on the thermal comfort and sanitary environment of the building,in order to provide a reference for the optimal design of such building air conditioning system.Through visiting more than 40 local shopping malls in Xi’an,statistical analysis was made on the building structure,building age,and internal atrium structure of the mall.The atrium of commercial buildings mostly adopts square forms to diverse,unique and novel forms;the investigation and study of pollutants in shopping malls has found that indoor pollutants in commercial buildings are roughly divided into three categories,namely gas pollutants,microbial pollutants and inhalable particulate matter pollutants.Through the testing and analysis of air parameters(including wind speed,temperature,humidity and carbon dioxide concentration)in the mall,and objective evaluation on the basis of indoor air quality theory,the statistical analysis of the flow of people in the mall was carried out with reference to the "black box theory",and it was found that the weekend traffic was twice that of the usual time,and the flow of people on some major festivals was three times the usual flow of people.On this basis,the paper establishes a CFD physical model,uses Airpak software to numerically simulate the air flow field in the mall,and verifies the simulation results and actual measurement results by combining the design data and the measured data.Through the simulation results of the airflow organization(including wind speed,temperature,air age,carbon dioxide concentration distribution and PMV and other parameters)in the summer working conditions,it is found that there is a temperature stratification phenomenon of heat and cold in the atrium of the mall and the nearby area;the wind speed directly below the air supply outlet is better,and there is a certain sense of blowing;there are some blind spots in the upper and lower air return methods near the wall,and the carbon dioxide concentration in these areas is high.Through the analysis of the simulation results,the influence of people flow,exhaust mode,exhaust outlet,exhaust ratio and other factors in the shopping mall in different periods on the distribution of airflow organization and carbon dioxide concentration in the shopping mall is discussed.The results showed that when the flow of people doubled,the indoor temperature rose by about 1 degree Celsius,the carbon dioxide concentration increased by about 168 ppm,and the number of dissatisfied people indoors increased by 17%,when the flow of people tripled,the indoor increase was about 2 degrees Celsius,the carbon dioxide concentration increased by about 333 ppm,and the number of people dissatisfied with the indoor environment increased by 40%.According to the different density of personnel in the mall in different periods,the variable air volume air conditioning system is proposed,and the simulation shows that the required air volume on Sunday is 86% of the holiday,and the air volume required on weekdays is 72% of the holiday,which can meet the needs of indoor personnel.Comparative analysis found that under the exhaust method of each floor,the indoor comfort is better and the carbon dioxide concentration is lower;under the exhaust mode of the exhaust at the top of the atrium,the indoor air age is smaller and the air is fresher.In the case of constant exhaust air volume,the exhaust outlet is added at the top of the atrium,which has a greater impact on the top airflow organization.Change the proportion of exhaust air on each floor and the top of the atrium,and find that the impact on different areas of the mall is different,roughly divided into three areas are the atrium area,the corridor near the atrium area and other areas,with the increase of the top exhaust ratio of the atrium,the comfort of the atrium area is getting better and better,and the comfort of other air-conditioning areas is getting worse and worse.The air age change trend in the air conditioning area,corridor area and atrium area is basically the same.Increasing the overhead air at the top of the atrium can greatly improve the time of indoor air retention.The investigation of the catering area in the shopping mall found that the kitchen air replenishment scheme was used in the adjacent room,and the simulation and analysis of different exhaust methods in the catering area found that the exhaust gas flow organization effect of the exhaust gas flow around the ceiling near the wall was better,and the number of exhaust outlets was changed without changing the exhaust air volume,which had less impact on the indoor airflow organization.The above research can provide some ideas for improving the indoor quality of large shopping malls by changing the exhaust method.