Impact Of Natural Ventilation On Indoor Air Quality In High-rise Apartments

People cannot live without air,and indoor air quality in residential buildings influences every person and family everyday.Despite the rapid urbanism and real estate market development in the past ten years or more in China,there is no significant improvement on indoor air quality?IAQ?in residential apartment buildings.Instead,the material and furniture outgassing from fine decoration has led to even worse sick building syndrome.Due to current status and trend on high-density community and high-rise residential apartment buildings,it is essential to conduct a systematic research on improving IAQ.Considering the tradition in using natural ventilation for improving IAQ,it is used as the main design optimization strategy to improve IAQ in high-rise residential apartment buildings.Through a careful literature review,this investigation found that,except CO,most of indoor air pollutants exceed standard limits in the last decade in China,such as formaldehyde,TVOC,benzene,etc.By comparing various IAQ analysis methods,the study also found that numerical simulation is more suitable than empirical and experimental method as a research method for investigating IAQ.In order to analyze the main source composition and the changing trend of indoor pollutant in residential buildings,the study monitored indoor air pollutant in three types of fine decoration high-rise buildings: unoccupied,occupied for more than one month,and occupied for more than one year in four different communities in Xi'an and Chongqing.The investigation found that most of the monitored pollutants concentration met the national standards.With the increase in the occupation,the concentration of formaldehyde,TVOC,benzene decreased.But some indoor pollutants such as CO,NO₂ concentration were still exceeding the standards in some rooms.The study revealed that with the significant differences on the building decoration materials in the market,it is more feasible to control the source strength of indoor pollutants if real estate developer is in charge of the decoration.Since the Chinese uses natural ventilation,it can be used to improve IAQ.But not the IAQ in all the rooms is satisfactory by natural ventilation.It is necessary to further study how to improve ventilation for entire apartment building and each apartment to control indoor pollutant concentrations.This investigation selected two high-rise residential communities in Chongqing and Xi'an for studying natural ventilation through numerical simulations by computational fluid dynamics?CFD?.Field measurements were also conducted to obtain data for validating the numerical simulation results.For outdoor wind distributions,the numerical simulation results agreed with the measured data.Since only steady outdoor wind speed from one direction was used for simulating natural ventilation in an apartment,the differences between the simulated results and experimental data were significant.Because actual outdoor wind changes direction and speed all the time,the numerical simulation was different from the real situation.When the wind was relatively steady,the simulated results agree well with the measured data.This study found that CFD is valid for simulating natural ventilation.This study simulated separately indoor and outdoor airflow and used outdoor airflow calculated as the boundary conditions for indoor airflow simulations.The method can reduce the computing cost while maintaining accuracy.Finally,this study presented a three-stage design strategy for optimizing natural ventilation in high-rise residential buildings in Chongqing,China.By using CFD program ANSYS Fluent,this investigation shows how to optimize ventilation design with the three-stage optimization strategy.First,each building orientation and distance between buildings were adjusted.Then a north-south wind tunnel and two east-west wind tunnels were created to enhance natural ventilation in the building.Finally,windows were designed to let wind flow through the apartment.The optimized design can reduce the age of air to less than 6 min in 90% of the rooms,compared to the age of air greater than 30 min in 50% of the rooms in a conventional design.After conducting field measurement in occupied apartments which is optimized with the developed design strategy and comparing with numerical simulation,the better natural ventilation performance of the whole building has been proven.In conclusion,the study shows that the proposed three-stage optimization strategy of natural ventilation can achieve better IAQ for high-rise apartments through community planning,building design,and floor layout optimization.