Gaseous Pollutant Transmission Through Windows Between Vertical Floors In A Multistory Building With Natural Ventilation

Natural ventilation,as a passive ventilation strategy,is widely used in residential building ventilation.Especially in the transitional season,residents often choose to open windows for ventilation to reduce indoor temperature and improve air quality.However,when the indoor air quality of a room is not satisfy the standard,it is very likely that other floors will be polluted by the cross air flow in the ventilation process.Generally,the cross flow between households is driven by wind and buoyancy,and the influence of uneven temperature distribution on the air flow on the outer wall of buildings under the action of solar radiation cannot be ignored.However,the existing studies usually assume constant wall temperature or adiabatic facade,so it is difficult to accurately reveal the cross-transmission characteristics of airborne pollutant.In view of this,this study takes the single-sided natural ventilation process of a residential building as an example to explore the influence mechanism of wind pressure,thermal pressure and solar radiation on the cross-transmission characteristics of pollutant,in order to provide a reference for the natural ventilation design of residential buildings.Firstly,the single-sided natural ventilation of a multi-storey residential building is selected as the research object,and the geometric model and mathematical model of the cross transmission of airborne pollutant under the effect of wind and buoyancy are established.The air thermal flow and the solar radiation heat gain of the building facade are respectively determined by the BSL k-ω turbulence model based on the Reynolds averaged equation and surface to surface radiation model.And scalar transfer model is used to describe the transmission of airborne pollutant.Then,the accuracy of the BSL k-ω turbulence model and surface to surface radiation model,as well as the boundary condition settings,are verified respectively by using the experiments of natural ventilation of buildings driven by wind and buoyancy and indoor air thermal flow under the effect of solar radiation.Finally,combined with the annual solar radiation characteristics in Dalian,the typical representative days are selected as the calculation conditions.And the verified mathematical model is used to calculate the pollutant transmission characteristics with the ventilation air flow under the combined effect of wind and buoyancy.Analyze the characteristics of flow field,temperature field and pollutant concentration field and quantify the air re-entry ratio and personnel infection risk in different households’rooms under different wind speed,wind direction,window structure,pollution source location and solar radiation intensity to deeply reveal the cross-transmission characteristics of airborne pollutant in a residential building.The results show that the outdoor wind speed and direction will directly affect the ventilation of residential rooms and the transmission of pollutants between floors.Overall,air change rate per hour in the resident room increases with the increase of outdoor wind speed,but under different wind directions and window structures,the increase and decrease of ventilation rate in the resident room are not consistent.Compared with the windward condition,the change range of air change rate with wind speed in the residential room under leeward condition is relatively small.The concentration of pollutants in the resident’s room is closely related to the air change rate.With the increase of air change rate per hour,the concentration level of pollutant gradually decreased.The personnel infection risk decreases as the floor rises compared to the personnel infection risk in the room where the source of contamination is located.The risk of human infection between adjacent floors is reduced by about one order of magnitude.Under leeward conditions,the personnel infection risk is significantly lower than that under windward condition.Compared with the three window structures commonly used in residential buildings:Awning Window(AW),Vertical Slide Window(VSW)and Turn Window(TURN),AW can better seal the pollutants to the room where the pollution source is located,thus effectively inhibiting the cross-transmission of pollutant in the vertical room.However,VSW has the worst ability to limit the cross-transmission of pollutant to the upper room,resulting in an increase of indoor personnel infection risk by nearly 57%.When the pollution sources are located in different floors,the corresponding cross-transmission characteristics of pollutant are also inconsistent.If the pollution source is at the bottom of the building,the pollutant will spread to the upper room with the buoyant air flow,showing significant unidirectionality.If the pollution source is located in the middle floor of the building,the pollutant will be transmitted between households in two directions,that is,people at both bottom and top floor room are infected by contaminants from the source room.In addition,the solar radiation intensity and its uneven distribution will also affect the cross-transmission of pollutant.With the increase of solar radiation intensity,the cross-transmission characteristics of pollutant become more significant.However,the inhomogeneity of temperature distribution on the building fa(?)ade caused by solar radiation strengthens the spread of pollutant across households to a certain extent.The research results have important theoretical significance and application value for accurately depicting the cross-transmission characteristics of airborne pollutant in a residential building,assessing the risk of infection from indoor personnel contaminants,establishing risk aversion strategies,and optimizing natural ventilation design.