Basic Research On The Statistical Analysis Of Limited Space Air Stability On Human Breathing Microenvironment

Since the outbreak of COVID-19,in order to control the spread of the epidemic,people spend more time indoors.How to improve indoor air quality and reduce the risk of disease transmission caused by human exhaled has become an important issue in indoor environmental control.Based on limited space air stability,the distribution and transmission mechanism of exhaled pollutants in the breathing microenvironment-a kind of objective microenvironment for indoor occupants-was studied by combining the indoor environmental conditions and human factors.Firstly,a four-person sitting human interpersonal breathing experiment was carried out in a full-scale test room.The indoor environmental conditions including limited space air stability and ventilation methods were combined with the human factors including indoor layout and wearing masks.CO₂was adopted as the indicator to study the transmission of exhaled pollutants.At the same time,by measuring the temperature distribution of the temperature boundary layer above the human head,the effect of different stability conditions on the human thermal plume was studied.Then,in order to further analyze the effect of different factors on the direction of pollutants transmission,cluster analysis and cross-correlation analysis were carried out on the time series formed by the experimental data.The cross-correlation was used to indicate the main direction of transmission under different stability conditions to give corresponding ventilation suggestions.Finally,a classification model based on the BP neural network is established to recognize the air condition in limited spaces indoor air stability whit different ventilation methods and human factors,aiming to optimize the design of ventilation system and indoor layout according to different transmission mechanism of exhaled pollutants.The results show that the diffusion and transmission mechanism of human exhaled pollutants in the human breathing microenvironment is dependent on many factors.In the unstable condition,the exhaled airflow is more difficult to maintain its inertial state.After being exhaled by the subject,it is rapidly mixed with the surrounding air,and the pollutants spread more widely.The pollutants in the breathing microenvironment are distributed more uniformly.The movement in the vertical direction is sensitive to the change of ventilation form.Floor air supply can further aggravate the mixing of pollutants and ambient air in the microenvironment.Therefore,these two engineering control methods are best for rapid diffusion and dilution of pollutants.In the stable condition,the exhalation airflow accumulated at the height of the mouth tends to move in the direction of the main flow and is hard to spread around.The human thermal plume is similar to exhaled pollutants,and its development and spread are also affected by air stability.Compared with the unstable and neutral types,the thermal plume also tends to move along the main flow direction.In the stable condition,the movement of pollutants in the horizontal direction is sensitive to the change of the ventilation methods.The exhaled airflow tends to move downstream with the ventilation airflow,and the main direction of transmission also changes with the direction of the incoming ventilation.When the exhalation direction of the subjects is perpendicular to the direction of the supply airflow,this transmission mechanism become more apparent at downstream area.Therefore,people should try to avoid staying in the downstream area for a long time,or local ventilation should be used to accelerate removal of exhaled pollutants in stable condition.When the subjects ore masks,the pollutants distribution in the breathing microenvironment is more even.In the unstable condition the horizontal direction is more sensitive to the change of the ventilation methods.Due to the change of the direction of the exhaled airflow,the areas of the exhaled microenvironment that are sensitive to environmental factors also change.In actual monitoring,the concentration of pollutants in the middle and upper parts of the exhaled microenvironment should be focused on.This study could be beneficial to establish a new ventilation design guidance method based on the air stability of limited space.In practical applications,the distribution and diffusion mechanism of pollutants under different stabilities should be utilized rationally to optimize the design of ventilation methods and indoor layout forms.