The Impacts Of Outdoor Particle On Indoor Environment And Control

Indoor air quality has been intensively concerned with the increase of outdoor and indoor pollutants.Particulate matters,one of the main pollutants that affect the indoor air quality,have become a hot issue in the field of building and environment.People often use air cleaners or fresh air machines to remove indoor particulate matters.However,there are almost no related studies on when it is suitable to introduce fresh air and how to deal with the ozone produced by electrostatic air cleaners as a by-product.Aiming at solving these two problems,this paper studies the change of indoor particle concentration and the ozone generation by theoretical analysis and experimental method.Firstly,based on the data published by Nanjing air quality publishing system from June 2014 to May 2015,the particle pollution level and concentration variation in Nanjing were analyzed.The results have shown that the annual concentration of PM2.5 and PM10 in Nanjing was 66.7μg/m3 and 112.7μg/m3 respectively.The particle concentration in winter and autumn was significantly higher than that in spring and summer.The highest particle concentration appeared at night or at noonwhile the lowest concentration appeared in the afternoon.During the 2014 Nangjing Youth Olympic Games,measures were carried out to control the particle concentration by reducing the emission sources.After the control methods were removed,the particle concentration of PM2.5 and PM10 increased 34.2%and 56.3%respectively.Secondly,we modeled the particulate concentration in rooms with natural ventilation.The results have shown that,when the outdoor particle concentration is lower than the balance-point concentration,fresh air can effectively dilute the indoor pollutants.On the contrary,it will aggravte indoor particle pollution when the outdoor particle concentration is higher than the balance-point.The effect of air exchange rate on the indoor particle concentration depends on outdoor particle cocncentration,particle penetration rate,particle deposition rate and dust source emission rate.Under certain levels of pollutant emissions,the imporvement of indoor air quality apparently reduces when the air exhange rate substantially increases.Thirdly,a testing bench was built to investigate the effects of operation parameters on the ozone generation rate and purification efficiency of the electrostatic filter.Experimental results have shown that the dust removal efficiency and ozone production rate of electrostatic precipitator are approxiamately 93%and 45 mg/h under rated conditions.Electric current can enhance the electrostatic filter’s ozone generation rate and purification efficiency while the air temperature has a negative effect on them.Reduction in the current decreases ozone generation rate and purification efficiency by 58%and 28%.An increase in air temperature from 16.5℃ to 24.5℃ decreases ozone generation rate and purification efficiency by 31%and 14%。In addition,air humidity has a positive effect on the electrostatic filter’s purification efficiency and a negative effect on ozone generation rate of electrostatic filter.An increase in air humidity from 6g/kg to 12g/kg decreases ozone generation rate by 27%,but it increases purification efficiency by 55%.Finally,we proposed a model to predict the particulate matter and ozone concentration in the rooms using different electrostatic purification devices.It was found that the indoor PM2.5 can be quickly diluted by both electrostatic fresh air machine and electrostatic air cleaner,but the ozone concentration in the room with a electrostatic air cleaner can be 2.7 times higher than that with a electrostatic fresh air machine.Calculations have shown that the purification effect of electrostatic purification equipments is positively related to the dust removal efficiency and air volume,and it is negatively correlated with the ventilation coefficient,indoor dust emission intensity and outdoor particulate matter concentration.