Air change rate measurements using indoor/outdoor ratio of PM2.5

According to past researches, most people spend 80%-90% of their time indoors. The ventilation is very important to people’s health and the comfortable surroundings around us. From the viewpoint of energy saving, mechanical ventilation will consume a large amount of additional energy. So variety of ways measuring natural ventilation is worth considering. In fact, in real life, many people tend to have their windows shut rather than open, and the reasons are complex.
Some reasons are due to safety, maintaining a good thermal environment, harmful outdoor pollutants, shielding from outside noise etc. Thus, it is necessary to set an index of low ventilation rate, in order to simulate the situation of windows shut or slightly opened. The ACH is controlled between 0.5 and 1, by adjusting the window openings. As measurement technique, the constant injection method can be used to measure the infiltration rate of natural ventilation. One useful way is the dry ice method, in which dry ice in an insulated container is used as a constant injection of tracer gas. Apart from dry ice method, the PM2.5 is considered to be another kind of tracer gas. The main sources of PM2.5 come from burning of fossil fuels. If there are no indoor sources, e.g. smoking or waste-combustion, we can assume that there are no initial indoor sources of PM2.5, where all sources come from outdoors. Then the I/O ratio of PM2.5 can be used to determine different ventilation rates.
In this study, the ACH from tracer gas method and I/O ratio of PM2.5 was compared. The relevance between ACH and I/O ratio will be verified through a specific equation to get further conclusion, through which we can get ACH directly by means of measuring I/O ratio of PM2.5.