ABSTRACT
The purpose of ventilation is to supply fresh air to, and meet the heating/cooling requirements and air quality of, occupants within an indoor environment. Ventilation fulfils this purpose by bringing fresh air into the airspace to replace and dilute the heat, moisture, and gaseous and particulate pollutants that eventually build up indoors. Ventilation is effective in controlling temperature, relative humidity, and gaseous concentration. Particulate pollutant control may be different from the control of gaseous pollutants and temperature, because particulate matter (PM) has distinct properties, such as gravitational settling, inertia, and spatial distribution. Particulate matter may require a combination of abatement techniques. Techniques such as filtration and dust source control, together with ventilation, have been used to keep PM at an acceptable level. Ventilation control for temperature and for gaseous and particulate pollutants can be similar when the airspace is completely mixed. For typical indoor environments, the thermal settling velocity of particles of concern is much smaller than the air velocity within the airspace, and thus the airflow patterns prevail in the transportation of particles, and the particle settling-velocity is often negligible. When air velocity is low and the particle size is large, particle-settling velocity should be considered.
