Types of Air Distribution
Nearly all schools currently use the mixed-airflow method for distribution and dilution of the air within the occupied space. Designers should investigate a method called vertical displacement ventilation or thermal displacement ventilation. This approach successfully uses natural convection forces to reduce fan energy and carefully lift air contaminants up and away from the breathing zone.
[Click on the image to begin the animation. Cool supply air (blue) slowly flows out of the two heating/cooling registers in the corners of the room, and spreads across the floor. As it is warmed by people (brown columns represent students) and other warmer objects in the room, it rises upward, continuously lifting polluted air up and away from the occupants. It is then collected and exhausted outdoors. This animation requires Windows Media Player or RealPlayer. Animation used courtesy of Dunham Associates, Minnesota, MN.]
Quick removal of concentrated air contaminants and building pressurization are two ways that exhaust systems affect IAQ. Special use areas such as science labs, vocational/technical shops, cafeterias, and indoor pools already have well established regulatory codes regarding ventilation with outdoor air and negative pressure requirements with respect to adjacent spaces. Less well recognized areas in schools where special exhaust ventilation is desirable are janitor closets, copy/work rooms and arts/crafts preparation areas where off-gasing from significant quantities of materials or products may occur. These areas should be maintained under negative pressure relative to adjacent spaces.