Thermal displacement ventilation (TDV) addresses problems with classroom ventilation by delivering cool air directly to the occupants of a space. The fresh air is supplied near the floor at a very low velocity, where it falls toward the floor and spreads across the room. As the air picks up heat from occupants and equipment, it rises to the ceiling and is exhausted from the space. Contaminants, including germs from the occupants, are carried up and out of the space instead of being mixed with the room air as they are with conventional ventilation schemes. TDV systems differ from underfloor air distribution systems in that they do not require a raised floor and they supply air at lower velocities.