Airflow can be controlled within each individual patient room using either down-flow or up-flow air distribution. In both cases, the airflow supply strategy will limit the amount of mixing with the existing air in the room. Up-flow, also called underfloor air distribution (UFAD) or displacement ventilation, uses the raised floor as the supply plenum. This design is commonly used in many applications today. Using natural convection, the cool air is supplied at or near floor level and then pulled up through the space toward the ceiling as the air warms. This floor-to-ceiling airflow creates a better indoor air quality by pushing the contaminants in the air toward the ceiling where they will be vented out of the room. In a medical facility, the diffusers would likely be mounted at the bottom of walls and other casework, a common practice in casino environments.
Down-flow design has been used extensively in lab and clean room environments. Acting in reverse of the more common UFAD design, the down-flow facility would use the raised floor as a return plenum. The clean air would be supplied from the ceiling as with traditional HVAC designs, only the air would be pushed toward the floor where a negative pressurized return plenum would be used to pull contaminates out of the space.