Type 1: High mixing ventilation
High mixing systems have both supply and return air located in the upper half of the room, typically at or near the ceiling. In this system, air is forced into the space from above the occupants. It mixes and exits the space at a similar level or height (near ceiling).
Type 2: Low mixing ventilation
Low mixing systems have both supply and return air located in the lower half of the room, typically at or near the floor. In a low mixing system, air is forced into the space at the same level as the occupants. It then mixes and exits the space at a similar level (near
floor or near occupants).
Type 3: Displacement ventilation (low to high)
Displacement systems have supply air in the lower portion of the room, typically at the base of a wall or through the floor. Return air for this system is in the upper portion of the room, either high on a wall or at the ceiling. Displacement systems typically feature lower air speeds, lower turbulence, and utilize laminar diffusers to minimize mixing in the space, especially between the upper (overhead) and lower (occupied) zones. Displacement systems are designed to only condition the occupied space and have clean air move through the occupied zone to the “dirty” overhead zone where there are no occupants.
It is assumed that if displacement or underfloor ventilation (UFAD) is selected that the system is well designed and operates as intended. This means that the air flows from the lower level to the upper level without experiencing phenomena like “lock up” that could potentially trap contaminants in the occupied zone.
Type 4: Underfloor ventilation
Underfloor ventilation systems or underfloor air distribution (UFAD) are similar in configuration to displacement (low to high) systems. These systems are designed to move clean air from low to high through the occupied zone. They differ from displacement systems in that they encourage mixing within the low-level occupied zone using specially designed diffusers, typically swirl type.
It is assumed that if underfloor ventilation or UFAD is selected that the system is well designed and operates as intended. Meaning that the air flows from the lower level to the upper level without experiencing phenomena like “lock up” that could potentially trap contaminants in the occupied zone.
