MIXED VENTILATION

In cleanroom technology, mixing ventilation refers to systems that blow HEPA-filtered air into a defined space (usually turbulent) and thus achieve a purification of the room air (colloquially - air dilution). The more turbulent the air is blown in (e.g. with swirl diffusers), the better the clean air mixes with the polluted air. In addition, the contaminated room air is extracted from the room as far away as possible from the point where the clean air is blown in, or close to the source of contamination. The air exchange rate is the ratio of the amount of air supplied [m³/h] to the room volume [m³]. It provides information on how often (theoretically) the air in the room is exchanged per hour. Typical air exchange rates are between 5 and 20.

Cleanrooms are usually operated under positive pressure by introducing slightly more clean supply air than mixed air is extracted in order to prevent contamination from adjacent rooms. Typical mixed air systems for ceiling installation can be ceiling diffusers for suspended particles, but also filter fan units with swirl diffusers, baffle plates or perforated plates. For rooms with very high ceilings (also for smaller areas within large rooms), suspended particle wall diffusers, displacement air diffusers or floor-mounted recirculation modules (Airboy) are also often used. These have the advantage that they discharge the clean air to where it is needed, e.g. at working height, and therefore often manage with a lower air volume than ceiling systems. With such systems, a clean room class up to ISO 6 or class C according to GMP is possible.