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closeAbsolute ventilation per occupant dominates, but....
Posted by hlevin on 25 Apr 2012 at 06:35 GMT
Protection against the transmission of airborne infection is increased by maximising absolute ventilation per occupant, which may be achieved by increasing the number of ACH or by increasing the room volume per occupant for a given rate of air exchange.
http://plosmedicine.org/article/info:doi/10.1371/journal.pmed.0040068#article1.body1.sec1.p2
Ventilation is not (normally) evenly-distributed in all areas or heights of a room's volume. The highest velocities will occur at and downwind from the opening through which air enters the room. As the air plume spreads out to affect the entire space, the velocity is reduced away from the entry opening. The local air exchange rate may vary in different parts of a room, and the "age of air" (its residence time prior to being diluted and/or removed) is an important indicator of ventilation efficiency. Effluents from patients out of the pathway of strong air flow are not as well diluted by ventilation as those that are in the direct pathway.