Air changes per hour (ACH) is a simple way to estimate the amount of ventilation in a fixed room or space. The CADR and room volume determines the ACH.
Take the CADR of a unit and divide by the room volume (in m³) = the number of air changes per hour you can achieve.
Importantly, ACH doesn't mean all of the air in the room is changed completely - clean air will constantly mix with the air already in the room. This mixing is not unique to Rediair, it's a factor in all ventilation systems. At a rate of 5ACH, assuming perfect air mixing, over 90% of the airborne contamination is removed after 30 minutes.