Air velocity and air flow and Air changes of AHU system in clean room

Air velocity: 
Speed of air under unit time, the units here are feet per minute(FPM).

Air flow measured in Cubic feet per minute(CFM):

= Air velocity(Feet per min) x Supply grill area(ft square)
= the results is in CFM.

Air changes per hour :

=Air flow x 60/ Total room area(Cubic feet)
= this gives air changes per hour
Limit is not less than 20 Air changes per hour