N = Q/V x 60 min/hr
Where:
Q= volumetric flow rate in cfm,
V = volume in cubic feet
N = air changes per hour (ACH) Note: in your lab this was referred to as RACH.
V = Qt
Where:
Q = volumetric flow rate in cfm
t = time in minutes
V = volume
Q = KG/C x 106
Where:
K = mixing factor, unit-less (also referred to a safety factor)
G = Generation rate of contaminant in cfm
C = Concentration at standard (PEL,TLV or REL) in ppm
Q = Required volumetric flow rate in cfm
You will also need molar conversions.
How long does it take to change the air in a room twice? Given a room 39 ft x 28 x 9 ft and a ventilation rate of 2,457 CFM?