Air Change Rate
Calculate air change rates - equations in imperial and SI units.
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Air Change Rate - Imperial Units
Air change rate - air changes per hour - expressed in imperial Units
n = 60 q / V (1)
where
n = air changes per hour (1/h)
q = fresh air (make up air) flow through the room (Cubic Feet per Minute, cfm)
V = volume of the room (Cubic Feet)
Air Change Rate - SI Units
Air change rate expressed in SI-units
n = 3600 q / V (2)
where
n = air changes per hour
q = fresh air (make up air) flow through the room (m3/s)
V = volume of the room (m3)
Example - Air Change Rate SI Units
With an air flow of 3 m3/s in a 20000 m3 room the air change rate can be calculated as
n = 3600 (3 m3/s) / (20000 m3)
= 0.54 (h-1)
Typical Air Changes per Hour
Typical air changes per hour for well-insulated spaces:
- no windows or exterior doors - 0.33 (1/h)
- windows or exterior doors on one side - 0.67 (1/h)
- windows or exterior doors on two sides - 1 (1/h)
- window or exterior doors on three sides - 1.33 (1/h)
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