Air Change Rate

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)