Air changes per hour
BG 87/2024, Useful Information Guide, written by Chin Hang “Kay” Lam and published by BSRIA in 2024, defines air changes per hour (ACH or AC/hr) as: ‘The flow rate of air supplied to or extracted from a room, expressed in m3/h, divided by the volume of the room. Also sometimes referred to as ‘air change rate’ or ‘air exchange rate’. Note that, in most types of ventilation systems, the air in a room is never completely changed – it is only diluted.’
--BSRIA
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