The Importance of Air Change Rate

Air Changes per Hour (ACH) is the number of times the entire air volume of a room is replaced within one hour. A low value means accumulation of pollutants and carbon dioxide, while an excessively high value causes noise and energy waste.

Mechanical ventilation system in a commercial building
Mechanical ventilation system in a modern commercial building

Required Rates per ASHRAE 62.1

Space Type Required ACH L/s per person
General offices 4 – 6 8.5 L/s
Meeting halls 6 – 8 10 L/s
Hospitals – Patient rooms 6 – 12 Per ISO 14644
Operating rooms 20 – 25 Unidirectional flow
Commercial kitchens 15 – 20 Full isolation
Parking garages 4 – 6 CO Detection Required
Warehouses 2 – 4 2.5 L/s/m²

Calculation Method

Airflow (m³/h) = ACH × Room volume (m³)

Example: A meeting room 100m² × 3m height = 300m³, with ACH=8 → required airflow = 2400 m³/h