What Units are Used for Ventilation and Air Infiltration?
Various units are used to describe the rate of ventilation. These include:
Volumetric flow rate: Ventilation and air infiltration is commonly expressed in terms of a volumetric air flow rate e.g. litres/s (l/s) or m³/s.
Per occupant air flow rate: Sometimes the volumetric flow rate is divided by the number of occupants in a space to give a flow rate for each occupant. This is commonly expressed in terms of litres/second for each occupant, i.e. l/s.p.
Unit area flow rate: Alternatively, the air flow rate may be divided by the floor area of an enclosure to give a unit area value, i.e. litres/second.m².
Air change rate: Air flow is also often expressed in terms of hourly ‘air change rate’ (ach). This is the volume flow rate of air into an enclosure (e.g. a room or the entire building) divided by the room (or building) volume.
Mass flow rate: Sometimes air flow rate is expressed in terms of the mass flow rate of air, e.g. kg/s. Mass flow is needed to determine the thermal energy carried by the air stream. It is also widely used in ventilation and air flow calculation techniques.
AIVC World Wide Web Edition Containing selected articles
and features from the printed editions.