But it is the density factor related to the occupancy type that responds to this need: This lower rate might seem counterintuitive at first because a densely occupied area needs more ventilation. Office spaces require 17 cfm/person however, an auditorium seating area only requires 5 cfm/person. Occupant density is also influenced by occupancy type and plays an important factor in the overall amount of ventilation air needed in a space ( Figure 1). For example, museums/galleries require a minimum combined outdoor air rate of 9 cfm/person, while animal areas in pet shops or weight rooms in health clubs require no less than 26 cfm/person. Most HVAC systems will recirculate some component of indoor air (filtered and reconditioned).Īn examination of the minimum combined outdoor air rates from Standard 62.1 reveals that ventilation requirements vary based on occupancy type - which impacts expected activity level (think heavy breathing and perspiration) and the potential for indoor pollution sources. It is important to acknowledge that we are referring to outdoor air specifically. For our purposes, we will measure the delivery of outdoor air in cubic feet per minute per person (cfm/person) based on the combined outdoor air rate. Thus, ASHRAE offers a combined outdoor air rate to simplify matters. If both sources are present and both (for example) produce perceivable odors, then the ventilation rate required for adequate dilution is the sum of the rates needed to handle each source separately. Sources originating from the building and its furnishings: response in cfm/sf.Sources originating from occupants and their activities: response in cfm/person.

Breathing zone airflow