ASHRAE Ventilation Guidelines

ASHRAE Standards specify that outside air for ventilation purposes should be introduced at the lowest volume necessary to maintain adequate indoor air quality.

Ventilation is defined as the process of supplying or removing air by natural or mechanical means to or from any space. This air may or may not have been heated or cooled. Ventilation is necessary to remove or dilute CO2, odors, and other contaminants from occupied or production process spaces.

Air contaminants are defined as gasses, such as CO, CO2, volatile organic compounds (VOCs), particulates, and other substances that affect indoor air quality (IAQ).

Dilution of indoor air is defined as a process that adds outdoor air (which is assumed to be less contaminated) to reduce the concentration of contaminants. This dilution can range from the use of "100% outdoor air" to a combination of outdoor and recirculated indoor air that has been filtered.

The ventilation rate is defined as the number of complete air changes for a given unit of time. Ventilation rate is also referred to as the cubic feet per minute (cfm) of outdoor air that is required for meeting minimum IAQ requirements.

ASHRAE Standard 62-l989, Ventilation for Acceptable Indoor Air Quality, specifies the outdoor air ventilation requirements at a minimum of 15 cfm per person in non-smoking areas, regardless of occupant usage, and a minimum of 60 cfm per person for smoking areas. Also the concentration of CO2 should not exceed 1,000 parts per million in conditioned spaces.

Appendix E of ASHRAE Standard 62-l989 contains a procedure for using cleaned recirculated air. Mechanical codes have also changed to allow increased recirculation rates based on the effectiveness of the air filtering equipment.

ASHRAE Standard 62-1989 is currently under review for revision. The proposed revision contains significant charges.