Title: Outdoor Air Supply
Course: WGF 106 DEVELOPMENT > Section: Content

Image | Heating, ventilation, and air conditioning (HVAC) systems are responsible for providing thermal comfort and fresh air to building occupants. HVAC systems are often the source of the largest opportunities for both energy and financial savings
Content
Outdoor Air Supply

Adequate supply of outdoor air, typically delivered through the HVAC system, is necessary in any office environment to dilute pollutants that are released by equipment, building materials, furnishings, products, and people. Carbon dioxide (CO2) is a normal constituent of exhaled breath; thus, CO2 will also increase during building occupancy. CO2 levels are routinely collected in air quality studies because they can indicate whether a sufficient quantity of outdoor air is being introduced to an occupied space for acceptable odor control. The American National Standards Institute (ANSI) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) develop consensus standards and guidelines for HVAC systems. ASHRAE notes in an appendix to standard ANSI/ASHRAE 62.1-2010: Ventilation for Acceptable Indoor Air Quality that indoor CO2 concentrations no greater than 700 ppm above outdoor CO2 concentrations will satisfy a substantial majority (about 80%) of visitors with regard to odor from sedentary building occupants (body odor). This would typically correspond to indoor concentrations below 1200 ppm since outdoor CO2 concentrations usually range between 375 to 500 ppm. However, CO2 is not an effective indicator of ventilation adequacy if the ventilated area is not occupied at its usual occupant density at the time the CO2 is measured. Elevated CO2 concentrations suggest that other indoor contaminants may also be increased. If CO2 concentrations are elevated, the amount of outdoor air introduced into the ventilated space may need to be increased.

ASHRAE guidelines provide specific details on ventilation for acceptable IEQ. A ventilation system expert can help meet ASHRAE ventilation guidelines in the building. ANSI/ASHRAE 62.1-2010 recommends outdoor air supply rates that take into account people-related sources as well as building-related sources. For office spaces, conference rooms, and reception areas, 5 cubic feet per minute of outside air per person (cfm/person) is recommended for people-related sources, and an additional 0.06 cfm for every square foot (cfm/ft2) of occupied space is recommended to account for building-related sources. In elementary and high school classrooms, 10 cfm/person plus 0.12 cfm/ft2 of outdoor air is suggested. To find rates for other indoor spaces, refer to Table 6-1 also found in ANSI/ASHRAE 62.1-2010.

Outdoor Air Quality

When present, outdoor air pollutants such as carbon monoxide, pollen, and dust may affect indoor conditions when outdoor air is taken into the building's ventilation system. It is important to properly install and maintain HVAC system filters, which can trap many particles. Controlling gaseous or chemical pollutants may require more specialized filtration equipment and sometimes relocation of the outdoor air intakes.
Attributions | Image courtesy of Sustainable Facilities Tool – U.S. General Services Administration Content courtesy of NIOSH – Centers for Disease Control and Prevention