CO2 Levels and Ventilation

• Occupants consume O2 and exhale CO2 at a rate primarily dependent on level of physical activity

• body size (surface area) and diet are also factors

• Serves as a surrogate for measuring occupant-generated pollutants; addresses the “people component” of proposed Addendum “n” to Standard 62-1999

• ASHRAE’s 1000 ppm guideline is very often misapplied 

• outdoor CO2 levels have increased

• nOutdoor air ventilation rate can be estimated based on the equilibrium CO2 level (with certain simplifying assumptions)

• Time required to reach an equilibrium concentration of CO2 will vary based on ventilation rate and occupant density:

• At 5 CFM/occupant in an office:  >12 hours

• nAt 5 CFM/occupant in a classroom:  ~3 hours

© 2008 Michaels Engineering Inc.  All rights reserved.