Michaels - CO2 Levels and Ventilation



	Using CO₂ levels as an indicator of adequate 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 not an instantaneous value; not a ceiling value outdoor CO₂ levels have increased ASHRAE guideline was based on 300 ppm outdoor concentration 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 20 CFM/occupant in an office: ~4 hours At 5 CFM/occupant in an office: >12 hours At 15 CFM/occupant in a classroom: ~1 hour nAt 5 CFM/occupant in a classroom: ~3 hours nReferences: ASHRAE Std. 62-1999, Appendix D; and ASTM Std. D6245, Standard Guide for Using Carbon Dioxide Concentrations to Evaluate Indoor Air Quality and Ventilation (May 1998)	Stay informed about current technologies and practices. Click here to subscribe to our FREE electronic News Briefs.



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