Indoor Carbon Dioxide Concentrations in Ventilation and Indoor Air Quality Standards
Andrew K. Persily
Indoor carbon dioxide (CO2) concentrations have played a role in discussions of ventilation & indoor air quality (IAQ) since the 18th century. Those discussions have evolved over the years to focus on the impacts of CO2 concentrations on building occupants, how these concentrations relate to occupant perception of bioeffluents, the use of indoor CO2 concentrations to estimate ventilation rates, & CO2based demand control ventilation. This paper reviews how indoor CO2 has been dealt with in ventilation and IAQ standards & guidelines in the context of these issues. While measured indoor CO2 concentrations are rarely close to health guidelines, much confusion has resulted regarding CO2 in ventilation & IAQ standards. For example, a CO2 concentration of 1800 mg/m3 (roughly equivalent to 1000 ppmv) has become a de facto standard in many discussions w/o a sound understanding of its basis or significance. And while there have been anecdotal associations of CO2 concentrations in this range with occupant symptoms such as stuffiness & discomfort, research results do not support these associations w/the CO2 itself. Several studies have shown associations of elevated CO2 levels with occupant symptoms, but these findings are likely due to lower ventilation rates elevating the concentrations of other more important contaminants along with the CO2. The relevance of CO2 concentrations to ventilation and IAQ standards is based primarily on 2 factors:their relation to indoor levels of bioeffluents & associated odors, & their relation to ventilation rates per person. Several studies of bioeffluent odor perception in chambers & buildings have shown correlations between dissatisfaction with these odors & both ventilation rate per person & CO2 level. Also, ventilation rates & indoor CO2 levels are related based on a single-zone mass balance of CO2. However, many individuals use CO2 concentrations to estimate building ventilation rates w/o understanding the associated mass balance theory.
36th Air Infiltration and Ventilation Centre Conference
Indoor Carbon Dioxide Concentrations in Ventilation and Indoor Air Quality Standards, 36th Air Infiltration and Ventilation Centre Conference, Madrid, -1, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=919027
(Accessed February 9, 2023)