Click here for the ASHRAE Position Document pdf
I am a member of ASHRAE, the professional society for air conditioning engineers. A Life Member actually, a designation you get if you hang around for 30 years.
Carbon dioxide concentration is inexpensive to measure and modern electronic control systems in buildings routinely have carbon dioxide sensors, with the ppm of carbon dioxide used as an input signal to determine the rate of outside air introduced.
In practice, I have typically seen the controls set to some set point value in the range of about 700 ppm to 1000 ppm. Outdoor air dampers are commanded to open when the carbon dioxide level exceeds the set point.
But why was this level chosen?
The link below takes you to a position document approved by the ASHRAE Board of Directors. This position paper is updated on a schedule as new information is discovered. The history of the use of CO2 concentrations in control systems is discussed in Appendix A. The conclusions of a number of studies are compared.
Here is a quote describing the issues discussed in the rest of the paper:
“While these topics have been studied for decades, incorrect application and misinterpretation of CO2 concentration as an indicator of IAQ and ventilation is common in the HVAC industry, research community, and the public. Despite many efforts to address these concerns in standards, guidance documents, technical publications, and conference presentations, significant misunderstanding of the application and meaning of indoor CO2 remains.”