How are CO2 concentrations related to ventilation rates?
Ventilation rates are inferred from carbon dioxide measurements. Occupants generate carbon dioxide, causing indoor carbon dioxide concentrations to exceed outdoor concentrations. The ventilation rate (rate of outside air flow into the building) can be estimated if the indoor carbon dioxide source strength and the concentrations of supply air and room air are known (ventilation is the only significant process for carbon dioxide removal). Indoor and outdoor CO2 concentrations are measured and the indoor CO2 source strength is estimated based on the number of occupants in a building and an estimate of their CO2 production. However, this method is subject to several sources of error which are described in detail elsewhere (Persily 1997, Mudarri 1997, ASTM D 6245-98) and summarized below: • Carbon dioxide concentrations have often not stabilized when the measurements are performed, and the use of non-steady-state values of carbon dioxide concentration in a steady-state mass balance equation