In IAQ-based ventilation, which parameter is commonly used to determine the need for outdoor air?

In IAQ-based ventilation, which parameter is commonly used to determine the need for outdoor air?

• A. Humidity
• B. CO2 concentration
• C. Temperature
• D. Air pressure

Answer: (B)

CO2 concentration is used because it directly reflects how much fresh outdoor air is needed to dilute occupants’ exhaled air. As people occupy a space and generate CO2, the level rises if ventilation isn’t supplying enough outdoor air. Keeping CO2 below a target indicates the system is providing adequate dilution, improving IAQ. Humidity, while important for comfort, doesn’t reliably signal when to introduce outdoor air. Temperature relates to thermal comfort and energy use rather than contaminant dilution. Air pressure affects infiltration but doesn’t measure indoor pollutant levels. CO2 serves as a practical, measurable proxy for occupancy and ventilation adequacy, making it the standard parameter for determining outdoor air needs.

CO2 concentration is used because it directly reflects how much fresh outdoor air is needed to dilute occupants’ exhaled air. As people occupy a space and generate CO2, the level rises if ventilation isn’t supplying enough outdoor air. Keeping CO2 below a target indicates the system is providing adequate dilution, improving IAQ. Humidity, while important for comfort, doesn’t reliably signal when to introduce outdoor air. Temperature relates to thermal comfort and energy use rather than contaminant dilution. Air pressure affects infiltration but doesn’t measure indoor pollutant levels. CO2 serves as a practical, measurable proxy for occupancy and ventilation adequacy, making it the standard parameter for determining outdoor air needs.