Exposure to Metabolic CO₂ in a Room with Mixing Air Distribution

In the current practice CO₂ is used as an indicator of exposure to indoor pollutants. Complete mixing of room air is assumed with mixing air distribution. Under this assumption, the representative CO₂ concentration used to assess the indoor air quality and/or to control the ventilation system is measured in the exhaust air or on the walls. However, factors like air flow interaction or pollution source strength and distribution in the space affect the CO₂ concentration field in a room. Consequently, this has an impact on occupants’ exposure to pollution. In this study, the impact of heat load distribution, number and location of diffusers, and distribution of occupants on the CO₂ exposure was studied experimentally. The experiments were conducted in a climate chamber. Seven persons and a breathing thermal manikin were the source of metabolic CO₂ in the room. The CO₂ concentration in the air inhaled by the manikin was measured. The results showed that the excess CO₂ concentration in the inhaled air was up to 48% higher than in the exhaust. Hence, the CO₂ concentration measured in the exhaust air or at the walls might not be the correct representative for the realistic occupants’ exposure assessment.