CO2 Based Ventilation Control – Importance of Sensor Positioning

Indoor carbon dioxide (CO2) concentration (c-n) is measured in buildings for the assessment and control of the air quality. The indoor CO2 c-n, measured at only one location in the room - either in the exhaust room air or at one of the walls, is considered the same as the concentration in the inhaled air and is used for ventilation control. The main objective of the current study was to identify if the CO2 cn in the exhaust air or at the walls is the same as the CO2 c-n in the air inhaled of the occupants. CO2 measurements were performed in a simulated meeting room. Seven subjects and one breathing thermal manikin were present in the room. The room was ventilated either via mixing or displacement air distribution. The CO2 exposure was assessed by measuring the CO2 c-n in the air inhaled by the manikin. The CO2 c-n was also measured close to the breathing zone, on the walls, and in the supply and exhaust air. The results show a substantial difference in the CO2 c-n measured in the air inhaled by the manikin compared to the CO2 c-n measured at the exhaust air and on the walls. The air distribution method was of a high importance. Non-uniformity of the CO2 c-n was found in the room during the two studied air distribution methods. The CO2 c-n measured at 0.3 cm behind the occupants and at 0.6 m height was the closest to the CO2 level in the inhaled air under displacement air distribution. For the studied setup with mixing air distribution, the CO2 c-n measured at 0.5 m above the occupants’ heads was the closest to the c-n in the inhaled air.