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Why to measure CO2?

Sensors in an HVAC environment


CO2 - NDIR CO2 sensing technology
Carbon Dioxide or CO2 is not only a by-product of combustion, it is also the result of the metabolic process in living organisms. Because carbon dioxide is also a result of human metabolism, concentrations within a building are often used to indicate whether adequate fresh air needs to be supplied to the space. Ventilation systems that are controlled based on the measured CO2 level can control the fresh air supply depending on the occupants and their activity level.

Moderate to high levels of carbon dioxide can cause headaches and fatigue, and higher concentrations can produce nausea, dizziness, and vomiting. Loss of consciousness can occur at extremely high concentrations. To prevent or reduce high concentrations of carbon dioxide in a building or room, fresh air should be supplied to the room.

NDIR is an industry term for “nondispersive infrared”, and is the most common type of sensor used to measure CO2. CO2 gas molecules absorb the specific band of IR light while letting other wavelengths of light pass through. Finally, an IR detector reads the amount of light that was not absorbed by the CO2 molecules or the optical filter. The difference between the amount of light radiated by the IR lamp and the amount of IR light received by the detector is measured. The difference is proportional to the number of CO2 molecules in the air inside the room.

Ventilation based on CO2-level is interesting in rooms with highly variable occupancy, such as meeting rooms, classrooms, universities, etc.