A CO2 sensor measures carbon dioxide concentration in indoor air, typically ranging from 400 to 5,000 ppm, to optimize ventilation requirements based on occupancy and air quality needs. These sensors use non-dispersive infrared (NDIR) technology to detect CO2 levels with accuracy of ±30 to ±50 ppm. Building codes increasingly require CO2 sensors for demand-controlled ventilation (DCV) systems to reduce energy waste from over-ventilation while maintaining indoor air quality standards.
Sensor Technology and Accuracy
NDIR sensors emit infrared light at 4.26 micrometers wavelength, measuring CO2 absorption to calculate concentration. Typical residential backgrounds measure 400 to 450 ppm, while occupied spaces reach 800 to 1,200 ppm. Office occupancy thresholds typically trigger ventilation increases at 800 ppm setpoint, with occupied classrooms reaching 1,500 to 2,000 ppm during instruction. Sensor drift requires factory or field calibration every 2 to 5 years to maintain accuracy specifications.
DCV System Benefits
CO2-based demand-controlled ventilation reduces outdoor air handling costs by 20 to 40 percent compared to continuous fixed-rate ventilation. Integration with VAV systems automatically reduces outdoor air damper position during low occupancy periods, decreasing HVAC fan energy and heating or cooling loads. Compliance with ASHRAE 62.1 ventilation standards requires CO2 sensors in spaces with variable occupancy like conference rooms, classrooms, and retail areas where benefits justify installation costs of 300 to 800 dollars per zone.