In building ventilation control, CO₂ isn't considered a contaminant with a strict danger threshold to avoid exceeding. Rather, it serves as an indicator of outdoor air dilution within a space, with outdoor CO₂ levels establishing a baseline reference. Indoors, CO₂ levels rise as occupants exhale during normal activities. The balance between CO₂ production and outside air introduction determines an equilibrium level, which varies depending on outdoor concentrations and ventilation rates.

Historically, it was assumed that outdoor CO₂ levels hovered around 300 ppm, but due to global industrialization, levels have increased to 400-500 ppm in urban areas, signaling global warming trends. Instead of setting a new baseline, many guidelines now emphasize the relationship between indoor and outdoor CO₂ differentials.

Demand Controlled Ventilation (DCV) utilizing CO₂ is an energy-efficient strategy endorsed by building codes and LEED certification. It adjusts ventilation based on actual occupancy and outdoor air dilution, ensuring both indoor air quality and energy savings. Most IAQ and LEED standards now compare indoor CO₂ levels relative to outdoor levels rather than using a fixed global average.

Monitoring outdoor CO₂ levels aids in assessing indoor levels. Specialized outdoor CO₂ sensors, such as the Global's CO2 series, offer accurate measurements in various weather conditions. Utilizing a dual-wavelength, non-dispersive infrared sensor and long-term adjustment signal processing, the Global's CO2 series ensures industry-leading accuracy and reliability. It provides analog signal outputs for integration with building automation systems and is available in standard or heated enclosures for diverse climates. Optional temperature sensors and adjustable relay outputs further enhance its versatility.