Carbon dioxide (CO₂) sensors play an increasingly important role in modern HVAC control strategies—especially in environments where occupancy varies throughout the day. When used correctly, these sensors help maintain indoor air quality, optimize ventilation, and significantly reduce energy consumption.
Why CO₂ Matters in HVAC Control
CO₂ is naturally present in the atmosphere. Outdoor concentrations typically range from 300–500 ppm. Indoors, CO₂ levels rise as people exhale. A person at rest produces around 456 liters of CO₂ per day, according to a New York Times estimate. As occupancy increases, CO₂ concentration increases—and that rise can be used as a signal for when to bring in fresh outside air.
This concept forms the foundation of Demand Control Ventilation (DCV).
Meeting Ventilation Requirements
ASHRAE standards require certain levels of fresh outside air during occupied hours to maintain acceptable indoor air quality. During unoccupied hours, conditioning outside air is not necessary—reducing energy demand.
But what about spaces that are not occupied continuously?
That’s where CO₂-driven control strategies become valuable.
What Is On-Demand (CO₂-Based) Ventilation?
Demand Control Ventilation uses CO₂ sensing to introduce fresh air only when occupancy levels increase. Instead of maintaining constant outside air ventilation, the system responds to real-time CO₂ concentrations.
This method is ideal for spaces with unpredictable or intermittent use, such as:
- Conference rooms
- Cafeterias
- Classrooms
- Auditoriums
- Worship centers
- Multi-purpose rooms
When CO₂ levels rise above normal thresholds, actuators open outdoor air dampers, increasing ventilation. When levels drop, dampers close—preserving energy and maintaining comfort