Section 6.2.5/Demand Control Ventilation
ASHRAE 62.1 Section 6.2.5 covers demand control ventilation using CO2 sensors to adjust outdoor air based on actual occupancy.
Demand control ventilation is permitted as a means of reducing outdoor air during periods of low occupancy. For spaces with high occupant density (design occupancy exceeding 25 people per 1,000 square feet) served by systems with outdoor air capacity of 3,000 CFM or more, DCV is required by many energy codes. The most common DCV method uses CO2 sensors to estimate occupancy: when CO2 rises above a setpoint (typically 800-1000 ppm), the outdoor air damper opens further. The system must maintain the minimum area-based ventilation rate (Ra) even when the space is unoccupied.
Why this section exists
Spaces with high design occupancy (conference rooms, auditoriums, classrooms, dining areas) are often occupied at a fraction of their design capacity. Without DCV, the HVAC system provides outdoor air for the full design occupancy at all times, wasting energy conditioning air that is not needed. DCV matches the outdoor air rate to the actual occupancy, saving 20-40% of ventilation energy in high-density spaces while maintaining indoor air quality.
What plan reviewers look for
Plan reviewers check for CO2 sensors on the mechanical control drawings in high-density spaces. They verify the CO2 setpoint and the control sequence that modulates the outdoor air damper. They check that the minimum area-based ventilation rate (Ra times Az) is maintained as a floor even when the CO2 level is low. They also verify that DCV is provided where required by the energy code.
Common violations
Related ASHRAE 62.1 requirements
Section 6.2.1 covers the zone outdoor air rate that DCV modulates.Section 6.3.1 covers system ventilation efficiency for multi-zone systems with DCV. ASHRAE 90.1 Section 6.5.3.7 and IECC C403.7.3 specify when DCV is required. Section 6.2.2 provides the Rp and Ra values used in DCV calculations.