What is CO2 used for in 62.1?

• A. CO2 is used as a common indicator to modulate outdoor air delivery in DCV schemes and to assess IAQ potential.
• B. CO2 is ignored in determining outdoor air deliveries.
• C. CO2 only affects energy consumption calculations.
• D. CO2 is used solely for occupant comfort temperature control.

Answer: (A)

CO2 in ASHRAE 62.1 is used as a practical indicator of occupancy and ventilation effectiveness. In demand-controlled ventilation, CO2 sensors monitor space concentration and the system adjusts outdoor air delivery to match occupancy: when more people are present, more fresh air is brought in; when fewer people are present, the supply can be reduced while still meeting IAQ goals. CO2 also helps assess IAQ potential—if CO2 levels rise above target, it signals that the current ventilation may be insufficient for the occupant load, indicating IAQ risk. This makes CO2 a useful, real-time surrogate for ensuring adequate ventilation without over-ventilating, rather than something ignored or used only for energy calculations or temperature control.