What condition triggers demand control ventilation (DCV) under ASHRAE 90.1 for high-occupancy spaces?

What condition triggers demand control ventilation (DCV) under ASHRAE 90.1 for high-occupancy spaces?

• A. For spaces larger than 1000 ft² with a design occupancy of ≥50 people per 1000 ft².
• B. For spaces with any occupancy if a CO2 sensor is present.
• C. Demand control ventilation is required for spaces larger than 500 ft² with a design occupancy of ≥25 people per 1000 ft².
• D. Only for spaces with a dedicated DCV system.

Answer: (C)

Demand control ventilation in ASHRAE 90.1 is required only when a space is both large enough to benefit from occupancy-based control and occupied at a density high enough to significantly impact ventilation needs. Specifically, spaces bigger than 500 ft² with a design occupancy of at least 25 people per 1000 ft² meet the trigger. This pairing ensures that DCV is applied where it can meaningfully reduce outside air and energy use without compromising indoor air quality. The idea behind the thresholds is to avoid unnecessary DCV in very small or sparsely occupied spaces, where energy savings would be minimal and the costs of control systems not justified. It’s not enough to have a CO2 sensor present alone, and it’s not required to have a dedicated DCV system; the trigger is the combination of floor area and occupancy density.

Demand control ventilation in ASHRAE 90.1 is required only when a space is both large enough to benefit from occupancy-based control and occupied at a density high enough to significantly impact ventilation needs. Specifically, spaces bigger than 500 ft² with a design occupancy of at least 25 people per 1000 ft² meet the trigger. This pairing ensures that DCV is applied where it can meaningfully reduce outside air and energy use without compromising indoor air quality.

The idea behind the thresholds is to avoid unnecessary DCV in very small or sparsely occupied spaces, where energy savings would be minimal and the costs of control systems not justified. It’s not enough to have a CO2 sensor present alone, and it’s not required to have a dedicated DCV system; the trigger is the combination of floor area and occupancy density.