The NEBB Professional 2026 - Quarter 3

Rethinking Demand-controlled Ventilation: What FMs should know

By Darryl DeAngelis

Demand-controlled ventilation (DCV) has long been promoted as a strategy to reduce energy consumption by adjusting outdoor airflow based on occupancy. In practice, many systems rely on carbon dioxide (CO2) levels as a proxy for the number of people in a space. However, while CO2-based DCV has been widely adopted for decades, its limitations are becoming in creasingly apparent — especially as facility managers are expected to deliver energy efficiency and verified indoor air quality (IAQ), occupant comfort and com pliance with evolving standards. Although the use of CO2 as an indicator of ventilation dates back 170 years, it was research in the 1980s led by P. Ole Fanger that shaped the modern use of CO2 DCV. His work established relationships among ven tilation rates, CO2 concentrations and perceived air quality to unadapted persons as it relates to body odor. Where CO2-based DCV comes from

This research informed early versions of ventilation standards, including ASHRAE Standard 62, which associated acceptable IAQ with approximately 1,000 ppm CO2 under typical conditions. It is important to note that this was based on an outdoor air CO2 lev el of 350 ppm, which has risen to an average of 425 ppm today. As CO2 sensor technology became more affordable in the 1990s, it enabled broader implemen tation of DCV strategies in commercial buildings. The problem: CO2 is not a direct measure of ventilation While CO2 can indicate occupancy trends, it is not a direct measurement of outdoor airflow. Several factors make CO2-based DCV inherently uncertain: • Variable CO2 generation rates (varies by age, gender, diet and activity level), which are typi cally unknown variables at design, commission ing, and test and balance that result in incorrect setpoints for CO2 and outdoor air rates.

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The NEBB Professional | Quarter 3 | 2026