The NEBB Professional 2026 - Quarter 3

• Indoor CO2 levels are influenced by outdoor CO2 concentrations, which are constantly ris ing and can fluctuate with season and locality. • Sampling error or placement of CO2 sensors can provide a lower or higher reading than ac tual conditions. • CO2 DCV is based upon achieving a steady state condition, and it is being used for a dy namic control. • CO2 DCV has inherent lag to actual population due to the need to fill a space volume to achieve steady state. • CO2 sensors have natural drift, can get dirty or degrade, and require periodic recalibration or replacement. • Air that reduces indoor CO2 levels does not necessarily have to come from outdoors; it only has to come from a source with less CO2 but may contain other contaminants. This makes tracking airflows and pressurization important. • Control logic is often incorrect, such as waiting until the room reaches a steady state condition (e.g., 1,500 ppm) resulting in under-ventilation,

or setting too aggressive a setpoint (e.g., 800 ppm), which can lead to overventilation.

As a result, an organization may unintentionally: •

underventilate its facility, affecting IAQ and occupant well-being, or overventilate , impacting comfort, increas ing energy use and operational costs.

•

The lag effect & steady state: Why timing matters

One of the most significant — and often overlooked — challenges of CO2-based DCV is lag. CO2 does not instantly reflect actual population. It takes time for CO2 to accumulate and reach a measurable level within the room and even longer to reach steady state. In large-volume environments such as theaters, gyms or auditoriums, this delay can be substantial. The effect is amplified when the actual occupancy is low er than design, which is the point of DCV to begin with.

READ, QUIZ, EARN! After reading the full issue, please go to the NEBB Learning Center at https://nlc.nebb.org to take a 5-question quiz to earn 0.25 NEBB CEC!

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The NEBB Professional | Quarter 3 | 2026