The NEBB Professional 2026 - Quarter 3

rates that are less than those required for the actual population. Because DCV is a form of dynamic reset, it also requires building exfiltration (building pressuriza tion) to be maintained under all DCV conditions.

• Large volume spaces may take an hour or many hours to reach measurable changes in CO2 levels.

• Ventilation systems that wait for CO2 to rise before responding are always reacting too late.

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Steady state values for different space types are provided Control logic that requires ventilation to be no less than area component airflow rate and increase immediately upon a rise in indoor CO2 levels above outdoor levels Includes minimum requirements for CO2 sensor placement Documentation requirements for min imum and maximum airflow rates and description of equipment, methods, control sequences Required operation and maintenance an nual and biennial verification and trien nial validation of CO2 sensor calibration, setpoints, airflow rates and sequences

This means occupants may experience periods of in adequate ventilation before systems respond. For ex ample, a 1,500-square-foot, 20-foot-high movie the ater with 150 seats may take 90-105 minutes for the whole volume to fill with CO2 exhaled from the audi ence and reach equilibrium. This is the lag. If the control logic waited for the CO2 to reach level, such as 1,000 ppm, then it is at least 20 minutes before ventilation starts and is always lagging. The problem is worse when fewer patrons attend the film. If only 50 people purchased tickets, then it would take 35 minutes to reach 1,000 ppm and five-and-a half hours to reach a steady state.

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What current standards say

ASHRAE Standard 62.1 requires DCV to be reset to the current population that shall not result in ventilation

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The NEBB Professional | Quarter 3 | 2026