In commercial buildings, the actual number of people within the building at any given time is frequently lower than the designed peak occupancy. If the building has a conventional HVAC system that delivers a fixed rate of outside air pegged to the peak occupancy, the result can be overventilation and a waste of energy and money.

A cost-effective solution in many situations is carbon dioxide-based demand controlled ventilation (DCV). This well-established technology uses one more carbon dioxide (CO²) sensors and a system controller to vary minimum outdoor air ventilation based on indoor CO² levels. Since humans exhale carbon dioxide at predictable rates depending on how physically active they are, indoor CO² levels can serve as a proxy for occupancy.

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