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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