US Patent 6919809 Optimization of building ventilation by system and zone level action

A method of selecting a ventilation control strategy from among a plurality of ventilation control strategies. The method comprises the steps of: determining if a CO2 signal is present and valid; selecting a CO2 based ventilation control strategy if the CO2 signal is present and valid; selecting a second ventilation control strategy if the CO2 signal is not present or is invalid; and operating using the selected strategy. The selection step occurs in a zone controller.