A method for operating an air handling unit of an HVAC system. The method includes opening an outside air flow control device to enable breathing air flow during a high outdoor air time period to a first zone having a first number of occupants and a second zone having a second number of occupants that is less than the first number of occupants. The outside air flow control device is then closed to enable conditioning air flow during a low outdoor air time period to the first and second zones. Further, a variable air volume (VAV) air flow control device provides desired amounts of breathing air to the first and second zones suitable for the first and second number of occupants, respectively. A VAV air temperature control device then provides conditioning air to the first and second zones having a suitable temperature for the first and second number of occupants.