Outdoor Air vs Ventilation Air

[ME27272727]

Can someone help me out with the difference between "outdoor air" and "ventilation air" as defined in the international mechanical code?

From chapter 2 definition of 2015 IMC:

Outdoor Air - Air taken from outdoors, and therefore not previously circulated through the system.

Ventilation Air - That portion of supply air that comes from outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air in a designated space.

Why it matters... From the 2015 International Existing Building Code:

809.2 Altered Existing Systems - In mechanically ventilated spaces, existing mechanical ventilation systems that are altered, reconfigured, or extended shall provide not less than 5 cubic feet (cfm) per person of outdoor air and not less than 15 cfm of ventilation air per person; or not less than the amount of ventilation air determined by the Indoor Air Quality Procedure of ASHRAE 62.

 

[EnergyProfessional]

Looks like ventilation air is all the supply air going to the space and OA is the portion that came from outside. Looks like they want 2/3 return air (10 of the 15 cfm)
i didn't read the rest of the code, so don't know the context.
Different codes never coordinate with each other.