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Outdoor Air vs Ventilation Air

Outdoor Air vs Ventilation Air

(OP)
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.

RE: Outdoor Air vs Ventilation Air

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.

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