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>Basically, the return air gets exhausted while heating the incoming/supply air when CO2 concentration > X.

That’s the basic idea of demand control ventilation but how are the two air streams interfacing? If our concern is air quality, how is cross contamination between the two mitigated?

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I was confused at first by a lot of diagrams I found online, but the wiki is pretty good. Basically think of a two way radiator. Hot air flows through air channel blades on the way out, cold air flows around the blades on the way in, with filtering optional at this point. Some systems indicate that they literally mix the air, which is obviously not going to be optimal, the air needs to be fully separated with the energy exchanging through a metal layer.

https://en.wikipedia.org/wiki/Energy_recovery_ventilation

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