Have you checked the examples folder. There has been so much improvement since I last did DCV (CO2) with DOAS that my comments may be out of date (as well as the code snitbits).
Important objects are:
ZoneAirContaminantBalance
Controller:OutdoorAir
Controller:MechanicalVentilation
ZoneControl:ContaminantController
Back in the day, there was something that e+ couldn't do (can't remember what now), and I used an EMS to control the VAV terminal damper positions based on CO2 and some other factors.
Very important is the Controller:OutdoorAir object. Read the io here very thoroughly. And very important is to look at the examples in the example files folder.
Good luck.
Jean.
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