Cannot find 'ProportionalControl' for system outdoor air method.

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Hi,

I'm using OpenStudio and want to model a demand responsive HVAC system which responds to an occupancy schedule. How is best to do this?

I've seen that you can control the CO2 levels using 'ProportionalControl' but can't find this input anyway on the interface? I'm using a VAV with reheat HVAC system. 'Demand Controlled Ventilation' is switched on.

Thanks for any help, Tom