This model is based on Buildings.Airflow.Multizone.Validation.ThreeRoomsContam.
In addition, a CO2 source has been added to the left
room in the bottom floor. At initial time, all volumes have zero
CO2 concentration. At t=3600 seconds,
CO2 is added to volWes. As time progresses,
the CO2 is transported to the other rooms, and
eventually its concentration decays.