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.