You will need to draw the thermal chimney as a separate zone in the geometry of the model. You can then either use the ZoneThermalChimney
object to account for natural ventilation through the thermal chimney that is connected to an adjacent zone (easier approach) or you can use the Airflow Network to define the pressure-driven airflow connections for the model.
In OpenStudio workflows, you usually add an EnergyPlus feature to your model in the application or through an OpenStudio measure using the OpenStudio SDK (Software Development Kit). However, it looks like the thermal chimney is not part of either. In this case, you will need to either manually add the thermal chimney to the IDF (EnergyPlus input file) created by OpenStudio or write an EnergyPlus measure to automatically add the thermal chimney when you simulate the OpenStudio model.
You can reference this post for more information on the ZoneThermalChimney
object you want to use in EnergyPlus. There is also an EnergyPlus example file named ThermalChimneyTest.idf (found in C:/EnergyPlusV9-3-0/ExampleFiles) that you can reference to see how the thermal chimney object is defined and how it works in combination with other objects. This post discusses using the airflow network as an alternative that is more accurate, but more difficult to setup.