Modeling buoyancy between a lower floor and an upper floor in EnergyPlus

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You can model buoyancy effect using the object "AirflowNetwork:MultiZone:Component:HorizontalOpening". According to the Input Output Reference, "The airflow across the opening consists of two types of flows: forced and buoyancy. The forced flow is caused by the pressure difference between two zones, while the buoyancy flow only occurs when the air density in the upper zone is greater than the air density in the lower zone. This opening also allows for the possibility of two-way flow when forced and buoyancy flows co-exist." This object must be linked to a FenestrationSurface:Detailed object.