This model is similar than Buildings.Airflow.Multizone.Validation.ThreeRoomsContam. However, the initial temperatures are such that at the start of the simulation, the flow direction between the three rooms reverses direction.
At the start of the simulation, the outdoor temperature is 15°C, and the temperatures of the volumes are 20°C at the top, 22°C at the bottom west and 25°C at the bottom east. Thus, initially there is a net flow circulation in the counter-clock direction. Because the volume on the east exchanges air with the outside, it cools down fast. Once it cooled down sufficiently, the flow direction between the three rooms reverses because the air in the bottom east is heaviest.
Modelica.Fluid.Systemto address issue #311.