The 3D model was imported and prepared as FBX, in the process the BIM HVACTool reads in all textures and materials.
The hangar is ventilated via air outlets under the ceiling. To maintain mass continuity, the mass flows are defined. Only if you use mass flow everywhere, mass continuity is easy to handle:
The background Mesh Size for snappyHexMesh Tool is about 20cm.
The mesh is about 200 million cells: