Ansys Employee

You need to define the boundaries based on what you know. I assume you know flow into the room, and one of leakage or flow out. Note, leakage wil need a boundary and unless you want to mesh the gaps around the doors it may be easier to omit it. 

Breathing is then a transient effect, with a mass flow, but also includes inhalation. You may want to rethink what you're trying to find out.