Imagine I have room that is very hot and it is colder outside. I want to cool it down using a fan.
There is only one door. I have one fan.
Where should I put it and which way should it blow?
I have two doors, one on each end. I still only have one fan.
Same as scenario 2, but I now have multiple fans.
For convenience, it is fine to assume that the room is a cuboid and that the fan emits no heat.