Air flow simulation in volume with fan and opening
 

Good day!

I have a simple task to model the air flow inside the volume of gas sampling chamber. Chamber contains 1 fan with known volume flow/static pressure curve, and 1 opening for inflation the gas from the outside.

My question is - what boundary conditions I need to set for this structure? Exhaust fan for fan and inlet-velocity (with 0 velocity) for opening? Or use outflow for opening?
The final task is to determine the volume air flow the fan will produce taking into consideration the resistance of flow channel and consequent pressure drop.

Thanks a lot in advance!