simulating the efect of a vent or a pump
 

How can i simulate the effect of a pump or a ventilator without modeling the geometry using CFX 5.5?

My problem invloves the use of a ventilator and i knw the volumetric flow rate. I only want to know how can I calculate the pressure raises at the ventilator in order to reach that volumetric flow rate.

I already have the geometry of my simulation and the location of the ventilator.