[Dani86]

Hi,

I'm studying mechanical engineering and I'm really new with the fantastic CFD world.
I'm modelling my first CFD model and I have a question (which may be silly but it's something that I want to understand).
I'm modelling a ventilation system for a room where there is a supply system and an extract system.
Each system has a dedicate fan. (please see attached a sketch).

With Solidwork Flow Simulation I'm modelling only the room with two openings (which represent the supply and extract grilles).
For the supply opening I have set up the flow rate= 100l/s
For the return I would like to do the same (because at the end what I know is that the flow rate for the inlet is = to the flow rate at the outlet. The same should be for the velocity right?)

Unfortunately I can't run this model because it seems that I can't define the inlet and outlet flow at the same time (see attached screenshot).
What I understand is that I should define the Inlet flow and the Outlet pressure if I want to run this model.
Can you explain me why?
If I have to set the Outlet pressure what should be the value? I can't use the environment pressure because the extract fan is creating a negative pressure and I don't know what is the value.
Can someone explain me how can I calculate the pressure at the extract grille?

Thanks for your answers.
I really appreciate your help!