Conditioned Room static pressure calculation

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I am simulating the conditioned zone in Energy plus to determine the infiltration rate. and once getting the infiltration values from energy plus, I would like to transfer it to Design builder and do the CFD analysis.

I am using Air Flow network in Energy plus.

When I am doing that, I can control the supply air flow rate by inputting the desired supply air flow rate. I do not know the static pressure prevailing inside the room. I have return air flow rate. how can I represent return air flow rate in E+ without using the option of Pressure controller?...I want certain amount of air should enter and certain amount should leave. I want to model this situation in E+ how to model return air as well?