Controlling the exhaust fan in order to have a depressurized zone.

edit

Hi everyone,

I am trying to model an AirflowNetwork for an apartment. My model aims to control the pressure of the room, in order to achieve it, the airflow rate of both supply and exhaust of the apartment have to be controlled. I figured how to pressurize the zone, and control the exhaust by making it a fraction of the supply using ' Zone HVAC: EquipmentConnections: Zone Return Air Node 1 Flow Rate Fraction Schedule Name', as a result, the pressure can only be positive.

What I am looking for now is to find a way to depressurize the zone (The exhaust airflow should be higher than the supply), it would be appreciated if anyone has a clue of how it can be done, or whether it is even possible to implement or not in E+.