I am wondering how I might model a common laboratory exhaust fan system in EnergyPlus and or OpenStudio. The term exhaust fan generally means a fan dedicated to a thermal zone or a system and it exhausts air from those components, maintaining a mass balance etc.

In large laboratories, an exhaust fan might actually only exhaust some of the buildings airflow and makeup or bypass and blend in outside air. The goals of the exhaust fan system is to maintain a minimum effluent discharge velocity or plume height. Therefore the fan system has a minimum volumetric flow (cfm) must pass through the fan. To maintain this minimum cfm, a bypass air damper is provided with the exhaust fan system to bleed unconditioned air to mix with the reduced lab exhaust volume. This allows the exhaust fan to maintain the desired discharge velocity.

My question is how I could even go about doing this in an energy model. I have a fairly good understanding of how the air-node networks and systems in energyplus are setup and I cannot seem to think of a way this could be done, outside of creating a completely DEDICATED zone and system to the exhaust fan system.

This article has a great example image of what I described here as well: http://www.greenheck.com/library/arti...

Any input would be much appreciated. Thanks.