How can I develop two different Air Loops in the OpenStudio model?

edit

EnergyPlus constrains a given zone to only one AirLoopHVAC system through the ZoneHVACEquipmentConnections object, which allows only a single "Zone Return Air Node" as opposed to a list of nodes. A zone is added to the AirLoopHVAC based system through the "Zone Air Inlet Node" (of which there can be many) and the "Zone Return Air Node" (of which there can only be one). @rraustad might be able to give more detail about why EnergyPlus is structured this way.

Zone equipment connects to a zone through the "Zone Air Inlet Node" and the "Zone Air Exhaust Node" (defined in ZoneHVACEquipmentConnections) both of which are extensible through a node list. Because of this you can have as many zone hvac components as you want.

OpenStudio doesn't let you do this because that is a constraint in EnergyPlus. The most common solution for this would be to provide ventilation through an air loop and conditioning through zone equipment.

There is actually an old old video on YouTube that demonstrates this with a packaged terminal heat pump as zone equipment, but I think without the energy recovery.

Another technique I have heard of in different use cases when someone wants to model two air loops in one zone, is to model it as two zones with zone mixing objects between the zones. I don't have any experience doing that to know how well it works.