It is possible to connect two AirLoop System in series?(OpenStudio)

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Hi, I have a model with a multiple AirLoops in series.

The model consists in a primary air AirLoop (AHU-1) feeding multiple VRF terminal units and two other AirLoops (AHU-2 and AHU-3). I have made the outside air AirLoop connected to the VRF but I don't know how to connect it to the other two. Is there a possibility to realize to connect two AirLoops in series in OpenStudio? How could it be done? If it is not possible, is it a valid solution to use a unitary system in the zone?

Thanks!