So, I am reasonably familiar with VRF and DOAS at this point, I believe.
The way I understand it, the DOAS is injecting OA directly into the thermal zone, instead of into the VRF terminal unit intake. If the OA conditions coming from the DOAS were identical to the RA conditions, I could see there might not be a difference, but if the OA conditions coming from the DOAS were different from the RA conditions, then injecting OA into the thermal zone vs. injecting it into the VRF terminal unit intake might have different results.
I believe there is a AirTerminal:SingleDuct:Mixer that might be able to accomplish injection into the VRF terminal unit intake, but I am afraid I do not know how to apply it in the context of VRF (there is no "air loop" to manipulate). Would you have any ideas? One of the challenges would be to identify the various nodes, I believe.
The VRF terminal unit (ZoneHVAC:TerminalUnit:VariableRefrigerantFlow) does have OA provisions (for example Cooling Outdoor Air Flow Rate), but I believe this then represents straight OA, i.e. not pre-conditioned OA from a DOAS.
Further, the above DOAS really is a standard air loop. What if the DOAS itself were a VRF outdoor unit with VRF terminal unit? If there was only one such VRF terminal unit, which seems "typical", one might still be able to force this into an air loop by "simply" applying the VRF performance curves to its coils and fans. However, it might be possible that one VRF outdoor unit drives two or more VRF terminal units, all of which take in 100% OA. What would one do then?
All this in the context of OpenStudio measures, by the way.
