As far as I know (AFAIK), no one has posted to equest-users to describe a way to accurately model heat recovery using an OA-FROM-SYSTEM DOAS assigned to a dummy zone. The main problem being that the OA-FROM-SYSTEM uses the dummy zone temperature as the return air temperature to the ERV.
In the case of this particular model, I think a more reasonable workaround would be to model energy recovery at each of the VAV units instead of modeling a dedicated DOAS. Model each VAV system with SELF-CONTAINED ERV-FANS and distribute the DOAS fan power amongst the VAV systems.

Regards,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer
134 South Fitzhugh Street???????????????? Rochester, NY 14608
T: (585) 698-1956 F: (585) 325-6005
bbishop at pathfinder-ea.com?????????? www.pathfinder-ea.com
Carbon Fee and Dividend - simple, effective, and market-based.