OpenStudio/EnergyPlus Thermal Zone Outdoor Air Balance with Exhaust Fan Only and 100% Outside Air System

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I am attempting to model an outdoor rest station with two large bathrooms. Based on ASHRAE 62.1 the restrooms have an exhaust airflow requirement of 70 cfm/toilet. Additionally, I am modulating the CFM by the occupancy schedule since there is very low occupancy during the winter.

In OpenStudio, I am using a Fan:ZoneExhaust object in each thermal zone with the Maximum Flow Rate option matching the CFM for the number of toilets. Using a 100% outside air system, I was hoping that the system would supply the correct amount of ventilation air to the space to supplement the exhausted air, without specifying any ventilation requirements.

However, in the error report, I am receiving the message:

  ** Warning ** GetOAControllerInputs: Controller:MechanicalVentilation="CONTROLLER MECHANICAL VENTILATION 1
  **   ~~~   ** Cannot locate a matching DesignSpecification:OutdoorAir object for Zone="THERMAL ZONE: 1 FEMALE RESTROOM".
  **   ~~~   ** Using default OA of 0.00944 m3/s-person and 0.0 m3/s-m2.

and

   ** Severe  ** Controller:MechanicalVentilation="CONTROLLER MECHANICAL VENTILATION 1", Design Specification Outdoor Air Object Name blank
   **   ~~~   ** For Zone="THERMAL ZONE: 2 MALE RESTROOM".
   **   ~~~   ** This field either needs to be filled in in this object or Sizing:Zone object.
   **   ~~~   ** For this run, default values for these fields will be used.

Which appears to be applying a Design Specified Outdoor Air that doesn't really balance with the Fan:ZoneExhaust object.

My question is, using the Fan:ZoneExhaust object with the Decoupled mode and Unbalanced (as seen in the documentation), is my fan being properly balanced with the 100% OA packaged rooftop system?

Should I specify a 0 DesignSpecification:OutdoorAir or will this incorrectly size my system?

What is the best method to balance my ventilation and exhaust flowrates for these spaces?

What about when I add energy recovery ventilation? How do I force the exhaust air back to my central system while keeping the correct ventilation requirements for the restroom?