Underfloor Parking Garage without mechanical ventilation

Hi, We are working on the certification of an office building under NC v2009 in Germany. The building is totally mechanically ventilated except for the undefloor parking garage which is naturally ventilated. However the natural ventilation does not comply with ASHRAE 62.1 "Exhaust not required if two or more sides comprise wall that are at least 50% open to the outside". However there are ventilation openings big enough to provide with natural air flow and in compliance with the local building codes for parking garages. There is also an expertise done to show compliance. We tried to use the compliance path using the european norms EN 13779 and EN 15251, but these norms only give guidelines for mechanical ventilation systems and for indoor air quality where persons are expected to be (offices, classrooms, ...). does anyone have any experience with this issue? Does anyone know what to do in this case? would a CFD-simulation help in any way? any hints are welcome! Thanks a lot