I was modeling a simple air loop in OpenStudio, in the exported EnergyPlus IDF file, the "Sizing:System" object shows that the "100% Outdoor Air in Cooling" and the "100% Outdoor Air in Heating" were automatically set to "Yes". I think this would lead to significant over sizing of the cooling and heating coils. However, I did not find a place in the OpenSutdio user interface that I can specify these two fields to "No".