Ideal AHU with 0% heat recovery vs. natural ventilation


I have a very general question about Ideal Air handling Units and the way they deal with heat recovery. I am modelling a building which has some zones without mechanical ventilation, just heaters. Since I still need a minimum air change rate of 0.5 h^-1, I modelled an ideal air handling unit with 0 % heat recovery. Am I aasuming this right, if I say that the air which gets into the building is the same air which would come into the building by opening the windows so that the desiderd air change rate is satisfied? Or is there still some minimal heat recovery since the ducts in which the air passes through get warmed up by the air going out? In other words: which is the best way to simulate air exchange when there is no mechanical ventilation in the room? Could I use the infiltration load instead by pushing it up a bit? That would also simulate fresh air reaching the interior. Unfortunately there is no way in HB to tell the windows to just open to satisfy the minimum air change rate.

Thank you,