I'm working on an energy model for a high-rise project in the Pacific NW that has office and residential, with residential being the top two-thirds of the building. In this region we are concerned with stack effect in the winter, and not so much in the summer. Due to issues with stack effect in numerous other high rises in the area, we are over-sizing our rooftop residential ventilation units (100% OA ducted to residences and serving the corridors) to be able to ramp when/if needed specifically for the purpose of combatting stack effect. My question is...how can we justify this to LEED and not get penalized for what is essentially a process ventilation load? The architect is providing elevator lobby vestibules in an effort to isolate the elevator shafts and limit the stack effect, but the ventilation units still need to be oversized as an extra precaution. We can provide calculations justifying the amount of ventilation, but it's difficult to predict how the stack effect will impact the building and how the unit will ramp-up, because it's so dependent on how the building is used. Our best modeled estimate would be to increase the ventilation air a scheduled amount as the temperature drops. Since the ventilation is not provided for normal ventilation purposes, I consider it as process ventilation and it should be equal in baseline and proposed.