[mhays]

I'm not an expert in venting requirements. Just the proposal/research guy for a general contractor that does schools, retail, biotech, industrial, office, multifamily, etc., in Seattle.

Depending on what you're venting, it could be a safety issue or a smell issue. Schools might need to vent a bunch of stuff, from kitchen exhaust to auto shop fumes to art fumes to humid locker rooms to natural gas in the labs. They have a mix of spaces with tons of people (classrooms) that require a lot of changes and other areas with few people that need fewer. A good HVAC concept will accommodate all of this at a decent first cost and operational cost. Nobody wants an operable window anywhere near your cafeteria vents. Nor do you want your intakes next to anything but pristine air. All of this gets tougher the more you stack things.