Fair point on that its vastness allows quick recycling. They do this in Germany a lot, where even in deep winter they'll open windows to recycle the air. I thi

Fair point on that its vastness allows quick recycling. They do this in Germany a lot, where even in deep winter they'll open windows to recycle the air. I think there are a few challenges to this: 1) It's mostly manual, compared to an automatic ventilation system. Perhaps if it were more automated, I'd agree with you. 2) If it's very hot or cold or humid outside, I think doing this can impact indoor conditions and I'm not sure how much that energy cost compares to other forms of ventilation. 3) Not every part of an indoor space is very close to a window. Large indoor spaces, underground indoor spaces, small ebclosed areas such as bathrooms in the middle of homes, etc., may make it hard to just open a window and flush out the "bad" air.