Major tangent, but a product that I can't believe doesn't seem to exist is window fans (not AC units) with passive shutters to prevent air leakage when not in use. I've actually built an exhaust fan in our rental house that somewhat meets these specs.

There are so many old houses that rely on window fans for fresh air or exhaust. The fact that these fans are literally just open fans with all the leakage that entails is quite inefficient.

This seems like a product with the same BOM cost as an existing popular product but with incremental energy benefits and no need for construction.