Ceiling Air Purifier
Imagine a high-capacity air filter that is extremely quiet and doesn't get in the way. I think I see how to build one; here's a prototype: By putting a fan on the ceiling you can have very long blades. This is important for keeping noise down: the longer your blades are the more air you move at a given rotational velocity, which is a major determinant of noise. Testing my prototype, it has a
Source: jefftk.com