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What this is actually doing is (theoretically at least) speeding the time to equalise inner/outer temperatures… and it’s quite neat because the speed of the fan will be proportional to the temperature gradient… the hotter it gets, the faster it will go. When it’s no longer needed, it will stop.

Trouble is, you can probably achieve the same thing using-no-moving-part methods… and as Amory Lovens continually points out, improving efficiency allows you to remove entire sub-systems. Doesn’t look as cool though.

Started off as a way of showing off his stirling engines… and now dozens of people have sent in examples of their own

There are also loads of these on Instructables and youtube.