A few years back I was talking to the
owner of Sunfrost (super efficnet fridges) about heat pipes and he said they already tried that
heat pipe idea in a fridge! that
they had made a number of fridges that used them! and it worked great, that it could be a retro fit to an exsisting fridge and with only a 1/2" hole thru the wall and no electricity to make it work, but there isn't any demand for fridges that use zero energy, partly because no one understood the idea, but as he said, it works really well.