Improving fridge efficiency

At some point over the next year we're planning to renovate our kitchen. We did a very minor renovation soon after we moved in, replacing the lino floor and swapping in an Ikea bench/drawer unit, but we want to do something much more extensive.

One of the things I've been thinking about is getting the best energy efficiency out of our fridge. I've always found it a bit odd the way they're designed. Fridges work by pumping heat from the inside out to the coils normally located on the back. Wouldn't it be much more efficent to arrange the fridge similar to a split air conditioner, with the heat-release coils in a cooler location? My basic understanding of thermodynamics makes me think the higher the difference in temperature between the liquid carrying heat from inside the fridge and the air around the coils, the higher the efficiency.

Along these lines, I was wondering if efficiency would be improved by getting cooler air flowing over the coils. Since our house has a raised, wooden floor, this could be done by putting a grill in the floor, so that the convection draws cooler air from under the house over the coils. Obviously there needs to be a way for the warm air to escape as well. This arrangement should result in something of a chimney effect, with cool air drawn in at the bottom, passing over the coils, then escaping at the top.

So I dropped a note to the Alternative Technology Association who publish the excellent ReNew: Technology for a sustainable future magazine. I expected, possibly, to get a response in the magazine at some point in the future. To my surprise, I received a response the same day from Technical Editor Lance Turner.

A number of people have suggested this mod over the years, however the most important thing is that air can escape from the top of the fridge - ie, the fridge has at least a 50mm gap between it and any of the walls of the alcove, especially the top of the fridge. So long as there is enough space for air to flow freely, you will get convection happening as the condenser heats up.

Lance goes on to suggest a forced-air fan to actually blow over the condensor, particularly if you can get it to work only when the compressor is on. Quite a neat idea, but I'm keen to go with a passive approach.

So it seems that my idea has some merit, but only if there's a good way for the heat to escape. I'll look into having the hot air vent into the roof space, as well as the vent at the bottom. I think that should result in some pretty substantial efficiency gains.