[Piwoslaw]

Originally Posted by pete c

My thought is to enclose this is an airtight box made of some sort of thin insulated board that you can buy for next to nothing at HD. Half inch thick or so should do. Use duct tape to hold the seams together and make it air tight. Place an input duct near the floor and an exhaust duct near the top.
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I believe there would be sufficient airflow thanks to the natural chimney effect when the fridge is running.

How about a chimney on the back of the fridge? - EcoRenovator.org

Originally Posted by pete c

During the summer, you'd get rid of that unwanted warm air. During the winter, you would be venting away wanted heat, but, the fridge itself should run quite a bit more efficiently due to the cold outside air running across the coils.

Why not disconnect the duct from the hole in the wall and have the warmer air help heat your kitchen?

Originally Posted by pete c

An even better solution for cold temps would be a figure out a way to pipe that cold air directly to the fridge.

Why pipe it? If the outdoor temp is in the right range, then just unplug the fridge, pack your stuff in a basket and put it outside. You can't get lower than using no energy.

Originally Posted by pete c

I actually like Piwoslaw's solution of placing frozen water bottles inside. So simple it is brilliant. I will do this next winter.

Not frozen water, just plain liquid water. Only add thermal mass (and decrease the volume of unused space), no phase-change stuff. Over at EcoRenovator, Daox did an experiment with putting water jugs outside to freeze and then moving them to the fridge. Yes, it reduced the refrigerator's energy consumption slightly, but in essence it was removing heat from the house, so the heating system had to work a little harder to make up for that.

Originally Posted by pete c

Another thought I had was to figure out a way to plumb some sort of heat exchanger to use cold potable water on it's way to the water heater.

This has been done, but I'm not sure if the gains are worth the effort.

The bottom line is: A refrigerator is often thought of as a space heater. This is true, but not to the extent that most people think. The radiator coils get warm, but most of that is the kitchen's heat which permeated through the insulation into the fridge. The only extra heat comes from the energy used to run the compressor (and the lightbulbs). So if you move that heat outdoors, you generally have a heat pump, specifically an air conditioner. You are pumping your house's heat outdoors. Good during cooling season, bad otherwise.

Now, since the only new heat produced by a refrigerator comes from running the compressor, then it would be best to reduce compressor use (or get a more efficient, scroll type compressor). This can be done by adding insulation - the longer it takes a given amount of heat to seep into the fridge, the less often the compressor will be needed.

Once you have better insulation and/or added thermal mass, you can put it on a timer to keep it from turning on for longer periods, eg at night or during the day when no-one is at home. You should keep track of the temperature inside, though, to make sure nothing spoils.