Tuesday, December 29, 2009

Making a refrigerator out of a chest freezer

Over a year ago, I read about an individual living off the grid somewhere in Australia who converted a chest freezer into a refrigerator. His experience showed him that he could run it as a refrigerator on about 0.1 kilowatt a day. His results were affected by the type of chest freezer he bought for the purposchest refrigeratore, one that is rated highly for its efficiency (I believe it has more insulation than regular models). Being a chest freezer with the lid on top, the cold air doesn’t “fall out” every time it’s opened, helping the compressor to need to work less to cool things back down.

The basic concept for converting a freezer into a refrigerator is quite simple. You have to override the compressor since the one in a freezer is meant to cool things on the inside down to near zero degrees (Fahrenheit). In the article I read, the individual included plans for building an external thermostat to override the freezer’s thermostat. That seemed a bit complicated, but I then found I could buy an external thermostat designed to do the same thing.

Northern Brewer has a couple different ones that they sell. Generally, these allow homebrewers to use a freezer to set the appropriate temperature for fermenting lager and to chill their kegs of beer. thermostatSo, I purchased one of the models they sell (I actually have two of them now so that I can convert another freezer into a refrigerator if necessary).

The external thermostat is plugged into an electrical outlet, and the freezer is plugged into the thermostat. A temperature probe connected to the thermostat is placed inside the freezer, and the desired temperature is set on the thermostat. I set ours at 38 degrees. The unit has a 3.5 degree temperature differential. The set point on the thermostat is adjustable from 20 degrees to 80 degrees (Fahrenheit). When the internal temperature drops below the set point, the power to the freezer is disconnected, stopping the compressor. When it rises above the set point, the compressor is once again powered.

It works quite well. The temperature inside the freezer stays regulated at refrigerator temperature. We’ve set up a 14 cubic foot freezer as our refrigerator. inside & temperature probeThere’s as much or more room for food storage inside than our previous 20+ cubic foot conventional refrigerator. Before switching to using it, I measured its power consumption over six days. During that time it averaged only 9 watts and hour. Our regular refrigerator used over 80 watts an hour.

There is no freezer in the refrigerator, of course. On solar power we will not have a freezer because of the amount of power required (both of our freezers average 55 watts an hour). So, we are adjusting to the limitation. However, the ability to have refrigeration even on solar is a definite blessing.

The main issue we’ve discovered with using a chest freezer as a refrigerator is water that condenses on the inside and then pools on the bottom. It’s a good idea to put some silicone caulk around the bottom edge of the walls to keep the water from starting rust there. I’ve read of others putting a small channel along the inside edge about a foot down from the top which directs the water to a single collection point or through the freezer drain.



This was very helpful! Thank you! My husband and I are planning on building a small cob/strawbale house next year for us and our daughter. I'm trying to find little hacks so we can reduce our footprint. :) We are in Tennessee and both work at a college as well. Our daughter is only one, but i fully intend on homeschooling. Seems we have a lot in common!

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