DIY Low-NRG Fridge: Coolest Ice Box Ever?

Tom Chalko built this low-energy refrigerator out of a chest freezer. He rigged it with a SparOmeter that measures power consumption (bottom left) and a $40 external thermometer (top right) with a battery-operated internal relay that cuts the power at a set temp. Says Tom:
In the first 24 hours my new chest fridge took 103 Wh (0.103 kWh) of energy. About 30% of this energy was consumed during the initial power up and re-arranging of the fridge content. The room temperature varied from 21oC during the day to 15oC at night. The fridge interior temperature was kept between +4o and +7o C. The fridge compressor was working only for about 90 seconds per hour. When the thermostat intervened - the fridge consumed ZERO power. The only active part was a battery powered temperature display. Results of my experiment exceeded all my expectations. My chest fridge consumes as much energy in 24 hours as a 100W light bulb does in just an hour. Not only it is energy efficient. I have never seen a fridge that was SO quiet. It only works 90 seconds or so every hour. At all other times it is perfectly quiet and consumes no power whatsoever. My wind/solar system batteries and the power sensing inverter simply love it. With my new chest fridge I have power to spare and I can use it to warm up my house in winter with a heat pump. I wonder why no one has ever thought of a chest fridge controlled by a digital thermostat...
Instructions are available at Build It Solar (links to PDF). [via Home Design Find]
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16 Responses to DIY Low-NRG Fridge: Coolest Ice Box Ever?

  1. Thuli says:

    The pic was lifted, possibly from here:

    Saw it years ago, it’s not that guys work of that I’m fairly sure, this has been up for years.

  2. irasanborn says:

    Homebrewers have been doing this kind of thing, turning chest freezers into keg fridges for quite a while, though few are as advanced as this. Very cool!

  3. Thuli says:

    Oops! Didn’t recognise the name

  4. Paul Coleman says:

    A farmer from the Hudson Valley in NY does something similar using a stock AC unit and a well insulated room. I have a friend who built a cooler this way and it works very efficiently.

    If you go to the “innovations” section of his site and scroll down to the coolbot, he has it linked. Yeah he’s selling the controller. I’m going to build a cooler room for my farm next year and this makes the process a lot easier.

    He’s also the guy who modified and documented changing his Allis Chalmers G tractor over to Electric….another project I want to tackle someday.

  5. technogeek says:

    Simple and elegant. I expect that the main reason this hasn’t been done more often is the same reason chest freezers are used primarily as secondary/long-term storage: people just don’t like the form factor. It takes up more floor space than an upright fridge, and it’s harder to see and retrieve stuff that’s farther from the door (though a few layers of sliding shelves might address that).

    I’m not sure I could sell myself on it as primary storage, and I’m a moderately green consumer. As _secondary_ it makes lots of sense… though secondary more often wants to be a freezer than a fridge.

  6. Rodney G says:

    Here is an example of comment #1:

    Not sure this is the same as the article, but it sounds similar.

  7. Edwarde Sanspoisson says:

    I need something like this so I can keep my mum a bit longer.

  8. phisrow says:

    Perhaps I’m missing something here. My understanding was that virtually all commercially available refrigeration systems(excluding the chintzy peltier-based in car units) operated on the principle of a thermostat turning a compressor on and off, as needed.

    Why would this system, where a freezer unit has a second thermostat throttling it back to refrigerator level duties, be more efficient than a unit calibrated for refrigerator temps out of the box? Is the insulation better?

  9. Charlie Stross says:

    Simple solution: gas strut lifters to raise wire mesh shelves out of the fridge when you release a latch. Yes, you have to open the lid then click a latch to get at the shelves — but it’s saving you a buttload of money each year.

    (Reason this ought to work: the typical refrigerated item is chilled by the cold air pooling in the bottom of the refrigerator, but is a lot denser than the air around it and takes a while to come into thermal equilibrium with its environment. Lifting a rack full of provisions out of the fridge won’t cause it to instantaneously warm up to room temperature — you’d have to leave it open for half an hour or longer. On the other hand, your typical fridge-shelffull of food doesn’t weigh more than two to five kilograms, which is well within the lift capacity of a gas strut, and not too hand to shove back down.)

  10. jitrobug says:

    Just for context, how much energy is a regular fridge of similar size using? (or similar storage capability, given that you can’t exactly stack things on top of a carton of milk)

    When I built a keg system, I considered a setup like this, but ended up using an old top & bottom fridge so that I’d get a little bit of extra freezer space too.

  11. Rickmccl says:

    @PHISROW – yeah I had to RTFA to find out.
    “After contacting some leading fridge manufacturers and discovering that no one has ever made and tested a chest fridge, I decided to make my own test. I bought a good chest freezer and turned
    it into a fridge.”

    I think the man’s point is that if it were done, it would be better. I also suspect that perhaps the better performing freezer-duty refrigeration components may cool the box quicker than something sized for maintaining a higher temperature, which may lead to greater efficiency due to shorter duty cycle. A higher-temperature duty refigeration design would probably be made smaller and cheaper, in the name of reducing costs for manufacturer and consumer. Reduced energy consumption may be more expensive than your focus group’s target price point. We still should be able to win just on the cold-air-sinks principle, but if it was that much better, wouldn’t it have been done already?

    Sorry for the vagueness, it’s my way of letting you know I’m not an expert.

  12. Anonymous says:

    Charlie, cold air is denser than warmer air and thus will tend to push it aside, like wet concrete pushes water out of the way if you drop it in a bucket. When you open your freezer door, cold air falls out the bottom of the opening and warm air is pulled in at the top to fill the space. Chest freezers gain almost all their vaunted efficiency by acting like a hole in the ground, where cold air will “puddle”, so that warm air does not enter when the door is opened. If you wanted to have the content of the freezer lift up to easy heights for examination and use, you’d have to calculate the speed of the lift and the aerodynamic configuration of the shelving extremely carefully to avoid creating an air current that would pull hot air in and spill cold air out. That’s not to say it can’t be done, just that it would likely be much harder than simply making a shelf that pops up. I personally think your idea is excellent and should be pursued.

  13. freshyill says:

    A glass lid would be a nice touch. Might decrease the energy efficiency a bit, but maybe that would be offset by not necessarily having to open it as much or as often to see what’s inside.


    One important thing to consider before performing this kind of modification is the operational conditions the refrigerant compressor system was designed for, and that bringing it outside of those conditions may reduce its lifespan and could even cause it to seriously malfunction (e.g. electrical fire, refrigerant leak, etc.).

    The compressor system is likely designed to run for longer than 90 second intervals, and is almost certainly not meant to have the power shut off in the middle of compressor cycle. However, given that it is a closed system using a highly purified fluid, as well as a consumer product approved by the Underwriters Laboratory (high safety factors), it should be fine.

    Another improvement to the chest fridge would be to move the compressor outside of the fridge body (somehow), as seating it below the fridge interior volume will have the heat generated every cycle rising and heating said volume.

  15. cans says:

    As IRASANBORN points out at #1, this is pretty common equipment for brewers and for people who like to serve keg beer.

    In college, we used the digital “Brewer’s Edge” variant of this sort of temp. regulator to control a Frigidaire standing freezer like this one. In maybe half a day, the combo would get twenty-four or so cases of beer to a perfect 37 degrees Fahrenheit. Great success!

    To those questioning why (#7), the answer is that the insulation quality and compressor performance of a chest or standing freezer is dramatically greater than that of a typical refrigerator. Also, when we were looking two years ago, no freezers or refrigerators had ultra-precise digital controls that allowed freezer usage at above-freezing temperatures. We set our adapted-fridge to chill beer to 37 deg F, with two deg of tolerance. No non-commercial refrigeration apparatus of which I am aware could match the performance (absurd!) for the price ($300 for an almost-new freezer on craigslist; $100 for the controller)

    And as to why it hasn’t been done (#10): the market is just too small.

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