Man Retrofits Freezer to Make an Ultra-Efficient Fridge

An off-grid experimenter in Australia, Tom Chalko, has retrofitted a chest freezer to create a fridge that uses only 100 watt-hours (0.1 kWh) per day! Why a chest freezer? Tom points out that vertical door refrigerators are inherently inefficient. As soon as you open a vertical fridge door the cold air escapes, simply because it is heavier than the warmer air in the room. When you open a chest freezer, the cool air stays inside, just because it’s heavy. Any leak or wear in a vertical door seal causes significant loss of efficiency.

Tom took a standard chest freezer (a Vestfrost SE255), added a $40 external thermostat, then wired the freezer to turn off when the desired temperature was reached. The thermostat runs on 2 AAA batteries which last for months. The freezer runs for about 90 seconds per hour and then shuts down completely, making it not only very efficient but very quiet.

Full article from Build It Solar (PDF File)

Via: Treehugger

11 thoughts on “Man Retrofits Freezer to Make an Ultra-Efficient Fridge”

  1. I’m not so sanguine regarding this idea. I’m fine with the concept and the execution, if it meet the users needs.

    I’m pretty willing to guess that the difference the author gets from a fridge compared to a chest freezer comes to only about four things:.

    First, I understand and agree the horizontal door of a freezer is good for retaining the otherwise collapsing and leaking of chilled air, as what occurs when a fridge is opened. The extent of this I do not know.

    Secondly I’m willing to argue that the effective difference of a new seal for a fridge and freezer are probably comparable and agree in part that maybe that of the fridge leaks a bit more as years go by. I don’t really know. I trus/hope a clean new versus and old dirty seal was not the real basis for the comparison (I do know that cleaning it will do wonders for either system, as you would see if you ran the so called dollar bill test).

    But it seems to me the primary claim for such efficiency is most likely a function of two missing elements in the comparison.

    Firstly, if the physical volume and hence the effective outside area of each machine is of the same size, the seals are at least initially equivalent (don’t significantly leak) and the machines are not opened as my fourteen year old son was once inclined to do, speculating on future consumption of mass quantities, then the primary conclusion for heat transfer differences (i.e., energy consumption) is the degree of the insulation package initially installed.

    This makes sense to me, because the original manufacturer’s design of the chest freezer is most likely have a better insulation package about the case (after all, it was designed to work from say, 0 F to ambient,, where the fridge was for say 40 F to ambient.) I understand the author uses a temperature controller designed to control the freezer box to a higher temperature, and I trust this meets his complete needs

    Still, however, the functionality of the machines are not directly comparable. Simply put, where do the other users put their ice cream (frozen peas, etc. etc?.) Easy to answer in the fridge, but oops not so easy in a chest converted to 40F. Is the solution to buy an entire second freezer for the items to be the frozen? Hmmm. (I’m not the carbon footprint czar, but two motors, two metal boxes, etc?) How does this all add up?

    So, to some extent neglecting the arguably true but perhaps overstated benefit of horizontal door, maybe a more pragmatic answer is simply to
    1) “wrap” the fridge with more/better insulation,
    2) check and keep door seals clean and tight, and
    3) put in a three second alarm bell for when your kids space out at the contents! (mostly kidding, but I think alarming it in a humane way may make some sense, if nothing else than for doors inadvertently left ajar.)



  2. ¨00goddess¨ He is not in the US and did his research locally withing his budget, I think you suffer from deep routed inferiority syndrome by trying to say how much better you dream to be with your improved version made of plain air. Its a great idea and please go and use that BS meter on yourself.

  3. I have actually made one of these for my house. I didn’t get as good stats as the aussie did for my fridge, but I used a similar method.

    I bought a thermometer controller, for converting any fridge or freezer into a kegorator (they are about $54 on Amazon), then you just put the thermometer in the freezer, plug the freezer into the thermometer control unit, and it turns it on and off to maintain the temp.

    Anyhow I now have a fridge that consume 10-11 watts an hour, which is fantastic (my ikea fluorescent lights use the same amount of electricity per bulb, if that helps you compare). I use a combination of freezer baskets, and stacking of stuff to make it work for our house. Even running the matching freezer I purchased to use as a freezer, the total energy usage comes out to that of a sunfrost refrigerator/freezer combo (that is running one unit as a freezer, and one as a refrigerator), at about a cost of $500 for the freezers and controller.

  4. One thing tips off my bullshit meter: he says that he contacted leading fridge manufacturers and found that no one was making or testing a chest fridge. This isn’t true- these are available in the U.S. They are being installed in many new luxury homes. They are built-in under the counter and pull out like large drawers. This solves the item arrangement issue that he has- the drawers are not as deep as is his chest, so it is easy to arrange things. Also, you can adjust the thermostat on each drawer to suit the food inside.

    Still, this is a great idea, very inexpensive, and I might do it myself when we get a house. I already have some ideas for improvement 🙂

  5. Man Retrofits Freezer to Make an Ultra-Efficient Fridge

    I’ve been off the grid this week in Northern California and the one thing I would really want is a bigger freezer. Yes – we have power and a fridge, but it’s not big enough to hold everything for…

  6. That’s a fantastic idea! I’ll keep searching for more efficient refrigerators, but the best I could find this morning was on They sell Sunfrost refrigerators that claim 18 kWh/month. At that rate, they’ve used as much energy in two months as the modified chest freezer will use all year.

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