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The Great Chest Fridge Conversion Project Begins!

21 April 2009 9 Comments

One of the big energy hogs in our house is our clunky old second fridge in the garage. I measured its energy consumption with the MS6115 power meter, and it uses a whopping 2.5 kWh/day!

Many Aussie houses have one of these beasts, which is a big reason why the NSW State Government is now offering money to people to hand them in for recycling.

Simply getting rid of the fridge is difficult, though. We have three young children, and so go through a lot of milk, yoghurt, and juice (and, truth be told, wine!). If we turned off the second fridge and only used our main one, we’d have to shop for milk and juice every couple of days. The second fridge gives us the space to store a weeks’ worth at a time.

A while ago I read in Renew, the magazine of the Australian Alternative Technology Association, a story about hacking a chest freezer to operate as a chest fridge. The author has posted about his chest fridge on his Mt Best web site.

The concept is actually very simple. You take a chest freezer, plug it into a temperature controller, and place the controller’s temperature probe inside the freezer. The device then just turns the freezer on and off at the wall depending upon the temperature inside it. If you set it to about 3 degrees C, it works as a fridge.

An alternative approach is to simply swap the freezer’s thermostat for a fridge one. Although technically reversible, this is a little more of a permanent hack. A very good article about it was recently published on the Aussies Living Simply web site.

Why would you want to do that?

Because chest freezers have great insulation (2-3 times thicker than a fridge) and open from the top (so you don’t lose all the cold air when opening them), this makes for an incredibly efficient fridge. Various people around the net are claiming they use just 0.1 to 0.3 kWh/day. That’s 1/10th of what my clunker of a fridge uses!

This simple idea has played on my mind for over a year now. So this weekend I began my own Chest Fridge Conversion Project.

First step was to obtain the freezer. I’ve been keeping an eye on eBay, newspaper classifieds, notice boards, etc for a while now. Finally, I discovered a guy around the corner from me selling a Westinghouse 210L chest freezer. Perfect! Twenty minutes and $90 later, I had a working chest freezer.

The thermostat used and sold by Mt Best is a little pricey for my project at $150, although it looks very good. I found an alternative temperature controller that works the same way at a home brew supply shop for just $50. Home brewing people use these with old fridges to maintain a constant temperature for optimum fermentation – exactly what I want to do (hopefully without the fermentation, though).

So I’ve ordered the FridgeMate Mk II digital temperature controller, and am eagerly awaiting its delivery. Stay tuned for an update!


  • Mrs Green said:

    Good luck with this – it sounds an exciting project. And I’m shocked at the amount of kilowatts an old second-hand fridge can use in a day!

    We have one larder fridge (under the counter type) for every day stuff, 1 large fridge (where we can store enough milk, yogurt and wine for a week!) and a freezer of the same size for freezing produce during harvest season.

    We went away for 3 days recently and I noted that all three (plus 2 energy efficient lightbulbs left on for security measures) had used 2.3 kwhs per day. They are all rated at A, but I think you can buy AA already.

    I too would like to get rid of the large fridge, but we just wouldn’t manage as dh eats a lot of salad.

    Looking forward to your updates on this project!

  • Darren (author) said:

    @Mrs Green: Yeah, I was amazed that it was that high too! The fridge is pretty old (probably 15-20 years), quite large, and is a fridge/freezer combo which probably adds to the load.

    I’d be very happy if replacing it could knock 2 kWh/day off our bill – that’d save us something like $120/year! Given that this whole project will probably only cost $150 or so, that’s a pretty good payback period.

  • Chrissy said:

    Hi Darren

    Great project! I hope it works out and look forward to the update!

    Cheers Chrissy

  • Darren (author) said:

    @Chrissy: Here’s hoping it works out now that I’ve gone out on a limb!

  • Nitai said:

    Please let us know asap what happened with this. I am off the grid and this chest fridge could be just what we need. But now today I read some claims that the horizontal aspect does nothing to help, although that was one of MTBest’s main arguments. Eagerly awaiting the update…

  • Darren (author) said:

    @Nitai: I am in the middle of writing a post on the chest fridge project – should go up either tonight or tomorrow night. It was completely successful, is running fine, and only uses about 0.2-0.3 kWh per day! The horizontal door does help a bit, I’m sure, since all the cold air wouldn’t fall out. I think the bigger benefit comes from the better insulation, though. My freezer’s walls are about 3 inches thick – double the thickness of the old fridge it replaced. Anyway, whatever the reason, I can’t argue with the power meter!

    If you’re off-grid, have a look at this set of instructions that includes a modification to reduce the start power surge of the compressor. That should make it much friendlier to your inverter. That document replaces the freezer’s internal thermostat – a different technique that is a bit more tricky and a bit more expensive, but probably neater and better as a permanent solution.

  • Nitai said:

    Thank you for the quick reply… I looked at the pdf you linked (I had found the same one a day or so ago)…and, well, a bit (a lot of bit) out of my league unfortunately. Maybe I will look a it again soon and see if I can manage with guidance from a friend. If I may humbly request that in your upcoming update you could include the outside temperature. I feel like I have not found enough consistent information regarding that. Summer is fast approaching here and the reason I want this chest fridge is because we started a raw milk business and need somewhere to keep all the milk very cold. Our propane fridge does not seem to be up to the task. Thank you for your time. Great blog!

  • Darren (author) said:

    @Nitai: You could use a simple thermostat like the one I’m using for starters, to see if it works for you. If the freezer is not too big and your inverter is a good size, you don’t really need the power surge suppression hack. You could always add it later if it turned out to be a problem.