Author Topic: Converted freezer into a super-efficient fridge -> 80+% electricity savings !!  (Read 6635 times)

Hawkeye

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Hey everyone,

Super excited to share my recent home project... was thinking of ways to further optimize our electricity use so thought about energy efficient fridges. After checking our old fridge's electricity consumption with a Kill-a-watt I calculated that it consumes ~ 1 kWh / day... not too bad to begin with, however I came across the following website of a slightly quirky (FIRE'd?) physics professor who claims that a freezer design is way better to preserve cooling and conserve energy.. and that a converted fridge can be way more energy efficient than the best "energy star" rated fridge available...

Website: http://mtbest.net/chest_fridge.html
(Very) detailed instructions: http://mtbest.net/chest_fridge_1.pdf

So it turns out there are actually tons of people on the internet who modify fridges for all kinds of purposes.. fermentation chambers, incubator, amphibians, etc...
I ended up getting a small cubic freezer for $40 from craigslist and bought a $15 temperature sensor (called STC-1000) online

After lugging the thing home on the NYC subway (great exercise and way to meet people ! ;) ) I started removing the old thermostat from the freezer and replacing it with the temperature sensor.. took me about an hour or so (I don't have electrician experience!)

I set it to cool (=turn on/off the compressor) between 40F (4C) and 45F (7C).. and the result was excellent.. everything is perfectly cool, but not frozen, and you can even see the exact temperature on the LED outside.. It can now be programmed for all sorts of ranges in case I ever want to brew beer or do similar projects.

And most importantly, the electricity consumption is now between 0.12 and 0.15 kwh  per day !!

My installation required removing the built in thermostat from the circuit (it's basically in between the power cord and compressor) and connecting the temperature sensor instead. It was surprisingly simple (no electrician type of work experience and took me maybe ?1 hour) Yes, using an external controller seems to be an even simpler solution that is less invasive/easier to reverse (haven't tried that)

Temperature controller is ~ $15 on Amazon; (requires some cutting of cables, but cheapest, and most versatile programming etc): STC-1000 Temperature Controller
External temperature controller is ~ $60 (does not require any installation basically simply cuts of the power to the freezer/fridge once temperature is reached): Johnson Controls External Freezer Sensor


Other plus: fiance loves it as well because it looks super cute, it saves space in our small apartment and I feel like a real electronics hacker :D.

« Last Edit: May 27, 2018, 11:30:03 PM by Hawkeye »

FIREySkyline

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This is interesting. Any explanation for why this is more efficient than a refrigerator? Shouldn't this be essentially how a fridge works?

JohnGalt79

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This is interesting. Any explanation for why this is more efficient than a refrigerator? Shouldn't this be essentially how a fridge works?

I believe one reason is that the cooled air doesn't spill out every time you open the door (door is on top), like it does in a traditional refrigerator (door is on front).

There are probably other reasons, but that is the one I remember.

By the way - congrats to the OP... well done!

BikeFanatic

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Great project.

boarder42

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Yeah cold air sinks. So when the door is opened you don't lose the cool air generated. This is why chest freezer are better than standup. And why this works for a fridge as well

monkeymind

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Very cool!

hgjjgkj

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This is an awesome project and congrats. In terms of annual savings what is your estimate? Also out of curiosity what's your NYC rent?

Gibbelstein

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This is a neat idea.
One small question: Is your sensor wired to the fridge where the old one was? Like, do you still only have to use one cord/plug, and does that .12kwh include the new sensor/controller? Because that is about a 90 day payback on the sensor.
« Last Edit: November 20, 2017, 10:58:29 AM by Gibbelstein »

katscratch

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I did this for a few years when I first had my house. It was ridiculously cheap to run! The thing turned on maybe once every two hours for about ten minutes unless I was opening the lid more than usual.

The only downside was controlling humidity.

I'd still be using it except I needed another chest freezer a couple years ago and stumbled on a really great deal on a dented display fridge.

Great work!

TheInsuranceMan

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I did this with a chest freezer, but I made it into a kegerator for our homebrewed beer.  We bought a temp controller similar to the one OP bought, but ours plugs into the existing cord, and then into the wall.  Pick your desired temperature, it'll run within 3 degrees of that.  Works great, and there isn't much better than cold beer on tap in my garage that I made myself, in the keezer I made myself.  :)

hgjjgkj

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Is this hard to use? I imagine it gets annoying having to bend over the whole thing to get to food? Would also imagine shelf space is reduced a lot?

Hawkeye

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Thanks for the positive feedback everyone! This was really fun to build an IMO is a great mustachian tinkering project...

FireySkyline: I believe the reason is primarily that the insolation of a chest fridge is in a different distribution.. So as John and Boarder said, it kinda works with gravity whereas an upright fridge constantly leaks lightly around the door..

Yes 0.12 kWh/day includes the sensor and the LED and it is only a single cord/plug etc. ! What I did so far I simply taped the probe of the sensor on the back and pass it through the lid. It still closes perfectly. there is likely a more elegant solution but it works!

It is definitely economical, of course even more so if you have an old freezer around ;)

It's small but extremely simple and convenient to use esp. if you have a Minimalist/Mustachian mindset.. I still get a high every time I hear the compressor kick it right when it reaches the temperature I programmed it to and how quickly it turns off again :)

My installation required removing the built in thermostat from the circuit (it's basically in between the power cord and compressor) and connecting the temperature sensor instead. It was surprisingly simple (no electrician type of work experience and took me maybe ?1 hour) Yes, using an external controller seems to be an even simpler solution that is less invasive/easier to reverse (haven't tried that)

Temperature controller is ~ $15 on Amazon; (requires some cutting of cables, but cheapest, and most versatile programming etc): STC-1000 Temperature Controller
External temperature controller is ~ $60 (does not require any installation basically simply cuts of the power to the freezer/fridge once temperature is reached): Johnson Controls External Freezer Sensor

jim555

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But what do you use as a freezer?  Is the temp even or do you need a small fan?  Does water build up?
« Last Edit: November 21, 2017, 06:34:55 PM by jim555 »

katscratch

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But what do you use as a freezer?  Is the temp even or do you need a small fan?  Does water build up?

When I did this I also had another chest freezer for a freezer. The temp was incredibly even - but I was super organized in how I packed things so that might have helped. I did have condensation in mine but just wiped it out with a microfiber towel weekly and it was fine. The only food really affected by the humidity was salad greens; other veggies did fine for the amount of time I stored them.

Mine was just done with a kegerator thermostat so not nearly as badass as this one! And I definitely wasn't transporting it on public transit! SO awesome, Hawkeye!

Hawkeye

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Hello I just wanted to give an update on the project after 200+ days and still going strong ! The converted chest freezer works great and integrates perfectly into our life style. Condensation has been minimal. At local electricity rates this has "paid for itself".

Have applied the same principle for our AC to save on electricity during the summer (may be debatable if having an AC is very mustachian in the first place) Alas, this has been a great success and saving electricity every day :D

nouveauRiche

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malacca

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I made a Kimchi refrigerator using a cheap freezer.

Kimchi requires a fairly constant temperature to control fermentation - used a controller from Johnson Controls.

It also doubles as a store all - all those veggies and fruit from garden, etc.

Much cheaper than $1000 they want for a Kimchi fridge!




Caroline PF

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Hello I just wanted to give an update on the project after 200+ days and still going strong ! The converted chest freezer works great and integrates perfectly into our life style. Condensation has been minimal. At local electricity rates this has "paid for itself".

Have applied the same principle for our AC to save on electricity during the summer (may be debatable if having an AC is very mustachian in the first place) Alas, this has been a great success and saving electricity every day :D

This is very cool. I am planning on doing this soon, so it's good to see that it's working out well for you.

One question: what do you do for organization/shelving in order to make it easy to retrieve the food at the bottom?

Hawkeye

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Hi Everyone, almost two years (well 1.5 at least) in, and the fridge is still going strong. Sadly, for me, I am moving and can't take it with me. So if you are interested in getting a bad-ass fridge, it is for sale for $40 to pick up in Manhattan Washington Heights: see here for details:

https://forum.mrmoneymustache.com/mustachian-marketplace/ultra-efficient-fridge-for-$40-in-nyc-area-mustachian-must-have-)

Bird In Hand

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I realize this thread was necro'd, but it was the OP who did it.  So a question:

Have applied the same principle for our AC to save on electricity during the summer (may be debatable if having an AC is very mustachian in the first place) Alas, this has been a great success and saving electricity every day :D

What principle from your freezer->fridge conversion did you apply to your AC usage?  Are you living in an apartment with the door in the ceiling?

Gone Fishing

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Just saw this in an off grid video.  They were using an upright freezer, and still claimed the savings.  My upright freezer has no internal fan, unlike my regular fridge.  So maybe that has something to do with the savings?

BTDretire

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You can call me skeptical!
 I think most of the saving is because his freezer is much smaller than his fridge  and the fact that when you open the door the cold air does not fall out.
 Now if you want to do this, the wiring doesn't need to be that complicated.
In fact I see no need to alter the freezer at all.
1- Set the freezer thermostat as low as it will go. This assures that it will always want to run.
2- Get the thermostat he recommends, I have one and use it for different uses. Even used it to experiment with Sous Vide, it worked fine.
3- Gather a power cord, an electrical box, an AC outlet, and your STC-1000.
Figure out how to wire the STC-1000 so that it energizes the AC outlet when the thermostat gets below 40*F or whatever temperature you program the STC-1000 for. Find or make a hole to run the sensor wire into the freezer and then plug the freezer into the AC outlet you installed into the electrical box.
 Now if I have peaked your interest, here's a link to at least 10 Youtube videos on how to wire the STC-1000, just note: you can wire it to turn on if the temp gets to high, (for cooling) or you can wire it to turn on if the temp gets to low, (for heating).
https://www.youtube.com/results?search_query=stc-1000+temperature+controller+wiring+diagram

Btw, if your freezer has a digital internal thermostat, his method will need to be followed*, but most small freezers I have seen don't have digital thermostats.
 * this because the digital system needs power all the time to work. Mechanical thermostats
when set to the lowest temperature will close the contacts (unless the freezer gets to that freezing temp) so then you can externally control it by use of the STC-1000.



Just some stuff I wrote, that didn't really apply.
I have torn a freezer apart, just because I wanted to know. The insulation is just Styrofoam.
But, you have the cooling pipe on the inside and the heat releasing pipe on the outside. That is why a freezer gets hot on the outside. These two high differential temperatures are only separated by that thin Styrofoam. It would be better if the heat releasing pipe was further away from the cooling pipe.
 Refrigerators can be that style, although generally the heat releasing pipe is only on the backside or they can mounted externally about 3" from the back wall. I'm sure you have all seen the pipes and with thin wires welded to them on the back of a fridge.

Lmoot

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I've been wanting some sort of "produce fridge" that functions as sort of a mini cool-room. But haven't found any such thing. Does anyone know if a wine fridge might work?  We have parrots and I get harvests from parent's homestead, and so we need to store a lot of produce which takes up half the fridge. It would be nice to be able to downsize to a smaller fridge, and have a smaller lower-energy fridge just for the produce, and certain grains/pellets, even cheeses.

habanero

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I've been wanting some sort of "produce fridge" that functions as sort of a mini cool-room. But haven't found any such thing. Does anyone know if a wine fridge might work?  We have parrots and I get harvests from parent's homestead, and so we need to store a lot of produce which takes up half the fridge. It would be nice to be able to downsize to a smaller fridge, and have a smaller lower-energy fridge just for the produce, and certain grains/pellets, even cheeses.

You can use any fridge and used said temperature controller (the STC-1000). It can be set to any temperature and the energy part will largely take care of itself as long as you don't open it frequently and/or have it set at a higher temperature than a regular fridge. Modern fridges are quite well insulated. I have one and use it as an extra fridge, a fermentation chamber for homebrewing or a curing chamber for meat.

As long as it is placed in an enviroment that is always hotter than the temperature you want you don't need anything else. If you want it to be warmer you also need some heat source (a lamp or whatever) - the STC-1000 can also control a heating source.

The general advice is to allow some temperature delta the interior temperature can fluctuate beween - this is to avoid too frequent start/stop cycles on the compressor. This is valid for both a freezer or a fridge.  The STC-1000 can also handle any delta you want.

FunkyChopstick

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yup. This most definitely falls into the bad ass category. 

Cadman

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One of the reasons this works so well with chest freezers is their lack of mullion heaters and circulating fans. Frostless refrigerators are designed to auto-defrost every few hours and they do this by kicking on heaters in key areas to melt frost and control humidity. This is why fridges from the 70's were such power hogs, heater strips -everywhere-. Today's fridges are much better in this regard, but still typically have a condenser fan and heaters in the evap area.

A pre-'65 non-defrost fridge uses very little power for this reason, but isn't quite as efficient as the modified chest freezer here since the cold air spills out when the door opens.