DIY super efficient fridge.

[kickflipjr]

Well its sort of a DIY.

Someone in Australia has come up with a simple conversion that will turn a chest freezer into a refrigerator that uses about 0.1 kWh per day (that is 93% less electricity than a normal fridge).

Mr. Electricity Link (http://michaelbluejay.com/electricity/refrigerators.html)

how to make a super-efficient fridge (http://mtbest.net/chest_fridge.html)

[omgwtfbyobbq]

Pimp! Def gonna bookmark this! Thanks for the links! :D

[diamondlarry]

WAY COOL! :thumbup: :thumbup: It shouldn't be very hard at all to convert that to 110/120 volt for use here in the USA.

[kickflipjr]

Someone on another forum I go to posted it. I thought someone on gassavers might like it.

[Ryland]

things like this have been around for many years, $65 will buy you one marketed twards home brewers, Check this out (http://kegman.net/9025.html)
Of course there are a number of chest type fridges on the market, and if you want to just save energy in the winter, SunFrost (http://www.sunfrost.com/) used to sell a heat pipe (http://en.wikipedia.org/wiki/Heat_pipe) option to their fridges, but no one understood them, so they didn't want the added cost.

[Randy]

Interesting. It's just a chest freezer with a new thermostat. His thermostat is a bit complicated due to it using zero power when not on.

I have an older fridge that I was thinking of replacing because it uses quite a lot of power (almost 5 kWh/day). Since I already have a chest freezer, the only challenge would be the footprint of a chest for a fridge. They make fairly small chest freezers though, and you wouldn't need a big one.

[DracoFelis]

Interesting. It's just a chest freezer with a new thermostat.
That's my understanding too. And isn't that the kind of "thinking outside the box" that we like here at gassavers. ;)

But IMHO the really nice thing about this, is that your total cost of doing this is the cost of a chest freezer (and those are reasonably cheap, and frequently have much more insolation than most "fridges" do) plus the plug in thermostat. And if you look around, you can get digital (control to 1 degree) 110v "plug in" (just plug the freezer into the thermostat's outlet instead of the wall, and you are "good to go") for around $100 (or even less if you go with the less accurate analog thermostats). And as far as I can tell, that "plug in thermostat" is all you need beyond the chest freezer (and any shelving you want to put in the freezer to make it more usable). So this should not only be an energy efficient "fridge", it should be a reasonably inexpensive one as well (likely cheaper than many "normal" fridges).

And if you ever want to remove the "conversion" (and use your freezer as an actual freezer), you just unplug the freezer from the thermostat, and plug it back into the wall (at which point the internal freezer thermostat will take over). So it is trivial to switch back and forth between "fridge" and "freezer", by simply using/removing the external "plug-in" thermostat (i.e. this "mod" is trivial to "reverse" if/when desired)!

BTW:
I haven't yet tried the freezer to fridge mod (but it is something I'm seriously considering in our house), but I'm pretty sure the theory is sound (i.e. it should work).

In fact, with some chest freezers, cutting the power occasionally is useful even if/when you want to keep your freezer as a freezer. For example, I did some tests, and discovered that I could put a digital 24 hour (appliance) timer on my chest freezer (around $18 at the hardware store), and set it to only power the freezer around 40 minutes every 2 hours (you need the digital timers for this, the cheaper analog units don't have fine enough control). My experiments showed that this is still often enough to keep things frozen in the freezer, but this approach saves over 1/2 of the power the freezer was using when plugged directly into the wall. This worked for me, because my freezer always uses over 150watts when plugged in (as verified by my Kill-A-Watt meter), even if/when the internal thermostat was set to kick off (and more power than that when the freezer was actively trying to cool things down). But with the timer, when the power is cut, the power is cut (the only power then being the less than a watt used by the appliance timer itself). And while the freezer does work a little harder when it's on (to cool things down, after they have warmed up a little with the power cut), that still results in over 1/2 of the power the freezer was previously using being saved. Granted this still works out to only about $4/month of electrical savings, but that's still something...

[Brock]

On another board I haunt a guy has done this and come up with some additions. A small fan, a drain to get rid of the condensate. Check it out.

http://www.wind-sun.com/smf/index.php?topic=1073.0

Actually that whole sub topic is good for general power efficient mods for the home :)

[James]

This is a great idea. I have yet to try it, but I have the perfect size chest freezer (6.3 cu ft) for the conversion. If anyone gets the thermostat, let me know how it works. For now we are using the freezer as a freezer, and for a fridge we are using the super efficient method of unplugging the fridge and storing stuff in the cold pantry. Works great here in VT.

One problem of using a timer to keep the freezer from always having access to power: larger swings in temperature. Food does not last nearly as long if it is frequently being brought up to 20 and then back down to 0...it does much better if it is brought up to 5 and then back down to 0, etc. For people who are only storing their food for a month the larger swings are ok, but if you are storing blueberries, meat etc for a long period of time like we are it helps to keep the temps from swinging so much.
-James

[WisJim]

A friend who was off grid build his own chest refrigerator, using a 12 volt Danfoss compressor (the compressor and all related parts, evaporator, condenser, controls, etc., was available as a kit designed for home-bult units--I don't know if such a kit is still available) His unit also had a fan and duct to bring in outside air if it was colder outside than in his refrigerator, so for much of the year, the compressor didn't run at all, just a small fan ran occassionaly, as needed.

[Brock]

You can still get them, they are pretty common in large boats. You can get them seperate or sort of pre assembled with a "cooling plate" you just mount inside a box of your choise. As Jim said if you can move the comperssor side outside or cool it with outside air it makes it much more effecient.

Last winter I had our chest freezer in our garage becasue of construction in the pantry area. It used 9.5kw for an entire month! In summer it uses about 1kw a day. I tried and tried to convince my wife to leave it out there, but no go :(

[WisJim]

A potential problem with having a refrigerator or freezer in an unheated space is that the oil in the compressor may get cold and stiff, causing the motor/compressor unit to wear out quicker than it would if the unit was in a heated space. Commercial equipment often has a compressor crankcase heater to prevent this problem. Older equipment seems to take cold temps better, but uses more energy when operating.

[Ryland]

SunFrost's web page (http://www.sunfrost.com/passive_refrig.html) has a great little write up on how their passive refridgerator assist works, when I talked to the owner of the compeny last, he said that the design worked really well, and that there is no reason that it couldn't be done, it's just a single tube filled with refridgerent, and a heat sink on either end of it, all you need to do then is drill a 1/2" hole thru your fridge, and a simaler 1/2" hole thru your house wall, maybe make it larger if you want to insulate around the heat pipe.

http://www.sunfrost.com/images/Heatpipe-fridge.gif

[DaX]

SunFrost's web page (http://www.sunfrost.com/passive_refrig.html) has a great little write up on how their passive refridgerator assist works, when I talked to the owner of the compeny last, he said that the design worked really well, and that there is no reason that it couldn't be done, it's just a single tube filled with refridgerent, and a heat sink on either end of it, all you need to do then is drill a 1/2" hole thru your fridge, and a simaler 1/2" hole thru your house wall, maybe make it larger if you want to insulate around the heat pipe.

http://www.sunfrost.com/images/Heatpipe-fridge.gif

I read the Wikipedia article on the heat pipe...neat stuff. This wouldn't work year round though, would it? You'd need some way to deactivate it, correct?

[Ryland]

you are correct that it wouldn't work year round, unless it got cold enough at night, but no, you wouldn't have to deactivate it if you had just a simple heat pipe tha relies on gravity to move the refridgerent back to the end that is trying to be cooled, some of the fancy heat pipes have what is almost a wick, so your refridgerent can move up hill, but if you just have a slight slope so your refridgerent can drip back to the bottom to be boiled, and start the cycle again, then it should work fine, and just cool your fridge when it's colder out side then it is in your fridge, and with a device like this insted of doing something like putting your fridge next to an outdoor wall, and cutting a large hole in the wall, you just drill a small hole, and run this tube thru, adjust the presure and refridgerant so that it will evaporate and cool down to 34 degrees, or whatever, then as long as it's cooler outside then it is in the fridge, the cycle will start.

[Randy]

I went ahead and tried this. I built a thermostat, mostly out of surplus parts I had sitting around. It's an all-analog design, similar to the one in the first article, and it was just intended to be a one-off thing. Then I bought a 9 cubic foot Whirlpool chest freezer for $300. It's bigger than what I was planning on, but it fit in the space very well and came with two baskets. Under one of the baskets, I zip-tied the temp sensor and fan (set to turn on when the fridge does). So I could return the freezer to stock in seconds.

It's certainly efficient. I had it set to turn on at 36 F, with a two degree drop, and it runs for about 6 minutes every hour. The killawatt says about 0.25 kwh/day, or 20 times less than my old fridge. The 13 cu ft freezer uses about 0.62, but I haven't tested this in the summer, or with the increased opening as my main freezer.

I've only been using it a week or so, but so far it's been easy to use. I need to work on shelving... it's not like a freezer where you can just stack stuff. It's got plenty of space as-is though. Condensation is a big deal: I'm going to put down some rubber shelf liner stuff in the bottom to help keep the things out of the water. I think the constant humidity would cause mold and mildew if turned up into the 40's. I'll know more about it as I use it longer-term.

[omgwtfbyobbq]

That's at least $200 per year in savings! :eek:

[Randy]

That's at least $200 per year in savings! :eek:

It's about $0.085 per kwh here, or $150 per year. Very good payback though. It also pushes me down to the 1.5 cent cheaper marginal rate.

These things aren't SUPER efficient: a sunfrost would beat this combo by at least 10%... for $3000. The DIY fridge delivers amazing bang for the buck.

[Telco]

Wow, the things some people come up with. I like this idea, but my wife hates chest style freezers because it's hard to get at everything. Not an issue for me being as I'm 6ft 4, but she's 5ft 3 and can't reach over to get to the bottom. If she gets a foot stool to get high enough, she runs the risk of falling in :D .

So... if I were to do something like this, I think I'd have to build a shelving system to go inside. I envision 3 shelving units that divide the fridge into thirds, with each shelving unit having its own standalone support structure. The shelving would be on sliders to allow the shelves to come up, with a spring assist to help lift the shelves up and down, one handed. Would need a counterweighted system that provides more assistance when heavy and less when light for this to work well. With this, you could reach in and lift a shelf and get anything on it, top to bottom, then slide it back down, without having to root around moving stuff to see what's squashed on the bottom.

I'll have to give this some thought...

[tulsa_97sr5]

Saw this a while back and love the idea. Very cool to see people here using it too. Ever since I first saw it I've had this crazy idea that I could build something like this around our bed and cut way back on AC usage.

[broodlinger]

Your biggest savings in a fridge is going to come from either a) insulating the outside, or b) insulating the inside.

And by inside, I mean that if you are opening the door to get a 16oz jar of sour cream, there's no reason to expose the entire contents of the fridge to ambient (i.e. summer) temperatures.

Supermarkets already know about this, that's why they have plastic flaps hanging from the ceiling.

Cost of plastic flaps?

[jwxr7]

just fyi I checked my fridge with my kill-a-watt. Ambient temps around 80 F and in 24 hrs it used 3.00 kwhrs. It's a whirlpool side by side style. I noticed it uses around 160 watts when the fan and pump are running but there was a time i noticed when the fan and pump where off and it was using over 400 watts for something (maybe frost control).