Introduction: Build an Ultra Efficient Fridge

Picture of Build an Ultra Efficient Fridge

This is my instructable on taking a regular refrigerator, and making it very efficient, by making use of the cold winter air. I got this idea while working on projects in my basement. I got tired of going up and down the stairs, to get cold refreshing beverages. I really didn't want to put a mini fridge down stairs due to the cost of running it all year long, so I started wondering how I could cut down the expense. I live in Iowa, so I thought, why not use the cold outside air to cool down the fridge during the winter time! What about summer though... I knew I'd need to be able to switch it back to the internal compressor pump in the summer. This is done by routing the existing fridge thermostat to switch on external low current push pull fans. This changes the power consumption from 120v 5 amps to 12v 500 milliamps. This idea can easily be adapted to larger size fridges with the use of some additional items. I will cover that at the end.
This project also has the potential to save tons of carbon in the atmosphere per year if larger companies sold this type of technology in future fridge models or people adapt to this idea to existing fridges. I tried to give as much detail as possible, so most people (I hope) can do this on their own. Most people should be able to look at the pictures and get the idea.

Step 1:

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Get yourself a mini fridge. I bought mine on craigslist really cheap.
Get the supplies for the fridge transformation.
4" insulated duct tubing. (You can sometimes get this for really cheap at a used construction recycling center)
2, 4" computer fans. (I pulled these out of old burned out computer power supplies)
Silicone caulk. (local hardware or home improvement stores carry these)
End wire caps (local hardware or home improvement stores carry these)
Small piece of 4" metal duct tubing. (local hardware or home improvement store carry these)
House wiring 12 gauge. (I had some left over from other home projects, you can sometimes get this for really cheap at a used construction recycling center)
Piece of plywood. (I had this left over from other home projects, you can sometimes get this for really cheap at a used construction recycling center)
Dual outlet box.
One 3-way switch.
One home outlet.
One outlet cover.
One long piece of dual wire.
Window and door foam seal.
Old 12v 500mA adapter.
Tools you will need.
Small saw.
Wire cutters.
Screw drivers, both phillips and regular.
Nibblers or tin snips.

Step 2:

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First thing you must do is mount the outlet box to the back of the fridge. Hold up the outlet box in an empty space next to the compressor, and marked the screw mounting locations with a marker.
Drill two small starter holes where you marked, and mount the outlet box using two sheet metal type screws.

Now you are going to wire up the switch to the outlet. Cut about two feet of home wiring. Do this again but this time pull out all the wire from the main insulation. So now you should have a total of six wires, three are still in the main insulation and three are not.

Now take the ground wire that you just removed out of the main insulation. At one end of the wire, make a small loop so it will wrap around the green screw on the 3 way switch. Now tighten the screw so the wire does not come loose.

Cut the ground wire you just attached, leaving about three inches, and loop the end as you did in the other step. Place this around the green screw on the outlet, but do not tighten the screw yet, just leave it wrapped around the screw.

Take the other wires that are still in the insulation, and strip about three inches of the main insulation. Then strip about a half inch off the white wire and black wire and remove the paper around third ground wire.

Now take and make a loop in the ground wire. Attach it to the green outlet screw that you have not tightened yet. Now that you have both wires attached, you can tighten it.

Take the single black wire, and attach it to one side of the switch, do not attach it to the single screw that is black.

Take the other black wire (the one still in the insulation with the other two wires) and attach it to the brass colored screw (hot side) on outlet.

Cut a three inch piece of the white home wire. Strip a both ends. Now connect it to the other side of the switch and to the outlets non brass colored (neutral) screw.

Now take the rest of the white single wire, strip and connect it to the other side of the switch, the only screw that is colored black.

Run all the wire through the back of the outlet box. There are little pieces in the back of the box you can punch out with a screwdriver for this.

Step 3:

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Now at the other end of the wires that you pushed through the outlet box, remove the cover over the motor connections.

Next you want to strip the insulation off of all the wires that were passed through the outlet box.

Now cut and strip the green wire that's coming in from the fridge's outside power cord, and take the bare wire from the outlet box and screw all of them together with the wire nut.

Now you'll need to take the black wire from the main power cord that goes straight to the motor, and cut and strip both ends. Connect the black wire (from the insulated group of wires) to the two stripped black wires and wire nut them.

Now take the only other black wire that goes to the motor and cut and strip both cut ends. Take the one black wire that does not have the connector to the motor on it, and wire nut it to the white wire going to the outlet box.

Now take the single black wire coming from the outlet box and wire nut it to the black wire that has the connector to the motor. Reconnect it to the motor.
If you have a multi meter you can test your work by connecting it to the outlet and see if it switches on with the thermostat. You should see 120v AC.

Make sure it looks like the diagram below.

Step 4:

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Now it's time to cut the holes. On the right side of the fridge, measure about 4 inches from the front and one inch from the bottom. Mark this point with a marker.

Take the long metal duct piece and place it at the marked point. Draw around it with a marker.

Now you will drill a starter hole for the nibbler. This needs to be done with care, with small fridges like this, they place the condenser tubing around the whole fridge casing. So to make sure you do not drill into one, start with a small drill bit, but drill slow and do not push the drill bit all the way in. As soon as it break through the metal, pull it out. Now stick a small screw driver in the whole and see if you can move it around at an angle in a circle. This will tell you if there is a condenser line at that point. If you do not feel one, then switch to a larger drill bit that the tip of the nibbler can access.

Now take the nibblers and cut around the marked spot for the duct tubing. I have one tube from the condenser, I ran into. If this happens drill another access hole on the other side of it and nibble the other side out. You will now have the piece we just nibbled, with two small pieces we couldn't cut. To remove it all I did was wiggle the metal piece back and forth until it broke loose.

Now perform the same steps for the exit hole on the top of the fridge, this time measure back about eight inches from the front, and one inch from the left side. This time I did not run into any condenser lines.

Now we want to place the duct work into the holes we just cut out. Open up the duct tubing and place a mark about four inches from the end. Draw a straight line from one side to the other, and cut it out. Do this again for our hole on the top of the fridge. Make sure you fold them back up into a tube.

Since I have a condenser line in the way on the inlet hole, I marked the duct tube at those points. Then with the nibblers cut straight down on those marked spots, so you will now have two slots that will go around the condenser line.

Fit the duct inside the holes until it's flush with the plastic inside. Take silicone and fill in around both the inside and outside edges where the tube meets the walls.

Step 5:

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Now that we have the fridge done, we can move to the fan unit. Measure the window that the fan unit is going to be placed. Take and cut out of plywood the size that will fit in the window.

Next take and draw two four inch holes that the vent covers will attach to. Make one higher than the other. The top one will be the exit and the bottom one will be the inlet, then cut them out.

Now remove the inside flaps on the vent clovers we won't need them, and remove the bottom cover.

Now take and cut out a piece of screen so that it will wrap around the bottom cover, and place it back into the vent.

Now mount the vent covers to the two holes we cut out.

Step 6:

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Now take and cut two pieces of the metal duct. Make these about 4 inches.

Take the two fans we have, and add some extra wire (about four feet) to them so we can attach them to the power adaptor later.

Now place the fans inside the metal ducts. I had to trim the corners of the fans to make them fit. Take some foam insulation (I used the type to seal around doors) and wrap it about four times around the outside edge of the fan, then push fan inside in the tube.

Now connect the duct with the fan, to the inside of the vent cover. Now we have two ducts with fans connected to both vents.

Now place the fridge where you will be using it. I am placing mine under the window so it's close to the fans. Now take one end of the flexible duct and connect it to inlet of the fridge duct tube. Take and cut it so you have enough length to connect it to the window fan. Do this with the output duct of the fridge too.

Next put window some foam around the edge of the wood that the fans are attached to. Then place the fans inside the frame of the window and close it so it fits tight. I put a piece of wood on the other side to add pressure to the opening, and to keep it tight.

Now connect the two wires from both fans to the transformer that will power the fans. Plug in the transformer to the outlet we added to the back of the fridge, and turn the switch to the outside setting. Plug in the fridge and see if the fans are operating.

Once confirmed that the fans are working, connect the other ends of the flexible duct to the other ends of the fan ducts.

Step 7:

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Congratulations, we are now ready for cheap winter time fridge cooling! You can now move on to the other the next section if you want to have the switching from the outside air, to fridge compressor controlled by an external thermostat.
Do to the cost of external thermostats, I left this out, to keep this project as cheap as possible. But I am planning on doing this to my main fridge, and using an external thermostat for that so it's all automatic.
Everything that was performed above applies to a larger fridge with the exception of where the input and output duct work goes. You can add an external thermostat to switch the outlet that the push pull fans connect to. This will allow you to have the fans turn off and on automatically during the fall and spring when temperatures go above the desired fridge temperature.

I have also thought of using solar panels to power the fans since they only us half an amp! This way you can be completely off the grid.


ArpitK13 (author)2017-04-25

Very Nice blog. Thanks! Here is a ultra low freezer a medical lab equipment.

Opcom (author)2009-04-23

Very good use of natural resources! Too bad I can't apply the reverse to my oven in Texas!! Even so, for a couple of months out of the year, it could be done, if not for the fridge proper, then for the beer fridge. It could save $100 or so in electricity, any resources saved are worth consideration.

TroyK11 (author)Opcom2016-02-04

I am guessing you could use a mirror or magnifying glass to heat some kind of thermal liquid while the sun is out. This liquid would stay hot for a long time and you could use it for a stove. There are some power plants in the desert that use the same principle.

kokla (author)Opcom2009-04-25

the texan summer oven might be a solar slow cooker like what kids used to make in gradeschool science class. definately a couple panes of glass either side of a tire innertube could cook rice in a couple of hours

nigel.begg.12 (author)2014-09-01

Thanks for stealing my idea and saving me the trouble of developing it. I have a few suggestions. You could make a similar arrangement for the freezer compartment with different thermostat settings. Also, in summer you could progam the motor heat to be vented outside and be allowed to remain inside in cold weather. Architects could anticipate the use of efficient fridges by including an air chimney to allow the exchange of warm air for cold through convection.

shardman1 (author)2009-04-24

Great for saving cost on electricity. Wouldn't worry about the carbon emissions since manmade global warming does not actually exist.

denswei (author)shardman12012-07-19

LOL. Perhaps the climate cynics can start by providing theory and evidence for why CO2 behaves one way in the lab (trapping IR heat, as predicted by quantum mechanics), and a different way in the atmosphere?

DallasDeckard (author)Etitan2010-11-03

Alaskan Big Bubba (author)Etitan2010-09-08

Come on now, it dosn't matter if your green or not, both sides have private interests and in reality the earth goes through temperature changes on it's own, did we not have an ice age and did man cause that? So what if the world is warming up, man can add to it, but not cause it. We still need to be concious and ideas like this are nifty, but be realistic.

shooby (author)shardman12010-09-10

Who cares whether it does or not? Using less resources is better, because suckers like us don't have to spend the time extracting, processing and transporting them.

kokla (author)shardman12009-04-25

oooh, someone's been drinking oil companies snake oil.

falcotheimpaler (author)2011-08-05

Do this to a computer, and I'm sold.

i did this to a computer a few years ago... consistently got 6*C temps from the cpu under load till i killed the main hard drive... condensation was the suspect... also, i like to comment on year old threads,

sorry, 6*F temps...

Kent (author)2010-09-08

You might find that even the fan is not needed in the winter. Warm air will rise, cold air will sink. Anytime it is colder outside, air will flow.
But as someone commented, this project does not save energy. The "wasted" energy is heating your room. In the summer it would save energy to have the heat vented outside. With an EER of 8, it costs 240 Watts in your air conditioner to get rid of 600 Watts of power from the fridge. The same principle holds for light bulbs. You have to look at the whole system, the whole house.

falcotheimpaler (author)Kent2011-08-05

It saves "energy" in the form of electricity he doesn't have to pay for.

Kent (author)falcotheimpaler2011-08-07

The energy being vented to the outside in the winter has to be replaced by other energy to keep the house at the desired temperature. He is saving refrigerator energy, and replacing it with heating system energy, so there is no savings. There is also some leakage of heat into the hoses, so overall, there is a net loss. Just put the whole thing outside.

nitehawk86 (author)Kent2011-01-24

Possibly, but if your home is heated by geothermal or gas, it is probably far more efficient on energy than a big electric heat exchanger.

NightLord (author)nitehawk862011-06-26

It is also far mor efficient if you heat your house with biomass...

BluTiger (author)2010-09-14


Skai (author)2010-09-12

this is really amazing. i think that i'm going to do solar panels, though, cuz solar panels can save all of my electricity bills for my entire house, instead of this just for my fridge. but maybe if i am not getting enough electricity from my solar panels, i can help myself be more efficient with my solar energy by doing this. awesome :)

anotherone (author)2010-07-21

nice job!

hitachi8 (author)2010-03-03

 Nice  ! 

leepinlarr (author)2009-05-31

I'm sure the btu's off a fridge, are not an issue

cyberdove (author)2009-05-12

In the winter, cooling a refrigerator helps heat the house. So when bringing in cold air from outside, you are increasing your heating energy consumption.

WilderLust (author)2009-05-11

very nice instructable; just make sure your air intake does not pickup any stinky air! if you are down wind from exhaust smell for example, you may have a certain strange flavor to you food... not smoked exactly but :-) i did something similar a while back with my big fridge and freezer but used electronics to control the switching depending on outside temperature.

dark sponge (author)2009-04-24

I'm guessing this won't work in Texas.....

_soapy_ (author)dark sponge2009-04-26

If you live anywhere that is cold at night, then it will work just fine for half the time. Deserts drop below freezing at night, and at those times it will actually be too cold for your fridge! This isn't going to be much use for me, but I have been considering trying to find a way to locate the compressor in the next room, where the heat is wanted, rather than right behind the fridge where it just heats up the fridge again! This idea has actually been used for thousands of years, already, just with a semi-outdoors larder or pantry with lots of stone to keep the temperature low. Using a couple of fans and temperature switches to update the design is genius.

dark sponge (author)_soapy_2009-04-26

Using temperature switches is a good idea, or maybe some of these hooked up to a microcontroller and some relays.

You could have one sensor outside and one in the fridge, and one relay control the fan and the other one the compressor. If the sensors detect that it is cold enough outside, it will switch on the fan. If the sensors detect that it is not cold enough, it will turn the fan off. If the temperature sensor in the fridge detects that the fridge is not cold enough and the one outside detects that it is not cold enough to use outside air, it will turn on the compressor.

kunalg (author)2009-04-23

The hot air outlet duct is facing downwards just above the cold air inlet. This can cause exhausted hot air to get sucked in along with the cold air. If the hot air outlet duct is turned so as to face upwards, the hot air will be able to escape up instead and will not mix with the cold air. This will increase the efficiency a wee bit more !

kokla (author)kunalg2009-04-25

that's a good idea, perhaps if the inlet and outlet where facing 180 degrees opposite left to right. I imagine in it's summer and your vent faces upwards, a water and dust ingress is compromised.

dexusno (author)kunalg2009-04-24

And will let rain fall into the hot air outlet...

BJMN (author)2009-04-23

Yes - living in central Manitoba in Canada, we have a surplus of cold air for a lot of the year! I've thought for a long time about doing something like this. We already keep our chest freezers in an uninsulated building outside, so they don't run for a large portion of the year, but I hadn't gotten around to doing anything with the fridge yet. I especially like the idea in the comments about re-routing the hot coils to the outside. My current house doesn't have AC, so getting some hot air outside in the summer would be a great idea. As an engineer, I see tremendous potential in just changing how we see and use heat - a tremendous amount of our energy output simply goes into moving heat around, and anytime I see something that does this naturally appeals to me!

votecoffee (author)BJMN2009-04-24

Good point about venting waste heat of compressor outside during summer to save on cooling bill. In winter, it can actually be beneficial to capture that heat. Changeable system would be good, with good insulation on ducting.

neffk (author)2009-04-23

Very nice. This is a very elaborate project. Could it be made more simple by simply venting the coils to the outside during the winter? That would reduce the project to duct work. I would take on more readily than re-wiring my wife's major appliances :)

votecoffee (author)neffk2009-04-24

You could do the coil thing (build a box around coils and vent to outside), and it would increase the efficiency a good bit. Would not cut off compressor completely though. Use less power but not none, assuming the fan is done with solar and not house current. If fan is run 24/7 off house current, it may become questionable how much you're saving.

proacguy (author)2009-04-23

The Idea is great!! The only thing I can caution anyone on is the bigger fridges have coils in the sides, back, and or top. So be careful when cutting the holes.

teeps (author)2009-04-23

wicked project sir! Immediately reminded me of my own instructable on using this concept to cool a desktop computer:

Excellent job and I certainly think that harnessing the weather like this is the way of the future (while certainly being a return to the past!)

frank bailey (author)2009-04-19

great job , sounds like you know what you were doing , the instructions were good with a lot of detail , . you got my vote

Tagarashi (author)2009-04-18

Great ible... What is sad though is even when you try and conserve energy. The energy companies just raise the rates.

unbentcrayfish (author)2009-04-18

If you could make to tubes and stuff smaller and less noticeable it would have more applicators and I would love this even more

gsl130 (author)2009-04-17

Do you have problems with freezing, or getting things too cold? I mean, with outside air temps dropping well below 32 F, what keeps things from freezing? On a similar note, I bet we could come up with a sensor to switch between compressor and outside air as needed to keep food from getting to warm on those balmy winter days. Awesome instructable!

nodyeliab (author)gsl1302009-04-17

Thanks! Nope no freezing, the existing thermostat turns the fans off or on, the switch in back determines if you want the thermostat to switch the compressor on and off or the fans . Yes, you can connect an external thermostat to switch between the fans and compressor, but due to the cost, I only mention using that option at the end of the instructable. I have thought of using a microcontroller to do that too, that would be another fun instructable!

abarker (author)2009-04-17

Very nice.. thanks for the tut. I remember reading an article years ago about a guy who dismantled his frig to maximize efficiencies. He took the coils off and moved them (I think maybe he tried several versions here). He placed them in his hot water tank to preheat his water. He also tried a version with the coils outside to take advantage of the temp differences. With the coils and pumps moved away, he super-insulated the actual box. Always thought it would be a good idea to move that expressed heat under my front sidewalk to melt the ice in the winter.

solis365 (author)2009-04-17

I'm pretty sure there are houses built around this concept. You mount a fridge next to your wall anyway, so just have a duct going from the outdoors, through the wall, and into the fridge. If houses/kitchens were built this way it would save tons! nice job. there are lots of families that have an extra fridge or chest freezer in the basement to store bulk food - imagine if they did this for those large freezers. it would save tons!

nodyeliab (author)solis3652009-04-17

Thanks, yea the hope is that more people will see this and get the idea flowing. Yes this has the potential to save tons of electricity and greatly reduce the amount of carbon in our atmosphere. I was also thinking of using solar panels to run the fans since they use only half an amp! This way it would it would be completely off the grid.

MechEngineerMike (author)2009-04-16

ive though about this concept last winter, good job on building it! perhaps you could improve your summertime efficiency by rerouting outside air to cool off the hot coils in the back. That way your fridge (in the summer) not only cools the inside of the fridge but also vents hot air outside to cool your house too!

Sandisk1duo (author)2009-04-15

5 amps/0.5 milliamps at what voltage?

nodyeliab (author)Sandisk1duo2009-04-16

This is 120v compressor at 5A. When it's switched to use outside air, it uses 12v@ 500mA

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Bio: I am a proud dad with two wonderful kids. I have an awesome wife that lets me play with all my toys. I like to ... More »
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