Introduction: Build an Ultra Efficient Fridge

About: 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 fly rc heli's. I like to program micro controllers, pic series and now Freescale (thanks Brad!), a…

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:

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:

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:

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:

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:

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:

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:

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.

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