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Old 09-20-15, 04:44 PM   #1
MEMPHIS91
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Default .25 kwh/day Refeigerator

Howdy guys, so I was looking for a way to power the fridge solar powered. I put a meter on my existing fridge and it read 2.8kwh in one day. Though that is doable I needed it to fit the solar system I already have (800 watt) and I needed it to pull zero stand-by power from my inverter.

I found tons of info and youtube videos on using a chest freezer so that is what I did. 11 cu foot Frigidaire chest freezer was ordered and arrived in one week. I had to order it because I could not find a good size for the place my old fridge was. But with free shipping, who cares.

To do the zero stand-by power, I decided to power a thermostat on 12v from my battery bank. zero stand-by is important so that my inverter can go to sleep and save me power at night. I ordered this beauty, http://www.amazon.com/gp/product/B00...ilpage_o00_s00 same one as from the heat pump food dryer build but this one is 12v and can be either C or F.

I wired the 12v power in the thermostat, looped the senor mid way into the chest freezer, and wired the compressor to the relay. SIMPLE.
I set the thermostat to on at 39F off at 36F.
The meter said I used .25kwh in a day!

Now I did loose a freezer, but I only needed a little one so I found a cheap 7 cu foot one that only uses .4kwh a day. So total would be .65kwh compared to 2.8kwh. May not seem like that big a difference. But knowing my fridge stays on even when the power is out is totally worth it. Plus every time I open the fridge I don't loose a lot of my cold air since cold air is heavy it stays in. I have also heard reports that the food stays fresher because the it stays more consistent.



Ideas to improve.
-Exterior condenser wrapped around the hot water heater tank? Thinking about 20 feet of 1/4" should do it.
-Replacing the R134a with R290/R600a, or just adding a little R290 to the R134a.
-Adding a layer of ice packs (the blue hard ones) on the bottom to add some mass to the load. Hopefully to retain the cold for longer periods of time.

Thanks for reading,
Enjoy.

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Old 09-20-15, 04:57 PM   #2
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Easy one here.

Put closed cell foam (aka blue board) on top of lid and underneath. Most often the back of the freezer does not have condenser coils under the metal outside "skin". You can literally feel the heat on the metal skin exterior. Insulate on non condensed surfaces.

Choose your rate of return. I used 3/4 inch closed cell foam (R6) on my freezers (top, bottom and back) and it dropped kW hr consumption by almost half.

Glued it on with spots of liquid nail every foot or so. Purposefully left a 1/8th inch air gap. Sealed the edges with metal foil tape.

As a 'fridge, I bet you get even better return.



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Old 09-20-15, 05:03 PM   #3
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Great idea! Foam would be great on the bottom and top!
Thanks!
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Old 09-25-15, 10:26 AM   #4
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The ice packs would help but you'll lose capacity. The same could be acheived by keeping more of any product in the fridge. I don't think you want to add any heat to your condenser from your water heater you want to reject as much as possibly. Years ago there was an attempt to save electricity by pumping the liquid line of the central a/c system, right after it left the compressor into the hot water heater to help heat the water and cool the refrigerant some but I haven't seen a new one in 10 years. The heat from a fridge sized compressor should be negligible, and a bigger consideration is getting the refrigerant charge right after adding that amount of line set. The exact refrigerant charge is very crucial in refrigerators. If you can find the mullion heater circuit you could put a timer or switch on it, they tend to draw about 40 watts, it keeps the door seal from freezing shut.
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Old 09-25-15, 12:11 PM   #5
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Gtojohn, thanks man yeah the line around the water heater was a crazy idea. I think my best bet at saving even more power is using R290 I will have to add some length to the cap tube though. Should save at least half the power.
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Old 10-26-15, 02:23 PM   #6
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I somehow missed this post. It is great, thanks for sharing!

It seriously makes me want to look into modding my fridge. Its no hog, but I'm sure it can be improved.

Any updates with the setup?
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Old 10-28-15, 09:44 PM   #7
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10.5 kwh after 40 days of running. I have had NO problems in fact I think the fruit and fresh stuff stays fresher longer. Took us a week or 2 to get use to, but worked out really well. I will be adding external condenser and R290 at some point. But heat in the heat greenhouse has taken most my time.
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Old 10-29-15, 07:04 PM   #8
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Remember elevated moisture levels can allow listeria to grow better.
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Old 10-31-15, 02:48 PM   #9
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Nice work there, I was considering a chest-type freezer to mod when I did my "Freezerator". I decided against the chest-type because my house is very small and I knew that objects would want to live on the lid.

Your numbers look great.

I just did a hasty calc, and your setup is using around $10/year electric and my "Freezerator" is using around $16/year (at my local electric rates).

So, I am obviously shedding blood for the convenience of a door.

Another advantage is that your chest-type freezer should solve the problem of condensation, as I assume that you have a drain-hole located in the bottom of your freezer chest.

It may be too soon for you to know, but is the volume of your unit correctly sized for your needs?

I ask this because, for myself, I realized that I had always had too much refrigeration capacity, and food would get lost and spoil. So for my lifestyle, smaller is much better.

One more thing... if you follow my "Freezerator" thread, I developed my own Arduino temperature controller while I was waiting for the Chinese unit to arrive. The Chinese unit has a nice big display so that I can see the temperature, but the Arduino unit I developed is actually superior because it doesn't rely on an electro-mechanical relay (SSR instead), and it allowed much finer temperature control (fractional degree choices of ON-temp and OFF-temp).

Best,

-AC
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Old 10-31-15, 04:35 PM   #10
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oil pan 4, Yes cleanliness is a huge part of our fridge routine. And most the bad foods for listeria we don't eat. (seafoods/pork) and the others are seal in vacuum tight containers.

AC, Thank you, that does look like a cheap cost for a door. ($6) And I'm sure that my freezer has a better insulation and enerystar numbers, so it may be less than $6.

The drain hole is awesome. I had to jack up one side to make all the water run into the hole, but I simply remove the plug and let it drain into cup once a week.

Capacity is just about right. I wanted it full for efficiency. But we do water kefir and and milk kefir so that adds to the amount of things we have in the fridge.

It's perfect with enough room just in case we make a lot for leftovers or something.

Yes a more accurate thermostat would be a plus. I have had some experience with arduino. I own 2 or 3, and might look into building one.
I remember see your build and the code in your thread, thank you for posting that.

I'll keep this updated when I do some more mods.

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