Off grid refrigeration idea

Off grid refrigeration idea

Postby montanamac » Mon Jul 26, 2010 1:36 am

One of the challenges when you decide to live "off grid" is how to keep your food cool without breaking the family budget. Most refrigerators stay around 40 degrees F. The goal is to have a method to maintain a temperature in this range without excessive cost. You could buy enough solar panels or plan to run a generator at regular intervals but both of these options will cost you a considerable sum. Most "off gridders" don't have piles of money so need to use other methods.

One method I researched a few years back is commonly known as a "thermal mass refrigerator". A couple of basics to keep in mind before we discuss the details of how to construct this cooler.

1) cold air goes down and hot air goes up
2) in our area it is always cooler at night than it is in the daytime

With this in mind ... what if you had a well insulated box with a top opening attached to a chimney open to the outside air at night and with a bottom outlet that vents out of the box. According to rule #1 above the cooler night time air will travel down the chimney .... through the insulated box and out the bottom assuming the incoming cool air is colder than the air inside the box. With this natural air flow of cool air the contents of the frig will be cooled until a balance of incoming air is matched to the contents of the insulated box. This should work pretty well at night but what about the daytime when the outside air is warmer than the contents inside the box? The warmer outside air will enter the box and warm the contents.

What if the "box" was inside of a larger box with the void between the two boxes large enough to contain a thermal mass to store the cooler temperature from the night air? The cold night air will flow down the chimney and flow through this void between the two boxes and then exit through the bottom exit pipe. The design I recall reading about used liquid containers lining the void between the boxes acting as a thermal mass. Water bottles might not work in the winter time for this thermal mass when the incoming air could be well below 32 degrees and thereby might freeze and break. The solution ... line the void area with cheap cans of beer! The alcohol in the beer will keep the cans from freezing solid. The beer cans would occupy the space between the two boxes top, bottom, back and both sides. The stored cold (in the beer cans) will be released later when needed to keep the contents of the smaller "box" cool during the warmer daytime temperatures. Cold air enters in the top and exits out the bottom outlet tube. Once the beer is colder than the contents of the smaller box this cold will be transferred to the contents of the small box in an attempt to equalize the temperatures.

Operation
1) every night ... open the inlet and outlet pipes for your thermal mass frig.
2) In the morning ... close the inlet and outlet pipes to prevent the stored cold from escaping.

Additional thoughts
Every time you open the door in a standard upright frig ... cold air escapes. Logically ... the less times you open the door the cooler the contents will stay.

You will need to construct a well insulated door with a good gasket seal.

Other thermal storage medium might include the blue ice packs that are available today in place of the cans of beer.

The thermal storage medium must be arranged so as to allow the free flow of cold air during the night around the inner box.

What if your frig was horizontal instead of vertical similar to a chest freezer? Remember, cold goes down! With this configuration the cold would not "dump out" when the door is opened and should take less to keep the contents cool.

This is not my original idea. I would like to give credit but don't remember where I first saw this information. Also ... I have not tried this idea but sure seems logical that it should work. If you decide to give it a try, please report your findings on the blog to share with others.

Mac McQuaid
Corvallis, Montana
montanamac
 
Posts: 46
Joined: Thu Feb 04, 2010 4:47 am

Re: Off grig refrigeration idea

Postby jpf1030 » Mon Jul 26, 2010 2:18 am

Howdy Mac,
I will post my reply thoughts in red text on your excellent posting on off-grid refrigeration...jpf
******************************************************************************************************************************************
One of the challenges when you decide to live "off grid" is how to keep your food cool without breaking the family budget. Most refrigerators stay around 40 degrees F. The goal is to have a method to maintain a temperature in this range without excessive cost. You could buy enough solar panels or plan to run a generator at regular intervals but both of these options will cost you a considerable sum. Most "off gridders" don't have piles of money so need to use other methods. One important project I've been trying to get BSOSC folks involved in is the solar ice maker. I've developed an internet friendship with the Jarislov Vanek family on this. He is a professor at Cornell University and his son Steven heads the effort now. However, Steven has been busy with his post graduate studies so the project has been shelved for a while, according to his mother's email to me. We have their excellent info which is enough to build the solar ice maker now. With this augmentation, your off-grid refrigeration thoughts will be a piece of cake.

One method I researched a few years back is commonly known as a "thermal mass refrigerator". A couple of basics to keep in mind before we discuss the details of how to construct this cooler.

1) cold air goes down and hot air goes up
2) in our area it is always cooler at night than it is in the daytime

With this in mind ... what if you had a well insulated box with a top opening attached to a chimney open to the outside air at night and with a bottom outlet that vents out of the box. Hmmm, in some cases like for refrigerating jugs of milk, etc. that you could set down in from the top, this sounds like a barrel with a stove pipe attached to the top at presently indeterminate length with an exhaust (reverse draft) horizontal pipe attached to the bottom. According to rule #1 above the cooler night time air will travel down the chimney .... through the insulated box and out the bottom assuming the incoming cool air is colder than the air inside the box. With this natural air flow of cool air the contents of the frig will be cooled until a balance of incoming air is matched to the contents of the insulated box. This should work pretty well at night but what about the daytime when the outside air is warmer than the contents inside the box? The warmer outside air will enter the box and warm the contents.

What if the "box" was inside of a larger box with the void between the two boxes large enough to contain a thermal mass to store the cooler temperature from the night air? Sounds like a 30 gal. barrel inside a 55 gal. barrel with the annulus filled with gravel and RV antifreeze (or whiskey or wine) with a manifold of tubes in the annulus to enable the air flow The cold night air will flow down the chimney and flow through this void between the two boxes and then exit through the bottom exit pipe. The design I recall reading about used liquid containers lining the void between the boxes acting as a thermal mass. Water bottles might not work in the winter time for this thermal mass when the incoming air could be well below 32 degrees and thereby might freeze and break. The solution ... line the void area with cheap cans of beer! The alcohol in the beer will keep the cans from freezing solid. Beer does not have high enough alcohol content not to freeze so you will have to stick to whiskey or wine for this medicinal purpose (confessions of a drinker to a non-drinker!) The beer cans would occupy the space between the two boxes top, bottom, back and both sides. The stored cold (in the beer cans) will be released later when needed to keep the contents of the smaller "box" cool during the warmer daytime temperatures. Cold air enters in the top and exits out the bottom outlet tube. Once the beer is colder than the contents of the smaller box this cold will be transferred to the contents of the small box in an attempt to equalize the temperatures. Wrapping the outside of the barrel and chimney pipe with radiant barrier over some firring strips creating an exterior annulus, to better activate the radiant reflective abilities of the radiant barrier would give beneficial insulating properties both directions, in and out. Outside the radiant barrier you can add f'glas batts for higher insulative values yet.

Operation
1) every night ... open the inlet and outlet pipes for your thermal mass frig.
2) In the morning ... close the inlet and outlet pipes to prevent the stored cold from escaping.

Additional thoughts
Every time you open the door in a standard upright frig ... cold air escapes. Logically ... the less times you open the door the cooler the contents will stay.

You will need to construct a well insulated door with a good gasket seal.

Other thermal storage medium might include the blue ice packs that are available today in place of the cans of beer.

The thermal storage medium must be arranged so as to allow the free flow of cold air during the night around the inner box. The description for manifold tubes in the annulus between two sizes of barrels would work just as well for two front opening nested boxes.

What if your frig was horizontal instead of vertical similar to a chest freezer? You are absolutely right on this for a number of physics reasons. Remember, cold goes down! With this configuration the cold would not "dump out" when the door is opened and should take less to keep the contents cool.

This is not my original idea. I would like to give credit but don't remember where I first saw this information. Also ... I have not tried this idea but sure seems logical that it should work. If you decide to give it a try, please report your findings on the blog to share with others. A couple of years ago, I really studied one a gal developed in Africa for native villages from buckets of sand designed around the swamp cooler principle that was really cool. She won some big award for the design. If you are interested, I will see if I can dig into the deep dark recesses of my computer to find the info. Jeff will be better at that. I started working with some co. in Sweden with some product that may be similar. They are just recently getting it commercialized. I had turned this project over to Jeff. He has stayed in touch with them and could advise you on that.

Thanks for an excellent post that I feel should be pretty high priority with serious preppers.
Happy Preparedness Trails,
jpf


Mac McQuaid
Corvallis, Montana
jpf1030
 
Posts: 1487
Joined: Wed Feb 03, 2010 4:49 pm

Re: Off grid refrigeration idea

Postby wesurvive » Mon Aug 09, 2010 7:28 am

I am also interested in the off grid refrigeration idea. I have looked around and found some different version, one included a ammonia and calcium version which was pretty cool, but had its downside as any leaks could be dangerous. Anyone with photos or diagrams could post what they find or have on here it would be great so we don't have to send around photo copies or email to everyone. I will find my links and post them here as well. Or if you have links..
Just scroll down the pages till you find the sources for solar refrigeration.
http://www.engr.sjsu.edu/jrhee/solar/projects.htm

http://dvice.com/archives/2008/08/solar_icemaker.php

And solar coolers (have to scroll down for that too.)
http://www.green-trust.org/2000/solar/solar.htm

Had some plans, but I think they were pdf, have to figure out how to get them on here.
You Must Survive. So prepare for it.
wesurvive
 
Posts: 797
Joined: Mon Aug 09, 2010 5:24 am

Re: Off grid refrigeration idea

Postby wesurvive » Mon Aug 09, 2010 8:00 am

You Must Survive. So prepare for it.
wesurvive
 
Posts: 797
Joined: Mon Aug 09, 2010 5:24 am


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