So I was browsing the Self Sufficient 'ish' sometime last year and came upon the article titled Keeping your cool, Replacing the Humble Refigerator by a guy named Nev Sweeney. He digs around some alternatives and dredges up the pot-in-pot system developed by one Mr. Mohammad Bah Abba in Nigeria, Africa. The gist is this: take a big, unglazed terra cotta pot and fill it with a little sand then put a smaller pot inside and fill the gap between with more sand. Add water and allow evaporation to provide the cooling. Mr. Sweeney indicates he was impressed with the results.
Well, I decided to go a bit further.
First, the science behind the whole thing is that of the wet-bulb thermometer. You know: the one that measures the dewpoint? The gist is that terrestrial air has some amount of moisture in it and that vaporizing (liquid) water to dissolve it in the (gaseous) air requires energy which comes from the heat that is present in the air. Because heat allows the transfer, a thermometer with a "wet bulb" will read a cooler temperature than a one with a "dry bulb". That is, something that is wet is always a little cooler than something that is dry. All because of evaporation.
Second, how can one convert this to something practical? Like, say, the ever present problem of keeping one's beer ... er ... beverage cool on a hot day.
So I developed the idea of a terra cotta beverage cooler. It works like this: you add water to elicit evaporation which causes cooling which keeps your beverage cool. Even on a hot day. And it's not just passive: it actually reduces the temperature of a warm beverage to something cooler.
The only catch is (as I found out) that it requires a low dewpoint.
Update:
The cooler didn't work all that well out in the desert. The used flower pots I started with had very little porosity, presumably all the pores had filled with minerals and dirt over time. Also, the sand wasn't easy to use, so I'd recommend trying small pebbles instead. You could even fill it with ice just to set the height of the concrete cap.
Well, I decided to go a bit further.
First, the science behind the whole thing is that of the wet-bulb thermometer. You know: the one that measures the dewpoint? The gist is that terrestrial air has some amount of moisture in it and that vaporizing (liquid) water to dissolve it in the (gaseous) air requires energy which comes from the heat that is present in the air. Because heat allows the transfer, a thermometer with a "wet bulb" will read a cooler temperature than a one with a "dry bulb". That is, something that is wet is always a little cooler than something that is dry. All because of evaporation.
Second, how can one convert this to something practical? Like, say, the ever present problem of keeping one's beer ... er ... beverage cool on a hot day.
So I developed the idea of a terra cotta beverage cooler. It works like this: you add water to elicit evaporation which causes cooling which keeps your beverage cool. Even on a hot day. And it's not just passive: it actually reduces the temperature of a warm beverage to something cooler.
The only catch is (as I found out) that it requires a low dewpoint.
Update:
The cooler didn't work all that well out in the desert. The used flower pots I started with had very little porosity, presumably all the pores had filled with minerals and dirt over time. Also, the sand wasn't easy to use, so I'd recommend trying small pebbles instead. You could even fill it with ice just to set the height of the concrete cap.
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The supplies are pretty simple:
And if you want it to be as portable and spill-resistant as mine:
- a tin can big enough to fit your beverage container
- an unglazed terra cotta flower pot big enough to fit the tin can and some sand
- some fine-grained sand
- if your pot has a hole, some sealant and a piece of plastic to cover it
And if you want it to be as portable and spill-resistant as mine:
- cement
- a 2"-3" piece of flexible hose
- more sealant
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Theoretically, placing the ice on top, in place of the cement cap should work well. Issue comes in, where does one obtain ice in the middle of the desert, with the closest civilization being 50+ miles away?
There wont be a problem with a cover, because that will only isolate the inside container from the hot environment. If its a terracota cover, then all the better, because it can be kept wet and contribute to the whole cooling.
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Taking the idea from another comment, by Royski, a simple test could be to wrap a wet towel around a container of water, and see how much it gets cooled. If the result is satisfactory, you could go buy a pot and construct the cooler.
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Before modern era, our people here in Kypros (Zypern) used to keep their water in pots, with an opening on top from where you poured water out. This mouth was kept covered with a simple cloth, or with the drinking cup itself, to keep dust out. In this way, water was always cool and refreshing. Slices of watermelon were also cooled by being left under the hot sunshine!!
Pots were known since millenia all over the world. So, keeping water in ceramic pots and then noticing that it becomes cool must have been a similarly ancient and universal practice. Asking who invented it is like asking who invented the wheel. And thinking that it was invented by the people of one's village..., hey, we all love our people, right? so, what's the problem if one thinks it was invented by an old man from his village?
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Didn't see yours (though I searched a few times before I submitted) and found it shortly after submitting - but nice for a single beer - looks more portable than mine which does weigh some!
You can view a detailed article here:
www.theruralindependent.com
One thing that has been an issue is that with use a crusty skin of salt forms on the inner and outer surface of the cooler, from salts leached out and then left behind by the evaporating water. Whether the salts are from the water, terracotta or the sand I don't know, but it is still coming through and it needs to be periodically scraped off or it interferes with the evaporation process and the set up seems less effective. A bit of water and Scotchbrite (or equivalent) seems to do the job admirably well.
Perhaps a plastic lid with appropriate holes cut out.
I have seen wine coolers which work on this principle and seem to do a good job.
Wine Cooler