Make an Evaporative Terra Cotta Beer Chiller

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Introduction: Make an Evaporative Terra Cotta Beer Chiller

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.

Step 1: What Will You Need?

The supplies are pretty simple:

  • 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

For the sealant, I have been very satisfied with Loctite's Handyman's All-Purpose Adhesive/Sealant (as available from Amazon). It's non-toxic, low-odor, strong, waterproof, bonds with almost anything, dries clear, and stays just a little flexible.

And if you want it to be as portable and spill-resistant as mine:

  • cement
  • a 2"-3" piece of flexible hose
  • more sealant

Step 2: Seal the Hole in the Bottom of the Pot.

If your pot has a hole in the bottom for drainage, this will need to be sealed. Otherwise, sand and water will leak right out. To do this, cut a small piece of plastic and glue it over the hole.

Step 3: Add the Sand and the Can.

Next, add a little sand to the bottom of the pot. The idea is to provide enough so the tin can will rest on it, but not so much that the can sticks out of the top too far.

Add a little at a time and press the can into the pot. As you get close, the can will start to mash down the sand. Keep adding until the can is resting on sand and there's a small gap between the can bottom and the edge of the pot.

Then it's as easy as setting in the can and filling the edges with sand. Leave a gap -- even if you're not going to use cement to seal it, if you fill it to the lip of the pot then there will be no place to add water and let it sink in.

Step 4: Add the Fill Tube and Cement.

Use a piece of rubber tubing to provide a fill tube. The idea is to make it big enough that you can actually add water (and to provide a reservoir as the water slowly wicks into the sand).

Mix up a tiny batch of cement -- about 1 cup. I'm no expert at mixing it but I know it shouldn't be like wet sand and it shouldn't be like soup. If it's too dry then it won't seal and if it's too wet then it will crumble once it's set up. If you're not familiar, try a batch and see how it works.

Anyway, insert the fill tube along the edge of the sand. Stick it into the sand just a small amount (maybe 1/10" or so) -- just enough that the cement won't flow around and seal it.

Add the cement around the edge and try to seal around the fill tube as best you can. If you want to make it look less industrial, you can add decorations into the cement -- once it cures you can't.

Let the cement cure overnight.

Step 5: Add Sealant Around Fill Tube.

I found that the fill tube didn't seal against the cement so when I added water, it just leaked out around the edges of the tube and barely wicked into the sand. I had to add sealant to make it work. Not much more to say ... just make sure you get into the gaps around the fill tube and go all the way around.

Step 6: Try It Out!

Once everything is good and dry, you're all set to go. I use a funnel to get enough water into the fill tube to let it wick into the sand. It takes a few minutes and the pot gets wet around the edges pretty quick.

Unfortunately, the last few weeks around here have had miserably high dewpoints. I did a test indoors where the air temperature was 77 degrees Fahrenheit but the dewpoint was over 60 degrees, so the inside of the can only got down to 75 degrees. I'll need to test it further when it's drier.

Fortunately, the whole point of the exercise was to make coolers for beverages while I'm in the August desert of Nevada for the Burning Man festival. The air temperatures can get over 120 degrees Fahrenheit but the dewpoints stay very low -- around 35 degrees or so. This is the ideal environment for a terra cotta cooler so I'm looking forward to how well it works.

Step 7: Download As PDF

In case you wanted to take advantage of the Non-Commercial License of this Instructable, feel free to download it as a PDF here.

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    30 Discussions

    I thought about trying rubbing alcohol ... with a continuous supply and a lot of wind I figure it would get very cold. Maybe do the same thing but title it "Evaporative Terra Cotta Ice Cream Maker". :-)

    Yeah. Not so environmentally friendly though (or cheap). Oo maybe with ethanol farmed from corn or whatever they use. And if the thing caught fire.. dear me.

    If it caught fire, you would have a bread maker. Seriously though, thought-provoking Instructable. I can see some potential for a larger unit. I would think it would be a good idea, too, to spread a wet cloth over top. Couldn't you also leave the cement off the top and put a layer of ice on top of the sand so that it would melt and absorb into the sand as well as assist cooling?

    Uh... if you have ice, who needs an evaporative cooler?. Put the ice in a container (preferably insulated) and put your beverage can in the ice.

    In my experience, placing the ice directly into the beverage would dilute the beverage, at an increasing rate as things warm up.

    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?

    Actually based on the physical principles involved you would get more cooling with water. Water has the highest specific heat of any convenient liquid (ammonia being higher, DO NOT USE AMMONIA!). The reason that alcohol feels cooler is because of the high rate of evaporation. Adding more surface area with water as the liquid would result in cooler inner chamber.

    Yeah, the cooling happens (again) through the terra cotta. A lid would actually be pretty nice to try to keep as much heat from re-entering the beverage as possible.

    One more thing that I forgot.
    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.
    -.

    It shouldn't be simply the concentration of dew in the air, but also related with how much wind you have. So, best answer should probably come from practice.

    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.
    -.

    Very nice improvenment of an ancient practice. I'll use it in my camping campaigns this summer.

    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?
    -.

    Funny that the technology is being "rediscovered" by the mainstream... (happens over and over... thats where Archimedes found his water screw system... and the eastern documents he found came from other sources) The scientist noted with this invetion came from a Nigerian potter by the name of Mohammad Bah Abba. He used a glazed pot in the center, and an unglazed one on the outside with sand in the middle. The history if this device dates back to the most ancient times, where these kinds of pots were used as cold storage. There are many references you can find on google, wikipeida, encyclopedia brit. etc. According to an amateur chem book, "The temperature inside can fall as far as 14 deg C (25 deg Fahrenheit) below that of the outside". This may be where the use of an unglazed coilpot, or where allot of the "ribbing" textures on the outsides of ancient clay pots were for. I dont suggest these devices be used as permanent devices as they need cleaning etc... but... interesting if you think of the device also as a filter. salts and minerals build up on the clay pot and in the soil. if you're using dirty water, organic materials are also filtered. The sand or woodshavings of such a type of device would then become excellent materials for composting. in more desert-like conditions this can be invaluable for creating soils that can support life. just a thought.

    I wouldn't use cement to seal the top, because, as is mentioned in the link at the top,

    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.

    1 reply

    I hadn't thought of that -- I assumed the salts appeared at the evaporation surface (i.e. the outside of the pot) but I guess they could gum things up inside too. I'll have to see what mine does when I get to test it in the desert in 2 weeks.