Zeer Pot Fridge

Look at this amazing technology they've thought up in Africa: http://practicalaction.org/zeer-pot-fridge

It's a clay pot inside a bigger clay pot, with wet sand in between the pots. As the water evaporates, it cools the inside of the pot where you can put vegetables, very useful in Africa where it gets really hot and there aren't electric fridges everywhere. We can definitely use this in the temperate regions too though, no reason why we shouldn't!

We use a similar approach here in Arizona. (We have no fridge) It works well in climates with low humidity because it works by evaporative cooling.

Instead of using pots, we wet down a shirt sleeve or pant leg and slip it over a two liter bottle to keep drinks cool in summer. I tend to just sit it in a couple inches of water so that it can wick it up through the day. If you have good airflow it works really nicely. Cool water to start with and a shady location will actually get drinks decently chilly.

You could easily cut the neck off a bottle so that fruits and veggies fit in, then put a moist cloth around it.

Thanks for sharing this, I learned something new today. How much temperature difference is made from this device?

I'm currently in Udaipur, Rajasthan, (on the edge of the Thar Desert) and thought I would try the Zeer pot fridge. I had to adapt two Rajasthani round-belly Ghara clay pots (which they use to cool drinking water by evaporation) because that's all they have, but the principle is the same. The larger pot had to be broken to allow the smaller one inside but the heights match perfectly. The climate here is perfect (hot and dry) and my pot is just outside the house under the eave for maximum evaporation. But it ain't working! Outside temperatures are between 30 and 36 Celsius, pot interior remains at 25 C and that's when I had a bottle of water inside to regulate the temps. Without the bottled water, the interior temperature remains at 29 C. I believe it should cool to 10 C when working properly. I pour between 500ml - 1 liter of water per day in the sand; too much water and the inside pot will float up. It's such a simple fridge what could possibly go wrong? Comments and suggestions, please?

Hi George,
I suspect drinking water pots are glazed so they don't leak. You need unglazed pots to use as a fridge so that evaporation is maximized.

Thanks Kathy, but the pots here are unglazed like these -
http://blogs.gonomad.com/traveltalesfromindia/files/2012/01/Clay-Pots-or-Ghara.jpg

This morning I decided to put more water in the sand so I wired the inner pot in place and filled the outer pot with water. The inner pot floated up and defeated my attempts so I've now cemented the inner pot in place and will try again when the cement has set. Reading about your adapted cooling system, I now wonder why I need to put sand in between the two pots. If evaporation is all that's required, why can't I simply pour water in between the two pots, just as you do to cool your drinks?

I too, have been intriqued and attracted to the Zeer Pot concept. I've experimented a little bit and have been somewhat disenchanted with the terra cotta garden pots as a source. It is true that for the Zeer Pot to work there needs to be evaporation, but the inside container doesn't have to be porous, it can be metal or plastic or watersealed pottery. My understanding of using sand as a medium or similar is to create more surface area for evaporation. The outside container must be unglazed and porous to allow the gas exchange and evaporation. But, as with the terra cotta/clay pots after some time of use, minerals and other water sediments will seal the pots pores and become less and less efficient. Perhaps an acid or ACV soak/wash could restore the porosity, but I've not taken these steps in my experiments as yet. Another material that I'm working with is Hypertuffa, it's a cement/perlite/peat-like mixture that you can mold/form into strong, but lighter than concrete container/shapes. Hypertuffa is also porous and can breathe. So, you can easily make a trough-like structure that could be fitted with a liner or within another or made with a separated inner/outer wall to achieve the Zeer Pot requirements.

Thanks, Ollie. My pots are new and still quite porous but I'll keep it in mind. I'll also have a look at Hypertuffa as I hope to use the same Zeer pot principle to cool the air in my house in the Caribbean. I have in mind a long tube in a wet trough (made from Hypertuffa perhaps?) running around the house for perhaps 180 ft. rather like the buried air tubes but above ground for evaporation. Buried air tubes won't work in the Caribbean as we have no cold seasons and very little temperature variances. I'll be happy if the incoming air could be around 23 C as it's a/c for free. I realise the Caribbean is very humid, but we have year-round sun and water evaporates off the roads like magic, so it might work. So far though, my Zeer pot hasn't been very promising. Does anyone have any idea what temperatures they cool to?

Well, one quantative study was performed in Ramona, CA by a student in his 2003 entry to the State Science Fair. It was found that the average daily temperature drop inside the system was 14 C (23.5 F), aka keeping produce at 15 C (59 F) while the outside temperature is 28 C (82.4 F). The very best temperature level, I've heard of was down to 6 C, which of course is under very optimum conditions of low humidity, dry interior where food is stored, air flow, etc...

An average of 10 C would be great! Surprisingly, nobody here has ever heard of these pots which could make life so much easier for the villagers. The town people think I'm backward because they all have electrical fridges and scoff at the Zeer pot. Moreso because my prototype isn't the spectacular success I promised. But I imagine the villagers would be happy to be able to keep their tomatoes, milk and even insulin at cool temps even without a fridge. They could also make cold water while working in the fields, etc. I don't suppose this will work in winter though. I'm interested in keeping veggies (and beer!) fresh longer in case of global collapse. I'm one lazy doomhead.

George - Some other ways, and this just might lower the temp even more, nothing wrong with having multiple methods, this first would be to use a shelving unit PVC, plastic, wire, whatever you have available and drape burlap/loose-weave material over it, top to bottom. You would have your fragile items placed apart from each other on the shelves keeping good air flow, on the top most shelf you would have a water reservoir that would re-hydrate the burlap as it wicked downward and dried and evaporated the moisture, cooling the interior. It works best if there is some kind of a breeze to blow thru. Drawback is that it can use a lot of water and you can't let it run dry...

Last idea to try, make up a solar funnel cooker, but use it at night pointed toward deep space and cool thru radiant cooling. When the night sky is clear and cloudless this will freeze water in jugs inside an insulated cooler. Good coolers here in the States can hold ice for 5-7 days, given you have an open, clear sky, properly aimed and un-disturbed. then easily you have an excellent passive method.

wow, pointing a funnel toward space at night can freeze water, please send details

i spend 40$+ per month on propane to keep a fridge working, and so far this spring i've just done without any refrigeration, so being able to make ice--or even really cold water would be amazing--maybe i could cool enough water to run through the radiant heating pipes in my cement floor-- please send details or a link or something

how big should the funnel be, what can it be made of, what sort of temp difference could i expect--will that work on an 80 degree summer night?

Bob - Look into these links, this is some info that I've gone by, you can find some PDF's on radiant cooling, if you would Google 'night radiant refrigerator' and you may find others since I searched last year... One post/blog, I remember said that they were successful using a auto windshield shade and formed it into a cone shaped reflector...

http://solarcooking.org/radiant-fridge.htm

http://www.provident-living-today.com/Alternative-Refrigeration.html

http://c2.com/cgi/wiki?SolarGeneratorThatWorksAtNight

Be sure to check/search on Permies as there are several posts, here is one to get you started...

https://permies.com/t/7317/cooking/Making-ice-solar-oven

There is a lot of info available, be 'creative' to think of keywords/ways to 'search' online. Experiment some to prove what different people say and the you can come up with your own ideas for your situation(s).

hey ollie,
good to talk with you

fascinating topic, i only read the link to wiki and there was a physicist there who read the other links and commented on them--so with only a few minutes of research i am certainly inspired to see about some sort of experiment which will be ongoing

evidently rays of cold have nothing to do with it (my physics "education" was screaming at me to give your response the heave ho but fortunately i was able to overcome my education)

isolating an object from external heat sources---ie radiant, conductive, convective,-- is the first step

pointing it to the night sky (without heat radiating clouds) is the next step allowing the object to be cooled by it's own natural radiation away from itself into the night sky is ingenious- Use several layers of plastic separated by air-- not glass around the object since most glass blocks radiation

once again even though science tells us there is no cool radiation from space, the net effect might as well be that there is

i don't think the size of the parabola is too important, since the heat source is what you're trying to cool by radiating away- who cares if it all goes one direction or another- probably doesn't even have to be a true parabola, although that might be most effective--and i would guess bigger is better if there are nearby tall structures that might radiate heat downwards into your reflector

and you might get ice if you started with cold water and the outside temps weren't too outrageously hot, but mostly we're talking several degrees of cooling, so expecting ice from 70 degree water in an 80 degree night sky might be overly ambitious, but i think this whole thing is well open to experimentation and optimization--this is possibly free refrigeration forever-- a roll of mylar lining an insulated parabolic trench and a water pipe sending cooled water through insulated pipes and with a pv circulating pump i may have the answer to keeping my house and my veggies cool in august


any other thoughts or experience?

I'm glad that I was able to 'hold' your attention. Yes, isolation and not allowing anything to block the line of vision and allowing the infra-red to work for you makes it happen. I reason it as, not so much that we are wanting deep space to do anything in the cooling except to remove heat and draw it off, similar result, but different method of getting there, more in reverse. As I've heard and I do have somewhere of using the auto sunshade to make the reflector, so not more that 2 - 3 feet square/rectangular or other similar material could work. I remember as a kid, hot water would freeze faster than cold, a lot of simple, little 'tricks' to work out to come up with a workable protocol.

You may not have the problem of animals, but we've had to protect from bears and such getting curious, so that could be another aspect...

so you've actually done this, what were the outside air temps when you were getting water to freeze

did you cover the whole system with plastic --or the older glass that allowed radiation to penetrate

this is really approaching the realm of science fiction, guess i should get an experiment together real quick while nighttime temps aren't so bad to get started

the idea that hot water would freeze faster also is a mind blower

thanks for sharing your experiences

It was back in the fall of 2010, up in the mountains of Central New Mexico. Temps were upper 70's, mid-80's during the day and then cooling off in the evening/nitetime. I can't remember, what they might of been, you were a little chilly, probably a light jacket, so...upper 40's, mid-50's, I'm guessing.

No, but if maybe you could, I didn't cover everything with the plastic, just my jar, I used polyethylene, I'd been told that would not inhibit the infra-red. Two layers, with a airlayer between centered within the parabola and 'aimed' to the clear, open sky.

The 'hot water phenomena' is called the Mpemba Effect, maybe by the heating the impurities are settled out/removed enough, or molecules aligned, etc...

I didn't have enough time to attempt very much, but it showed promise, even tho' not always consitent due to weather variables. You need an unobstructed view of the clear sky for the whole nite, no rain or clouds, still wind, away from trees, buildings, structures... Also, I wanted to try just 'aiming' an opened 7-day cooler with some water in the bottom of it into the dark sky and see what effect that would have.

with temps cooler like that i could see how you might be able to get ice, but i admit to puzzlement and the counter intuitive nature of this whole thing

the problem with virginia is the lack of clarity of the night sky and numerous trees etc around here

but i have been thinking about methods that might make optimum use of the effect

if the water was in a black painted (on the outside) metal container, it could be open or closed with the water inside --conduction would be speeded by the metal and the black would radiate more heat away and the parabola would send it out

probably using high surface to volume would enhance the transfer, and setting the pan or column of water with the narrowest part obstructing the parabola radiating the heat into space

does that sound right?

Yes, that is the 'track' that I'm following so far, you could be right that maybe my graniteware might be more effective... Again, I need to get back and begin more trials and record my results...

when you get some results post to this thread so i get an email note--i really want to hear about whatever you are able to document

i'll do the same --of course right now i'm swamped and the weather is pretty overcast, but some night if the night sky looks promising maybe i'll get something together--even a few degrees difference would be awesome, and i don't see why we shouldn't get some results--
bob

Good idea, will do...

Ollie Puddlemaker wrote:

George - Some other ways, and this just might lower the temp even more, nothing wrong with having multiple methods, this first would be to use a shelving unit PVC, plastic, wire, whatever you have available and drape burlap/loose-weave material over it, top to bottom. You would have your fragile items placed apart from each other on the shelves keeping good air flow, on the top most shelf you would have a water reservoir that would re-hydrate the burlap as it wicked downward and dried and evaporated the moisture, cooling the interior. It works best if there is some kind of a breeze to blow thru. Drawback is that it can use a lot of water and you can't let it run dry...

Last idea to try, make up a solar funnel cooker, but use it at night pointed toward deep space and cool thru radiant cooling. When the night sky is clear and cloudless this will freeze water in jugs inside an insulated cooler. Good coolers here in the States can hold ice for 5-7 days, given you have an open, clear sky, properly aimed and un-disturbed. then easily you have an excellent passive method.

Thanks, Ollie! Your first method sounds a lot like the air-coolers they have here in India -
http://en.wikipedia.org/wiki/Evaporative_cooler

I had one when I lived here some years ago and it works very well, but rooms become very damp from the moisture.

Your second idea sounds like sci-fi but is worth a try.

I cemented my inner pot to my Zeer fridge so it doesn't float and filled the sand with water. It still doesn't drop below 25 C, or about 10 degrees below air temps. One unexpected benefit I got when I moved it inside, is that the evaporated moisture now blows out through the nearby fan, cooling my room, perhaps like the evaporative cooler you described.