Instructables

A Practical Zeer Pot (evaporative cooler / non-electrical refrigerator)

FeaturedContest WinnerContest Winner
Picture of A Practical Zeer Pot (evaporative cooler / non-electrical refrigerator)
20140506_191201.jpg
20140506_191217.jpg
20140510_142445.jpg

A zeer pot is an evaporative cooler used in rural Africa and the Middle East to keep vegetables fresh. They consist of two terra cotta pots, one nested inside the other, with the gap between them filled with wet sand. The sand serves as a thermal mass that helps keep the pot cold once it has cooled down, and acts as a wick to spread the moisture up the walls of the pot. When placed in a shaded, breezy location, the evaporation of water off the outer surface chills the pot. If you have a good breeze, or a fan powered by a solar panel blowing the pot, the pot can get quite cold. Imagine that chill you get when you step out of a pool when the wind is blowing. Now imagine that wet wind chill going on all day. That's what the pot feels with a constant breeze.

Unless the air is very dry and the pot is exposed to a constant breeze, they generally do not become as cold as a refrigerator, but they will keep vegetables fresh for a couple of weeks. If you do have cool dry air and a constant stiff breeze, the interior of a zeer pot can chill down to around 40˚F.

Think of it as an open-cycle refrigerator. Conventional refrigerators evaporate a refrigerant in a closed circuit to absorb heat from their interiors, then compress the refrigerant vapor in the coils in back to condense it and to expel heat. The zeer pot simply uses water as its refrigerant, and leaves the condensation to nature.

Zeer pots were re-discovered and popularized in the early 2000s by the Nigerian teacher Mohammed Bah Abba. By manufacturing and mass distributing zeer pots to the poor, he was able to bring refrigeration to tens of thousands of impoverished farmers and home makers, enabling them to extend the usable life of their produce from days to weeks. For his efforts Bah Abba was awarded the Rolex Award for bringing life-changing technology to people in need.

In the under-developed parts of Africa and the Middle East, zeer pots use custom made pots prepared by local potters. Here in the developed world, we need to settle for pre-made pots from the hardware store. There are some drawbacks, but also some advantages afforded by these limitations, as you will see.

What makes this zeer pot practical?

There are other zeer pot instructables out there, but this one is optimized for practicality. If the capacity is too small, the cooling capacity too low, or if it an eyesore or is annoying to use nobody would want to use it. This zeer pot uses a large glass pot lid, has an interior basket divider, and sits on a rolling cart. It even has a layer of decorative pebbles over the sand to make it look pretty. The terra cotta pot legs hold the pot off the rolling cart with enough clearance to let the bottom surface contribute to evaporation; this adds about 10%-15% more evaporative surface. The inner pot is bolted down so that it doesn't float up when you charge the pot with water. Nearly everything I used in this project was purchased at a hardware store, and it can be made in a few hours, plus a day to let the sealants cure.

I will be building a zeer pot array for A Place for Sustainable Living in Oakland (California) based on this design. The goal is to use an array of zeer pots to displace the use of at least one of their refrigerators. The design shown here is the outcome of my experimentation with making zeer pots for them.

(Be sure to read all the notes to all of the photos. Many important details are listed there.)

Parts list with prices

Prices are rounded to the nearest dollar. (I must admit, this is by no means the inexpensive original African zeer pot, which cost $2 to make. You're going to spend well over a hundred dollars on this design. This one is for people are intentionally going out of their way to go off grid or to pursue sustainable options.)

Items are mostly from Orchard Supply Hardware (Berkeley, CA). The pot lid was from Kukje market (Daly City, CA), and the sandwich basket was from Web Restaurant Store.

  • 18" unglazed terra cotta pot— $30 @ Orchard Supply Hardware
  • 14" terra cotta pot—$15 @ Orchard Supply Hardware
  • terra cotta pot feet, quantity: 7— $1.79 each, so about $13 @ Orchard Supply Hardware
  • heavy duty planter caddy with five casters—$30 @ Orchard Supply Hardware
  • 50 lbs of sand; the finer the better, pre-washed — $6 @ Orchard Supply Hardware
  • 4" long 1/2" bolt
  • 2" washers for a 1/2" bolt, quantity: 5
  • jamb nuts for 1/2" bolt, quantity: 4
  • Refrigerator thermometer: $8 @ Orchard Supply Hardware
  • Silicone Sealant—$5 @ Orchard Supply Hardware
  • 13.5" glass pot lid — $8 @ Kukje Market (Korean markets usually have these; wherever you are, if there's a korean market or housewares shop, you're in luck.)
  • sandpaper
  • 12" diameter sandwich basket— $7 at Web Restaurant Store
  • 8" eyelet or hook bolt and a pair of nuts and washers— about $6 @ Orchard Supply Hardware

Note: won't work as well in high humidity

If you live in a hot and humid area, the zeer pot probably won't work well; high humidity results in much less evaporative cooling. (However, a friend of mine who used a zeer pot to cool water in a humid part of Africa tells me that even with the humidity, it worked surprisingly well, so this is not definitive.)

Note: direct sunlight will cancel out all cooling effects

On the day I was doing the zeer pot seminar at the Place for Sustainable Living, we accidentally left one in direct sunlight. The amount of heat imparted by the sun totally overwhelmed the evaporative cooling effect. The cooling is supposed to come strictly from wind-induced evaporation, not from evaporation due to sun exposure. Sun exposure causes evaporation by imparting heat; wind exposure causes evaporation by lifting away water molecules, which carries away heat proportional to the heat it takes to evaporate the quantity of water carried away. If you do build a zeer pot, make sure you keep it in the shade for best effect.

Note: outer pot must be unglazed clay or terra cotta

At the hardware store, I saw a lot of fake terra cotta pots made of orange plastic. These are not usable for the outer pot of the zeer pot; the zeer pot cools by wind evaporating water that has been wicked through the outer surface. Plastic fake terra cotta is not porous, and will not work as an evaporative surface.

Glazed terra cotta pots also don't work for the outer pot. The inner pot doesn't necessarily have to be made of unglazed terra cotta, but the outer pot must be unglazed because glazed pots won't wick moisture to the outer surface for evaporation.

Note: many medium sized zeer pots work better than one giant zeer pot

The ability of a zeer pot to cool its content depends on the surface area to volume ratio. As you make the zeer pot larger, the volume will increases proportional to the cube of the linear dimensions, but the surface area only increases proportional to the square of the linear dimensions. Because the volume increases much faster than the surface area, one huge zeer pot will actually perform much worse than several smaller zeer pots. The size of the zeer pot in this instructable is about as large as you can make them while having a practical rate of cooling. You can always make them smaller; making them larger is not likely to give you reasonable performance. If you are serious about going off-grid, you would do better to make several zeer pots of this size than to make one huge zeer pot.

 
Remove these adsRemove these ads by Signing Up
1-40 of 86Next »
jkimball1 month ago

Can you provide a temperature reading of the inside of the pot, compared to the outside?

A semi permanent installation of one of these next to a rain barrel would be a good green combination, especially if the "first flush diverter" sent the waste water to this.

Berkana (author)  jkimball1 month ago

Someone did some performance measurements of the zeer pot for the California state science fair:

http://www.usc.edu/CSSF/History/2003/Projects/J022...

he found that the temperature inside dropped to about 23.5˚F below ambient, with an inside temperature of 59˚F when the ambient temperature was 82˚F.

Berkana (author)  jkimball1 month ago

Unfortunately, the Place for Sustainable Living presently has the zeer pots I built for them indoors, where there isn't a breeze, so I don't have a reading for how effective it is with a breeze under regular use. Without a breeze, the interior temperature is mildly cooler, something like 5˚-10˚F, depending on ambient conditions. The plan is to eventually have them in a permanent home where it is always breezy, but until then, the best I can tell you is that on the first night we chilled the pots in the breeze, the temperature reading from the thermometer ranged from 15˚-20˚F below ambient by midnight, with a temperature of about 50˚.

For a table of lowest achievable temperature vs. ambient temperature and humidity of someone else's zeer pot, see this:
http://rebuildingcivilization.com/content/build-ev...

(The table attached to this comment is a screen shot of the table in the link above.)

I suspect heir zeer pot didn't have as much evaporative surface area s the one I built, so I don't know if the data translates, but this should give you some idea of what you can expect.

minimum temp.png
mfiscarcrazy made it!23 days ago

Great project! We used the Zeer pot during our annual 4th of July camping trip! It worked great and we cant wait to use it again!

IMG_1486.JPG
Berkana (author)  mfiscarcrazy14 days ago

I notice that your pot is resting on the ground rather than on a stand or on pot feet. I highly recommend the pot feet; air circulation under the pot adds to the cooling power.

How large is your inner pot?

Berkana (author)  mfiscarcrazy14 days ago

Excellent! I'm glad my design is being used. ^_^

Very nice! Excellent learning experience as one works through the different laws of thermodynamics. I liked the comment that if someone has this much trouble sourcing the glass lid, that's probably the least of the issues you will face.

kidharris1 month ago

There are a several things I like about this zeer pot - the wire basket, the pebbles, the caddy (if you have a need to keep moving it), and it is attractive. In addition the instructable is well written and I'm sure will get more people interested in alternative forms of refrigeration.

However, the inner pot should be impermeable to water so that the food area can not be contaminated by the refrigerant water and can be cleaned easily. The lid should be insulated or better yet a metal lid (better heat conduction) covered by several thickness of cloth (an attractive , quilted, sewn together pad?) which can be wetted to provide more evaporation. The cloth will still act as insulation after it drys out. Instead of a major source of heat gain you will have an additional source of evaporation/heat loss.

For those contemplating duplicating this particular pot, I personally don't think it is a good idea to have ceramics loaded in compression by bolts. I think that is a very real source of failure. The hole in the bottom of the outer pot could be sealed many other ways or left open (glue a cloth on top of the hole to prevent the sand from coming out) to allow excess water to drain out. If you added some wick material in before adding the sand and put a tray/saucer under it then the excess water can wick back up into the pot and can also provide more evaporation. A wire or cloth screen could be fitted over the tray to prevent mosquitoes from laying eggs in it in mosquito territory. Use a plastic/metal bucket or pot with no hole in the bottom for the inner pot. If you have a floating problem then secure the inner pot from the top. You can also simply replace the sand with absorbent material.

Berkana (author)  kidharris1 month ago
I considered securing the inner pot from above, but there wasn't any way to do this that didn't involve even more work. sealing the holes and securing the inner pot with the bolt and washers was the easiest and most economical solution.

In response to both perspectives, I would like to moderate by pointing out that the starting point is the desire or the need to become educated or proficient at figuring out life skills. I think both ways do this. The issue of who to appeal to is not insignificant. In my neighborhood, no one would dream of trying to figure out refrigeration- when the power when off briefly last night I heard the whir of all their generators kick on, while I searched for my flashlight and tried to remember that instructible using crayons and dental floss.

Sadly, we have to appeal to both ignorant and uneducated when presenting ways to survive, and visual appearance is a factor. Simplicity will hopefully come as we learn for ourselves to actually TRY something, learning by doing. My hope is that we can eliminate fear of failure as a barrier to making an attempt, as we learn more about what doesn't work and why when we have our hands in the game.

Warning. The rest of my comment is aimed at providing additional info to people who are interested in more info on "zeer pots" and is pretty long winded.

I am not trying to put this design down but I'm not sure that many people would want to spend almost $150 to build a $0 - $40 item. This shouldn't be compared to Mohammed Bah Abba pots. His idea was to build affordable, simple to make and maintain coolers out of locally available and/or mostly free stuff.

I believe in the KISS (Keep It Simple Stupid) approach to design. Abba's design has 4 parts (1 big porous pot, 1 smaller glazed pot, sand, and a cloth and/or pottery lid) all of which could be found or hand made locally and is considered more as a survival item. This pot has in excess of 25 parts to buy, assemble, and maintain, and I would consider it more as a novelty item. A large metal pot with a lid found at a garage sale or flea market for a few dollars would be a better and cheaper alternative for the inner pot. I don't however believe that you would be able to find these metal pots readily available in the middle of an African desert.

The other advantage to using ceramics and sand (besides being able to make your own or find localy cheap) is thermal mass, which is a double edged sword. Although it takes longer to heat up after you have cooled it, it also takes longer to cool down to start with. Having a light weight portable pot to put the fresh produce in for the trip home or to get some quicker cooling and then transfer either the produce or the inner pot from the "quick" cool pot to the ceramic pot could combine the best of both alternatives.

I think everyone should know how to make one of these in case of an emergency, although in a real emergency the water may be more important to you than food, waste water could be used as the refrigerant.

I don't think that zeer pots will catch on here in the USA for everyday use because it requires too much attention and most people can't or don't want to provide the attention necessary for success as long as electric refrigeration is available. Inattention results in spoiled food. If you want to make one for busy people then you need to automate the refilling process. As long as you have a running water supply and electricity this can be simply a mater of using an irrigation timer and a water line. A higher reservoir tank and drip irrigation could be useful, but you would still have to fill the reservoir periodically.

In addition I think it is important to let readers know that the outer pot can be replaced by many other approaches. Anything that will support itself and allow evaporation will work. My favorite is a canvas bag filled with water, suspended from a metal frame, with a either a plastic bag or plastic/metal inner pot/lid. The sand is not necessary when it is easier for the water to saturate the outer skin and evaporate off. You could also put an absorbent material between the canvas and the pot to keep it fro sloshing around.This is more difficult than it sounds because if any of the wet part of the canvas bag touches the metal it will start leaking/dripping there, just like the old style canvas tents. Heavy canvas bags filled with water are a good way to provide cool drinking water in hot dry climates and were widely used here in the American deserts when I was a kid. We used to keep them tied to the front grill of the car while traveling and suspended in the shade while camped.

Lighter weight, more efficient, cheaper, more portable designs are possible and don't have any ceramics in the at all. There are several instructibles on these and some can be bought commercially fairly cheap. These usualy have an absorbent material in between the outer perforated metal or plastic "pot"/screen and inner "pot" with a lid or cap.

Wetted rags wrapped around a metal pot will also work for a cooler, you just have to keep wetting them.

Keep it in the shade and promote as much airflow past it as possible, but remember that on windy days you will have to replenish the water more often. If you want to know how cool it can get on a particular day you can calculate the wet-bulb temperature or ...watch the weather on TV and see if they give the wet-bulb temperature for that day.

I wonder if you'd consider doing an 'ible on your canvas bag version (or other approaches you've used)? Sounds very interesting!

Berkana (author)  kidharris1 month ago

While it is true that this pot is by no means as affordable as Mohammed Bah Abba's zeer pots, the audience is different. To be sure, this instructable is for people with the luxury of choosing to do this, and competes against refrigerators, whereas Bah Abba's pots were for poor folk, competing against no refrigeration and food going bad in a day or two. With this in mind, I spent a lot of effort trying to appeal to people in this situation, going out of my way to make it look nice with the glass lid, the decorative rocks, the inner basket, and rolling stand. If you do away with those items, you could definitely make it much cheaper. Doing a way with the bolt and using plugs would make it easier, but unless it's practical, it won't make an impact among the audience I'm trying to reach.

My next version will be to reproduce a pot version of the Coolgardie Safe (the Australian mine town evaporative cooler, which was a box with burlap wicks covering it), using stock pots, wicking material, and rope. This may end up being cheaper, especially if the materials can be salvaged, and will likely be much lighter.

I forgot to mention that one of the advantages of sand is that it doesn't rot. If you chose an absorbent material it also should not rot or should be easy to change, clean, or dispose of as needed.

Berkana (author)  kidharris1 month ago
The bolt does not compress the terra cotta to any significant load;, they merely seal the hole, but more importantly, they keep the inner pot from floating up as the sand is saturated. I made simpler pots without the bolt, and the floating of the inner pot was a real problem.

A lid that contributes to cooling would definitely help if that is a priority, but visibility of the contents was important enough for our application that we opted for the glass lid.

In my opinion, there isn't really a need to drain extra water; this extra water simply lets the zeer pot be watered less frequently. When the zeer pot is exposed to wind or a fan, it can evaporate water at a pretty high rate, and extra water hasn't been a problem.
rlee191 month ago

The application, and scope of the original project in Africa interests me. I noticed 'Berkley' in your information. There are over 7 thousand homeless in San Jose and one of the major issued they face is that even when they can get food, they have no way of keeping it for any period of time. Have you considered reproducing the original project a little more directly? It might be in need of some fine tuning, but it might be a way to help a lot of people.

Berkana (author)  rlee191 month ago
I have not thought of how to adapt this to help the homeless. This method is too heavy and too dependent on water for it to be practical for the homeless. Even in Africa, zeer pots are for those who are settled and who do farming, not for nomads.
JKPieGuy1 month ago

This would be a great thing to keep in a basement to store excess fresh Vegetables from the Garden.

Berkana (author)  JKPieGuy1 month ago
The biggest difficulty with using a zeer pot in the basement is the lack of a good breeze. without air flow around the outer pot, the zeer pot will not cool down. If you could create a solar updraft chimney to draw air into the basement to circulate around the pot, that would be best. Also, finding some way of capturing the wind at night to keep the evaporation going even when the sun has set would be good.

That is a very valid point. Didn't realize that it needed some airflow until re-reading it. Must have over looked that (Sorry). Though that would be cool to try something that you had suggested so that you could use it in the basment. The reason why I thought, was because my Grandparents said that they used to store carrots and other root vegetables in a container of sand in the basement.

jpalma81 month ago

this could be combined with a small fan, so you can cool a room in a house?

more efficiently clear the fan would spend at least light possible, even with a very remote solar panel

Berkana (author)  jpalma81 month ago
There are other evaporative coolers that might be better suited for cooling the air in a house. If you want to cool the air, terra cotta and sand are not necessary. All you need is a wick type material and a fan. A damp air filter should work. You just need some way to keep it damp.
Berkana (author)  jpalma81 month ago
The most efficient natural way to cool a house would be to build a windcatcher to draw air through a moist basement. The cooling principle is the same: evaporation will lower the temperature of the air. This was used in ancient Persian palaces and other large buildings.

See this:
http://en.m.wikipedia.org/wiki/Windcatcher
LCPope1 month ago

I love this idea. I have seen images elsewhere, but the directions regarding how to make one are great! I would greatly appreciate it if I could use the main image in a book about sustainability that I am writing. I will give you credit and send readers to this site. Please email me at LCPope@gmail.com

Defy571 month ago

Would you happen to know the weight before and after adding the water? Did you transfer the pots without sand and fill in place? My sister lives in a very breezy area and I think this would be perfect storage for her Aquaponic veggies.

Berkana (author)  Defy571 month ago
My best guess is that the finished assembly weighed about 110 lbs, and about 120 lbs when wet.

does it work at high temp like summers in india??.

Berkana (author)  Chitlange Sahas1 month ago

Is it humid in India? If it is humid, it might not work as well. As long as it is in the shade and there is a breeze, it is going to provide some cooling power. My friend says that these still work where it is humid, but they work best when it is dry.

I did make the same .. Check my i'able

http://www.instructables.com/id/Homemade-clay-refrigerator-BEING-ECOFRIENDLY-/ . When i used it in humid cliamate it didnt show any cooling effect.

It should, provinded you do not expect to get low temp (as keeping ice cream frozen) nor preserve food for a long time (experiment with how long you can keep milk before using it for this technique).

Butter is a good product to test how efficient the contraption is.

Also do not forget that cold temp. will vary according to outside temp.

daenergymon1 month ago

I have seen something similar used to storing butter on the countertop.

I know it doesn't work in our high humidity area.

https://www.facebook.com/LivingOffGridReally

kliu81 month ago

I know this sounds silly, but if only these things were not so heavy they could make great ice boxes inside (large) cars or vans. Just lower the windows at the back seat for a good breeze.

Berkana (author)  kliu81 month ago
I'm working on a light weight variant that uses a large aluminum pot and a felt wick. Subscribe to my instructables feed to get news when it's ready.

Unfortunately they will not work any where humid. Unless you live in an arid area dont waste your time.

hoadie1 month ago

This is a great instructable, I really enjoyed reading it.

Something worth considering is the Coolgardie Safe. These were extremely popular in Western Australia before refrigeration became popular. It to relies on evaporation although doesn't have the benefit of the thermal mass offered by this pot system.

It's tried and tested :)

http://en.wikipedia.org/w/index.php?title=Coolgardie_safe

Berkana (author)  hoadie1 month ago
Very interesting. I might try to reproduce this coolgardie safe.

There's also a product called the Miticool that is essentially a box form zeer pot with a water reservoir on top:

http://www.mitticool.in/product_detail.php?product_id=4
Dark Solar1 month ago

Nice update of ancient tech!! India, @3000 BC, same principles used with natural draft funneling to produce cold drinking water and sometimes ice. Maybe try a solar updraft tower to generate breeze rather than fan/solar panel combo?

Berkana (author)  Dark Solar1 month ago
The solar updraft tower is a great idea. I will try doing that as the next step in the evolution of the zeer pot.
primosanch1 month ago
Very nice. Thanks for sharing.
mdallmann1 month ago

It may be fun to combine a "Zeer Pot" with a "Drinking Fountain". Having the inlet water you drink run through a coiled up copper tube inside the Zeer pot and the waste water draining into the sand. This way your children will have cool water to drink when playing outside. I will be making one of these for sure.

1-40 of 86Next »