The Pot-In-Pot Evaporative Refrigerator or “Zeer Pot” is an astoundingly simple but effective device.
The refrigerator consists of two ceramic pots of different sizes, sand, water and a towel or cloth. It cools the inner chamber and its contents using evaporative cooling, much like a swamp cooler.
Constructing the pot-in-pot refrigerator is an easy process. Obtain two ceramic flower pots, one large and one the next size down, so they nest one inside the other with a gap between them. If there are holes in the pots, cover them with duct tape or fill the holes in with putty so that no sand or water escapes out the bottom of the large pot, or enters the smaller pot. Pour a layer of sand in the larger pot. Set the smaller pot inside the larger pot and pour more sand into the space between the pots. Fill this gap completely. You’ll want to make this gap relatively even so the sand surrounds the inner pot.
To use your “zeer pot,” add just enough water to the sand between the pots to wet it. Do not add too much water or the inner pot will float up, causing your sand to sink under the inner pot. If you notice you have too much water, press down on the inner pot and tip the excess water out. Place the items you want to cool inside the inner pot. Wet a towel or thick cloth and place it over the pots, sealing the air inside. Set the refrigerator outside in the shade. Your contents should be chilled in a few hours. Check the water level and towel wetness every so often and add water as needed.
As the water evaporates from the sand and towel of your “zeer pot” pot-in-pot evaporative refrigerator, it takes the heat out of the air inside the inner chamber. As the air cools, so does the contents of your refrigerator.
I constructed one of these things and set a can of diet iced tea inside this morning. By this afternoon the temperature outside was about 95 degrees. I had a thermometer inside the chamber as well, but unfortunately it stalled around 70F. The can of tea was much cooler than that, so I’m relatively certain the thermometer is broken. If I were to venture a guess after drinking the tea, I’d say it was closer to 50-55F. Not as cold as a household refrigerator, but it worked great and used no power.
The one downside to the pot-in-pot refrigerator is it works best in dry air, preferably with a breeze to aid in evaporating the water. Humidity levels over about 50% make the water evaporate more slowly, thus limiting the evaporative cooling effect. But on a hot dry summer day, during a power outage or other emergency, or camping or if you’re into sustainable living, this is an excellent way of keeping your perishables longer or just cooling your beverages.