Remember the video that made the rounds a while back on how you could heat your home using just a flower pot and a tea light? I have yet to find anyone who actually got that to work, so I was a little skeptical when I heard about making a refrigerator from a couple pots and some sand. It was still intriguing though; if it worked it would be a great way to store medications that need to be kept cool (such as insulin) during a grid-down situation, as well as extending the life of fruits and veggies.
The zeer pot is a container made of two different sized clay pots with a layer of wet sand in between. The pot cools as the water evaporates, which gives you non-electric refrigeration in hot, dry climates. It was invented in rural Nigeria in the 1990s, and sells (over there) for only about 40 cents, giving families that grow their own food the ability to preserve it.
An evaporative cooler like this works as water evaporates, in much the same way that sweating cools you down. The sweat takes the heat from your body as it evaporates and turns to a gas.
So let's get building! We purchased almost all the items for the zeer pot at our local Home Depot. You'll need:
- 2 unglazed terracotta clay flower pots of different sizes - The small one should be big enough to hold whatever you want to keep cold, and the large one should be big enough to hold the small one with about 2" - 3" around the edges.
- Sand - We used regular play sand
- Duct tape
- A lid that will fit the smaller pot (optional)
To start, use a couple strips of duct tape to cover the holes in each of the pots. Add a layer of sand to the larger pot, smoothing it out as you go. You need enough in the bottom of the large pot so that you can set the small pot inside it and have the lips of the two pots be on the same level.
In fact, you should really have the inner pot just a tiny bit higher, maybe 1/8" if you can.
Go ahead and center the small pot inside the larger one, and begin adding sand to the space in between.
Add it evenly around the edges; if you add too much on one side at once you may wind up shifting the inner pot to one side. Continue filling the space until you've reached the upper edges, and pack the sand down as much as you can.
Keep filling and packing until the sand is tight, and then smooth it out.
You may have had some sand spill into the inside pot while you were filling; go ahead and remove it however you want - by hand, a wet rag, vacuum, etc.
Now it's time to add the water. You'll want to pour the water slowly onto the sand while constantly moving your water container - you don't want to flood just one area. The sand may compact some more as your pour; just add a little more to the holes. Keep filling until the sand is soaked, but don't fill it so much that water is standing.
If your inner pot is lower than the outer, then you may wind up with some sand and water running down inside it as you fill. It's no big deal, just wipe it out with a wet rag when you're done.
Once you're done adding water, you're ready to add whatever you want to cool. You may want to wait a little bit, however; if your pots were sitting out in the sun then they're going to start off pretty hot. No sense baking whatever you put in there, let them cool down a bit first.
Move your zeer pot to it's permanent home - it should be in a shaded location with good air circulation. Go ahead and cover the top - if you found a lid that would fit, put it on and cover that with a damp piece of cotton cloth.
If you don't have a lid, just use the damp cloth. A solid lid plus the cloth will keep it cooler though.
After a while you should see the outer pot starting to darken - that's the water soaking out of the sand and evaporating. If only the top half of the pot is turning dark, that's a sign you need to add more water. You'll need to water the sand at least twice a day, usually in the morning and the evening. If you're able to elevate the entire pot on a wire rack, that will give it a little bit more cooling ability, since the bottom of the pot would be exposed to airflow.
So how did it work for us? It definitely got cooler, but not by much. We tested it when the weather was in the low 90s, and the inside of the pot cooled down to about the mid-70s, or a 15 degree difference. But to be honest, I wasn't expecting much - the zeer pot works best in dry conditions with low humidity, and here in Texas we were at about 50% humidity with very little wind. There's a reason they don't sell evaporative coolers here! With very low humidity you could probably get it down into the 50s or 60s.
For us, where we live, this wouldn't be a practical way of storing medications like insulin during the summer if we had no other refrigeration, at least not long term - for over 30 days you want to keep it under about 46 degrees; this would help keep insulin currently being used at "room temperature" for less than a month. It would also extend the life of fruits and veggies for us. In a more arid (dry) climate, you'd have better results.