Conventional refrigeration does an incredible job keeping food fresh. But that technology hasn’t helped desert dwellers without steady electricity. A more recent development in refrigeration—the Zeer pot-in-pot refrigerator—only requires water, sand, and a hot, dry climate to preserve produce through evaporative cooling. Here’s how to make the simple gadget.
Materials and Tools Required
- two terra cotta pots with a 2-3 inch difference in diameter. The smaller pot should be glazed and preferably lacking a drainage hole. If the inner container is double glazed (on its inner and outer walls), non-potable water—say seawater—can be employed.
- a bag of sterile sand
- a square of burlap cloth large enough to cover the top of the inner pot
- a trowel
Building It
1. If your pots have drainage holes, plug them with a bit of cork, caulk, or other waterproof material. If you don’t, moisture from the sand will seep into the lower pot and immerse the stored goods or seep out the bottom of the larger one.
2. Put down a one-inch deep, level layer of sand in the bottom of the large pot. Set the smaller pot on top of that layer and center it in the larger one. Make sure that the smaller pot’s lip is even with the larger one’s.
3. Fill sand in around the sides of the of the two pots, leaving about an inch of space below the lip.
4. Pour cold water over the sand until it is thoroughly saturated. Put your food into the smaller pot. Cover that with a burlap cloth, also soaked with water. That’s it! Just be sure to refill the water regularly, about once or twice a day.
How It Works
The Zeer was developed in 1995 by Mohammed Bah Abba, a Nigerian school teacher that hailed from a family of pot makers. The design is incredibly simple: a glazed earthen ware pot nestled inside a larger, porous one with a layer of wet sand separating them. As the water evaporates through the surface of the outer pot, it draws heat from the inner one, keeping up to 12kg food fresh for as long as three to four weeks without using a single watt of electricity.
For his efforts, Bah Abba was awarded the $75,000 Rolex Award for Enterprise in 2000 and the World Shell Award for Sustainable Development in 2001 to help spur its development. Presently, Bah Abba sells about 30,000 Zeer per year for 200 Nigerian naira ($1.30) a piece. Via How To Make an Electricity-Free Refrigerator.
Many years ago I worked on the development of linear motors, where one of my older colleges had previously been involved in refrigeration development. He realised that most of an electric fridges energy was spent starting and stopping the pump so he had the idea that if you left the pump running continuously and switched the fridge light on and off periodically as a temperature control, you could save energy. They built a prototype which was not successful because everything in direct light cooked slightly, whilst everything in the shade froze.