Zeer Pot Fridge
It's tough to get a side-by-side Frigidaire when you live in North Darfur in Sudan. Even if you could get one, you wouldn't be able to power it. So what's a family to do when fruits and vegetables, exposed to the extreme heat, spoil in one or two days? Thanks to Practical Action, a U.K.-based nonprofit focused on using technology innovation and dissemination to reduce poverty, many African farmers and villagers use an amazingly simple clay refrigerator known as a zeer pot.
In its finished form, the refrigerator consists of one earthenware pot nestled inside a second larger pot, with a layer of sand in between. Making one requires little training and just a few easy steps. First, villagers use clay and water to make molds, which they dry in the sun. Then they press fresh clay around the molds to form the desired pots. After adding a base and rim to each, they dry the pots in the sun and then fire them in a pit of hot ashes. After cooling, the pots are ready for assembly. A layer of sand is placed in the bottom of the larger pot. The smaller pot rests on this layer. And, finally, sand fills the space between the two. To make the pot functional, villagers wet the sand, fill the smaller pot with vegetables and then place a wet rag over the whole thing. Once built, they place the pot on a stand for maximum air flow.
Twice a day, they must return to the pot and add more water to the sand, but the effort has a significant payoff, extending the life of vegetables two to three weeks. How does it work? By evaporative cooling: As water evaporates from the sand, through the porous outer pot, it pulls heat from the inner chamber, dropping the temperature several degrees. As a result, more food fills up hungry bellies instead of refuse piles.