Pot-In-Pot Clay Refrigerator or zeer is a low cost traditional technology that can provide cooling refrigeration without electricity. The technology was perfected in Nigeria by Mohammed Bah Abba, between 1995-1997. It can extend the useful life of fruits and vegetables. Spinach for example that would normally spoil in a day can now last 12 days. Tomatoes can last 20 days.
The principle behind the Clay Pot-in-Pot Refrigerator is evaporative cooling. As the water in the sand between both pots evaporates, it moves to the drier outer pot, by the laws of thermodynamics. This causes a temperature drop by taking away heat from the inner chamber of the pot. The temperature drop destroys bacteria and other pathogens, thereby decreasing the rate of spoilage.
To construct a pot refrigerator a large and small clay pot is needed and regular sand. Sand is placed at the base of the larger clay pot. The smaller pot is placed inside the larger pot, and adjusted till the top of both pots are level. More sand is added in the space between both pots. Fruits and vegetables are placed in the pot and covered with a wet cloth. The sand in between is wet. By the process of evaporative cooling, the refrigerator is kept cool inside and will extend the life of fruits and vegetables. The sand will have to be watered twice a day, and items checked daily.
The following table list the useful life of items that are zeer refrigerated and non-refrigerated.
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Plantseed.com. Pot-in-Pot(pdf). Retrieved 7-June-2011.<https://www.planetseed.com/uploadedFiles/Science/Laboratory/Energy/Pot-in-Pot_Refrigerator/pot_refrigerator.pdf>
Oluwasola, Oluwemimo(2011). Pot-in-Pot Enterprise:Fridge for the Poor(pdf). United Nation Development Program. <http://growinginclusivemarkets.org/media/cases/Nigeria_PotInPot_2011.pdf>