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Zeer pot refrigerator
A zeer pot refrigerator, also known as a pot-in-pot refrigerator, or simple a Zeer (in Arabic) is a type of clay pot evaporative cooling device that provides a way to keep vegetables fresh without the use of electricity. The pots are simple devices that can be produced locally by artisans, and made from local clays. The zeer pot consists of two pots, one inside the other with a layer of sand in between that is kept damp to provide water for the evaporative cooling process. Clay pot coolers have been used for centuries to help farmers reduce food spoilage and waste, increase their income, and limit the health hazards of spoiled foods. Clay pot coolers are typically used at the household level due to their simple construction and relatively small size. The zeer pot was popularized in 1995 by Mohammed Bah Abba in Nigeria.
An analysis of this technology can be found here.
Several key considerations are important for determining if a zeer pot refrigerator will provide effective cooling and storage. Zeer pots provide the most benefits when they are used in low humidity climates (less than 40% relative humidity), the temperature is relatively hot (maximum daily temperature greater than 25 °C), water is available to add one and three times per day, and it can be located in a shady and well-ventilated area.
Zeer pot, or pot-in-pot refrigerators are composed of two clay pots with the same shape but different sizes. One pot is placed inside the other and the space between the two containers is filled with sand, which retains the water added. Food is placed inside the interior pot, and both pots are covered with a lid or a damp piece of cloth. The first step of making a clay pot cooler is forming the clay pots, two pots should be formed of similar shape with one being smaller so that it can fit inside the other. Many potters use round concrete molds embedded in the ground and a pestle to beat a clump of clay into a spherical pot, however a complete spherical shape is not ideal. Alternatively, different sized basins made of plastic or metal can be used as molds if they have the desired dimensions. The clay pots are then completely dried, a process which may take 3-7 days. After drying the pots are fired, this process varies region to region but generally takes place over a large fire. After setting the fire, the pots should remain there for around 24 hours before being removed, cooled, and utilized to build pot-in-pot coolers.
Suggestions for further research
Because of poor road conditions and lack of fast transportation from the fields to the market place, many farmers experience rapid drop of quality on their vegetables. The price they can get out of their produce on the market depends on this quality. And it is potentially much profit for each farmer to make here if we can develop a transportation vessel of the same principle as the zeer pot. The design and material choice needs to fulfill some requirements, such as low weight so it not waste too much fuel of the transportation vehicle. And it needs to be sturdy and reusable or recyclable. And perhaps even able to combine with solar still technology?[Suggested project]
Researching chimney addons, to reach into air higher up, with more wind speed[Suggested project]
Researching how to increase surface area of the sand layer[Suggested project] (possibly you can make the outer clay pot's interior and exterior surface carved, rugged, roughened or chiseled, to increase surface area, to increase evaporation. There are zeolits, with extremely large surface area, very porous)
- Zeer pot refrigeration (design) - detailed design issues and modeling.
- Emily Cummings upgraded modern version : http://www.emilycummins.co.uk/about#inventions
- MIT D-Lab https://d-lab.mit.edu/resources/projects/evaporative-cooling-technologies-improved-vegetable-storage