Keeping it Cool - Clay Pot Refrigeration

Who: Mohammed Bah Abba
Where: Nigeria
What: For less than $2 for a clay pot system to refrigerate up to 12 kg of produce.

This is a relatively old story but a great one. In 2000 Mohammed Bah Abba was awarded the Rolex Award for Enterprise for his innovative Pot-in-Pot system to provide affordable, electricity free, refrigeration in arid Nigeria. Mohammed took an old local understanding of the cooling properties of evaporating water, combined it with the ancient tradition of making clay pots, and turned into a useful, world-changing innovation: a "desert refrigerator" that helps reduce food spoilage and increases income by increasing the shelf-life of farmers' produce for sale.

"Eggplants, for example, stayed fresh for 27 days instead of three, and tomatoes and peppers lasted for three weeks or more. African spinach, which usually spoils after a day, remained edible after 12 days in the Pot-in-Pot storage." [source]

The Pot-In-Pot system consists of two earthenware terracotta pots of different diameters, one placed inside the other. The space between the two pots is packed with sand, the sand is kept wet by pouring water into the sand about twice a day. Produce is placed within the inner pot and then covered with a damp cloth, and the system is left in a dry ventilated area. As the water in the sand evaporates throughout the day, the law of thermodynamics ensures the tempature in the inner pot drops. Our bodies use the same technique to keep us cool.

How well does it cool? Well, one quantative study was performed in Ramona, CA by student Garret Rueda in his 2003 entry to the state Science Fair. Rueda found that average daily temparature drop inside the sytem was 14 C (23.5 F), aka keeping produce at 15 C (59 F) while the outside temparature is 28 C (82.4 F).

Finally, the Rolex Awards Committee makes a great point about ideas vs. innovation in their article about the Pot-in-Pot award: "Good ideas are indeed rare, but good ideas that actually become good projects and bring lasting benefits are even rarer still," In other words, an innovation is an idea that is brought to life and changes people's lives.

Related Links

A Short History of Refrigeration from the History Channel.
Terracotta Water Cooler for the office.
The Coolgardie Safe - An Australian invention from the turn of the 20th century, but a bit more complicated, metal and heavier than two clay pots!
Amish Water Cooler - in use by the Amish for decades, link courtesy of WorldChanging