For hundreds of years a similar type of cooling has been employed by desert dwellers around the world. The concept is explained by a simple law of thermodynamics. When moisture comes in contact with dry air it evaporates. You see, water has this amazing characteristic of having a very high retention of heat (it is used in cooling nuclear reactors after all).
This ancient technology has been used for cooling water for hundreds of years. Mohammed Bah Abba took this idea one step further. By placing one pot inside another and filling the gap in between the two pots with moist sand he was able to create a refrigeration system that requires nothing more than a little bit of moisture.
The moist sand filling the gap between the two pots draws heat away from the inner pot and dissipates the heat through the evaporation of the moisture. The inner pot is filled with perishable foods that would normally last for mere days, but with this system can last for weeks.
Mohammed Bah Abba's invention awarded him the Rolex Award for Enterprise, and has been recognised as a very important contribution to societies with limited energy resources, or where energy costs are prohibitive. Many families no longer rely on their children to "rush sell" their food goods and can now sell when the demand arises due to the reduction of spoilage. Many children can now continue going to school because their families need less of their time to sell their produce.
Mohammed is a a lecturer at polytechnic college in Northern Nigeria, and comes from a family of pot makers. He drew on his childhood experience and invented his Pot-in-Pot cooling system in 1995 and received the Rolex Award in 2000. He has been recognised by the United Nations and has worked as a consultant with them.