The Zeer Pot – the Pot-In-Pot refrigerator
This low-tech, low income solution to lack of refrigeration uses evaporation to cool containers.
The double-walled pot has an inner volume where food or medicine can be stored, and an outer volume where sand is loaded. A little water is added to the sand, and the process of evaporation cools the inner container. All the technolgy required is pottery (nearly universal). The inventor was a teacher in Nigeria.