Today I've been reading about low-tech refrigerators - electricity-free, they can keep food up to 10oC lower than ambient, using evaporation as the cooling mechanism. First I bumped into this piece of news about a young English woman and her invention; then I read up about Zeer pots, used throughout Africa. They're an adaptation of an ancient design. In northeastern Brazil the local people use similar earthenware jars to keep water fresh.

Later on I found this old design also based on evaporation, called an absorption-gas refrigerator. The Icyball was designed in 1927, and run on anything combustible. Part of it is heated, which in turn keeps the other side close to 0C for a day or so. This design has been improved recently, to run on non-toxic liquid (the original used ammonia). Check out a short video about this invention.