Since water has greatest density at around 4 °C, putting the vaccine chamber at the bottom of a thermo-syphon regulates the temperature at between 2 °C and 8 °C, as long as there is ice and the heat-exchange capacity is not overloaded.
[citation needed] A refrigeration device was shown for this purpose by Adam Grosser at a TED Talk in 2007,[3] but had not been produced commercially as of 2020.
[5] In September 2008 it was reported that Malcolm McCulloch of Oxford University was heading a three-year project to develop more robust appliances that could be used in locales lacking electricity, and that his team had completed a prototype of his renewal of the Einstein refrigerator.
[7] The Free Piston Stirling Cooler, a type of mechanical refrigerator, was brought to market before 2010 by Twinbird Corporation of Japan.
[8] In 2016 Will Broadway won the James Dyson Award for a vaccine cooler based on a miniaturisation of the bi-fluid Icyball technology.