Image Ross Parry Agency via Daily Mail
Congratulations to Emily Cummins for building a portable evaporator fridge out of household parts in her grandpa's potting shed. The Daily Mail claims that she has "invented an Amazing Solar Powered Fridge," which would be a terrific thing if it was a) solar powered and b) she invented it.
The Daily Mail's illustration describes it as having a "gap between the inner and outer layer that is filled with sand, wool or soil, that can be soaked with water." they continue and say that "the sun's rays heat this wet material and the water evaporates off."
Right. Putting it in the sun increases evaporation, cooling the interior? I suspect not, but evaporative cooling can be used to make an effective and cheap cooling system for Africa, like Mohammed Bah Abba did ten years ago.
Warren described it earlier:
[Take] two pots, one inside another. Fill the space between the two with moist sand, and you have a most ingenious fridge. (That’s very modern if you live in one of the 90% of villages that don’t have electricity.) The water in the sand naturally migrates towards the outer pot, where it evaporates causing a temperature drop around the inner pot.
In Al Fashir, the capital of North Darfur, ITDGPractical Action and the Women’s Association for Earthenware Manufacturing have been experimenting with a traditional storage container called a zeer, invented by a teacher called Mohammed Bah Abba.
A lidded earthenware pot is fitted inside a larger pot with an insulating layer of sand in between. This sand layer can be kept cool by adding water regularly, thus providing a refrigerated storage space at minimal cost.
The results of these trials were amazing. Carrots, tomatoes and okra could now be kept in good condition for nearly twenty days, whereas previously they would have been unsaleable after two or three.
While evaporative cooling has been around for millenia, according to Rolex:
The city of Qena in Upper Egypt is renowned for its porous-clay cooling vessels – a tradition spanning more than three millennia. In Burkina Faso, the Jula people’s traditional jars are sometimes soaked in water before goods are stored in them, so that they stay cool by evaporation. This single-pot design is similar to the pot-in-pot, but less efficient.
The double wall system is a dramatic improvement. In most of the versions we have seen, the porosity of the clay is an important component; Emily has made her version of a non-porous metal. Perhaps there is something about it that I am missing, that lets it work better in the sun than in the shade.
But every swamp cooler and fridge I ever heard of right back to the Australian Coolgardie Safe worked better in the shade and relied on moving air to increase evaporation rather than sitting in the sun.
Solar Powered Refrigerator Could Bring Health and Energy Savings to Rural India