Reply #9: What you need already exists. It's called an absorption refrigerator. [View All]

[Xithras]

Though it fails on the "easy to make" front, absorption refrigerators require only HEAT to cool the contents inside. There are already absorption refrigeration systems that use lensed solar heat to drive the process, and a small well insulated or partially buried unit can be run on this alone. Larger units in industrialized countries are typically powered by propane, but small units in primitive areas could be augmented by anything from wood to cow dung if solar power is insufficient.

If you've ever rented an RV, you've seen one of these things in action. Basically, instead of water (which has a high boiling point) they'll use something like ammonia in a closed system since it boils at a much lower temperature. The ammonia evaporates, cooling the chamber, and mixes with hydrogen. That mix then attatches itself to water. If the water is heated, the pure ammonia will distill back out and can be reused again. The great thing about the system is that it has no moving parts and has nothing to wear out. If the system is kept sealed and a little heat is applied, it just works.

BTW, these were actually quite common in American homes in the early 20th century, but lost favor to compressor refrigerators because these don't get quite as cold. An evaporative freezer might take a day to turn a tray of water into ice, while a compressor one can do it in only an hour or two. Still, the technology is widely used and is uber-reliable. The only problem is that it tends to be very expensive for people in poorer parts of the world because it's not something that can be built without specialized equipment.