Making a homemade refrigerator that runs on fire

..cools down to 18 C. (about zero Farenheit)

A question is this: what practical use would this device have?

I can think of possibilities. However, for this to be practical, you'd have to know just how much cooling in terms of BTU, can be expected.

A clue is that he uses a 12 oz. soda to show that it can cool it down (for a summer day).

Cooling down one soda at a time doesn't sound like much.