The fundamentals of refrigeration are also at work in another important household appliance: the air conditioner. It's estimated that around 5 percent of all the electrical energy used in the U.S. is expended to keep our homes cool. That's pretty amazing, especially when you consider the fact that the principle behind most refrigeration is simple. Here it is in one sentence: When a liquid evaporates, it absorbs heat in the process. If you want to get rid of heat, you need to coax a liquid to convert to its gaseous state Before refrigeration, preserving food was a big job. You could salt foods, and in winter, you could bury food in a snow drift and hope the critters didn't find it. To stay stocked with the essentials, though, you had to work at it -- or be rolling in money. Refrigeration is one invention that changed the way we conduct our daily lives. Name: M. Naeem mob# 0543496216