Refrigeration is a process in which work is done to move heat from one location to another. The work of heat transport has traditionally been driven by mechanical work that requires fuel, but it can also be driven by heat, magnetism or electricity. Refrigeration has many applications including household refrigerators, industrial freezers, cryogenics or heating and air conditioning units. Heat pumps may use the heat output of the refrigeration process and also may be designed to be reversible but similar to refrigeration units.
The first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in 1756. Cullen used a pump to create a partial vacuum over a container of diethyl ether that boiled and absorbed heat from the surrounding air. The experiment even created a small amount of ice but it had no practical application at that time. In 1842, an American physician, John Gorrie, designed the first system to refrigerate water to produce ice. He also conceived the idea of using his refrigeration system to cool the air for comfort in home and hospitals. His system compressed air, then partly cooled the hot compressed air with water before allowing it to expand while doing part of the work needed to drive the air compressor. That isentropic expansion cooled the air to a temperature low enough to freeze water and produce ice, or to flow through a pipe for effecting refrigeration otherwise as stated in his patent granted by the U.S. Patent Office in 1851.
With the invention of synthetic refrigerants based mostly on a chlorofluorocarbon chemical, safer refrigerators were possible for home and consumer use. These refrigerants were considered at the time to be less harmful than the commonly used refrigerants of the time, including methyl formate, ammonia, methyl chloride and sulfur dioxide. The intent was to provide refrigeration equipment for home use without danger, especially danger to livestock. During the 1970’s, the compounds were found to be reacting with atmospheric ozone, an important protection against solar ultraviolet radiation, and their use as a refrigerant worldwide was curtailed in the Montreal Protocol of 1987.
You can keep food cold without refrigeration, especially if you have land where you have a spring or a creek flowing across the land. In this situation you need to divert a small portion of the creek and have it flow through a spring house. You should build your spring house out of cement block and it should have no windows. Whatever light there is should come in when you open the door. You should plaster the walls on the inside. The spring house should have a rock or cement floor. You can also have a light bulb in the spring house if you want to. A spring house will keep things like milk, eggs, orange juice etc just like a regular refrigerator. The refrigerator will keep food safe and cold for about 4 hours if unopened. A freezer that is full will hold the temperature for approximately 48 hours and half of that if only half full. If you can find a block of dry ice, a 50 pound block will keep the unit cool for approximately 2 days. The kill off zone for bacteria is 145° F and prepared foods must be kept at a temperature of at least 140° until served or bacteria will start growing again even in the event of power outages.