Refrigerators are arguably the best invention ever devised. Prior to refrigerators, the only way to preserve food was by salting it, a process used for thousands of years that made for really salty food. Even then, the process wasn’t perfect. Salted food would still spoil, and the meat, or whatever it was, had to be highly spiced in order to make it edible. This is one of the reasons merchants were so anxious to make it to the Spice Islands and, indirectly, how North America was discovered.

Refrigeration works by slowing down the bacterial activity that exists in all perishable foods. Milk, for instance, wouldn’t last four hours out of the fridge. In the fridge, pasteurized milk can last up to two weeks. Frozen foods can last much longer than that, since freezing something stops bacterial activity altogether.

Our refrigerators are something we take for granted. We put food in the fridge, and provided there isn’t a power cut, we expect the fridge to keep it nice and cool. But how does the process work?

The system relies on four major mechanical things: a compressor, external coils, an expansion valve, and internal coils. Along with the mechanical things, fridges would be useless without the refrigerant that is the real star of the “keeping things cool” show.

The refrigerant has a really low boiling point. This is important, because if it boiled at the same temperature as water, for instance, it could only keep things at 100 degrees Celsius. Many industrial machines use ammonia which boils at -27 degrees Fahrenheit—just above freezing, but since ammonia is harmful, household refrigerators use other refrigerants.

The refrigerant gas is compressed as it leaves the internal parts of the fridge, effectively raising its temperature and allowing it to vent heat as it runs around the external coils. During this process it changes from a gas to a liquid, albeit a very pressurized one. As it re-enters the internal part of the fridge, it passes through an expansion valve which divides the external pressurized system from the internal depressurized system. Upon entering the depressurized part of the system the refrigerant immediately returns to its gaseous state and passes through the internal coils, picking up heat and boiling until it gets shot back out by the compressor. The cycle repeats.

So that, in essence, is how refrigeration works. Whether you are looking at a fridge at your local Home Depot in Honolulu, or ordering an industrial sized system from refrigeration contractors in Red Deer, the system is the same. What’s cooler than that?