There's a natural inclination in human physiology that makes us crave coolness against our bodies.
Too hot? We're uncomfortable. Too cold? Same thing. Hence, the necessity of air-conditioning methods, a history that goes back further than many would believe.
Many of humanity's earliest societies experimented with methods and devised ways to cool the interior of their homes. Ancient Egyptians would hang moist rugs in their doorway, which cooled during the night and combined with the wind to help reduce temperatures inside. Ancient Romans used their aqueducts, which fed cold water into their walls, the water radiating outwards and bringing down inside temperatures. However, this technology disappeared after the fall of the Roman Empire and the beginning of the Dark Ages.
During Medieval times--with an unfortunate lack of Roman technology--people relied on conditioning techniques from Ancient China. The iconic Chinese hand fan was used for a long time; however it was the invention of a large rotary fan in the 2nd century that began helping people cool their homes and not just themselves individually. These large fans were hand-operated and remained the best way to cool homes until the 1800's.
With outbreaks of Yellow Fever popping up all across the country in the 18th and 19th centuries, Dr. John Gorrie--a physician who specialized in studying tropical diseases--wanted to find a way to keep patients cool while they were in sick rooms suffering from their affliction. For this reason, he developed an ice machine which used compressed air to blow the cold air over the patients. While his idea did eventually fail to make a significant impact, it did help spur innovation in the ideas of temperature control.
However, it wasn't until 1902 when a man named Willis Carrier invented modern air conditioning. Using ideas that were thousands of years old along with new innovations from Nikola Tesla, Benjamin Franklin, Michael Faraday and others, Carrier developed an electric machine that blew air over coils full of cold water. Carrier's air conditioning unit controlled temperature and humidity and was originally invented for increasing the efficiency in a printing plant. It would take a decade before these air conditioning units entered private homes though.
In 1914, a wealthy man from Minneapolis had Carrier install his invention in his mansion. As time passed, commercial businesses began to install large units to cool their stores. However, home air-conditioning struggled during the depression and during World War Two; but with the economic boom of the 1950's, the industry thrived in private residences.
Carrier's invention changed the way we live. Without it, many technological components--such as large computer servers, which need to maintain a low temperature--wouldn't have been a legitimate possibility. Today, we enjoy air conditioning whether we're at the movies, walking through the mall, eating at a restaurant or sitting around the house, proving that humanity's come a long way in its cooling methods.