In ordinary conversation, when the term air conditioning is mentioned, people automatically take it to mean cooling room temperature. Technically speaking, though, air conditioning is the process of controlling room temperature through various means that involve ventilation, heating and cooling. In construction, it is referred to as HVAC.
In 1902, The New York Stock Exchange was the very first building to use air conditioning units that separately cooled and heated the air. Later that year, Willis Havilland Carrier installed the very first electrically-run air conditioning unit at a printing plant. The unit not only cooled the air but also controlled the humidity.
In those times, air conditioning was mostly used in manufacturing facilities to improve products by controlling the effects of humidity, thus, increasing employee productivity. It was several decades later, in the 1950s, that homes and automobiles started to be fitted with the air conditioning technology.
An air conditioning unit cools the air through a refrigerant, a substance that alters the temperature of the air. In the early stages of its development, air conditioning units used harmful gases such as ammonia and methyl chloride as refrigerants. They were soon replaced by another type of chemical, the patented substance called Freon.