Do you know how many citizens in the United States have air conditioning units in their homes? The fact is that almost 100 million out of 7 billion citizens in the United States have air conditioning units in their homes. . Air conditioning units began to be used in 1902, but were not officially called "air conditioners" until 1906, by Stuart Cramer (Air Conditioning and Refrigeration Timeline). Until the 20th century, people tried to achieve air conditioning by draping saturated rugs indoors and installing water-powered fans. Leonardo DeVinci built a mechanical fan that was the very first of its kind. The cycle that air goes through before entering your home is called the refrigeration cycle. The definition of refrigeration cycle is: a sequence of thermodynamic processes by which heat is removed from a cold body and expelled to a hot body. The refrigeration cycle is made up of nine different elements of equal importance which are: two fans, a liquid line, a suction line, a compressor, a condenser, an evaporator coil, a doser and a filter for filtration of the air flowing through the house. The creation of the air conditioning unit by Willis Haviland Carrier marked the launch of the modern idea. But it was thanks to Benjamin Franklin and John Hadley, who discovered the Originated that the evaporation of alcohol and other evaporated volatile liquids could cool an object enough to freeze water. .HVAC is the acronym for Heating, Ventilation and Air Conditioning. HVAC systems can be used for residential, commercial or industrial buildings. The HVAC unit is also responsible for changing and redistributing outside air. In doing so, the system takes...... middle of paper ......s. They must then supervise the work of these people. For small buildings, contractors normally size and select HVAC systems and equipment. There are many industry standard sizing and design guides available from trade associations such as the AirConditioning Contractors of America (ACCA). For longer buildings, mechanical, architectural, or building services engineers may be required by law to design and specify HVAC systems. Specialized mechanical contractors will work with the design plans to construct and commission these systems. In conclusion, HVAC is a special unit that helps heat and cool homes and buildings. Making people's daily lives a lot easier was when my grandparents were growing up, as they went from having to lift the windows for air to having to just press on a button. What is the simplest way to live in my opinion.