Did you know that the first commercial application of air conditioning was in 1902? And yet, residential central A/C didn’t come into its own until the 1960’s. According to the US Department of Energy, air conditioning use skyrocketed in the 1970’s. Since then, A/C units have become more efficient, such that new air conditioners use fifty percent less energy than units from the 1990’s. Additionally, new technologies are making A/C units increasingly environmentally friendly. New developments in air conditioning include non-vapor compression technology, which will be fifty percent more efficient and doesn’t use Hydrofluorocarbons (energy.gov).