Air conditioning (also A/C, air conditioner) is the process of removing heat and controlling the humidity of air in an enclosed space to achieve a more comfortable interior environment by use of powered 'air conditioners' or a variety of other methods including passive cooling and ventilative cooling. Air conditioning is a member of a family of systems and techniques that provide 'heating, ventilation, and air conditioning' (HVAC).
Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used within vehicles or single rooms to massive units that can cool large building. Air source heat pumps, which can be used for heating as well as cooling are becoming increasingly common in cooler climates.
According to the IEA, as of 2018, 1.6 billion air conditioning units were installed which accounted for an estimated 20% of energy usage in buildings globally with the number expected to grow to 5.6 billion by 2050. The United Nations called for the technology to be made more sustainable to mitigate climate change using techniques including passive cooling, evaporative cooling, selective shading, windcatchers and better thermal insulation. Refrigerants used within air conditioners have caused damage to the ozone layer and are also exacerbating climate change.