An air-conditioning system must be effective regardless of outside climatic conditions and involves control over four fundamental variables: air temperature, humidity, movement and quality. Industrial air-conditioning usually requires better precision as regards temperature and humidity control. Some application also demand a high degree of filtering and removal of contaminants. Comfort air-conditioning on the other hand, as well as needing to satisfy personal temperature-humidity requirements, also involves other fields such as architectural design, weather forecasting, energy consumption and sound emissions to recreate the ideal conditions for human psychophysiological well-being. The main process underlying air-conditioning is the exchange of heat and water vapour between the indoor and outdoor environments and the people inside the air-conditioned space.