Air conditioning is the process of removing heat and moisture from the interior of an occupied space to improve its thermal comfort. This is usually achieved through a refrigeration cycle, in which a refrigerant is used to cool and dehumidify the air. Air conditioning systems are commonly used in homes, vehicles, and commercial and industrial buildings to provide a comfortable indoor environment, especially during hot weather. The types of air conditioning systems include central air conditioning, room air conditioners, and portable air conditioners.