The document discusses air conditioning systems. It begins with definitions of air conditioning and its purpose of altering air properties like temperature and humidity for comfort or industrial processes. It then discusses the history of air conditioning and its inventor Willis Carrier in 1902. The document outlines different types of air conditioning like comfort cooling and industrial cooling. It discusses factors for human comfort like temperature, humidity and air velocity. It explains the basic elements of an air conditioning system including the compressor, condenser, expansion valve and evaporator. It concludes by describing different air conditioning system types like window units, split systems, central systems and package units. It also discusses new technologies like district cooling systems and chilled beam systems.