Air Craft Air Conditioning System: Description

The air cycle system functions by using air from either the engines or the Auxiliary Power Unit (APU). Airflow from the engines, as bleed air, or APU to the Air Cycle Machine (ACM or Pack) is controlled by various Engine Bleed valves and System Control Valves. The bleed airflow is modulated by Pack Flow Control Valves, and the air is thermally adjusted by means of air-to-air heat exchangers and Mix Valves.An air cycle machine (ACM) is the refrigeration unit of the environmental control system (ECS) used in pressurized gas turbine-powered aircraft. Normally an aircraft has two or three of these ACM. Each ACM and its components are often referred as an Air Conditioning Pack. The Air Cycle cooling process uses air instead of Freon in a gas cycle. No condensation or evaporation of a refrigerant is involved, and the cooled air output from the process is used directly for cabin ventilation or for cooling electronic equipment.