As the airplane ascends to higher altitudes, the air pressure decreases, necessitating an air conditioning system to ensure a sufficient supply of oxygen for passengers at pressures similar to those at ground level.
The primary source of air supply for modern commercial aircraft comes from the engines. Outside air is drawn in and compressed through multiple stages to facilitate the combustion process that generates thrust for the aircraft.
Before reaching the combustion chamber, a small portion of the air is redirected from the air ducts. This air is at high pressure and temperature, and in addition to providing for passengers, it also serves to de-ice the wings and other aircraft components, according to Lufthansa Technik.
Air circulation system on the aircraft. (Photo: Lufthansa Technik).
The airflow, referred to as “bleed air”, is cooled through a heat exchange method down to a temperature of 200 degrees Celsius. Controlled by the flight crew via valves, it is routed to the air conditioning system to further reduce the temperature to a level suitable for passengers.
The cooled air is then mixed with previously used air from the aircraft cabin in a mixing chamber. Finally, control valves direct this air back into the cabin, dividing it into various zones. The use of recirculated air increases humidity, enhancing passenger comfort.
The separation of the aircraft cabin into different zones allows for independent temperature adjustments in various areas, such as between the economy and business class sections. These two areas can have significantly different heat emissions from passengers, as the economy section tends to be more crowded.
The temperature of the air is adjusted to be warmer or cooler by altering the percentage of hot air components. The flight crew can monitor this temperature through the ECAM (Electronic Centralized Aircraft Monitor).
The number of zones depends on the type of aircraft. The Airbus A320 has two distinct zones, while the A330/A340 series features six.
Additionally, there is a filtration system capable of removing 99.999% of known viruses and bacteria from the air.
