On aircraft, cabin air quality contributes significantly to the comfort and well being of passengers and crews alike. Air quality, temperature and pressure are important parameters which are directly controlled by the environmental control system.
Commercial aircraft operate primarily in the troposphere and lower stratosphere, depending on their geographic position. This is an environment that is hostile to life; the outside temperature can drop to below -50C, the ambient pressure can decrease to less than 200hPa (hectopascal), which is one fifth the ambient pressure on the surface of the earth and high ozone concentrations may occur.
During flight, pressurized outside air is taken from the compressor stage of the engines (bleed air) upstream the combustion chamber, where temperatures up to 400°C can be reached, passed through a pre-cooler unit and conveyed to the “air conditioning pack” at a temperature of approximately 200°C. Alternative bleed air supply sources during ground, or near ground operations, supplying the air conditioning pack with pressurized and consequently hot bleed air, are the Auxiliary Power Units (APU) and High Pressure Ground Carts (HPGC).
A mixer unit, installed below the cabin floor in front of the centre wing box, mixes outside air with cabin air. The cabin air is taken from the under-floor area and drawn through recirculation filters by recirculation fans. The quantity of re-circulated cabin air mixed with the outside air varies from 40% to 60% and improves efficient removal of heat loads at a moderate temperature gradient, and increases the humidity by making use of the cabin air. The latter contains humidity contributed by the passengers whilst outside air, being very cold, is almost completely dry.
Honeywell supplies the Air Management System specifically designed for A350 XWB: the bleed air, environmental control, cabin pressure control and supplemental cooling systems. Honeywell has more than 50 years´ background in environmental and cabin pressure control systems to manage all of the air used on the aircraft for environmental control, including cabin heating and cooling, and cabin pressurization for increased passenger comfort and safety.