Environmental control system (aircraft)

Air conditioning in airplanes ( engl. environmental control system, ECS, German and environment control system) is the three system components exchange of air, pressure, and temperature control in the cabin of the aircraft for crew, passengers and baggage rooms. The air conditioning is required in commercial aircraft order with enough air pressure, a sufficient oxygen supply and a reasonable ambient temperature to provide the necessary atmosphere in the cabin passengers at flight altitudes above 11,000 meters.

Compared to "normal" air conditioning units for temperature control, for example in buildings or vehicles, the application of this term for the ECS in an aircraft is incomplete inasmuch as here takes place the pressure and oxygen supply. The air conditioning in airplanes therefore are distinguished from the ordinary air conditioning systems by a different construction and energy source with a much larger power consumption and high security requirements.

Larger passenger aircraft with multiple engines usually have two to three redundant, independent, parallel aggregates (german air conditioning packs, abbreviated packs ). Bleed air is used, the so-called air - P2 (English bleed air ) from the compressor of the jet engine. This air is up to 200 ° C hot, depending on the take-off point has a pressure of several bars, but is also limited depending on the engine version in the crowd. The collected amount depends on that about every 1.5 to 2 minutes must be the air in the aircraft cabin exchanged or processed. The system must be tuned to keep the pressure and the temperature in the cabin. The internal pressure is regulated by a controllable discharge valve in the fuselage of the aircraft (English outflow -valve ), the temperature as required by cooling (when operating near the ground ), and optionally auxiliary electric heater in very cold outdoor air in flight, provided that the heat content of the bleed air is not sufficient. As required, the fresh air needs to be dehumidified or humidified. On the ground and in aircraft jet engine without which takes place " climate " with an auxiliary power unit (English auxiliary power unit, APU).

In the Boeing 787 but no bleed air of the engines is used, but the air conditioner is operated electrically. The engines have very strong generators for this purpose.

In order to save energy for the APU and to achieve an improvement in air quality at the airport, more and more airports are upgrading their terminals with PCA air conditioning systems from (PCA = pre -conditioned air), which passed to the jetway conditioned air to the aircraft.

Function and main assemblies

Cooling turbine and heat exchanger

Figure 1 shows the principle of operation of the two heat exchangers (including heat exchangers) in a Vapor Cycle System. The procedure corresponds to that of a refrigerator or a heat pump.

The air cycle machine ( cooling turbine - Image 2 ) is the heart of the air conditioner of a commercial aircraft. It comprises a radial compressor (2), a turbine ( 7) and a plurality of heat exchangers ( Sheet Heat Exchanger ) generating conditioned air from the bleed air.

The bleed air (Fig. 3 (1) ) at a pressure of about 3 bar, and up to 200 ° C, temperature passing through the first heat exchanger (Fig. 3 ( 4) ), which is cooled by the outside air (English ram air). After the pressure increase and the associated warming is a second heat exchanger ( Figure 3: (6 ) ) and then through the turbine ( Figure 3: ( 7) ), in which the air expands and therefore cools further. The rotational energy of the turbine, in turn drives a shaft (Fig. 3: (20) ) to the compressor. At the output of the turbine, the temperature is about 0 ° C and is mixed with hot air from the bleed air system (Fig. 3: 10 ) () to obtain the desired temperature.

Ensuring that the system works well on the ground, here are the heat exchanger by a blower, the " Turbo Fan", supplied with cooling air. The turbo fan is driven electrically (Boeing 727), by an air motor (Boeing 737 Classic) or mechanically by the wave of cooling turbine (Boeing 737- NG).

Mixing chamber

The mixing chamber (german mixing -chamber - Image 5: (23 )) is the mixing and distributing the air conditioner. Here, the air is further heated from the pack as needed with bleed air. In addition, a part of the already filtered and used cabin air with the aid of one or more fans, the recirculation fans admixed (Fig. 5 - (18) ). From here the air is made ​​available for further distribution.

Outlet valve

The pressure valve, also called outflow valve, is an adjustable flap in the rear part of the pressure cabin. It regulates function of the flight phase, the internal pressure. At the bottom it is open and is regulated during startup automatically by the cabin pressure regulator (English cabin- pressure- controller) to keep then in cruise an air pressure as in about 2400 meters above sea level (based on standard air pressure). If the automatic control of cabin pressure failure, the exhaust valve can be adjusted electrically by a hand controller.

Safety devices

Should not open the outlet would be a risk of dangerous excess pressure in the cabin. Therefore located in the aircraft skin relief valves (English overpressure -relief -valves ) which open at a differential pressure in the cabin with respect to the outside of about 0.6 bar. Should not close, the air conditioning failed, or create a large hole in the aircraft skin, the exhaust valve, which located above the passenger oxygen masks are automatically activated when the cabin pressure drops about 4300 meters altitude below a corresponding air pressure.

History

Honeywell Aerospace in 1940 built the first heat exchanger for pressurized cabins in the Boeing B -307. 1944 air expansion turbine was developed for cooling the cabin of a Lockheed P-80 (german air expansion turbine ), a pressurized cabin. The first air circuit air conditioning (german air cycle ECS - environmental control system ) was used in 1945 at the Lockheed Constellation. The first " steam cycle cooling system " (English aircraft- type vapor cycle cooling system ) was used in 1956 by Honeywell Aerospace in the Lockheed L- 188 Electra. The Boeing 727 was 1961 the first complete " pneumatic circuit environment air control system " (English pneumatic air cycle ECS - Environmental Control System).