Air conditioning (airplane)
An air conditioning in the aircraft (engl. Environmental control system , ECS ) comprises the three system components exchange of air, pressure, and temperature control in the cabin of the aircraft for the crew, passengers and luggage compartments. Commercial aircraft need air conditioning in order to provide passengers with the necessary atmosphere in the cabin with sufficient air pressure , sufficient oxygen supply and an appropriate ambient temperature at altitudes of up to 11,000 meters .
Compared to "normal" air conditioning systems only for temperature control, e.g. B. in buildings or vehicles, the ECS also takes care of the air pressure in aircraft. The air conditioning systems in aircraft therefore differ from the normal air conditioning systems in that they have a different design and energy source with a significantly greater power requirement and high safety requirements.
Larger passenger aircraft with a plurality of engines usually have two or three redundant , independent, parallel units (engl. Air conditioning packs , abbreviated packs ). Is used bleed air , (Engl. The so-called. P2 air bleed air ) from the compressor of the jet engine . This air is up to 200 ° C, has an overpressure of several bar, depending on the take-off point, but is also limited in quantity depending on the engine version. The amount removed depends on the fact that the air in the aircraft cabin has to be exchanged or treated approximately every 1.5 to 2 minutes. The system must be tuned to maintain the pressure and temperature in the cabin. The internal pressure is regulated by a controllable discharge valve in the fuselage of the aircraft ( outflow valve ), the temperature is regulated as required by cooling (when operating close to the ground) and, if necessary, additional electrical heating in the case of very cold outside air in flight, provided the heat content of the bleed air not enough. The fresh air must be dehumidified or humidified as required. On the ground and in aircraft jet engine without the "climate" is performed using a auxiliary power unit (Engl. Auxiliary power unit, APU).
The Boeing 787 does not, however, use bleed air from the engines because the air conditioning is operated electrically. The engines have very powerful generators for this purpose.
In order to save energy for the auxiliary power unit, to extend its maintenance cycles and to improve the air quality at the airport, more and more airports are equipping their terminals with PCA air conditioning systems (PCA = pre-conditioned air ), which are installed on the passenger boarding bridge , via floor tanks or combustion-powered Ground units pass conditioned air to the aircraft. There, air that is down to −25 ° C (typically +2 ° C) is dried and blown into the aircraft.
Function and main assemblies
Cooling turbine and heat exchanger
Image 2: Air-Cycle-Machine (ACM) = cooling turbine - the core of the packs (legend: click on the image)
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Fig. 1 shows the principle of operation of the two heat exchangers (also heat exchangers) in a vapor cycle system. The mode of operation corresponds to that of a refrigerator or a heat pump.
The air cycle machine ( cooling turbine - Fig. 2) is the heart of the air conditioning system in a commercial aircraft. It includes a radial compressor (2), a turbine (7) and a plurality of heat exchangers (engl. Heat exchanger ) that produce air-conditioned from the air bleed air.
The bleed air (Figure 3: (1)) at a pressure of about 3 bar and up to 200 ° C temperature passes through the first heat exchanger (3: (4)), which from the outside air (engl. Ram air ) cooled is . After the pressure increase and the associated heating, a second heat exchanger (Fig. 3: (6)) is passed through and then the turbine (Fig. 3: (7)), in which the air expands and therefore cools down further. The rotational energy of the turbine in turn drives the compressor via a shaft (Fig. 3: (20)). At the exit of the turbine, the temperature is around 0 ° C and is mixed with hot air from the bleed air system (Fig. 3: (10)) in order to obtain the desired temperature.
So that the system also works on the ground, the heat exchangers are supplied with cooling air by a fan, the " turbo fan ". The turbo fan is driven electrically (Boeing 727), by an air motor (Boeing 737 Classic) or mechanically by the shaft of the cooling turbine (Boeing 737-NG).
Image 4: Environmental Control System of the Boeing 737-300 (environmental control system) = air conditioning - on the ground - packs switched on ( image with legend ) - (please click on the image for a detailed explanation of the numbers)
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Fig. 5: Environmental Control System of the Boeing 737-300 (environmental control system) = air conditioning - with the engines running ( picture with legend ) - (please click on the picture for a detailed explanation of the numbers)
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Mixing chamber
The mixing chamber (engl. Mixing chamber - Figure 5: (23)) is the mixing and distributing the air conditioner. Here, the air from the packs is further heated with bleed air as required. In addition, part of the already used and filtered cabin exhaust air is mixed in with the help of one or more blowers, the recirculation fans (Fig. 5 - (18)). From here the air is provided for further distribution.
outlet valve
The pressure valve , also known as the outflow valve , is an adjustable flap in the rear part of the pressure cabin. It regulates the internal pressure depending on the flight phase. It is open on the ground and is automatically regulated by the cabin pressure controller during take-off , in order to maintain an air pressure of around 2400 meters (based on standard air pressure ) during cruise. If the automatic control of the cabin pressure fails, the outlet valve can also be adjusted electrically using a manual controller.
Safety devices
If the outlet valve does not open, there is a risk of dangerous overpressure in the cabin. That is why there are overpressure relief valves in the aircraft skin , which open when there is a differential overpressure in the cabin from outside of around 0.6 bar. If the outlet valve does not close, the air conditioning fails or a large hole appears in the aircraft skin, the oxygen masks above the passengers are automatically activated when the cabin pressure drops below an air pressure corresponding to an altitude of around 4,300 meters.
history
Honeywell Aerospace installed the first pressurized cabin heat exchanger in the Boeing 307 Stratoliner in 1940 . 1944 was air expansion turbine (engl. Air expansion turbine ) for the cooling of the cabin of the Lockheed P-80 developed a pressurized cabin . The first air circuit air conditioning (. Engl air cycle ECS - environmental control system ) at the 1945 Lockheed Constellation used. The first " vapor cycle refrigeration system " (eng. Aircraft-type vapor cycle cooling system ) was 1956 by Honeywell Aerospace in the Lockheed L-188 Electra used. The Boeing 727 was in 1961 the first complete " pneumatic circuit environment air control system " (English. Pneumatic air cycle ECS - Environmental Control System ).
literature
Lufthansa Flight Training - Airframe and systems 2 , Commercial Aviation School , Bremen March 2001
Web links
- Commercial airliner environmental control system (PDF file; 742 kB)
- Conception and development of aircraft air conditioning systems (PDF file; 620 kB)
Individual evidence
- ↑ Didier Gendre, Nicolas Orvain, Dariusz Krakowski: Be cool, be efficient. In: Airbus FAST 62.Retrieved on May 24, 2020 .