environment control system

Topics: Cabin pressurization, Boeing 787, Airliner Pages: 6 (2070 words) Published: September 21, 2013
The Environmental Control System of an airliner provides air supply, thermal control and cabin pressurization for the passengers and crew. Avionics cooling, smoke detection, and fire suppression are also commonly considered part of the Environmental Control System. Contents

[hide]
1 Overview
2 Air supply
3 Cold Air Unit (CAU)
4 Ram Air System
5 Air distribution
6 Pressurization
7 Humidity
8 Health concerns
9 Myths and misconceptions
9.1 Turning off packs to save fuel
9.2 Reducing air supply to the cabin
9.3 Better air quality in first class
9.4 Better air quality on the flight deck
9.5 Lack of pressurization in the cargo hold
10 References
11 External links
[edit] Overview
The systems described below are specific to current production Boeing airliners, although the details are essentially identical for passenger jets from Airbus and other companies. An exception was Concorde which had a supplementary air supply system fitted due to the higher altitudes at which it flew, and also the slightly higher cabin pressure it employed. [edit] Air supply

On most jetliners, air is supplied to the ECS by being "bled" from a compressor stage of each turbine engine, upstream of the combustor. The temperature and pressure of this "bleed air" varies widely depending upon which compressor stage and the RPM of the engine. A "Pressure Regulating Shutoff Valve" (PRSOV) restricts the flow as necessary to maintain the desired pressure for downstream systems. This flow restriction results in efficiency losses. To reduce the amount of restriction required, and thereby increase efficiency, air is commonly drawn from two bleed ports (3 on the Boeing 777). When the engine is at low thrust, the air is drawn from the "High Pressure Bleed Port." As thrust is increased, the pressure from this port rises until "crossover," where the "High Pressure Shutoff Valve" (HPSOV) closes and air is thereafter drawn from the "Low Pressure Bleed Port." To achieve the desired temperature, the bleed-air is passed through a heat exchanger called a "pre-cooler." Air from the jet engine fan is blown across the pre-cooler, which is located in the engine strut. A "Fan Air Modulating Valve" (FAMV) varies the cooling airflow, and thereby controls the final air temperature of the bleed air. On the new Boeing 787, the bleed air will instead be provided by electrically driven compressors, thereby eliminating the inefficiencies caused by bleed port system. [edit] Cold Air Unit (CAU)

The Cold Air Unit, or "Airconditioning pack" is usually an air cycle machine (ACM) cooling device. Some aircraft, including early 707 jetliners, used vapour-compression refrigeration like that used in home air conditioners. An ACM uses no Freon: the air itself is the refrigerant. The ACM is preferred over vapor cycle devices because of reduced weight and maintenance requirements. On most jetliners, the A/C packs are located in the "Wing to Body Fairing" between the two wings beneath the fuselage. On some jetliners (Douglas Aircraft DC-9 Series) the A/C Packs are located in the tail. The A/C Packs on the McDonnell Douglas DC-10/MD-11 and Lockheed L-1011 are located in the front of the aircraft beneath the flight deck. Nearly all jetliners have two packs, although larger aircraft such as the Boeing 747, Lockheed L-1011, and McDonnell-Douglas DC-10/MD-11 have three. The quantity of bleed air flowing to the A/C Pack is regulated by the "Flow Control Valve" (FCV). One FCV is installed for each pack. A normally closed "isolation valve" prevents air from the left bleed system from reaching the right pack (and v.v.), although this valve may be opened in the event of loss of one bleed system. Downstream of the FCV is the CAU (Cold Air Unit), also referred to as the refrigeration unit. There are many various types of CAu however they all use typical fundamentals. The bleed air enters the primary "Ram Air Heat Exchanger", where it is cooled by either ram air, expansion or a combination of...
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