The cold air then enters the compressor, where it is re-pressurized, which reheats the air. A pass through the secondary «ram air heat exchanger» cools the air while maintaining the high pressure. The energy extracted from the air passing through the turbine is used to power the compressor. This article explores the 787’s no-bleed systems architecture and explains how the airplane’s efficiencies are realized. Avionics cooling, smoke detection, and fire suppression are also commonly considered part of an aircraft’s environmental control system.
The cabin pressure is controlled by a «cabin pressure schedule», which associates each aircraft altitude with a cabin altitude. For a sub-zero bootstrap CAU, the moisture is extracted before it reaches the turbine so that sub-zero temperatures may be reached. Reduced maintenance costs and improved reliability because the architecture uses fewer parts than previous systems. Aircraft cabin pressure is commonly pressurized to a «cabin altitude» of 8000 feet or less.
The sock retains the dirt and oil from the engine bleed air to keep the cabin air cleaner. Control panel for a Boeing 737-800 ECS The environmental control system (ECS) of an aircraft provides air supply, thermal control and cabin pressurization for the crew and passengers. Archived from the original (PDF) on February 27, 2012. Retrieved December 31, 2012. ^ Select Committee on Science and Technology (2000). «Chapter 4: Elements Of Healthy Cabin Air». Science and Technology — Fifth Report (Report). House of Lords.
That means that the pressure is 10.9 pounds per square inch (75 kPa), which is the ambient pressure at 8,000 feet (2,400 m). Note that a lower cabin altitude is a higher pressure. The power, which comes off the generators at variable frequencies, is conditioned in the electronics bay before being distributed to the appropriate systems.
The air then passes through a turbine which expands the air to further reduce heat. For this reason, air is commonly drawn from one of two (or in some cases such as the Boeing 777, three) bleed ports at different compressor stage locations. Boeing believes that using electrical power is more efficient than engine-generated pneumatic power, and expects the new architecture to extract as much as 35 percent less power from the engines.
Similar in operation to a turbo-charger unit, the compressor and turbine are on a single shaft. Air from the «mix manifold» is directed to overhead distribution nozzles  in the various «zones» of the aircraft. 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. Pneumatic systems that divert high-speed air from the engines rob conventional airplanes of some thrust and increase the engine’s fuel consumption.
The new airliners such as the Airbus A350 and Boeing 787 will have lower maximum cabin altitudes which help in passenger fatigue reduction during flights. The bleed air enters the primary «ram air heat exchanger», where it is cooled by either ram air, expansion or a combination of both.
The reverse happens as engine pressure decreases. To achieve the desired temperature, the bleed-air is passed through a heat exchanger called a pre-cooler. Improved reliability due to the use of modern power electronics and fewer components in the engine installation. Then, the air usually will pass through a water separator coalescer or the sock. Expanded range and reduced fuel consumption due to lower overall weight.
Retrieved 2007-10-20. ^ Bagshaw, Michael (September 2008). «The Aerotoxic Syndrome» (PDF). European Society of Aerospace Medicine. One of the advantages of the no-bleed electrical systems architecture is the greater efficiency gained in terms of reduced fuel burn — the 787 systems architecture accounts for predicted fuel savings of about 3 percent. The 787 also offers operators operational efficiencies due to the advantages of electrical systems compared to pneumatic systems in terms of weight and reduced lifecycle costs.
Air supply Main article: Bleed air On jetliners, air is supplied to the ECS by being bled from a compressor stage of each gas turbine engine, upstream of the combustor. Air cannot flow backwards through the engine except during a compressor stall (essentially a jet engine backfire), thus the bleed air should be free of combustion contaminants from the normal running of the aircraft’s own engines. The ducting used to pass the pressurized air around the airplane employs check valves and pre-coolers, and is itself made of titanium, which adds hundreds of pounds of weight to the airplane. There are many various types of CAUs; however, they all use typical fundamentals.
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. Reduced maintenance costs, due to elimination of the maintenance-intensive bleed system. By Mike Sinnett, Director, 787 Systems The primary differentiating factor in the systems architecture of the 787 is its emphasis on electrical systems, which replace most of the pneumatic systems found on traditional commercial airplanes.
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