What are the advantages of this new air conditioning system compared with the traditional engine bleed systems? More engine output power, or easier adaption to future aircraft design?
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$\begingroup$ In addition of the answers, there is a general trend towards more electric aircraft ("MEA") with savings in mass, fuel, complexity and gains in reliability. $\endgroup$– minsCommented Feb 4, 2018 at 12:17
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2 Answers
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Boeing is moving to a bleedless system with the 787 Dreamliner and GEnx engines. In the past engine bleed air has been used extensively for ECS (Environment Control System) e.g. cabin pressurization and air conditioning, as well as anti and de-icing, ozone removal and many other uses.
Nevertheless Boeing firmly believes that the overall efficiencies and improved reliability are a large step forward. Moving to a bleedless system will reduce the mechanical complexity of the 787 by more than 50% compared to the 767. The new system is expected to be save about 3% in fuel and 15% more efficient overall.
The move to a bleedless architecture has been the subject of much enthusiast debate e.g. here because while many advantages are apparent it's not immediately obvious that the increased electrical loads to replace the pneumatic functions isn't a moot point. Additionally, Rolls Royce wasn't willing to commit to developing a bleedless system, so the Airbus A350 XWB will continue to use bleed air pneumatic systems.
Boeing summarizes the primary bleedless architecture benefits as being:
- Improved fuel consumption, due to a more efficient secondary power extraction, transfer, and usage.
- Reduced maintenance costs, due to elimination of the maintenance-intensive bleed system.
- Improved reliability due to the use of modern power electronics and fewer components in the engine installation.
- Expanded range and reduced fuel consumption due to lower overall weight.
- Reduced maintenance costs and improved reliability because the architecture uses fewer parts than previous systems.
- 787 No-Bleed Systems: Saving Fuel and Enhancing Operational Efficiencies
Pneumatics have long been one of the weakest links in modern airliners. Moving to an electric system should increase reliability of a number of sub-systems, portend reduced long term maintenance costs and aids in the improvement of many components.
One example of the advantage of moving to an "electric aircraft" is to facilitate the move from hydraulic to electric braking. I think it's a great move.
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1$\begingroup$ Why has this not been implemented before? Is there something that allows this now that wasn’t available in the past? $\endgroup$– TomMcWCommented Feb 6, 2018 at 2:39
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3$\begingroup$ @TomMcW The interest in bleed less air systems (moving to an "electric aircraft") is being driven by improvements in solid state electronics. Pneumatics and bleed air do a lot of work on a traditional aircraft. So it takes a lot of specialized electronics to control all of the new electric systems that replace pneumatics. It's more recently that really good control systems at sane prices are becoming available for large aircraft. $\endgroup$– user28563Commented Feb 8, 2018 at 19:39
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According to this paper from Boeing its CAC is simply more efficient than the old style bleed-air designs and reduces fuel usage.
In the no-bleed architecture, electrically driven compressors provide the cabin pressurization function, with fresh air brought onboard via dedicated cabin air inlets. This approach is significantly more efficient than the traditional bleed system because it avoids excessive energy extraction from engines with the associated energy waste by pre-coolers and modulating valves. There is no need to regulate down the supplied compressed air. Instead, the compressed air is produced by adjustable speed motor compressors at the required pressure without significant energy waste. That results in significant improvements in engine fuel consumption.
Boeing lists the reasons/advantages for the move to electrical systems here.
Improved fuel consumption, due to a more efficient secondary power extraction, transfer, and usage.
Reduced maintenance costs, due to elimination of the maintenance-intensive bleed system.
Improved reliability due to the use of modern power electronics and fewer components in the engine installation.
Expanded range and reduced fuel consumption due to lower overall weight.
Reduced maintenance costs and improved reliability because the architecture uses fewer parts than previous systems.
