Refrigeration – Automatic control – Air compessor – cooler and expander
Reexamination Certificate
2001-03-08
2002-05-21
Doerrler, William (Department: 3744)
Refrigeration
Automatic control
Air compessor, cooler and expander
C165S205000, C165S235000, C454S071000, C454S076000, C062S150000, C244S129200, C055S448000
Reexamination Certificate
active
06389826
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 100 11 238.2, filed on Mar. 8, 2000, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a high capacity air conditioning system especially for a passenger transport aircraft, having a redundant and multi-staged admixing of recirculation air to serve several air conditioning zones within the aircraft while achieving a redundant fault tolerant protection against air duct icing in the air conditioning system during operation.
BACKGROUND INFORMATION
It is generally known to provide air conditioning for the passenger cabin spaces in commercial passenger transport aircraft. To achieve this, highly compressed engine bleed air is tapped from the engines, and supplied into one or more air conditioning units (e.g. so-called air conditioning packs) where the high pressure air is expanded to an appropriate pressure for introduction into the pressurized aircraft fuselage and also cooled to a lower temperature. Then, the cooled air with an appropriate pressure is delivered through an air duct network into the several passenger cabin air conditioning zones.
Due to the large thermal load of the passengers, lighting, etc. within the passenger cabin air conditioning zones, it is generally necessary to cool the incoming supplied air very considerably in the air conditioning units to provide a sufficient cooling capacity. Thereby, the air temperature very often reaches low temperatures far below the freezing point of water. The external atmospheric fresh air, which is supplied into the air conditioning system in the form of engine bleed air, has a sufficiently high moisture content, especially at lower altitudes in the atmosphere, so that this moisture will be condensed out of the air and frozen in the form of ice, frost or snow, when the air is cooled to very cold temperatures in the air conditioning unit.
For this reason, it is necessary to protect the air duct system connected downstream of the respective air conditioning unit from the danger of such snow, frost and ice accumulating therein, i.e. by preventing the ice-forming conditions. This is important, because accumulations of such ice can ultimately lead to a partial or complete blockage of the air flow through the affected air duct, or can lead to the formation of loose snow and ice deposits that travel through the duct system with the air flowing therethrough until they reach a warmer location and melt, thereby causing uncontrollable liquid puddling and/or leaks. In either case, and especially if a duct blockage reduces or totally stops the supply of fresh air to the passenger cabin air conditioning zones, this will lead to discomfort or health risks for the passengers.
For the above reasons, it is generally required in the field to avoid the danger of ice formation in air conditioning systems in aircraft, by various conceptual solutions to this problem. Various conventionally known solutions will now be discussed. A first conceptual starting point for a solution is to avoid reducing the temperature of the air conditioning air below the freezing point of water, i.e. to maintain the output air of the air conditioning packs above the freezing point. In that case, however, in order to provide the required total cooling capacity or energy, it is necessary to provide a correspondingly increased mass flow of the cooled air, which requires tapping more energy-rich bleed air from the engines.
Moreover, in order to achieve comfortable passenger air conditioning zone inlet temperatures and sufficiently high ventilation properties, it is typical to mix recirculated passenger cabin air (or generally fuselage interior air) with a corresponding quantity of the cooled air. Such a measure is generally known as “air recirculation”. Such a solution is realized in the Airbus A300-600 and A310 aircraft, which, however, consumes an undesirably high quantity of engine bleed air for cooling the passenger air conditioning zones, since the degree of cooling of the air in the air conditioning units is limited to remain above the freezing point. Thus, the fuel consumption of the engines is undesirably increased.
The Boeing B747 aircraft also realizes or embodies the above discussed solution. In that aircraft, however, the air conditioning system attempts to raise the temperature of the cooling air by mixing cold air and recirculation air in a first recirculation stage following a distribution manifold. This measure is carried out with reference to each air conditioning zone. The desired ventilation and comfort properties are achieved by addition of further recirculation air in a second stage. Splitting or separating the recirculation into stages in this manner allows a reduction of the air duct cross-sectional sizes and the associated weight of the air ducts between the stages. However, the danger of ice accumulation with the associated danger of air duct blockage is not completely avoided, because the first air mixing stage is only provided downstream of the air distribution stage. This is true for both normal operation as well as failure or fault mode operation.
In the event of a failure of one recirculation unit, the supply of air provided by the still-operable second recirculation unit cannot compensate for this failure of the other recirculation unit. Moreover, in this context, the air conditioning unit outlet temperature remains limited to above the freezing point, just as in the above discussed Airbus A300-600 and A310 aircraft. In order to compensate for the loss of cooling energy, the only solution is to increase the mass flow of energy-rich engine bleed air, which leads to an increased fuel consumption.
Efforts have been made to avoid this above mentioned disadvantage in the Airbus A340 and A320 aircraft, in that the entire cooling and recirculation air is collected or pooled together in a common mixing unit. In that manner, a high failure redundancy is achieved to allow a fault tolerant or emergency operation in the event of cooling air and/or recirculation air supply failures.
In view of the above described conceptual basis, it is apparent that icing of the cooling air supply ducts within the pressurized fuselage will not be avoided, and complicated duct arrangements connecting to a mixing chamber as well as additional flow-influencing components will be necessary, in order to optimally configure and embody the mixing process. Moreover, a residual danger of icing in areas of air flow separation still remains and cannot be completely excluded. A further disadvantage is that rather large dimensions of the air duct cross-sections and a rather high weight of the air duct system are unavoidable, in comparison to the arrangement of the Boeing B747, in order to provide the entire required air conditioning air quantity for achieving the required ventilation and comfort characteristics, in a central mixing chamber and then to supply and distribute this air from the common central mixing chamber to the several separate zones.
As a further development, the Boeing B777 aircraft to some extent realizes a combination of the systems of the Boeing B747 and the Airbus A340/A320 aircraft. Namely, the Boeing B777 aircraft uses a central mixing chamber, to which are allocated a first cool air supply with a constant recirculation air admixing and a second cool air supply without a constant recirculation air admixing. To complete the air flow in order to achieve corresponding required ventilation and comfort properties, a further constant recirculation air quantity is locally admixed into the previously mixed air described above. However, the second cool air supply without the recirculation air admixing suffers the above mentioned disadvantages of duct icing, or more directly the resultant temperature limitations of the air and the associated cooling energy losses that are necessary for avoiding duct icing. Also in the event of a failure of the recirculation air admixing into the cooling air
Buchholz Uwe Albert
Scherer Thomas
Airbus Deutschland GmbH
Doerrler William
Fasse W. F.
Fasse W. G.
Zec Filip
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