Aeronautics and astronautics – Aircraft structure – Passenger or crew accommodation
Reexamination Certificate
2001-06-20
2002-12-10
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft structure
Passenger or crew accommodation
C244S119000, C244S121000
Reexamination Certificate
active
06491254
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for controlling the environment within an enclosed space. More particularly, the present invention relates to an environmental control system for providing controlled ventilation of the interior space of an aircraft body, such that interior condensation and corrosion is reduced, cabin air quality is improved, the cabin can be humidified to healthy levels without increasing condensation and associated deleterious effects, and envelope fires can be directly suppressed and vented.
BACKGROUND OF THE INVENTION
In the embodiments of the invention described below and illustrated in the appended drawings, the “body” of an aircraft is comprised entirely within the fuselage, and excludes the wings and tail surfaces, as well as those portions of the nose and tail cones which extend beyond the respective nose and tail pressure bulkheads. However, it will be understood that the present invention is equally applicable to other aircraft geometries (such as, for example flying wing and lifting body designs). Thus in general, and for the purposes of the present invention, the “body” of an aircraft will be considered to be that portion of the aircraft which is pressurized during normal cruising flight, and within which it is desirable to control the environment in order to enhance safety and comfort of passengers and crew.
For the purposes of the present invention, the body of an aircraft is considered to be divided into a cabin, one or more cargo bays, and an envelope which surrounds both the cabin and the cargo bay(s). The terms “cabin” and “aircraft cabin” shall be understood to include all portions of the interior space of the aircraft which may be occupied during normal flight operations (i.e. the passenger cabin plus the cockpit) The term “envelope” shall be understood to refer to that portion of the aircraft body between the cabin (and any cargo bays), and the exterior surface of the pressure shell (including any pressure bulkheads) of the aircraft. In a conventional jet transport aircraft, the envelope typically comprises inter alia the exterior fuselage skin; nose, tail and wing root pressure bulkheads; insulation blankets; wire bundles; structural members; ductwork and the cabin (and/or cargo bay) liner.
The term “ventilation air” is defined as outside air typically introduced as bleed air from an engine compressor. For the purposes of this invention, “ventilation air” shall be understood to be outdoor air brought into the cabin by any means, for example, engine bleed air, either with or without filtering. “Ventilation air” does not include recirculation air or cabin air, filtered or otherwise reconditioned, which is supplied back into the interior space of the aircraft. For the purposes of this invention, “recirculation air” shall be understood to comprise air drawn from the interior space of the aircraft, possibly conditioned, and then returned to the cabin.
To facilitate understanding of the present invention, the following paragraphs present an outline of condensation/corrosion, air quality, and fire problems encountered in typical jet transport aircraft, and conventional measures taken to address such problems.
Moisture Condensation Problems
Aircraft are subjected to sub-zero temperatures (e.g., −50° C.) when flying at cruising altitudes. While the aircraft skin is slightly warmer than outside air due to air friction, temperatures behind and within the insulation blankets (particularly adjacent the skin) cool to 0° C. to −40° C., depending upon flight duration and altitude. When cabin air passes behind the insulation, it can reach the temperature at which its moisture starts to condense (i.e., its dew point). Further cooling beyond this temperature will result in additional condensation (as liquid water or ice) on the skin and other cold sinks.
Cabin air circulates behind the insulation, drawn through cracks and openings by pressure differences created when the cabin is depressurized during ascent for example, and during flight by stack pressures (buoyancy effect). Stack pressures are created by density differences between the cooler air behind the insulation and the warmer air in front of the insulation. The density difference creates a slight negative pressure in the envelope (relative to the cabin) near the ceiling of the cabin and a slight positive pressure in the envelope near the floor of the cabin.
The effects of this condensation range from a simple nuisance through increased operation costs to decreased aircraft life. The more an airplane is used, the greater its occupant density and the lower the ventilation rate per person, the higher its potential for condensation problems. Cases have been reported of water dripping from the cabin paneling. Wetting of insulation increases thermal conduction and, over time, adds weight, increasing operating costs. This condensation increases the potential for electrical failure. It can lead to the growth of bacteria and fungi. It causes corrosion, leading to earlier fatigue failure and reduced aircraft life. Some estimates place capital and maintenance costs attributable to such condensation at up to $100,000 annually for larger, heavily utilized passenger aircraft.
Conventionally, passive measures have been used to cope with the envelope moisture problem. These include anti-corrosion coatings, drainage systems, and deliberately maintaining cabin humidity well below American Society of Air-Conditioning Engineers (ASHRAE) Standard recommended levels.
U.S. Pat. No. 5,386,952 (Nordstrom) teaches a method for preventing moisture problems by injecting dehumidified cabin air into the envelope. However, the installation of dehumidifiers, as taught by Nordstrom, increases electrical consumption, occupies additional volume, and adds dead weight. Thus in a recently published study (“Controlling Nuisance Moisture in Commercial Airplanes”) Boeing Aircraft Company concluded that active dehumidification systems, such as those taught by Nordstrom, are not cost-effective, even though they can reduce moisture condensation within the envelope. Additionally, the dehumidification system taught by Nordstrom is incapable of addressing related cabin air quality issues, as described below.
Cabin Air Quality
Relative humidities above 65 percent which commonly occur in aircraft envelopes for even relatively low cabin humidities can support microbial growth under appropriate temperature conditions. Such growth can include Gram-negative bacteria. yeasts and fungi. Where sludge builds up anaerobic bacteria may grow, producing foul smelling metabolites. Saprophytic microorganisms provide nutriment for Protozoa. Exposure to aerosols and volatile organic compounds (VOCs) from such microbial growth can result in allergenic reactions and illness.
The relative humidity of outside air at typical cruising altitudes is frequently less than 1-2% when heated and pressurized to cabin conditions. Consequently, since cabin air normally is not humidified, on longer flights some passengers may experience dryness and irritation of the skin, eyes and respiratory system, while asthmatics may suffer incidences of bronchoconstriction. High air circulation velocities compound this problem. While humidification of the cabin air during flight would alleviate the “dryness” problem, it would also exacerbate the potential for microbial growth and damp material off-gassing in the envelope.
Thus, although it would be of benefit for health purposes to maintain higher cabin air relative humidities which are within the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Standard, this is made impracticable by the envelope condensation problem.
Other air contaminants in aircraft causing sensory irritation and other health effects can originate from ventilation air, passengers, materials, food, envelope anti-corrosion treatments, envelope microbial growth, etc. Ventilation air contaminants originate outdoors and within the engine (when bleed air is used). Potential contaminant gases
McNeil Campbell S. L.
Mitalas Gintautas P.
Preston Keith F.
Walkinshaw Douglas S.
Barefoot Galen L.
Hoffman Wasson & Gitler
Indoor Air Technologies Inc.
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