For parched Dubai 2009 visitors here in the desert it is hard to imagine that excessive humidity could be an issue. But no matter what the local outside environment, it can soon become a problem inside an aircraft full of people, not only in terms of passenger and crew comfort, but also in terms of the amount of fuel burned in carrying the excess payload of water generated by condensation.
Each person on board an aircraft produces about 3.5 ounces of water per flight hour, so 400 passengers riding on an airliner for 10 hours could produce just over 109 U.S. gallons of water.
In September, the International Air Transport Association (IATA) acknowledged this dilemma when it included the Zonal Drying system developed by Sweden’s CTT Systems in its latest Technology Road Map report on methods for carriers to reduce fuel consumption. IATA listed Zonal Drying as one of 21 available technologies that it recommends its members to retrofit and said that this step alone could result in a 1-percent reduction in the amount of fuel burned. This is a significant endorsement at a time when airlines are facing both spiraling costs and the prospect of having to account for their carbon emissions through Europe’s new emissions trading scheme.
According to CTT (Stand W473), the elimination of unwanted humidity can also protect an airline’s bottom line by avoiding corrosion of the airframe and aircraft parts that can result in costly maintenance. This in turn can protect the asset values of a fleet.
At the same time, the atmosphere inside aircraft cabins and cockpits can actually have too little humidity, which can have a debilitating effect on those on board, worsening both immediate fatigue and the lingering effects of jet lag for passengers and crew. In a building on the ground the relative humidity would normally be between 50 and 60 percent, but in an aircraft at 33,000 feet this would drop to 5 to 15 percent because the outside air is extremely dry at that altitude and about half of the air inside is drawn in through the engines. To deal with this dilemma, CTT’s Cair system can be installed to work in tandem with the Zonal Drying system to ensure that the right level of humidity is maintained where it is needed in the aircraft, without generating excess condensation where it is unwelcome.
According to CTT vice president for sales and marketing Ulf Liljenberg, airlines in the Middle East, especially those keen to improve flying conditions for first- and business-class passengers, have shown strong interest in the Cair system. Similarly, Cair has also been selected for installation in more than 30 larger VIP aircraft. The need to create humidity is actually greater in aircraft cabins with relatively few passengers because there are fewer people to generate natural moisture.
The Zonal Drying system, consisting of a fan, a heater and a rotor, takes air from the aircraft atmosphere, removes the moisture from it and then blows it into the gap between the cabin and the aircraft skin. This creates a barrier of dry air which in turn dries out the aircraft’s insulation blankets that would otherwise be saturated with condensation.
At the same time, the relative humidity of the air coming into contact with cold surfaces is lowered, reducing condensation. Depending on the aircraft type, the Zonal Drying unit is installed either in the crown area at the top of the fuselage or beneath the cabin floor.
The Cair system works in tandem with CTT Zonal Drying system, using one or more humidifiers connected to a water supply. The humidifiers include a pad of fiberglass with specially designed, moistened air channels. When dry air passes through the moist surface of the pad the water evaporates and the air is humidified as it cools. The size of the pad is determined by the volume of airflow to be humidified, and by regulating the water supply and the temperature of the air as it reaches the pad, the system can run automatically. Minerals and other water contaminants are trapped in the pad. According to CTT, the risk of spreading bacteria through the system is minimal because the water evaporates as it transfers into the air and so cannot carry bacteria.
For aircraft cabins, the humidifier is installed in air supply ducts leading to the area to be humidified. CTT can also provide separate humidifiers to serve the cockpit and crew rest areas.
The Zonal Drying system is to be standard equipment on Boeing’s new 787, with two units to be installed in each of the new widebodies. Aircraft crew rest compartments will have humidifiers, and they can be an option in the cockpit. Zonal Drying is already available as buyer-furnished equipment on the new generation of 737 single-aisle airliners.
Last year, Airbus decided to offer both the Zonal Drying and Cair systems as optional supplier-furnished equipment (SFE) for the new A350. Crew humidifiers are already optional SFE for the larger A380.
Through supplemental type certificates, CTT either can now or will be able to
retrofit the equipment throughout the A320/330/340 family and on 747s, 777s, 757s and 767s. Liljenberg told AIN that the company would like to be selected to provide its technology as standard equipment on both Airbus and Boeing next generation single-aisle airliners. He said that even in the depressed conditions now facing the air transport sector, operators are interested in discussing Zonal Drying in particular, recognizing the way it could improve their balance sheets.