Water weight from condensation can be a big problem for airliners, especially as flights get longer and load factors get higher. According to Swedish-based CTT Systems, each passenger exhales around 100 grams of water per hour, so 300 souls on board breathe out 30 liters per hour for up to 17 hours at 2.2 pounds per liter. You can say that the aircraft took off with all that weight, so what’s the big deal?
Well, that moisture rises with warm air to the crown of the fuselage, above the cabin ceiling. At 35,000 feet, when it contacts the minus-54-degree C aircraft skin, a lot of frost forms. That frost melts on descent into warmer air and gets sopped up by the insulation blankets. So, all that water weight that the passengers happily shed on a long flight pads the aircraft’s love handles—not good for fuel consumption and carbon emissions. Not to mention issues of mold, corrosion and possible water damage to wiring, much of which runs through the space above the cabin.
Swedish-based CTT Systems’ Anti-Condensation System sucks up the moist air from the crown area or cargo area and divides it into two airstreams. The first feeds past a slow-moving silica-gel rotary drum to absorb humidity. A specially designed “piccolo” duct, (with regularly spaced holes; like the instrument) releases the now-dry air between the ceiling panels and the external skin of the aircraft.
Electric heaters warm the second airstream before it, too, passes by the silica-impregnated rotor. This heated air sucks up the absorbed moisture from the gel and jettisons it overboard via the aircraft’s air-recirculation system or through the outflow valve.
In tests, three CTT-equipped easyJet Airbus A320s each “lost” more than 440 pounds in three months. As with most diets, when the Anti-Condensation Systems – which have an installed weight of 64 pounds – were deactivated over the next three months, those pesky pounds came right back. As part of the tests, there was also a 40 percent reduction in unscheduled antenna, sensor and computer replacements per 1,000 flight hours.
According to CTT, “For an Airbus A320 or Boeing 737, a [440-pound] weight reduction translates into … a 0.4 to 0.6 percent reduction in fuel consumption. It also reduces CO₂ emissions by more than 65 [metric tons].”
One less-mainstream but interesting application of the technology is on a Boeing 747SP operated under an 80/20 partnership between NASA and Germany’s Stratospheric Observatory for Infrared Astronomy (SOFIA) to observe outer space. Operating at altitudes above atmospheric water vapor (which absorbs infrared radiation), the 747 carries a telescope mounted under a large upward-opening door in the fuselage. On long missions (up to 12 hours), the telescope is exposed to extremely low temperatures. The delicate surface of the primary mirror might be damaged by condensing moisture during descent.
For this application, CTT Systems developed an oversized version of the Anti-Condensation System, which is activated several hours before the end of the mission to warm the air and achieve a safe dew point. It stays on several hours after landing so the telescope remains dry as it assumes ambient surface temperatures.