cabin air quality

[skua]

Having spent much of the last week de-hydrating at FL350-370, I pondered why cabin air cannot be humidified. Is it:

1. because it would screw up the electrics? or
2. because the water required would constitute an unacceptable weight penalty?

[Capt Sheepdip]

Assuming that the occupied space in your 747-400 is about 500 cubic metres, and that the air is changed 10 times each hour gives a fresh air input rate of 5000 cubic metres per hour. To humidify this outside air to a nice comfortable 50% relative humidity at about 22 deg C would require 60kg of water per hour. Would this screw up your logistics?
You cannot use spray or ultra sonic humidifiers because they would allow all the dissolved salts within this water to enter your cabin, and there would be a high risk of bacterial infections such as Legionella.
Due to this you have to use electrical energy to vapourise the water and I reckon this would require about 40kVA of power. That's about 100A from a 400V bus. Unless you can spare this I guess you have to stick with the moisturiser or go back to the damp conditions of the Fleet Air Arm!

[Jump Seat Rider]

I'll ponder over this question on my next 12 hour flight, which is on Sunday

[exeng]

Some aircraft do have cabin air humidifiers, or did at any rate. The 747 classic was one, however they were not thought to be that effective and reliability was a problem. On that A/C there were 2 dedicated to the pax cabin and one 1 to the flight deck. The flight deck humidifier was a fairly frequent cause of 'smoke on the flight deck'.


Regards
Exeng