Does anyone understand how this is?
The normal jet aircraft air conditioning pack takes all the water out of the air.
The old B737-200/300 type had a bag type water separator, which just about worked when it was new, and then a 35degF sensor that kept the air above freezing to stop the remaining water freezing in the heat exchangers.
Later packs from B757/ B734/A320 onwards had really efficient water extractors which guaranteed that all the water was removed. The packs could then run down into Minus temps, and M15degC is not unusual. This greatly increased the efficiency of the pack. On the ground in the humid Middle East this was greatly appreciated.
But the air in the cabin was very dry as a result. Hunidifiers were tried on some long haul aircraft for the flight deck, but not very successfully.
Now long ago I remember flying on the Gulf Air VC10s, and when we descended into BAH the roof vents rained on us as we descended into the humid air of the Gulf. Not very nice! The VC10 had rootes blowers instead of engine bleed air to produce the air supply. The B787 has something similar, but electric powered instead of driven off the engine gearbox. Perhaps this is how they get more humidity in the cabin (but hopefully not too much!)
All this is OK below say 10000ft.
But 90pc of the B787 flying will be at 37000ft where the air is dry outside. Where will the more humid air come from? Will they carry water on board? Or is there something I don't understand?
Another point from the roll out show was the claim that the B787 can be more humid because carbon fibre does not corrode so much and aluminium aircraft must be kept dry!
Well I meet B777 that arrive from the Far East where it rains a lot. As they taxy in there is water draining out of all the fuselage drains. Water that was on the freight as it was loaded, and had drained into the bilges, and is now draining out as the aircraft has depressurised. If aircraft had to be kept dry, everyone would fit these Swedish Dryers that are advertised in Flight, but very few do.
Yours confused of Tunbridge Wells.