What is recirculation fan for?

[kuobin]

Hello everyone:
Most of commercial jets have recirculation installed,Is that just for fuel saving?or...Somebody say it can make cabin more humid?Does any know?:rolleyes:

[mondriver]

Well...does what it says on the tin really....

..re-circulates air.

(Either cabin air, or equipment cooling air.)

:ok:

[Charles Darwin]

Some fuel savings involved in this circulation.

[barit1]

Well, the recirc does save fuel by reducing the bleed air required from the engines, but it's still bleed air (via the a/c packs) that does the pressurization. Even on a 747, one engine can keep the cabin pressure up.
But to keep it well distributed (prevent stagnant spots for passenger comfort) you either need multiple packs running (with a lot of excess cabin air escaping via the outflow valve), or fewer packs with the recirc fan(s) running.

All this will change with the 787 though.

[rhovsquared]

Barit1, are you refering to the novel electric prssurization system? :ok:

anyone have more info about this system's philosophy?

[captjns]

It converts 115V AC into loud noise... especially in the cockpit.

[elpilote]

the recirculation fan suystem reduces the air conditionning system pack load and the engine bleed air demand. that's it

[nugpot]

The CRJ is one of the only airliners that does not use recirculation of cabin air. Small volume of cabin plus 2 engines suplying bleed air. Also, the CRJ is just a stretched Challenger and that had an even smaller cabin.

Although I have no statistical data, it is well known in my company that the incidence of pilots coming down with colds and flu is lower on the CRJ pool than on our other aircraft that uses recirculated cabin air.

[vapilot2004]

Recirculating Fan - (AKA Gasper Fan)

Also gives cabin inhabitants the illusion of incoming
air with packs off. And yes, this does add more humidity to the passenger cabin. Flight deck usually gets 100% outside air.:p

Barit1, are you refering to the novel electric prssurization system?

anyone have more info about this system's philosophy?

Not sure of exact scheme of air production - but I can tell you that the RR Trents for the 787 have 2 starter/generators fitted that combined generate 1/2 Megawatt from each engine.

RE:707 - Turbo-compressors - basically what it says - with the pressurized
inlet air isolated from engine air. This was done to ensure cabin air quality. At that time they thought the engines might spew kerosene fumes into the system in everyday operation.

[411A]

>>Re:707....At that time they thought the engines might spew kerosene fumes into the system in everyday operation<<

Sorta like the BAe146...yep, that's it:ugh:

Also, Re: B707, who can forget the turbo fan...and I don't mean the engines, either.

[rhovsquared]

Thanks VApilot2004... I guess only Rolls and Royce along with Mr. Boeing :} and God know the exact philosophy in that new design. Frankly in this case,
if it weren't Boeing; I wouldn't be going :D :\ :}

[VNAVSPD]

Recirculating Fan - (AKA Gasper Fan)


Are they really the same thing? Why does the 744 have both?

[vapilot2004]

Apologies VNAVSPD - sort of a terminology/technology gotcha the Gasper fan is. (old terminology, that is) :)

The Gasper fan blows air through the overhead vents (gaspers) even with packs off and also provided adequate and even temp airflow during limited pack operation.

Now we have a recirculating fan that more or less does the same thing - except that it provides airflow to the ceiling outlets, sidewalls and overhead vents thanks to a lighter, lower amperage,yet more powerful motor.

If I recall correctly, the purpose of the gasper fan on the 742 was to provide additional cool air flow (from the cold air plenum) to the passenger outlets during hot weather operations, while the recirculating fans could blow hot or cold.

[The Real Slim Shady]

On the 737NG the recircs draw air from the forward cargo compartment into the mix manifold to reduce demand on the packs.

On the Fokker 100 the recircs simply stir the cabin air: cabin air is drawn through roof filters and distributed via sidewall and floor outlets back into the cabin without going back into the air conditioning system.

[GLOBUSAIR]

Fokker 100 aircraft are renowned for cabin heat issues in the warmer months of the year. The system fitted to the aicraft is overpowering on the smaller Fokker 70 variant and underpowered on the Fokker 100. Stork are now offering a RECAS Upgrade program for the Fokker 100. Two powerful suction fans mounted on the very aft bulkhead of the aircraft draw warm air out of the cabin allowing the fresh cool air from the overhead vents to be more effective.

The results of this new system have been very good and when combined with the traditional options such as an external aircon unit and switchin off cabin lighting... the temperature in the cabin is perfect.

Not entirely on topic but interesting info i thought on the whole aircon/air thingy...