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Braybuddy
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Recycling Cabin Air

Tue Mar 22, 2005 11:55 pm

I think I remember reading somewhere that airlines recycle cabin air to save fuel. Is this true and how does it save fuel?
 
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Starlionblue
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RE: Recycling Cabin Air

Wed Mar 23, 2005 12:29 am

It is true. Some of the air is recycled. I can't think of how it saves fuel.
 
SlamClick
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RE: Recycling Cabin Air

Wed Mar 23, 2005 12:30 am

Re-using some of the already-conditioned air means you are taking less bleed air off the engines. Less bleed air equals less energy tapped off the engine for that purpose.

The air about to exhaust from the cabin is closer in temperature than the bleed air is, to what you want to pump into the cabin, so less work for the air cycle machines.

Everything the engines do for us burns fuel. They burn fuel of course, making thrust for us. They also burn fuel running generators, hydraulic pumps, and air bleed. There is no free energy. Using a 'recirc' mode reduces fuel burn measurably.
 
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Braybuddy
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RE: Recycling Cabin Air

Wed Mar 23, 2005 1:34 am

Thanks for the info. I travelled home from Sydney two weeks ago and have had a nasty chest infection since. I suspected it may be due to recycled air in the cabin.
 
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HAWK21M
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RE: Recycling Cabin Air

Wed Mar 23, 2005 1:39 am

Has there been any studies to compare the Pollution/CO2 levels in Cabin air between Recirculation fan cabins to non Recirculation fan cabins.
regds
MEL
 
Tod
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RE: Recycling Cabin Air

Wed Mar 23, 2005 1:46 am

Which commercial aircraft don't have recirc systems?
 
AvionicMech
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RE: Recycling Cabin Air

Wed Mar 23, 2005 4:22 am

It saves on fuel by switching the air-conditioning packs between high and low flow modes. For example on the 767 when you turn the right recirc fan off it puts the right pack into 'high flow' mode and vice versa for the left pack but you have to have both packs on for it to be in 'low flow' in the first place. If they are in high flow then there is obviously more bleed air demand on the engines which means more fuel burn.

There are lots of inputs into controlling the high and low flow of the packs such as if the flaps extending past 1 unit, will put them in to low flow to give the engines more power due to less bleed air demand, in case it is needed for a go-around. Also arming the cargo fire extinguishing system will put them into low flow so you don't give the fire more oxygen. Having an engine out also changes the high/low setting etc etc.

Hope that makes sense Braybuddy, if not I will explain it better.

Regards

Avionic Mech
 
troubleshooter
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RE: Recycling Cabin Air

Wed Mar 23, 2005 6:33 am

Quoting Tod (Reply 5):
Which commercial aircraft don't have recirc systems?

As far as I remember, the CRJ100/200 is not equipped with a recirculation system. It uses always fresh air.
 
ha763
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RE: Recycling Cabin Air

Wed Mar 23, 2005 1:05 pm

Quoting Braybuddy (Reply 3):
travelled home from Sydney two weeks ago and have had a nasty chest infection since. I suspected it may be due to recycled air in the cabin.

More likely due to aircraft having extremely dry air and close proximity to other passengers who may have been sick. You can do a search and find that the air in aircraft is replenished by fresh air more often than in buildings with air conditioning. This is a quote from a summary memo about a hearing conducted by the Subcommittee on Aviation of the US House Transportation and Infrastructure Committee about cabin air quality:

In addition, the World Health Organization (WHO) states,

“The quality of aircraft cabin air is carefully controlled. Exchange with outside air and filtration of recirculated cabin air provide a total change of air 20-30 times per hour. This level of ventilation is much greater than that in any building and ensures that contaminant levels are kept low. Modern aircraft recirculate up to 50% of cabin air. The recirculated air is passed through HEPA (high-efficiency particulate air) filters, which trap particulate material, bacteria, fungi and most viruses. Consequently, recirculated cabin air is very clean.”


http://www.house.gov/transportation/...viation/06-05-03/06-05-03memo.html

Quoting Troubleshooter (Reply 7):
Quoting Tod (Reply 5):
Which commercial aircraft don't have recirc systems?

As far as I remember, the CRJ100/200 is not equipped with a recirculation system. It uses always fresh air.

The 717 is also a 100% fresh air system.
 
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HAWK21M
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RE: Recycling Cabin Air

Wed Mar 23, 2005 6:06 pm

Quoting Tod (Reply 5):
Which commercial aircraft don't have recirc systems

What about the B732.
regds
MEL
 
FredT
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RE: Recycling Cabin Air

Wed Mar 23, 2005 11:02 pm

Furthermore, the recirculated air is typically filtered well enough for any contageous particles to be caught.

Cheers,
Fred
 
Tod
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RE: Recycling Cabin Air

Thu Mar 24, 2005 12:06 am

Quoting FredT (Reply 10):
recirculated air is typically filtered well enough for any contageous particles to be caught.

That's Boeing approach.

During the SARS problem, Boeing recommended continuing to run the recirc fans as long as the aircraft had been fitted with HEPA type filters.

Thanks MEL! Sure enough, no filters listed for the 732.
. . . .and thank you to Troubleshooter and Ha763!

Figured that might be the case, but I don't have AMM's for CRJ aircraft.

Happy trails,
Tod
 
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HAWK21M
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RE: Recycling Cabin Air

Thu Mar 24, 2005 12:59 am

Quoting FredT (Reply 10):
Furthermore, the recirculated air is typically filtered well enough for any contageous particles to be caught

Maybe the concern is CO2 increase.
regds
MEL
 
CRJ200Mechanic
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RE: Recycling Cabin Air

Thu Mar 24, 2005 5:55 am

Quoting Troubleshooter (Reply 7):
As far as I remember, the CRJ100/200 is not equipped with a recirculation system. It uses always fresh air

That is correct. They are always pushing out fresh air. Now if an engine fails, I'm not sure if the pack off the good engine will go into low flow or not. I don't remember them tells me that in CRJ school.
 
Newark777
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RE: Recycling Cabin Air

Thu Mar 24, 2005 10:26 am

There was an interesting article in the New Scientist this week about airplane recirculated air in relation to the SARS epidemic.

Better plane ventilation could cut spread of disease
19 March 2005
Andy Coghlan
Magazine issue 2491
Air should be circulated twice as fast in aircraft cabins during outbreaks of diseases such as SARS, according to a new review of passenger planes
AIR should be circulated twice as fast in aircraft cabins during outbreaks of diseases such as SARS, according to a review of how diseases spread on passenger planes.

The review challenges the prevailing notion that only passengers sitting within two rows of an infected person are at risk. This rule of thumb is based on the spread of tuberculosis aboard aircraft, but the review highlights a case in March 2003 when a single passenger with SARS infected 18 others (both confirmed and probable) on a flight from Hong Kong to Beijing (see Diagram). "This was just a three-hour flight, and some infected passengers were seven rows from the one passenger that had the disease," says team member Mark Gendreau of the Lahey Clinic Medical Center in Burlington, Massachusetts.


http://www.newscientist.com/article.ns?id=mg18524915.300

Harry
 
FredT
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RE: Recycling Cabin Air

Thu Mar 24, 2005 4:33 pm

Quoting HAWK21M (Reply 12):
Maybe the concern is CO2 increase.

As was stated above, you still get more fresh air per capita per time unit than in most buildings.
 
CosmicCruiser
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RE: Recycling Cabin Air

Thu Mar 24, 2005 7:13 pm

For the planes I've flown there is no recycled air. The MD-11 has ECON mode where the packs just operate in low mode and can be turned off in the event of a loss of packs. In animal charters where high flow and cold temps are required you fly with ECON OFF.
 
AA737-823
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RE: Recycling Cabin Air

Fri Mar 25, 2005 7:10 am

The 777 is also a 100% fresh air aircraft.

As far as other aircraft, I know that the 757 and 767 recirc is 50%. I don't think it's adjustable, either, unless the flight deck crew turns the recirc fans to OFF... I don't know why they'd do that. That's coming straight from the CBT (computer-based-training) program.

It's not uncommon for people to get sick on airliners, but it generally has more to do with LOTS of people in a SMALL space that come from a WIDE VARIETY of backgrounds. Think... ELEMENTARY SCHOOL CLASSROOM!!!
 
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HAWK21M
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RE: Recycling Cabin Air

Fri Mar 25, 2005 1:12 pm

Quoting AA737-823 (Reply 17):
The 777 is also a 100% fresh air aircraft.

What about the A330/340s & A380s.
regds
MEL
 
AA737-823
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RE: Recycling Cabin Air

Mon Mar 28, 2005 4:26 pm

The 330 and 340 design predates the 777 by nearly a decade. (first flight of 777 was 1995, and the A340 was what, 1987???)
I am pretty sure the Airbusses don't have 100 percent fresh air onboard.
 
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HAWK21M
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RE: Recycling Cabin Air

Mon Mar 28, 2005 5:56 pm

Is that a trend then....That later Models will opt for the 100% Fresh Air system.
regds
MEL
 
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Jetlagged
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RE: Recycling Cabin Air

Mon Mar 28, 2005 6:58 pm

Recirculation fans don't change the bleed flow requirement from the engine. They just stir up the air inside the cabin. This may become necessary when packs have a low flow or ECON mode. This means flow of air into the cabin is reduced, so some means of increasing the air flow around the cabin is required. It's a bit like the effect of a ventilation fan in a room.

The use of recirc fans in the 757 and 767 got a lot of bad press. This may be why newer aircraft have higher flow packs, thus not requiring recirc fans. They aren't anything new however. The 747-100 had four of them and didn't have half flow packs as designed.
 
Tod
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RE: Recycling Cabin Air

Tue Mar 29, 2005 3:08 am

Quoting AA737-823 (Reply 17):
The 777 is also a 100% fresh air aircraft.

Nope.

Right about door three, above the ceiling on the right is the fan and filter box.
 
Tod
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RE: Recycling Cabin Air

Tue Mar 29, 2005 3:12 am

Quoting Jetlagged (Reply 21):
It's a bit like the effect of a ventilation fan in a room.

It just gives the illusion of fresh air.

744 gasper system is 100% recirc from above the main deck, just aft of the upper deck.
 
DfwRevolution
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RE: Recycling Cabin Air

Tue Mar 29, 2005 8:20 am

Quoting AA737-823 (Reply 19):
The 330 and 340 design predates the 777 by nearly a decade. (first flight of 777 was 1995, and the A340 was what, 1987???)

The A340 was launched in 1987, but did not fly until 1992-1993. Don't know the exact date off the top of my head, but the A340 predated the 777 by less than half a decade.

Quoting AA737-823 (Reply 19):
I am pretty sure the Airbusses don't have 100 percent fresh air onboard.

Fresh air % isn't a function of new/old. The 757 has a notorious amount of recycled air, much more than the aircraft it replaced!

Also, there is more to air quality than just fresh or recycled. The 787 atmosphere will probably be the best flying because of its higher pressurization and cabin humidity.
 
dl757md
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RE: Recycling Cabin Air

Tue Mar 29, 2005 8:25 am

Quoting CosmicCruiser (Reply 16):
For the planes I've flown there is no recycled air. The MD-11 has ECON mode where the packs just operate in low mode and can be turned off in the event of a loss of packs

Actually, the MD-11 has 4 cabin recirc fans located in the ceiling above the cabin.

Quoting Tod (Reply 22):
Quoting AA737-823 (Reply 17):
The 777 is also a 100% fresh air aircraft.

Nope.

Right about door three, above the ceiling on the right is the fan and filter box.

That's one. There are 4 recirc fans on the 777. In addition to the one you mentioned, which is actually called the aft upper recirc fan, there is the fwd upper recirc fan located in the ceiling above the fwd door, and left and right lower recirc fans which are located in the mixing manifold aft of the fwd cargo compartment and ahead of the landing gear bay.

Quoting Jetlagged (Reply 21):
Recirculation fans don't change the bleed flow requirement from the engine. They just stir up the air inside the cabin.

Couldn't be any further from the truth. As stated in several other posts they do reduce the amount of bleed air needed because they reduce the volume of conditioned air needed and they eliminate the need to cool the air that has been recirculated at least from the 200deg C or so that it comes off of the compressor.

Dl757Md
 
Tod
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RE: Recycling Cabin Air

Wed Mar 30, 2005 1:02 am

Quoting DfwRevolution (Reply 24):
The 787 atmosphere will probably be the best flying because of its higher pressurization and cabin humidity.

Cabin humidity is a double edged sword.

For comfort and health, proper humidity is nice, especially on very long flights.
This is addressed with a flight deck humidifier on 747s, some also have a humidifier for the door 5 crew rest.

The down side of having a good level of humidity in the cabin is that you also have the same inside the ducting, causing stuff to grow more rapidly, offsetting the heath benefits by spewing mold and other yuck. To this end, some 744 operators has disconnected their crew rest humidifiers.
 
CosmicCruiser
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RE: Recycling Cabin Air

Wed Mar 30, 2005 1:23 am

Quoting Dl757md (Reply 25):
Actually, the MD-11 has 4 cabin recirc fans located in the ceiling above the cabin.

Not sure if that's true in the freighter ver. At least there's no mention of them in the A/C manual as part of the pneumatic/pressurization sys. nor is it taught . Still, air comes in/ air goes out.
 
Tod
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RE: Recycling Cabin Air

Wed Mar 30, 2005 3:01 am

When converting 742 and 743 to SF configuration, I've always removed all recirc and supplemental air systems.
 
B747FE
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RE: Recycling Cabin Air

Wed Mar 30, 2005 4:32 am

In the B747 classic pax configuration, the recirculation system provides a method for supplementing airflow to the main and flight deck. It consists of four 3-phase, 115 volt, 400-Hz AC recirculation fans plus another three supplemental air fans installed in aircraft with 1/2 flow pack valves.

In order to save fuel some aircraft were modified with 1/2 flow valves.
On the others and depending on certain factors, is an approved practice to use only two ACM's on cruise, closing the RAM Air Intake of the third one and therefore reducing the drag.
Recirculation fans are always on except Zone #1 (Flight deck). On long range flights I will turn them off periodically for brief periods of time (2-5 min) to refresh the entire aircraft air in the zones.

In Freighters and Special Freighters a fan is provided only for the flight deck.

Regards,
B747FE.
 
Tod
Posts: 1716
Joined: Sat Aug 28, 2004 6:51 am

RE: Recycling Cabin Air

Wed Mar 30, 2005 6:27 am

Quoting B747FE (Reply 29):
Special Freighters a fan is provided only for the flight deck

Do you happen to know where this fan is located?

cheers,
Tod
 
B747FE
Posts: 217
Joined: Mon Jun 21, 2004 11:09 pm

RE: Recycling Cabin Air

Wed Mar 30, 2005 7:48 am

Quoting Tod (Reply 30):
Do you happen to know where this fan is located?

Flight Deck Recirc. Fan is located behind a sidewall lining at the aft end of Bay 4, left side, lower forward cargo hold, if I remember correctly.
Location is slightly different in -300 and airplanes with 280 in. upper deck extension.

Regards,
B747FE.

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