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B738HT
16th Sep 2014, 13:29
Question on the PACK NNC:
After pushing the TRIP RESET, if both the PACK lights keep illustrated, why we set R RECIRC FAN AUTO & L RECIRC FAN OFF?

We know that RECIRC FAN could reduce the packs' working load, I guess turn off the fan would reduce the warm air from E&E bay to cabin, but why not turn both L&R fans off?

cosmo kramer
16th Sep 2014, 16:30
We know that RECIRC FAN could reduce the packs' working load
Recirculation fans have no effect on pack workload. It's myth and poorly written in the FCOM.

With recirculation fans OFF, the airflow in the cabin is below what is required for certification, but it doesn't change the workload on the pack.

Had Boeing build the aircraft without recirculation fans, they would have had to make the pack deliver more airflow in order to make certification requirements.

Hence, the recirculation fans saves fuel (as written in the FCOM), compared to if the aircraft was built without recirculation fans.

In any case, recirculation fans off, doesn't increase pack load and subsequent fuel consumption (you won't find anything about increased fuel consumption in the MEL either). But if the aircraft is full, your cabin crew will most likely complain that they can't breathe in the cabin and ask you to turn the temperature down, even by normal temps (as they can't find any other reasonable explanation for the sticky air).

P.s.
My QRH have no mention of the recirculation fans in the pack trip off NNC. What 737 do you fly?

de facto
16th Sep 2014, 17:13
Each recirc fan recirculate half of the required amount of air in the cabin.
If the recirc fans were off,or non existent,the bleed demand would be higher since all air source to the mix manifold would come from the packs alone.

The right fan recirculates air from the cabin and the Equipment cooling exhaust.
By keeping the fan in auto,you maintain a minimum of air circulation therefore a cooler temperature...i understand it as a need of a light breeze in a hot summer day:O
The left is selected OFF as recirculating air from a closed pressurized air conditionning bay wouldnt seem to help cooling the cabin.

Kramer,i guess you dont fly the NG.

cosmo kramer
16th Sep 2014, 17:22
If the recirc fans were off,or non existent,the bleed demand would be higher since all air source to the mix manifold would come from the packs alone.
Nonsense... That is the myth I mentioned. It is exactly like I wrote in my previous post. Look in your mel for recirculation fans, and show me the extra fuel you need to carry (none, as there is no higher demand on the pack).

I do fly NG. The pack are fixed and always deliver the same output, no matter what the condition of the cabin is (recalculations fans on or off). Those flows are either normal flow or high flow.

Skyjob
16th Sep 2014, 17:26
Multiple versions of air conditioning systems in the NG gents...

6/7 and 8/9 are different from each other.

The reason for turning the left recirculation fan off is similar to closing shades, turning off galleys and IFE, opening flight deck door and opening the outflow valve: reduce any heat created inside the airframe and maximise all remaining available ventilation!

cosmo kramer
16th Sep 2014, 17:33
What I wrote applies to 600-900. Recirculation's fans are/fan is there, because without them/it (or off), the cabin airflow doesn't meet certification requirement.

If they are/it is on or off, doesn't change a thing about the output of the pack (which is always the same for the selected flow rate).

de facto
16th Sep 2014, 17:38
Kramer

Come on,you really think it would show a few kilos ,if that,of fuel needed int he MEL,really?:ugh:...from the AMM:
The purpose of the right recirculation fan is to recirculate the conditioned air from the collector shroud. This will reduce the requirement for bleed air taken from the engines for air conditioning to the passenger cabin.

Less bleed required,less? Think what you want of it.....
AMM:
S AUTO
With both packs operating in AUTO, each pack regulates to normal flow rate approximately 55 Ibs/min. This is the normal in-flight schedule. It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate. As cabin altitude increases, the pack valve is biased to supply a lower airflow rate.

Now if you fly the Ng..i suggest you read your QRH slowly again....until you get to the recirc fan part.

B738HT
16th Sep 2014, 21:29
I think the PACK TRIP OFF NNC is for B737-700, and I am talking about the 737-800.

galdian
16th Sep 2014, 23:28
Where I am on 73-8 the NNC is only headlined PACK and the recirc fan switching are items 9 and 10 of 17 steps.

cosmo kramer
17th Sep 2014, 00:08
Come on,you really think it would show a few kilos ,if that,of fuel needed int he MEL,really?...from the AMM:DeFacto, you are always such a wise ass... Do you really think they would have built in a heavy recirculation fan system, that requires maintenance and cost fuel every leg to carry, if the penalty was only a few kg of fuel of omitting it?

Thrust me, the packs have no clue what is going on in the mix manifold. Your AMM quote doesn't say otherwise.

Her is help to decipher your AMM, as it say EXACTLY what I wrote initially:

This will reduce the requirement for bleed air taken from the engines for air conditioning to the passenger cabin......as compared to if the aircraft had NOT been equipped with recirculation fans, as the higher amount of bleed air would have been necessary to meet cabin flow certification requirement.

This is the normal in-flight schedule. It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate...but requires a recirculation fan to meet desired cabin ventilation rate...

...aka if a recirculation fan(s) is/are not there, the desired (regulatory required rate for certification) will NOT be met.

Checkmate. You should ask the questions on this board and not answer them as you are usually wrong. But Keep backtracking, you never had a history of being able to admit fault. I don't expect you to do otherwise in this thread. :ok:

cosmo kramer
17th Sep 2014, 00:15
Yes, you are right that the recirculation fans are indeed in the checklist. I was looking at a an older version (800) QRH of my own computer. The points are indeed in my current company QRH as point 9 and 10, so it must be a added recently to the checklist.

Point 9/10 are AFTER it has been establish that BOTH pack have tripped and cannot be restored. So the purpose of the switching would be to remove a source of heating of the cabin.

B738HT
17th Sep 2014, 02:40
Would you like to tell me the exact difference between L&R RECIRC FAN, or which compartment the fans recircle?

de facto
17th Sep 2014, 06:54
Kramer,
I love to steer :mad: with you its hilarious,you seem to know my history..its not reciprocal and i hope you dont mind.
Please read my post slowly....and digest...then type.

Now if my posts are generally wrong,please excuse me..as still waiting for proof of it and I am not considering your inputs as facts and correct either.
If you prove me wrong with facts/docs rather than pure say then yes ill mea culpa anytime...even with you...

Yes, you are right that the recirculation fans are indeed in the checklist. I was looking at a an older version (800) QRH of my own computer
Glad we cleared that one early enough in the discussion.

Now back to the subject,

You write:Do you really think they would have built in a heavy recirculation fan system, that requires maintenance and cost fuel every leg to carry, if the penalty was only a few kg of fuel of omitting it?

I never said so...but as usual you put words in my mouth...they built it to meet the recirculation output of the packs up to the published service ceiling.
I said MEL may not reflect a fuel penalty as it may be really minimal..
Hence my reference of the AMM:
It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate. As cabin altitude increases, the pack valve is biased to supply a lower airflow rate.



You write:
If they are/it is on or off, doesn't change a thing about the output of the pack (which is always the same for the selected flow rate).
I never said the opposit, i said if the fans were off,more bleed output will be required for the packs to give their scheduled volume of air....this uses extra fuel,as minimal as it may be.

After i wrote:Quote:
If the recirc fans were off,or non existent,the bleed demand would be higher since all air source to the mix manifold would come from the packs alone.

You wrote:Nonsense... That is the myth I mentioned.

So Here form the AMM:
Recirculation System
The recirculation system uses a fan to move air from the passenger compart- ment to the main distribution manifold. This reduces the amount of air that the packs need to supply.
You understand that sentence?:ugh::ugh:

...aka if a recirculation fan(s) is/are not there, the desired (regulatory required rate for certification) will NOT be met.

I never said otherwise.

But if the aircraft is full, your cabin crew will most likely complain that they can't breathe in the cabin and ask you to turn the temperature down, even by normal temps (as they can't find any other reasonable explanation for the sticky air).

Well here im baffled....when the fans are off the air becomes sticky?
So you are saying that the recirculation fans remove humidity?
My ears are wide open.

de facto
17th Sep 2014, 07:03
B738HT Would you like to tell me the exact difference between L&R RECIRC FAN, or which compartment the fans recircle?


Recirculated air is drawn from the space in the air conditioning distribution bay by the left recirculation fan, the air is drawn through filters and is discharged into the mix manifold. It mixes with air from the packs or external conditioned air for distribution into the passenger compartment.

Conditioned air in a collector shroud is recirculated by the Right recirculation fan.
The shroud collects air from the passenger compartment exhaust grilles in the carpet risers and the equipment cooling exhaust.

cosmo kramer
17th Sep 2014, 08:40
Defacto, there is probably a reason that you can only find a job in China, A your technical knowledge, B your ability to read and C your attitude. Look at the thread history and who started to get personal. Thank you I do know how to read my manuals, which you obviously need help doing.

Glad we cleared that one early enough in the discussion
Actually that post was for Galdian, but I am glad to hear you can read a step-by-step 18 point checklist too. Well done! :D

I never said so...but as usual you put words in my mouth...they built it to meet the recirculation output of the packs(???) up to the published service ceiling.
As usual you are writing BS. The packs doesn't recirculate anything. And it has nothing to do with service ceiling. You are so full of crap, it unbelievable that you are truly a pilot. They are there to ensure sufficient airflow through the cabin at all levels. It has nothing to do with pressurization, the aircraft pressurizes fine without Recirculation Fans!! They are simply there to move the air around in the cabin, because otherwise the air is not moving fast enough to meet certification requirements.

I never said the opposit, i said if the fans were off,more bleed output will be required for the packs to give their scheduled volume of air....this uses extra fuel,as minimal as it may be.
Ahh backtracking started. "You never said that" :ok: Except, get it into your head that the packs deliver more than enough from the get go to pressurize the aircraft. Their scheduled volume of air is sufficient, only with RFs off the air won't move around in the aircraft at the required (for certification) flow rate.


As I started out, the cause of this myth, is the poor wording of Boeing. Or rather the wording is ok, but they don't complete the sentence.

The recirculation system uses a fan to move air from the passenger compart- ment to the main distribution manifold. This reduces the amount of air that the packs need to supply.
...compared to an aircraft built without RFs, as such an aircraft would have been required to have the packs supply a higher output to keep the air moving fast enough to meet cabin flow rate certification requirements. A.k.a. to pump in more air and open the outflow valve more.

Well here im baffled....when the fans are off the air becomes sticky?
That's because you are less fortunately gifted, that this baffles you. When the air doesn't move (or moves too slowly), and you have close to 200 people breathing in and out, yes the air does become sticky. And the O2 level will go down. Kind of like classroom training and everyone looks sleepy (Defacto probably fast asleep), it usually helps to open the window 5 mins. Alas we don't have that option in a 737, so we have to have either packs in high flow (costs a lot of fuel) or have recirculation fans on.

de facto
17th Sep 2014, 09:18
Defacto, there is probably a reason that you can only find a job in China, A your technical knowledge, B your ability to read and C your attitude. Look at the thread history and who started to get personal. Thank you I do know how to read my manuals, which you obviously need help doing.

Already done my china tour but thanks!

The packs doesn't recirculate anything
Where did i write that they do??do you read english??

I wrote the FANS help the required recirculation output of the packs to meet the packs cabin scheduled flow rate to the optimum of 55 lbs/min in AUTO and that obviously to its max ceiling.

The air that is recirculated come from the packs,no???

Here again what i wrote earlier from the AMM:
With both packs operating in AUTO, each pack regulates to normal flow rate approximately 55 Ibs/min. This is the normal in-flight schedule. It provides optimum airplane performance, but requires a recirculation fan to meet de- sired cabin ventilation rate. As cabin altitude increases, the pack valve is biased to supply a lower airflow rate.

They are there to ensure sufficient airflow through the cabin at all levels.

Correct except when the air recirculated from the fans is missing,the packs need to provide more air to to the mix manifold?right?you understand that?

Again i never wrote recirc fans are for pressurization!!!you are an idiot.
I wrote fans air input to the mix manifold help packs in providing airflow to the cabin,packs are there for the pressurization.

When the air doesn't move (or moves too slowly), and you have close to 200 people breathing in and out, yes the air does become sticky

If they are all full of:mad: like you for sure..:ok:
Cold sticky air ,awesome!
Listen to your CA,turn down the temp next time and your ACM will do the work of your lack of knowledge!

Alas we don't have that option in a 737, so we have to have either packs in high flow (costs a lot of fuel) or have recirculation fans on

Oh now you tell me.....
So I see,your aircraft are junk,you cant use packs in high,and you dont want to cool the cabin,then you wonder why its sticky indeed.....marvelous:D:ugh:

aveng
17th Sep 2014, 09:19
Correct me if I'm wrong, but isn't there a correlation with one pack off and the recirc switch position to putting the remaining pack in 'high flow' mode.

cosmo kramer
17th Sep 2014, 09:38
Already done my china tour but thanks!
Ahh, back at home in India? ;)

The packs doesn't recirculate anything
Where did i write that they do??do you read english??
here... (I do, apparently you have a problem remembering what you write):
they built it to meet the recirculation output of the packs

The air that is recirculated come from the packs,no???
No, it comes from the cabin and the E&E compartment.... Back to the manuals son.

I wrote the FANS help the required recirculation output of the packs to meet the packs cabin scheduled flow rate to the optimum of 55 lbs/min in AUTO and that obviously to its max ceiling.
I can't believe it. Ha ha, it's almost sad there you say it again, get it into your head. The Packs don't recirculate anything. And there is no such thing as a required recirculation output. Listen, you obviously have no grasp of these things. There is a required flow rate in the cabin, for cooling, odor control and maintaining reasonable O2/CO2 levels.

cosmo kramer
17th Sep 2014, 09:47
Correct me if I'm wrong, but isn't there a correlation with one pack off and the recirc switch position to putting the remaining pack in 'high flow' mode.
No, with one pack off, the other pack will always operate in high flow mode regardless of RFs switch position (with flaps up).

de facto
17th Sep 2014, 09:57
Their scheduled volume of air is sufficient, only with RFs off the air won't move around in the aircraft at the required (for certification) flow rate.

Correct,,what you dont seem to understand is that packs Air and recirc fans air are used to move this air around in the cabin...
Air from packs and recirfan meet in the mix manifold and then out into the cabin...wall risers for the packs to get cool dry ACM non sticky in.

We agree or not?

With fans off.....its fine/optimum until high cabin altitude when as the AMM states and posted here zillions time:As cabin altitude increases, the pack valve is biased to supply a lower airflow rate

You write that the packs..They are there to ensure sufficient airflow through the cabin at all levels.

What in the sentence above from the AMM are you not able to grasp???:ugh:

AIRFLOW(packs and or recirc fans) RATE IS DIRECTLY LINKED TO RECIRCULATION RATE!!!!!!

cosmo kramer
17th Sep 2014, 10:08
I'll admit to one "error" and that is the choice of word "sticky". English is not my first language of the 5 I speak. "Stuffy" would perhaps have been a better choice. :ok:
It's like the air is standing still in the cabin (it won't be standing still, but move too slowly). Lowering the temperature won't help, except cold stuffy air seems more comfortable than normal temperature. Still the O2/CO2 levels will be uncomfortable (but not in anyway dangerous), which may make pax and cabin crew tired/cause headache etc. Like I compared already, it's like being a lot of people in a small room without opening the window occasionally to let in fresh air.

I missed the backtrack of the century!
Ah, so now you tell me....
So I see,your aircraft are junk,you cant use packs in high,and you dont want to cool the cabin,then you wonder why its sticky indeed.....marvelous

In other words, the recirculation fans are only there for pax comfort. They change absolutely squad about packs output. Of course you can actively switch the packs to high flow, I prefer to leave the recirculation fans on. :ok:

de facto
17th Sep 2014, 10:10
Ahh, back at home in India?

Not sure what you mean by that,but no...
Quote:
they built it to meet the recirculation output of the packs


This meant that the recirculation fans are designed to help optimise the packs output(airflow) by adding its own airflow therefore an end result of an optimum (re)irculation in the cabin....more airflow..better ventilation.
Get it?
The air that is recirculated come from the packs,no???
No, it comes from the cabin and the E&E compartment.... Back to the manuals son.

Jesus christ....the air that is used to ventilate(recirculated inside the cabin to ventilate)comes from the mix manifold...this air is RECIRCULATED from the fans(yes cabin,E/E...) and the PACKS!!
Your air that the packs gave was reused by the recirc fans so yes it is recirculated!

cosmo kramer
17th Sep 2014, 10:16
You write the packs..
They are there to ensure sufficient airflow through the cabin at all levels.

No, I wrote that "the Recirculation Fans are there to...", not the pack.

Man, you're confused.:D



As cabin altitude increases, the pack valve is biased to supply a lower airflow rate

...completely independent from position of recirculation fan switches. I don't know how you got those two thing mixed together.

Lord Spandex Masher
17th Sep 2014, 10:34
What's the APU fuel flow difference, packs on, between recirc fans on and off?

How about engine fuel flow between recirc fans on and off?

Nada.

de facto
17th Sep 2014, 10:37
In any case, recirculation fans off, doesn't increase pack load and subsequent fuel consumption (you won't find anything about increased fuel consumption in the MEL either). But if the aircraft is full, your cabin crew will most likely complain that they can't breathe in the cabin and ask you to turn the temperature down, even by normal temps (as they can't find any other reasonable explanation for the sticky air).

Ok so the RF are off,you have sticky air...you say ****.
I tell you use the ACM to cool the cabin then you reply that you cant use packs in high.
I write that your aircraft are junk,you dont use high mode or cool the cabin....then you write:wait for it:
In other words, the recirculation fans are only there for pax comfort. They change absolutely squad about packs output. Of course you can actively switch the packs to high flow, I prefer to leave the recirculation fans on.
You must be high!:ugh:
You write the packs..
Quote:
They are there to ensure sufficient airflow through the cabin at all levels.
No, I wrote that "the Recirculation Fans are there to...", not the pack.

Ok here is your post:
As usual you are writing BS. The packs doesn't recirculate anything. And it has nothing to do with service ceiling. You are so full of crap, it unbelievable that you are truly a pilot. They are there to ensure sufficient airflow through the cabin at all levels. It has nothing to do with pressurization,

Mea culpa...your sentence started by a Subject "the packs"...to which after you used "TheY" and i read it as ..the packs..

completely independent from position of recirculation fan switches. I don't know how you got those two thing mixed together

Because you arent reading!!!
Cabin ventilation gets air (airflow) from recirc fans and packs via the mix manifold..right??
As cabin altitude increases,airflow of PACKS is decreasing below its optimum,the recirc fans airflow helps such ventilation to keep the cabin optimum ventilation.(yes in ventilation,there is recirculated air from the packs(indirectly i give you that,as it is reused/recirculated by the fans).

Get it?:rolleyes:

framer
17th Sep 2014, 10:47
English is not my first language of the 5 I speak.
You should ask the questions on this board and not answer them as you are usually wrong.
there is probably a reason that you can only find a job in China,
You are so full of crap, it unbelievable that you are truly a pilot.
That's because you are less fortunately gifted, that this baffles you.
Back to the manuals son.
Listen, you obviously have no grasp of these things.

There are two possibilities here:
1/ Cosmo is a troll
2/ There is someone out there flying unsuspecting passengers around who has serious identity based emotional issues.

If it is possibility 2 and you recognise it Cosmo, PM me and I will try to help. My father is a very intelligent man but due to certain childhood occurrences and a couple of unlucky breaks later in life he went down the very unhealthy road of finding his own ' self worth' , or 'value' , in being correct when others were wrong. It was very sad to watch but it is something that can be worked through. I have seen it first hand and the relief as the charade is dropped (over time ) is huge for the individual involved, a normal life can be lived.

If it is possibility 1, crack on mate, very very well done :)

de facto
17th Sep 2014, 10:53
Kramer for your records:

You wrote :
1)I write nonsense
2)Im a wise ass
3)i am wrong
4)I couldnt find a job due to my knowledge,ability to read and attitude.(that was a funny one as i spent quite a few years there)
5)I am writing bull ****
6)I am full of crap
7)If i am back in India,pejorative,condescending tone,,,i guess for the Indian pilots.
8)that im confused......yes i was with some of your sentences...

In turn i wrote that you are must be high and that you are an idiot.

Keep this in your files as a retrospect next time you preach someone about his verbal/written CRM skills.

de facto
17th Sep 2014, 10:54
Priceless,
Framer beat me to it:D

cosmo kramer
17th Sep 2014, 11:12
Thank you for your input Framer, I tend to respond like that when being insulted by nitwits... I see you are trying to put me in a bad light, I don't like your either. :ok:
When someone clearly in the wrong, uses ":ugh:", tells me to read my manuals, generally in a condescending tone and calls me stupid and an idiot, I fight back. Although more eloquently, thanks for highlighting the best ones. :p

Lord Spandex Masher, bang on the money!!! :)

Cabin ventilation gets air (airflow) from recirc fans and packs via the mix manifold..right??
As cabin altitude increases,airflow of PACKS is decreasing below its optimum,the recirc fans airflow helps such ventilation to keep the cabin optimum ventilation.(yes in ventilation,there is recirculated air from the packs(indirectly i give you that,as it is reused/recirculated by the fans).
Yes I "got it" from my first post in the thread:
Recirculation fans have no effect on pack workload. It's myth and poorly written in the FCOM.

With recirculation fans OFF, the airflow in the cabin is below what is required for certification, but it doesn't change the workload on the pack.

It seems like your backtrack is nearing it's completion. Now you just have to admit that....

If the recirculation fans are switched off:
1) The pack output doesn't change (obviously there will instead be less output from the mix manifold, which is what I have been saying all along)
2) Hence, there is no increase in bleed demand
3) Hence, there is no increase in fuel flow


Defacto:
If you prove me wrong with facts/docs rather than pure say then yes ill mea culpa anytime...even with you...
Really, last time I even provided you with photo evidence (the max altitude discussion). You just disappeared from the discussion. I assume you will do the same this time. :D

de facto
17th Sep 2014, 11:49
Aye aye aye aye:ugh:

The pack output doesn't change
WRONG,it has a scheduled output,an optimum but it reduces as the cabin goes higher.
Here is an explanation of how the pack reduces its airflow as cabin altitude increases.
Again AMM:
The high flow servo is selected when solenoid “B” is de-energized, low flow is selected when solenoid “B” is energized. As cabin altitude increases, a bellows expands and biases the servo spring balance to produce a lower airflow rate.
The recirculation help in this condition by increasing airflow,ventilation at higher cabin altitudes!

As cabin altitude increases,packs that need to keep as close to an optimum air flow,let more bleed into the upstream sense port.
More bleed means more fuel..as minimal as it is..



Really, last time I even provided you with photo evidence (the max altitude discussion). You just disappeared from the discussion. I assume you will do the same this time

How about it?you like to fly with close to max,at max or above? What was it?

cosmo kramer
17th Sep 2014, 12:02
As cabin altitude increases, a bellows expands and biases the servo spring balance to produce a lower airflow rate.
The recirculation help in this condition by increasing airflow,ventilation at higher cabin altitudes!
Do you even know what a bellows is? Trust me, the recirculation fans will not influence the packs in any way. The will continue their schedule no matter what you do with the recirculation fans... And it doesn't help to capitalize "wrong", it won't make you right.

Next time you fly, do the checks Lord Spandex Masher suggested. Maybe they are simulated in MSFS too. :ok:

de facto
17th Sep 2014, 12:35
The will continue their schedule no matter what you do with the recirculation fans...

Did i write that the fans influence the packs flow schedule directly?NO, but indirectly yes.

Was your comment :Quote:The pack output doesn't change right or wrong? Please tell me.

It was wrong and now you get it right?

Good,so now you agree the pack airflow rate decreases at high altitude (after all it is only the AMM).
What you dont get into your head is that a lower flow is sensed by the pack via these bellows as the pack is directly connected to the mix manifold.
As the fans are off,and the cabin is high,the pack flow rate (systematically/biased to reduce) as cabin increase,a lower flow is sensed by the pack which opens its upstream port to let in more bleed air....

I was looking for your max altitude thingy (which i hope you will explain where i was wrong and again im ready for mea culpa...by wrong i dont mean in disagreement with you,obviously) i found this about recirc fans in pprune...the poster "yeelep" is a mechanic on 737:
Question was:RMC, that's a poor justification for a couple of reasons. One, even with the recirc. fans on, the left pack is the source of air to the flightdeck. Two,the recirc. fans draw air through HEPA filters.
Quote:
On the other side of the coin can someone confirm that with the fans off no recirculation would mean a greater bleed offtake (slightly higher fuel consumption).
Yes.

Ill send him a message and maybe he can explain in simple terms and clearer i admit our issue here.

Skyjob
17th Sep 2014, 13:20
de facto and cosmo kramer, please, STOP having this stupid "I'm right and you're wrong" match on here.

You BOTH act like children not older than those in pre-school!

Keep it factual, provide evidence based proof to the conversation and refrain from having a dig at each other or others for that case.

A Professional Pilots Rumour Network has NO place for adolescent behaviour like you display here.

You are both providing the same quotes repeatedly, we've seen them, read them, and tried to digest your inputs, like we do those of others providing similar.

cosmo kramer
17th Sep 2014, 14:05
You are right Skyjob, to anyone reading this thread please accept my apologies of being sucked into discussing with that moron...

For the benefit of other reading the thread, a bellows is a small pressure sensitive bag. The 737 is a crude and much mechanical aircraft. And so is a bellows. Where exactly these are located, I won't play wise and say that I know. They could be on the pack in the pack bay and use outside air pressure to deduct the expected cabin altitude, or the could be remote from the pack (doubt it as according to DeFacto's quote, the bellows is connected with the servo spring).

Even if we were to assume that they are somehow sensing the pressure in the cabin, like DeFacto claims, it doesn't change a damn thing. :{ Since recirculation fans have nothing to do with pressurization, which I mentioned several posts back already. On or Off, the pressure remains the same in the cabin, outflow valve won't change position. Because the recirculation fans are not adding any air mass to the inside of the aircraft, neither are they removing anything when off.

In the most basic terms, the recirculation fans are like buying two standing fans, and placing them in the aisle of the aircraft. They are just there to keep the air in motion in the cabin.

de facto
17th Sep 2014, 14:36
Skyjob,
Keep it factual, provide evidence based proof to the conversation and refrain from having a dig at each other or others for that case.
As you will notice as you digest through our posts and kramer constant and latest insult above,that my posts are using technical information from the AMM rather than basic say.(not sure what other info i can use to explain my idea,.and yes Kramer the Pack assemply gets input from actual cabin altitude.Id send you pictures of the pack assemply diagram and its link to the mix manifold but the latest naming did it.

Im ready to be explained otherwise..maintenance input accepted,just not by arguments such as
recirc fans blow air in the cabin like in a car and packs pressurize the aircraft.

Im done here..as all i had to contribute was written on this subject.

cosmo kramer
17th Sep 2014, 18:33
I knew you would back out! :D

We can stop the guesswork, as I have a diagram too from the AMM:
http://s29.postimg.org/dahhlo4nb/image.jpg

The bellows do indeed have sense ports direct from the cabin. But as clearly visible it all takes place prior to the mix manifold. Hence, it is all exactly as I have been saying. The pack doesn't care what is going on in the mix manifold (I.e. If the recirculation fans are on or off).

The pack will deliver their fixed flow (biased for cabin altitude) and the outflow valve will adjust to maintain pressure accordingly.

The only responsibility of the recirculation fans is to... wait for it... recirculate the air in the cabin.

Skyjob
17th Sep 2014, 20:52
Having (after commenting on not to have a you're wrong I'm right match on here) taken the time to read through the AMM for my own reassurance of system knowledge and for the benefit of ALL readers here not having access to this document, the following extracts, make of them what you want:

AIR CONDITIONING - DISTRIBUTION - INTRODUCTION
Recirculation System
The recirculation system permits ventilation of air in the passenger cabin areas. The recirculation system decreases the use of engine bleed air. This enables better thrust management and decreases fuel consumption.


AIR CONDITIONING - DISTRIBUTION - GENERAL DESCRIPTION
Recirculation System
The recirculation system uses two fans to move air from the passenger compartment to the mix manifold. This system reduces the amount of air that the packs need to supply.

AIR CONDITIONING - RECIRCULATION SYSTEM - INTRODUCTION
Purpose
The recirculation system supplies air for ventilation. The use of cabin air for ventilation decreases the use of air from the engine bleed system.
General Description
The recirculation system collects cabin air to use with pack air in the distribution system. The distribution system supplies air to the passenger compartment area.
Operation
The recirculation fans are enabled when you move the RECIRC FAN switches to the AUTO position. Recirculation fan operation depends on air conditioning pack operation.

AIR CONDITIONING - RECIRCULATION SYSTEM - RECIRCULATION FAN
Functional Description
The recirculation fans pull air in from the passenger cabin and supply it into the main distribution manifold.
The right recirculation fan pulls in air from the collector shroud in the forward cargo compartment.
Floor grilles in the passenger compartment permit airflow into the collector shroud.
The left recirculation fan pulls in air from the distribution compartment.

cosmo kramer
18th Sep 2014, 01:43
Here is one more:
Recirculation
This part of the A/C system recycles approximately 50 percent of the cabin air for ventilation purposes. This reduces the quantity of fresh air from the pneumatic system for ventilation. The left and right recirculation fans and filters are the primary components.
So, it's great the system is there, as we would otherwise have poor ventilation of the cabin... same goes if you turn it off.

Skyjob
18th Sep 2014, 09:08
Cosmo, we ALL know it recycles the air, it's what it is designed for.
But similarly it reduces fuel by reducing output from the packs.
Not a direct correlation but an indirect effect of the system.

de facto
18th Sep 2014, 10:16
Skyjob,as i wrote:
Did i write that the fans influence the packs flow schedule directly?NO, but indirectly yes.
As of now,my boeing technical pilot source(boeing team) seems to agree that an increase in bleed demand for same thrust setting,(pack work load increases as less cool air into the manifold,therefore an indirect increase in fuel consumption due to the recirc fans off.
He will ask confirmation to his ops engineering and will get back to me in the morning.

Concerning the original question,why during both pack remaining illuminated,the kept fan is off and right fan is left in auto,he will confirm it tomorrow as well.

Concerning :It's like the air is standing still in the cabin (it won't be standing still, but move too slowly). Lowering the temperature won't help, except cold stuffy air seems more comfortable than normal temperature. Still the O2/CO2 levels will be uncomfortable (but not in anyway dangerous), which may make pax and cabin crew tired/cause headache etc. Like I compared already, it's like being a lot of people in a small room without opening the window occasionally to let in fresh air.

Boeing guy wrote:Selecting recirculation fan (s) off will result in lower cabin humidity levels, but the total fresh air remains unchanged unless the packs are selected to HIGH flow. Also, cabin temperature gradients may be affected by selecting the recirc fans off inflight. Selecting the recirc fans off may prevent the cabin air from circulating in the normal manner, creating pockets of slightly colder areas within the cabin. Selecting high flow will not necessarily improve this situation

framer
18th Sep 2014, 10:46
I'm surprised nobody has mentioned the Overboard exhaust valve.
You're at 10,000ft, doing 290kts, outflow valve open, cabin heating up, what would happen to the Overboard Exhaust Valve if the right Recirc fan was turned off?

cosmo kramer
18th Sep 2014, 11:59
But similarly it reduces fuel by reducing output from the packs.
Not a direct correlation but an indirect effect of the system.
The myth just won't die.

I'll make a video on my next flight. Absolutely nothing happens to the fuel flow when turning off the recirculation fans. It does however get quieter, because the air is no longer being recirculated! :eek:

de facto
18th Sep 2014, 12:41
what would happen to the Overboard Exhaust Valve if the right Recirc fan was turned off?

It will open,as the right recic fan as the function of smoke removal and the air pulled by the exhaust fan (cabin and E/E) will go out...instead of being directed around the forward cargo bay for heating..

I'll make a video on my next flight. Absolutely nothing happens to the fuel flow when turning off the recirculation fans. It does however get quieter, because the air is no longer being recirculated!
Please keep your video,the fuel consumption is so small it is useless.
Air is not being recirculated but is circulating....packs provide cabin conditioned air via the passengers center and side walls of the cabin.

Let's just see what boeing engineering has to say.

cosmo kramer
18th Sep 2014, 12:57
Please keep your video,the fuel consumption is so small it is useless.
So what exactly are we discussing here? :E
Then you agree?

de facto
18th Sep 2014, 13:06
Agree to what?
I said from the very beginning,as we were discussing about the MEL not reflecting it as a fuel penalty because of the negligeable amount.

cosmo kramer
18th Sep 2014, 15:49
Agree to what?
I said from the very beginning,as we were discussing about the MEL not reflecting it as a fuel penalty because of the negligeable amount.

Ok, from the AMM:
Recirculation
This part of the A/C system recycles approximately 50 percent of the cabin air for ventilation purposes. This reduces the quantity of fresh air from the pneumatic system for ventilation.

Do you really think a "negligible amount" of fuel, can compensate for 50 precent lack of ventilation?

de facto
19th Sep 2014, 09:40
B737HT,

Here is the answer from BOEING ENGINEERING on your PACK NNC question:
In the PACK NNC , the effect of the recirculation fans is optimized if only the right fan is operating because the fan motors are a heat source.

The left recirculation fan draws air from the area immediately around the mix bay while the right recirculation fan draws air from the "horseshoe duct" beneath the forward passenger cabin. Operation of the right recirculation fan promotes airflow through the grilles in the forward passenger cabin and better ventilation is achieved with the right fan than with the left.

Also,

The step to turn off the left pack may soon be removed as it already has been removed from the master QRH for the -800 that Boeing uses. Not sure when that will be sent to the operators.


Basically what i wrote in my post #3.

Now concerning the MYTH,non sense FCOM misinterpretation of extra fuel consumption by turning OFF the recirculation fans that Cosmo keeps on blabbing about,here what BOEiNG ENGINEERING via General ELECTRIC have to say:
According to GE and our flt ops engineering department there will be a slight increase in TSFC when the fans are turned off due to increased bleed air demand from the engines. Just as you expected.

Best regards,

Amadis of Gaul
19th Sep 2014, 14:09
Just out of idle (or morbid) curiosity, how many more pages do you guys plan on keeping this up?

cosmo kramer
19th Sep 2014, 16:34
What a credible source.. :D Just as credible as mine:
Dear Cosmo,
Just as you expected, there is of course no increase in fuel consumption with the recirculation fans off. They are only there to increase ventilation in the cabin. They do not add to the pressurization of the aircraft when ON, hence when turned OFF there is no change in the bleed demand.
Best regards
Your Boeing engineer
:p

framer
20th Sep 2014, 05:18
The difference being that the source of De facto's quotes are easily believable whereas it's hard to tell if you are purporting to present a real quote, or if you are being facetious and openly making up a pretend quote.
Which is it Cosmo? Have you been stumped by Boeing and GE saying there is an increase in TSFC and made up a "joke quote" in response or are you saying that your quote is genuine?

B738HT
20th Sep 2014, 17:17
Got it. Additionally, can we monitor the BITE test page of APU fuel consumption with recircle fans on/off on ground to check out you guys' discussion ?

Skyjob
20th Sep 2014, 18:31
Good idea B738HT, but that does not take into account the mentioned pressurisation of the aircraft having an effect on the bellows...

cosmo kramer
20th Sep 2014, 22:57
There is no difference in APU Fuel Flow with recirculation fans off.

However, there is a significant difference with one pack off (which I believe is common knowledge). The FF and EGT of the APU is higher when running one pack, instead of both.
E.g. left pack off to reduce cockpit noise during briefing, telephone calls etc. For the same reason I demonstrate this by opening the APU maintenance page in the FMC, to teach my colleagues to switch off the left recirculation fan instead, which leads to a similar decrease in noise levels.

The reason for this discussion is there is a common misunderstanding, that there is a significant increase in FF if the recirculation fans are switched off during flight. As a example in the above case - if switched off on ground and forgotten to be turned back on. The argument against it is sometime: "But they are not of any checklist to be caught if we forget to turn it back on. We might be using a lot of extra fuel.

The misunderstanding lies in that people think the packs (in auto), recovers the lack of 50% ventilation: They do NOT.

50% ventilation will be missing in the cabin, leading to the stuffy air mentioned, cold air pockets, lack of oxygen (not deadly levels mind you, but enough to cause discomfort) etc etc. The total oxygen in the volume of air inside the aircraft is normal, but it won't be distributed evenly, because the air locally is not moving fast enough. There will be no increase in fuel flow on the FF indicators, as can be easily demonstrated by turning the recirculation fans off during flight. Outflow valve won't move either. There will be a slight pressure bump (as seen on the cabin vertical speed descending for a very brief moment), because the velocity of the airflow is changing. All other parameters remain the same through out the switching: Outflow valve position, bleed duct pressure indication and FF - not the slightest change!

Anyway, SUPPOSE we assume that DeFacto is right (which I do not think he is, for the record), but anyway lets ASSUME:

It doesn't change the fact of what I mentioned so far. Recirculation fans on, or off, there is no measurable change in fuel flow on the engines. The FF indicators measure to 10 kg. Hence, EVEN if DeFacto would be right, that it has a tiny effect on the packs, it would be:

1) In the order of 5 kg pr. engine pr. hour (more would likely cause a rounding up/down in the last digit).

2) This TINY amount of fuel/increase in bleed air, would have NO WAY of recovering a 50% loss of ventilation.

3) Hence: The recirculation fans were NOT installed to save this TINY amount of fuel! They are installed to save the HUGE amount of fuel that would otherwise have been required, had the aircraft NOT been equipped with recirculation fans.

If they hadn't been installed at all, the packs would have needed to supply significantly more air to the cabin for ventilation, which would have resulted in a significant increase in bleed requirement and hence fuel. Otherwise the aircraft would not have met certification requirements for cabin ventilation:
FAR 25 section 831:
For normal operating conditions, the ventilation system must be designed to provide each occupant with an airflow containing at least 0.55 pounds of fresh air per minute.

THIS is the point I have argued all along. Frankly, it doesn't matter if DeFacto is right (which for the record, I still believe he is not) if there is a tiny insignificant increase in FF. In any case, all my points still stand. :ok:

Amadis of Gaul
20th Sep 2014, 23:01
Seriously, nobody cares.

cosmo kramer
20th Sep 2014, 23:30
Yet, you continue to comment. If you don't care, you are free to click on another subject. :ok: