jm-airbus320
Posts: 294
Joined: Tue Aug 29, 2000 2:49 am

Air Conditioning System In Aircrafts

Thu May 31, 2001 10:51 am

Does anyone know exactly how these systems work?
 
RAAFController
Posts: 124
Joined: Wed May 30, 2001 9:50 am

RE: Air Conditioning System In Aircrafts

Thu May 31, 2001 10:58 am

On the older aircraft designs....such as 747 classics, feed/bleed air was brought from the engines. Ususally it is very hot so it is brought along the wing leading edge to serve as an anti-icing measure. The actual aircon unit is located behind the galley on the upper deck (ie where the roof gets very low). Here it is cooled and rehumidified (about 6% humidity, which is nothing). It is then pumped into the aircraft cabin through the various vents you see. To pressurise/depressurise the a/c there are valves at the rear of the fuselage which allow air to escape from the cabin (it gets sucked out due to the pressure diff during flight)

There is a myth that the air is simply recirculated. this is not true. Designs say the air should be totally replenished every 3 mins......don't ask me if this happens in reality.

Hope this helps
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Air Conditioning System In Aircrafts

Thu May 31, 2001 2:58 pm

Do you mean how an AC PAC operartes?

JET
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Air Conditioning System In Aircrafts

Thu May 31, 2001 10:42 pm

RAAFController,

Where did you get your information ?

On the 747 the air used for air cond is taken from either the 8th stage HP comp (hi pwr) or the 15th stg (lo pwr) of the engine (JT9). It then passes through a pre-cooler to reduce the temp to 350 degs F, followed by a pressure regulating valve to reduce the pressure to 45 psi. It now passes into the leading edge ducting (nothing to do with anti-ice) and travel down to the air cond bay located below the centre wing fuel tank.

In this compartment there are 3 air cond packs that work identically. The air enters the pack through a flow control valve (FCV)and passes through another heat exchanger into the compressor of an air cycle machine (ACM). Once compressed the air passes into yet another heat exchanger to cool it after being compressed. From there it goes through the turbine of the ACM where it is cooled futher. Now it goes through a water exctractor and into the cabin ducting.

After the FCV there is a tapping that allows some of the hot air to by-pass the ACM. This air is re-introduced d/stream of the ACM turbine to control the temp to that of the coolest cabin demanded temperatue

To adjust the air temp to that demanded by cabins that require a warmer temp there is a trim air system that takes a supply of hot air fron the pneumatic system and adds it as required to the distribution ducts going to the various a/c cabins.


 
katekebo
Posts: 678
Joined: Sat Apr 14, 2001 12:02 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 2:04 am

There is a good description at Boeing site
http://www.boeing.com/commercial/cabinair/
 
FBU 4EVER!
Posts: 980
Joined: Sat Jan 27, 2001 6:53 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 3:08 am

VC-10 has a very good description of how the aircond. packs operate,but haven't you got the 8th and 15th stages mislabelled?The lower the stage,the lower the power.At least that's how it works in "my" JT-8D Fuel to Noise Converters Smile
"Luck and superstition wins all the time"!
 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: Packs - Kate, VC10 Was Right

Fri Jun 01, 2001 3:18 am

VC-10 is right

High Stage used during low power steeings, Low Stage used during Higher power settings. Why...simple! Low stage puts out more than enough during higher power settings. The 8 and 9 comes off the High Pressure Compressor on the Jt9 engines. And for the most part most aircraft use High Pressure Compressor air for bleed air (B737 - uses 5 and 9 from HP compressor).

Cdf
 
RAAFController
Posts: 124
Joined: Wed May 30, 2001 9:50 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 8:06 am

VC-10,

The information came from a book called 'widebody'. Its a very interesting book on the histroy and development of the 747 and its foundations such as the 707 etc.

I can't vouch for its accuracy, but I would say that it is well researched. Other than the location of the air con pacs, and the argument over anti-icing measures or not, it does seem to agree with what you say.
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 9:02 am

RAAF, it is obviously not well researched..JT
 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 2:19 pm

RAAF....the information contained in that book is completely false. VC-10 was correct.
Basically, aircraft take bleed air from the engines and cool it. (using an Air Cycle Machine and Ram Air). I'm giving it to u as basic as I can!!

Trust me...whoever researched that probably asked a pilot!!

I'm Kidding
Cdf
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 3:42 pm

There is no argument about anti-ice, it's wrong. The closest the pneu duct comes to the L/E is about 3 feet - not very efficient for anti-iceing.
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 6:53 pm

I just reread all the posts and nobody answered the question yet. Im at work, and Ive got the time, so here we go. As stated above, bleed air is taken from the lower pressure bleed in flight, passed through a precooler that is cooled with engine fan air, then through the ducting to the airconditioning bay. Here it passes through the primary heat exchanger, cooled by ram air, then through the compressor side of the air cycle machine(looks like a big turbo charger). So its been cooled twice, and compressed slightly. Now it goes through the secondary heat exchanger then the turbine side of the air cycle machine. Now you have cooled it again in the heat exchanger, and the pressure drop across the turbine side cools it again by reducing the pressure. Interesting to think that you can get air at less than 30 deg.F from air that started at 400+ degrees? In flight, you dont need to cool it as much, so you divert most of the airflow around the ACM, to retain some of the heat. The ram air across the heat exchangers can also be reduced to control the temerature drop across them. The system also has a water seperator system, overheat protection and what is known as the 35 Degree system, to prevent ice from forming in the system. Widebodies and even some of the newer narrow bodies also use a system called trim air. To be honest, I have never truly understood how that system works, so I wont comment..JT
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 7:20 pm

The trim air system isn't that bad.

The pack produces air to the temp demanded by the coolest zone in the cabin. Now other compartments may require warmer air so a supply of hot air is taken from the pneu duct. This air passes through a Trim Air Regulating Valve which reduces the pressure to 4 psi above cabin pressure. The air now passes to a manifold off which there are a number of tappings, the number of tappings corresponding to the number zones in the a/c. The amount of air that passes into each tapping is controlled by a Trim Air Valve.

Now the Trim Air Valve position is controlled by the Zone Controller. The controller knows the actual zone temp and the demanded temp and from this will control how far open the Trim Air Valves will be. Logically then the Trim Air Valve for the zone that wants the coolest temp will be closed as the packs are delivering that temp while the other zones Trim Air Vlvs will be postioned some where between open & closed depending on the demanded temp.

Once past the Trim Air Vlvs the hot air is added into the distribution ducts for the repective zone.

Incidentally recirculated air has been mentioned. Only the pax cabin get this air, the Flt Dk receives 100% fresh air
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 7:25 pm

OK, that makes sence, but why is it nessasary? Why cant the temp be controlled by the mix valves alone? Is it a way of dividing the cabin better? ..JT
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 7:57 pm

By mix valves do you mean the Turb By-pass Vlvs on in the pack ?

If so on an a/c like the 747 you would then need a pack for each zone and there are 6 zones. It's a method of fine tuning the rqd air temp throughout the cabin
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 8:28 pm

Different planes, differant terms. I meant the valve that diverts the air away from the acm. Thanks for the info..Jt
 
VC-10
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Joined: Tue Oct 26, 1999 11:34 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 8:41 pm

Yes, that's the Turbine By-pass Vlv
 
RAAFController
Posts: 124
Joined: Wed May 30, 2001 9:50 am

RE: Air Conditioning System In Aircrafts

Fri Jun 01, 2001 9:11 pm

Thanks heaps JT-9D and VC-10. It is always good to find out the correct info. I wonder how many other things i believed (especially from that book) which are not as true as I would have hoped! The advantages of having a forum like this....someone always knows the whole story.

Thanks again. Maybe I shoudl stick to Military Aircraft???  Smile/happy/getting dizzy

Regards, Dave
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Air Conditioning System In Aircrafts

Sat Jun 02, 2001 12:47 am

Raaf, stick around. All are welcome..JT
 
tom775257
Posts: 141
Joined: Fri Dec 22, 2000 1:51 pm

RE: Air Conditioning System In Aircrafts

Mon Jun 04, 2001 7:05 pm

Hi y'all,
I didn't see anyone mention the catalyst sytem (but I could just be going blind), as far as I know at least in the larger Boeings (and I assume other aircraft) the hot bleed air is directed over a catalyst to remove Ozone before even the primary heat exchanger, by reacting 2 free radicals on 2x O3 molecules to give 3 02 molecules, hence not screwing up people's lungs at altitude.
Please correct me if I'm wrong! I am just a lowly wannabe.
Tom
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Air Conditioning System In Aircrafts

Tue Jun 05, 2001 6:51 am

Lol, wannabees are people too. I think you are right. I remember some discussion of that in class, but I was thinking about hops combining with barley, not ozone at the time. I think you are correct though..JT
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Air Conditioning System In Aircrafts

Fri Jun 08, 2001 3:22 am

VC-10, sorry, you did answer the question. Im not sure how I missed your post. Guess I was reading too fast?..JT

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