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Air Conditioning System In Aircrafts  
User currently offlineJm-airbus320 From Jamaica, joined Aug 2000, 304 posts, RR: 0
Posted (13 years 2 months 4 days 3 hours ago) and read 5019 times:

Does anyone know exactly how these systems work?

21 replies: All unread, jump to last
 
User currently offlineRAAFController From Australia, joined May 2001, 125 posts, RR: 0
Reply 1, posted (13 years 2 months 4 days 3 hours ago) and read 4783 times:

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


User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 2, posted (13 years 2 months 3 days 23 hours ago) and read 4754 times:

Do you mean how an AC PAC operartes?

JET


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 3, posted (13 years 2 months 3 days 16 hours ago) and read 4734 times:
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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.




User currently offlineKatekebo From United States of America, joined Apr 2001, 702 posts, RR: 6
Reply 4, posted (13 years 2 months 3 days 12 hours ago) and read 4716 times:

There is a good description at Boeing site
http://www.boeing.com/commercial/cabinair/


User currently offlineFBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 7
Reply 5, posted (13 years 2 months 3 days 11 hours ago) and read 4700 times:

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"!
User currently offlineCdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 27
Reply 6, posted (13 years 2 months 3 days 11 hours ago) and read 4698 times:

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


User currently offlineRAAFController From Australia, joined May 2001, 125 posts, RR: 0
Reply 7, posted (13 years 2 months 3 days 6 hours ago) and read 4683 times:

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.


User currently offlineJT-8D From United States of America, joined Dec 2000, 423 posts, RR: 3
Reply 8, posted (13 years 2 months 3 days 5 hours ago) and read 4676 times:

RAAF, it is obviously not well researched..JT

User currently offlineCdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 27
Reply 9, posted (13 years 2 months 3 days ago) and read 4671 times:

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


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 10, posted (13 years 2 months 2 days 23 hours ago) and read 4666 times:
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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.

User currently offlineJT-8D From United States of America, joined Dec 2000, 423 posts, RR: 3
Reply 11, posted (13 years 2 months 2 days 19 hours ago) and read 4667 times:

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

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 12, posted (13 years 2 months 2 days 19 hours ago) and read 4655 times:
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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


User currently offlineJT-8D From United States of America, joined Dec 2000, 423 posts, RR: 3
Reply 13, posted (13 years 2 months 2 days 19 hours ago) and read 4651 times:

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

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 14, posted (13 years 2 months 2 days 18 hours ago) and read 4647 times:
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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


User currently offlineJT-8D From United States of America, joined Dec 2000, 423 posts, RR: 3
Reply 15, posted (13 years 2 months 2 days 18 hours ago) and read 4647 times:

Different planes, differant terms. I meant the valve that diverts the air away from the acm. Thanks for the info..Jt

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 16, posted (13 years 2 months 2 days 18 hours ago) and read 4651 times:
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Yes, that's the Turbine By-pass Vlv

User currently offlineRAAFController From Australia, joined May 2001, 125 posts, RR: 0
Reply 17, posted (13 years 2 months 2 days 17 hours ago) and read 4651 times:

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


User currently offlineJT-8D From United States of America, joined Dec 2000, 423 posts, RR: 3
Reply 18, posted (13 years 2 months 2 days 13 hours ago) and read 4644 times:

Raaf, stick around. All are welcome..JT

User currently offlineTom775257 From United Kingdom, joined Dec 2000, 153 posts, RR: 0
Reply 19, posted (13 years 1 month 4 weeks 1 day 19 hours ago) and read 4620 times:

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


User currently offlineJT-8D From United States of America, joined Dec 2000, 423 posts, RR: 3
Reply 20, posted (13 years 1 month 4 weeks 1 day 7 hours ago) and read 4609 times:

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

User currently offlineJT-8D From United States of America, joined Dec 2000, 423 posts, RR: 3
Reply 21, posted (13 years 1 month 3 weeks 5 days 11 hours ago) and read 4571 times:

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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