Air Cycle Machine for the Home?

[washer111]

This is a hypothetical question. 

 

The system is what allows for aircraft airconditioning on the ground, using hot, high pressure air bleed from the engines, and thus no electricity. 

 

Liebherr have developed a unit for electric trains. It is unclear whether this is electrically driven or not, although I'd assume so. The group claim 20-40% decrease in "lifecycle costs" over traditional closed-loop, vapor cycle (i.e. R-22/410a based units). 

 

My question is whether such a system could be used in the home or commercial environment, and whether it is more efficient than a closed-loop system. The system is naturally a heating solution, with a mixing system to divert hot, compressed air to the turbine for expansion (and thus cooling). 

 

Benefits (Mostly for Consumer):

- Essentially no parts, aside from the compressor and turbine

- Uses the (free) atmosphere as the refrigerant

   - Leaks don't effect efficiency

   - Don't result in costly environmental damage (e.g. global warming), or replacement of precious gases

 

Negatives:

- Potential power usage (unknown)

- No profit can be made from parts; System is very simple and thus failure cannot be engineered readily into its design

 

Note: The systems seem to come in two varieties; the first being the traditional system where the air that undergoes compression and expansion is what you get blown at your face, as on an aircraft. 

The system Liebherr seems to push uses additional heat exchangers; where the air that is compressed, and/or expanded is used to heat or cool air passing over a heat exchanger. 

 

http://www.bahnindustrie.at/upload/dokumente/576/Liebherr_Air_Cycle_Technology_Leaflet_Sept_2010.pdf

(Image from http://thisisecs.com/2wheel.html)

[this post was last edited: 9/10/2015-06:33]

 

[tolivac]

BUT--------FUEL is burned to run the APU--Auxillary Power Unit-usually located in the tailcone of the airplane.Besides power the plane HVAC system while the plane is on the ground-the APU provides electircal power to power the planes systems while it is parked at the airport.While the plane is in flight the HVAC systems and electric power are then powered by the planes engines.As the plane is prepared for takeoff-all engines started and running-you will see a blink in the plane lights and momentary intterruption in the HVAC-this is the transition from the APU to the plane engines.Oh yes the APU also provides the air pressure required to start the planes "pimary" engine.Then the primary engine is running it is used to start the others.The APU is a small gas turbine engine.For some military airplanes it is contained in a GSU-Ground Support Unit,Start Cart,or "Huffer".
In the newest generation of airplanes-the "bleed" air from the APU or main engines simply runs another turbine-the bleed air turns an air turbine that power the planes air systems.This is for safety-to prevent any oil from failed or leaking engine seals and gasses from getting into the planes passenger and other occupied spaces.

 

[tomturbomatic]

Thank you for the excellent explanation, Rex and Washer111 and thanks, Washer111 for introducing the topic.! In years past, I have seen the ground support units in use and suspected that the blink was the transfer from that power source to the energy produced by the plane's engines once they were up and running. A companion on the Metro trip home was telling me about someone mentioning this system a couple of weeks ago, but he did not quite remember what was being explained and could not tell me more than it was simpler than regular air conditioning which made it more of a shame that Metro could not keep the cooling in the cars operating. I will print this out to show to him. Thanks, again.

 

[washer111]

That "blip" in the power is a normal occurrence. 

 

If my research serves correct, the only aircraft without this "blip" is the MD-90 (mostly used by Delta). It uses a unique system (VSCF, Variable Speed Constant Frequency) generator drive, with some sort of digital inverter system. However it works, it allows for a seamless transition between sources.*

 

Funnily enough, was watching an "Inflight Documentary" of the Thai DC-10, and you could clearly hear the "POP!" and cutout of the safety demonstration* as the engines were started

*This actually happened after the sound of wind blowing from someone with a life jacket. I found this amusing... 

 

[tolivac]

I beleive this cooling system was called "venturi cooling"It was used in some firefighters suits to keep the fire fighter cooled while in high temps.The suit was fed with compressed air-and the air passing thru the venturi gave a cooling effect.
Yes,the blip in the power and HVAC in passenger planes is of course normal.It can also occur if the airport is supplying the "GSU" thru an air hose going to the plane and power cables.The air is supplied by a VERY LARGE 40PSI air compressor(Atlas Copco makes them for this)and the power is 60 Hz power converted to 400 Hz.In older days the power was converted by a motor generator genset-now it a solid state convertor.The 40 PSI air supplies the HVAC and the main engine starting.The air starters on these can be rated up to so many hundreds of pounds of 40PSI air per minute.The portable starters would use a small jet engine-or a diesel engine running the compressor.
Yes,in newer airplane the "blips" may not be noticed because of the changes in technology-the hard switching replaced by solid state switching.
Suppose the problems with the venturi cooling is that it requires large amount of compressed air to operate-and compressing the air requires energy-and more so than a regular refrigeration compressor system.

 

[tolivac]

Metro car AC-remember an incident about an AC compressor unit in one of the Metro cars bursting-the compressor is under one of the large "4 seaters" on the Metro car.The blown compressor destroyed the seating unit-fortunately no one was sitting there!The compressors were replaced and redone by the Metro maintenance techs Was due to cracks in the compressors flywheels.

 

[whirlcool]

While I haven't been to 787 school, I did find this note about the Air Conditioning System on the Boeing 787. It may have the kind of system you are discussing here. I know it's electrically operated rather than bleed air operated.

http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_02_1.html

 

[tolivac]

EXCELLENT information on the Boing 787 Dreamliner's systems.Electrical starting and other systems replacing bleed air systems is a new direction.with modern solid state and electronic systems-this is now possible.Motors running at higher voltage and DC,and high frequencies redcues their weight.And with better perm magnet motors-this is also another way to reduce weight and improve efficiency and reliability.And with the electrics replacing engine bleed air-makes engines simpler.Just took more modern technolgies to do this.Wonder if this will become retrofitted on some older Boeing planes.Stay tuned.Like this approach.I knew things were changing-but the Boeing doco shows it!And this gives better redudency,too!

 

[whirlcool]

There were a lot of teething problems with the 787 when it first came out. It has a lot of batteries onboard to ensure smooth power. In early models some of those batteries have caught fire in flight. This lead to a short grounding of the plane while Boeing figured the problem out. They eventually did and have no more problems.

I don't think they'll retrofit older aircraft with the new system, but in anything new they come up with this is what they'll probably have. The 787 is just more than a step ahead in aircraft technology, it's a leap!

 

[washer111]

I agree the 787 is an interesting and advanced aircraft for our times. Although it seems Airbus erred (perhaps rightly?) on the side of caution, and kept more traditional systems in place, and avoided a lot of the Boeing's teething issues. 

 

One major problem on the 787 and its composite fuselage is apparently going to be fixing fatigue-related items going forward. Its not a straight-forward and simple as a traditional ribbed-aluminum skin, with the fuselage skin comprising of large, single pieces, as opposed to the smaller panels on the traditional airframe. 

Then there is the scrapping; which apparently carries huge costs due to government taxes. At least someone can benefit from the lack of beer cans(!) lol. 

 

[tolivac]

In a way the 787 system is what is old is new again-Beleive it was planes that used J79 engines used an electric starter-the starter required 400 or even 1000A @ 27VDC to roll the engine over and start it.This required a start cart that contained an engine-genset that developted the high amperage 27VDC to start the engine.A warning was on the planes dash telling pilots not to attempt to start the engine with the on board batteries.They couldn't provide the current.However-when that fighter plane was in the air-the starter motor then was a generator that provided 27VDC to run the planes electrics and charge the on board batteries.A small hole in the engines air intake nose cone provided cooling for the starter-motor.It was one of only a few engines that electric started in the older 1950's era military planes.That starter motor weighed in at over 80lbs.An air starter developing the same power was less than 30Lbs.Hydraulic starter can be even lighter-but strangely used on gas turbine stationary engines.The hydraulic power from a small tractor can start the engine.That starter is like the air one-only like 20 lbs in weight.But the air or hydraulic starter can't generate electric power.A seperate PTO and genrator on the engine is needed.The combo starter-motor can save weight with new technology.(787 system)
The scrapping of planes in the US does pay back--the aluminun,copper,other metals makes it worthwhile.A demolition excavator equipped with shear cutters can break down even a 747 plane in a matter of hours.Of course the ehgines are salvaged for reuse as stationary engines-for industrial and power generation.They are sold for this.Same with the metals and the electronics-often the seats are resold,too-for replacement in other planes or---furniture!I can remember an online website that sold furniture made from airplane parts.Desks made from wing parts,Airliner chairs resold as desk chairs and so on.So the scrapped plane can easily make a profit!But--Plane fans get saddened by the sight of the demo excavator working over the plane!It is cut and ripped apart!Could see where that could be depressing to some!Videos on YouTube show that.Same sort of thing when locomotives are taken down for scrap.