# Air Circulation and Filtration in Planes and Trains



## Devil's Advocate (Dec 14, 2021)

I have no problem with people taking their mask off in bedrooms, showers, and lavatories (and it's unenforceable regardless) but I do have a problem with the lack of robust HEPA-filtered ventilation. Hopefully future car and compartment designs will resolve this oversight. Not just for pandemics but for improved health of passengers by way of a reduction in airborne irritants and contaminants such as diesel exhaust, break dust, and solvent fumes.


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## Exvalley (Dec 16, 2021)

Devil's Advocate said:


> but I do have a problem with the lack of robust HEPA-filtered ventilation.


That's where the airlines have an advantage.


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## Qapla (Dec 16, 2021)

Exvalley said:


> That's where the airlines have an advantage.



Except that the train has a constant supply of fresh air that can be brought in while traveling down the tracks and the airlines recycle the air ... kind of hard to pull in fresh air at 30,000 feet.


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## Exvalley (Dec 16, 2021)

Qapla said:


> Except that the train has a constant supply of fresh air that can be brought in while traveling down the tracks and the airlines recycle the air ... kind of hard to pull in fresh air at 30,000 feet.


Huh? It's not hard at all to pull in fresh air at 30,000 feet. 50% of the air circulated in the cabin is from the outside. The other 50% that is recirculated is filtered through HEPA filters. The air in the cabin is renewed every 2-4 minutes.


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## Qapla (Dec 16, 2021)

Learn something new every day ... I don't think trains have to compress the air to make sure it has enough oxygen though.


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## west point (Dec 17, 2021)

Qapla: almost all aircraft built today get their new air from the engines. The engines are built to have a small portion of air from the compressor section. The is provided by automatic bleed air valves. The air is hot so it has to be cooled before going thru the air conditioning "packs". That bleed air is also sed for engine anti icing and wing and tail anti icing or deicing depending on design.

A few early jets DC-8s were one took the bleed air and ran it thru a turbo compressor that supplied cabin air. Guess there were worries of JTD4-various engine oil contaminating the bleed air.

Many newer jets also can use APU bleed air especially on the ground.


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## jis (Dec 17, 2021)

west point said:


> Qapla: almost all aircraft built today get their new air from the engines. The engines are built to have a small portion of air from the compressor section. The is provided by automatic bleed air valves. The air is hot so it has to be cooled before going thru the air conditioning "packs". That bleed air is also sed for engine anti icing and wing and tail anti icing or deicing depending on design.
> 
> A few early jets DC-8s were one took the bleed air and ran it thru a turbo compressor that supplied cabin air. Guess there were worries of JTD4-various engine oil contaminating the bleed air.
> 
> Many newer jets also can use APU bleed air especially on the ground.


The 787 does not use bleed air.


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## jis (Dec 18, 2021)

Moderator's Notes: Posts above this one were moved here from the following thread:






Mask requirements on Amtrak


The travel mask mandate has been moved from Jan 18 to mid March. https://www.cnet.com/health/mask-mandates-will-be-extended-through-mid-march-for-planes-and-more-what-to-know/ My trip is in April. What are the odds it will be extended again?




www.amtraktrains.com





Please feel free to carry on the discussion of this interesting subject here. Thanks.


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## west point (Dec 18, 2021)

jis said:


> The 787 does not use bleed air.


What does it use? I had ideas what would be better/


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## PVD (Dec 18, 2021)

they use an electrically driven system with the idea that it is more energy efficient an results in measurable fuel savings



AERO - 787 No-Bleed Systems


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## west point (Dec 18, 2021)

PVD said:


> they use an electrically driven system with the idea that it is more energy efficient an results in measurable fuel savings
> 
> 
> 
> AERO - 787 No-Bleed Systems



BOY! How much I wish my airplanes had that 787 system. Pneumatics used to drive pilots and also in my case inspections after depot checks. Trying to explain all the ducts would just get blank stares from some persons. Eliminating CSDs and IDGs also important since you had to check oil levels as they used engine oil and occasionally the oil could leak both ways to / from engine.

It appears that the electrical system works similar to modern AC traction locos. It does appear the inverters operate both ways? Inverters seem to have other names since they have more functions,

Hydraulics are simpler with just the total of 6 pumps including RAT. The L-1011 was crazy with a total of 4 systems with each being an engine driven pump. 2 on center engine. 2 pneumatic pumps, 2 electric pumps and a RAT. But if all 4 systems fail it is bye - bye CFIT. My electric pumps once had a problem of sucking air. Can you imagine operating with foamy hydraulic fluid and air in a hydraulic system? a


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## jis (Dec 18, 2021)

west point said:


> It appears that the electrical system works similar to modern AC traction locos. It does appear the inverters operate both ways? Inverters seem to have other names since they have more functions,


In the AC microgrid solar installation at my home the component that connects the backup battery to the AC microgrid is a number of what are called "microconverter". They convert from AC to DC when energy flows from the AC microgrid to the battery and when the energy flows the other way they convert from DC to AC. Of course each Solar Panel is attached to the microgrid through a microinverter.


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## UserNameRequired (Dec 19, 2021)

west point said:


> BOY! How much I wish my airplanes had that 787 system. Pneumatics used to drive pilots and also in my case inspections after depot checks. Trying to explain all the ducts would just get blank stares from some persons. Eliminating CSDs and IDGs also important since you had to check oil levels as they used engine oil and occasionally the oil could leak both ways to / from engine.
> 
> It appears that the electrical system works similar to modern AC traction locos. It does appear the inverters operate both ways? Inverters seem to have other names since they have more functions,
> 
> Hydraulics are simpler with just the total of 6 pumps including RAT. The L-1011 was crazy with a total of 4 systems with each being an engine driven pump. 2 on center engine. 2 pneumatic pumps, 2 electric pumps and a RAT. But if all 4 systems fail it is bye - bye CFIT. My electric pumps once had a problem of sucking air. Can you imagine operating with foamy hydraulic fluid and air in a hydraulic system? a



Personally, as a passenger on a 787, I found the lack of volume on the 787 ventilation most uncomfortable. More uncomfortable than any other commercial turbine aircraft I have rode on. Stuffy, hot, low volume from the vent was awful. The seats seemed like some of the smallest width too, which added to the discomfort. I was so happy to get off that thing. I normally tolerate to slightly enjoy commercial flying, but not the 787.


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## jis (Dec 19, 2021)

UserNameRequired said:


> Personally, as a passenger on a 787, I found the lack of volume on the 787 ventilation most uncomfortable. More uncomfortable than any other commercial turbine aircraft I have rode on. Stuffy, hot, low volume from the vent was awful. The seats seemed like some of the smallest width too, which added to the discomfort. I was so happy to get off that thing. I normally tolerate to slightly enjoy commercial flying, but not the 787.


Did this happen on all your 787 rides or on just one? Or on a specific airline on multiple flights?

Because I have not found these maladies in any of my two dozen flights on 787s. Maybe I have lower standards than you?


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## UserNameRequired (Dec 19, 2021)

jis said:


> Did this happen on all your 787 rides or on just one? Or on a specific airline on multiple flights?
> 
> Because I have not found these maladies in any of my two dozen flights on 787s. Maybe I have lower standards than you?


Just one, British Airways. If I have to ride another, I will but apprehensively. I suppose it could have been the way the crew configured the system for that particular ride? I did choose lowest cost seats but did not like the lack of volume of air coming from the vents.


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## Devil's Advocate (Dec 20, 2021)

UserNameRequired said:


> Personally, as a passenger on a 787, I found the lack of volume on the 787 ventilation most uncomfortable. More uncomfortable than any other commercial turbine aircraft I have rode on. Stuffy, hot, low volume from the vent was awful. The seats seemed like some of the smallest width too, which added to the discomfort. I was so happy to get off that thing. I normally tolerate to slightly enjoy commercial flying, but not the 787.


I believe all current Boeing aircraft use the new low-profile gaspers with reduced airflow regardless of engine type. I do not like the current design either but you can plan around it thanks to the ubiquity of power connections on newer aircraft. Check out the bendable USB fan below. There are larger designs with clamps and increased air flow as well. These have worked well for me on Asian carriers with higher temps and no gaspers.






https://www.amazon.com/ARCTIC-Breeze-Mobile-Flexible-Portable/dp/B003XN24GY/


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## dadonatrain (Feb 21, 2022)

Just curious…I told my wife at supper I’d feel relatively safe Covid-wise riding in a train since we’d all be masked up (mostly) and if I’m in a sleeper I could shut my door and have that addl layer of protection a lot of the time.

She replied what about the fact that air is being recirculated inside the coaches and compartments and other train equipment? It made me recall one of the objections to cruise ships.

I wonder what the prevailing opinion is on this issue for train travel? Is it really closed off like some say cruise ship cabins are? The trains are hardly hermetically sealed, like a plane is.


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## neroden (Feb 21, 2022)

Amtrak should do better; it is possible to put all recirculated air through a HEPA filter and have a large percentage be fresh It does not appear that this is happening, based on the evidence we have so far.


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