Turn off the left and right air conditioning components after cabin temperature

[YUHAO WANG]

Good morning, I once had a friend take Air China flight 106 from Hong Kong to dalian. But the co-pilot smoked on the way. According to an investigation, the co-pilot had intended to turn off the recirculating fan. But he turned off the  left and right air-conditioning pack unit by mistake. After the incident, he heard the air conditioner turn off in the cabin. And since then the temperature has soared to unbearable levels. This is a 737ng aircraft. In addition, after the air conditioning components are out of work, only the high-temperature bleed air of the engine is left. If it is a model 744, will this cause the cabin temperature to rise rapidly? Best wishes.

[John H Watson]

The engines supply air to the pack air cycle machines to provide cool and pressurised air to the cabin, but the engines also provide hot air to individual cabin zones to adjust the temperature of individual cabin zones. If all the packs are turned off, the pack air cycle machine stops working and the hot air to the individual cabin zones is also turned off. There is one master trim air valve which stops the hot air reaching all the cabin zones. This master trim air valve is only opened if there is at least one pack operating and the Trim Air switch on the overhead panel is on.

This means that there will be no air going to the cabin. Depending on the outside air temperature, the cabin will usually get hotter. Electronics, lights and warm human bodies generate a lot of heat. If the packs have been running for a while (and the cabin is cool), the temperature rise may take a while to be noticed. 

[YUHAO WANG]

hello，dear  John H Watson。Thank you very much for your patient reply, but I have turned off all the air conditioning components in PSX, and then confirmed that the outflow valve is in the fully closed position. After 30 minutes, the temperature dropped significantly. What is the reason?
Best wishes

[John H Watson]

What was the outside air temperature?

[YUHAO WANG]

At that time, the aircraft was cruising at 36000ft, so the temperature outside the cabin was far lower than the temperature inside the cabin. However, Air China 106 was cruising at the same altitude, and the temperature obviously increased. Therefore, I have this question

[John H Watson]

Sorry, I have no explanation. The 737NG (master) trim air valve (PRSOV) will close if the packs are turned off. The pack valves provide pneumatic "muscle" to open the trim air valve.

The heat in the cabin is then a product of OAT, cabin insulation, heat from electronics, cabin air volume, sun radiant  heat, fuselage paint colours, cargo heat, passenger load, etc.

[Hardy Heinlin]

In PSX there are no control parameters for the radial temperatures of the passengers' clothes or fuselage paint etc.

I think there must be a threshold where the aircon independent heat producers (humans, electronics, sunlight) provide less heat than the sum of previously stored heat + OAT. At that point the cabin temperature will start to decrease. If there was no such limit, the aircraft wouldn't need an aircon. It would then work like a Passivhaus.


|-|ardy


P.S.: I'm not sure, but another factor might play a role when comparing the 737 to the 747: The 747 cabin has a greater volume than the 737. The size ratio of these is not equivalent to the ratio of the amounts of heat producers (the cabins have a round shape). When the packs are off, the cabin pressure drops. This causes certain changes regarding humidity and temperature. And the intensity of that, I guess, depends on the ratio of cabin size versus heat producers. In other words: The cabin height may be twice as high, but the humans are not twice as high. There are more seats across the horizontal platform, but the vertical size of the passengers is not greater.

[YUHAO WANG]

Ok, thank you very much. I know I made a mistake in understanding heat. I had always thought that the heat was coming from the engine's hot bleed. But will it raise the temperature in most cases? Remove human heat and electron heat. Air China flight 106 is a night flight. There is no sunshine, but the temperature is extremely high. Just a question.
王禹皓
best wishes

[Hardy Heinlin]

Ram air is another heat producer. The skin of the Concorde fuselage, for example, got very hot :-)

If I subtract the temperature components of all living creatures, electrical equipment and OAT, then I would say the only remaining components are ram air (friction heat from the cabin skin) and bleed air from the engines.


Regards,

|-|ardy


I think in this context we can also neglect cosmic ray :-)

[Jeroen Hoppenbrouwers]

Wild guess: maybe it was not so much the rising cabin temperature that was very uncomfortable, but the rising humidity? With no ventilation, 200 breathing people will rapidly cause the air to be really bad. Add in a good amount of CO2 and less and less O2 and I can imagine people start sweating.

Hoppie

[skelsey]

I would think 150 (or on a 744, perhaps 400) people in a confined space with no ventilation (packs off would result in outflow valves closing in an effort to maintain delta P) would very quickly result in very high temperatures.

A quick scan around Google suggests that a human being is roughly a 100W heater, so in a Jumbo you're looking at perhaps 40 kW plus all the other heat-generating stuff in an aeroplane (IFE and other electrical equipment, galleys, etc).... I could see it getting extremely stuffy very quickly.

Edit to add: don't underestimate the heating effect of combined body heat from living creatures -- I am sure I can recall cases of fires being caused in aircraft holds as a result of large numbers of chicks being transported in close proximity and literally creating enough heat to ignite

[Hardy Heinlin]

OK, OK :-)

You guys want to see this effect in PSX, but since PSX provides no user interface to select the number of passengers, I'm supposed to implement a function that sets the number automatically by linking it with the ZFW and a little random factor, and it should only apply on non-freighters as on freighters we mostly want to transport non-living cargo ...


|-|

[Steve - Browny]

OK, OK :-)

You guys want to see this effect in PSX, but since PSX provides no user interface to select the number of passengers, I'm supposed to implement a function that sets the number automatically by linking it with the ZFW and a little random factor, and it should only apply on non-freighters as on freighters we mostly want to transport non-living cargo ...


|-|

idea =

1. Set number of cabin crew in the model settings
2. Have a pax input where you can link it to ZFW so if you drag the ZFW down it reduces pax based on 100kg average (80kg weight + 20kg bags average)
3. The lowest ZFW that you can slide to is based on the number of crew specified in the model file.
4. During boarding, you can have a number saying how many pax are currently on the aircraft (might get some late pax or even no shows)

But that's taking it the extra mile and probs not in the scope of things...

[Hardy Heinlin]

Steve, it's just about a random temp rise by a few degrees in a random time to a random maximum :-)

(I won't spend more than 2 minutes for this implementation.)

[evaamo]

it should only apply on non-freighters as on freighters we mostly want to transport non-living cargo ...

I flew in a COMBI from AMS to MEX a few months ago, and after a few hours en route I found, to my surprise, that my daughter had made some particular friends... there were horses being transported in the cargo space that is next to the galley that separates the cabin from the cargo hold. There is a panel in the bulkhead that can be lifted to access the cargo hold and she was allowed to feed them and touch their heads during some parts of the long flight back home.

We were told that if the flight is too turbulent, the horses might get too stressed and they would crap all over their space in the hold... making the air just a bit uncomfortable for the poor souls flying economy ;-)

Anyway... the reason I mention this is that maybe you could also take into account such situation during the implementation of this functionality you mentioned ;-)

I'm kidding, of course! (about simulating this not about the story!)

-E
   

[Jeroen Hoppenbrouwers]

Somebody is going to wire their home aircon to PSX to increase the simulation experience.

Hoppie

[Britjet]

Simfest already has the packs controlling the flight deck cooling fan..
Peter

[Will]

In a closed cabin while on the ground, I have no doubt that the temperature would rise. In my experience, the sunlight entering through the windows is more than enough to heat up the cabin, even with no passengers inside and no electronics turned on.

But while flying at cruise altitude?

Are we suggesting that the heat generated by all the stuff in the cabin exceeds the heat removed by flying through air that is at -50C? That stretches the imagination a bit. The insulation would have to be extremely efficient.

[Hardy Heinlin]

I don't know. But aside from that, I would expect the ratio of "meat versus air" to be greater in a 747 than in a 737.

This is the passenger platform in a 737, with about 6 meat balls along the diameter of the cabin circle:

OOO OOO


And here 10 balls in a 747:

OOO OOOO OOO


The size of the meat balls are equal on all aircraft types. But the radius of the cabin cell is different: The cabin is not only wider; it's also higher.

A 747 is just a bigger 737. But the meat volume the 747 carries is not equivalently bigger, it's just wider: Wider by 4 meat balls.

If the cabin is as small as one meat ball, the ratio of "meat versus air" is 1:0. In that case the total meat shape has the same height as the cabin.

In a big tube-like space ship that is 1000 feet wide and high, with 300 human meat balls across the center platform, the ratio would be something like 0.01:1 -- i.e. almost the entire cabin would consist of air, with very little meat to heat the air.


|o|ardy

[RogerH]

(puts on best 'Homer Simpson' voice...) "Mmmmm, meatballs..."