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VLJ510

Cabin/Cockpit temp regulation

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Hi community, my only problem gladly is the 'AUTO' function and even sometimes the manual adjustment of the temperature control zones are often hard to control to keep a comfortable temp. More so my question is in regards to AUTO temp control. Right now on my flight from KDFW to KFLL the FWD and AFT cabins are at 40C while to cockpit hit 60C as I work my way to FL380! While on the ground at DFW with 38/39C (100F) outside temps was a nice inside summer temp of 20 to 23C with packs on AUTO. Now in flight on the way up to cruse even with the PACK on moved to HIGH I often find the temps are again very hot. However I'm not reviving any ZONE TEMP indications and the temps within the PACKS are 18C and 24C yet cabin temps are 40C+ and the cockpit a insane 60C (I'm melting) although I have gotten them before. I think 2 times outta the 29 30 flight I've done. -Any one else having high cabin and cockpit temps at any point in flight? -Is it because in AUTO in climb or takeoff it's moved off is retain the power for the climb by not running the PACKS? I know on the MD11 you could turn PACKS off for a takeoff to revive a bit more power. Also a finishing note before I post, in the time I've written the above using the knobs and not AUTO I have regulated the temps to 20 to 23C. So maybe I just don't understand the AUTO mode and need to just manually set temps with the knobs off of AUTO. Any insight and/or your experience with this would be appreciated! Thanks in advance!

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Yes, I read that a few days ago when I was reading on the ZONE TEMP reset button while at KLAS with 103F outside temps and the ZONE TEMP prompted a overhead indication warning and believe a Master Caution too. But doesn't reference any info on AUTO about how it chooses to regulate these three zones. And why when ambient temps are very high on the ground it can regulate these temps in comparison to while in flight working up though cooler ambient temp why this only went up until I manually adjust the knobs off of AUTO. Also the question of, if this is selected to AUTO is there any conservation points of the Bleed Air to the PACKS to obtain more power for the takeoff/climb? As well 40C cabin and 60C cockpit and no ZONE TEMP warning or Master Warning on the FO side as I have gotten this Master Warning before in regards to the "Air Cond". I would have like a warning to alert me to the temps as I might have been able to jump on the problem sooner. Overall I think I will adjust my personal SOP and not use AUTO as I've had consistent zone temps from point A to B.

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I will check as I've never checked temperature in flight, AUTO, with no alert is normal for me.Stupid question but, Are you looking for cabin temperature or ducts? Cont cabin has no temperature indication as the pilots feels it.Supply duct temperature is the air temperature measured in the ducts, is almost similar to the air that will come out from the outlets, it will mix to the cabin air, by warming it or refreshing it. It is normal that air in supply ducts is warm at high altitude as outside is very cold. It is normal also that in sunny summer days on ground, you will find very low temps in that ducts.

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I also find that keeping the temps at normal levels gives me a lot of work during a flight. The best control i get when i set all the knobs in manual 9.00 o'clock position when on the ground and at 10 during flight. A nice 22C temp, but sometimes the AFT temp rises for no reason to 40C.

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I will check as I've never checked temperature in flight, AUTO, with no alert is normal for me.Stupid question but, Are you looking for cabin temperature or ducts? Cont cabin has no temperature indication as the pilots feels it.Supply duct temperature is the air temperature measured in the ducts, is almost similar to the air that will come out from the outlets, it will mix to the cabin air, by warming it or refreshing it. It is normal that air in supply ducts is warm at high altitude as outside is very cold. It is normal also that in sunny summer days on ground, you will find very low temps in that ducts.
Thanks for checking this if you could. Yes I'm check the right temps. And CONT CAB dose indeed show temp, it's just comment since the point that the pilot and FO would feel the temp but but it also gives a indication. I can feel the temp in my house now but I still can go look and see the registered temp without having to guess. The same could be said for the back as well that the passengers and flight attendant would also feel the temp and in if using your logic then no indication would be need there as well. Also none of my questions where directed to dust temps as I only reference mine for a conclusion and not questioning these temps!
I also find that keeping the temps at normal levels gives me a lot of work during a flight. The best control i get when i set all the knobs in manual 9.00 o'clock position when on the ground and at 10 during flight. A nice 22C temp, but sometimes the AFT temp rises for no reason to 40C.
Thanks for reply buddy, sounds like sweet spot for me too 9 o'clock. I however never get a abnormal temp like you in the AFT once I switch off auto and manually takeoff the system.

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I also find that keeping the temps at normal levels gives me a lot of work during a flight. The best control i get when i set all the knobs in manual 9.00 o'clock position when on the ground and at 10 during flight. A nice 22C temp, but sometimes the AFT temp rises for no reason to 40C.
Yeah, I observe the same behaviour. In the Auto setting my cabin temperature goes up to 40°, while the airtemp in the duct goes up to 60°. It seems like the auto setting is demanding hot air for the cabin, which doesn´t make sense. When I turn the selector down to cold, everything goes back to normal (Cabin temp 23°, Duct temp 10°).
Thanks for checking this if you could. Yes I'm check the right temps. And CONT CAB dose indeed show temp, it's just comment since the point that the pilot and FO would feel the temp but but it also gives a indication. I can feel the temp in my house now but I still can go look and see the registered temp without having to guess. The same could be said for the back as well that the passengers and flight attendant would also feel the temp and in if using your logic then no indication would be need there as well.
There´s no indication for the temp in the cockpit. What you refer to is the CONT CAB SUPPLY DUCT temperature, and not the actual air temperature in the cockpit. There´s only an indication for the FWD and AFT Cabin air temperature.

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Yes Sir, I only then see theses zones cool maybe a bit faster and/or more a difference in the two passenger zones.

Yeah, I observe the same behaviour. In the Auto setting my cabin temperature goes up to 40°, while the airtemp in the duct goes up to 60°. It seems like the auto setting is demanding hot air for the cabin, which doesn´t make sense. When I turn the selector down to cold, everything goes back to normal (Cabin temp 23°, Duct temp 10°). There´s no indication for the temp in the cockpit. What you refer to is the CONT CAB SUPPLY DUCT temperature, and not the actual air temperature in the cockpit. There´s only an indication for the FWD and AFT Cabin air temperature.
Yeah, I observe the same behaviour. In the Auto setting my cabin temperature goes up to 40°, while the airtemp in the duct goes up to 60°. It seems like the auto setting is demanding hot air for the cabin, which doesn´t make sense. When I turn the selector down to cold, everything goes back to normal (Cabin temp 23°, Duct temp 10°). There´s no indication for the temp in the cockpit. What you refer to is the CONT CAB SUPPLY DUCT temperature, and not the actual air temperature in the cockpit. There´s only an indication for the FWD and AFT Cabin air temperature.
Thanks for the info, would then the CONT CAB be a close indication to the cabin temp give or take a bit +/-?

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It's worth noting that whatever the temps of FWD and AFT cabins are,the system will only use an average of both. Eg. FWD 40 AFT 60 The actual temp would be about 50. It might also help to turn off the trim air for a few minutes.The trim air bypasses the packs so is warm bleed air. Fred.

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Thanks for the info, would then the CONT CAB be a close indication to the cabin temp give or take a bit +/-?
Not really, it just shows you the air demanded which flows through the ducts into the cabin. So its more like a trend indication for the cabin. When the duct temp is 60° (as we both observed), the system is trying to heat the cabin up very rapidly. A Duct temperature which represents the actual cabin temperature is possible, but very unlikely I think. Just think about all the people sitting in the cabin and the amount of heat they produce. The air conditioning system has always send in a lower temperature to keep the cabin cool, which means that the temperature in the ducts should be always a bit lower. But I´m actually not 100% sure about that Whistle.gif
It's worth noting that whatever the temps of FWD and AFT cabins are,the system will only use an average of both. Eg. FWD 40 AFT 60 The actual temp would be about 50. It might also help to turn off the trim air for a few minutes.The trim air bypasses the packs so is warm bleed air. Fred.
Thanks for the info. I´ll try it out the next time I fly into an airport with an high outside air temperature.

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It's worth noting that whatever the temps of FWD and AFT cabins are,the system will only use an average of both. Eg. FWD 40 AFT 60 The actual temp would be about 50. It might also help to turn off the trim air for a few minutes.The trim air bypasses the packs so is warm bleed air. Fred.
Packs (400-800-900) works together to satisfy the coldest demand, trim air supplies hot bleed air to "trim" the temperature to the various demands.Inside the cabin, a passenger at the forward rows will feel the fwd pass cabin temp, one in the aft, the aft temp, only who is at the middle of the cabin (or just near) will feel an average of them.As told before, if supply duct temp is very high, or very low, the cabin section is very cold or very hot. When temperature will stabilize in the ducts to a value that will be never equal to the cabin one (maybe possible but rare) the cabin has reached its temp. Control cabin is a little oven, with a lot of lights, instruments, screens, it's very hot expecially on ground.

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Note that the temperature control is always AUTO in the 737NG. You are simply selecting the desired temperature. Other Boeings (such as the 747-400) had a MAN detent which allowed the pilots to manually control the mix of hot and cold air.

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Note that the temperature control is always AUTO in the 737NG. You are simply selecting the desired temperature. Other Boeings (such as the 747-400) had a MAN detent which allowed the pilots to manually control the mix of hot and cold air.
Ding ding ding. We have a winner. Guys, the Auto mode is the entire range except for the OFF position. The word Auto just happens to be at the 12 o'clock position as part of that entire arc that's painted. Look how the word is part of the arc. RW, a lot of guys take there pens and mark where they find the comfort range. 22-24 degrees in the back and about 15-18 in the ducts are pretty good rough numbers. In the real plane this summer, that was somewhere around 1 o'clock.

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6-700 has the manual control for the mix valves.On 8-900 the arc will set temps from C (18°C) to W (30°C)In OFF condition the relative trim air prsov will close.With the main trim air OFF (panel) the system will work in unbalanced average mode, left pack will do the cockpit requirements, right pack will satisfy the average of the cabin temp selections.

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Last time on a flight I came to the strange situation @ FL350 where pack temps were around 20C, FWD and CONT CAB temp was around that too while AFT temp was a little over 40C. All switches on AUTO, PACKs on, TRIM AIR on, RECIRC fans on. TAT was around -10C. Just don't get what's happening even after reading the FCOM. The way I understand is if the PACK temperatures are around 20C then FWD and AFT cabin temperatures should not be much higher. Can anyone enlighten me what I'm doing wrong? Thanks,

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Pack temperature is the working temperature of the ACM (air cycle machine). The packs can only generate cold air, as this is the working principle. To warm it the system uses hot bleed air. This flow is not sensed by the pack temp. sensor. The mixed air temperature is sensed by duct sensors.For pilots the only needed temperature during flight (in normal condition) is the cabin temperature that is sensed by 2 sensors that are inside the overhead bins, one forward, one aft.There is no indication about the control cabin temperature, but there is a sensor needed by the packs controllers to work properly.The temperature on the packs will be always lower or equal of the cabin temp, the duct temperature can be from 2°C to 88° (duct overheat) normally lower than 65/70°C. The amount of hot or cold air depends on the curve calculated by the pack controllers.Imagine a hot cabin, at 40°, the pack will work creating as much cold as they can (with their limitation), the duct temp will slowly reach low values of 10, 8°, but the cabin will never reach this temperature as the cabin is big, is heated by the sun etc...In flight, at FL350, TAT says -10 but SAT will be much lower, we can have -50° at these altitudes. The packs will be almost bypassed by the hot air that must warm the plane because uotside temp want to freeze the airplane. So duct temp will be 40 or higher, all depends on the capacity of the plane to insulate its cabin from the outside.I'm loading flight sim and I will check this right now.

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Ok, over 10 minutes at cruise altitude:All temperatures from left to right of the selector:Supply duct:CONT CAB: 20°FWD : 26°AFT: 34° Cabin temperature:FWD: 25°AFT: 26° Pack temp:RH: 18°LH: 24° Flight level 350. temperature were 15°C on ground (standard)This is the switch configuration. immaginecn.jpg

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