Cabin temperatures

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There are stories of budget airlines turning down the temp [...]

On that note, one thing that I haven't seen mentioned in this thread, is that the default cabin temperature without any heating, is very cold, because it's very cold outside at cruise altitude (usually around -40 degrees*). Cooling only operates when on the ground; the aircraft quickly changes to heating mode as soon as it passes around 10,000 feet, even in the hottest local weather. Heating requires bleeding off energy from the engines, either via bleed air or electrical systems, which reduces their efficiency, so keeping the cabin cool saves money and would make sense for a budget airline regardless of blanket sales.

I was boiling hot on a recent Sri Lankan airlines flight. I've noticed that South Asian carriers tend to have warmer cabins, perhaps as it's more appreciated by people used to a warmer climate? Qantas long-haul flights are always super cold and I presumed it's that way because they were saving money compared to a warmer temperature.

* Trivia: -40 is the same in both degrees C and degrees F.
 
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I have almost passed out on hot cabin - flights. Interesting.
 
I have almost passed out on hot cabin - flights. Interesting.
Worst hot flight I’ve had was on JAL, SYD-FRA via Japan. I had stumped up the extra for PE and suffered through an insanely hot cabin the whole way… all requests for decreasing the cabin temp were ignored but most of the other pax where sleeping with full blankets etc while I was contemplating stripping to my daks (not really). No amount of sake and beer helped but the food served was the best I’ve yet had on PE!
 
On that note, one thing that I haven't seen mentioned in this thread, is that the default cabin temperature without any heating, is very cold, because it's very cold outside at cruise altitude (usually around -40 degrees*).
Oh yes, it's a tad nippy outside. That's one reason why it's always so cold if you sit near doors. There is metal to metal contact with the outside and that effectively creates a freezer surrounding the door frame. Put a can of drink on the floor next to a door, and it will freeze. The windows in the coughpits of the Boeings were the same, and were generally covered with ice at the end of a trip, which would rain on you during the descent. Airbus didn't have the issue, presumably because they incorporated a thermal break in the design.
Cooling only operates when on the ground; the aircraft quickly changes to heating mode as soon as it passes around 10,000 feet, even in the hottest local weather. Heating requires bleeding off energy from the engines, either via bleed air or electrical systems, which reduces their efficiency, so keeping the cabin cool saves money and would make sense for a budget airline regardless of blanket sales.
The act of pressurising the air increases its temperature. The output from the packs is reasonably comfortable at low levels, but very quickly makes its way into the unsurvivable. At cruising levels it's in the region of 80ºC. The air cycle machines cool it, using heat exchangers, bringing to down to the lowest demanded temperature. Bleed air (which is very hot) is used to warm other zones. The upshot though, is that cooling is active at all levels.
I was boiling hot on a recent Sri Lankan airlines flight. I've noticed that South Asian carriers tend to have warmer cabins, perhaps as it's more appreciated by people used to a warmer climate? Qantas long-haul flights are always super cold and I presumed it's that way because they were saving money compared to a warmer temperature.

* Trivia: -40 is the same in both degrees C and degrees F.
From the Airbus manual:

CABIN AND coughPIT TEMPERATURE REGULATION
The flight crew can:
- Select the coughpit temperature with the coughPIT selector on the AIR panel
- Select the cabin temperature with the CABIN selector, if the temperature of each cabin zone cannot be selected from the Flight Attendant Panels (FAPs)- Set the CABIN selector to PURS SEL. In this case, the cabin crew can directly select the temperature of each cabin zone.
The temperature selection ranges from 18 °C to 30 °C.
The pack controller automatically controls the pack outlet temperature to set the temperature of L3 the mixer unit to the lowest cabin temperature demand. Therefore, the cabin zone with the lowest heating demand does not receive any trim air.

The pack controller regulates the outlet temperature of its associated pack by adjusting: - The Temperature Control Valve (TCV)
- The ram air inlet
- Both ram air outlets
- The Turbine Bypass Valves (TBVs).

Each trim air valve adjusts the temperature of its assigned coughpit and cabin zone.

FLOW REGULATION
The flight crew can use the AIR FLOW selector on the AIR panel to adjust the flow of cold air from the packs, and recirculated air from the cabin/coughpit.
If only one pack operates, or if the APU supplies bleed air, the pack controller automatically adjusts the airflow to high(HI) demand, regardless of the selection on the AIR FLOW selector.

AUTOMATIC MODE
The airflow in the coughpit and cabin is automatically controlled by:
- The pack controllers, that control the pack valves
- The ventilation controllers, that control the rotation speed of the cabin fans.

MANUAL MODE
When the flight crew sets the AIR FLOW selector to one of the following positions, the airflow in the coughpit/cabin is manually selected:
- AIR FLOW selector set to MAN: The pack airflow is a default value
- AIR FLOW selector is set to LO: The pack airflow is 80 % of the MAN default value
- AIR FLOW selector set to HI: The pack airflow is 120 % of the MAN default value.

When in manual mode:
- The airflow calculation does not take into account the number of passengers entered on the MFD, nor the aircraft flight level
- The airflow calculation depends on the temperature regulation selection on the CARGO
- The rotation speed of the primary fans remains constant.
 
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I've seen pax alert FAs about cabins being too hot before and they said they'd look into it. Unsure if anything changed though.
The cabin crew have a limited level of control over the cabin temps, which can be changed zone by zone. The pilots have a more powerful, but less targeted means of control.
 

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