Trying to move the OT discussion over here.
Originally Posted by
siliconflyer
Agree Kix. When outside is -50C as is at cruising altitude, bringing upto 28C is less "eco" than say 23C.
siliconflyer, I have posted the explanation from Boeing earlier below.
http://www.flyertalk.com/forum/18958711-post30.html
Basically the outside air is not dense enough and has to go through the engine compressor to pressurize and the air is heated too as a result. After that those air has to be cooled by the AC system before getting into the cabin.