My understanding is as follows, but please feel free to correct me!!
The ACM is just driven by bleed air passing over its turbine.. its RPM is therefore dependant partly on the temperature selected (colder, faster).
I thought the mass flow controller keeps the demand on bleed air fairly constant, so changing temp shouldn't significantly change the fuel usage. The changing temp would only affect whether more air goes over the ACM or bypasses it as trim air.
I would suspect that turbofan operation would affect economy more significantly because the air used to drive the turbofan (in the pack) is dumped into the Ram air duct for the pack and not used for pressurisation.
(Please note I am assuming the 'Pack valve' acts as a mass flow controller, with the 'Air mix valves' acting as temperature controllers. The turbofan valve is upstream of the pack valve.)
Last edited by tom775257; 22nd May 2004 at 17:10.