The subject addressed by this work, currently discussed in
Europe following an European Commission inquiry, is the evaluation
of the possibility to prevent the MAC (Mobile Air Conditioning) use
below 18°C and its benefits in terms of CO2 emissions saving. This
strategy, while providing an uncertain fuel consumption saving, has
to be faced with basic safety and cabin comfort conditions. The
OEMs (Original Equipment Manufacturers) may evaluate to address
these concerns by controlling the cabin absolute humidity
content.
In order to maintain safety it should be acceptable to turn the
AC on based on other inputs, such as air distribution modes
(defrost or floor/defrost), windshield wiper usage, rear defroster
usage, etc. FGA (FIAT Group Automobiles) exploited our proprietary
prediction tool to assessing the yearly fuel efficiency that can be
achieved in real use by means of the testing results of
representative vehicles. Based on a model allowing evaluating the
actual vehicle fuel consumption in a NEDC (New European Driving
Cycle) with operated MAC as a function of ambient enthalpy, the FGA
results show a relevant benefit in operating the MAC system only at
temperatures over 18°C ambient.
The actual impact on the fuel consumption experienced by the
customer might anyway be lower than the maximum declared one, as
not all drivers are used to always operate their vehicle with the
A/C ON. This may explain some OEMs' concern in assessing such
high a consumption reduction benefit, which may drive the consumers
to false money saving expectations.
