Browse Publications Technical Papers 2013-01-1506
2013-04-08

Effects on Real Life Fuel Efficiency of Raising the MAC Engagement Temperature 2013-01-1506

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.

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