Evaluation of the Energy Consumption of a Thermal Management System of a Plug-In Hybrid Electric Vehicle Using the Example of the Audi Q7 e-tron

The transition of vehicle propulsion technologies away from conventional internal combustion engines toward more electrically dominant systems such as plug-in hybrid electric vehicles (PHEV) poses new challenges for vehicle thermal management systems. Especially at low ambient temperatures, consumer demand for cabin comfort as well as legislatively imposed safety considerations significantly reduce the electric driving range because only electric energy can be used for heating during emissions-free driving modes. Recent developments to find energy efficient thermal management systems for electric and plug-in electric vehicles have led to the implementation of automotive heat pump systems. As an alternative approach to meet dynamic heating demands and safety regulations, these systems use heat at a low temperature level, for example the waste heat of electric drivetrain components, to heat the passenger compartment efficiently and therefore increase the electric driving range. Under moderate and humid environmental conditions, thermal management systems operate in a so called reheat mode. This safety-relevant reheat mode is characterized by the cooling and resulting dehumidification of the in-stream air and the subsequent heating to maintain cabin comfort. This work presents the numerical and experimental analysis of energy consumption of the AUDI Q7 e-tron heat pump system. Taking into account the different climate conditions of Europe, China and the United States as well as appropriate driving patterns, a methodology for estimating the annual real-world energy consumption of such a thermal management system is developed. The result of using this integrated heat pump concept results in an average increase of electric driving range of more than 10%.