State of The Art of Advanced Vehicle Thermal Management Systems

Research output: Book/ReportCommissioned report

Abstract

Vehicle thermal management has always been, and will continue to be a crucial element for driving. The vehicle is subjected to numerous sources of heat from within and outside, and there are equipment and zones that need cooling or heating and occupants whose thermal comfort is of concern. This is not only a question of performance, but more importantly of operability and safety. During driving it's important that the driver feels comfortable and relaxed and that the windshield and all windows provide a clear view, free of ice or mist.
Environmental conditions and weather are obvious thermal parameters to which the car will be subjected. How they impact thermal performance of the vehicle and how their influence can be mitigated when not desired needs to be understood.
For conventional vehicles with internal combustion engines, there is abundant waste heat generated that needs to be dissipated to the environment in order not to overheat the thermal engine. In cold weather conditions, this waste heat is employed for cabin heating in favour of occupants' thermal comfort, but in summer this excess heat is forcibly evicted to the environment. In hot climate conditions engine waste heat is rather an extra heat source impacting cabin thermal comfort negatively.
With internal combustion engines getting smaller in size and more efficient, especially when combined with advanced drive systems like in hybrid electric vehicles, less waste heat is generated. A positive evolution one could say, but the beneficial effects that classically resulted from big engines' abundant heat generation are reduced and should be understood and carefully compensated with intelligent solutions. In cold conditions engine heat may not be sufficient to ensure cabin thermal comfort, and so additional cabin heating systems are necessary. Also important for the sustainability of hybrid electric vehicles is the fact that an internal combustion engine performs best when sufficiently heated and operating at the right temperature. At low operating temperatures there is more friction, a higher fuel consumption and increased toxic tailpipe emissions.
For cooling of the hybrid electric vehicle, the evolution of the classical air conditioning system with belt-driven compressor toward the electric compressor operating independently of the engine is ongoing. With advanced drivetrain concepts, the main battery is of considerable size and the electric compressor can operate making use of its energy. Compressors with belt drives can also be found in micro hybrids for example, which only have a stop start function. When the vehicle is at standstill and the engine is not running, the air conditioning is not running and cabin comfort can quickly diminish. To solve this problem, newly developed cold storage evaporators are employed to provide cooling comfort when the engine is not running.
When considering pure electric vehicles, a first important observation is the total absence of a thermal engine and thus no associated waste heat. The electric drive motor and power electronics in the vehicle are very efficient and don't generate a lot of loss heat. This good vehicle propulsion efficiency is one of the main benefits of electric vehicles, contributing to sustainable mobility. In general, installation of dedicated heating systems in electric cars is therefore necessary to overcome cold climate conditions. This is not only the case to ensure vehicle cabin comfort, but also to improve the performance of the vehicle's - mainly lithium-ion in present day EV's - traction battery.

Since Heating Ventilation and Air Conditioning (HVAC) requirements can be quite demanding, their consumption of electrical energy in EV's poses major challenges. Electrical vehicles today have an expensive traction battery pack on board that is limited in energy capacity, and driving range is already limited. Using this valuable energy for HVAC purposes instead of vehicle propulsion, can have dramatic consequences for the autonomy of the EV.
Original languageEnglish
PublisherElectrabel GDF SUEZ
Publication statusPublished - 23 Jan 2014

Keywords

  • Thermal comfort management
  • Electric vehicles
  • Air conditioning
  • MAC

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