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In a typical plug-in hybrid electric vehicle (PHEV) installation, there exist multiple, potentially separate, cooling circuits. These circuits may have individual cooling/heating requirements or they may have common aspects. Opportunities exist for combining circuits for series applications for cost, weight and efficiency benefits. However, careful consideration must be paid to the compatibility of these circuits both in terms of temperature range requirements, but also in terms of the thermal loading of the systems on the cooling circuits. This paper presents details of a cooling system for a PHEV demonstrator recently completed by MAHLE Powertrain. The opportunities for the integration of several cooling circuits, including the cabin heating, ventilation and air-conditioning (HVAC) system, to optimise the system from a cost, package-space and weight perspective are discussed.

Contradictory requirements like a quick heat up of the compartment vs. a quick heat up of the engine (especially in cars with fuel efficient engines) show that there is a need for a highly sophisticated climate control system to optimize the operation points. This could be done by a suitable system and a close interaction between the control systems for climate, engine and coolant management. Additionally we can improve the climate control system to a comfort management system by using sensors for air velocity and humidity. With today's technology we can build up a calculation model to determine a comfort-factor for the occupants and use this factor for the climate control instead of only using the compartment temperature as controlled variable.

Next to air temperature, humidity, and air quality, it is sound emission that exerts a significant impact on the driver's and passenger's comfort. Major progress in vehicle acoustics has motivated vehicle manufacturers and systems suppliers to evaluate HVAC systems no longer by their air conditioning performance alone. Sound emissions and sound quality have become additional important criteria for the development of new HVAC systems. In the initial conception phase, where systems and packaging considerations are made, acoustic optimization must begin with preliminary system studies and feasibility studies. In this phase acoustics should be based on fairly general systems specifications which describe the desired degree of acoustic comfort. In the subsequent design phase follows the specification of the acoustic goals and the optimization of the HVAC unit. Detailed analysis and optimization of air flow and blower are the common targets for improvement at this time.