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With more vehicles adopting fuel-saving engine start-stop routines and with the number of hybrid and electric vehicles on the rise, automotive A/C (air conditioning) systems are facing a challenge to maintain passenger comfort during the time when the compressor is inactive due to engine shut down. Using PCM (Phase Change Material) in the evaporator enables it to store cold when the compressor is active and release it to the cooling air stream when the compressor is not running. A unique feature of Delphi's design is that a refrigerant thermosiphon mechanism inside the evaporator drives the energy transport between the PCM and air stream. Delphi's PCM evaporator extends comfort for short duration idle stops, reduces emissions, and increases fuel economy and electric drive range. In this paper, the design aspects of a thermosiphon based PCM cold storage evaporator are described and the performance and operation of the PCM evaporator in a MAC (Mobile Air Conditioning) system discussed.

The thermal systems of commercial vehicles are changing to reduce operational costs and tailpipe CO₂ emissions and to address anti-idling legislation. As these systems transition they must recognize that waste heat from the internal combustion engine can longer be the only means of providing hot coolant for heating. The Unitary HPAC (Heat Pump Air Conditioner) provides the hot coolant needed for heating in addition to cold coolant that can be used for cooling. The Unitary HPAC is a refrigerant system that is coupled with a coolant system. It produces hot and cold coolant that is used to manage the vehicles thermal needs. It has the ability to scavenge heat from unused sources, which allows it to provide heating with COP's (Coefficient of Performance) greater than 1. The Unitary HPAC can be applied to any vehicle that does not have enough hot coolant available for heating purposes.

The Unitary HPAC (Heat Pump Air Conditioner) System has been developed to enable a heat pump system in passenger vehicles. Unitary HPAC uses technology of reversing the coolant instead of refrigerant to distribute heat from where it is generated to where it is needed. Integrating this system in a plug-in hybrid vehicle reduces the energy required by the heating and air conditioning system, reducing the grams of CO₂ per mile by up to 25%. Although this system can be applied to any passenger vehicle, it is most beneficial to hybrid and electric vehicles, because it provides an additional source of hot coolant. These vehicles provide less waste heat than conventional internal combustion engine vehicles so they must rely on electric heaters to provide the heat needed for comfort. The electric heaters are an energy draw that reduces the electric drive range. The Unitary HPAC system will extend the electric range significantly.