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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.

Vehicle acceleration induced pressure spike on the high side of an Air Conditioning (AC) system is causing considerable concerns, especially for systems with high efficiency compressors. Head pressure surge in the order of one to two hundred pounds per square inch can be observed within a time span of 10 seconds or less. As the industry moves to meet increased system durability standards and passenger comfort requirements, clear understanding of the underlying mechanisms is required so that the impact of the head pressure spike can be minimized or eliminated. The present investigation seeks to understand the mechanisms of the head pressure spike phenomenon through both experimental and mathematical analyses. Experimentally, extensive testing has been conducted in environmental wind tunnel. Our mathematical analysis is based on the mass conservation principle for the refrigerant flow through the high side of an AC system.