Browse Publications Technical Papers 2009-01-0543
2009-04-20

Air Conditioning System Utilizing Vehicle Waste Energy 2009-01-0543

This paper describes conceptual design modifications that can be made to conventional, non-hybrid passenger vehicles, to allow the air conditioning refrigerant compressor to be powered by vehicle waste kinetic energy occurring during those times when the driver’s foot is off the gas. Without affecting passenger comfort, such compressor engagements, using regenerated waste energy, directly offsets engine fuel otherwise consumed for equivalent engine driven engagements. This results in significant fuel savings when the air conditioning system is operating during traffic pattern conditions.
In conventional system operation, a magnetic clutch mounted on an engine-driven drive pulley is electrically controlled to engage the compressor and restore refrigerant pressure each time its state of pressurization bleeds down to a predetermined minimum set-point. Vehicle waste energy generation, however, which allows the engine to be rotated via existing vehicle momentum during deceleration (overrunning), rather than via engine fuel, is controlled by the position of the driver’s foot on the gas in accordance with the state of traffic. By coordinating compressor operation with those times when the driver’s foot is off the gas, vehicle waste energy can be utilized to power the compressor.
In order to show the conceptual viability of identifying and harnessing vehicle waste energy to power the compressor, road test data was compiled on two test vehicles operating under simulated traffic pattern conditions. The air conditioning systems of the test vehicles were modified, via external test circuits, to automatically engage the refrigerant compressor magnetic clutch every time the driver’s foot stepped off the gas, and disengage when the driver stepped back on.
Analysis of the test data showed a significant percentage reduction of engine-driven refrigerant re-pressurization cycles, these having been replaced with equivalent vehicle waste energy-powered re-pressurization cycles during engine overrunning conditions. Although not directly measured in this study, any reduction of engine driven compressor operation likely translates into a degree of savings of the extra fuel normally consumed during air conditioner operation, as most of the extra engine fuel consumed when operating the air conditioner comes from the additional engine load of operating the compressor.
With such testing establishing the ability to identify and harness vehicle waste kinetic energy to power the compressor, two concepts are presented that could be adapted to the air conditioning systems of OEM vehicles to allow vehicle waste kinetic energy to seamlessly power a very significant portion of air conditioning compressor engagements during traffic pattern driving conditions.

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