Electric Air Conditioning for Class 8 Tractors 2006-01-0165
Air conditioning and heating of heavy-duty truck cabs is an important contributor to engine efficiency, fuel economy and driver comfort. The air conditioner condenser coil and engine radiator typically share a common cooling fan, making it necessary to run the large engine cooling fan to provide condenser cooling. Engagement of the radiator cooling fan consumes a large amount of energy, further contributing to engine exhaust and noise emissions. Even under moderate temperature conditions, when the conventional engine-driven air conditioning compressor is not in use, the belt drive system adds a small speed-dependent parasitic load to the engine.
Electrically driven air conditioning systems have the potential for lower energy consumption than their mechanical counterparts: Electrically driven air conditioning systems can reduce engine idle time by decoupling the air conditioner system from the engine cooling fan while offering near zero parasitic load when not in use.
This paper covers the design, integration, and testing of an electric air conditioning system for a Class 8 tractor for day cab cooling and is a continuation of the efforts initially published in SAE paper 2004-01-1478 . A 42 VDC electric air conditioning system consisting of a variable speed compressor, remote condenser with a variable speed cooling fan, and a thermostatically controlled expansion valve was integrated into an existing Class 8 tractor. The OEM evaporator, in-vehicle ducting, and air speed control were unmodified. The electrical power for the electrified air conditioning system is supplied by a fuel cell auxiliary power unit. The Class 8 tractor has been in-service in the desert of Southern California.
Included in the paper is a detailed description of the different control schemes examined and the control scheme implemented. Energy consumption and driver comfort for each scheme is evaluated. Future system improvements and possible system enhancements are also identified.
All work has been performed at Southwest Research Institute and SunLine Transit Agency and is funded by the US Army RDECOM TARDEC National Automotive Center (NAC).