Executive Summary

​The A/C compressor aids the movement of the refrigerant for the cab air conditioning system. Although it only operates as required, sleeper compartments require A/C when the truck is parked. The modern air conditioning system for vehicles includes a belt-driven, clutched compressor that takes power from the engine to drive a refrigerant through a closed-cycle system of heat exchangers and valves. The heat exchanger and refrigerant system are designed to remove heat from the passenger compartment of the vehicle and reject that heat through the air conditioning condenser coil that is located in front of the radiator.

​The only electrically-driven air conditioning compressors on the market now are ones used for battery APUs and ones that are installed on hybrid-electric transit buses. Currently, none are available or projected for standard on-highway vehicles.

Engine Driven Accessories
What Others Are Saying

​SuperTrucks

  • From 2009 to 2015, the Department of Energy sponsored a program with industry manufacturers to demonstrate at least a 50% improvement in freight efficiency. The project leads were Daimler, Cummins/Peterbilt, Volvo Trucks USA, and Navistar. Each of the four teams created demonstration vehicles incorporating a variety of new technologies to highlight the feasibility of meeting this aggressive goal.
  • As part of researching this subject, the NACFE study team interviewed each SuperTruck team to understand its analysis and choices relative to variable engine-driven accessories. It is important to note that most of the fuel economy and freight efficiency gains were achieved through improvements in aerodynamics, weight reduction, rolling resistance reduction, and powertrain improvements.
  • Note that all four teams chose to implement a form of waste heat recovery as part of their technology choices. The fuel economy gains for this technology are far higher than those available through improvements in accessory systems.

Fleets

  • On reliability: “The past few years have given us a lot of new challenges to manage due to the introduction of less-than-reliable new technology like aftertreatment systems or electric APUs. When it comes to accessories technology improvements, the new equipment must be proven reliable before I’ll be willing to implement it in my fleet across the board.”
  • On payback: “Any optional new technology that we implement must meet return on investment guidelines before it will be considered as part of a large purchase. Given that the fuel economy savings from new accessories are generally small, this makes measuring the potential improvement from anything new very difficult for us. This means it’s a harder sell to our management to make the investment.”
Decision-Making Tools

​The study team developed a Confidence Matrix, an OEM Availability Matrix and an Engine-driven Accessories Power Use Chart to assist fleets. The Confidence Matrix is designed to inform fleets of the study team’s confidence in the technology being studied vs. the payback the fleet should expect to receive from the technology. Technologies in the top right of the matrix have a short payback, usually thanks to their low upfront cost, and moreover are found to have enough performance data that fleets can be highly confident in those short payback times, usually because the technology is more mature or otherwise has a more substantial track record of results. The OEM Availability Matrix shows the current availability (as of March 2017) of these engine-drive accessories at the various truck builders. The Engine-driven Accessories Power Use Chart shows the various places the energy from fuel  is used in a Class 8 truck.

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Decision-Making Tools

Conclusions
  • ​Fuel economy gains from currently available variable engine-driven accessory technologies are modest.
  • The payback for these devices is extended based on today’s fuel prices.
  • Duty cycle of each accessory is critical to the ROI calculation.
  • There is a significant concern for subsystem reliability of these new variable engine-driven accessory technologies.
  • Payback of many of the new accessory technologies is currently insufficient to result in high levels of adoption.
  • Future enabling technologies like higher vehicle system voltage, increased energy storage, and waste heat recovery will likely improve ROI of new variable engine-driven accessories.