Keeping cool

Advanced insulation packages, solar reflective film, and other thermal-management technologies enable heavy vehicles to reduce idle climate control loads, as demonstrated by NREL's CoolCab project.

In the U.S., an intercity long-haul truck averages approximately 1800 h/year of idling, primarily for sleeper cab hotel loads, consuming 838 million gal (3.17 billion L) of diesel fuel across the entire long-haul fleet. Including workday idling, over 2 billion gal (7.6 billion L) of fuel are used annually for truck idling. The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) is working on solutions to reduce idling fuel use through the CoolCab project. The objective of CoolCab is to work closely with industry to design efficient thermal-management systems for long-haul trucks that minimize engine idling and fuel use while maintaining cab occupant comfort. If the fuel savings from new technologies can provide a one- to three-year payback period, fleet owners will be economically motivated to incorporate them, the researchers believe.

NREL conducted an experimental test program at its Vehicle Testing and Integration Facility in collaboration with Volvo Trucks; Aearo Technologies LLC/E-A-R Thermal Acoustic Systems; 3M Corp.; and Dometic Environmental Corp. The impact of thermal load-reduction technologies on idle-reduction systems was characterized by conducting thermal soak tests, overall heat transfer tests, and 10-h rest period A/C tests. Technologies evaluated included advanced insulation packages, a solar reflective film applied to the vehicle's opaque exterior surfaces, a truck featuring both film and insulation, and a battery-powered A/C system. The results demonstrated technologies that reduce heating and cooling loads for long-haul truck idling by 36% and 34%, respectively, which yielded a 23% reduction in battery pack capacity of the idle reduction system.