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It's official: Hybrid vans save energy

The frequent stops and starts that characterize the average day in the life of a delivery van would seem to be the perfect environment for hybrid vehicle technology. Now, there is proof to back up this assertion.

The National Renewable Energy Lab recently wrapped up 18-month tests of second-generation diesel hybrid delivery vans used by the delivery service UPS. Researchers compared eleven hybrid vans and eleven conventional vans at a UPS facility in Minneapolis. On-vehicle data logging, fueling, and maintenance records were used to evaluate the performance of the vans. The conventional and hybrid groups switched route assignments during the study to provide a more balanced review.

You'd expect the hybrids to get better mpg than the conventional vans, and they did. That held true for low speed, high stops-per-mile routes (better by about 20%) and those with longer highway legs and less dense delivery zones (better by about 13%).

However, there were some interesting differences in maintenance and operating costs and in reliability. There was no statistically significant difference in total maintenance cost per mile between the two. Propulsion-related maintenance cost per mile was 77% higher for the hybrids. However, this was only 52% more when considered on a cost per delivery day basis. And the total cost of operation per mile for a hybrid vehicle was 3% more than the cost of operation for the diesel group, but not found to be statistically significant. The hybrid group also had a cumulative uptime of 92.5% compared to the conventional group uptime of 99.7%.

The hybrid vans tested are an evolution from 50 hybrids that UPS originally had in its fleet. The new hybrids have more advanced control algorithms and an integrated “engine off at idle” feature that automatically stops and restarts the engine at stoplights and other short stops when certain conditions are met.

NREL says the hybrid and conventional vans all are still new enough that much of the maintenance is completed under warranty. All maintenance for the hybrid drive, developed by Eaton Corp., was done by Eaton mechanics. These maintenance costs are not included in the maintenance-cost analysis.

NREL admits not accounting for warranty repairs in the evaluation of total maintenance cost does offer an incomplete picture of total maintenance cost. Even without warranty costs, however, NREL says this analysis reflects the actual cost to UPS during the period selected.

NREL says the total maintenance cost per mile of $0.219 for the hybrid vans was 30% more than the $0.168 for the conventional vans but was not statistically significant; total maintenance costs directly were only 6% greater. The propulsion-related maintenance cost per mile of $0.074 for the hybrid vans was 77% more than the $0.042 for the conventional vans; propulsion-related costs directly were only 45% greater. The total maintenance cost per day of $10.90 for the hybrid vans was 11% more than the $9.80 for the conventional vans. The propulsion-related maintenance cost per day of $3.68 for the hybrid vans was 52% more than the $2.43 for the conventional vans.

The higher hybrid maintenance costs are driven by more labor hours in most categories with transmission-related hours being seven times higher than on the diesel vans. There was no statistically significant difference in group total maintenance costs per month considered directly.

Another measure of system reliability is the up-time or availability of the vehicles. NREL says that UPS records instances in which a vehicle is not available to load in the morning as scheduled. Scheduled maintenance events of any kind do not get recorded in this way, so only unscheduled maintenance is included. The hybrid group missed substantially more days of operation than the conventional group (200 days vs. 13 days), especially during the first three months of the study.

The NREL report is free and is available here: http://www.nrel.gov/docs/fy12osti/55658.pdf

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