With a $750,000 grant from the TIGGER Program, the Tri-County Metropolitan Transportation District of Oregon (TriMet) is replacing the existing bus cooling system in 39 buses in its fleet with a more efficient electrically-powered system to enhance bus performance, reduce emissions, and increase the average fuel efficiency.

TriMet retrofitted each of the 39 hydraulically-driven bus cooling systems with a miniHYBRID thermal kit, a fully contained cooling system manufactured by Engineered Machined Products (EMP). A high output alternator and a system of heat exchangers and eight electronically controlled electric fans replace the original bus alternator and cooling system. The miniHYBRID kit includes temperature sensors for the engine charge air and engine jacket water flow paths to separately optimize cooling of those systems. Previously, TriMet helped EMP bring this miniHYBRID electronic cooling system to market by funding its development, testing, and evaluation in transit applications, and in May 2009, TriMet and EMP were honored with the EPA Clean Air Excellence Award.

The miniHYBRID system has reduced fuel use by an average of 5% in each bus that it was installed. Each TriMet bus travels approximately 50,000 miles annually and uses an average of 11,869 gallons of diesel fuel; with the miniHYBRID system, each retrofitted bus reduced its annual diesel fuel consumption by an average of 593 gallons. The reduction was most evident during mild and cold weather – during the warm summer months, increased engine cooling requirements led to a smaller reduction in fuel use.

This bus efficiency improvement project has reduced TriMet’s annual diesel fuel consumption, and the fuel savings directly translate into energy savings and emissions reductions for TriMet. The improved vehicle mileage achieved by each bus also reduces exhaust emissions by more than 5%. Based on this successful project demonstration, TriMet is including the EMP miniHYBRID system on its future bus orders. This project also shows other transit agencies how the EMP miniHybrid thermal system can be used to retrofit existing transit fleets to achieve fuel savings and reduce greenhouse gas emissions in a cost-effective manner.