New Rooftop RLF Bus HVAC System is the Result
As bus operators await the January 1, 2010, implementation date of new U.S. Environmental Protection Agency (EPA) regulations for heavy-duty diesel engine emissions, bus builders and engine manufacturers are adding diesel particulate filters (DPFs) to the buses. To accommodate the DPF, bus original equipment manufacturers (OEMs) are being forced to rearrange the components in the already-limited space in the rear of the bus – where the majority of HVAC systems are located.
Thinking outside the box, New Flyer, Thermo King's largest bus customer, was one OEM that began looking to the roof and for a new HVAC unit design. New Flyer challenged Thermo King to create a new rooftop unit that would weigh the same as a rear-mount unit (roof-mounted units are typically 50- to 60-percent heavier), cost the same as a rear-mount unit (roof-mounted units cost, on average, 15- to 20-percent more) and meet, or exceed, the cooling performance of a rear-mount unit.
Thermo King answered the call by introducing a totally new "hybrid" HVAC concept to the transit market – one that combined the best of previous rooftop HVAC designs with the best of the rear-mount HVAC design.
In February 2008, Thermo King began working with New Flyer on a HVAC solution while a new bus was being designed. As typical in new bus designs, available space is the determining factor in the physical configuration of the HVAC unit. To further challenge the team, New Flyer needed the first working prototype by August 2008 so that it could be installed in time for the bus to be launched at the 2008 APTA Expo, an industry tradeshow that only occurs every three years. For the next four months, the Thermo King and New Flyer engineering teams met weekly, beginning with a concept, and working through many challenges. There were compromises along the way, but the innovative mindset of the Thermo King engineering team enabled the creation of a viable concept: the RLF 1-M1.
Six months from project start, the first prototype was delivered and the unit was on the bus at APTA when New Flyer unveiled its new DPF-equipped bus to the transit market.
"This was a truly, innovative team effort," said Steve Johnson, product manager, large bus and rail HVAC. "This project had many contributors, including representatives from sales and marketing, service, supply management, manufacturing and the model shop. Also typical of bus projects, at least half of the engineering staff played some role in the success of the project.
"It took many dedicated individuals from all departments at Thermo King to deliver this brand-new solution to New Flyer – and to the industry – without compromising reliability, weight, performance or cost."
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Innovations at a Glance: RLF1-M1 Bus HVAC Unit
- Unique one-piece design. (Typical roof units are two pieces, joined at installation with both pieces on the roof. RLF has the evaporator in the roof.)
- Single roof cut-out to prevent leaks. (Typical roof units require multiple cut-outs, increasing the likelihood of leaks, and require more installation time.)
- Single evaporator heater assembly, which reduces plumbing.
- Next generation controller, which brings multiple enhancements that benefit Thermo King and New Flyer.
- Next generation brushless motors, a totally new concept with significant weight and cost reductions.
- Lowest weight of any rooftop unit, which helps the bus manufacturer meet total weight and axle weight objectives.
- Fits CNG, hybrid and diesel buses. Developing one configuration for multiple applications was one of the greatest challenges overcome in the RLF design.
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