Bethel University, a Christian university based in St. Paul, Minnesota, needed to replace two of its residence halls’ rooftop HVAC units. The equipment had been built in 1977.
“One of the driving forces to replacing the old units was trying to get better ventilation, drier air and make it more comfortable inside the dorm rooms,” said Chuck Broz, HVAC technician supervisor at Bethel University.
As a result, the university selected the Rebel rooftops, specified by Tim Harris, sales engineer and Daikin Applied representative with Schwab Vollhaver Lubratt Inc. The 7-ton Rebel rooftop units’ direct-expansion technology has benefitted the university in saving large amounts of chilled water from its central chiller plants in a two-pipe system.
“One of the biggest reasons we selected the Rebel units was to get, from the DX (direct expansion) side, significant efficiency while being able to put in the re-heat air with very little moisture content,” Broz said.
Officials say the rooftop units provide high part-load efficiencies at a 20.6 integrated energy efficiency ratio, which surpasses the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ 90.1 standard by 84 percent.
“Rebel has some of the highest IEER ratings in the rooftop market because of the inverter compressors,” said Matt Dodds, applications engineer at Daikin Applied. “In combination with the energy-recovery wheels, these units are 60 percent more effective at removing moisture from the air.”
Installation of the units was scheduled to meet the university’s budget and timetable when the dorms weren’t occupied. Units were installed in August 2013, August 2014 and March 2015.
“Both time constraints and special contracting required the provision of adapting curbs on the roof so that existing openings could be used,” Harris said. “Those were key challenges to the project.”
Broz credits the mechanical installation services by Egan Co., along with the Daikin service group, as critical to the success of the project.
“Everyone’s level of effort including installing new curbs, to pulling the old equipment off and installation of the electrical and hot water lines, made this a very efficient and well-done installation job,” he said.
The two installed Rebel units also feature Daikin’s Intelligent Equipment real-time control technology, which benchmarks performance and monitors system operation.
“Our energy managers use IE to gather data and we use it to see the detail of operational data and monitor the units,” Broz said. “We also appreciate that we can connect remotely to the units on laptop or smartphone.”
Bethel University officials say the school’s administrators and its students are pleased with the comfort levels the new HVAC market technology provides. There is a dramatic difference in humidity levels between the original and Rebel units, Broz added.
“We’ve maintained everything below 55 percent humidity with the Rebel unit,” he said. “With our existing equipment, we were well over 80 percent humidity throughout the building space, even with the fan coils in the dorm rooms, because various doors are left open.”
Energy savings are also significant, given reduced natural gas consumption with less reliance on the chiller plants that serve the complex, as well as the reduced electrical consumption of the Rebels versus existing rooftops. Also, the technology on the Rebels (which heats up outside air) provides significant energy savings especially during Minnesota’s cold winter months.
“In the winter, we’ll use IE to look at the energy side to optimize use of the energy wheels, instead of using building heat, especially as it relates to the restrooms and showers,” Broz said. “In the summer, we use IE to see if we’re doing an effective job of keeping the dew point and humidity at low levels,” he said.
Broz also noted that the extremely low-audible output of the Rebel units goes unnoticed by students.
“The Rebel units are very quiet due to the inverter compressor technology,” he said.