by Shane Henson — December 11, 2013—Daikin Applied’s Rebel commercial rooftop heating, ventilation and air-conditioning (HVAC) unit offers commercial building owners significant energy and dollar savings, according to a recent report by scientists at the U.S. Department of Energy’s (DOE) Pacific Northwest National Laboratory.
The scientists’ report analyzes the operation of the Daikin Rebel, which was one of two HVAC units to meet the DOE’s High Performance Rooftop Unit Challenge, a competition for manufacturers to create a rooftop unit that significantly exceeds existing DOE manufacturing standards. Daikin Applied was the first to produce such a unit, which was studied in depth by PNNL researchers; Carrier Corp. also met the challenge. The work is part of a broader DOE program known as the DOE Rooftop Campaign, which promotes the adoption of efficient rooftop units.
The PNNL study, conducted by scientists Srinivas Katipamula and Weimin Wang, is an in-depth look at the performance of the Rebel compared to other rooftop units in use today. The devices are usually nestled on building roofs, far from view but crucial to occupants’ comfort. The devices demand a significant proportion of the 18 quadrillion BTUs of energy that the nation’s commercial buildings swallow every year, says PNNL.
The PNNL team estimates that if current rooftop units were replaced with devices similar to the Rebel over a 10-year period, the benefits in terms of energy saved and reduced pollution would be about equal to taking 700,000 cars off the road each year. Put another way, the reduced energy draw could idle about eight average-size coal-fired power plants in each of those 10 years.
As part of their study, the team ran simulations for a typical 75,000-square-foot big-box store in three cities: Chicago, Houston, and Los Angeles. They compared performance of the Rebel to three types of units: those in use today, those that meet current federal regulations for new units, and those that meet the more stringent requirements of the ANSI/ASHRAE/IES Standard 90.1-2010: Energy Standard for Buildings Except Low-Rise Residential Buildings. DOE designed the Rooftop Challenge to exceed the ASHRAE standard.
The team found that the Daikin Rebel reduced energy costs and use as follows:
- Compared to units in operation today that are ready for replacement, energy costs were 33% less in Chicago, 44% less in Houston, and 45% less in Los Angeles. The Rebel slashed energy demand by 15%, 37%, and 36%, respectively.
- Compared to new units that meet current federal regulations, costs were cut 29%, 37%, and 40%, in Chicago, Houston, and Los Angeles, respectively. Likewise, energy demand was reduced 12%, 30%, and 32% in those three cities.
As expected, savings were a bit less when compared with new units that meet today’s strictest ASHRAE standards. Costs to run the Rebel system were 15% lower in Chicago, 27% lower in Houston, and 18% lower in Los Angeles. Energy demand was 8%, 23%, and 15% lower, respectively.
While the cost of the unit was not part of the team’s analysis, Katipamula estimates it would take at least a few years for the latest technology to pay back the increased investment in the newer units. The team’s analysis did not include a look at some of the unit’s additional features, such as its potential to save energy used for heating.
Available in 3- to 15-ton size ranges, Rebel cooling or heat pump units are ideal for low-rise commercial buildings, notes Daikin.
