DOE finds super-efficient rooftop technology

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New super-efficient rooftop units that heat and cool commercial buildings offer significant energy and dollar savings, according to the U.S. Department of Energy's (DOE) Pacific Northwest National Laboratory (PNNL) -- reducing energy costs an average of 41 percent compared to units in operation today.

Credit: P199/Wikimedia Commons

New PNNL research analyzes the operation of a commercial rooftop HVAC unit (Daikin) which competed in DOE's Rooftop Challenge, part of a broader DOE program known as the DOE Rooftop Campaign to promote the adoption of efficient rooftop units.

The PNNL research estimates that if current rooftop units were replaced with devices similar to the challenge winner 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 and idle about eight average-size coal-fired power plants every year. Further, if all rooftop units with a cooling capacity of 10 to 20 tons were replaced immediately, DOE officials estimate the cost savings at around $1 billion annually.

The PNNL team ran simulations for a typical 75,000-square-foot big-box store in three cities: Chicago, Houston, and Los Angeles, comparing the performance of the challenge winner to three types of units: those in use today, those that meet current federal regulations for new units, and those that meet more stringent ASHRAE 90.1-2010 standards.  

Compared to units in operation today that are ready for replacement, energy costs of the challenge winning unit were 33 percent less in Chicago, 44 percent less in Houston, and 45 percent less in Los Angeles and slashed energy demand by 15 percent, 37 percent, and 36 percent, respectively.

Compared to new units that meet current federal regulations, costs were cut 29 percent, 37 percent, and 40 percent, in Chicago, Houston, and Los Angeles, respectively. Energy demand was reduced 12 percent, 30 percent, and 32 percent 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 winning system were 15 percent lower in Chicago, 27 percent lower in Houston, and 18 percent lower in Los Angeles. Energy demand was 8 percent, 23 percent, and 15 percent lower, respectively.

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