Big Energy Savings Lurking On Rooftops

Companies know that putting solar panels on their big-box rooftops can produce energy that can be a big money and emissions saver. And we know that painting rooftops white can cool a building down in the summer and lead to savings on air conditioning.

But when it comes to big, fat energy savings — on big, flat roofs, especially — it looks like few things can beat the new energy efficient heating and cooling units that have emerged from the U.S. Department of Energy’s Rooftop Challenge competition.

rooftop challenge

The unassuming but apparently quite Daikin Rebel. (image via Daikin Applied/PNNL)

Researchers at the Pacific Northwest National Laboratory say that tests of the first of two units to meet the high standards specified by the DOE showed average  savings of about 41 percent compared to units in operation today. The lab put that in perspective:

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.

The PNNL researchers went deep to draw their conclusions; they say they ran simulations for a typical 75,000-square-foot big-box store in three cities: Chicago, Houston, and Los Angeles, then “compared performance of the (Daikin) Rebel to three types of units: those in use today, those that meet current federal regulations for new units, and those that meet more stringent requirements, known as ASHRAE 90.1-2010 standards.” They note that the feds set up the Rooftop Challenge to beat the ASHRAE standards.

Now, the question you might be asking yourself about now could be: Are these fancy units way more expensive than today’s less-efficient ones — to the point of being beyond realistic reach? On that count, PNNL said: “While the cost of the unit was not part of the team’s analysis, (researcher Srinivas) 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 savings depend very much on the particular conditions — the climate, the size of the store, the materials used in the construction, and so on,” Katipamula in a statement. “We’ve developed Energy Plus software models that allow building designers or owners to calculate for themselves the cost-effectiveness of installing a newer unit that meets the DOE rooftop challenge.”

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.