Delaware and Maryland were already in. El Paso, Orlando, San Diego, and Spokane were in.

On Tuesday, Mayor Nutter, flanked by federal energy and environmental officials, announced that Philadelphia also was joining a U.S. better-buildings challenge and launched an energy race among the city's biggest buildings.

As in weight reduction, the biggest losers win.

The challenge is to reduce energy use 5 percent by Sept. 30, 2015. But building operators are encouraged to do more.

At the end of the challenge, the three top-performing buildings in Philadelphia will be awarded $5,000.

"We know that there is a significant opportunity to cut energy use and costs, as well as reduce greenhouse gas emissions through more efficient operations," the mayor said.

Missy A. Quinn, chair of the nonprofit Building Owners and Managers Association of Philadelphia, whose member buildings define the city skyline, applauded the move.

"We have often said, 'Don't legislate change; incentivize us,' " she said. "While energy efficiency is one of the areas where we already place a tremendous focus, this will allow our true champions to shine."

Many of BOMA's 400-plus members have already made improvements, such as retrofitting their buildings' lighting and upgrading their air-conditioning systems.

One goal is making sure a building starts up and shuts down according to usage by its occupants, not some clock that can't turn off the lights when no one is home.

Those that have already made significant improvements may not win the challenge, but no matter, said Donald S. Haas, director of operations at Three Logan Square, owned by Brandywine Realty Trust.

"Believe me, if you're ahead of the curve, there is no better feeling that everyone catching up to you," he said.

In Philadelphia, buildings account for 62 percent of greenhouse emissions, said Alex Dews, policy and program manager for the mayor's office of sustainability.

The city - including the housing authority and school district - has joined the Department of Energy's Better Building Challenge, through which states, municipalities, corporations, and educational institutions commit to energy savings of 20 percent or more over 10 years.

The latest DOE update showed that more than 190 participating organizations are seeing roughly a 2.5 percent decrease in energy use per year, an amount that eventually would total savings of $80 billion a year if all U.S. buildings and homes improved at the same rate.

In accepting the Mayor's challenge, Quinn issued one of her own, saying that she was so confident in BOMA's capabilities that "I would be willing to wager our top three member buildings will outperform the city's top three participants. What say you, Mr. Nutter? You in?"

ENERGY SAVERS?

Among the competitors are all city-owned buildings and some commercial buildings, including:

City Hall

Municipal Services Building

One Parkway Buildings

Free Library

Recreation centers

Firehouses

Aramark building at 1101 Market

Three Logan Square at 1717 Arch.EndText

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