Remember when all a hotel had to do to show its concern for the environment was to ask its guests to reuse their towels?

Hotels now are rolling out all sorts of green programs, in part because their business guests in particular are demanding it, and in part because the hotels are finding that going green saves money.

"Environmental issues are one of the hottest issues within the travel industry right now," said Bill Connors, the executive director of the National Business Travel Association. The association is addressing the topic of eco-friendly elements in hotel design and operations for the first time at its annual convention in July.

Connors' view is borne out by the rise in hotels registering to be certified under the United States Green Building Council's Leadership in Energy and Environmental Design program, a commercial-building rating system. "I think it's a really noticeable trend," said Max Zahniser, a program manager.

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