NEW YORK (Fortune) -- Deep in the bowels of Credit Suisse's U.S. headquarters at 11 Madison Avenue, far below the gleaming trading floors where fortunes are made and lost every day, lie 64 neoprene ice storage tanks, seven feet high and six feet in diameter.

A steel chiller produces ice during the evening hours, when electricity is less expensive, more plentiful and generated without as much strain on the environment. That ice, stored in the big tanks, is used to chill water the following day. The water is pumped into a cooling system, producing the chilled air that keeps employees (and critical data-center equipment) from overheating on sweltering July days.

In previous summers, the 2.2-million square foot building had a peak electrical demand over ten megawatts - enough to power 2,000 homes. Water chillers used to run only during peak daytime hours, gobbling up a great deal of energy. But thanks to the innovative "thermal ice storage-based" cooling system described above, Credit Suisse (Charts) has lowered its peak energy usage by over 900 kilowatts, saving about one million dollars a year.

"When we ran the numbers, we thought the return on investment would take three and a half to four years," says William Beck, head of critical engineering systems at Credit Suisse. "But now it looks like it will pay for itself in two and a half years."

When Wall Street firms see green, it's usually in the form of piles of money that they earn in fees for brokering a hot IPO or shepherding a mega-merger. And with the Dow rising to new heights - it crossed the 12,000 barrier for the first time last week - there's plenty of green to go around this year.

But these days, financial titans like Credit Suisse, Morgan Stanley (Charts) and others are starting to pursue a different kind of green. In addition to chasing investment opportunities in areas like renewable energy, alternative fuels and carbon trading, investment banks are slowly "greening up" their own facilities with energy-saving systems.

While Corporate America's newfound obsession with green initiatives has been well documented (see "Wal-Mart Saves the Planet"), the leading investment banks haven't made much noise in this arena until fairly recently.

One notable exception is Goldman Sachs (Charts). The firm raised eyebrows by promulgating a particularly aggressive environmental policy, one that begins "with a focus on minimizing the impact of our own operations," according to the company.

Last November, Goldman's 1.5-million square foot facility in Jersey City, New Jersey, became one of the largest buildings in the country to get certified by the U.S. Green Building Council (USGBC) for its environmentally conscious design.

"As a result of our energy-efficient chillers and HVAC system, [it] saves 3.6 million kilowatt-hours per year," says a Goldman spokesperson. The building harvests daylight, uses storm water for cooling, and even has walls that "enhance visibility to migrating birds, reducing migratory bird mortality," according to the company. And the firm's new downtown Manhattan headquarters, slated for a 2009 opening, aims to use 25 percent less energy than a typical building of the same size.

But Goldman isn't the only one active in this arena. Credit Suisse, Morgan Stanley and others are rolling out energy-efficient cooling systems designed by Trane, the global leader in commercial air conditioning systems. A $6 billion division of American Standard (Charts), Trane supplies heating and cooling systems to one out of two buildings in this country, from Coca-Cola's headquarters in Atlanta to Chicago's McCormick convention center to the Washington Monument.

Todd Coulard, head of Trane's Energy Services Group in New York/New Jersey, says Trane is in talks with about a half-dozen Wall Street firms who are eager to see the same savings that Credit Suisse has enjoyed.

More recently, Morgan Stanley hired Trane to replace the 17-year-old air conditioning system in its Purchase, New York, office with an ice-storage design featuring 48 11-foot-high tanks housed in a former storage room in the basement. The new system, finished in May, will save the company about a half a million dollars on its electrical bill each year and will serve as a model for similar projects around the globe, according to James McAleer, the firm's vice president of facilities.

These installations aren't easy - at Credit Suisse, the engineers had to set up rigging hoists in the elevator shafts to get the old system out and the new one in. "It's a challenging undertaking," says Coulard. It helps that New York State kicked in $300,000 for Morgan Stanley and $820,000 for Credit Suisse as incentives to reduce their energy costs, which in turn improves the reliability of the state's electrical grid, particularly in the New York metropolitan area.

Indeed, New York City's Energy Policy Task Force has identified thermal ice storage as an important potential resource for the city. (Interestingly, the Empire State Building once considered such a system, but its complexity led to the project getting scrapped.)

"The commitment of large companies like Morgan Stanley and Credit Suisse to improve energy efficiency in their facilities is highly commendable," says Peter Smith, president and CEO of the New York State Energy Research and Development Authority (NYSERDA). "These types of projects should be used as a model for other companies looking to save energy and reduce costs."

Of course, some Wall Street power brokers did not see the benefit of such green facilities right away. Credit Suisse's Beck says he got some "blank stares" when he first started talking up the project inside the firm, "but once I put the business case in front of them, they said, 'OK, why aren't we doing this in more places?'" Emboldened by the results at 11 Madison Avenue, the company is considering a similar system for a new facility in Switzerland.

Going green also has PR value, and helps a firm's recruitment efforts, but it's more than a marketing tool: Based on a recent analysis by the U.S. Green Business Council, the aggregate total return of publicly held companies affiliated with the USGBC outperformed the Dow by over 18 percent from 2000 to 2004.

Still, despite widespread interest and bottom-line benefits, there is still plenty of resistance to green campaigns. A survey of nearly 500 architects, contractors and engineers commissioned by Building Design & Construction magazine in 2003 found that while nearly all (97 percent) saw the green phenomenon growing, more than half (58 percent) had been rebuffed in efforts to persuade colleagues or clients to try a green project.

Kermit had it right - it ain't easy being green.

____________________________

The Greenest Office in America

Wal-Mart sees green