Distributed energy will contribute power to the first high-rise to strive for the Platinum designation awarded by the US Green Building Council's Leadership in Energy and Environmental Design (LEED).

Scott Frank

Set at One Bryant Park, the largest development site in Manhattan, the prestigious skyscraper will host a range of innovative, high-performance technologies designed to minimize energy and water consumption. It all starts with an onsite, natural gas–fired cogeneration system connected in parallel with electrical service from New York City's Consolidated Edison Co. (Con Edison).

"Onsite generation is a significant aspect of the design initiatives of the project," says Scott Frank, P.E., associate partner of Jaros, Baum & Bolles, the engineering firm handling power and HVAC systems for the structure. Frank notes that the "greening" of building systems is in full force now. "It's a groundswell that's really quite striking to see in the numbers," he says. As a result, Frank has become the de facto specialist in sustainable design at his firm. The choices have given him plenty of design directions to contemplate.

Although construction began in mid-August, Frank is still evaluating generator systems. With 1.1 million square feet reserved for the headquarters of Bank of America's operations, plus an additional 1.1 million square feet of office space for other tenants and Henry Miller's (50,000-square-foot) Theater, Frank expects the building's peak load requirements to run as high as 15 MW. Plans call for the cogeneration unit to supply 3 to 5 MW of the demand, with the balance coming from Con Edison.

The cogeneration system is dedicated to the building. However, the simplest engineering option is to operate it in parallel with power from the grid supplied at a 13,000-V level. "Often, systems like this would spend a lot of time trying to rearrange and reconfigure the electrical distribution in order to organize the load so it can be served directly by the generator," Frank explains. "That brings a lot of other challenges as to what happens when those loads vary and they're not adequate to satisfy the output of a generator. The system has to initiate all sorts of other responses, which adds to cost and liability issues."

The design calls for utilizing waste heat for steam air conditioning as well as a combined cycle configuration directing heat to a condensing turbine to generate additional electricity. The turbine plays an important role by reducing the pressure of the steam to meet the heating system's demands, and finally condensing it from gas back to liquid.

Some of Bank of America's operations are 24/7, so evening power demands should fall into the 3- to 5-MW range, thus allowing the cogeneration system to operate at its capacity around the clock. "The economics of a cogeneration plant warrant a demand upon the system every hour of the year," Frank notes.

To help keep the demand consistent and lessen daytime loads (when power rates are higher), some of the generator's power will be devoted to making ice during the evening. "Thermal storage is a time-proven technology for shifting demand," Frank says. "Instead of running all the air conditioning during the daytime hours when electricity is most expensive, you generate ice at night when it's cheaper and [there's] less demand upon the utility's infrastructure. Then it's melted during the day for refrigeration."

Architects Cook+Fox have also specified energy-saving innovations to mitigate daytime air-conditioning loads, such as filtered under-floor displacement air ventilation, advanced double-wall technology, and translucent insulating glass. Daylight dimming and LED lights will reduce electric usage, and carbon dioxide monitors will automatically introduce more fresh air when necessary.

Other LEED considerations include a gray-water system to capture and reuse all rain and wastewater, and planted roofs to reduce the urban heat-island effect. According to Bob Fox, a partner at Cook+Fox, Bank of America and developer The Durst Organization are leaders in a growing trend toward environmentally friendly buildings. "The client was right with us on the choice of onsite power," Fox says, adding that this isn't the first time The Durst Organization chose distributed energy. In 1999 the company approved onsite fuel cells in its Four Times Square project.

"One of the goals of our clients is to initiate change, and Four Times Square was a poster child for the Department of Energy and Wonderful Building," says Fox. "We're expecting to use 5 megawatts at the Bank of America Tower so we don't need more power, but the client has OK'd the site for installation of fuel cells if we want to use it as a test laboratory."

One advantage of fuel cells would be their low pollution and emissions status, but Frank says that the natural gas turbine will have the lowest emissions from readily available commercial technology. "From a regional standpoint, onsite cogeneration uses gas more efficiently than a power plant, so the total amount of carbon and NOx emissions are reduced per Btu of natural gas," notes Frank.

All told, the efforts to qualify the project for LEED Platinum status have inspired enthusiastic support from a number of private and public organizations. The Natural Resources Defense Council contributed to the creation of a net zero–carbon dioxide target and the integration of the cogeneration plant. Also, the Rocky Mountain Institute consulted with tenants on reducing power consumption in the trading and data-center environments. The New York State Energy Research and Development Authority will contribute almost $1 million for energy-modeling, engineering, and energy-saving equipment. And finally, New York State will contribute almost $7 million for the project through its Green Building Tax Credit.

The credits should help offset a special rate tariff imposed by Con Edison. Frank says that the utility accepted something of a burden in agreeing to supply seamless power with the potential for supplying 100% of the peak load demand in an emergency. "There will be scheduled peak outages for the cogeneration plant, or the plant could fail. Hopefully never, but it's certainly a possibility," says Frank. "So we need full capacity on the street at all times for the total load of building, even though it may never materialize."

ED RITCHIE is a writer specializing in energy, transportation, and communication technologies.

DE - January/February 2005