Archive for ‘Cook + Fox Architects’

March 14, 2011

Towering Green Ambitions: A Manhattan skyscraper wraps a package of tightly coordinated technologies inside a faceted glass skin.

November 2010
Cook+Fox Architects

By Joann Gonchar, AIA

Bank of America Tower

The Bank of America Tower sits diagonally across from Bryant Park and next to 4 Times Square (bottom right-hand corner), the country’s first green commercial highrise.
Photo © David Sundberg/Esto

This past spring, the owners of the 55-story Bank of America Tower, which sits catty-corner from New York City’s Bryant Park, celebrated the building’s opening with a reception in the lobby—almost two years after the first occupants moved in. If the “opening” party seemed a bit anticlimactic, the event did mark an important milestone. It coincided with an announcement that the $1 billion, 2.2 million-square-foot tower had achieved Platinum certification under the U.S. Green Building Council’s LEED Core & Shell rating system—making it the first U.S. skyscraper to achieve this designation.

Designed by Cook+Fox Architects and jointly owned by the developer, the Durst Organization, and the bank (which is also the lead tenant), the 1,200-foot-tall, glass-clad, steel-framed building rises from a 7-story podium that conforms to Manhattan’s street grid. It then tapers and seemingly twists to achieve a sleek, crystalline form. A host of integrated strategies helped the tower earn Platinum, including rainwater and graywater recycling, an advanced air filtration system, a concrete mix that replaces about 45 percent of the Portland cement in the foundations and core with blast furnace slag, and a cogeneration plant that produces both electricity and steam for on-site use.

The building has many green bells and whistles, to be sure. But these features were chosen on the basis of operational and economic criteria, as well as sustainability goals, say project team members. “The clients weren’t interested in demonstration technologies that wouldn’t work,” says Serge Appel, AIA, Cook+Fox project architect.

The developer was willing to consider unusual strategies, but not without thorough evaluation. Before settling on cogeneration for example, consultants vetted several other on-site energy generation technologies. They monitored wind velocities with an anemometer mounted on the roof of 4 Times Square (an adjacent Durst tower completed in 1999 and widely considered the first green commercial highrise in the U.S.). But the results showed that conditions were too gusty for wind turbines. They explored incorporating photovoltaics into the skin and the podium roof, and determined that both would be in shadow too much of the time. They investigated geothermal energy, but decided the site was too tight for the number of required wells. They even discussed generating methane from tenants’ paper waste in an anaerobic digester. However, the bank was worried about the security of its discarded documents.

They eventually implemented a 4.6 MW natural gas-fired cogeneration plant which went on-line this summer. It is expected to satisfy about 65 percent of the building’s annual electricity demand. The strategy, also known as combined heat and power (CHP), derives its efficiencies from making use of the heat that is a byproduct of the generation process. At the Bank of America, the heat is used to make steam, which in turn heats the building and its domestic water supply. It also is used to operate an absorption chiller for cooling.

As with most office buildings, the tower’s demand for electricity is lower during off hours. However, “the economics of the CHP would only make sense if it could run pedal to the metal 24-7,” says Scott Frank, PE, a partner at Jaros Baum & Bolles, the project’s mechanical engineer. So, in order to even out the load profile, designers included a 44-tank thermal energy storage system. It makes ice at night with excess electricity. During the day, the melting ice supplements building cooling. The team estimates that the CHP plant, working in concert with the energy storage system, will reduce daytime peak electricity demand by 30 percent.

The CHP plant, which designers say is the first large-scale installation of its type in a New York City office tower, was the building’s most logistically challenging feature to realize. The team needed to route natural gas lines through the densely occupied structure and isolate the equipment for noise and vibration. There was also a maze of permitting hurdles, including approvals from the fire department and the local utility.

Although the CHP plant was the most effort-intensive building system, other features also involved careful coordination. For instance, the project’s construction manager, Tishman, oversaw subcontractors installing base-building components of the underfloor air system, such as core wall cladding, corridor curbs, and perimeter fin-tube enclosures. Meanwhile, the tenants’ individual fitout contractors were responsible for installation of elements within the office spaces, including the raised floor panels. In order for the system to function properly, all needed to follow strict installation guidelines and maintain the air-tightness of the floor plenum.

For Gensler, the architect that designed the bank’s LEED Gold office space and trading floors, a key challenge was the limited availability of green materials when the firm started its work seven years ago. For example, principal Ej Lee wanted all of the wood in the millwork to be certified by the Forest Stewardship Council (FSC). But Lee and her team could not find suitable veneers and decided that only the substrate would be FSC-certified.

Another difficulty was devising a layout compatible with the client’s corporate culture that would also allow access to daylight and views for a majority of occupants. Gensler pushed for private offices positioned next to the building core and surrounded by open workstations. But the bank maintained that it would need perimeter offices to attract and retain executives. The realized scheme does have perimeter offices, but with all-glass fronts facing the rest of the interior floor area in order to limit obstruction of views and allow daylight penetration.

The tower’s exterior curtain wall is made up of floor-to-ceiling, double-lite insulated units of low-iron glass. To help control heat gain and glare, the units include a low-e coating as well as a ceramic frit that covers 60 percent of the glass where the curtain wall meets the floor and ceiling. The pattern gradually decreases in density toward the vision portion of each panel. Non-metallic spacers in the aluminum mullion system and extra mineral wool insulation at the floor slabs help achieve a U value for the assembly of 0.38—a thermal resistance that is better than most glass towers built in New York City over the last decade, but still below prescriptive code requirements.

Although a more solid facade would have likely provided greater thermal resistance, the team maintains that the all-glass skin was crucial to the building’s architectural expression and its economic model: The transparency “allowed us to get market-rate rents and invest in other [high-performance] systems,” explains Don Winston, PE, director of technical services at Durst.

Even with its crystalline curtain wall, the building’s energy model shows a 20.97 percent cost savings over a building designed to meet the 2004 version of ASHRAE 90.1, Appendix G, according to the project team. If only core and shell energy are considered (i.e., if the tenant spaces are excluded), the model indicates performance that is 54 percent better than the standard.

Winston has been monitoring the tower’s performance, and preliminary results indicate that it is operating more efficiently than the energy model. But without more data, he says, “I’m not confident to say just how much better.” Winston is committed to releasing the actual performance information, but not until the CHP plant has been up and running for at least a year. We hope he will share that data with us for publication in GreenSource.

TEAM
Owner A joint venture between the Durst Organization and Bank of America
Project developer The Durst Organization
Design architect Cook+Fox Architects
Executive architect Adamson Associates Architects
Interior architect Gensler
Engineers Jaros, Baum & Bolles (mechanical); Severud Associates (structural); Mueser Rutledge Consulting (geotechnical)
Construction manager Tishman Construction Corporation
Code consultant JAM Consultants
Cogeneration design Waldron Engineering & Construction
Commissioning agent The Fulcrum Group
Exterior wall consultant Israel Berger & Associates
Energy/environmental consultant Viridian Energy & Environmental
LEED consultant e4 inc.
Lighting consultant Cline Bettridge Bernstein Lighting Design
Roofing and waterproofing Darius Toraby Architects
Solar design/photovoltaic consultant Solar Design Associates
Wind consultant altPower
Base building acoustician Shen Milsom & Wilke
Exterior maintenance consultant Entek Engineering

SOURCES
Structural system Owen Steel Corp.
Thermal storage Calmac Manufacturing Corp. Icebank
Cogeneration plant Solar Turbines Mercury 50
Underfloor air distribution Tate Access Floors
LED lighting IO Lighting

Bank of America Tower

The expansive Jerusalem stone-clad lobby helps tie the 1,200-foot-tall tower to the Earth and Manhattan’s street grid.
Photo © Cook+Fox Architects

Bank of America Tower

An open-tread stair connects the Bank of America’s trading floors on levels 3 through 6. The stair, and an illuminated red glass box, are visible from the street.
Photo © Paul Rivera/Archphoto

Bank of America Tower

Floor-to-ceiling glass in offices and the associated views were key selling points for the tower’s developer.
Photo © David Sundberg/Esto
Bank of America Tower
The bank occupies more than 75 percent of the tower, or about 1.6 million square feet. Its spaces include private perimeter offices, which have all-glass fronts to ensure access to daylight and views for employees occupying open office areas.
Bank of America Tower
Through the 20th floor, the Bank of America is square in plan with two small pieces of floor plate that cantilever to the east and west. The perimeter walls enclosing the floors above slope and cant. The resulting angular facets and irregularly shaped floor plates create a tapered effect and open up views to the diagonally adjacent Bryant Park and to surrounding buildings.
Bank of America Tower
Bank of America Tower

http://greensource.construction.com/green_building_projects/2010/1011_Bank_of_America_Tower.asp

March 1, 2011

Lighting One Bryant Park | Cook+Fox and Cline Bettridge Bernstein Lighting Design

One Bryant Park has its own distinctive identity on the night skyline.

ONE BRYANT PARK HAS ITS OWN DISTINCTIVE IDENTITY ON THE NIGHT SKYLINE.
COURTESY COOK + FOX

When the Durst Organization and Cook + Fox approached Cline Bettridge Bernstein Lighting Design (CBBLD) to execute the exterior lighting scheme for One Bryant Park, they already had a very clear idea of how they wanted their building to appear at night. The crystalline volume of the 55-story tower features a variety of facets, sliced away from the mass of the building, that orient views through the forest of midtown skyscrapers surrounding the structure. This is most apparent on the southeast exposure, which faces onto Bryant Park itself, where the corner of the building is cut away from the 22nd floor up through the parapet, creating an inverted triangular facade element. Here, the architects established a double curtain wall, the exterior glass surface forming the smooth plane seen from the street, while the interior is notched in plan to create additional corner office space. Cook + Fox and the developer both wanted this inverted triangle to glow at night—to shine out on the skyline even brighter than the lantern-like, already glowing glass tower. And of course, the job would have to be accomplished without exceeding the stringent energy requirements demanded to achieve a LEED Platinum rating.

Courtesy CBBLD.
Courtesy CBBLD.

TOP AND ABOVE: LED COVE LIGHTS INSTALLED WITHIN THE WALL CAVITY AT THE SPANDRELS. THE LEDS ARE TUNED TO A COOLER WHITE THAN THE INTERIOR, MAKING THE SECTION STAND OUT ON THE LANTERN-LIKE BUILDING. [CLICK TO ENLARGE.]
COURTESY CBBLD

As tall as those marching orders may have been, they were not the last of the challenges that the project presented to CBBLD. The design team was impressed, and concerned, by the minimalism of the structure and the clarity of the low-iron glass. These were great features for giving the tenants unobstructed views to the park and skyline, as well as for flooding the interiors with copious quantities of salubrious unfiltered daylight, but those same aspects made the space Teflon, so to speak, for electric lighting. There was nothing upon which the light could cling, no surface that would hold it and create the glowing effect the architects so desired. The joke around the office was that they would have to fill the cavity with smoke and shine light up through its hazy mantle for anyone to notice any illumination at all. Cook + Fox was unwilling to add anything to the structure or the glass itself that would impede the view/daylight continuum. Furthermore, they insisted that whatever fixtures CBBLD inserted into the space must not be visible from the interior.

In the end, the solution was quite simple. The architects wavered an inch from their transparency hard line and added a touch of translucent fritting on each exterior glass panel, high up where it wouldn’t trouble the eye. It proved enough, however, to catch the light and create a subtle striated pattern of illumination on the exterior, an effect, after all, that even matched the romantic rendering first presented to CBBLD. To make the light, the team settled on high-output 15-watt LED cove fixtures placed in the spandrel sections of the elevation, where they would be well out of sight. They also tuned the white LEDs to 5,000K, establishing a cooler light within the double wall that contrasts with the warmer, 3,000K-T5 fluorescent strip lighting on the building’s interior.

As elegant as the solution was, it didn’t work all the way up the elevation, where two other architectural conditions presented themselves—the mechanical floors, which run from 52 to 56, and the parapet, which goes from 57 to the sky. Cook + Fox wanted a consistency to the appearance of the lighting scheme in spite of these differences, and so CBBLD went about fabricating as close a facsimile of the office floors as was possible. The mechanical floors step back from the lower parts of the tower, and on the resultant ledges, the team inserted frosted glass panels. They backlit these with floor-mounted 58-watt T5 fluorescent lamps, tuned to the same 3,000K color temperature as the office lighting. Within the cavity created between the frosted panels and the exterior wall, the designers placed the same 5,000K LED fixtures as used on floors 21 through 51, only bracket-mounted rather than cove. This strategy created a similar depth and contrasting tone of light as below. The team also backlit the rest of the mechanical floor’s facades, which are translucent glass, with 58 watt T5 fluorescent lamps, further reinforcing the consistency of lighting throughout the elevation of the building.

One Bryant Park.

COURTESY COOK + FOX

Lighting the parapet, which extends in some places asmuch as 50 feet above the roof, was an entirely different ballgame. There would be no constructing of a backing wall of frosted glass, as on the mechanical zones. CBBLD also had to contend with the helter-skelter ambient light of nearby Times Square. The solution was to use 400-watt metal halide floodlights behind the double wall section to simulate the lighting provided by T5s below, and 269-watt metal halide up-lights paired with each vertical column of the glass wall to reproduce the effect handled by the LEDs. The remainder of the parapet was lit with 150-watt metal halide up-lights, again to establish consistency of light all the way to the tippy top of the tower.

Then there is the spire, which reaches a full 1,200 feet into the air. Cook + Fox and Durst felt this element should be lit in a changing array of colors, both to complete the overall architectural composition at night, and as a civic gesture on the skyline similar to that offered by the Empire State Building. In answer, CBBLD outfitted the spire, a sort of triangular vertical truss in form, with strategically placed 50-watt RGB color-changing LED up-light fixtures. The luminaires are linked to a DMX control station, allowing One Bryant’s management to adjust the color on demand.

CBBLD also completed the lobby lighting scheme, though there is no room to discuss that here. Throughout the project, CBBLD counted every watt; there isn’t an incandescent on the job. The watt-scrimping paid off. The lighting scheme helped the base building earn its LEED Platinum rating, and it did so without sacrificing a little splash on the exterior, proving that a building doesn’t have to be boring to be green.

Aaron Seward