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Credit Buro for Reconstruction-Westarkade, Frankfurt

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PostPosted: Fri Jul 01, 2011 7:57 pm    Post subject: Credit Buro for Reconstruction-Westarkade, Frankfurt Reply with quote

2011 Best Tall Building Europe
     KfW Westarkade

Kreditanstalt für Wiederaufbau, Westarkade, Frankfurt, Germany
Completion Date: May 2010
Height: 56 m (184 ft)
Stories: 14
Gross Floor Area: 18,116 m² (195,000 ft²)
Use: Office
Owner: KfW Bankengruppe
Design Architect: Sauerbruch Hutton
Associate Architect: Architekten Theiss Planungsgesellschaft mbH
Structural Engineer: Werner Sobek GmbH
MEP Engineer: Reuter Rührgartner GmbH; Zibell, Willner & Partner
Project Manager: Architekten Theiss Planungsgesellschaft mbH

Already being touted as one of the most energy-efficient office buildings in the world, KfW Westarkade is projected to use approximately half the energy of an average European office building, and one-third of a US-based one. The building addresses the prevailing wind direction to exploit it for controlled natural ventilation of the offices by means of its double-layered façade, which allows for the building to be naturally ventilated eight months out of the year.

The tower’s airfoil shape and encircling cavity make the most of prevailing winds for natural ventilation. The cavity also provides protection from solar gain.

“The streamlined form integrates itself into its surrounding context, while simultaneously standing out through the playful use of color. Whereas many buildings use color as a way to mask an otherwise unremarkable building, here it contributes an additional rich layer to what is already a remarkable building.”  –  Peter Murray, Awards Juror,

More info from the Magazine Green Source:
The recently completed KfW fits remarkably well into the context. Situated in Frankfurt's affluent Westend neighborhood, the building, known as the Westarkade, provides office space for 700 employees and includes a conference center. At its base, the building has a curvy four-story podium that reinforces the street edge and defines a small green space to the rear. It also serves as a backdrop to the nearby Palmengarten or Palmtree Garden, a public botanical garden. The podium connects to the adjacent KfW buildings on several levels, so the building forms an extension to the KfW ensemble of buildings from the seventies, eighties, and nineties.

The 10-story tower that rises from the podium has a flowing form that responds to prevailing wind directions and the sun's daily and yearly path. Yet it is also reminiscent of the jazzy architecture of the late forties and early fifties, the era when the bank was founded. According to Sauerbruch Hutton Project Architect Tom Geister, the tower is shaped like a wing in order to maintain access to daylight and the best possible views for the occupants of the neighboring KfW buildings.

Energy models predict that the new building's primary or source energy consumption for building operations (excluding the data center and other process loads) will be only 9.1 kWh per square foot. Monitoring by researchers from the University of Karlsruhe, to be completed this summer, will determine if the model was accurate. The simulation was conducted according to the parameters of the German EnEV 2004, the country's strict guidelines for building insulation and energy conservation.

A number of tightly coordinated strategies should help the building meet its ambitious targets. These include thermal activation of the slabs and a recovery system that captures heat from the data processing center and from exhaust air. A supplemental raised floor ventilation system, used only when outside temperatures are below 50°F or above 77°F, supplies fresh air drawn through a duct buried beneath a below-grade parking garage. The duct carries the air from an intake louver located at the site's edge near the botanical garden, modulating it with the constant temperature of the earth.

The sawtooth-shaped outer skin of the new KfW building includes multicolored automated flaps that open, depending on the weather.

The building's most unusual feature is a specially devised double-skin facade, dubbed a “pressure ring” by the design team. “Originally we wanted to call it a ‘gauge-pressure ring,' but we thought that would sound intimidating,” says Bjoern Roehle, a physicist in the Munich office of Transsolar KlimaEngineering, the firm responsible for the building's climate-control concept.

The envelope consists of an encircling sawtooth-shaped cavity, 28 inches wide at its deepest point. It encloses automated blinds that help block solar gain and control glare. This “ring” is defined on the exterior by a skin made up of fixed, tempered-glass panels and colorful ventilation flaps, and on the interior by alternating operable and fixed argon-filled insulated glazing units incorporating a low-E coating. The dynamic system negates the effects of variable pressure around the building, enabling natural ventilation much of the year. It also allows occupants to open windows in the inner skin, regardless of the season, without drafts or heat loss. The system reduces detrimental cross ventilation—a typical problem in high-rise buildings with operable windows—to a “convenient minimum,” explains Geister.

The building has a roof-mounted weather station that monitors wind direction and speed, among other factors, and controls the outer skin's ventilation flaps. Depending on conditions, the building management system opens or closes the flaps to introduce fresh air and create a zone of consistent pressure surrounding the curtain wall's inner skin, while also producing a slight pressure differential between the cavity and the building's interior. The air is then drawn into offices through floor vents near the perimeter, or through the occupant-controlled windows, and subsequently exhausted naturally to the negatively pressurized corridor, and ultimately through the building core.

Colorful facade panels, also deployed at GSW and by now a signature Sauerbruch Hutton device, animate the elevations. In the Frankfurt building, the architects combined red, blue, and green panels, with a different hue dominating each elevation. This colorful and innovative envelope, along with the building's highly coordinated climate-control systems, should help KfW establish a new benchmark for red, blue—and, of course, green—design in Europe.

Ulf Meyer is an architectural writer and educator based in Berlin and the U.S. He was named the Hyde Chair of Excellence 2010 at the Univ. of Nebraska-Lincoln.
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