e-newsletter
digital edition
product info
advertise
Mcgraw Hill Construction
comment

CASE STUDY:
KFW Westarkade

Frankfurt, Germany

Colors n Curves: A new bank headquarters in Frankfurt may well be the world's most energy-efficient office tower.

May 2011
Sauerbruch Hutton

By Ulf Meyer

Photo © Jan Bitter

Rate this project:
Based on what you have seen and read about this project, how would you grade it? Use the stars below to indicate your assessment, five stars being the highest rating.
----- Advertising -----

KEY PARAMETERS

Location Frankfurt, Germany(Main River watershed)

Gross area 420,000 ft2 (39,000 m2)

Completed May 2010

Annual purchased energy use (based on simulation)24 kBtu/ft2 (277 MJ/m2)

Annual carbon footprint (predicted) 9 lbs. CO2/ft2 (43 kg CO2/m2)

Program Subdivisible project rooms, adaptable workstations, laboratory, monitoring room, director’s office, and conference room

   
Heating Cooling   Temp./Dew Points   Precipitation

 

TEAM
Owner KfW Bankengruppe
Architect Sauerbruch Hutton
Commissioning agent Green Building Services
Engineers Transsolar Energietechnik (energy concept); ZWP Ingenieur-AG, Köln (mechanical); Reuter Rührgartner (electrical); Werner Sobek (structural/facade)
Consultants Mosbacher & Roll (facade); Sommerlad Haase Kuhli (landscape); Licht Kunst Licht (lighting); Müller-BBM (acoustical)

Sources
Metal/glass curtainwall FKN/Wicona (glass facade) BGT, Bischoff Glasstechnik (colored glass)
Cabinetwork/custom woodwork Westermann (conference wall)
Doors Schörghuber; Hörmann; Blasi
Wallcoverings (corridors) Rehau; Thermopal; Kronospan
Paneling Federle Westermann (partition)
Special surfacing Pleyers. bau innovationen
(high grade plaster)
Floor and wall tile Jura Kalkstein (natural stone, ground floor); Villeroy & Boch (tiles)
Elevators/escalators Schindler
Interior ambient lighting Zumtobel

Shrouded in shades of many colors, it is a building that claims to be green. And so it is. It is not often that a midsize bank building has good reason to make that claim, but the new 400,000-square-foot, $85 million expansion of the headquarters for the KfW Bank in Frankfurt, designed by Sauerbruch Hutton Architects of Berlin, does. If it performs as intended, the building will consume about 7 kWh (24,000 Btu) per square foot per year, making it one of the world's most energy-efficient office towers.

KfW, an abbreviation for Kreditanstalt für Wiederaufbau, or Credit Buro for Reconstruction, was founded in 1948, largely with money from the post-World War II European Recovery Program, also known as the Marshall Plan. Today, it is owned by the German government and is one of the 10 largest banks in the country, employing 3,500 people. Among its many initiatives is the funding of Germany's ambitious energy-conservation programs, including existing building retrofits and photovoltaic panel installation. Since 2006, KfW has distributed $1.4 billion for CO2reduction programs that stem from the Kyoto Protocol. The bank also defined KfW-40 and KfW-60two widely cited energy standards used as credit criteria.

Being at the forefront of Germany's tough energy policies, it was only logical that the bank would want a green building when the need to expand its existing headquarters arose. The German-British architecture duo of Matthias Sauerbruch and Louisa Hutton, selected in 2004 as the result of a design competition, were no strangers to this task. Among their many ambitious green projects is Berlin's GSW building, completed in 1999 and widely regarded as one of the world's first environmentally friendly high-rise towers.

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 50F or above 77F, 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 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.

 

This article appeared in the May 2011 print issue of GreenSource Magazine.

 Reader Comments:

Sign in to Comment

To write a comment about this story, please sign in. If this is your first time commenting on this site, you will be required to fill out a brief registration form. Your public username will be the beginning of the email address that you enter into the form (everything before the @ symbol). Other than that, none of the information that you enter will be publically displayed.

We welcome comments from all points of view. Off-topic or abusive comments, however, will be removed at the editors’ discretion.

----- Advertising -----
Click here to go to product info Page
Sweets, Search Building Products
Search
Reader Feedback
Most Commented Most Recommended
Rankings reflect comments made in the past 14 days
Rankings reflect comments made in the past 14 days
Recently Posted Reader Photos

View all photo galleries >>
Recent Forum Discussions

View all forum discusions >>