The “Oasis” winter garden at Lufthansa Aviation Center, designed by Ingenhoven Architects
Ever since founding Ingenhoven Architects in 1985, at age 25, Christoph Ingenhoven has been guided by the philosophy of Nachhaltigkeit. This is an old German term that once meant “protecting and maintaining a forest on a long-term basis,” but which has come to mean “sustainability.” In the context of design, the young architect saw Nachhaltigkeit as the quest to obtain an optimal balance between a building's surface area and its volume, a design that would, in effect, allow a building to breathe naturally without wasting energy.
Ingenhoven's first big chance to implement this approach to design came in 1991, when his Düsseldorf-based firm won an international competition for a headquarters tower in Essen for RWE, one of the biggest energy suppliers in Europe.
Ingenhoven's winning concept involved maximizing the use of natural ventilation by employing a double-skin, “breathing” façade. Warm air trapped between the skins would be used to warm the interior in winter and be expelled in the summer through a complex system of mechanical flaps activated by thermal sensors. In the early '90s, double-skin façades were new, even in Germany, and RWE's board was a bit hesitant, but they went along with Ingenhoven's scheme. The resulting 29-story, 417-foot RWE Tower, with 30% less energy usage than comparable high-rises, became one of the earliest public expressions of Nachhaltigkeit worldwide.
Flying high with Lufthansa
In 1999, Ingenhoven's firm reached new heights by beating nine other firms in an international competition for the Lufthansa Aviation Center, a tubular structure, 175 meters in length by 50 meters in width, at Frankfurt-am-Main's international airport. Completed in 2006, it houses more than 1,800 Lufthansa employees.
Ingenhoven's long, paraglider-shaped building uses 10 “passage wings” and nine enclosed “winter gardens” to serve as buffer zones, not only for controlling inside air temperature and ventilation, but also to dilute the noise from the airport, surrounding highways, and nearby high-speed trains.
The plan for the 63,000 square meters of occupied space alternates finger-shaped wings with the five- to seven-story winter gardens in a staggered, “comb-like,” arrangement (see schematic). Low-e insulating glass tempers the air in the winter gardens, even when outside temperatures range from minus-15°C in winter to 35°C in summer. The tempered air then flows to the office wings, each of which has at least one winter garden on its long side; this significantly reduces the amount of air conditioning needed to make the offices comfortable. Double-wall glazing is used only in the fingers whose walls are directly exposed to the exterior.
Floor plan of Lufthansa Aviation Center, Frankfurt-am-Main, showing the nine winter gardens (green), the 10 finger-shaped office wings (gold) flanking the winter gardens, and the central passage (red). The winter gardens temper the air circulating into the offices. Image: Ingenhoven Architects
One concern with such a system, however, is that it can overheat in summer wthout adequate ventilation. To address this problem, Ingenhoven's team equipped the glazed surfaces with airfoil elements that utilize electrically operated flaps and board-shaped spoilers in the roof to exhaust air and fumes and moderate the temperature in the winter gardens. The shape of the spoilers and their placement in the roof structure was tested by Gartner AG and IFI to prevent reverse airflow from strong winds or smoke intake in the event of a fire.
Ingenhoven Architects’ addition to the European Investment Bank, Kirchberg, Luxembourg, completed in August 2008. V-shaped internal structures visible through the glass skin form multi-story winter gardens in the 170-meter-long building, rated “very good” by the BREEAM system. Image: Ingenhoven Architects
A more recent example of the designer's approach to Nachhaltigkeit is the newly completed European Investment Bank (EIB) addition, in Kirchberg, Luxembourg, yet another international competition win for Ingenhoven's firm. Here, next to Sir Denys Lasdun's original EIB, Ingenhoven's 13,000-sm transparent vault of glass covers a series of V-shaped internal structures, forming winter gardens in the multi-story volumes between the sides of the V's. Building Team members include Werner Sobek Ingenieure GmbH, IC Consult, Beljuli, and S&E Consult.
The 170-meter-long, 72,500-sm addition, built at a cost of €135 million, is the first building on the Continent to earn a “very good” rating from the BREEAM certification system, Because it is largely heated and cooled through natural ventilation, the EIB uses only 64% of the electrical energy, 75% of the cooling energy, and 53% of the heating energy of a standard new building in the Kirchberg area.