Behind an exterior highlighted by floors that project outward at different angles, the new headquarters of Norddeutsche Landesbank in Hanover, Germany, boasts an unusual combination of energy-conservation features. They include a heat-exchange system connected to 120 foundation piles that have embedded plastic tubing — one of the first such applications in Germany.
Plastic tubing is also incorporated into the concrete floors on the lower stories of the 750,000-sq.-ft. building. Relying on the stable temperature of the subsurface water that flows through this tubing, heat is removed from the building in summer and added in winter, according to Stefan Behnisch, a principal with the building's Stuttgart, Germany-based architect, Behnisch, Behnisch & Partner. "The building mass is optimized and used as a cooling element," he notes. Its energy concept was developed by Transsolar, also of Stuttgart.
By controlling the water flow, the building's interior temperature can be balanced. For example, the difference between solar-induced heat buildup experienced on the south side of the building and its cooler north side can be equalized.
The heat-exchange system makes a substantial contribution to the building's heating and cooling requirements. However, additional capacity is obtained by using steam supplied by a district heating system, which utilizes heat that is a by-product of electrical generation.
The building is naturally ventilated by introducing air along its perimeter. Maximum floor widths of 45 ft. provide rows of offices on either side of a corridor and give every occupant access to operable windows. Flaps beneath the windows can be opened when rain precludes the opening of windows.
Air is drawn through office areas and through a gap in the wall that separates them from corridors. Several "chimneys" in corridors on each floor exhaust the air at roof level. To facilitate this flow, corridors have suspended ceilings that extend slightly into office areas.
The building encloses a ground-level courtyard. "Clean" air is drawn from it into the exterior wall sections, enabling ventilation to be provided even in sections of the curtain wall that face vehicular traffic.
Adjustable louvers on the building's south elevation are designed to maximize the use of natural light. The uppermost slats are angled independently of the lower slats in order to redirect light to reflective ceilings.
Because water for each toilet room and kitchenette is heated locally, a large hot water circulation system was not needed, which reduced the amount of necessary piping, Behnisch notes.
On upper floors that are supported by cantilevers as long as 60 ft., it was not possible to incorporate tubing in the concrete because of the heavier steel framing required. Cooling panels were therefore installed within suspended ceilings.
The building's array of energy-saving features all help to lessen the production of carbon dioxide. "We need less [mechanical] heating, and almost no cooling," Behnisch says. "We just use less energy."
The 180-ft.-tall structure, one of the tallest buildings in Hanover, houses 1,500 employees of the bank. Its unusual design was the result of the owner's desire for a "special" building. "We worked closely with the owner," Behnisch says. "The design was the outcome of a mutual development process."