Piano's Beyeler Foundation Museum
The lineal pavilion is constructed over a 14-foot- (4.3-meter-) deep reinforced-concrete basement. The walls of the galleries are not structural but contain reinforced-concrete columns at 20-foot (6-meter-) centers to support the roof. Roof overhangs are supported by steel columns also encased in stone. The four long walls, each 354 feet (108 meters) long and 20 feet (6.1 meters) high, sit under a lightweight crystalline roof canopy 93 by 417 feet (28.3 by 127 meters) in plan.
The steel roof structure gives continuous support for the various glass layers, comprising glass ceiling and internal louvers, double-glazing, and the posts that carry the exterior inclined glass shading.
It was agreed that daylight should be used as the light source across the whole ground floor, and that the design of the building should seek to maximize the number of hours during which the collection could be viewed by daylight. However, best-practice standards for exposure of works of art to daylight in terms of time, levels, and spectral content could not be compromised by the desire to provide a daylit environment.
Following studies of lighting conditions in Basel, Arup recommended a target daylight factor of 4 percent, which is around double that in most European galleries. An active shading system to control interior light levels within predetermined limits, particularly on bright summer days, was also prescribed as an essential part of the lighting strategy.
These performance requirements were met by the development of a multilayered roof. The outermost element is the layer of fritted glass brise-soleil inclined and positioned to prevent direct sun penetration during all museum opening times but also to maintain optimum admittance of diffused light.
Below this lies the weatherproof layer consisting of a double-glazed skin with an ultraviolet filter that removes those parts of the electromagnetic spectrum most likely to damage the paintings to be displayed below.
Immediately below this layer are computer-motorized aluminum louver blades that control light levels in each room of the museum. These levels can be arranged to suit the management of the building and the conservation of the collection. When the museum is closed, for example, the louvers are closed to prevent exposure of artworks to daylight.
The louver system lies in the zone between ceiling and roof, which is designed as a "loft thermal buffer zone" and combines with the exterior brise-soleil to prevent 98 percent of incident solar radiation from reaching the gallery spaces below.
The lower boundary of the loft is formed by a laminated-glass ceiling designed to support maintenance access to the louver-blind motors and electric lights in the loft. The electric illumination is designed to complement the daylighting strategy: as daylight fades, triphosphor linear fluorescent fittings gradually compensate, contributing to the maintenance of ideal lighting levels.
The lowest layer in the system forms the visible ceiling of the ground-floor galleries: a grid of perforated metal panels incorporates a paper that diffuses light once more and adds a layer of opacity to the contents of the loft thermal buffer zone. The uniform lighting system is augmented by small low-voltage spotlights positioned on stems at the junctions of each ceiling panel. These can add highlighting and directional light essential for modeling effects of sculpture.
Energy and Environment
Thermal buffer spaces extend from the roof to the east and west sides of the facade, helping to limit the effects of climatic extremes on the building — 12 degrees Fahrenheit (-11 degrees Centigrade) in winter and 91 degrees F. (33 degrees C.) in summer. The heated and ventilated loft means that, despite the 100 percent glazed roof, perimeter heating is needed only in the north and southernmost galleries.
The east facade is climatically buffered by the service and ancillary rooms, and to the west the "winter garden" performs the same task, while providing a resting place with views across the countryside.
These buffer zones help to reduce reliance on mechanical systems — particularly important in Switzerland, where air conditioning is strongly discouraged. The national policy is to abandon development of nuclear power and to reduce the country's reliance on predominantly nuclear-generated power from France.
Regulatory frameworks therefore focus on the reduction of energy demand. For this particular building type, a statement of need must be submitted to the local authority that justifies the requirement for mechanical systems. The case for the Beyeler — based on the intention to display, conserve, and store valuable works of art — was supplemented by a dynamic analysis of annual energy use.
Heating and Ventilation System
A true displacement system of ventilation was chosen for the Beyeler. This was designed to minimize air velocities in proximity to artwork. The air is delivered at very low velocities from linear floor grills, which are made from wood to integrate both visually and functionally with the oak strip floor.
Floorboards on either side of the grills can be removed to enable access to the ductwork plenum below (for cleaning) and to electrical sockets (for flexible display). Perimeter heating is through trench connectors installed below the same wooden grills under the windows.
The air supply to each gallery module is controlled by variable-air-volume boxes installed in the services corridor at the basement level. This 6-foot (1.8-meter-) wide space runs for most of the building length and contains supply and return ducts, which are fed by two air-handling units, each able to provide up to 50 percent fresh air in favorable exterior conditions.
Additionally, the primary air-handling units each incorporate thermal wheels to recover heat from exhaust air in winter and also obtain more heat following dehumidification by transferring heat from the extract air.
Ernst Beyeler's collection had originally been installed in his home, where the works were daylit and came alive in naturally changing conditions. Although this museum may not rank among Piano's defining buildings, Beyeler's desire to recreate these conditions in the new gallery has been largely fulfilled. The spaces for display are tranquil and undisturbed by the intrusive visual noise of engineering and constructional technique.
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Dean Hawkes and Wayne Forster are practicing architects who teach at the Welsh School of Architecture at Cardiff University. Hawkes received the international PLEA Award 2000 for his contribution to teaching, practice, and writing in the field of environmental design.
This article is excerpted from Energy Efficient Buildings: Architecture, Engineering, and Environment, copyright © 2002, available from W.W. Norton & Company and at Amazon.com.