(JBED) - Summer 2006 - The Whole Building Design Guide

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daylight and natural ventilation through windows controlled by the occupants. A slender ring around a generous courtyard, NORD/LB has extremely shallow floor plates, even by German standards. Portions of the building have offices on only one side of social corridors. With the use of glass partitions, a spectacular quality of light washes through the building at all times. This is an architecture that intends to maximize the skin to volume ratio, not minimize it. Double skins at NORD/LB have been 22 Journal of Building Enclosure Design used in only two zones, and in both cases for very specific reasons. First, they have been applied to the long face of the building where needed to block traffic noise from a multi-lane boulevard. This again is driven by German space quality standards and sound walls are recognized as one of the corollary benefits that justify the double envelope (Osterle, 2002). A second application has been made on the southwest face of the 16-storey tower that was added to the scheme to provide offices for the board of directors. The entire building is fitted with automated, external shading louvers. At the higher levels these shades would often be forced to retract into their shelters on windy days if it were not for the protection offered inside the buffer space. The afternoon heat gain through this one exposure on breezy summer days was considered unacceptable, motivating the second leaf of glass. At the lower levels, where wind velocities never reach the critical level, the external louvers are free to deploy as needed. Where a covering layer of glass is not required by wind or acoustics, none is applied. This clearly demonstrates that in the climate of central Europe, shading is the design issues, not thermal losses, even for a building with such an extensive surface. There is an interesting cultural footnote. On the quiet streets of this German town, shading louvers can extend all the way down to the sidewalk without any sign of damage. In the United States we might need the outer glass just for protection from vandalism. The sound wall at NORD/LB happens to occur largely on a north face, so the double façade there returns little benefit in the dissipation of heat. However, it does have a second role in providing fresh air to offices that would otherwise face auto exhaust. The large interior courtyard of the building is a reservoir of clean air. This air is drawn through a flat plenum under the lowest office level. (Corresponding to the white volume at the base of the detail: Figure 9). In the relevant sections, baffles direct air into the base of the façade cavity and it is drawn by stack effect through louvers at the top of the façade. The occupants are then free to enjoy a clean and quiet source of fresh air through the operable windows of the inner skin. This simple transformation eliminates the need for vent panels in the sound wall; openings that would compromise the acoustic performance. Transsolar also teamed with Allmann, Sattler, Wappner on the design of an office complex in Munich (Figure 10). A low rise element again wraps the edge of the site with a really robust sound wall against the autobahn. There is an office tower in one corner with a more conventional form than NORD/LB. The scheme demonstrates a full palette of environmental strategies: shallow floor plate with easy ac-
cess to the perimeter, concrete structure with radiant cooling, operable glazing across the entire façade, displacement ventilation using a podium floor, a wind driven exhaust stack and a fan assisted supply sharing the same vertical shaft, an evaporative cooling tower on the roof operated at night, ground source wells operated during the day. Air flows in the rooms are boosted by small fan coil units at the perimeter that fit under the podium floor. These are fed with hot and cold water but no air duct system is required. Munich has district heating so there are no on-site strategies for that side of the energy equation. Fitting in among these strategies is a double façade for the tower. It is so simple in its concept and crisp in its detailing that it could easily be mistaken for a single leaf assembly (Figure 11). The façade is a unitized curtain wall with an overall depth that is not much greater than standard wind mullions. The inner leaf of insulating glass is divided at chair rail height into two operable units. The cavity is partitioned at the same point and contains operable shading louvers in the upper region. The outer leaf is a perforated stainless sheet in the lower zone and plate glass above. Generous amounts of ventilation air can be taken through the perforated metal by opening the lower sash. The larger, upper sash is the vision zone and the true double skin. By simply allowing the perforated metal to overlap this unit slightly at the top and the bottom, there is free ventilation of the cavity behind the outer leaf of glass. This can be used to dump heat gain from the shades or to admit a moderated air flow by opening the upper sash behind its protective outer leaf. It was first thought that projecting fins would be needed to create turbulence and to ventilate the cavities. Flow modeling revealed that the strips of metal mesh, top and bottom, were adequate on their own. It is remarkable how simple this double skin system has become. The key to the scheme is that maintenance access comes through the fully operable inner glass leaf. In the United States, this would in itself be a very radical proposition, but in Germany a large percentage of operable glass is a given in the building culture. For visual continuity, the low rise portion of the complex has the same cladding units on the courtyard façade, except that the outer leaf of glass in the upper zone is omitted. This repeats the lesson that protection of the external shading devices from wind velocities at height is the primary motivation for the double skin. Allmann, Sattler, Wappner and Transsolar have identified the performance attributes that are needed from the façades and achieved these with directness, clarity and true elegance. EXPLORATIONS IN THE AESTHETIC DOMAIN The technical benefits of the glass double façade have not yet been established with the certainty of those for the rainscreen wall. Nevertheless, we have already seen that, like the rainscreen, the double skin is a trigger for aesthetic explorations that run far beyond the functional basis of the concept. Herzog and De Meuron, Swiss architects of the first rank, completed very sophisticated double façades early in their rise to international prominence. Their “re-wrap” façade in Basle (SUVA Building, 1993) is a marvel of piston actuators and glazing technology. By contrast, their Laban center for Dance in London (Deptford) is wrapped in a simple layer of polycarbonate panels (Figure 12). The wall section displays all of the attributes of a double façade: open grills at the base, operable vents at the inner leaf that draw air from the cavity, maintenance gangways between the skins that so far have seen limited use. But, these are not the driving forces behind the design. Subtle tinting of the polycarbonate gives the flush façades an abstract, lyrical quality as they hover above an earthy, post industrial context. Inside, the dance studios receive a serene wash of colored light so beautiful that the 2003 RIBA Stirling Prize could have been won for this effect alone (Figure 13). The tour de force of glass façades remains Peter Zumthor’s Kunsthaus, Bregenz (Figure 14). Here the building is clad from parapet to ground plane with identical laminated panels. No other material is present except for the front door and the stainless steel brackets that support the glass. Inside is an equally minimalist structure. Each gallery fills a floor, with art displayed against the turned up edges of concrete “trays” that are suspended three times above one another like memo boxes Figure 9 - East façade detail, NORD/LB. Behnisch Behnisch and Partner. Figure 10 - Münchner Tor, Munich, Germany, 2003. Allmann, Sattler, Wappner. Figure 11 - Façade unit, Munchener Tor. Allmann, Sattler, Wappner. Figure 12 - Laban Centre for Dance, Deptford, UK, 2000. Herzog & de Meuron. Figure 13 - Studio interior, Laban Centre. Herzog & de Meuron. Summer 2006 23
Page 1: JBED Summer 2006 Journal of Buildin
Page 6: Message from NIBS David A. Harris,
Page 10 and 11: Feature Dynamic, Integrated Façade
Page 12 and 13: 1. COMMERCIALLY AVAILABLE SOLUTIONS
Page 14 and 15: procure them for the final building
Page 16 and 17: obstruction and/or daylight reflect
Page 19 and 20: Feature All That Glass Is there an
Page 21: façade at the street corner. It is
Page 26 and 27: Feature Architectural Glazing for S
Page 28 and 29: could consist of lites that have di
Page 30: esidents. Another concern from the
Page 33 and 34: from the California Central Valley
Page 37 and 38: Feature Window Comfort & Energy Cod
Page 39 and 40: By Valerie L. Block and Tammy Amos,
Page 41 and 42: Feature How Does Fenestration Fit I
Page 43: Council (ICC), one might expect tha
Page 46 and 47: Industry Update By James C. Benney,
Page 48 and 49: BEC Corner HOUSTON-BEC By Andy MacP
Page 50: Buyer’s Guide AIR BARRIERS Dupont

(JBED) - Summer 2006 - The Whole Building Design Guide

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