Technology: Breathing Facades - Facade Technology toward Decentralised, Natural Ventilation
In the construction of transparent building envelopes, next to the structural and building-physics solutions, the concept for ventilating the building interior plays a decisive role. While, on the one hand, American office buildings in particular are still ventilated by means of central air-handling plants, in Europe, residents and occupants are accustomed to ventilating spaces by opening windows or other apertures. A mild climate and a high quality of outdoor air are a good basis for natural ventilation. In decentralised systems - in contrast to centralised climate-control systems - operable facade elements are required for the individual rooms. In this way, fresh air can be supplied via the facade - a short path - doing away with the complex, copious ductwork as well as the central plant. Generally speaking, decentralised systems involve simply opening and closing windows; they also have a positive impact on the occupants' sense of well-being. While building envelopes that are completely closed can be sealed without difficulty, when a decentralised ventilation system is selected, attention must be paid to minimising heat loss in winter and energy gains in summer, and to keeping the system functioning without drafts when winds are strong. In buildings with smaller wind loads and less stringent sound-control requirements, single-shell systems are economical. However, particularly in skyscrapers, the external sun protection must also function when winds are strong; this may be accomplished, e.g., by introducing an additional outermost layer of glass known as a baffle plate. The German firm Josef Gartner Ltd. has been developing facades with different versions of double-shell systems since the 1980s - and these are now increasingly being employed for decentralised facade ventilation in the Anglo-Saxon lands. In German-speaking countries, in contrast, prefabricated facade modules, either with or without deflector skin - including ventilated cavity - as wind protection, have come out ahead.
