SYSTEMS ANALYSIS.

This sophisticated stubby tower at the Hanover trade-fair grounds was built as a permanent exposition of Expo 2000's theme Man-Nature-Technology, showing the best environmental control techniques of the turn of the century.

Passive and active energy-saving devices are no longer exceptional in Germany. Legislation encourages solar energy use and wind parks. Environment taxes on fuel have increased insulation standards. Eco-architecture no longer has to make ideological statements with symbolic features. As one of the latest examples, Hanover's International Trade Fair administration tower looks no more spectacular than a Japanese lantern of screen facades and sandwich layers, set off by a communications tower looking like an elaborate hat pin.

Hanover, an otherwise unexceptional small town in Germany, received two economic boosts post-1945; the establishment of West Germany's largest trade fair organization and the decision to extend and renovate the grounds with both temporary and permanent buildings for the millennial Expo (AR October 2000). In accordance with the 'Man-Nature-Technology' theme, Herzog + Partner were asked to improve comfort conditions in existing halls and, as a prototype for later exhibition structures, to design Hall 26. Their latest permanent landmark development is the Fair's new administration tower. At a modest 20 storeys it is Hanover's tallest building. Administrative staff occupy 250 workplaces, placed around the perimeter on 14 office floors; there is also an executive floor of suites, and reception and entertaining.

Concurrent with the outcry against battery farming, German architects increasingly subscribe to the European design of workplaces for humans: non-toxic building materials, environmental comfort through individual regulation, and low energy consumption. But, although German codes of practice for workplaces define thermal requirements, other factors are important for a subjective sense of wellbeing, such as perceived room temperature, symmetry of surface temperatures, user influence and balancing fluctuating values. Few of the principles now categorized under the heading 'environmentally friendly architecture' are new. The art lies in their refinement.

The Hanover Trade Fair administration building facade is made up of lightweight, non load-bearing external wall elements, developed from studies Herzog and his team have been working on since 1978. Cladding is a refined form of a system first used in Lohhof, near Munich, in 1984. It is a system that can be equally well used on both new and existing structures. A Middle-Eastern inspired wind tower, making use of convection currents, lies at the heart of the building services concept.

Internal heat gains are often all that is necessary to heat a building constructed according to modern building regulations. Rooms with large internal gains need cooling, which is considerably more expensive in energy terms than heating. Here, cooling is provided with minimum exploitation of resources by using structural elements as thermal reservoirs of coolness from night-time air. Coolness can then be released by natural time delay over the following day. Night-time cooling energy is transferred to a water circulation system via a hybrid cooling plant.

By wrapping the building in a two layer facade, a protective buffer zone is created. This allows rooms to be naturally ventilated, even during gusty wind conditions. The buffer zone also has structural, fire-fighting and constructional advantages. As the projecting and cantilevered concrete floor slabs define each zone, every floor maintains its fire-fighting integrity.

Eight 3m high strips of louvres in the outer skin ventilate the zone. Louvre adjustments are computer controlled and based on satellite weather station information, previous wind tunnel tests and analytical values. To refine responses, actual external temperature (as opposed to broad brush seasonal categories), time of day, solar impact on the facade, wind speed and direction, are all taken into account.

The internal skin has sliding windows and air inlets in apron panels. A mechanical element closes the inlets when a window is opened. Used air is removed over ducting and passed over a rotary heat exchanger before being discharged. Heat recovered in this way meets most of the additional internal space heating needs. There is always a choice of mechanical or passive air conditioning. In winter, the passive system makes use of the buffer zone for cooling and the mechanical system provides heating. Solid floors laced with water filled pipes become thermoactive slabs. Simultaneous heating of floor and ceiling slabs, in contrast to normal purely floor heating, reduces differences between air and surface temperatures. In summer, the systems are reversed and air from the buffer zone tempers the internal spaces while the mechanical system injects cooler air into work spaces. It is estimated that this network of constructional, passive and mechanical, systems will reduce building operating costs by 2.50 to 25.00 DM pe r square metre, in comparison with conventional technology.

The reduction in building material tolerances, thinner, lightweight components, the move from wet to dry construction systems all required development of compensatory machines. They replaced previous generations' reliance on, for instance, a building's orientation in the landscape, massive stone brick walls, sash windows, fireplace chimneys and natural time delayed air movements. We have almost come full circle with the rediscovery of passive and free physical phenomena. The question is whether the developed world's activities have not irreparably damaged these meteorological cycles so as to preclude their future availability. But after the circus has packed up, Herzog's building remains as a modest reminder of what is actually possible.