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An intriguing proposal for an energy efficient office block at the headquarters of a German curtain walling company.

Glasbau Seele are a relatively young Bavarian company specialising in innovative curtain walling construction. The company also has an enlightened attitude to architectural patronage, by making its own headquarters and production plant the subject of a series of competitions. Most recently, through this process, Ian Ritchie Architects were selected to implement a design for a new production hall (AR January 1995 p10). Prior to this, the German practice of Kauffman + Theilig completed the first phase of the production plant and are now working on a proposal for a new administration block.

Kauffmann + Theilig's proposal aims to create an energy efficient building of maximum transparency. The curving glazed skin, moored on one side by an angled wall, billows out and envelops the nine storeys of office space. The stepped arrangement of floor plates creates a silver of an atrium and thermal buffer zone between the glazing and the edges of the floor slabs. Considerable analysis has gone into the use of energy in the new block, using computer models to simulate the heating demands of a typical office floor. In this case the programme used was TRNSYS (Transient System Simulation Programme) developed by the University of Wisconsin, which includes not only heating load analysis, but can be used study the effects and interaction of a range of heating and ventilation components.

The building is orientated to the north, to minimise problems of overheating and glare. The atrium acts as a thermal buffer zone, limiting transmission losses from the offices. A typical office building with double glazing was used as a reference standard, to which Kauffmann + Theilig's proposal of a high rise building with two layers of glazing in conjunction with a more responsive ventilation regime, could be compared. Initial results for heating demand and resulting room temperature showed little variation between the two conditions. Further analysis was made varying the type of glass used. With two layers of single glazing, (on the external atrium skin and the offices) the atrium cannot be used without artificial heating between mid October to mid April; replacing this with two layers of low emissivity glass extends the occupation period from mid November to the beginning of March. The latter solution also has other advantages in that heating load required to bring the atrium temperature up to the required comfort level of 15 deg C during winter months is smaller.

Ventilation strategies were also considered. In winter, exhaust air is removed from the offices and rises by a stack effect through an insulated shaft where it is fed through a heat exchanger warming fresh air that is blown into the atrium. Heat build-up on the south face can be used to supplement the heat exchanger. Air from the atrium flows back into the offices via a convector. In summer fresh air is drawn through the atrium and rises up it due to the stack effect; offices are ventilated from the core.

These principles are clearly an attempt to integrate built form and environmental control, yet are still at the hypothetical stage. Only when actual energy consumption and comfort levels can be monitored over a period of time, will the true effectiveness become known. Such detailed studies will reveal valuable lessons for the future.