Breathing in Berlin
With high internal loads, the prime requirement is for ventilation and cooling, but winter heating is provided by the air handling system and radiators, supplied from the district heating system. Perimeter radiators are provided with individual thermostatic radiator valves, sized for a 7-degree-Fahrenheit (-14-degree-Centigrade) winter condition. Air extracted from the building is returned to the central plant room on the 22nd floor (below the roof) via risers for heat recovery in the winter.
High equipment loads generate a requirement for comfort cooling, but the implementation of a "peak lopping" system, allowing higher comfort temperatures of 81 degrees F. (27 degrees C.) when the outside temperature is 90 degrees F. (32 degrees C.), enable cooling to be provided without refrigeration.
The cooling necessary during very high summer temperatures is provided by spray coolers and desiccant thermal wheels, the latter regenerated from the district heating supply. The heat for the thermal wheels in summer is a byproduct of electricity generation for the local grid, and as such adds very little carbon dioxide to the atmosphere that would not already be produced for electricity.
The ventilation strategy required special design consideration given the height of the building and the consequent need to avoid draughts and unpredictable ventilation when windows are open. The outer glazing system of the west face provides the buffer needed to protect the interior, and also forms the solar flue which drives the ventilation when the wind speed is low.
The flue also moderates wind flow through the offices when it is windy, irrespective of wind direction. Mechanical ventilation provides air changes during seasonal weather extremes, when the windows have to be closed. Air is supplied from the main plant room via the floor, using swirl diffusers recessed into a raised floor system which acts as a plenum.
The floor plenum is divided into three zones, which are fed with air from local risers, allowing all floors to be mechanically or naturally ventilated, with up to three tenant zones per floor.
The building's central management system determines whether to turn on the mechanical ventilation, but occupants can select individual zones within a floor in either mechanical or natural ventilation mode by a simple wall-mounted zone controller.
The glazing gives the GSW tower its character. Daylighting objectives led to the adoption of a low sill height of 24 inches (600 millimeters) with the glazing extending the soffit of the floor above.
The western glazing comprises an inner double-glazed system incorporating bottom-hung outward opening windows which ventilates the interior into the cavity. In this cavity is a series of vertically pivoting and sliding panels that are 18 percent perforated.
The opening window is the "control point" for air flow into the flue, and model tests were made of it to ensure that its airflow/ pressure-loss characteristics were as modeled. The outer single skin of the thermal flue is glazed with laminated single-paned glass.
The glazing to the east side is triple glazed with mid-pane blinds, openable only for cleaning purposes. A high-level hopper provides ventilation in cold weather, while a vertically pivoting, wind-protected panel allows single-sided ventilation to cellular east-side offices.
The relatively low floor-to-floor height of 10.7 feet (3.25 meters) led to the selection of a narrow floor plan with a maximum wall-to-wall depth of 36 feet (11 meters). The walls are fully glazed from a low sill to the underside of the soffit.
This provides extremely good daylight to the office floors from both sides, and much reduces the need for artificial lighting even when the shading systems are closed, because good daylighting is always available from at least one side.
The west glazing is shaded by vertically pivoting and sliding panels which are 18 percent perforated and the east glazing is shaded by integral blinds. The 18-percent perforations in the vertical louvers in the thermal flue provide a bright environment with spectacular views across Berlin.
The offices are predominantly daylit, but are illuminated to 28 footcandles (300 lux) by electric lighting. The lighting in the offices consists of linear fluorescent fittings with specular 60-degree-cutoff louvers. The light fittings are recessed into slots in the exposed concrete soffit.
The lighting control system is based on the European Instabus (EIB) system, which was primarily adopted to provide flexibility and to enable room layouts to be changed without rewiring. The row of light fittings adjacent to the windows is automatically switched off by photocells within the facade to encourage the use of daylight. The remaining lighting is manually switched in groups. Occupants can override the automated daylight-linked switching.
The building management system (BMS) controls the key elements of the environmental system. The BMS controls airflow in the thermal flue by opening and closing the dampers at the top and bottom, and makes recommendations to the users about the selection of natural or mechanical ventilation by means of the green and red lights on the window transoms.
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Michael Wigginton is a award-winning author, architect, and professor of architecture at the University of Plymouth. Jude Harris is an associate at Jestico + Whiles in London and was the project architect for the award-winning "House for the Future" project in Cardiff.
This article is excerpted from Intelligent Skins, copyright © 2002, available from Architectural Press and at Amazon.com.
Architect: Sauerbruch & Hutton
Energy, thermal flue, services, and structural consultant: Arup
Structural design: Arup IGH Planning Association