As part of the development of the Northern Link in Stockholm, Rundquist Architects has designed two ventilation towers, located in different areas within the National City Park in Stockholm, one at Frescati and another in Värtan. Their function is to ventilate the air from Northern Link’s traffic tunnel and to reduce the emission levels at its entrances. Being placed within the National City Park, the towers’ design in relation to the park environment is very important.
Concept, Material and Geometry
The towers are made in wood in order to relate to the park environment while challenging preconceptions about how technological functions are usually designed. The idea of using a natural and site adapted material like wood throughout, and not just as a cladding material, has great symbolic value for the Northern Link project. The towers have been optimized to function in interplay with the architectural form. Wood as a natural material represents both low tech and high-tech, embedding cutting edge timber engineering from design to fabrication and construction. The construction is 20 m high and is shaped as a super-triangle that pivots upwards, along its axis. The internal geometry and structure helps optimizing the exhaust air flow; the larger space at the bend into the tower and at the top, where the triangle sections are wider, reduces the air resistance at the exit.
The twist gives the towers a sleek and interesting expression, suggesting the shape of the air movement. The towers are clad with horizontal cedar sheets which follow the swiveling shape, accentuate the sculptural impression and create a varied image that change over time and with the viewing angle.
Production and Construction
The towers were parametrically 3d modelled to allow optimization and adjustments throughout the design process. The different constructive components have been picked out from the model, labeled and sorted out as workpieces in an automated process before the files were exported to the CNC machine that milled the parts out of cross laminated spruce panels. The elements have then been delivered on site and combined into super triangles stacked on each other and tensioned together by vertical tie rods of steel that were fitted with springs to avoid tear of the structure when the wood moves.
Function & Geometry
The towers’ function is to divert the polluted air inside the Northern Link traffic tunnels to reduce emission levels at the tunnel entrances. An underground duct connects each tunnel with the corresponding tower. Fans of the channel have been designed to create a specific airflow through the ventilation towers for emissions at tunnel portals will be sufficiently low. The tower's interior geometry and structure affect the resistance for the outflowing air and thus the air flow. The towers have been optimized to function in harmony with the architectural form.