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Type: Headquarters, Office

Size: 775,000 sq ft / 72,000 sq m

Height: 33 floors; 531 ft / 162 m

Status: Completed 2003

Recognition : AIA National Honor Award; AIA Chicago Chapter Award; Urban Land Institute Award for Excellence ‑ International; Best New Skyscrapers of the Year; Licht‑Architektur Preis; Deutscher Stahlbau Award; CTBUH 10 Year Award

With integrated environmental strategies such as passive ventilation, daylighting, solar shading, geothermal heating, and structural efficiency, Post Tower makes a statement for a new way of building. Serving as the headquarters of Deutsche Post in Bonn, Germany, it is designed to maximize occupant comfort and environmental efficiency.

The 40-floor tower stands at the edge of the city adjacent to the Rhine River. Its plan is defined by a split and shifted oval, which orients the tower to take advantage of prevailing winds and views of the landscape. Nine-story sky gardens fill this 7.4-meter space that divides the office bays. 

A breathing twin shell façade ventilates the building year-round without the use of a central mechanical system. The interstitial space insulates the interior from harsh conditions and creates a buffer zone for passive ventilation, while mechanically operated exterior sunshades and a shingled south façade prevent solar gain and excess heat buildup. Automated operable flaps on the outer façade open based on the exterior temperature, wind velocity, and pressure differentials, and operable windows on the inner façade further facilitate opportunities for natural ventilation. This holistic design approach resulted in energy savings of 30% over the conventional German office building in the first year of operation. 

Heat pumps and heat exchangers source geothermal energy beneath the Rhine River and provide base heating and cooling through thermally activated slabs at each floor. Supply air for variable heating and cooling is drawn from the tempered façade cavity and conditioned by decentralized under-floor units before delivery to the interior space through the raised floor via the displacement method. This preconditioned air is then re-used to condition the sky gardens before being exhausted to the outside. The decentralized mechanical strategy eliminates mechanical shafts and spaces on each floor, increasing the usable area and flexibility of programming.

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