A ventilation system that provides a comfortable interior for buildings with double-skin glass facades Glass envelopes are being used increasingly in today’s buildings. For such structures, floor ventilation provides an optimal solution for air inflow and outflow. Double-skin facades maximize thermal retention in the cavity between the two glass layers, thereby conserving energy and ensuring a comfortable interior. This technology was integrated into Bonn's new Post Tower. The ventilation units are installed in the subfloor. Air is drawn in and expelled through grills integrated into the surface of the floor. Supply, exhaust, recirculation units or combined units can be used, depending upon which functions are required. A broad range of subfloor units are available: heat recovery systems and units with acoustically insulated exhaust ducts without fans, as well as complex units and systems outfitted with filters, flap valves, volume flow controllers, fans or heat exchangers. Units are selected and optimized according to the specific requirements of a given enclosure. The ventilation system devised by FassadenSystemLüftung GmbH (FSL) for Bonn’s 163 meter-high Post Tower greatly enhances the quality of this office building, the highest in the state of North-Rhine Westphalia. The FSL system optimally combines energy conservation, flexible use and a comfortable interior. It is anticipated that the advanced technologies used in the Post Tower will also make the property a highly profitable investment. This semi-elliptical office building has a decentralized ventilation system that enables intake air to flow into the building through its double skin facade, whose opening is controlled by the ratio of temperature to air pressure. The FSL system draws air into the building from the cavity between the skins. Intake air is purified by easily replaceable filters. An automatic non-return valve prevents backflow, and acoustic insulation reduces ambient noise to a barely audible level. The heat exchanger allows intake air to be cooled or heated. The fan is equipped with a variable power supply voltage that allows different volume flows to be realized. Hence, this system provides flexible, individualized interior comfort.