Ventilation One of the passive ventilation systems of the design of London City Hall are the displacement floor grills that are placed below the windows in order to supply the office spaces with fresh air.
The displacement ventilation systems are used to cool the committee rooms and the debate chamber. During winter, a hygroscopic thermal wheel extracts heat and moisture from the air and is used to preheat the air supply. During the summer, the same system is used to cool the incoming air supply. Source: http://aedesign.files.wordpress.com/2010/06/london-city-hall-andrea-gonzalez1.pdf