Retrofit of a belt-driven fan with a volume flow of 25,700 m³/h in the administration building of a German television station. In the pictures the two old rails of the old fan are still clearly visible on the floor. The fan was spring-mounted on these rails. The ECFanGrid system is so well balanced that even if the fans are mounted rigidly, no vibrations occur in the air handling unit. Balancing is carried out according to DIN ISO 21940-11 in quality grade G2.5 or G6.3 depending on the impeller size. In order to comply with VDI 6022, a second filter stage was previously required behind the belt-driven fan (belt abrasion dust). After the retrofit, it was possible to remove the filter stage and thus reduce the pressure losses of the system, which led to further energy savings.