1. An apparatus comprising: a fan ( 120 ); an electronically commutated electric motor ( 110 ) serving to drive the fan; a sensing apparatus ( 140 ) for sensing a volumetric air flow generated by the fan ( 120 ) and for generating a measured volumetric air flow value (Vmess); a volumetric flow rate control arrangement ( 160 ) for automatically controlling the volumetric air flow rate ( 125 ) generated by the fan ( 120 ) to a predetermined target volumetric air flow value (V_s), said volumetric air flow rate control arrangement ( 160 ) being adapted to generate a target rotation speed value (N_s) for the electric motor ( 110 ); and a rotation speed controller ( 170 ) which automatically controls the rotation speed of the electric motor ( 110 ) to the target rotation speed value (N_s) generated by the volumetric air flow rate control arrangement ( 160 ).