Energy-conserving ventilating fan

A ventilating apparatus adapted for placement in a cylindrical air duct (260), comprising:

• an axial fan (120) having an axial fan wheel (122) dimensioned to fit inside the cylindrical air duct;
• an electronically commutated electric motor (110) serving to drive the axial fan so that, during operation, the fan transports air axially through the duct;
• an air-conducting tube (248) mounted in the duct (260) adjacent the axial fan (120);
• a thermal anemometer (140) in said air-conducting tube 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).