The motor of an EC fan is in fact a direct current motor; its rotor carries permanent magnets and, instead of brushes, an electronic board on the motor feeds current to the windings in sequence. Because the board itself rectifies the alternating current of the mains, the fan is connected to a normal 230 V or 400 V line and no separate drive is needed. Since no current circulates in the rotor, losses are lower; the motor runs cooler and its life is longer. Because both motor and drive fit into the same body, space is also saved on the panel side.
Motor efficiency is 50–70% in conventional asynchronous (AC) fans, whereas in EC fans it is around 85–90%. The real gain comes from speed control: the power drawn by a fan varies with the cube of the speed. When the speed falls to 80% the power falls to about half, and at 50% to one eighth. Noise also falls noticeably with speed. Because condenser fans rarely need full speed at night and in the winter months, annual fan consumption falls by 30–50% in most plants. The difference in investment mostly pays back in a year or two.
The speed is set with a 0–10 V signal from the controller or via Modbus communication; in the condenser it is tied to the condensing pressure, in the evaporator to the room temperature or the running state of the compressor. In the evaporator there is an additional gain: because the fan draws less electricity the heat it gives to the room also falls, which means the compressor runs less as well. Turning the fan at low speed when the compressor has stopped keeps the room temperature even. Several fans are connected to the same signal and all turn together at the same speed.
Points to watch: an EC fan is not connected to a phase-cut speed controller or a frequency drive; its electronics are damaged. The signal cable is run separately from the power cable. The electronic board is more sensitive to lightning and voltage surges than an AC motor; a surge arrester in the panel is recommended. In the event of a fault the motor and board are mostly replaced together. In our catalog the evaporator and condenser options with EC fans are indicated model by model. When ordering, the supply voltage and signal type should be stated separately.