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Taking A Look At EC Fans

EC fans are generally recognised as being the latest thing in energy efficient air movement technology, but what is an EC fan and what makes it so special? EC stands for Electronically Commutated which basically means it’s a fan with a brushless DC motor.

Basic DC motors rely on carbon brushes and a commutation ring to switch the current direction, and therefore the magnetic field polarity, in a rotating armature.  The interaction between this internal rotor and fixed permanent magnets induces its rotation.  In an EC motor, the mechanical commutation has been replaced by electronic circuitry which supplies the right amount of armature current in the right direction at precisely the right time for accurate motor control.

DC motors are around 30% more efficient than AC motors because the secondary magnetic field comes from permanent magnets rather than copper windings.  An AC motor consumes additional energy solely to create a magnetic field by inducing a current in the rotor.

To control the motor accurately and efficiently the integrated electronics have to continuously monitor the motor speed and adjust the control input.  By making this circuitry available to external sources it’s possible to provide simple speed control options.  Dependent on the motor type, any sensor which can provide a 0-10V or 4-20mA input can be directly connected to provide a closed loop control for temperature, pressure or whatever parameter you choose to measure.  No need to worry about DC supplies for the sensors either as this can be provided by another connection on the motor.  In fact, simply connect a potentiometer and you have infinitely variable speed control.

So how does this affect energy efficiency?   Well, doubling the speed of a motor increases its power input by a factor of 8 so it’s very wasteful to run a fan faster than is required.  If you can tailor the fan speed to match the demand, the potential for energy saving is huge.  Even when compared to on/off operation, EC speed modulation is much more efficient.

EC fans can also contribute to increasing the overall efficiency of an application.  In a cooling system for example, keeping the refrigerant pressure constant rather than having it rise and fall as fans switch on and off has been found to reduce the load on the compressor resulting in even greater energy saving.

If two motors are producing the same output but one has a greater power input then you can be sure that the surplus energy is being dissipated as heat.  If an application is designed to remove heat then it will have to do extra work just to remove the heat produced by the fan motor itself, so EC fans will improve the efficiency of the whole system.

The available range of AC input EC fans is expanding all of the time.  There are axial and centrifugal fans, forward curved and backward curved, single inlet and double inlet, single phase and three phase and they are often directly interchangeable with their AC equivalents.

A common use for EC fan replacement is in the close control or computer room air conditioning application. The fans in these units run 24/7 so even relatively minor energy savings on previous works have paid for themselves in as little as 18 months.  Consider the application where the computer room use has altered and you have too many units for the capacity and it is easy to see that by reducing the fan speed to match the required capacity will have significantly shorter payback periods.

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