T5FM Engineering Series
Volume 1, Issue 2
DC-Powered Electrically-Commutated Plug-Fan Technology for Data Center Precision Cooling
As data center facility managers and design engineers continue to show preference for products that aid at data center energy consumption reduction, there’s a big push towards utilizing equipment that can help increase efficiency, lower operating costs, and reduce the data centers carbon footprint.
Older data center cooling solutions typically involved CRAC/CRAH equipment which contained belt-driven fans spun by traditional AC electric motors. This equipment typically ran dirty (because you have a belt) and inefficient. Electrically Commutated or EC fans are generally recognized as being the latest thing in energy efficient air movement technology, but what is an EC fan and what makes it so special?
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 In an EC motor, the mechanical commutation has been replaced by electronic circuitry, which converts AC to DC and control the fan speed by regulating the power to the motor by supplying the right amount of armature current in the right direction at precisely the right time for accurate motor control. Permanent magnets are mounted inside the rotor with the fan impeller attached – which eliminates the belt.
EC Fan Examples
Put simply, 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. But this is only half the story. The use of modern electronics in controlling the motor has opened up many other possibilities which contribute to using less power.
How does this affect energy efficiency?
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. Adjusting the fan speed to match the demand opens up huge opportunities for energy saving in applications such as data center cooling. 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.
EC Fans Are Lowered Into Position Below the Raised Floor
AC vs. EC
AC motors operate at a certain point on their performance curve, which coincides with their peak efficiency. On either side of this operating point, the efficiency can drop off considerably. Conversely, EC motors have an almost flat efficiency curve, which stays relatively constant across the speed range, a range which is not limited by synchronous speeds or as susceptible to voltage fluctuations as an AC motor. This makes the EC fan much more flexible in terms of being able to use the same product to match the performance requirements of different applications while still benefiting from increased efficiency.
EC Plug-Fan Advantages:
- Up to 40% energy savings over traditional centrifugal fans
- 100% speed controllable without needing to install added components like VFD’s
- Efficient speed control
- Integrated electronics with power supply is built into the fan
- Operate cooler ensuring long motor life
- Steady predictable performance over the full voltage range
- Modular and compact design makes installation and removal easy (10-minute change-out)
- Direct drive, no belts, cleaner operation and maintenance free bearings
What about cost?
The slightly higher capex costs for EC fans in comparison with conventional motors are mostly amortized within the shortest operation time because of the low energy consumption and lower installation costs (no transformer control, VFD, or phased angle control is necessary). The huge energy savings potential provided by EC motors reduces opex, which translates into payback periods as short as a few months, and motor life savings of hundreds of dollars in a typical application such as data center cooling.