Using EC Plug Fans to Improve Energy Efficiency

A U.S. Environmental Protection Agency survey released in 2007 concluded that IT
data centers consumed 61 billion kW of electricity at a total cost of $4.5 billion in 2006.
As energy costs continue to rise, energy conservation has become a top-of-mind issue
for data center management.
The data center cooling system is a primary target for energy efficiency improvements.
An Emerson Network Power analysis of data center energy usage found that cooling
systems-comprised of cooling and air movement equipment-can account for
approximately 38 percent of energy consumption.
Recently, Emerson Network Power has been studying the energy efficiency of different
types of fan systems because the fans that pressurize the raised floor are a primary energy
consumer. On chilled water cooling units, the fan comprises most of the energy usage.
Using electrically commutated (EC) plug fans and variable frequency drive (VFD) are two
effective methods for improving energy efficiency by controlling the fan speed. The energy
efficiency gains come from decreasing the input power.
If cooling units are oversized, the fan speed can be reduced. The motor power varies with
the cube of the motor speed.
Motor kw2 = Motor kw1 x (speed2/speed1)3
For example, a 10 percent reduction in fan speed results in an energy savings of 27
percent. A 20 percent reduction in fan speed results in 49 percent energy savings. In order
to prevent over-dehumidification, the water flow rate to the chilled water coil should also
be reduced by the same percent as the fan speed.