Using EC Plug Fans to Improve Energy Efficiency of Chilled Water Water Cooling Systems in Large Data Centers
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 in data centers has become a top-of-mind issue for data center management.
The data center cooling system is a primary target for energy efficiency improvements. A Vertiv™ 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, Vertiv 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
or 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.
Vertiv™ wanted to compare the energy efficiency of centrifugal blower systems to EC fan systems. Rather than make the comparison based on estimations created using blower curves and static pressure calculations, three units were sent to independent testing lab Intertek for a “live” test. The first step was to determine the appropriate performance testing method.
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