Up to 37% of a data center’s energy costs can be attributed to cooling infrastructure. A central part of cooling data centers is moving the air, and a big part of air movement is the cooling unit’s fans. Incremental changes in the type of fan, airflow direction and fan speed offer opportunities for energy efficiency have created better options for today’s fan designs.
In the U.S., CRAC (Computer-Room-Air-Conditioner) fans used to be forward-curved centrifugal fans inside the unit blowing air directly down into the underfloor at full steam.
The new fans “direct drive” fans are also known as plug or plenum fans. Instead of operating through belts and pulleys, the fan motor is connected directly to the fan. In addition, the opening through which a plug fan blows air is bigger, thus allowing for a more even distribution of air underneath the raised floor. With the smaller opening of a centrifugal fan, the air velocity is initially much higher, which can lead to unpredictable and inefficient airflow patterns under the raised floor.
Controlling the CRAC (Computer-Room-Air-Conditioner) fan speed a common law regarding fans goes as follows:
Fan 1 power = Fan 2 power X (Fan 2 speed/Fan 1 speed) 3
This cubic relationship means that if you can reduce fan speed by 10%, fan power consumption decreases by 27%. If you reduce fan speed by 20%, fan power drops by 49%.
With centrifugal fans, users can buy an extra VSD, also called a variable-frequency drive (VFD) that attaches to the motor and can throttle power up and down. Meanwhile, electronically commutated (EC) plug fans are inherently variable speed, because users can dictate how much voltage goes into the fan.