EC Fans for Data Centers
What are EC Fans?
Actually EC fans are a combination of an EC motor attached to a backward curve plenum fan. The combination provides an extremely efficient means to deliver air to Data Centers.
What is a backward Curve Fan?
A backward curve fan is a fan with blades that tilt away from the direction of rotation. This makes the fans able to operate with changing static pressure as this does not overload the motor and suitable to Data Center operation. Fan efficiency is the ratio between the power transferred to the air stream and the power delivered by the motor to the fan and depends on the type of fan and impeller. For similar air flows at the same system pressure, backward curve plenum fans are 15% to 20% more efficient than their forward curve counterpart.
What makes an EC Motor so special?
Electrically Commutated or EC motors internally operate on DC rather than AC. It is well established that DC motors are more efficient than AC motors since they don’t suffer losses from changes in polarity or losses through brushes. An AC motor will reach a maximum efficiency of 75%, whereas EC motors can achieve efficiencies in the low 90% and can do so over a higher range of RPM than an AC motor, making a EC motor particularly suited to variable air applications.
How much of a Data Centers Energy usage is related to air movement.
The graph below illustrates energy usage in the data center. While air movement is only 12% of the total, since the fans operate 100% of the time, the associated energy dollars can be considerable. In addition, CRAC or CRAH units operating with EC fans will also show a savings in both Cooling energy and Maintenance costs.
Why is a Data Center suited to Variable Air Flow?
To put it simply, the load profile of a data center or the IT equipment it contains is not constant. In fact loads can vary considerably over a 24 hour period, so when you consider that HVAC equipment operates 365 days per year, there is considerable potential to save energy by moving only the amount of air required to match the load at any given time. These facts aside, even at 100% air flow, the EC motor and fan combination will be more efficient due to the internal motor efficiencies stated above plus the backward curve fan efficiencies. In addition it should be noted that EC motors will generate less heat than an AC motor. Since the motor is in the airstream, this reduction will actually increase the delivered capacity of the CRAC or CRAH unit.
Are there other advantages to EC Fans?
Yes. Eliminating the belts, pulleys, bearings and shafts typical of most CRAC or CRAH units reduces maintenance costs and Data Center reliability. All of these items require periodic maintenance. Belts should be adjusted quarterly and replaced annually. Bearings should be greased at the same time and should be replaced every three years along with the fan pulleys. As the belts ware they create dust which can affect IT equipment. EC fans have no belts or pulleys and their bearings are sealed. All of this combines to provide more efficient and reliable operations with less service cost over the lifetime of the Unit.
Who can benefit from an EC Fan Conversion?
Any data center with CRAC or CRAH units are candidates for a conversion. Ideally the units will be 8 to 12 years old. While they could be newer, it is advisable that the units are out of the warranty period. In addition, the data center load should be at least 10% below the aggregate cooling capacity. This allows for upside savings and makes the ROI shorter. This can be easily determined by reading the UPS kW output and compare to the total tonnage of the units in the data center.
Is there a downside to an EC Fan Conversion?
Original equipment manufacturers will argue that replacing a unit is a better alternative to a fan conversion. While all manufacturers offer an EC fan option on new equipment, they have been slow to offer retrofit kits. Bick offers an engineered solution designed for the operating conditions present within the customer’s data center. We take current operating conditions such as floor static pressure and coil temperatures into account when selecting the appropriate fan size. While there is always some risk when working in a live data center, Bick’s 50 years of experience working in these environments makes us the most qualified.
Advantages of the EC Fan
- Lower running cost – significantly more efficient motor and improved drive efficiency
- No belt drives – reduce maintenance (no changing or adjusting)
- No belt dust and therefore no contaminating of mission critical equipment, including servers, disk drives, telecom switch gear, etc.
- Lower (audible) noise – no AC inverter whine if you have a VFD
- Less vibration; motor shaft and fan shaft are in line and in the same plane
- Due to individual direct drive nature of EC Fan, redundancy is built into each unit containing multiple fans…particularly Chilled Water CRAH units (greater allowable coil air volume range)
- Fan speed is continuously adjustable via a signal from the system controller without the use of VFD’s
- Higher floor static pressure due to optimized air distribution into raised floor
- Phase independent – rotation direction set by operating parameter