CRAH VFD Upgrade Kits Provide Serious Reduction in Data Center

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By Eric Gallant

It seems that every manufacturer and consultant in the data center industry has a green spin for their marketing campaign. Every new product launch is advertised as a major step toward and greener and more energy efficient data center. Each new design tweak is heralded as the greatest thing since hot aisle/cold aisle. It can be a challenge to separate products and strategies that offer some actual benefit from the greenwashing. It can be even more challenging to separate the products that offer truly meaningful benefits from those that offer vanishingly small gains.

One product category where technology advancements have provided verifiable and significant energy benefits is the Computer Room Air Handler (CRAH). Earlier this year I had a unique opportunity to do a side by side comparison of a constant volume fan CRAH to one with the newer VFD fan technology. One of my customers wanted to add an additional air handler to small POP room for redundancy. The room had an existing 22 ton ATS CRAH that was installed in 1999 that featured the traditional constant speed technology.  We installed a new Stulz-ATS Cyberair 2 with the same cooling capacity and featuring EC fan technology. (An EC fan is a type of high efficiency VFD fan used by Stulz-ATS) With the units installed side by side and the room’s heat load characteristics kept the same we were able to measure the amp draw of each unit. We found that the new unit maintained the same room temperature and used less than 50% of the power drawn by the constant speed unit. In addition, the new unit is dramatically quieter and requires significantly less maintenance.

For years, the centrifugal fans that move air through CRAHs were driven by constant speed electric motors. Regardless of the temperature in the room or the pressure under the floor, these fan motors ran at constant speed and delivered a constant volume of air. Temperature was controlled by adjusting the amount of chilled water flowing through the unit. But the fan and its motor ran wide open all the time.

Over the last few years, all of the major CRAH manufacturer’s have launched new models that use variable speed drives (VSD) to turn the fans.  These new drives automatically adjust their speed based either temperature or under floor pressure. As a result, the unit uses only as much energy as it needs to maintain its set-point. In addition to improvements in fan motor technology, the fan has also been radically redesigned providing additional efficiency gains.

Of course, not all applications will see a 50% reduction in power usage for their CRAHs. However, the 20 to 60% drop in power consumption that is claimed in the Stulz-ATS literature is completely realistic. If you assume that you pay $0.10/kw-hr, that type of energy reduction could save you $1,700-$4,900 in energy costs per year for every CRAH in your data center. There are additional cost savings because the EC fans don’t have pulleys, shafts,
sleeves and belts and other parts that need periodic maintenance. The fact that these units don’t use belts to drive the fans also means that there is no belt dust coming from the unit. This could mean that you see additional cost savings from reduced under-floor cleaning costs.

As if those benefits were not appealing enough, Stulz-ATS has just made the upgrade to VFD technology even more cost effective. They have put together modification kit that allows older constant speed fan CRAHs to be retrofitted with VFD motors and fans in the field. The drop-in replacement also includes a new control module and electronics package. Best of all, the Stulz-ATS retrofit is not limited to older Stulz-ATS and ATS units. They are now offering drop-in fan replacement kits for the most common Liebert units too.

Prices for these retrofit kits vary by CRAH size and model. However, a good budget figure for a kit (including turnkey installation) is roughly a third of the cost of a new VFD CRAH (not including any installation costs). In sum, for roughly $15K you can upgrade existing CRAHs with new technology that saves up to $5K per year. That’s the type of short ROI efficiency gain that makes sense for nearly every organization


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