Is your Data Center a Fixer Upper? Ideas for Retrofitting Your Legacy Data Center

It never fails…you get home from work, get the kids in bed, sit down on the couch for some much needed mind-numbing and flip through channels until you land on one of the multitude of home renovation shows that catches your eye. Two hours later, you are still glued to the TV and probably wondering how these families were lucky enough to get picked to have a team of professionals turn their outdated home into a modern masterpiece. Have you ever wished a team of professionals would come renovate your data center? Here are some common ideas for data center mechanical renovations that may bring you back to reality and save you energy, money, and hassle!


Add VFDs to your CRAC units:

A variable frequency drive (VFD) varies the speed of a motor. In the data center world, VFDs are commonly found on pumps, cooling tower fans, large AHUs and more recently on CRAC units. VFDs help you take advantage of the fan affinity laws. In short, airflow is directly related to motor speed while motor power consumption varies as the cube of the change of speed. So if speed decreases from 100% to 50%, power consumption decreases from 100% to 12.5%. A small change in fan speed can have a dramatic effect on energy consumption!

There are several options in the market for “VFD retrofit kits” for your legacy CRAC units. Most CRAC manufacturers offer kits for their units or you can go with a more vendor-neutral, custom approach. Whichever option you choose there are a few important things to consider:

  • Controls upgrades – some of the older control software may have to be upgraded to make the VFD work properly including the possible addition of monitoring external to the CRAC unit.
  • Motor replacement – many legacy fan motors are not rated for use with a VFD (inverter duty)
  • Grounding rings – adding a VFD may require adding a grounding ring to the motor shaft to protect the bearings
  • Fan sail switch – make sure the CRAC unit safeties allow you to slow the fan down to the level you wish
  • Limits on DX Units – DX coils require a minimum air speed across the coil that could minimize potential savings
  • Harmonic Distortion – adding VFDs could cause harmonic issues based on the characteristics of your data center

Replace centrifugal fans with EC fans:

As an alternative to adding VFDs to CRACs, many facilities are choosing to replace the centrifugal fans in their legacy CRAC units with electrically commutated (EC) fans. EC fans, like VFDs, allow the user to vary the fan speed directly at the motor, reducing energy usage. EC fans are also more efficient than centrifugal fans and typically require less maintenance and can even offer additional redundancy as some kits allow for active replacement of a failed fan.

As with VFD kits, most of the major CRAC manufacturers now offer “EC fan conversion kits.” A few important things to consider:

  • Installation difficulties – the EC fan upgrade is a much more intrusive process than simply adding a VFD. The install will require more unit downtime and more space than the VFD upgrade
  • Controls upgrade – legacy controls software will almost certainly need to be upgraded or the entire control panel may need to be replaced.
  • Less maintenance – no belts, pulleys, open bearings or shafts to worry about



Install return air plenums/extensions:

CRAC units work more efficiently with higher return air temperatures. One way to get higher return air temperatures at the unit is to increase the height of your return air inlet. Pulling the air from higher in the space also helps prevent mixing and recirculation into your cold aisles. Sheet metal plenum extensions are relatively inexpensive, quick and easy to install and can even look nice if done correctly. Here are a few things to consider:

  • Ceilings – if you have an existing ceiling consider using it as a return air plenum and installing plenum extensions through the ceiling to get the return air back to the CRAC
  • Stratification – if you have a high ceiling or roof in your data center, some hot air may be stratifying at the top of the space. In this case, installing plenum extensions could hurt you by disturbing this stratification and putting more load on your CRACs


So whether you are a do-it-yourselfer or if you would rather rely on the pros, there are several ways to save an aging data center. You just have to decide what gives you the most bang for your budget!


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About Matt Rothwell


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Matt Rothwell manages the Critical Systems group at McKenney’s, which specializes in data center projects ranging in size and complexity with a focus on renovations, expansions, and greenfield projects. Matt, a graduate of Georgia Tech and former McKenney's co-op, works with his team to cultivate existing and new relationships through the development and implementation of energy savings strategies.

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