Data Center

The Domino Effect: How energy efficiency in Data Centers may lead to power factor issues

How energy efficiency in Data Centers may lead to power factor issues

Ever notice how changing one thing leads to a domino effect? I mention this only because I treated myself to a new HDTV – well, it started with the TV, but it resulted in an upgrade cascade I hadn’t anticipated. For example, I had the new TV, but to enjoy the high definition I needed to upgrade to a high def PVR, which will result in new charges from my cable provider. And then I heard the 7.1 surround sound demo and all of a sudden I really needed one of those too, including the down-firing subwoofer. I’ve rationalized the whole thing by telling myself this is not unique to home electronic purchases. The same is true for all technology – upgrades can have unanticipated consequences.

Blade servers and leading PF

A perfect example would be today’s blade servers, which are gradually replacing legacy servers in data centers. These new servers are wonderful – they allow us to develop smaller, high density data centers that have much greater efficiency. But here’s the domino effect: the ‘low harmonic’ power supplies in today’s blade servers have input capacitors that produce leading power factor (PF) – somewhere around .9 leading PF at full load, and worse at lighter loads. Leading PF creates significant issues for older UPS systems that provide critical power for the application. When leading power factor hits older UPSs, their capacity must be de-rated. If leading PF goes too far, UPSs may trip, which in turn could activate backup generators. Unfortunately these generators dislike leading PF as much as a UPS, and they may destabilize and shut down. Now you have a dark data center –just imagine your resulting costs.
So you replace that old UPS system with a shiny new system designed to handle leading PF better than the old system. Your new UPS even has this great feature called ‘eco-mode’ which saves energy when appropriate. But when eco-mode activates, it transfers all loads to the utility. Utilities really don’t like poor PF – leading or lagging – and may even financially penalize you. Your site may not shut down but any eco-mode savings quickly evaporate.

Unity = maximum efficiency

Obviously, we need to eliminate leading PF, thus eliminating PF-related utility penalties and allowing your servers to run at maximum efficiency. It also permits safe operation of servers whenever they operate with backup generators. Thankfully, there are products that can help make your UPS harmonize (no pun intended) with leading PF – generally known as electronic VAR injection equipment.
This electronic device is designed to provide reactive current compensation to correct for poor leading or lagging PF. They are designed with stepless injection, a small footprint, and, best of all, no bad interaction with loads or sources. They can be installed on a UPS output, so old or new systems can operate at full capacity without interruption, and will bring the PF in alignment with the utility to eliminate penalties. They’ll also prevent generator tripping, relieving any related safety issues.
I think the lesson here is this: as new technology comes on-line, there will be new challenges and adjustments at every turn. We are always going to be adapting to unanticipated outcomes. Just like the new entertainment system I’m still trying to install at home. Who would have thought that a simple TV purchase would lead to changing the whole room to accommodate all these new speakers? Now I’ll probably have to re-paint the walls in a color from a complementary palette.


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