Power Management

Why Eco-mode UPSs and Free Power Quality Make Energy Management Systems Even More Important

In the data center industry we’ve been talking for years about the need for reliable power and how best to ensure we get it. At Schneider Electric in particular we’ve long espoused the need for energy management systems as a key component of ensuring reliable power.

In fact, we recently published a revised version of a white paper that came out about 10 years ago on this very topic. Titled “How Energy Management Helps Maximize Power Reliability,” the paper made the case that customers needed energy management systems because the electrical power grid, on its own, wasn’t reliable enough to consistently deliver power to our increasingly important data centers.

What struck me in re-reading the paper was how energy management systems are still vitally important today as data center operators apply new technologies including eco-mode UPS systems and so-called free power quality (FPQ) techniques.

Eco-mode UPSs essentially operate in a bypass mode at least some of the time. Normally, a UPS takes in AC power, rectifies it to DC, performs some filtering on the DC power, then converts it back to AC. A small amount of power is lost in the conversion processes – the price to pay for “clean” power.

When operating in bypass mode, an eco-mode UPS doesn’t perform that conversion; it just takes in the AC power and passes it through so long as the power looks clean. If it sees a disturbance of some form or an outage, then it switches over to the usual double conversion mode. The idea is to save the energy lost in that conversion process if it’s not really necessary to perform it.

FPQ is essentially the idea of using additional energy sources instead of UPSs to provide backup power. (Members of The Green Grid can check out their white paper no. 63 for a thorough discussion of the topic.) It may be a third utility feed or a cogeneration source, such as a micro-grid consisting of solar or fuel cells. The idea is, with more backup power sources available in case the primary power goes down, you can keep critical loads up without relying on UPSs. FPQ does require design techniques that ensure power is transferred quickly enough to keep the loads up, but with today’s clustered server architectures and virtualization techniques, that’s not an insurmountable problem. (I do, however, have a problem with the name “free” power quality because providing these additional power sources is certainly not free.)

While it’s true you can save money with either of these approaches, it does come with some risk because you are taking away UPS backup. But energy management systems can help mitigate that risk.

Without UPSs in place, or when UPSs are running in eco-mode, IT loads are no longer protected by the double conversion process that filters out disturbances. So IT loads are likely to see more power sags and other power quality anomalies. Energy management systems can alert data center operators when those anomalies become dangerous for the IT loads.

In recent years Schneider Electric has supplied power quality monitoring solutions to cloud service providers and retailers to provide the power system data they need to intelligently operate their data centers.  These data centers deploy StruxureWare Power Monitoring Expert Data Center Edition along with power quality meters as tools to maximize system efficiency and understand the potential for impact on mission critical IT loads.

The StruxureWare Power Monitoring Expert solution captures power quality disturbances including sags, swells, and transients, all of which represent threats to system reliability. When IT equipment transfers to backup generation or double conversion UPS mode, the system has the ability to capture the sequence of events with system-wide time stamp resolution as low as 1 millisecond.

This information – both power quality and sequence of events – is used by engineers and data center operators to continually monitor and improve their systems. When detailed disturbance data is shared with utility power providers, they can often make improvements to their switching practices to minimize impact on the data center.  At the opposite end of the electrical distribution system, they can see how server power supplies respond to system disturbances to insure that dual-corded systems respond properly.

So the more things change, the more they stay the same. Check out the updated version of “Powering the Digital Economy: How Energy Management Helps Maximize Power Reliability.” I think you’ll find the arguments it makes for energy management systems still resonate today, perhaps even more so. And for more on the same topic, click here to download another free white paper, “Maximizing Data Center Reliability and Utilization Using Enterprise Energy Management Technology.”


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