As is the case with air conditioners, newer uninterruptible power supply systems also operate leaner than older ones. Older systems can be 80% efficient, but newer models drive that number above 90%.
UPS efficiency numbers are typically represented at 100% load by vendors--something that most sites never see because it would mean you'd have no ability to add IT equipment. Adding redundancy to the UPS system, either N+1 or 2N, increases your PUE and utility costs. Redundancy and power efficiency will compete against each other, whether you are talking about UPS, AC units, or the servers themselves. The solution: Understand that some redundancy is necessary even though it reduces power efficiency, and balance that need against energy costs. For example, if you currently have a UPS that provides another standby unit, you are adding inefficiencies that could be evaluated if a complete redundant system isn't required for the business.
Computer manufacturers are creating more energy-efficient servers than were available even a few years ago. All manufacturers seem to have swallowed that little green pill, creating "green" or "eco-friendly" servers that do more while consuming less power. However, replacing servers with more energy-efficient models can actually drive your PUE numbers higher if you don't perform the necessary facility reductions for air conditioning and UPS. If you install new servers that are 20% more efficient, you'll need to reduce your air conditioning load and UPS to maintain PUE. It's important to keep both sides of the equation in check, especially if you have different IT and facility organizations.
Beware The Numbers Game
Like all metrics, energy-efficiency measurements aren't foolproof. With the pressure on to cut costs, managers might be tempted to make their conservation efforts look more fruitful than they are. By using metrics selectively, an IT admin can skew numbers to make a company look more power efficient than it is.
Most companies are measuring energy use and finding ways to save in good faith. But not all. "A trend we see developing as a result of the push to improve PUE is the sleight of hand played with the development of the calculation," says Mark Welsco, director of mission-critical design for Worldwide Environmental Services, which provides environmental assessment, design, and remediation services for computer facilities.
PUE is a measurement of energy into the system against energy required to operate the IT hardware. It's a static measurement, Welsco says, so choosing when the measurement is taken can have a dramatic effect on the result. Welsco recalls one site manager reporting that a company would simply measure overall input while systems were operating on free cooling at night and IT loads were down, and measure the hardware side at 6 p.m., when IT systems were at peak consumption, then use this for the basis of the calculation.
Falsifying PUE for a facility might be good for a company's (or manager's) image--at least temporarily--but it won't lower power use or costs, and carries some risk of coming back to haunt everyone involved.
To put a modern spin on the old adage "measure twice, cut once," IT needs to measure continuously to find energy savings. Organizations that are committed to conserving electricity and driving down operating expenses will have to focus on tracking PUE over time, managing the server and facility equipment load, and reporting actual results.
Knowing how and what to measure is only the beginning.