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General Information
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May 22, 2009
• Vol.31 Issue 15
Page(s) 30 in print issue
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Measure PUE
Is Your Enterprise Energy Efficient?
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| Key Points
• PUE is a relatively easy number to obtain. Your goal over time is to see how low you can get the number—the closer to one, the better.
• Measure total power entering the data center at its input power meter. Measure net IT equipment usage at the UPS.
• Utilize an efficiency-savings spreadsheet to get an idea of how much your enterprise will save. | | Calculating PUE (power usage effectiveness) is an easy way to gauge energy distribution within your data center. PUE is the ratio of electricity coming into the data center to the electricity specifically used to power IT equipment. It is a widely accepted benchmarking standard proposed by the Green Grid, a nonprofit consortium, to help IT professionals determine the energy efficiency of their data centers and to help them monitor the impact of their efficiency efforts.
“In most organizations, people have no idea what their data center power efficiency is,” says Kenneth Uhlman, director of data center business development at Eaton (877/785-4994; www.eaton.com). “Most organizations don’t know how much energy is spent—or wasted—in their data centers.”
Of course, before you can raise your data center’s energy-efficiency level, you need to know exactly how efficient it is. This is where PUE comes in, says Jon Haas, director of Intel’s eco-technology program office. The measurement ratio gives data center managers a starting point from which to look at decreasing the amount of power running into the data center.
“PUE is a way to understand how the energy coming into your data center gets apportioned and partitioned,” Haas explains. "The goal is to decrease power that goes to [the] infrastructure and to make sure as much of that power as possible goes to the IT equipment, which does the productive work from the data center perspective.”
 Gather Measurements
In 2007, the Green Grid released its PUE metric: Take the amount of total data center facility energy and divide it by the energy used exclusively for the IT equipment (computer, storage, and network equipment, as well as the switches, monitors, and workstations used within the data center). Haas says the more efficient the data center, the closer that number is to one.
“A measurement of one means all the power is going to the IT equipment,” he explains. But most of today’s data centers don’t meet that perfect target. The idea is to try to lower your data center’s PUE over time to as close to one as possible. But, as with most things, a number of external factors can affect the PUE measurement and can vary from data center to data center, depending upon the type of enterprise.
Still, at many data centers, only about 3% of the energy entering the center is used for computing, Uhlman says. Other considerations, such as heating and cooling, account for the remaining energy.
Measuring the PUE at your data center is relatively straightforward, Uhlman explains. You can measure total power in at the data center input power meter. Net IT usage is measured at the UPS. Those two data points create the ratio.
Calculations & Spreadsheets
In a recent report, the Green Grid defines three levels for measuring PUE. The basic level is what Uhlman outlines in the previous paragraph, and it is measured monthly. At the intermediate level, the measurement becomes more exacting. For this measurement, facility power is the data center input power minus the shared cooling number. Measurements at this level are collected daily. At the advanced level, facility power is the data center input less shared cooling plus power for building lighting and security. Advanced-level measurements are gathered every 15 minutes.
When PUE is measured every 15 minutes, managers are better able to determine how variable their facility’s data energy consumption is and to isolate those variables. They can also determine whether and how much outside factors, such as security issues, affect variability.
The next step is to determine how much money your enterprise will save in energy costs by improving data center efficiency, Uhlman says. After calculating your current PUE benchmark and entering in some basic data about your facility, many of the efficiency-savings spreadsheets available will let you enter different goals to see how much your enterprise will save. One such spreadsheet is available from 42U (www.42u.com). An efficiency ROI spreadsheet, for example, lets you determine ROI on infrastructure assets such as power or cooling you’re considering adding.
Meet With Facilities
Before moving forward with efficiency upgrades, Uhlman urges IT managers to meet with their facilities managers. Together, department heads can hash out how best to increase efficiencies. In many enterprises, these two departments don’t speak enough or are even at odds with each other when it comes to determining how to best cut energy use.
“In the data center space, the person that buys the IT computers is the chief information officer and the person that pays the energy bill is the vice president of corporate real estate,” he says.
In many instances, IT departments have been unaware of the data center’s energy costs prior to gathering PUE measurements. Uhlman explains that measuring PUE gets everyone on the same page and ready to converse and take definite steps to move forward.
“So, the CIO would then say, ‘I need to buy more energy-efficient computers. They’ll cost me more up front, but the carbon footprint and energy bill will go down,’” he says. “Before, he may have been looking at it like: ‘I don’t pay the energy bill. I have a fixed budget from which to buy computers. I’m just going to buy inefficient computers because they’re the least expensive.’”
Don’t Dare To Compare
Uhlman cautions that enterprises should not be overly eager to compare their data center’s PUE to the PUE of other data centers. A number of factors, including the way the measurement is taken, can affect PUE numbers. And, of course, comparing data centers across industry or data centers located at various U.S. locations can make for a meaningless match.
The Green Grid is working to define segments of the data center industry to offer better PUE targets across these segments. PUE is affected by factors that include whether the site is used primarily for testing or production; if the business is financial, health care, data center colocation, or something else; and what the data center’s tier level is, according to the organization. Uhlman adds that a center in a cooler climate may be able to support less-expensive cooling methods than does a center located in Phoenix. 
by Jean Thilmany
Top Tips
• PUE compares power coming into a data center and power used strictly for IT equipment to measure the center’s energy efficiency.
• You can gather measurements at intervals that range from monthly to every 15 minutes depending on how tight an energy usage snapshot you need.
• Don’t compare your data center’s PUE to the PUE of other data centers. A number of factors, including the way the measurement is taken, can affect the PUE number.
• When looking to make your data center more energy-efficient, remember to include the facilities management department in conversations. |
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