Energy-Efficiency Metrics Are The First Step

Accurate measurements can help IT save power and money, but plan carefully to avoid false starts.



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electric meter IT leaders face ever-increasing pressure to reduce power consumption in the data center and beyond. Whether it's the corporate desire to cut costs in every area or customers' growing environmental awareness, that pressure amounts to a lot more than friendly reminders to turn off the lights.

But once all the off switches have been hit and unused devices unplugged, how do you know what your next steps should be? A good place to start is to figure out just how much juice your gear consumes, relative to non-IT devices. Armed with this information, you can take steps to reduce the overall energy footprint of your data center, then the rest of your facility.

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Still, building an accurate energy profile is a challenge for many organizations. You can't improve what you can't measure, yet the meter on the outside of the building doesn't tell you how power gets allocated once it's inside. Specialized measuring devices like the Kill A Watt can't be used on all your gear.

Green Measures
Enter the Green Grid, a nonprofit consortium of IT professionals and vendors, which has developed two energy metrics that can help IT staffs calculate and trend efficiency: Power Usage Effectiveness (PUE) and Data Center Infrastructure Efficiency (DCiE). Although these metrics are used primarily in data centers, the concept can certainly be adopted in other areas. For example, you could figure out how much of an office building's total power relates to heating/cooling or office equipment using either metric.

The PUE metric expresses efficiency as a fraction in which total facility power is the numerator and IT equipment power is the denominator. IT equipment power includes the load associated with all IT-related equipment, from computers, storage, and network gear to keyboard, video, and mouse switches; monitors; and workstations. Total facility power includes IT equipment power plus power delivery components such as switch gear, uninterruptible power supplies, generators, batteries, and cooling system components.

The Green Grid's DCiE expresses efficiency as the inverse of PUE (rendered as 1/PUE). Both metrics measure the same data in the same fashion, and a value of 1 is the ideal (albeit impossible to achieve) result in both cases. The major difference is the way that each expresses the measurement. DCiE tells you how much load your IT equipment is using, as in 75% or 0.75 is dedicated to IT load. PUE can tell how much additional load is required to support your IT equipment, or how much of your electricity use is not dedicated to IT devices.

Impact Assessment: Energy Metrics
(click image for larger view)



1 Is The Loneliest Number
A PUE value of 2 indicates you need twice as much power to run the facility as your IT equipment demands. That same PUE score of 2 would be represented as 0.5 or 50% in DCiE--again indicating that half your energy consumption is dedicated to non-IT load requirements.

As mentioned, achieving a PUE score of 1 is an impossible goal--it would mean that your IT equipment was using every watt of power entering your facility, with none going to lighting, air conditioning, and the non-IT devices that are vital to everyday operations. In addition, your electrical infrastructure contains inefficiencies as it distributes voltage. Still, you should try to get as close as possible. Driving each number toward 1 will reduce mechanical and electrical overhead, cutting costs.

The Green Grid's metrics can show you how efficiently you're using power, but the devil is in the variables. Measuring power efficiency also requires the right equipment for the facility. For example, total power usage can be measured at the meter, but only if that meter is dedicated to the data center or other facility in question. If your entire organization is in one building or you're in a multitenant site, you'll need to tap other techniques to calculate total facility power. These include installing dedicated metering equipment for incoming service or using breaker interface modules to calculate and measure power consumption. Both of these approaches will do the job but can cost thousands of dollars, depending on the size of the area. You'll probably need an electrical contractor to assist with installing the appropriate equipment, which will vary by site.

Measuring IT power load is easiest --relatively speaking--at the power distribution unit (PDU) that's usually located in electrical rooms or on the raised-floor environment. These units generally support only IT equipment and display power output on an LCD. IT equipment power usage can be measured with intelligent power strips as well, although installing hundreds of these power strips would be a daunting chore and not a cost-effective use of IT personnel time.

You can take measurements manually by reading equipment displays on a routine basis and calculating the PUE over time using common office software. Larger sites with deeper pockets can install building management system software. Systems like those from Eaton Foreseer, Johnson Controls, ALC, or JACE interface with utility meters, switch gear and breakers, PDUs, and power strips to measure PUE.

Installing a building management system solely for PUE calculations won't make financial sense: These systems can cost hundreds of thousands of dollars including software and support, wiring, labor, and other costs. But expanding the project to monitor everything--uninterruptible power supplies, batteries, air conditioning equipment, generators, fire suppression, automatic transfer switches--across a facility might make a building management system a more justifiable expense. These systems let IT managers see exactly what each piece of equipment is doing at any point in time.

Cut The Costs

Green By Numbers
Top 5 Tips To Maximize Metrics
  1. Start in familiar territory. Data centers use massive amounts of power, and metrics like PUE were originally designed for data centers.
  2. Measure more than once. To accurately calculate power consumption and potential savings, you need to track usage over time.
  3. Use your numbers to rate your options. Will you achieve greater savings from more efficient air conditioning or by rewiring your IT systems?
  4. Be realistic. You'll never cut your electricity bill to zero, and a PUE of 1 is impossible to attain. But that doesn't mean you shouldn't try.
  5. Don't cheat. A real 1% energy savings will get you into less trouble than any amount of fake savings.
Once you can accurately measure PUE, you can start to drive closer to 1. Power-reduction strategies will be different in each facility, but ultimately you'll need to focus on reducing electricity usage for non-IT equipment as well as IT gear. Although they're not always inexpensive fixes, energy-savers can be as simple as reducing redundancy in the air conditioning system or installing more efficient uninterruptible power supplies and servers.

In the data center, if your raised-floor space includes area for expansion, you probably have air conditioners installed to meet future demands. These units and their accompanying outdoor equipment, such as pumps and fans, are probably running, although they're not yet needed. Determining the right amount of air conditioning is best left to qualified data center consultants, because you have to take into account the amount of heat generated by current and future IT equipment, outdoor temperature profiles, and heat from motors and other ancillary equipment in the data center. Heat generated is represented in kilowatts, and once the magic number is determined, you need to provide at least that amount in your cooling system. Adding redundant cooling infrastructure will protect you from failures but will cost a significant amount and reduce overall efficiency.

Newer air conditioning equipment is far more energy efficient than older models, offering free cooling techniques that can dramatically reduce energy consumption under the right outdoor conditions. Free cooling leverages lower outdoor temperatures.



Leaner UPS Delivers Savings
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.

InformationWeek Green - May 4, 2009 InformationWeek Green
Download the entire InformationWeek "green" issue,
our May 4 magazine distributed solely in pdf form.
(Registration required.)
We will plant a tree
for each of the first 5,000 downloads.

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