Energy-Efficiency Metrics Are The First Step - InformationWeek

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4/29/2009
04:30 PM
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Energy-Efficiency Metrics Are The First Step

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

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.

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