Electronic Design

Putting Data-Center Power In Perspective

I had the opportunity to meet Roger Tipley at the recent Power Electronics Technology Exhibition & Conference in Dallas. Roger is a senior technologist and engineering strategist at Hewlett-Packard as well as a board member of an organization called The Green Grid (www.thegreengrid.org).

The Green Grid has been operating since January and has already grown to 102 members. It is a consortium of information technology companies and professionals whose goal is to improve energy efficiency in data centers around the world. Tipley’s keynote address was entitled “Opportunities for Energy Efficiency Innovation in the Power Electronics Industry.” He began by pointing out that he would be talking “completely end to end” as far as opportunities in the entire supply chain of energy, from the source of electricity to the ultimate consumer of it.

Measurement is key
Before delving into opportunities, Tipley pointed out the need for measurements of energy efficiency. The Green Grid has proposed power usage effectiveness (PUE) and its reciprocal, data-center infrastructure efficiency (DCiE). These metrics enable data-center operators to quickly estimate the energy efficiency of their data centers and compare the results against other data centers. This helps them determine the energy efficiency improvements that need to be made.

For a better idea of what these measurements represent, think of power consumption in the data center as having two components. One is the total facility power. This includes everything that supports the IT equipment load: power delivery components like the UPS, switch gear, generators, PDUs, batteries, and distribution losses external to the IT equipment; cooling system components like chillers, computer room air conditioning units (CRACs), direct expansion air handler (DX) units, pumps, and cooling towers; compute, network, and storage nodes; and other component loads such as data-center lighting.

The other component of the equation is IT equipment power. This includes the load associated with all of the IT equipment, such as compute, storage, and network equipment, along with supplemental equipment such as KVM switches, monitors, and workstations and laptops used to monitor or otherwise control the data center.

The PUE measurement is simply the total facility power divided by IT equipment power, while DCiE is the reciprocal of PUE. While both of these metrics are essentially the same, the group points out that they can be used to illustrate the energy allocation in the data center differently.

In support of these measurements, the group announced last month the grand opening of the Schneider Electric Technology Center. This state-of-the-art testing facility in O’Fallon, Mo., will be made available to The Green Grid to further enable progress on the part of the group’s Technical Committee. This 97,000- square-foot facility includes research and development labs along with dynamic test facilities. American Power Conversion (APC), a business unit of Schneider Electric, is one of the founding members of The Green Grid.

Where's the opportunity?
From end to end, Tipley explained where he sees opportunity knocking for power systems designers. For example, he pointed out that converting coal to electricity with today’s technology yields only about 35% of the actual energy available in that source. Not very good. Transmission losses aren’t bad, only about 2%, which leaves 33% for a facility like a data center.

Other energy sources, such as wind, are potentially up in the 60% yield range. So there are opportunities for designers working with wind turbines to deliver energy much more efficiently than is now possible with a source such as coal.

But The Green Grid doesn’t really focus on the inefficiencies in the power plant, which are significant, or with the smaller losses that occur in the transmission of energy to the facility.

Instead, The Green Grid is focused on power in the data center itself and using that power more efficiently. The opportunity here lies in more efficient designs for both the facility and the IT equipment. Tipley said that a poorly designed data center might use two-thirds of the available power on cooling equipment. Another part of Tipley’s talk covered the various power-distribution configurations being used in data centers today. Of course, each of these configurations has advantages and disadvantages. On its Web site, the group has published a white paper entitled “Qualitative Analysis of Power Distribution Configurations for Data Centers” that provides a good overview of seven different configurations and their pros and cons.

For more information on The Green Grid, visit the group’s Web site. To view a video of the keynote, point your browser to electronicdesign.com/shows/power2007/index.cfm.

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