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By Loren Snyder
Data Centers Article Use Policy
Maximizing energy use in data centers can be done in a number of ways. Some areas to focus on are air-flow management, economizer use, and understanding PUE.
Any facility manager who oversees an organization with an in-house data center knows that data centers are energy hogs. That’s largely because — as ASHRAE’s technical committee 9.9 says — data centers have traditionally been cooled via brute force. Often that means that legacy data centers seemingly aren’t much warmer than meat lockers, with common thermostat setpoints at or near 55 degrees F.
That’s beginning to change. Equipment racks are now set up in hot-aisle/cold-aisle configurations, setpoints have been creeping warmer, and IT equipment manufacturers are building servers that withstand higher temperatures and don’t have thermally shadowed components.
It’s not just higher data center temperatures that are helping to increase energy efficiency. Another step in the process came in 2010, when Energy Star used Green Grid’s PUE (power usage effectiveness) standard and benchmark information from more than 100 data centers in the United States to establish energy-use guidelines — both for standalone and in-house data centers.
And in mid-November 2013, ASHRAE released for review standard 90.4P, a new standard that augments ASHRAE 90.1 and is specific to data center operation. ASHRAE explains the need for the standard:
“The purpose of this Standard was to create a performance based approach that would be more flexible and accommodating of innovative changes which rapidly occur in the data center design, construction, and operations. Data center applications are unlike their commercial building counterparts in two significant ways: Significantly higher plug loads and rapidly changing technology for the IT equipment and associated power/cooling approaches.
The standard allows for more economizer operation for most climate zones and higher data center temperatures. The latter item would enable still greater economizer use and is made possible by increasingly energy-efficient equipment and computing equipment that is tolerant of higher operating temperatures.
The wider use of PUE as the yardstick of measurement for data center efficiency is playing an important role in holding down energy use. “PUE is a measure of how efficiently a data center uses energy; it’s a ratio of the total amount of energy used by a data center in relation to the energy used by the computing equipment,” says Robert Cassiliano, chairman and CEO of the 7x24 Exchange.
To calculate PUE, facility managers need to determine peak electric demand in kW for the entire computing room, including IT equipment and supporting infrastructure, divided by peak electric demand for the IT equipment.
The calculation came as a result of Green Grid’s desire to eliminate confusion in the industry and standardize calculation methodologies, says Munther Salim, global energy and sustainability practice leader for Hewlett Packard’s critical facilities services.
Traditionally, a PUE ratio of 1.0 or less was considered ideal, and the U.S. Environmental Protection Agency notes that most data centers have a PUE of between 1.25 and 3.0, but the new ASHRAE standard specifies mechanical design PUEs below .50 for most cities across the nation, and below .30 for annualized mechanical design. SPC 90.4P uses two charts — one for mechanical design and the other for annualized values — for a handful of cities across America, from Fairbanks to Miami and Baltimore to Boise.
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