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Task Force Recommends Metric for Measuring Data Center Efficiency
Inconsistent metrics have led to inconsistent results
-- by Rutrell Yasin
A task force of industry groups and government agencies released recommendations to help data center managers measure and report on overall data center efficiency by using four categories of power usage effectiveness.
As business demands and energy costs for data centers rise, owners and operators in industry and government have put a premium on the energy efficiency of the data center as a whole, frequently using energy efficiency metrics. However, the metrics are not always applied clearly and consistently.
A group of leaders from industry and government met on January 13 to discuss data center energy efficiency measurements, metrics, and reporting conventions. The organizations included the 7x24 Exchange, ASHRAE, The Green Grid, Silicon Valley Leadership Group, Energy Department's Save Energy Now and Federal Energy Management Programs, the Environmental Protection Agency’s Energy Star program, the U.S. Green Building Council, and the Uptime Institute.
The outcome of the series of meetings that occurred since January is the document, Recommendations for Measuring and Reporting Overall Data Center Efficiency. The goal of the document is to recommend a consistent and repeatable measurement strategy that allows data center operators to monitor and improve the energy efficiency of their facilities.
The report recommended using PUE, an energy-efficiency metric agreed upon by data center owners and operators, according to the document. It addresses how to measure PUE in dedicated data centers and standalone buildings whose exclusive purpose is IT operations and their support functions.
PUE is defined by the formula: PUE equals total data center energy consumption or power / IT energy consumption or power.
The task force recommends four measurement categories for the measurement of PUE within a data center facility:
PUE Category 0: This is a demand-based calculation representing the peak load during a 12-month measurement period. IT power is represented by the demand (kW) reading of the uninterruptible power supply system output (or sum of outputs if more than one UPS system is installed) as measured during peak IT equipment utilization. Total data center power is measured at the utility meter(s) and is typically reported as demand kW on the utility bill.
PUE Category 1: This is a consumption-based calculation. The IT load is represented by a 12-month total kilowatt hours (kWh) reading of the UPS system output (or sum of outputs if more than one UPS system is installed). This is a cumulative measurement and requires the use of kWh consumption meters at all measurement points. The total energy is typically obtained from the utility company bills by adding the 12 consecutive monthly kWh readings as well as annual natural gas or other fuel consumption (converted to kWh), if present.
PUE Category 2: Another consumption-based calculation, its IT load is represented by a 12-month total kWh reading taken at the output of the power distribution unit (PDU) supporting IT loads (or sum of outputs if more than one PDU is installed). This is a cumulative measurement and requires the use of kWh consumption meters at all measurement points. The total energy is determined in the same way as Category 1.
PUE Category 3: Also a consumption-based calculation, the IT load is represented by a 12 month-total kWh reading taken at the point of connection of the IT devices to the electrical system. This is a cumulative measurement and requires the use of kWh consumption meters at all measurement points. The total energy is determined in the same way as Category 1.
The task force will continue to meet to develop recommendations for how to measure PUE for data centers in larger mixed-use facilities.
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Rutrell Yasin is senior technology editor for Government Computer News magazine.