Data Center Power Usage Effectiveness (PUE)Data Center Power Usage Effectiveness (PUE)

The EPA and the IT industry are working together to identify methods in which energy efficiency can be measured, documented, and implemented in data centers.

Increasing data center efficiency is of interest to nearly everyone. But this does not mean everyone is going green. Becoming efficient however does produce some greening results.

The U.S. Environmental Protection Agency (EPA) has launched three initiatives which are described in the "ENERGY STAR Data Center Energy Efficiency Initiatives". The EPA and the IT industry are working together to identify methods in which energy efficiency can be measured, documented, and implemented in data centers. The three current EPA initiatives are:

Guiding Principles for Energy Efficiency
The EPA document states, "These guiding principles are meant to help the industry have a common understanding of energy efficiency metrics that can generate dialogue to improve data center efficiencies and reduce energy consumption."

The first set of recommendations worth reading is about measuring Power Usage Effectiveness (PUE) at dedicated data centers. It can be found in "Recommendations for Measuring and Reporting Overall Data Center Efficiency". PUE is a metric for reporting the overall data center infrastructure efficiency. The closer the PUE is to 1.00, the more effective the IT operation. A number greater than 1.00 means lower effectiveness. I think it is impossible for the PUE to even be close to 1.00 since the total power energy consumption will include non-IT devices as well as IT devices. A way to define the total data center power consumption is to measure the power entering the data center at the connection to the electrical utility company. The PUE for a dedicated data center is calculated using the following formula:

PUE = Total data center energy consumption (includes IT and non-IT energy like cooling, lighting and support infrastructure) / IT energy consumption (Category 0-3) The efficiency of the data center is the reciprocal of the PUE, where:

Efficiency = IT energy consumption / Total data center energy consumption

In this case, an efficiency of 1.00 would be perfect, but not really possible. Therefore the data center efficiency will be less than 1.00, probably about .80 to .90. There are four PUE measurement categories for the data center. The higher the Category number, the more accurate the measurement.

* PUE Category 0 is the demand-based calculation representing the peak load during a 12 month measurement period. This category is only used for all-electric data centers, not centers using other energy sources such as chilled water.

* PUE Category 1 is the 12-month load as it is read at the UPS system output. This measurement is a better measurement than Category 0 because it captures the impact of fluctuating IT and cooling loads.

* PUE Category 2 is the 12 month total kWh reading at the Power Distribution Unit (PDU) This measurement is the same as Category 1 but does not include the losses with PDU transformers and static switches.

* PUE Category 3 is the 12 month total kWh read at the connection point of the IT devices to the electrical system. This is the most accurate since it does not include non-IT devices such as fans.

Summary of the Four PUE Measurement Categories

One of the recommendations is to measure annual power consumption in kilowatt hours (kWh). The enterprise should attempt to calculate an initial PUE even if the measurements are not all inclusive. This will produce a benchmark for future PUE calculations for comparison. If you use the PUE formula to calculate the PUE, it is recommended that the Category number be defined with the PUE result, otherwise the resulting PUE will have no real meaning and cannot be compared accurately to other data centers.

ENERGY STAR Rating for Data Centers
Strategic energy management helps to control energy consumption and costs. The EPA has tools and resources that can help the enterprise create an energy management program that includes benchmarking the data center’s energy performance, making no-cost and low-cost operations and mangagement improvements and earning recognition for the energy management successes.

The first resource in this section supports how you benchmark your data center in Portfolio Manager. The Data Center Quick Reference Guide is available for additional guidance. You can also review the frequently asked questions about the data center rating model for further guidance.

ENERGY Star Data Center Product Specifications
The EPA has launched the development process for the Version 2.0 specification for Computer Servers. Draft 1 of the specification was distributed on April 9, 2010 All materials related to the development process are posted to the Version 2.0 ENERGY STAR Version 2.0 Server Specification Development Page.

This section is divided into three parts:

* ENERGY STAR Computer Server Specification Development
* ENERGY STAR Data Center Storage Specification Development
* ENERGY STAR Uninterruptible Power Supplies Specification Development

The "ENERGY STAR Data Center Energy Efficiency Initiatives" document is loaded with many references and supporting documents that are worth archiving even if you do not read them immediately. The enterprise can keep abreast of the energy efficiency initiatives by returning to the EPA site periodically.