Editing Data center (section)

===Energy efficiency and overhead===
The most commonly used energy efficiency metric for data centers is [[power usage effectiveness]] (PUE), calculated as the ratio of total power entering the data center divided by the power used by IT equipment.

:<math> \mathrm{PUE}  =  {\mbox{Total Facility Power} \over \mbox{IT Equipment Power}} </math>

PUE measures the percentage of power used by overhead devices (cooling, lighting, etc.). The average USA data center has a PUE of 2.0,<ref name="energystar1">{{cite web |title=Report to Congress on Server and Data Center Energy Efficiency |url=http://www.energystar.gov/ia/partners/prod_development/downloads/EPA_Datacenter_Report_Congress_Final1.pdf |publisher=U.S. Environmental Protection Agency ENERGY STAR Program}}</ref> meaning two watts of total power (overhead + IT equipment) for every watt delivered to IT equipment. State-of-the-art data centers are estimated to have a PUE of roughly 1.2.<ref>{{cite web|url=https://microsite.accenture.com/svlgreport/Documents/pdf/SVLG_Report.pdf|title=Data Center Energy Forecast|publisher=Silicon Valley Leadership Group|access-date=2010-06-10|archive-url=https://web.archive.org/web/20110707080409/https://microsite.accenture.com/svlgreport/Documents/pdf/SVLG_Report.pdf|archive-date=2011-07-07|url-status=dead
}}</ref> [[Google]] publishes quarterly efficiency metrics from its data centers in operation.<ref>{{cite web|url=https://www.google.com/about/datacenters/efficiency/internal/|title=Efficiency: How we do it – Data centers|access-date=2015-01-19|archive-date=2019-09-30|archive-url=https://web.archive.org/web/20190930070102/http://www.google.com/about/datacenters/efficiency/internal/|url-status=live}}</ref> PUEs of as low as 1.01 have been achieved with two phase immersion cooling.<ref>{{cite web | url=https://www.networkworld.com/article/969739/immersion-cooling-firm-liquidstack-launches-as-a-stand-alone-company.html | title=Immersion cooling firm LiquidStack launches as a stand-alone company | access-date=2024-02-28 | archive-date=2024-02-28 | archive-url=https://web.archive.org/web/20240228183457/https://www.networkworld.com/article/969739/immersion-cooling-firm-liquidstack-launches-as-a-stand-alone-company.html | url-status=live }}</ref>

The [[U.S. Environmental Protection Agency]] has an [[Energy Star]] rating for standalone or large data centers. To qualify for the ecolabel, a data center must be within the top quartile in energy efficiency of all reported facilities.<ref>Commentary on introduction of Energy Star for Data Centers {{cite web|title=Introducing EPA ENERGY STAR for Data Centers|url=http://www.emerson.com/edc/post/2010/06/15/Introducing-EPA-ENERGY-STARc2ae-for-Data-Centers.aspx|format=Web site|publisher=Jack Pouchet|access-date=2010-09-27|date=2010-09-27|url-status=dead|archive-url=https://web.archive.org/web/20100925210539/http://emerson.com/edc/post/2010/06/15/Introducing-EPA-ENERGY-STARc2ae-for-Data-Centers.aspx|archive-date=2010-09-25 }}</ref> The Energy Efficiency Improvement Act of 2015 (United States) requires federal facilities—including data centers—to operate more efficiently. California's [[California Energy Code|Title 24]] (2014) of the California Code of Regulations mandates that every newly constructed data center must have some form of airflow containment in place to optimize energy efficiency.

The European Union also has a similar initiative: EU Code of Conduct for Data Centres.<ref>{{cite web|url=http://iet.jrc.ec.europa.eu/energyefficiency/ict-codes-conduct/data-centres-energy-efficiency|title=EU Code of Conduct for Data Centres|publisher=iet.jrc.ec.europa.eu|access-date=2013-08-30|archive-date=2013-08-11|archive-url=https://web.archive.org/web/20130811202339/http://iet.jrc.ec.europa.eu/energyefficiency/ict-codes-conduct/data-centres-energy-efficiency|url-status=dead}}</ref>