So, what’s the upshot? Google says its data centers use 50 percent less energy than the typical data center.
Among the metrics Google tracks is, as expected – its facilities’ PUE (Power Usage Effectiveness), which is a ratio of the amount of power consumed by the computing equipment to the total power used by a data center (which would include overhead power such as lighting and even cooling). As Google notes in its blog, as an example: if a data center has a PUE of 2.0, that means that for every watt of energy that powers the servers, another watt powers the cooling, lighting and other systems. An ideal PUE would be 1.0.
According to Google, its trailing 12-month average PUE in 2011 was about 1.14, an improvement from the 1.16 average in 2010. Google does apparently include everything in its PUE calculation. In addition to electricity used to power the servers and cooling systems, it includes the oil and natural gas that heat offices, and Google also accounts for system inefficiencies like transformer, cable and UPS losses and generator parasitic energy draw. The PUE represents the performance of all of Google’s data centers.
The company collects its metrics via multiple (dozens or even hundreds, according to the report) on-line power meters in its data centers. Energy used by the cooling infrastructure and IT equipment is collected via separate meters.
Google first started reporting PUE numbers in 2008, and at that time its trailing 12-month energy-weighted average was 1.20. Google’s best quarterly PUE performance in 2011 came in at 1.12, which the company says was accomplished despite adding two new facilities and during a quarter with warmer than average temperatures. One of Google’s data centers actually reached a PUE of 1.08 in one quarter, according to the company.