Google put out a blog post today discussing efficiency improvements the company has been making with its data centers, along with the company’s general philosophy around said efficiency.

“In the same way that you might examine your electricity bill and then tweak the thermostat, we constantly track our energy consumption and use that data to make improvements to our infrastructure. As a result, our data centers use 50 percent less energy than the typical data center,” writes Joe Kava, Senior Director, data center construction and operations at Google.

One of the key metrics Google uses to track efficiency is power usage effectiveness or PUE, which Kava describes as a ratio of the total power used to run a data center to the amount used to power the servers. “For instance, 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,” he explains.

To make a long story short, Google has improved its PUE from 1.16 in 2010 to 1.14 in 2011. It was as high as 1.20 back in 2008, when Google started publishing the number (it does so on a quarterly basis now).

The quarterly PUE was even better for Q4 2011 than it was for the year. Google posted its best quarterly PUE number to date at 1.

Measuring PUE is one of five best practices Google lists for its data centers. The others are: managing airflow, adjusting the thermostat, using free cooling and optimizing power distribution.

The company recently brought attention to how it users river water to cool its Georgia data center:

Google has data centers in South Carolina, Iowa, Georgia, Oklahoma, Carolina, Oregon, Finland, Belgium, Hong Kong and Singapore. On average, a user’s search query travels 1,500 miles.