Central to the attraction of data centres is their ability to deliver the highest possible power consumption efficiencies. This is measured as a ratio, known as power usage effectiveness (PUE), between the amount of electricity needed to power the IT equipment and that needed to power facility features such as air conditioning and lighting. A PUE of 1.0 is ideal.
The top consumer of power within a data center is cooling. A computer server's CPU is the site of a huge amount of electrical activity, which means it generates a lot of heat, and requires constant cooling. Too much heat is deadly for computer circuits, whose pathways, measured in nanometres, can degrade due to melting. Computer programs can also degrade due to compromises of the data within basic electronic files, which, after all, consist of a series of electrons as subject to the effects of heat and cold as any other physical object. Temperatures around a CPU can reach 120 degrees. One of the solutions to mitigate this is to handle all hot air and cold air separately. This means the hot air does not get a chance to impact the temperature of the cold air. Through a specially designed venting and cooling system, the hot air can channelled out and continuously replaced with chilled air.
While individual data centres are achieving PUEs of 1.07 through efforts of this nature, the overall number of data centres continues to climb, tending to mitigate the overall beneficial effect of such efficiencies. According to a study on data center electricity use, by Jonathan G. Koomey, consulting professor at Stanford University, electricity used by data centres worldwide increased by about 56% from 2005 to 2010 (while it doubled from 2000 to 2005). In the US it increased by about 36%. The US hosts approximately 40% of the world's data center servers. It is estimated that US server farms, as data centres are also called, consume between 1.7% and 2.2% of the national power supply.
For example, Apple's new USD 1 billion "iDataCenter" in North Carolina is estimated to require as much as 100 MW of power, equivalent to that required to power 80,000 US homes or 250,000 European Union homes. Greenpeace's 2010 Make It Green report estimates that the global demand for electricity from data centres was on the order of 330 billion kWh in 2007, close to the equivalent of the entire electricity demand of the UK (345 billion kWh). However, this demand is projected to triple or quadruple by 2020.