Well there are Google's papers they presented at the data center summit and the whole open compute project which touches on this as well.
Simply put the evolution has followed this path:
Machine Room -> air temp is 68 degrees 24/7/365
Modified Machine Room -> rows of machines are lined up alternately facing toward each other and away from each other, cold air is preferentially directed up from the floors in the 'cold' aisles.
Tolerance Limits -> Google and others establish that 'commodity' machines work just fine at an ambient temperature of 80 - 90 degrees F so they cut back on the level of cooling, substitute external air when its cooler than 75 degrees outside.
Full containment -> various systems to provide cooling just to the active hardware, places like SwitchNap in Vegas build structures around the rows, third parties put plastic enclosures around rows to contain cold air, or to force all hot air out of a plenum.
Most of the 'win' has been reducing the temperature differential between the data center and ambient air, and reducing the volume of air that has to be cooled.
Once you do that, alternate air cooling methods (like evaporation cooling) can be used rather than compressor chillers.
Simply put the evolution has followed this path:
Machine Room -> air temp is 68 degrees 24/7/365
Modified Machine Room -> rows of machines are lined up alternately facing toward each other and away from each other, cold air is preferentially directed up from the floors in the 'cold' aisles.
Tolerance Limits -> Google and others establish that 'commodity' machines work just fine at an ambient temperature of 80 - 90 degrees F so they cut back on the level of cooling, substitute external air when its cooler than 75 degrees outside.
Full containment -> various systems to provide cooling just to the active hardware, places like SwitchNap in Vegas build structures around the rows, third parties put plastic enclosures around rows to contain cold air, or to force all hot air out of a plenum.
Most of the 'win' has been reducing the temperature differential between the data center and ambient air, and reducing the volume of air that has to be cooled.
Once you do that, alternate air cooling methods (like evaporation cooling) can be used rather than compressor chillers.
[1] http://www.google.com/about/datacenters/best-practices.html (they have additional tricks up their sleeve)
[2] http://opencompute.org/project_category/data-center-technolo...