http://www.youtube.com/watch?v=zRwPSFpLX8I
http://www.datacenterknowledge.com/archives/2008/10/14/google-raise-your-data-center-temperature/
http://www.avtech.com/About/Articles/AVT/NA/All/-/DD-NN-AN-TN/Recommended_Computer_Room_Temperature_Humidity.htm
http://en.wikipedia.org/wiki/Data_center#Physical_layout

2004 Version / 2008 Version
Low-end temperature - 20°C (68°F) / 18°C (64.4°F)
High-end temperature - 25°C (77°F) / 27°C (80.6°F)
Low-end moisture - 40% RH / 5.5°C DP (41.9°F)
High-end moisture - 55% RH / 60% RH & 15°C DP (59°F DP)