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ASHRAE's data center temperature and humidity guidelines have changed extensively through the years. In 2004, ASHRAE published the first vendor-neutral temperature standards, which established a recommended range of 68 to 77 °F (20 to 25 °C) and indicated that the temperatures were to be measured at the IT equipment air inlet. Prior to that, the air temperatures were more based on anecdotal knowledge and worst case scenario (often 68 °F, 20 °C). It is hard to believe that the recommended air temperature range has widened from 64 to 81 °F (18 to 27 °C) in less than 10 years, with allowable ranges that go as wide as 41 to 113 °F (5 to 45 °C). There are also radical changes in the humidity ranges.

The net result is a wide range of opportunities throughout the world for more economical and reliable cooling solutions, including compressor-less cooling. ASHRAE has also created water temperature classes for liquid-cooled equipment. This presentation provides critical insight into these groundbreaking environmental class changes and some critical aspects of the associated decisions.