ASHRAE Technical Committee (TC) 9.9 published the 5th Edition of their Thermal Guidelines for Data Processing Environments in March 2021. While there are other minor clarifications, updates and corrections, the primary updates center around the air-cooled relative humidity limits, addition of a new air-cooled class for high density compute equipment, and several major updates to the liquid cooling chapter.

The focus of today’s blog will be on the addition of a new air-cooled class for high density equipment.

As the debate “to liquid cool or not to liquid cool” continues, there has been an increase in the presence of high density air-cooled deployments where reliable operation of the ITE requires environmental conditions outside of the already-established air classes. As a result, the ITE manufacturers in the IT Subcommittee created a new air-cooling class, “H1”. This new air-class provides thermal guidance for air-cooled high density applications. What is considered high-density? Unfortunately, due to the variety of ITE designs on the market, you need to contact your ITE manufacturer to determine whether or not the facility must be designed and operated per the H1 guidelines, or more conventional air class guidelines.

As you might imagine, due to the increased power density of ITE in the H1 class, and the fact that the chips themselves still have similar maximum temperatures, the H1 class thermal envelope is cooler than that of A1 – notably the upper end of the recommended range is 22°C (71.6°F), while the upper end of the allowable range is only 25°C (77°F). Additional information, including extensive application notes are in the Guidelines.

To learn more about the updates to ASHRAE’s Fifth Edition of Thermal Guidelines, check out our recent webinar titled, Understanding ASHRAE’s 5th Edition of Thermal Guidelines: What’s New and How It Can Impact Your Facility.