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 updates made to the liquid cooling chapter due to the continued emergence of liquid cooling deployments, technologies, and supporting ITE.

For those familiar with the liquid cooling guidelines, the most obvious change will be that of the liquid cooling class designations. Previously, the classes were designated W1, W2, W3, W4 and W5. Each of those classes had a lower temperature limit of 2°C, while the upper limits were 17°C, 27°C, 32°C, 45°C and Over 45°C respectively. The deficiency in the original designations didn’t really appear until the debate began over adding a class between 32°C and 45°C.

As interest and regulatory demand for heat recovery and reuse from data centers continues to grow, there has been increased interest in utilizing liquid cooling to efficiently transport the waste heat to various hosts. As such, several manufacturers are designing liquid cooled solutions that operate around 40°C entering facility water, though few are capable of operating consistently above 45°C. The need to add a class for 40°C wasn’t debated, though what to call it was. In the end, due to the need for enhanced flexibility, not to mention making it easier for users to remember what temperature goes with the class, the 5th Edition redesignated the classes based on their upper temperature limit – therefore the classes are now W17, W27, W32, NEW class W40, W45, and the now named W+. Honestly, we couldn’t come up with something better for “W+” in the relatively short time we had to make the changes before the document had to go to publication. This new means for designation allows the committee to adjust the W classes as required based on industry demand, without confusing the issue of “which version of W3 do you mean?”

The other major clarification with regards to the liquid cooling classes included in this update is HOW compliance with a W-class is defined. Previously, it was not well defined, and some manufacturers were classifying their ITE as “W4” if it was able to operate anywhere between 32°C and 45°C. However, from the perspective of an engineer designing a Facility Water System, or an Owner procuring ITE, it was difficult to validate whether or not certain ITE could be plugged into the FWS and operate correctly. In the above example, the FWS would have to be designed to W3 to ensure it could support W4 ITE. As such, we clarified the definition that compliance with a particular W-class requires “full, unthrottled operation of the ITE at all temperatures within the respective W-class”. Now, a facility designed to support W32 ITE can support any ITE which is W32 compliant. Of course, the owner and design engineer will need to collaborate to determine what amount of temperature overlap between FWS design is appropriate for the particular design – ie how far below the intended ITE W-class temperature the FWS can support.

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.