ASHRAE TC 9.9 Thermal Guidelines edition that renamed the liquid W-classes (W17/W27/W32/W40/W45/W+) and added W40 and the H1 air class
5th ed. (2021)observed
| Value kind | observed — Reported measurements, counts, and specifications keep the precision and scope stated by their source; an exact specification is not treated as a range. |
|---|---|
| Caveat | The fifth edition revised an existing liquid-class scheme; liquid classes W1–W5 predate it. The same edition adds the H1 air class (15–25 °C allowable, 18–22 °C recommended). |
| As of | 2021 |
| Source | ASHRAE, Emergence and Expansion of Liquid Cooling in Mainstream Data Centers (2021), p. 4: fifth-edition class changes. · ASHRAE, Emergence and Expansion of Liquid Cooling in Mainstream Data Centers (2021), p. 4: the W classes are renamed W17 (previously W1), W27 (W2), W32 (W3), W40 (new), W45 (W4) and W+ (W5), all with a 2 °C lower limit; the change appears in Thermal Guidelines for Data Processing Environments, Fifth Edition (ASHRAE 2021). |
| Review | checking…review by 2027-06-13 · slow cadence |
| Recorded changes | last 2026-09-16 · 3 revisions tracked |
| Claim id | ashrae-tc-9-9-thermal-guidelines-edition |
Where the guide uses it
← Full numbers register — every date-stamped figure in the guide, with revision history.