ASHRAE TC 9.9, the technical committee responsible for key data‑center thermal guidelines, has released a free‑to‑download technical bulletin titled TCS Coolant Integrity and System Readiness Best Practices. Opening with an unusually stark warning for a standards‑body document: “It is too easy to violate direct‑to‑chip cooling system operational and warranty requirements.”

Published in May and hosted on the committee’s public document portal, the bulletin outlines four failure modes where Thermal Cooling System (TCS) performance deviates from design specifications. Issues remain hidden during commissioning and surface as hardware damage months later. The release coincides with widespread direct‑to‑chip liquid‑cooling adoption driven by high‑density AI processors.

This subject was previously covered by Dell’s Tim Shedd on Podcast #152, addressing coolant chemistry, filtration and latent failures stemming from commissioning shortcuts, where he previewed the upcoming bulletin. Contributors include Shedd and Meraj Mohebi (Dell), Dustin Demetriou (IBM), Ashwin Siddarth (AMD), Chris Campbell (Vertiv), Vali Sorell (Oracle), plus engineers from Fluid2Chip and DLB Associates, reflecting cross‑industry shared pain points.

Four Failure Paths

Coolant composition: Most single‑phase systems are engineered for a nominal 25 % propylene‑glycol (PG25) mix. Deviations alter viscosity, density, specific heat and thermal conductivity, cascading into shifted pressure drop, changed pump operating points, degraded heat‑exchanger performance and unstable CDU control. Glycol must satisfy TC 9.9 quality rules or OEM specifications. Mixing different coolants without impact assessment triggers a mandatory structured technical review.

Air management: Entrained air reduces heat transfer, causes pump cavitation and accelerates corrosion, while extending commissioning timelines. Degassing works best under high operating load temperatures, meaning air‑related faults may emerge weeks after go‑live. Guidance specifies air‑separator placement on the warm low‑pressure return near CDU inlets, venting at all high‑points, and avoidance of air‑trapping geometries: vertical dead legs, inverted U‑bends and unvented flexible hose sections.

Stainless‑steel passivation: Welding, grinding and on‑site fabrication destroy stainless steel’s protective chromium‑oxide layer. Without cleaning and re‑passivation complying with ASTM A380/A967 standards, free iron contaminates coolant and fouls cold‑plate microchannels and turbulators. The bulletin states explicitly: “An individual installed component that is NOT passivated can jeopardize the operation of the system.”

System pressure ratings: A complete hydraulic pressure‑cascade model is advised, covering steady‑state running, flush‑and‑fill pressures, static head, relief‑valve configuration and expansion‑tank pre‑charge, plus connection‑disconnection transients. It references IEC 62368‑1 requiring hydrostatic safety testing at 1.5× maximum working pressure. Relief‑valve set‑points must sit below OEM‑published thermal‑template maximum pressure to prevent costly IT‑equipment overpressure damage.

Operational field checklist

The latter portion delivers practical operational guidance drawn from real‑world experience. Coolant concentration and quality require laboratory validation at initial fill, after major fluid top‑ups and on a recurring schedule, with baseline fluid specifications included in project hand‑over documents. A noted caveat for vacuum filling: glycol blends may partially separate under vacuum; post‑fill laboratory sampling is required to confirm mixture uniformity. For air‑venting, automatic vents should be capped or valved off once the loop is confirmed air‑free.

 The document concludes with a field‑verification checklist mapping risks, validation steps, acceptable evidence and root‑cause context, readily reusable within commissioning QA workflows.

This bulletin complements TC 9.9’s 2024 Liquid Cooling: Resiliency Guidance for Cold Plate Deployments. It serves as informational guidance and does not override OEM requirements or local regulatory codes. Tim Shedd’s podcast episode offers supplementary conversational coverage of liquid‑cooling plumbing discipline.

Beijing Qianxing Jietong Technology Co., Ltd.
Sandy Yang/Global Strategy Director
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