Cooling
Coolant and water quality
The default coolant is PG25: 25 % propylene glycol in water with an inhibitor package. Glycol lowers the freezing point and holds back biological growth; inhibitors keep pH in range and protect brazed joints. Filtration is sized to the smallest passage in the loop, which is the cold-plate micro-channel. New loops are flushed and pressure-tested before any IT load, then sampled yearly.
Source: https://www.opencompute.org/documents/guidelines-for-using-propylene-glycol-based-heat-transfer-fluids-in-single-phase-cold-plate-based-liquid-cooled-racks-final-pdf Checked 2026-09-18 unverified
Attempted direct fetch this session (WebFetch and curl with a browser user agent); OCP's Cloudflare bot challenge returned HTTP 403 both times. Not independently confirmed.
| Figure | Value | Source |
|---|---|---|
| PG25 freeze point | about -10 deg C | https://blog.se.com/datacenter/2026/08/14/what-coolant-for-data-center-liquid-cooling-pg25-dielectric-fluids-ashrae-recommendations/ Direct fetch (curl with a browser user agent; WebFetch returned 403 for this host) confirms: 'PG25 offers freeze protection down to about -10C (14F).' Exact match to the value. |
| Loop pH | 8.0 to 10.5 | https://www.opencompute.org/documents/guidelines-for-using-propylene-glycol-based-heat-transfer-fluids-in-single-phase-cold-plate-based-liquid-cooled-racks-final-pdf OCP's guideline lists fluid pH as 8.0 to 10.5, while noting that the value depends on corrosion-inhibitor formulation and can be lower with organic acid technology. |
| Filtration | side-stream filter finer than 5 micron, plus a coarser inline filter | https://www.opencompute.org/documents/guidelines-for-using-propylene-glycol-based-heat-transfer-fluids-in-single-phase-cold-plate-based-liquid-cooled-racks-final-pdf Corrected 2026-10-07. This row used to say 'match the cold-plate channel, not a generic 5 micron'. The OCP guideline it cites says the opposite: section 4.4 recommends side-stream filtration below 5 micron, treating 10 percent of the flow, to keep particles out of the cold-plate microchannels, and allows a coarser inline filter (for example 50 micron) as an addition, not a substitute. Read from the PDF on 2026-10-06. |