Base Specification for Single Phase Water-Based Cold Plate Coolants v1.3

Overview

The acceptance limits are clear: conductivity below 2,000 uS/cm, pH 8.0-10.5 (buffered), turbidity below 5 NTU and total viable bacteria count below 1 CFU/ml. The base water must be purified, with low conductivity and TDS, and ASTM Type IV reagent water is given as an example. In other words a purified base water is wanted rather than tap water, with an inhibitor and biocide package added afterwards.

The specification calls for inhibitor and biocide packages, so corrosion and microbial growth stay under control over the loop's life. The limits underpin fluid-quality checks at commissioning and during continuing monitoring; how often to measure is this summary's design suggestion, not a requirement of the specification itself. The biocide package covers the microbial side that the inhibitor does not protect, while the inhibitor limits corrosion on metal surfaces. Together they aim to keep the narrow channels in the cold plate from clogging.

The scope is the fluid in the cold plate TCS loop; the facility water (FWS) needs separate limits. The ASHRAE TC9.9 water-cooled servers white paper gives TCS conductivity of 0.2-20 micromho/cm, turbidity below 20 NTU and pH 8.0-9.5, while this specification gives 2,000 uS/cm, 5 NTU and pH 8.0-10.5. The values do not align, so the project specification must state which source governs.

Key points

1. Conductivity below 2,000 uS/cm.
2. pH 8.0-10.5 (buffered).
3. Turbidity below 5 NTU.
4. Total viable bacteria count below 1 CFU/ml.
5. Base water: purified, low conductivity/TDS (e.g. ASTM Type IV reagent water).
6. Inhibitor and biocide packages are required.

Using it in design

• In the commissioning and operations module, generate a TCS fluid-quality test plan with these acceptance limits (conductivity, pH, turbidity, total viable count) at fill and at periodic intervals (default quarterly).
• Define water/inhibitor and PG25 options with property sets in the coolant catalog.
• Show the TCS pH difference between the ASHRAE white paper (8.0-9.5) and this specification (8.0-10.5) and make the project pick one.

Who should read it

Engineers who audit cold plate TCS fluid quality during commissioning and operation.

Related standards

• OCP ACS Cold Plate Requirements
• ASHRAE TC9.9 Liquid Cooling Guidelines

Publication details

Authors

Philip Yu

Publisher

Open Compute Project

Year

2026

Document number

v1.3

Document language

English

Source type

Industry body

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation