Scaling for the Future: Liquid Cooling's Role in AI Data Centers (Mike Connaughton, Jacques Fluet)

Overview

The article by Mike Connaughton and Jacques Fluet, published in BICSI ICT Today for July/August/September 2025 (Vol. 46, No. 3, p. 14), compares direct-to-chip (DTC), immersion and rear-door heat exchanger (RDHx) cooling from an ICT infrastructure viewpoint. It refers to ANSI/TIA-942-C, which was released in May 2024 and covers cabling, power, cooling, redundancy and security. Liquid is said to transfer heat up to 20 times more efficiently than air.

On floor loading, immersion imposes the highest load because of the dielectric fluid volume. DTC adds the weight of piping, pumps and CDUs, while RDHx adds heavier doors and liquid. DTC has minimal thermal inertia and high heat flux, so it needs redundant manifolds, couplings, dual pumps and automatic switchover of heat rejection. Redundancy of pumps and CDUs is therefore a basic design topic.

Monitoring points differ for each system: coolant inlet and outlet temperature (at the rack manifold for DTC, the rack for immersion and the door for RDHx), pump pressure, fluid level or volume, fluid quality, leaks and dew point should be monitored. This list forms a practical checklist for closing monitoring gaps that would otherwise be overlooked. The sensor and cabling needs of these monitoring points should be considered at the design stage so that no measurement point is missing at commissioning.

For cable and pipe routing, immersion requires all cabling to exit from the top of the rack, and any submerged cable must be chemically compatible with the coolant. RDHx may need deeper racks to fit thicker doors plus cable and manifold routing. The article also touches on safety and operational procedures. The record rests on the article's summary; numerical cooling capacities or costs are not included.

Key points

1. ANSI/TIA-942-C was released in May 2024 and covers cabling, power, cooling, redundancy and security.
2. Liquid can transfer heat up to 20 times more efficiently than air.
3. Immersion imposes the highest floor load; DTC adds piping, pumps and CDU weight; RDHx adds heavier doors and liquid.
4. DTC has minimal thermal inertia and high heat flux, needing redundant manifolds, couplings, dual pumps and automatic switchover of heat rejection.
5. Monitor coolant inlet/outlet temperature, pump pressure, fluid level/volume, fluid quality, leaks and dew point.
6. Immersion requires all cabling to exit from the top of the rack, and submerged cables must be chemically compatible with the coolant.
7. RDHx may need deeper racks to fit thicker doors plus cable and manifold routing.
8. Related references: ANSI/TIA-942-C and ASHRAE TC9.9.

Using it in design

• Catalogue liquid cooling systems with floor-load contribution, required sensors and cabling exit constraints (top-only for immersion).
• Require DTC designs to show redundant pumps or CDUs and automatic switchover.
• Check cable tray clearance from coolant pipes.
• Flag cables in immersion tanks that are not immersion-rated.

Who should read it

Engineers planning liquid cooling together with ICT infrastructure in AI and high-density data centres.

Related standards

• ANSI/TIA-942-C
• ASHRAE TC9.9

Publication details

Authors

Mike Connaughton; Jacques Fluet

Publisher

BICSI ICT Today

Year

2025

Document number

Vol. 46, No. 3 (Jul/Aug/Sep 2025), p. 14

Document language

English

Source type

Standard

Access

Free to read

Licence

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

Citation