Designing for AI Workloads (ASME Digital Infrastructure column)

Overview

This column appears in ASME's Digital Infrastructure series and is written by Robert Sty, global data center practice director at HDR. Its subject is the topics met in the mechanical design of liquid-cooled AI halls. It starts from the jump in density, noting that air-cooled racks were typically 10-20 kW while AI cabinets can exceed 100 kW.

The author describes coolant distribution units (CDUs) as the boundary between the facility water system (FWS) and the technology cooling system (TCS). CDUs regulate flow, temperature and pressure to each cabinet and are typically installed N+1, with variable-speed drives on the pumps. On temperature classes, the ASHRAE W classes cover facility water temperatures and the S classes cover TCS supply to IT. This distinction clarifies which loop should be described with which temperature range.

AI training and inference workloads create large and fast power swings, so thermal transients matter. To handle them, TCS piping volume and sometimes small buffer or thermal storage tanks are used, and solutions are validated with CFD. In piping, the advice is to keep cooling water above the room dew point, to use looped piping for redundant paths, to select joints and materials carefully, and to install leak sensors.

The column cites ASME B31.9 for building services piping and ASHRAE 90.1, 90.4 and 189.1 as applicable references. As a limit, it is a column; it gives no detailed calculation method or numerical sizing criteria. Even so, it presents in compact checklist form which topics mechanical design should watch in high-density liquid-cooled halls, and it should be read alongside the ASHRAE TC 9.9 liquid cooling guidelines.

Key points

1. Air-cooled racks were typically 10-20 kW; AI cabinets can exceed 100 kW.
2. CDUs separate FWS from TCS and regulate flow, temperature and pressure to each cabinet; typically installed N+1.
3. AI training and inference cause large, fast power swings; CDU pumps use variable-speed drives.
4. TCS volume or small thermal storage tanks buffer temperature rise, validated with CFD.
5. ASHRAE W classes cover facility water temperatures and S classes cover TCS supply to IT.
6. Keep cooling water above room dew point; use looped piping for redundant paths, careful joint and material selection and leak sensors.
7. Applicable references: ASME B31.9 for building services piping, ASHRAE 90.1/90.4/189.1.

Using it in design

• Default CDUs to N+1 per row or pod.
• Warn when TCS supply temperature is set below the room dew point.
• Provide a TCS loop-volume and buffer-tank check against a user-defined load step (kW over seconds).
• Add looped layout, leak detection and material selection to the piping design checklist.

Who should read it

Engineers designing the mechanical systems of high-density liquid-cooled AI halls.

Related standards

• ASME B31.9
• ASHRAE 90.4
• ASHRAE 90.1
• ASHRAE TC 9.9 Liquid Cooling Guidelines

Publication details

Authors

Robert Sty

Publisher

ASME (Digital Infrastructure column)

Year

2026

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