Part of the day: CRAH / CRAC / fan walls / in-row units

Assembled by the nightly build from this catalog’s own entry for CRAH / CRAC / fan walls / in-row units (6.03, Layer 6 — Facility cooling & HVAC). The tables below are rebuilt every night; published 2026-10-17.

CRAH, CRAC, fan-wall, and in-row units circulate conditioned air across IT equipment in air-cooled halls, using either facility chilled water (CRAH) or an internal refrigerant circuit (CRAC).

CRAH units draw chilled water from the facility loop (6.05) and blow conditioned air across server intake; CRAC units carry their own compressor instead of relying on facility chilled water. Fan walls and in-row units are denser evolutions of the same function, pushing more air per rack as air-cooled density rose before designs crossed over to liquid cooling. As AI racks move chip heat into liquid loops (Layer 5), CRAH capacity does not disappear — it typically shrinks to cover the residual air-cooled heat load per rack (networking, storage, lower-density equipment) plus emergency and backup air cooling, even in halls that are mostly liquid-cooled. Where a facility stays fully air-cooled, CRAH and fan-wall counts still scale directly with heat load. Investors should watch the shift in mix between CRAH-served air cooling and liquid-side CDUs as the main determinant of demand here, and how much redundant CRAH capacity operators retain per rack even in liquid-first designs.

AI delta: Liquid cooling absorbs most of the chip heat load in AI racks, so CRAH and fan-wall demand per rack falls even as total site CRAH capacity keeps growing to serve the residual air-cooled load and act as backup.

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