{
 "id": "6.03",
 "slug": "crah-crac-fan-walls-in-row-units",
 "url": "/parts/facility-cooling-and-hvac/crah-crac-fan-walls-in-row-units",
 "name": "CRAH / CRAC / fan walls / in-row units",
 "qualifiers": null,
 "layer": {
  "id": 6,
  "name": "Facility cooling & HVAC"
 },
 "parent_id": null,
 "children": [],
 "summary": "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).",
 "description_md": "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.",
 "bottleneck_status": null,
 "scale_tiers": [
  "enterprise",
  "hyperscale_building",
  "ai_campus",
  "gw_class"
 ],
 "density_modes": [
  "air",
  "hybrid"
 ],
 "scale_notes": "Sole cooling method at air-cooled enterprise and hyperscale halls; shrinks to a residual and backup role per rack once a site is liquid-cooling-first at ai_campus and gw_class scale.",
 "flow": [
  "heat"
 ],
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}