# Rear-door heat exchangers

Part ID: 5.07 · Layer 5 (Liquid cooling (IT-side: chip to CDU))

A heat exchanger mounted on the rear door of a server rack that cools exhaust air with chilled water or refrigerant before it leaves the rack, without cooling the chips directly.

The rear-door heat exchanger is an air-assist approach rather than a direct-to-chip one: it sits behind a rack of otherwise air-cooled servers and pulls heat out of the exhaust air using a chilled-water or refrigerant coil before that air re-enters the room, rather than cooling the die directly the way a cold plate does. It is typically deployed where a facility wants to raise the density it can support without redesigning every server for direct liquid cooling, or as a supplement in racks that mix liquid-cooled accelerators with air-cooled networking and storage. Because it works at the rack-exhaust level rather than the die level, it has a lower cooling ceiling than a direct-to-chip loop and is generally positioned as a bridge or hybrid option rather than the primary cooling path for the highest-density AI racks. Investors should watch it as a hybrid-density play: demand depends on how much of the installed base stays on air or mixed cooling rather than converting fully to direct-to-chip.

## Companies

| Company | Role | Confidence | Ownership | Ticker | Note |
|---|---|---|---|---|---|
| Legrand | manufacturer | inferred | public | LR.PA |  |
| Motivair | manufacturer | inferred | subsidiary |  |  |
| nVent | manufacturer | inferred | public | NVT |  |
| Vertiv | manufacturer | inferred | public | VRT |  |
| Coolcentric | manufacturer | inferred | private |  |  |
| Huawei | manufacturer | inferred | private |  |  |
| Rittal | manufacturer | inferred | private |  |  |
| Stulz | manufacturer | inferred | private |  |  |

Confidence tags: disclosed = company/filing statement; reported = trade press or partner list; inferred = taxonomy lead.