Who makes rear-door heat exchangers for AI data centers

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.