What Is Rear-Door Heat Exchanger (RDHx)?_
A rear-door heat exchanger (RDHx) is a liquid-cooled coil mounted on the back of a rack that captures heat from server exhaust air before it returns to the room. RDHx units let air-cooled and hybrid GPU racks reach higher densities than room cooling alone supports, and are often paired with direct-to-chip liquid cooling to remove the residual air-side heat that cold plates do not capture.
Technical Details
RDHx units are either passive (relying on server fans to push air through the coil) or active (with integrated fans). Facility chilled or technical-loop water flows through the coil; as hot exhaust passes through, heat transfers to the water and near-room-temperature air exits the back of the rack. Capacity depends on water supply temperature, flow rate, and air volume, with modern units rejecting tens of kilowatts per rack. In Blackwell-class deployments, direct-to-chip cold plates remove the bulk of GPU heat while an RDHx or room liquid cooling handles the remaining air-cooled components (NICs, power shelves, DIMMs). Installation requires facility water connections, condensation management when supply water is below dew point, and integration with the building management system.
How Leviathan Systems Works with Rear-Door Heat Exchanger (RDHx)
Leviathan Systems installs and connects rear-door heat exchangers as part of hybrid and high-density cooling builds, coordinating the facility water tie-ins and leak-detection integration.
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