Door Heat Exchanger

Overview

Door Heat Exchangers (Door HX, also called Rear Door Heat Exchangers or RDHx) are rack-mounted liquid-to-air heat exchangers that capture the hot exhaust air from IT equipment as it exits through the rear of the rack. The heat is transferred to a liquid coolant loop, reducing the thermal load on room-level CRAH/CRAC units and enabling higher rack densities in existing air-cooled facilities. Door HX technology serves as a transitional or complementary approach alongside direct-to-chip cooling, particularly valuable for retrofitting air-cooled data centers or handling mixed air/liquid-cooled environments.

The OCP Cooling Environments project has formalized this technology through the Door HX Specification Rev 1.0 (published January 2026) and is developing the Mega AALC (Active Air Liquid Cooling) sidecar concept targeting 1 MW cooling capacity with 30-40% cost reduction versus traditional RDHx designs. The sub-project is led by Jabari George (LGTS) and coordinates across multiple workstreams: corrosion testing (Valeo), system-level validation (OVHCloud), AALC sidecar design (Meta), and TCS flow control (Grundfos, Lawrence Berkeley National Lab). AMD leads the Mega AALC sub-project, with contributing companies including Stulz, Vertiv, and Rittal.