Definition
A Rear Door Heat Exchanger (RDHx) is a data center cooling technology that removes heat from server exhaust air through a heat exchanger mounted on the rear of a server rack.
Instead of allowing hot exhaust air to return directly to the data center room, the RDHx captures the heat at the rack level and transfers it to a liquid cooling loop, typically using chilled water or another cooling fluid.
RDHx is commonly used for high-density racks and hybrid cooling environments where conventional room-level air cooling becomes increasingly difficult to scale.
For a deeper explanation of how RDHx systems work, their key components, applications, and role in high-density cooling, see ATTOM’s What Is a Rear Door Heat Exchanger? guide.
How RDHx Works
A typical rear door heat exchanger operates as follows:
- Servers discharge hot exhaust air toward the rear of the rack.
- The air passes through the heat exchanger mounted on the rack’s rear door.
- Heat transfers from the exhaust air into the circulating cooling fluid.
- Cooled air is released back into the data center room.
- The heated fluid returns to the facility cooling system for heat rejection.
Because heat is removed close to the rack, RDHx can reduce the amount of heat that must be handled by room-level cooling equipment.
RDHx for High-Density Computing
RDHx is particularly useful when rack power density exceeds the practical capacity of conventional air cooling.
Typical applications include:
- High-density server racks
- AI and GPU infrastructure
- HPC environments
- Data centers upgrading existing air-cooled systems
- Hybrid air and liquid cooling architectures
RDHx can provide additional rack-level cooling capacity without requiring every server to be redesigned for direct liquid cooling.
RDHx vs. Other Cooling Technologies
| Technology | Where Heat Is Removed |
|---|---|
| Air Cooling | From the data center room through conditioned air |
| RDHx | From hot rack exhaust air at the rear of the rack |
| Direct-to-Chip Cooling | Directly from high-power components through cold plates |
| Immersion Cooling | Directly from IT equipment immersed in dielectric fluid |
RDHx is therefore a useful intermediate approach between conventional room-level air cooling and component-level liquid cooling.
Related Terms
- Liquid Cooling
- Immersion Cooling
- Direct-to-Chip Cooling
- Air Cooling
- CRAH (Computer Room Air Handler)
- High-Density Computing
- AI Data Center
- Thermal Management
Related ATTOM Solutions
ATTOM provides cooling solutions for conventional and high-density data center environments, including architectures that combine air cooling with liquid-based heat removal.
Explore ATTOM’s Rear Door Heat Exchanger solutions for high-density AI and data center applications.
