Views: 0 Author: Site Editor Publish Time: 2026-02-13 Origin: Site
An RDHx (Rear Door Heat Exchanger) connected to a dry cooler forms a closed-loop, liquid-based heat rejection system that removes server heat directly at the rack level and dissipates it outdoors without mechanical refrigeration. The process is straightforward, efficient, and highly scalable.
Servers exhaust hot air from the rear of the rack
The air passes immediately through the RDHx coil mounted on the rack’s rear door
Hot air is cooled before it re-enters the data hall
This prevents hot-air recirculation and stabilizes inlet temperatures.
Inside the RDHx, heat is transferred from air to a water or water-glycol loop
Depending on the design:
Passive RDHx relies on server fans
Active RDHx uses integrated fans for higher heat densities
The warmed liquid exits the RDHx
Circulation pumps move it through a closed hydronic loop
Typical temperature rise across the RDHx: 5–15 °C
The warm liquid flows to an outdoor dry cooler
Axial fans force ambient air across finned coils
Heat is rejected directly to the atmosphere
No chillers, compressors, or cooling towers are required.
After heat rejection, the cooled liquid returns to the RDHx
The loop continuously repeats during IT operation
System control valves and fan speed modulation maintain stable temperatures.
| Parameter | Typical Range |
|---|---|
| Supply water temperature | 20–35 °C |
| Return water temperature | 30–45 °C |
| ΔT (water side) | 5–15 °C |
| Rack heat density | 10–80+ kW per rack |
| Glycol concentration | 20–40% (outdoor systems) |
Higher water temperatures improve dry cooler effectiveness and maximize free cooling hours.
Heat removed at the source (rack level)
No chilled water plant required
100% free cooling in most climates
Low parasitic power (only pumps and fans)
Scalable from a few racks to entire data halls
This architecture is ideal for GPU, AI, and HPC deployments.
When connected to a dry cooler, an RDHx functions as a direct, liquid-based heat rejection pathway from the server rack to the outdoor environment. By combining rack-level heat capture with dry cooler free cooling, this solution supports high-density IT loads while significantly reducing energy consumption and cooling complexity.
