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The CDU acts as the central control & heat transfer hub of the entire liquid cooling system. It connects the facility cooling infrastructure on one side, and all rack-level liquid cooling hardware on the secondary IT loop.
The CDU’s plate heat exchanger receives chilled water (primary loop) from the building chiller or cooling tower.
Heat collected from IT loads is transferred across the plate heat exchanger to the primary facility water.
The CDU monitors primary supply/return temperature and feeds signals to the BMS, so the chiller can adjust its cooling capacity dynamically.
The primary loop never enters server racks; it is fully isolated by the CDU plate heat exchanger.
The CDU pumps conditioned secondary coolant (glycol water) to all racks and collects heated return fluid. Connected rack devices include:
RDHX Rear Door Heat Exchanger Coolant flows into the rear door coil to absorb hot air from servers. Heated coolant returns to CDU for re-cooling. Multiple RDHX racks can share one row CDU.
GPU / CPU cold plates Direct-chip cold plates absorb heat from GPUs and processors. Hot coolant returns to CDU. Often deployed together with RDHX in mixed cooling racks.
Optical module cold plates High-power 1.6T /3.2T optical transceivers use micro-channel cold plates. The CDU maintains stable coolant temperature to prevent optical wavelength drift and bit error rise.
Rack quick-disconnect valves & isolation manifolds: Each rack has on-off valves. The CDU can trigger isolation to cut off water supply for a leaking rack, without shutting down the whole row.
Leak detection sensors: Water leak sensors on RDHX / cold plates send alarm signals back to CDU controller and DCIM. CDU will close isolation valves upon critical leak alarm.
CDU continuously uploads data: secondary supply/return temperature, flow rate, loop pressure, pump status, filter differential pressure, liquid level.
Receives setpoint commands from BMS, e.g. adjust secondary coolant temperature to avoid condensation.
Generates alarms for low flow, pressure drop, high temperature, pump fault or filter clogging.
Plate heat exchanger: Heat exchange boundary between primary and secondary loop.
Circulation pumps: Deliver pressurized secondary coolant to racks; run in N+1 redundancy.
Filters: Remove particles from returning coolant to protect cold plates and RDHX coils from blockage.
Expansion tank / auto vent: Compensate thermal expansion and purge air bubbles from the secondary loop.
CDU pulls cold water from the building cooling plant, reconditions the secondary coolant, distributes it to RDHX, GPU cold plates and optical module cold plates in racks, recovers heated fluid, rejects heat to the facility water, and communicates with BMS/leak sensors for safety and closed-loop control.
