What is CDU

CDU (Coolant Distribution Unit) is the core unit of liquid cooling system. It separates facility chilled water and IT coolant loop via built-in plate heat exchanger, provides circulating power, precise temperature & flow control for downstream RDHX, GPU cold plates and optical module liquid cooling.

The CDU comes with a built-in plate heat exchanger, which completely separates the two sets of water circuits. The liquids do not mix with each other, only exchanging heat

1. Primary side (Facility loop) : Ordinary cold water from the chiller unit/cooling tower in the computer room.

2. Secondary side (IT loop, Technology loop) : Clean ethylene glycol coolant is sent to the cabinet to supply the RDHX rear door heat exchanger, GPU cold plate, and optical module cold plate, absorbing heat from IT equipment.

technological process:

The secondary side coolant absorbs heat and heats up in the cabinet → flows back to the CDU → transfers heat to the primary side cold water in the CDU board → the cooled secondary coolant is pumped back to the cabinet for circulation by the CDU water pump.

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>Benefit: Once the dirty water in the computer room never enters the server cabinet, protecting IT hardware.

Main internal components of CDU

1. Plate Heat Exchanger (Core Heat Exchanger) : Heat exchange between cold and hot fluids, isolating primary/secondary circuits;

2. Circulating water pump (often with N+1 redundancy) : provides flow and pressure to the secondary circuit;

3. Filter : Filter impurities in the coolant to prevent blockage of the cold plate and RDHX coil;

4. Pressure, temperature, and flow sensors: Real time monitoring and automatic adjustment;

5. Fluid replenishment tank, stabilizing valve, exhaust valve: Maintain system pressure and automatically replenish water;

6. Controller+Communication Module : Docked with DCIM/BMS, remote alarm and linked leakage protection.

Three core functions

1. Heat exchange+cold and hot isolation: Transfer the heat of IT equipment to an outdoor cold source, while isolating the water quality to prevent primary water pollution of the cabinet side pipelines;

2. Allocate cooling capacity, precise temperature and pressure control : Allocate stable flow to multiple cabinets, control the secondary side water temperature (usually higher than dew point to prevent condensation);

3. Safety monitoring and protection : Valve will be closed and alarm will be reported in case of abnormal pressure, loss of flow, or leakage signal linkage.

Three forms of CDU

1. In rack CDU : 4U/6U, placed inside the cabinet, matched with a single cabinet , suitable for small-scale renovation (commonly used for RDHX single cabinet renovation);

2. In row CDU (In row CDU): Floor to floor between cabinet rows, serving one row of cabinets, mainstream in intelligent computing centers;

3. Skid mounted large CDU: megawatt level, centralized cooling source in the computer room, large cluster of tens of thousands of cards.