CDU Specifications And Selection (board Replacement, Circulation Pump, Redundant Design)

Overview of CDU Core Selection Parameters

The first step in selection is to determine the system boundary:

1. Total heat load: The maximum simultaneous heating power of all downstream cabinets (RDHX+GPU cold plate+optical module cold plate) in kW

2. Secondary circuit: medium (commonly 25%~35% ethylene glycol aqueous solution), temperature difference between supply and return water (typical 5 ℃/8 ℃/10 ℃), target supply water temperature (usually 22-27 ℃, higher than dew point to prevent condensation)

3. Total pressure drop of the system: all resistance caused by the end of the cabinet pipeline+RDHX/cold plate+branch pipe+filter+plate replacement

4. Primary side condition: Water supply temperature of chiller/dry cooler (L2L CDU)

>Flow calculation formula:

> Q (m³/h)=0.86 × P (kW) ÷ ΔT (℃)

Plate Heat Exchanger Selection (L2L CDU Core Components)

1. Key selection points

1. Heat exchange area : based on maximum heat load+safety margin (1.1-1.2 times redundancy); Cannot load at full capacity, insufficient margin during high temperature season.

2. Board material

-Standard ethylene glycol circuit: 304 stainless steel plate, EPDM rubber gasket

-High corrosion/long-term high temperature: 316L stainless steel plate

-Fluorinated liquid circuit: requires special materials, conventional board replacement is not applicable

3. Design pressure : ≥ 1.6 MPa (industrial liquid cooling standard); Test pressure 1.5 times the working pressure

4. Terminal difference control : The terminal difference between the primary return water and the secondary supply water should be controlled at 1-2 ℃. If the terminal difference is too large, it means that the plate replacement area is insufficient.

5. Flow channel form: single-sided flow/diagonal flow; Match the traffic on both sides.

2. Risk points of board replacement

-Small spacing between plates, sensitive to water quality → CDU inlet must be equipped with a filter;

-Gasket aging is a leakage risk point, and EPDM (ethylene glycol resistant) is preferred;

-Plate replacement cannot operate at high temperatures for a long time, as it will accelerate the aging of the gasket.

>

>L2A CDU does not have plate heat exchangers and is replaced with finned air cooling coils.

Selection of circulating pump (secondary circuit pump)

1. Two core indicators

1. Flow rate: Calculated based on the total heat load, with a reserved margin of 10-20%;

2. Head ≥ Total pressure drop of the entire secondary circuit (pipeline, RDHX/cold plate, filter, plate replacement, valve), plus safety margin.

2. Pump Type

-Horizontal/vertical shielded pump, stainless steel centrifugal pump (liquid cooled CDU mainstream), low leakage, suitable for ethylene glycol.

-Motor: Efficient IE3/IE4, running continuously for 24 hours.

3. Pump operating temperature range

The temperature of the medium is generally 15~45 ℃, and cannot exceed the upper temperature limit of the pump seal.

Pump Redundancy, a high-frequency focus for customers

N+1 redundancy (most commonly used in the industry, mainstream in AI data centers)

-Example: Two pumps (1+1), each pump can handle 100% of the design flow rate. One for use, one for backup.

-Logic: Running pump failure → System automatically switches to standby pump without stopping; No risk of interruption.

✅ Recommendation: High density GPU, optical module liquid cooling, production room.

N No redundancy (single pump)

-Single pump, pump failure leads to direct interruption of CDU and IT equipment overheating protection shutdown.

✅ Applicable: POC testing, edge small nodes, non core laboratories.

N+N parallel redundancy (super large cluster)

Multiple pumps are connected in parallel, and if any one fails, the other pumps will jointly bear all the flow; High cost, megawatt scale large-scale modular CDU.

Selection of supporting accessories (linked with plate replacement/pump)

1. Filter: secondary circuit inlet, 100-200 μ m, pressure difference monitoring; High pressure differential alarm, indicating filter blockage, protective plate replacement, cold plate, RDHX microchannel.

2. Expansion tank: absorbs thermal expansion and contraction, stabilizes system static pressure; The selection is based on the total water volume of the system.

3. Automatic exhaust valve: arranged at a high point to eliminate air blockage and prevent pump cavitation and local overheating.

4. Sensor: supply and return water temperature, pressure, flow rate; BMS/DCIM communication.

5. Isolation valve: Cabinet level manual/electric ball valve, single cabinet leakage isolation.