CDU Units
CDU units are the heat exchanger platform that isolates facility water from IT coolant in liquid-cooled AI racks.
Loop Design
A CDU sits between the facility chilled-water loop and the secondary loop that feeds server cold plates or rear-door heat exchangers. A plate heat exchanger isolates building water chemistry from treated IT coolant, so facility-side pressure, glycol content and corrosion inhibitors remain on the primary side.
DC Power sources CDU platforms from 300 kW to 1.2 MW cooling capacity per unit. That spans single-rack deployments up to cluster-level heat rejection, with primary/secondary flow control, filtration and top-up circuits sized for the secondary loop.
CDU Unit Specification Ranges
| Parameter | Value |
|---|---|
| Cooling capacity per unit | 300 kW – 1.2 MW |
| Primary/secondary isolation | Plate heat exchanger, factory pressure-tested |
| Secondary loop fluid | 25% propylene glycol / deionized water |
| Primary loop fluid | Facility chilled water or condenser water |
| Pump configuration | N+1 or 2N variable-speed centrifugal pumps |
| Flow control | 2-way or 3-way modulating valves |
| Leak detection | Point, cable, or dual-zone leak sensors |
| Control interface | Modbus TCP/RTU, BACnet IP/MSTP, SNMP |
| Electrical supply | 480–600 V 3-phase, 50/60 Hz |
| Secondary supply temperature | 18–32°C typical setpoint range |
Redundancy and Control Features
- N+1 or 2N pump redundancy keeps coolant moving if one pump fails.
- Plate heat exchangers rated from 300 kW to 1.2 MW isolate the primary loop.
- Variable-speed drives trim flow to match 120 kW rack heat loads.
- BMS integration via Modbus, BACnet, or SNMP reports temperature, pressure, and leak alarms.
Sizing Guidance
AI racks now cross 120 kW per cabinet, making liquid cooling mandatory rather than optional. At that density, a 1.2 MW CDU serves about 10 cabinets if you budget 120 kW per rack and no diversity factor.
Procurement should lock CDU capacity early and allow for pump redundancy. Guangdong computing-hardware factories are booked into next year, so confirm allocation before rack PDU and busway orders; primary loop entering water temperature and glycol concentration must be frozen before release.
Secure CDU Allocation
Lock CDU capacity before rack delivery: 300 kW to 1.2 MW platforms with N+1 pumps, BMS integration, and leak detection are available for data hall deployments.
What to specify in a CDU RFQ
- cooling capacity in kW at your delta-T
- primary loop temperature and pressure class
- secondary loop fluid type and filtration spec
- redundant pump count and control protocol
- leak detection and dry-contact alarms
- commissioning and FAT documentation
Sizing rule of thumb
Size the CDU against the simultaneous peak, not the nameplate: a hall of 120 kW racks rarely peaks everywhere at once, and oversizing pumps costs efficiency at partial load. Ask for the efficiency curve at 30, 60 and 100 percent load — a good CDU keeps pump power below 4 percent of moved heat at 60 percent load.
