What Is a CDU (Coolant Distribution Unit)?The Interface Between Facility Water and Chip-Level Cold Plates
How coolant distribution units isolate, filter, and regulate liquid loops for direct-to-chip cooling — and where ToneCooling cold plates fit into that loop.
A Coolant Distribution Unit (CDU) is the mechanical interface between a data center’s facility water loop and the secondary loop running through server-level cold plates. It isolates the loops, filters particulates, and regulates flow, pressure, and leak detection — protecting electronics from facility-side water quality variation. CDUs are defined under ASHRAE TC 9.9 guidelines.
A CDU manages the loop; a cold plate manages the chip. ToneCooling designs and manufactures the direct-to-chip liquid cold plates that sit downstream of a facility or in-row CDU — see our AI Server Liquid Cooling Kits for platform-specific cold plate assemblies engineered to match standard CDU flow and pressure specifications.
Who This Page Is For
- Data center facilities engineers evaluating in-row vs. in-rack CDU architecture before finalizing cold plate specifications
- Server OEM thermal engineers who need cold plates pre-validated against a specific CDU’s flow rate and pressure drop budget
- Procurement teams comparing direct-to-chip liquid cooling vendors and need to understand where CDU and cold plate scope divide
- Reference: ASHRAE TC 9.9 — Liquid Cooling Guidelines for Datacom Equipment Centers
In-Row CDU vs. In-Rack CDU vs. Facility-Level CDU
| Type | Typical Capacity | Placement | Best Fit |
|---|---|---|---|
| In-rack CDU | 20–100 kW | Inside the server rack | Single high-density rack, fastest deployment |
| In-row CDU | 100–1,000+ kW | Between rows, shared across multiple racks | Multi-rack AI/HPC clusters |
| Facility-level CDU | 1 MW+ | Centralized mechanical room | Greenfield hyperscale builds |
Where cold plates fit: Regardless of CDU tier, the secondary loop terminates at server-level cold plates mounted directly on GPUs, CPUs, and IGBT power modules. ToneCooling engineers cold plates to the flow rate (LPM) and pressure drop (kPa) budget of the customer’s chosen CDU — see How to Choose a Liquid Cooling Solution for AI Servers.
How We Work With You
| Stage | What You Get | Typical Timing |
|---|---|---|
| Loop compatibility review | Flow/pressure matching against your CDU spec sheet | 1–2 business days |
| DFM + thermal simulation | CFD validation of cold plate against your chip TDP | 3–5 business days |
| Prototype | CNC-machined or FSW cold plate sample | 6–8 weeks |
| Production | Vacuum-brazed or FSW batch production | 4–6 weeks |
Manufacturing Process
ToneCooling cold plates for CDU-fed secondary loops are built using FSW (friction stir welding), vacuum brazing, or CNC-machined micro-channel construction depending on flow requirement and chip TDP — see FSW vs. Vacuum Brazing process selection guidance.
Validation
Every cold plate is pressure-tested and leak-tested before shipment to match CDU-side leak detection tolerances, and flow/pressure-drop tested against the customer’s stated CDU operating point.
NDA and Confidential Projects
Cooling loop architecture and CDU vendor selection are often confidential at the design stage.
- We sign a mutual NDA before reviewing your loop schematic or CDU spec sheet
- DFM review and quoting continue under NDA
Prototype to Series Production
Typical Project Profile
Illustrative composite, not a specific customer project.
An AI infrastructure integrator specified an in-row CDU rated for 2.5 LPM per node at 35 kPa max pressure drop. ToneCooling supplied CNC-machined copper cold plates engineered to that exact flow/pressure budget, validated via CFD before prototype cut, with full pressure and leak test reports delivered alongside the first article sample.
Why ToneCooling
Three contracting entities, matched to where you buy from.
Huizhou manufacturing (FSW + vacuum brazing + CNC machining under one roof) + ToneCooling Texas LLC (US entity support) + ToneCooling Europe OÜ (EU entity support) — three-entity backing for cold plates engineered to match any CDU architecture, from in-rack to facility-level.
FAQ
What is the difference between a CDU and a cold plate?
A CDU manages the coolant loop — isolation, filtration, flow regulation, and leak detection. A cold plate is the component mounted directly on a chip or power module that transfers heat into that loop. They are separate, complementary components in a direct-to-chip liquid cooling system.
Can ToneCooling supply CDUs as well as cold plates?
ToneCooling manufactures direct-to-chip liquid cold plates. We work alongside your chosen CDU vendor to ensure hydraulic compatibility — flow rate, pressure drop, and coolant chemistry — rather than supplying the CDU itself.
What flow rate and pressure drop should I plan for?
Typical AI server cold plates operate in the 1.5–3.5 LPM range per node with pressure drops under 35–50 kPa, but exact figures depend on chip TDP and channel geometry. Send your CDU spec sheet for a compatibility review.
What coolant chemistry do ToneCooling cold plates support?
Cold plates are validated with deionized water, PG25/PG50 propylene glycol mixtures, and 50/50 ethylene glycol-water (EGW) blends, consistent with ASHRAE W-series water quality classes.
Do you provide leak testing before shipment?
Yes. Every cold plate undergoes pressure and leak testing before shipment, with test reports available on request.
Ready to review your cooling loop?
