CDU and secondary loop
Selected against load, operating temperatures, flow, pressure drop, redundancy and serviceability, with the rating conditions stated.
A CDU's nameplate capacity is a number at one approach temperature. The approach is what matters: it sets how warm the secondary loop runs for a given facility supply, which sets your free-cooling hours and your return-water grade at the same time. A few kelvin of approach can be worth hundreds of hours a year in a temperate climate.
Published approach targets now cluster at 3–4 K. Google's Project Deschutes, the first CDU specification submitted to the Open Compute Project (v1.0 released in February 2026), lists 3 K at a 2,000 kW thermal load with 500 gpm on both loops; KAORI, a heat-exchanger maker, cites 4 K or less as a common design target, and AVC states its CDUs are designed to 4 K. The last two are manufacturer statements, not independent tests. An approach figure is only comparable when it comes with the load fraction, the flow on both sides and the fluid, so we ask for all three.
Filtration has tightened with the cold plates it protects. One CDU maker now describes 25 µm full-flow filtration on the secondary loop as the new default, replacing 50 µm; another describes 25–50 µm full flow plus side-stream filtration below 5 µm on about a tenth of the flow, and Deschutes adds a 0.2 µm side-stream loop. We write the filter rating, the basis of that rating and the change-out pressure drop into the CDU specification.
We select CDUs from several manufacturers against the project's approach, turndown and redundancy requirements, and we require the manufacturer's FAT for pump seals, heat-exchanger gaskets and filter housings, the enclosed boundaries that leak quietly.
Specification and interfaces
The fields buyers compare. Values depend on the configuration, so we do not publish one set of numbers; each project gets a data sheet with every row filled in at stated conditions.
| Field | How it is stated | Value |
|---|---|---|
| Rated heat load and rating conditions | kW at a stated facility supply temperature, secondary supply temperature, approach and fluid | Configured per project; data sheet on request |
| Primary (facility) flow and pressure drop | Flow at rated load and the pressure drop across the CDU at that flow | Configured per project; data sheet on request |
| Secondary (TCS) flow and available pressure | Flow at rated load and the external pressure available to the rack loop at that flow | Configured per project; data sheet on request |
| Pump redundancy | N, N+1 or 2N; whether pumps can be replaced while running; staging logic | Configured per project; data sheet on request |
| Maximum allowable working pressure | For each loop, with the factory test pressure | Configured per project; data sheet on request |
| Wetted materials | Metals, elastomers and plastics in contact with each fluid, named | Configured per project; data sheet on request |
| Coolant compatibility | Fluids and glycol concentrations the unit is rated for | Configured per project; data sheet on request |
| Filtration | Full-flow rating and its basis; side-stream filtration if fitted; change-out pressure drop | Configured per project; data sheet on request |
| Interfaces and communications | Pipe connection type and size; control and monitoring protocols; alarms and signals exchanged | Configured per project; data sheet on request |
| Dimensions and weight | Footprint, height, dry and operating weight | Configured per project; data sheet on request |
| Service clearances | Front, rear, side and top access needed for maintenance | Configured per project; data sheet on request |
| Scope of supply | What is included and what is not: controls, sensors, first fill, factory test, commissioning support | Configured per project; data sheet on request |