DC-LC liquid-cooling water quality for AI data centres

Mark Cullens

Sep 5

5 min read

Rows of server racks inside a high-density AI data centre

Direct answer
1. Separate the liquid-cooling loops
2. Establish supplier and material requirements
3. Define fill-water quality
4. Manage closed-loop chemistry
5. Control particles and microbiology
6. Monitor condition without overreacting
7. Design make-up, dosing and side-stream treatment
8. Protect interfaces and redundancy
9. Commission and preserve cleanliness
10. Operate and investigate excursions
11. How Crescent Engineering can support the project
12. References and further reading

Direct answer

DC-LC is the water-quality and conditioning package that protects the facility side of liquid-cooled AI infrastructure. It should define and maintain the chemistry delivered to coolant distribution units or other heat exchangers while preserving hydraulic separation from technology cooling loops.

The correct limits depend on materials, temperature, oxygen ingress, inhibitor chemistry, microbial risk and the requirements of the IT and CDU suppliers. A generic “closed-loop water” specification is not enough for high-density equipment with narrow passages and mixed materials.

1. Separate the liquid-cooling loops

A typical direct-liquid-cooling system has a facility water system, a heat exchanger within a CDU and a technology cooling system serving cold plates. Immersion systems introduce a dielectric-fluid circuit with different quality and material requirements. These fluids should not be treated as interchangeable.

DC-LC normally conditions the facility loop and may provide fill, filtration, dosing, expansion and monitoring. The CDU maintains separation from the IT loop. Battery limits must state which supplier owns each fluid, heat exchanger, sample point and alarm.

The wider choice between cooling architectures is discussed in the air, evaporative and liquid-cooling guide.

2. Establish supplier and material requirements

Compile the allowable water chemistry from chillers, heat exchangers, CDUs, piping, pumps and IT vendors. Resolve differences before procurement. Materials may include carbon steel, stainless steel, copper alloys, aluminium, elastomers and brazing compounds, each with different corrosion sensitivities.

Record operating and standby temperature, velocity, pressure, oxygen exposure and expected make-up. ASHRAE water classes describe thermal capability, but temperature class alone does not define chemical compatibility.

The Open Compute Project provides connection guidance for facility water systems and advanced cooling solutions. Use it alongside project-specific supplier limits rather than as a substitute for them.

3. Define fill-water quality

Fill water should be clean, chemically compatible and free from constituents that will create deposits or consume inhibitors. Depending on the metallurgy and chemistry programme, treatment may include filtration, softening, reverse osmosis, demineralisation or blending.

Avoid assuming that the lowest possible conductivity is always best. Very low mineral water can be aggressive if pH, alkalinity, dissolved gases and inhibitors are not controlled. Conversely, untreated potable water can introduce hardness, chloride and biological nutrients.

Specify cleanliness and sampling for temporary fill hoses, tanks and flushing equipment. The initial fill can introduce more contamination than years of normal make-up.

4. Manage closed-loop chemistry

Select an inhibitor programme compatible with every material and vendor warranty. Control pH, inhibitor residual, conductivity and relevant corrosion indicators within an agreed envelope. Glycol may provide freeze protection or biological benefit, but it changes viscosity, heat transfer, pump duty and analytical requirements.

Minimise uncontrolled make-up because fresh water introduces oxygen and dilutes inhibitors. An unexplained increase in make-up is a leak signal, not simply a chemical-dosing issue.

Keep the facility loop chemistry separate from tower water. The cooling-infrastructure integration guide explains how these systems connect thermally without sharing contamination.

5. Control particles and microbiology

Narrow heat-exchanger channels and cold-plate passages make particulate cleanliness important. Use strainers and side-stream filtration sized for the relevant particle load and required cleanliness, with differential-pressure monitoring and safe maintenance isolation.

Microbial growth can occur in warm, low-flow branches or during prolonged construction. Treatment must be compatible with materials and vendor limits. Avoid uncontrolled oxidant addition to a closed loop without a corrosion and elastomer review.

Dead legs, oversized headers and idle future branches should be eliminated or provided with a defined flushing and preservation strategy.

6. Monitor condition without overreacting

Online measurements may include temperature, pressure, differential pressure, flow, conductivity, pH and make-up volume. Laboratory analysis can add inhibitor residual, metals, glycol condition, microbiology and particle information.

Trend results against a baseline rather than reacting to one isolated value. Rising iron or copper may indicate active corrosion; increasing make-up may explain conductivity drift; differential pressure may reveal fouling.

Set alarm, action and shutdown levels separately. Not every chemistry excursion should trip cooling, but every excursion needs a controlled response that protects IT availability.

7. Design make-up, dosing and side-stream treatment

DC-LC may include a small treated-water make-up unit, batch or automatic dosing, expansion vessel, degassing, side-stream filtration and sample panel. Capacity should reflect initial fill, commissioning losses, planned maintenance and credible leak response.

Automatic dosing can maintain stability, but it should not conceal chronic leakage. Apply daily and cumulative make-up limits with escalation. Provide secondary containment and safe chemical handling.

8. Protect interfaces and redundancy

Define supply temperature, return temperature, flow, pressure, differential pressure and maximum rate of change at every interface. Agree who controls the CDU valve and pumps during normal operation, maintenance and loss of communications.

Redundancy should include the water-quality functions needed to keep a standby hydraulic train usable. Common chemical systems, sample panels or expansion arrangements can become hidden single points of failure.

9. Commission and preserve cleanliness

Commissioning begins with fabrication cleanliness, capped pipework and controlled storage. Flush by zone at a velocity and sequence that removes debris without damaging equipment. Verify strainers, particle load and chemistry before connecting sensitive devices.

Pressure tests, flushing fluids and biocides must be compatible with final materials. Record water source, volume, chemicals and disposal. After acceptance, maintain circulation or apply an approved preservation method; a clean loop can deteriorate during idle construction periods.

10. Operate and investigate excursions

Create response procedures for loss of flow, high differential pressure, chemistry deviation, leak detection and contamination between loops. Preserve samples before corrective dosing where possible.

Use corrosion coupons or probes where appropriate and inspect filters for evidence. Root-cause review should combine chemistry, hydraulics, materials, maintenance and control history.

The proof and assurance guide provides a framework for retaining evidence across commissioning and operation.

11. How Crescent Engineering can support the project

Crescent Engineering can reconcile vendor water specifications, establish fill and operating chemistry, design packaged make-up and side-stream conditioning, define controls and sampling, and support flushing, commissioning and ongoing monitoring.

Crescent Engineering — Water Treatment