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  "title": "Coolant distribution unit and separated loops",
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  "description": "Controls the IT coolant loop and transfers collected heat to another cooling system.",
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  "publishedDate": null,
  "revisionDate": "2026-10-07",
  "author": null,
  "topic": "Thermal infrastructure",
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      "title": "Coolant distribution unit and separated loops",
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      "title": "What crosses between the two separated loops?",
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      "title": "Explore in Atlas",
      "url": "https://semiaifoundry.com/ai-atlas/#cdu"
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    {
      "title": "Vertiv — Understanding Coolant Distribution Units",
      "url": "https://www.vertiv.com/en-anz/insights/articles/educational-articles/understanding-coolant-distribution-units-cdus-for-liquid-cooling/"
    },
    {
      "title": "NREL — Data-Center Heat-Balance Analysis",
      "url": "https://www1.eere.energy.gov/buildings/publications/pdfs/rsf/reducing_data_center_loads_large_scale_low_energy_office_building.pdf"
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    {
      "title": "Liquid-cooling coldplate",
      "url": "https://semiaifoundry.com/learn/atlas/coldplate/"
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    {
      "title": "Integrated accelerator rack: GB200 NVL72 example",
      "url": "https://semiaifoundry.com/learn/atlas/rack/"
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      "title": "GB200 compute tray",
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  "content": "Thermal infrastructure · Atlas v1.3.0\n\n# Coolant distribution unit and separated loops\n\nControls the IT coolant loop and transfers collected heat to another cooling system.\n\n[Explore in Atlas](https://semiaifoundry.com/ai-atlas/#cdu)Rack- or row-scale thermal service module\n\nLearning objectiveTrack a coolant loop as a power boundary.\n\n## The mechanism\n\nA coolant distribution unit sits between the cooling needs of IT equipment and the available facility heat-removal system. In a liquid-to-liquid design, a controlled secondary loop circulates through the equipment while a heat exchanger transfers energy to the primary facility loop. The fluids do not need to mix. Pumps, filters, sensors, and control valves help maintain the required flow, pressure, fluid quality, and temperature. The atlas renders the two loops in separate colors so viewers can trace heat crossing the exchanger while following the actual fluid paths independently. CDU designs vary, including liquid-to-air arrangements. A CDU manages and transfers heat; the final destination still lies elsewhere in the facility cooling chain.\n\n1.  Circulate secondary coolant through the IT equipment.\n2.  Transfer its heat across an exchanger to the primary cooling side.\n3.  Control the secondary conditions while the facility carries heat onward.\n\n## Science and assumptions\n\n### Sensible heat transport\n\n$$\n\\dot Q=\\dot m c_p(T_{\\mathrm{return}}-T_{\\mathrm{supply}})\n$$\n\nHeat transport equals mass flow times specific heat times the return-to-supply temperature rise.\n\nSymbols and units\n\nQ̇\n\nHeat transported at the selected coolant-loop boundary\n\nW\n\nṁ\n\nCoolant mass flow\n\nkg/s\n\nc\\_p\n\nCoolant specific heat capacity\n\nJ/(kg·K)\n\nT\\_return\n\nReturn-fluid temperature\n\n°C\n\nT\\_supply\n\nSupply-fluid temperature\n\n°C\n\nHeat transport increases with mass flow, fluid heat capacity, and the temperature rise across the equipment. This relates device heat load to the thermal circuit that carries it away.\n\nAssumptions Single-phase sensible heat with approximately constant $c_{p}$ and steady flow; real equipment must also satisfy pressure, approach-temperature, and control limits.\n\n## Engineering example\n\nFor a known mass flow and temperature rise, Q̇=ṁ$c_{p}$ΔT; the CDU does not make heat disappear, it moves it to a plant boundary.\n\n## Distinctions and tradeoffs\n\nA liquid-to-liquid CDU is not the final heat sink and does not require the two fluid circuits to mix.\n\nLiquid transport supports dense heat loads. Pumps, controls, fluid quality, and facility integration add system requirements.\n\nAccelerators can sustain useful work only while heat is removed. CDU control connects chip cooling to building infrastructure.\n\n## Specifications and interfaces\n\nIllustrated design\n\nLiquid-to-liquid CDU\n\nOther architectures exist.\n\nSeparated circuits\n\nPrimary and secondary loops\n\nHeat crosses the exchanger without intentional fluid mixing.\n\nControlled variables\n\nFlow, pressure, temperature\n\nEquipment- and facility-dependent specifications.\n\n### Interfaces\n\nWarm IT coolant Input\n\nHeat collected from equipment\n\nFacility loop Output\n\nTransferred thermal energy for rejection\n\n## Check your understanding\n\n### What crosses between the two separated loops?\n\n1.  Model parameters\n2.  Heat\n3.  The entire secondary fluid inventory by design\n\nAnswer and reasoning\n\nHeat\n\nThe heat exchanger transfers thermal energy while maintaining separate fluid paths.\n\n## Evidence and scope\n\nThe model excludes pump power, exchanger approach temperature and redundancy.\n\nNo current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions.\n\n## Sources\n\n-   [Vertiv — Understanding Coolant Distribution Units](https://www.vertiv.com/en-anz/insights/articles/educational-articles/understanding-coolant-distribution-units-cdus-for-liquid-cooling/)\n-   [NREL — Data-Center Heat-Balance Analysis](https://www1.eere.energy.gov/buildings/publications/pdfs/rsf/reducing_data_center_loads_large_scale_low_energy_office_building.pdf)\n\n[Published lesson data](https://semiaifoundry.com/ai-atlas/lesson-data/cdu-ba276d9443d0bfb9.json) · [Atlas releases and licensing](https://semiaifoundry.com/ai-atlas/licenses.html)\n\n## Continue exploring\n\n### Foundations\n\n-   [Liquid-cooling coldplate](https://semiaifoundry.com/learn/atlas/coldplate/)\n\n### Related lessons\n\n-   [Integrated accelerator rack: GB200 NVL72 example](https://semiaifoundry.com/learn/atlas/rack/)\n-   [GB200 compute tray](https://semiaifoundry.com/learn/atlas/compute-tray/)\n-   [Facility cooling and final heat rejection](https://semiaifoundry.com/learn/atlas/cooling-plant/)"
}