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Technical guideFree to read2024

Data Center Liquid Distribution Guidance & Reference Designs, Rev 1.0 (OCP Advanced Cooling Facilities)

Open Compute Project · Don Mitchell, John Menoche et al.

This 2024 OCP Advanced Cooling Facilities white paper gives concept-level guidance for integrating liquid-cooled IT into data centers: connecting to existing facility water systems through CDUs, door heat exchangers on facility water, and elevated-temperature loops that bypass chillers.

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Overview

The method rests on the heat-transport relationship Q = volumetric flow x delta-T x density x specific heat, and by volume water carries about 3,300 times the heat of air. The paper uses it to give a table of pipe size against kW for concept sizing, but states clearly that the table is concept-level only and needs validation by a licensed engineer.

The temperature discussion matters: at W45 and above, cold plate and immersion allow evaporation-free free cooling in all climates, and 35-60 degC liquid loops are common. Door heat exchangers return air to the ASHRAE TC9.9 range (typically below 27 degC) and often connect directly to facility water without a CDU. The condensation section notes that the highest dew point supported by ASHRAE TC9.9 air classes is 28 degC, that TCS should be kept above dew point, and that alarms should cover transitions.

On redundancy the best practice is redundant pumps and backup power (UPS or generator) for CDUs and TCS. The paper also covers space planning for pipe routing and tap-offs. It is a reference-design white paper; it gives no detailed hydraulic calculation, valve selection or cost, so the pipe table and CDU layout results must be validated by an engineer under project conditions.

Key points

  1. Q = volumetric flow x delta-T x density x specific heat; by volume water carries about 3,300 times the heat of air.
  2. Cold plate and immersion allow evaporation-free free cooling in all climates at W45 and above; 35-60 degC liquid loops are common.
  3. Door heat exchangers restore air to the ASHRAE TC9.9 range (typically below 27 degC) and often connect to facility water without a CDU.
  4. The highest dew point supported by ASHRAE TC9.9 air classes is 28 degC; keep TCS above dew point and alarm during transitions.
  5. Best practice: redundant pumps and backup power (UPS/generator) for CDUs and TCS.
  6. The pipe size versus kW table is concept-level only; licensed-engineer validation is required.

Using it in design

  • In the liquid-cooling calculator implement Q = m*cp*delta-T for TCS/FWS sizing (water cp 4.18 kJ/kg-K, PG25 option) and size pipes by maximum velocity.
  • Add a dew-point check: TCS supply >= room dew point + 2 K (default margin).
  • For Tier III/IV intent default CDU pumps to N+1 and put CDUs on UPS.
  • Offer facility-water class presets W17/W27/W32/W40/W45/W+.
  • Label pipe-table results as 'conceptual'.

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Who should read it

Mechanical designers settling early-stage piping and CDU layout in liquid-cooled halls.

Related standards

  • ASHRAE TC9.9 Liquid Cooling Guidelines
  • ASHRAE 90.1
  • OCP ACS Cold Plate Requirements

Publication details

Authors
Don Mitchell; John Menoche; John Gross; Vali Sorell; John Musilli
Publisher
Open Compute Project
Year
2024
Document number
ACF Rev 1.0
Document language
English
Source type
Industry body
Access
Free to read
Licence
Copyright retained; citation only — the publisher’s terms apply to the original document

Citation

Don Mitchell; John Menoche; John Gross; Vali Sorell; John Musilli (2024). Data Center Liquid Distribution Guidance & Reference Designs, Rev 1.0 (OCP Advanced Cooling Facilities). Open Compute Project. ACF Rev 1.0. https://www.opencompute.org/documents/ocp-acf-reference-design-guidance-white-paper-r1-pdf/

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