Deploying Liquid Cooling in the Data Center: A Guide to High-Density Cooling (1 MW IT load)

Overview

The guide's main example is 20 racks x 50 kW = 1 MW. Each rack sends 37.5 kW to liquid and 12.5 kW to air, which at cluster scale is 750 kW liquid and 250 kW air. Cold-plate flow is taken as about 1.5 L/min per kW (0.4 gpm/kW), giving 56.25 L/min for a 50 kW rack and 1,125 L/min for the cluster. A reader can thus turn a ratio like "75% liquid" straight into pipe and pump flow.

Technology choice is tied to rack density: passive rear doors suit roughly 5-25 kW racks and active rear doors 50-70 kW, while direct-to-chip is treated for higher densities. The newest AI servers are noted as approaching 6-10 kW TDP each, which explains why 50 kW per rack is becoming ordinary.

CDU placement (in-rack, end-of-row, centralised) and redundancy get separate treatment. Row-level N+1 needs two CDUs, one on duty and one standby, which carries a floor-space cost. The filtration rule is clear: cold plates with 100 micron fin pitch need filtration no coarser than 50 microns. On the electrical side, the paper discusses what changes when 100 x 10 kW racks become 20 x 50 kW racks. The introduction rests on Uptime data: 17% of data centers already use liquid cooling and another 61% are considering it. The guide dates from 2023 and centres on one 1 MW example; at far higher densities (racks above 100 kW) these flows and ratios should be revalidated.

Key points

1. Worked example: 20 racks x 50 kW = 1 MW; 37.5 kW/rack to liquid and 12.5 kW to air (750 / 250 kW cluster)
2. Cold-plate flow ~1.5 L/min per kW; 56.25 L/min per 50 kW rack; 1,125 L/min cluster
3. Passive rear doors suit ~5-25 kW racks; active rear doors 50-70 kW
4. Cold plates with 100 micron fin pitch need filtration no coarser than 50 microns
5. Row-level N+1 CDU redundancy requires two CDUs (one duty, one standby)
6. Newest AI servers approach 6-10 kW TDP per server
7. Survey: 17% of data centers already use liquid cooling; another 61% considering it

Using it in design

• Calculation default: DLC flow = 1.5 L/min per kW of liquid-captured heat; to adjust by dT use flow = P/(4.18 x dT) L/s.
• Default secondary-loop filtration to 50 micron.
• In the rear-door catalog apply thresholds: passive <= 25 kW, active <= 70 kW racks.
• For CDU redundancy, show the floor-space cost of row-level N+1 against a centralised CDU gallery.

Who should read it

Facility and mechanical engineers converting an existing air-cooled hall to hybrid liquid cooling.

Related standards

• ASHRAE TC9.9 Liquid Cooling Guidelines
• OCP Advanced Cooling Solutions

Publication details

Authors

Vertiv

Publisher

Vertiv

Year

2023

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation