The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Direct liquid cooling (DLC) carries heat away from server hardware in a circulating liquid loop instead of relying on room air to remove that heat first. In the common direct-to-chip design, cold plates contact selected high-heat components; coolant absorbs their heat and transfers it through a heat exchanger to the facility cooling system. Other server parts may still need air cooling, so DLC does not automatically replace every fan, chiller, or cooling tower.
What “direct liquid cooling” means
DLC describes cooling that brings liquid to the IT equipment or its components. In a direct-to-chip system, a liquid loop connects to cold plates mounted on hot components inside servers. That is different from a rear-door heat exchanger or a room- or rack-level system that captures heat from air: those approaches transfer heat to liquid but do not necessarily deliver coolant directly to server components. Immersion is another distinct configuration, in which hardware is placed in dielectric liquid.
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ASHRAE describes component-level liquid cooling as delivering the cooling medium to the equipment chassis, often directly to components. Such systems need dedicated piping distribution, specialized heat exchangers, and connections to the facility’s climate-control system.
How a direct-to-chip cooling loop works
- A component produces heat. A processor or another high-heat part warms during operation.
- A cold plate captures heat. The plate is attached to the component, and heat conducts into coolant flowing through it.
- The IT-side coolant carries heat away. The warmed coolant travels through the technology cooling loop toward a heat exchanger, often integrated with or connected to a coolant distribution unit (CDU).
- The CDU transfers heat between loops. It manages or separates the IT-side loop from the facility-side loop, transferring heat without necessarily mixing their fluids.
- The facility rejects the heat. The building’s cooling infrastructure removes heat from its water loop. In the U.S. Department of Energy’s illustrated arrangement, heat passes from the IT chilled-water loop to a condenser-water loop and then to a cooling tower.
The CDU and heat exchanger are important because the server loop and facility loop can have different requirements. “Liquid-cooled” does not mean there is one continuous coolant circuit from the processor to the outdoors.
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How the main cooling approaches differ
| Approach | Where liquid removes heat | What to expect |
|---|---|---|
| Direct-to-chip cold plates | Selected components, through plates attached to them | Coolant removes heat from those components; other server parts and the room may still rely on air cooling. |
| Immersion cooling | Hardware placed in a nonconductive dielectric liquid bath | Single- and two-phase arrangements exist. ASHRAE says nearly 100% of equipment heat can be rejected to liquid in a full-immersion configuration, potentially reducing auxiliary air-cooling infrastructure. |
| Hybrid facility cooling | Liquid handles some IT heat while room-air systems remain in use | CDUs can serve liquid-cooled IT while CRAHs or direct-expansion (DX) systems maintain room conditions or cool components not served by liquid. |
These options have different system boundaries. Cold plates are commonly included under DLC, but DLC should not be used as a synonym for immersion alone. Conversely, a system that moves heat from room air into liquid is not necessarily direct component cooling.
Why data centers consider DLC—and what it cannot promise
Liquid can carry heat from high-heat components without first requiring room air to absorb it. That can reduce the burden on server fans and room-air cooling. The practical result depends on the entire design, including which components are covered, the facility’s heat-rejection equipment, and whether chillers are needed. The DOE says DLC may offer opportunities to reduce power usage effectiveness (PUE) and water usage effectiveness (WUE) in some applications; it does not establish a universal outcome.
Some configurations can bypass chillers under suitable conditions; others use them. Heat rejection may still involve cooling towers. ASHRAE also identifies specialized piping and redundancy as part of liquid-cooling system design. Therefore, DLC by itself does not guarantee lower energy use, no water use, or elimination of chillers or cooling towers.
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What adoption figures say—and what they do not
Uptime Institute’s May 2024 Cooling Systems Survey found that 22% of respondents reported some DLC use, while 61% said they were not using it but were considering it. The survey included 964 industry respondents and was conducted from February 8 to March 13, 2024. These are respondent shares, not percentages of global data-center capacity.
Among surveyed DLC users, 64% reported water-cooled cold plates, 30% dielectric-cooled cold plates, 26% single-phase immersion, and 13% two-phase immersion. Respondents could select multiple types, so the percentages are not mutually exclusive and should not be added together. Uptime analyst Jacqueline Davis described adoption in 2024 as gradual and uneven, with substantial deployments concentrated in HPC-related uses such as academic research, engineering, AI model development, and cryptocurrency. These figures provide dated context, not a 2026 market census.
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What to check when evaluating a DLC design
- Coverage: Which components are cooled by liquid, and what share of the server’s total heat does the loop capture?
- Remaining air cooling: Which components and room conditions still depend on fans, CRAHs, DX systems, or other air cooling?
- Coolant conditions: What coolant and supply temperatures do the equipment and cooling system require?
- Heat rejection: How does the facility ultimately reject heat, and does the design rely on chillers, cooling towers, dry coolers, or a combination?
- Loop and CDU arrangement: How are IT-side and facility-side loops connected and separated?
- Operations: How are piping, serviceability, redundancy, and failure response handled?
- Deployment context: Is the system intended for a new facility or a retrofit?
There is no universal winner among cold plates, immersion, and hybrid arrangements; the right comparison depends on these design and operating requirements.
Understanding the DOE’s water-temperature classes
The DOE’s 2024 design guide lists ASHRAE water classes W17, W27, W32, W40, W45, and W+. The numbered labels indicate upper server-supply-water temperature limits in degrees Celsius, and the guide says they replaced the earlier W1–W5 naming. These labels do not mean every server supports every class. Confirm the requirements for the specific equipment and the applicable ASHRAE edition.
Quick Recap
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Sources
- ASHRAE, Chapter 20: Data Centers and Telecommunication Facilities
- U.S. Department of Energy FEMP, Cooling Water Efficiency Opportunities for Federal Data Centers
- U.S. Department of Energy, Best Practices Guide for Energy-Efficient Data Center Design (2024)
- Uptime Institute, Cooling Systems Survey 2024: Direct liquid cooling (May 2024)
- Jacqueline Davis, Uptime Institute Journal, “Water cold plates lead in the small, but growing, world of DLC” (October 30, 2024)
- ASHRAE, Integrated Design Principles | AI Data Center Energy Performance Framework
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