Liquid cooling is not a new response to AI: it was used in mainframe-era computing by roughly the late 1960s or early 1970s. What is new is the scale and breadth of its deployment in modern data centers, where rising chip and rack heat densities are putting air cooling under pressure. The shift is an expansion of an established engineering approach, not a simple replacement of air cooling or a single technology taking over.
What does liquid cooling mean in a data center?
Liquid cooling moves heat away from IT equipment through a circulating liquid rather than relying only on room air to carry heat from components to the facility cooling system. “Water cooling” is often used as shorthand, but the term liquid cooling covers different designs and points of heat transfer. The liquid may collect heat at the rack, circulate through equipment, or reach cooling hardware at the electronics themselves.
A facility may use a cooling distribution unit (CDU) to transfer heat between the technology cooling system serving IT equipment and facility water. That interface matters: liquid at a server or rack does not, by itself, describe how heat ultimately leaves the building.
Why is liquid cooling attracting renewed attention?
Modern electronics are concentrating more heat into equipment and smaller areas. ASHRAE’s 2023 handbook chapter on data centers and telecommunication facilities describes increasing heat density as making it harder for air to cool electronics. Liquid can move waste heat into facility loops and reduce the amount of air that must flow through a rack, but the right design still depends on equipment compatibility, facility infrastructure, and the way heat is rejected.
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AI workloads are an important driver of the current scale-up, but liquid cooling is not required for every data center or every device. Air and liquid systems can coexist; the decision depends on heat density and what the installed equipment and facility can support.
How the main liquid-cooling approaches differ
ASHRAE distinguishes cooling at the rack, at the datacom equipment, and at the electronics. These approaches differ mainly in where liquid enters the heat-transfer chain.
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- ARCTIC's P12 PRO FAN: More power at any speed - more powerful and quieter than the P12, especially at low speeds. Higher maximum speed for optimal cooling performance under high load
- NATIVE OFFSET MOUNTING FOR INTEL AND AMD: Shifting the cold plate center towards the CPU hotspot ensures more efficient heat transfer
- INTEGRATED VRM FAN: PWM-controlled fan that lowers the temperature of the voltage converters and thus ensures reliable performance
- INTEGRATED CABLE MANAGEMENT: The PWM cables of the radiator fans are integrated in the sheathing of the hoses so that only a single visible cable is connected to the motherboard
| Approach | Where heat is collected | What the distinction means |
|---|---|---|
| Liquid-cooled rack | At rack or cabinet level | A heat exchanger transfers heat from air to liquid at the rack or cabinet. The equipment may still use air internally to move heat to that exchanger. |
| Liquid-cooled datacom equipment | Within the equipment | Liquid circulates within the IT equipment to carry heat away. |
| Liquid-cooled electronics | At the electronics | Liquid is delivered to the electronics without another heat-transfer mechanism between the electronics and the liquid. |
These categories are not interchangeable labels for one universal system. A useful design comparison asks where liquid is introduced, how heat passes from the technology loop to facility heat rejection, how much heat the equipment produces, and what airflow remains necessary.
What does “fifty years” mean in this history?
The half-century framing describes an established approach returning at greater scale; it should not be read as a precise, continuous adoption timeline. In ASHRAE Journal Podcast Episode 44, David Quirk said, “liquid cooling is really nothing new. It’s been in the industry, going back to the mainframe days, but what is new is the scale that it’s now being deployed in the industry, and largely driven by artificial intelligence software applications.” In the same episode, Dustin Demetriou described the technology as having been around “since the-probably late-1960s, early-1970s with mainframe computers.”
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Those remarks support a broad account of mainframe-era use and present-day expansion, not a year-by-year history. The available sources do not establish a complete chronology, adoption rate, or market share across the intervening decades. ASHRAE’s 2021 white paper connects rising IT power and lower package case-temperature requirements with future liquid-cooling needs, and recommends designing future data centers so that liquid cooling can be added. That is a recommendation in a white paper, not a binding standard.
Does liquid cooling improve efficiency or reduce water use?
Neither result is guaranteed by the presence of liquid. The U.S. Department of Energy’s Federal Energy Management Program (FEMP) describes direct liquid cooling as transferring heat from IT equipment directly to a recirculating chilled-water loop instead of first transferring it to room air. FEMP says some direct liquid-cooling systems show promise for reducing power usage effectiveness (PUE) and water usage effectiveness (WUE), but also notes that added control loops and a detailed operations-and-maintenance plan are important.
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- ARCTIC's P12 PRO FAN: More power at any speed - more powerful and quieter than the P12, especially at low speeds. Higher maximum speed for optimal cooling performance under high load
- NATIVE OFFSET MOUNTING FOR INTEL AND AMD: Shifting the cold plate center towards the CPU hotspot ensures more efficient heat transfer
- INTEGRATED VRM FAN: PWM-controlled fan that lowers the temperature of the voltage converters and thus ensures reliable performance
- INTEGRATED CABLE MANAGEMENT: The PWM cables of the radiator fans are integrated in the sheathing of the hoses so that only a single visible cable is connected to the motherboard
Water use depends on the complete facility, including its heat-rejection method, climate, controls, and operating practices. A recirculating loop describes how heat is carried from equipment; it does not, by itself, establish how much water the facility consumes overall. Nor does a lower PUE automatically prove lower water use: PUE and WUE describe different aspects of performance.
FEMP reported a case example for the National Laboratory of the Rockies data center with a PUE of 1.06 and WUE of 0.7 in its January 9, 2019 guidance. Those figures describe that specific facility example, not a typical result or a guarantee for liquid-cooled data centers generally.
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What are ASHRAE’s liquid-cooling water classes?
ASHRAE’s 2021 white paper lists W17, W27, W32, W40, W45, and W+ as liquid-cooling water classes. In that guidance, the number indicates the class’s upper temperature limit; all listed classes share a lower limit of 2°C (35.6°F), and W+ means beyond W45.
These classes are design guidance, not a universal rating of a cooling product or a promise that every system can use every class. Temperature capability must be considered with the equipment and facility design. Because ASHRAE guidance can be updated, facilities making a current design decision should check the latest applicable ASHRAE reference rather than relying on the 2021 list alone.
What should a facility compare before choosing a cooling design?
- Point of liquid introduction: Determine whether the design cools at rack level, within equipment, or directly at electronics.
- Heat-transfer path: Map how heat moves from IT equipment through the technology loop and any CDU to facility water and final heat rejection.
- Heat density and airflow: Compare the equipment’s heat load with available rack airflow; liquid may reduce airflow needs without eliminating air cooling everywhere.
- Energy and water performance: Evaluate PUE and WUE for the specific facility, climate, heat-rejection method, controls, and operating plan rather than assuming liquid cooling is inherently more efficient or uses less water.
- Reliability and maintenance: Account for control loops, operational procedures, maintenance capability, and compatibility with installed equipment.
ASHRAE’s 2023 handbook discusses Standard 90.4 as a data-center efficiency standard developed to balance efficiency with reliability. Applicable requirements depend on the project and current standards material; this overview is not compliance advice.
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