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Data Center Cooling Systems

The six ways a data center gets rid of the heat its servers generate, what share of U.S. facilities actually use each one, and why those numbers don't add up to a clean 100% — because most data centers run more than one at once.

Last updated September 29, 2026

Terms

Air cooling
Chilled air pushed through the server room by CRAC or CRAH units (Computer Room Air Conditioner/Handler), the way data centers have cooled servers since the 1960s. Still the baseline in the large majority of U.S. facilities.
Liquid cooling
Coolant piped directly to a cold plate mounted on the chip itself (also called direct-to-chip or DLC), removing heat far more efficiently than air once a rack draws tens of kilowatts — the case for nearly every AI accelerator rack built today.
Immersion cooling
Entire servers submerged in a tank of dielectric (non-conductive) fluid that carries heat away directly from every component, not just the chip. The most thermally effective method and the least commonly deployed.
Evaporative cooling
Water evaporated to absorb heat, either in a cooling tower feeding a chilled-water loop or in an adiabatic unit that pre-cools incoming outside air. Highly efficient, but it consumes large volumes of water.
Free cooling
Using outside air or water directly, without running a mechanical chiller, whenever the climate outside is cool enough — an "economizer" mode. Not a separate cooling medium so much as a way of running air or evaporative systems more efficiently.
Hybrid cooling strategy
Running more than one of the above in the same facility — typically air cooling for lower-density legacy racks and liquid cooling for high-density AI/HPC racks, side by side.

Why this is suddenly a live question

2025
Average rack power density: about 16 kW, well within what air cooling alone can typically handle.
2026
Average rack density jumps to about 27 kW — a 69% year-over-year increase, driven by AI accelerator racks that individually run far hotter than the average.
2027 (projected)
Industry forecasts put the newest AI racks at 45–100+ kW — a density range air cooling generally cannot handle on its own, which is why liquid cooling adoption is accelerating specifically in new AI-focused builds.

Uptime Institute Global Data Center Survey figures, via industry reporting; see sources.

What share of U.S. data centers actually use each method

Perimeter air cooling (CRAC/CRAH)75%
Direct liquid cooling (cold plate)22%

Uptime Institute's 2025 Cooling Systems Survey (1,033 respondents, April–June 2025) — these are the two categories with a clean, survey-based adoption number. They add up to more than 100% because most organizations run both: air cooling for most racks, liquid cooling for the densest ones.

A closely related but separate Uptime measure — its broader Global Data Center Survey — found 19% of data centers had deployed some liquid cooling by early 2026, with another 36% planning to adopt it within 12 to 24 months. The two Uptime figures (22% and 19%) come from different survey instruments asking slightly different questions, which is itself a useful reminder that "percentage of data centers using X" depends heavily on exactly what's being asked and of whom.

Immersion, evaporative, and free cooling: thinner data, real trends

Immersion, evaporative, and free cooling don't have a clean, comparable "percentage of U.S. data centers" figure the way air and direct liquid cooling do — no survey asks operators to check a box for each of these specifically, and the categories overlap with each other and with the two above. Here's the best evidence available for each:

Immersion cooling remains the smallest deployment by far. In a spring 2024 survey of IT professionals by The Register, just 6.5% said they planned to go fully immersion-cooled by 2026 — and immersion is itself a minority share within the broader direct-liquid-cooling market, behind direct-to-chip cold-plate systems. Nearly all liquid-cooling adopters use cold plates, not immersion tanks.

Evaporative cooling isn't really a rival to air cooling so much as the mechanism most air-cooled U.S. data centers use to reject heat outside — a cooling tower or adiabatic pre-cooler evaporating water to chill air or water before it does the actual cooling work. Industry coverage describes it as still the dominant heat-rejection method nationally, and it's water-intensive: an efficiently run evaporative system uses roughly 1,000 liters of water per megawatt-hour of IT load, and a single large campus can consume millions of gallons a day.

Free cooling (running on outside air or water without a mechanical chiller whenever the climate allows it) is less a fourth category than an efficiency mode layered onto air or evaporative systems. A 2019 Uptime Institute survey of more than 500 cooling vendors and consultants found 84% said at least some of their customers used indirect free air cooling, and 74% said the same for direct free air cooling — vendor perception of customer deployment, not a census of operators, but directionally consistent with ASHRAE's Standard 90.1, which as of its 2022 edition requires economizers in commercial air-handling systems across most U.S. climate zones, making some form of free cooling close to a code-mandated baseline nationally.

Hybrid is quietly the real answer

Because only 22% of organizations use any direct liquid cooling at all, and only 6.5% plan to go fully immersion-cooled, the arithmetic points to a clear conclusion: almost none of the growing liquid-cooling deployment is liquid-only. Industry coverage of 2026 data center builds describes hybrid cooling — standard air cooling for legacy and lower-density racks, direct-to-chip liquid cooling for AI and HPC racks, in the same facility — as the dominant strategy for new builds specifically because operators have to support both older equipment and next-generation AI accelerators under one roof. A facility running hybrid cooling shows up in the survey numbers above as both an "air cooling" user and a "liquid cooling" user — which is exactly why those two figures add up to more than 100%.

Nonpartisan, plainly

There's no single, official census of which U.S. data centers use which cooling method — the numbers above come from a handful of industry surveys, run by different organizations, asking different questions of different audiences (operators in some cases, vendors and consultants in others), and they don't always agree with each other. That's not a reason to distrust them; it's a reason to cite each one specifically rather than present a single tidy percentage that doesn't exist. What's not in dispute: air cooling remains the majority baseline, liquid cooling is growing fast from a small base almost entirely because of AI hardware, and hybrid setups — not a clean switch from one method to another — are how most data centers are actually handling that transition.

See something wrong at a data center near you?

Noise, unpermitted construction, water or air complaints, or anything else worth documenting — Erin Brockovich's team runs a crowdsourced tracker where residents can report data center issues directly.

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Talking points

These are the questions we think you should ask those who are running for office and will represent you. We don't give our opinion on the answer, but we DO think you should be talking about them.

  1. Should there be a public database listing every data center's cooling technology and daily water consumption, the way many other large industrial water users already have to report?
  2. Should we have a data center moratorium — anywhere from a temporary pause to a permanent cap — until water and electricity impacts on the surrounding community are better understood, and who should have the authority to decide when it's lifted?
  3. Should a data center have to disclose whether it draws from municipal drinking water or from reclaimed/non-potable water, and should that choice be a permitting requirement rather than left to the operator?
  4. Who should pay for the electric grid and water infrastructure upgrades a new data center requires — the company building it, or ratepayers and taxpayers generally?
  5. Should state and local tax incentives for new data centers be conditioned on water- and energy-efficiency commitments (for example, a minimum share of liquid or free cooling), instead of being granted unconditionally?
  6. Should local communities have final say over whether a data center gets built nearby, or should siting decisions be preempted by state or federal policy to keep pace with AI infrastructure demand?
  7. If a data center is approved using air cooling today, should it be required to retrofit toward liquid or free cooling as its rack density rises, rather than simply drawing more water and electricity over time?

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