Data Center Liquid Cooling: The AI Heat Solution

Stroll right into a typical information heart and one of many first issues that jumps out at you is the noise—the low, buzzing sound of hundreds of followers: followers subsequent to particular person computer chips, followers on the again panels of server racks, followers on the community switches. All of these followers are pushing sizzling air away from the temperature-sensitive laptop chips and towards air-conditioning items.

However these followers, whirr as they may, are not chopping it. Over the previous decade, the power density of probably the most superior laptop chips has exploded. In 2017, Nvidia got here out with the V100 GPU, which attracts 300 watts of energy. Most of that energy dissipates again out as warmth. Three years later, in 2020, Nvidia’s A100 got here out, drawing as much as 400 W. The now-popular H100 arrived in 2022 and consumes as much as 700 W. The latest Blackwell GPUs, revealed in 2024, eat as much as 1,200 W.

“Highway maps are taking a look at over 2,000 watts [per chip] over the subsequent yr or two,” says Drew Matter, president and CEO of the liquid-cooling firm Mikros Technologies. “In actual fact, the trade is making ready for 5-kilowatt chips and above within the foreseeable future.”

This energy explosion is pushed by the plain wrongdoer—AI. And all the additional computations consuming all that added energy from superior chips are producing unmanageable quantities of warmth.

“The common energy density in a rack was round 8 kW,” says Josh Claman, CEO of the startup Accelsius. “For AI, that’s rising to 100 kW per rack. That’s an order of magnitude. It’s actually AI adoption that’s creating this actual urgency” to determine a greater method to cool data centers.

Particularly, the urgency is to maneuver away from followers and towards some type of liquid cooling. For instance, water has roughly 4 occasions the precise warmth of air and is about 800 occasions as dense, which means it could take in round 3,200 occasions as a lot warmth as a comparable quantity of air can. What’s extra, the thermal conductivity of water is 23.5 occasions as excessive as that of air, which means that warmth transfers to water far more readily.

“You’ll be able to stick your hand right into a sizzling oven and also you gained’t get burned. You stick your hand right into a pot of boiling water and you may immediately get third-degree burns,” says Seamus Egan, normal supervisor of immersion cooling at Airedale by Modine. “That’s as a result of the liquid transfers warmth a lot, a lot, a lot, far more rapidly.”

The information-center trade by and huge agrees that cooling chips with liquid is the long run, no less than for AI-focused information facilities. “As AI has made racks denser and warmer, liquid cooling has grow to be the de facto answer,” Karin Overstreet, president of Nortek Data Center Cooling, stated by way of e mail.

However there are a variety of the way to do liquid cooling, from the straightforward and easy to the advanced and barely bizarre.

On the easy finish, there’s circulating chilled water by chilly plates hooked up to the most popular chips. Then there’s circulating not water however a particular dielectric fluid that boils contained in the chilly plate to remove the warmth. A 3rd method is dunking the complete server right into a fluid that retains it cool. And, final and most splashy, is dunking the server right into a boiling vat of liquid.

Which technique will find yourself being the trade commonplace for the high-end AI factories of the long run? At this level, it’s anybody’s guess. Right here’s how the 4 strategies work, and the place they may discover probably the most use.

#1: Single-Part Direct-to-Chip Cooling

Essentially the most technologically mature method is to make use of water. Already, many AI information facilities are using such direct-to-chip liquid cooling for his or her hottest chips.

On this scheme, metallic blocks, referred to as chilly plates, with channels in them for coolant to flow into, are positioned straight on prime of the chips. The chilly plates match the dimensions of the chips and go contained in the server. The liquid is often water, with some glycol added to stop bacterial progress, stabilize the temperature, shield in opposition to freezing and corrosion, and enhance the viscosity of the liquid. The glycol-water combination is compelled by the chilly plate, whisking away warmth proper from the supply.

Corporations like Mikros Applied sciences are pursuing single-phase direct-to-chip liquid cooling. On this method, a chilly plate is positioned on prime of the most popular chips. Liquid is circulated by the chilly plate, whisking away warmth. Marvell Technology

The glycol water is generally stored in a closed loop, circulating from the chilly plates to a heat-exchange unit, which cools the liquid again down, after which again to the chilly plate. Contained in the heat exchanger, a separate loop of “facility water” is used to chill down the glycol water. The power water is in flip cooled by both a chiller—an electrically powered refrigeration unit—or a dry cooler, an outside unit that makes use of followers to blow ambient air over the water because it strikes by pipes. A dry cooler is far easier and extra vitality environment friendly than a chiller, nevertheless it works solely in cooler climates—it could’t cool the water beneath the ambient temperature.

One issue with this method is that placing a chilly plate on each single heat-producing part in a server is unfeasible. It solely is sensible to place chilly plates on probably the most energy-dense elements—specifically GPUs and a few CPUs—leaving smaller elements, like power supplies and reminiscence items, to be cooled the old school means, with followers.

“The pattern is shifting towards a hybrid-cooling answer,” Overstreet says. “So liquid cooling does about 80 % of the cooling for the server room or the info corridor, and about 20 % is the present air-cooling answer.”

#2: Two-Part Direct-to-Chip Cooling

With GPU energy densities displaying no indicators of leveling off, direct-to-chip water cooling is hitting a restrict. You’ll be able to, in fact, enhance the circulate of water, however that can use extra vitality. Or you may function the chips at a better temperature, which can lower into their efficiency and in the long term degrade the chips. Thankfully, there’s a 3rd choice: to squeeze a bit extra out of the physics of warmth trade.

The additional cooling energy provided by physics comes from latent warmth—that’s, the vitality it takes to vary section, on this case from liquid to fuel. Because the liquid boils off the GPU, it absorbs that additional latent warmth because it turns into fuel, with out rising temperature.

Corporations like Accelsius are proposing two-phase direct-to-chip liquid cooling. Right here, a chilly plate can also be positioned on prime of the most popular chips, and the liquid circulating by the chilly plate boils straight atop the chip. Huge Thought Productions

That’s principally how two-phase direct-to-chip cooling works. On this scheme, a specifically formulated dielectric liquid circulates by chilly plates sitting atop high-energy chips and boils into vapor. The vapor is then fed again to a warmth exchanger, which cools the fluid utilizing facility water.

“It’s actually boiling to chill,” says My Truong, chief know-how officer of the startup ZutaCore, which makes two-phase direct-to-chip cooling programs.

Water boils at 100 °C (at atmospheric strain), which is just too excessive for correct chip operation. So that you want a specifically formulated fluid with a decrease boiling level. ZutaCore’s chief evangelist, Shahar Belkin, explains that the fluid they use is sourced from chemical suppliers like Honeywell and Chemours, and boils at a temperature as little as 18 °C, which will be adjusted up or down by tweaking the strain within the loop. As well as, the fluid is dielectric—it’s not electrically charged until polarized by an exterior electric field. So, in contrast to water, if among the fluid spills onto the electronics, it gained’t harm the expensive tools.

With water, the temperature will increase drastically because it flows over the hot chips. Which means the incoming water must be stored chilly, and so the power water requires cooling with chillers in most climates.

With boiling dielectric fluid, nevertheless, the fluid stays roughly the identical temperature and easily adjustments section right into a vapor. Which means each the liquid and the power water will be stored at a better temperature, leading to vital vitality financial savings.

When liquid boils on prime of a sizzling chip, the chip is cooled not solely by contact with the cooler liquid, but in addition by the latent warmth it takes to induce a phase change. Accelsius

“Due to the actually environment friendly boiling course of that occurs on the chilly plate, we will settle for facility water that’s 6 to eight levels hotter than [with] single section,” says Lucas Beran, director of product advertising at Accelsius, one other startup engaged on two-phase direct-to-chip liquid cooling.

The 2-phase setup additionally requires decrease liquid circulate charges than the standard single-phase water method, so it makes use of much less vitality and runs much less danger of damaging the tools. The circulate price of two-phase cooling is about one-fifth that of single-phase cooling, Belkin says.

With single-phase water cooling, he says, “you’ll should circulate a gallon per minute into the chilly plate” for probably the most superior chips working at 2,000 W. “This implies very, very excessive strain, very, very excessive circulate. It signifies that pumping shall be costly, and [the cooling system] will truly hurt itself with the excessive circulate.”

#3: Single-Part Immersion Cooling

Direct-to-chip liquid cooling gives far more cooling capability than simply blowing air, nevertheless it nonetheless depends on chilly plates as intermediaries to do the cooling.

What when you might bypass the chilly plate altogether and simply dunk the complete laptop server in coolant? Some corporations are doing simply that.

On this method, the info heart is organized round immersion tanks fairly than racks, every tank roughly the dimensions of a fridge. The immersion tanks are stuffed with a dielectric fluid, often an oil, which have to be nonconductive and have sturdy thermal switch properties, says Rachel Bielstein, world gross sales supervisor of immersion cooling at Baltimore Aircoil Co. The fluid additionally requires long-term stability and low environmental and fireplace danger.

Sustainable Steel Cloud is advocating for single-phase immersion cooling, during which a complete server is submerged in a vat of liquid to maintain it cool.Firmus Technologies

With immersion cooling, every part will get cooled by the identical fluid. After the oil has whisked away the warmth, there are numerous approaches to cooling the immersion fluid. Baltimore Aircoil, for one, has designed a warmth exchanger that circulates facility water by coils and plates contained in the tank, Bielstein explains. “The heated water is then pumped to an out of doors cooler that releases the warmth into the air, cools the water, and sends it again to the warmth exchanger to soak up extra warmth from the tank. This course of makes use of as much as 51 % much less vitality versus conventional designs.”

The workforce at Singapore-based Sustainable Metal Cloud (SMC), which builds immersion-cooling programs for information facilities, has discovered the modifications that should be made to servers to make them appropriate with this cooling technique. Past eradicating the built-in followers, the corporate swaps out the thermal-interface supplies that join chips to their heat sinks, as a few of these supplies degrade within the oil. Oliver Curtis, co-CEO of SMC and its sister firm Firmus, informed IEEE Spectrum the modifications they make are small however vital to the functioning of SMC’s setup.

“We’ve created the proper working surroundings for a pc,” Curtis says. “There’s no mud, no motion, no vibration, as a result of there’s no followers. And it’s an ideal working temperature.”

There are some chips whose energy density remains to be too excessive to be fully cooled by the slow-moving oil. In these instances, it’s vital so as to add chilly plates to extend the oil circulate over them. “Single-phase immersion has already hit the boundaries” for cooling these superior chips, says Egan of Airedale by Modine. Including chilly plates to immersion cooling, he says, “will certainly present assist for extra superior chip architectures and cut back the warmth load on the single-phase dielectric fluid. The brand new problem is that I now want two separate cooling-loop programs.”

#4: Two-Part Immersion Cooling

If nobody cooling technique is sufficient by itself, how about placing all of them collectively, and dunking your information heart right into a vat of boiling oil?

Some corporations already are.

“Two-phase immersion might be probably the most moon-shot know-how in the case of data-center liquid cooling,” says Beran, of Accelsius.

However Brandon Marshall, world advertising supervisor of data-center liquid cooling at Chemours, says that is the place the trade is headed. “We imagine from the analysis that we’ve accomplished that two-phase immersion goes to come back up in a fairly affordable means.”

At their lab in Newark, Del., the Chemours workforce is creating a specifically formulated liquid for two-phase immersion cooling. On this method, the server is dunked right into a vat of liquid, and the liquid boils atop the new elements, cooling the system. Chemours

Marshall argues {that a} two-phase—often known as boiling—liquid has 10 to 100 occasions as a lot cooling capability as a single-phase liquid, because of its latent warmth. And whereas two-phase direct-to-chip cooling may fit for the chips of immediately, it nonetheless leaves many elements, akin to reminiscence modules and energy provides, to be air cooled. As CPUs and GPUs develop extra highly effective, these reminiscence modules and energy provides will even require liquid cooling.

“That listing of issues shouldn’t be going anyplace,” Marshall says. “I feel the immersion-cooling piece goes to proceed to develop in curiosity as we transfer ahead. Individuals are going to get extra comfy with having a two-phase fluid within a rack similar to they’ve [with] placing water in a rack by single-phase direct-to-chip know-how.”

Of their lab in Newark, Del., the Chemours workforce has positioned a number of high-power servers in tanks stuffed with a proprietary, specifically formulated fluid. The fluid is dielectric, in order to not trigger shorts, and it’s additionally noncorrosive and designed to boil on the exact temperature at which the chips are to be held. The fluid boils straight on prime of the new chips. Then the vapor condenses on a cooled floor, both on the prime or the again panel of the tank.

Of their lab in Newark, Dela., the Chemours workforce is testing their two-phase immersion cooling fluid. On this method, the entire server is dunked right into a tank with dielectric liquid. The warmth from the server boils the liquid, leading to cooling. Chemours

That condenser is cooled with circulating facility water. “All we want is water despatched on to the tank that’s about 6 levels decrease than our boiling level, so about 43 °C,” Marshall says. “The fluid condenses [back to a liquid] proper within the tank. The temperature required to condense our fluid can get rid of the necessity for chillers and different advanced mechanical infrastructure most often.”

In accordance with a latest case study by Chemours researchers, two-phase immersion cooling is less expensive than single-phase immersion or single-phase direct-to-chip in most climates. For instance, in Ashburn, Va., the 10-year complete value of possession was estimated at US $436 million for a single-phase direct-to-chip setup, $491 million for a single-phase immersion setup, and $433 million for a two-phase immersion-cooling setup, largely because of decrease energy necessities and a simplified mechanical system.

Critics argue that two-phase immersion makes it exhausting to keep up the tools, particularly because the oils are so specialised, costly, and vulnerable to evaporating. “Once you’re in an immersion tank, and there’s greenback indicators evaporating from it, that may make it a little bit of a problem to service,” Beran says.

Nonetheless, Egan of Airedale by Modine says his firm has developed a method to largely keep away from this subject with its immersion tanks, that are meant for edge functions. “Our EdgeBox is particularly designed to keep up the vapor layer decrease down within the tank with a layer of air above it and nearer to the tank lid. When the tank is opened (for a brief upkeep interval), the vapor layer doesn’t ‘circulate out’ of the tank,” Egan wrote by way of e mail. “The vapor is far heavier than air and due to this fact stays decrease within the tank. The minimal vapor loss is offset by a buffer tank of fluid inside the system.”

For the foreseeable future, individuals within the trade agree that the facility calls for of AI will maintain going up, and the necessity for cooling together with them.

“Except the ground falls out from below AI and all people stops constructing these AI clusters, and stops constructing the {hardware} to carry out coaching for large language models, we’re going to want to maintain advancing cooling, and we’re going to want to resolve the warmth drawback,” Marshall says.

Which cooling know-how will dominate within the coming AI factories? It’s too quickly to say. However the quickly altering nature of information facilities is opening up the sector to numerous inventiveness and innovation.

“There’s not solely an awesome marketplace for liquid cooling,” says Drew Matter, of Mikros Applied sciences, “nevertheless it’s additionally a enjoyable engineering drawback.”