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 now not slicing 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 pulls 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, devour as much as 1,200 W.

“Street maps are 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 perpetrator—AI. And all the additional computations consuming all that added energy from superior chips are producing unmanageable quantities of warmth.

“The typical 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 might soak up 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 way more readily.

“You possibly can 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, common supervisor of immersion cooling at Airedale by Modine. “That’s as a result of the liquid transfers warmth a lot, a lot, a lot, way more shortly.”

The information-center trade by and enormous agrees that cooling chips with liquid is the long run, not less than for AI-focused information facilities. “As AI has made racks denser and warmer, liquid cooling has turn out to be the de facto answer,” Karin Overstreet, president of Nortek Data Center Cooling, stated through e mail.

However there are a selection of how to do liquid cooling, from the straightforward and simple to the advanced and barely bizarre.

On the easy finish, there’s circulating chilled water by way of chilly plates hooked up to the most well liked 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 whole 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 methodology 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-Section 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, known as chilly plates, with channels in them for coolant to flow into, are positioned immediately on high of the chips. The chilly plates match the scale of the chips and go contained in the server. The liquid is normally water, with some glycol added to stop bacterial progress, stabilize the temperature, shield towards freezing and corrosion, and improve the viscosity of the liquid. The glycol-water combination is pressured by way of 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 approach, a chilly plate is positioned on high of the most well liked chips. Liquid is circulated by way of 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 ability water is in flip cooled by both a chiller—an electrically powered refrigeration unit—or a dry cooler, an out of doors unit that makes use of followers to blow ambient air over the water because it strikes by way of pipes. A dry cooler is way less complicated and extra vitality environment friendly than a chiller, but it surely works solely in cooler climates—it might’t cool the water beneath the ambient temperature.

One problem with this method is that placing a chilly plate on each single heat-producing element 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 manner, with followers.

“The development is transferring 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-Section Direct-to-Chip Cooling

With GPU energy densities displaying no indicators of leveling off, direct-to-chip water cooling is hitting a restrict. You possibly can, after all, improve the move of water, however that can use extra vitality. Or you may function the chips at the next temperature, which is able to minimize into their efficiency and in the long term degrade the chips. Happily, there’s a 3rd choice: to squeeze a bit extra out of the physics of warmth trade.

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

Corporations like Accelsius are proposing two-phase direct-to-chip liquid cooling. Right here, a chilly plate can be positioned on high of the most well liked chips, and the liquid circulating by way of the chilly plate boils immediately atop the chip. Massive Thought Productions

That’s mainly how two-phase direct-to-chip cooling works. On this scheme, a specifically formulated dielectric liquid circulates by way of 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 methods.

Water boils at 100 °C (at atmospheric stress), which is simply 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 may be adjusted up or down by tweaking the stress within the loop. As well as, the fluid is dielectric—it’s not electrically charged except polarized by an exterior electric field. So, in contrast to water, if a few of the fluid spills onto the electronics, it gained’t injury the pricey gear.

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 ability water requires cooling with chillers in most climates.

With boiling dielectric fluid, nonetheless, the fluid stays roughly the identical temperature and easily modifications section right into a vapor. Which means each the liquid and the ability water may be stored at the next temperature, leading to important vitality financial savings.

When liquid boils on high of a sizzling chip, the chip is cooled not solely by way of contact with the cooler liquid, but in addition by way of 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 and marketing at Accelsius, one other startup engaged on two-phase direct-to-chip liquid cooling.

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

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

#3: Single-Section Immersion Cooling

Direct-to-chip liquid cooling presents way more cooling capability than simply blowing air, but it surely nonetheless depends on chilly plates as intermediaries to do the cooling.

What in the event you may bypass the chilly plate altogether and simply dunk the whole 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 scale of a fridge. The immersion tanks are crammed with a dielectric fluid, normally an oil, which should 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 hearth danger.

Sustainable Metallic Cloud is advocating for single-phase immersion cooling, during which a whole 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 way of coils and plates contained in the tank, Bielstein explains. “The heated water is then pumped to an outdoor 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 group at Singapore-based Sustainable Metal Cloud (SMC), which builds immersion-cooling methods for information facilities, has discovered the modifications that should be made to servers to make them suitable with this cooling methodology. 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, advised 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 crucial so as to add chilly plates to extend the oil move 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 methods.”

#4: Two-Section Immersion Cooling

If nobody cooling methodology 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 relating to data-center liquid cooling,” says Beran, of Accelsius.

However Brandon Marshall, world advertising and marketing 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 performed that two-phase immersion goes to come back up in a reasonably affordable manner.”

At their lab in Newark, Del., the Chemours group 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 recent elements, cooling the system. Chemours

Marshall argues {that a} two-phase—also called boiling—liquid has 10 to 100 occasions as a lot cooling capability as a single-phase liquid, as a consequence of its latent warmth. And whereas two-phase direct-to-chip cooling may match for the chips of as we speak, it nonetheless leaves many elements, reminiscent of reminiscence modules and energy provides, to be air cooled. As CPUs and GPUs develop extra highly effective, these reminiscence modules and energy provides can even require liquid cooling.

“That record of issues shouldn’t be going anyplace,” Marshall says. “I believe 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 identical to they’ve [with] placing water in a rack by way of single-phase direct-to-chip know-how.”

Of their lab in Newark, Del., the Chemours group has positioned a number of high-power servers in tanks crammed 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 immediately on high of the recent chips. Then the vapor condenses on a cooled floor, both on the high or the again panel of the tank.

Of their lab in Newark, Dela., the Chemours group 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 typically.”

Based on 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 whole 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 as a consequence of decrease energy necessities and a simplified mechanical system.

Critics argue that two-phase immersion makes it exhausting to keep up the gear, particularly because the oils are so specialised, costly, and vulnerable to evaporating. “While 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.

Nevertheless, 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 ‘move out’ of the tank,” Egan wrote through e mail. “The vapor is way heavier than air and subsequently 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 ability calls for of AI will hold going up, and the necessity for cooling together with them.

“Except the ground falls out from underneath 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 wish to maintain advancing cooling, and we’re going to wish to unravel 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 knowledge facilities is opening up the sector to quite a lot of inventiveness and innovation.

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