Exploring the Difference of Nautilus’ Water Heat Sink Technology in the Data Center

“So, you’re just liquid cooling, right?” …  “What’s the difference between your technology and direct-to-chip or immersion?” … “Maybe you’re a little different, but do those differences matter?”

As we’ve talked to potential colocation customers and data center industry experts, we’re frequently asked how the Nautilus cooling technology is different from “liquid cooling” in a data center. And we completely get it – we’ve introduced new technology. And new approaches to existing problems can be challenging to communicate, but we think we can do it in a simple way.

First, let’s start by talking about the differences between heat rejection at a micro level and a macro level. When we’re thinking about micro level heat rejection, we’re exploring all the ways to get heat out of data center devices — servers, storage, networking, and the like. At the macro level, we’re thinking about ways to remove heat from a data hall. In both cases, there’s an energy transfer medium, like air or water, and the energy transfer medium could be the same at both micro and macro levels.

Nautilus works at the macro level by offering water-based heat sink cooling, and that’s a unique approach that gives us distinctive advantages over any other data center cooling method.

Cooling the Data Center

Traditionally, data centers cool at both the micro and macro level with air.

On the micro side, let’s go into an individual server as an example, modern servers contain multiple processors, solid-state drives, RAM modules, and high-speed networking devices. All semiconductors in a server are typically designed to operate at ambient temperatures between 0C and 70C with custom heat sinks to extract the heat produced by the device and multiple fans to produce airflow that removes the heat and ensures the devices operate within design parameters. Without chilled air at the front of the server, the server fans would be unable to cool the devices and rapidly overheat and shut down. Within the server room, where we can see (and feel) all the heat generated by the servers, storage and network gear would cook the room (and the hardware) without chilled air.

That brings us to the macro side. Somewhere in the building, a computer room air conditioner (CRAC) is blowing the cooled air into the server room. There, it’s drawn in by server fans, blown over the hot components, heated, ejected from the servers and the rack, and finally brought back to the CRAC. The hot air from server rooms throughout the building are brought into the CRACs, using a heat exchanger and compressed refrigerant, the heat is pushed out of the building using more air. There’s a loop for cool air to and from the server rooms, and another loop for hot air that’s ejected from the building. Another macro option is using a CRAH. The CRAH takes the chilled incoming air from the evaporative chiller and pushes it through the data hall. The warm air is just dispelled out or pulled out using fans through the roof.

At the macro level, data centers with liquid cooling combine all the micro-level liquid from all the data center systems and then pump them to a central location for cooling. But here’s where they often make a mistake.

Most of them transfer the heat in the cooling liquid to air, using a heat pump, into a refrigerant loop, and then pump hot refrigerant out of the building, blow air over it, and expel masses of hot air out of the building. Others pump the heat, using refrigerant, to enormous evaporative coolers that take potable water, pump heat into it, and then evaporate it into the atmosphere, carrying heat away. Those phase changes from liquid to air are inefficient, require extra power, and force designs that use very large amounts of exhaust air or water to cope with the concentrated heat in the liquid (remember, liquid holds thousands of times more heat than air can).

So is there a way to improve? We believe that’s where Nautilus comes in. We do liquid cooling at both micro and macro levels, and we keep all the liquids liquid.

Instead of taking heat from a liquid and putting it into the air, we take heat from a cooling liquid and put it into water using a heat exchanger. Then we pump the warmer water (about 4-6 degrees Fahrenheit, in our design) into a natural body of water, a river, or a sea. We use natural water as a data center sized heat sink.

What are the advantages of the Nautilus method?

  1. We ideally keep heat in a liquid all the time, but always at the macro level.
  2. We avoid the inefficiency of phase changes. We don’t have to convert a liquid into a gas like a heat pump or an evaporative chiller does.
  3. We don’t blast very hot air out of a data center.
  4. We don’t waste water by converting liquid water into water vapor.
  5. We don’t use drinking water for evaporative cooling. We can use greywater, discharge from water treatment plants, or natural water, including saltwater.
  6. Our approach is as thermodynamically efficient as possible, with subsequent cost and reliability efficiencies.

The Nautilus approach also has another advantage. With CRACs, CRAHs, and other technologies, it’s usual to push or pull air over dozens of feet. With immersion cooling, it is usual to pump the viscous hydrocarbons used over hundreds of feet before getting them to a heat exchanger. Our designers put the heat exchanger as close to the heat source as possible, cutting the energy needed to pump micro-level air, glycol, or oil.

And while the ideal way (most efficient way) is to keep both micro and macro heat in liquid, Nautilus works with any micro-level cooling technology. We can take micro-level air and put that heat into water. We can take direct to chip liquid and put that heat into water. We can take heat from immersion-cooled servers and put that heat into water.

We also have within-data center cooling advantages that air can’t match. For example, in one of our data centers, we supply water that’s 70 degrees F to a 15-kilowatt rack and cool it. At that point, the water is 85F, which is still cool enough to cool another rack.

Our approach minimizes the environmental approach in a way other technologies can’t. All the other mechanical cooling approaches use large amounts of water, produce large amounts of hot air, and typically use polluting coolants. Our approach makes natural water four degrees warmer than it was. That’s it.

So you’ve seen the advantages of what we can do, but the critical takeaway is a simple one: most people who claim to be doing liquid cooling are only using liquid for part of the equation. We do it all. Our water heat sink tech makes a difference.

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