The dielectric fluid from 3M inside a tank boils 45C to carry heat away from the boards and allow them to operate continuously at full power without risk of failure due to overheating.
Inside the tank, the vapour rising from the boiling fluid contacts a cooled condenser in the tank lid, which causes the vapour to change to liquid and rain back onto the immersed servers, creating a closed loop cooling system.
The immersive cooling coils that run through the tank and enable the vapour to condense are connected to a separate closed loop system that uses fluid to transfer heat from the tank to a dry cooler outside the tank’s container. Because the fluid in these coils is always warmer than the ambient air, there’s no need to spray water to condition the air for evaporative cooling
“We are the first cloud provider that is running two-phase immersion cooling in a production environment,” said Husam Alissa, a principal hardware engineer on Microsoft’s team for datacentre advanced development in Redmond, Washington.
“Air cooling is not enough,” said Christian Belady, distinguished engineer and vice president of Microsoft’s datacentre advanced development group in Redmond. “That’s what’s driving us to immersion cooling, where we can directly boil off the surfaces of the chip. Liquid cooling enables us to go denser, and thus continue the Moore’s Law trend at the datacentre level,” he said.
Liquid immersive cooling is a proven technology from suppliers such as Iceotope in the UK.
Microsoft investigated liquid immersion as a cooling solution for high-performance computing applications such as AI and found two-phase immersion cooling reduced power consumption for any given server by 5 percent to 15 percent.
For example, software that manages cloud resources can allocate sudden spikes in datacentre compute demand to the servers in the liquid cooled tanks. That’s because these servers can run at elevated power via overclocking without risk of overheating.
“For instance, we know that with Teams when you get to 1 o’clock or 2 o’clock, there is a huge spike because people are joining meetings at the same time,” said Marcus Fontoura, a technical fellow and corporate vice president at Microsoft who is the chief architect of Azure compute. “Immersion cooling gives us more flexibility to deal with these burst-y workloads.”
Adding the two-phase immersion cooled servers to the mix of available compute resources will also allow machine learning software to manage these resources more efficiently across the datacentre, from power and cooling to maintenance technicians.
“We will have not only a huge impact on efficiency, but also a huge impact on sustainability because you make sure that there is not wastage, that every piece of IT equipment that we deploy will be well utilized,” he said.
Microsoft, together with infrastructure industry partners, is also investigating how to run the tanks in ways that mitigate fluid loss and will have little to no impact on the environment.
“If done right, two-phase immersion cooling will attain all our cost, reliability and performance requirements simultaneously with essentially a fraction of the energy spend compared to air cooling,” said Ioannis Manousakis, a principal software engineer with Azure.
If the servers in the immersion tank experience reduced failure rates as anticipated, Microsoft could move to a model where components are not immediately replaced when they fail. This would limit vapor loss as well as allow tank deployment in remote, hard-to-service locations.
What’s more, the ability to densely pack servers in the tank enables a re-envisioned server architecture that’s optimized for low-latency, high-performance applications as well as low-maintenance operation, Belady noted.
Such a tank, for example, could be deployed under a 5G cellular communications tower in the middle of a city for applications such as self-driving cars.
For now, Microsoft has one tank running workloads in a hyperscale datacentre. For the next several months, the Microsoft team will perform a series of tests to prove the viability of the tank and the technology.
The datacentre advanced development team is also exploring the potential to use hydrogen fuel cells instead of diesel generators for backup power generation at datacentres.
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