OVH punts hybrid water and immersion cooling for high performance systems European cloud operator OVHcloud has just celebrated 20 years of using water cooling technology in its datacenters, leading up to the development of a hybrid system that combines both water and immersion cooling to drive greater efficiency when operating demanding workloads. OVH, like some of the larger cloud operators, has …
For this reason, OVH looked at capturing the heat at its source, putting a water block on top of the CPU (and later GPU), through which water circulates to absorb the heat, then it is extracted outside of the rack and ultimately outside of the building.
Especially for the AMD FirePro cards I guess...
I note OVH have effectively looked at the rack cabinet as effectively being a large box containing many CPUs and thus have scaled the well tested gaming PC solutions. Once you target the big heat producers (CPU's & GPU's), simpler and cheaper solutions are more than adequate for managing the temperature of "warm" components.
I'm thrilled that server farms are cooling their equipment more efficiently. That is obviously a Good ThingTM.
However, I do have one question : the amount of heat that needs evacuating does not depend on the manner in which the cooling is done. So, how is it that I am reading about economies ?
Granted, air cooling requires noisy fans and proper airflow, which is not always obvious to ensure. Liquid cooling is easier since the heat is leaving through a pipe, not just through the rules of thermodynamics, so it's a sight easier to know what you're doing, but in the end, there is still a fan pushing (or pulling) air through a grill, and that's where the cooling is happening.
Far be it from me to knock liquid cooling. I have been an active proponent of it for almost two decades (aka, before it became common), but the amount of heat to evacuate does not change, even the operating comfort does.
When I adopted liquid cooling for my first AMD Thunderbird, it made a world of difference. My home office was silent. The only noise left was the soft whirr of a pair of hard disks. It was astonishing, and I never went back to pure aircooling.
Nowadays, my home rig has watercooling on the motherboard, on the graphics card and, of course, I bought a CPU cooling kit with a ginormous radiator. So I have a 3-fan radiator for my GPU (which, in all honesty, never makes a sound) and a two-fan radiator for the CPU (which makes more noise, annoyingly), in addition to the chassis and PSU radiators. Still, I will never go back to pure aircooling.
But the heat is still there. It still needs to be taken away. The only advantage of watercooling (apart from reduced noise levels) is that you don't have to rely on iffy air thermodynamics. I do not see any other gains.
The cooling system itself uses electricity to move the heat away from where you don't want it. Usually it does this by pushing the coolant (air, water) around. More efficient cooling systems use less electricity to move a given amount of heat. That's where the touted energy savings are coming from.
The stuff OVHCloud are talking about doing here is passively cooled, so they're able to get very close to zero energy being used by the cooling system. Hence the claimed PUE almost equal to 1. It's really impressive because normally it's hard to get passive cooling to scale up to moving lots of heat.
In a PC, in theory a liquid cooling system may use less electricity than just fans because the liquid system moves heat from the CPU to the radiator very efficiently, and then moving heat from the radiator to the environment is much cheaper than moving heat directly from the CPU to the environment would've been. The radiator is easier to cool than the CPU because it has a much bigger surface area. Also the radiator tends to maintain a fairly uniform temperature too because it's made of metal and full of circulating water. If you want to bring the electricity cost of cooling down even further, I've heard of DIYers using huge radiators which are so big they can be passively cooled. I remember reading once about someone going to a scrapyard and picking up a car radiator.
Isn't the point also that you're not pushing cool air around a cold corridor and then sucking it through the various racks? What OVH are doing is taking the heat from where it is (the CPU) to a heat exchange via water which is a better medium for heat transfer.
At least, that's my understanding....
The reason for liquid cooling is really simple - you can run it at temperatures higher than humans can tolerate. We have heat exchangers running off of chilled water in place of every third rack, and run our hot aisles at 100F, so for most of the year heat just "flows downhill" - you just need pumps to circulate the water through an evaporative cooler out back. (well, there's another heat exchanger stage because the outdoor water's really dirty, but close enough) In the summer the outdoor temps can get up to 100F, with high humidity, so we need to run traditional AC chillers to push the heat "uphill".
If we could run our hot aisles at 150F we'd never need the chillers and everything would be really efficient, but for obvious reasons we can't - it's bad enough working in there at 100F, and I think OSHA would have something to say at temperatures much higher than that. If you connect the cooling water directly to the CPUs etc. rather than going through the air in the pod, it's easy to run those high temperatures (150F is only 65C) and get good cooling efficiency, while keeping a human-tolerable air temperature.
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