Free Cooling: the Server Side of the Story
by Johan De Gelas on February 11, 2014 7:00 AM EST- Posted in
- Cloud Computing
- IT Computing
- Intel
- Xeon
- Ivy Bridge EP
- Supermicro
Performance?
Yes, we did monitor performance. But it simply was not worth talking about: the results at 20°C inlet are almost identical to those at 40°C inlet. The only difference that lower temperatures could make is a slight increase in the amount of time spent at higher Turbo Boost frequencies, but we could not measure any significant difference. The reason is of course that some of our VMs are also somewhat disk intensive.
Conclusion
The PUE optimized servers can sustain up to 40°C inlet temperature without a tangible increase in power consumption. It may not seem spectacular but it definitely is. The "PUE optimized" servers are simply improved versions; they do not need any expensive technology to sustain high inlet temperatures. As a result, the Supermicro Superserver 6027R-73DARF cost is around $1300.
That means that even an older data center can save a massive amount of money by simply making sure that some sections only contain servers that can cope with higher inlet temperatures. An investment in air-side or water-side economizers could result in very large OPEX savings.
Reliability was beyond the scope of this article and the budget of our lab. But previous studies, for example by IBM and Google, have also shown that reasonably high inlet temperatures (lower than 40°C) have no significant effect on the reliability of the electronics.
Modern data centers should avoid servers that cannot cope with higher inlet temperature at all cost as the cost savings of free cooling range from significant to enormous. We quote a study done on a real-world data center by Intel:
"67% estimated power savings using the (air) economizer 91% of the time—an estimated annual savings of approximately USD 2.87 million in a 10MW data center"
A simple, solid and very affordable server without frills that allows you to lower the cooling costs is a very good deal.
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ShieTar - Tuesday, February 11, 2014 - link
I think you oversimplify if you just judge the efficiency of the cooling method by the heat capacity of the medium. The medium is not a heat-battery that only absorbs the heat, it is also moved in order to transport energy. And moving air is much easier and much more efficient than moving water.So I think in the case of Finland the driving fact is that they will get Air temperatures of up to 30°C in some summers, but the water temperature at the bottom regions of the gulf of Finland stays below 4°C throughout the year. If you would consider a data center near the river Nile, which is usually just 5°C below air temperature, and frequently warmer than the air at night, then your efficiency equation would look entirely different.
Naturally, building the center in Finland instead of Egypt in the first place is a pretty good decision considering cooling efficiency.
icrf - Tuesday, February 11, 2014 - link
Isn't moving water significantly more efficient than moving air because a significant amount of energy when trying to move air goes to compressing it rather than moving it, where water is largely incompressible?ShieTar - Thursday, February 13, 2014 - link
For the initial acceleration this might be an effect, though energy used for compression isn't necessary lost, as the pressure difference will decay via motion of the air again (but maybe not in the preferred direction. But if you look into the entire equation for a cooling system, the hard part is not getting the medium accelerated, but to keep it moving against the resistance of the coolers, tubes and radiators. And water has much stronger interactions with any reasonably used material (metal, mostly) than air. And you usually run water through smaller and longer tubes than air, which can quickly be moved from the electronics case to a large air vent. Also the viscosity of water itself is significantly higher than that of air, specifically if we are talking about cool water not to far above the freezing point of water, i.e. 5°C to 10°C.easp - Saturday, February 15, 2014 - link
Below Mach 0.3, air flows can be treated as incompressible. I doubt bulk movement of air in datacenters hits 200+ Mphjuhatus - Tuesday, February 11, 2014 - link
Sir, I can assure you the Nordic Sea hits ~20°C in the summers. But still that tempereture is good enough for cooling.In Helsinki they are now collecting the excess heat from data center to warm up the houses in the city area. So that too should be considered. I think many countries could use some "free" heating.
Penti - Tuesday, February 11, 2014 - link
Surface temp does, but below the surface it's cooler. Even in small lakes and rivers, otherwise our drinking water would be unusable and 25°C out of the tap. You would get legionella and stuff then. In Sweden the water is not allowed to be or not considered to be usable over 20 degrees at the inlet or out of the tap for that matter. Lakes, rivers and oceans could keep 2-15°C at the inlet year around here in Scandinavia if the inlet is appropriately placed. Certainly good enough if you allow temps over the old 20-22°C.Guspaz - Tuesday, February 11, 2014 - link
OVH's datacentre here in Montreal cools using a centralized watercooling system and relies on convection to remove the heat from the server stacks, IIRC. They claim a PUE of 1.09iwod - Tuesday, February 11, 2014 - link
Exactly what i was about to post. Why Facebook, Microsoft and even Google didn't manage to outpace them. PUE 1.09 is still as far as i know an Industry record. Correct me if i am wrong.I wonder if they could get it down to 1.05
Flunk - Tuesday, February 11, 2014 - link
This entire idea seems so obvious it's surprising they haven't been doing this the whole time. Oh well, it's hard to beat an idea that cheap and efficient.drexnx - Tuesday, February 11, 2014 - link
there's a lot of work being done on the UPS side of the power consumption coin too - FB uses both Delta DC UPS' that power their equipment directly at DC from the batteries instead of the wasteful invert to 480vac three phase, then rectify again back at the server PSU level, and Eaton equipment with ESS that bypasses the UPS until there's an actual power loss (for about a 10% efficiency pickup when running on mains power)