Friday, February 10, 2006

Servers as Steam Engines

Electronics and heat. They go together like a horse and... Well, there's a reason they call it waste heat. Sometimes it seems like you're feeding the servers to watch them cook. First you have to pay for all that electrical energy going into a data center. Then you have to pay for more electrical energy to suck the heat out of the data center. Seems wasteful to say the least.

Well, that's the state of the art today. Just like your head gets warm when you're active, all those processors and their ancillary circuits get warm when they think. Electronic brainpower just streams thermal energy. It's not very efficient, either. You can get a good burn from a microprocessor that isn't all that smart. Start bunching them together in closed equipment racks and you've got yourself an electronic furnace.

So far all this heat rejection has been handled by fans and blowers within the equipment and racks, aided by rooftop air conditioners. But, friends, we're headed for a meltdown. Haven't you noticed that you really can't stand to set a laptop computer on your lap anymore? The same thing is happening on a larger scale in the server rooms. Temperatures are going up, and up.

Why? The driver is speed. If digital circuits were perfect, they'd hardly consume any power at all. A perfect switch is on or off. When it's on, there is only a slight heat generated by the low resistance of the junctions and interconnections. When the circuit is off, it is open and shouldn't draw current at all. In practice there is a tiny leakage current through the semiconductors. But that's not what's cooking us out. The problem is that electronic switches do not change states instantaneously. They actually transition from off to on to back off again. It's more of like turning a light dimmer up and down, rather than flipping a light switch.

The losses occur every time there is a transition. When transitions are few and far between, like in a digital watch, a little button battery can provide all the power you need. But speed things up to, say, a few Gigahertz and you've got yourself a digital hand warmer. Or lap warmer.

With more and faster electronic brainpower being packed into smaller and smaller rack spaces, the heat problem is escalating. The latest racks are now turning to liquid cooling. Water is more dense than air and can carry away more heat. IBM and Hewlett Packard are offering water cooling as an option for their server racks. Other companies are running refrigerant lines right through the racks. It's like you cool your food and drinks at home in a fridge.

The most exotic plan yet seems to be the liquid carbon dioxide cooling system announced by British company Trox. Now, mind you, carbon dioxide boils at around 200 degrees below zero so it needs to be kept under pressure to remain a liquid. Spring a leak and you'll get dry ice which will evaporate into carbon dioxide gas but won't drown your processors.

I don't think it's going to stop there. The circuit frequencies and component density are surely going to keep increasing as IT companies feel the need for speed. At some point we'll be in danger of a real meltdown, with server racks scorching their way into the Earth toward China. Or toward us if the servers are already in China.

Perhaps we can learn something from the nuclear power industry. They don't just pull out the control rods and watch the water glow. They're doing something useful with all that pent up energy. The heat generated by the nuclear reaction boils water, producing steam that can be used to heat buildings or turn generator turbines. The water systems both cool the hot core and convert otherwise wasted energy to steam heat or electricity.

So, how long will it be before some enterprising startup announces the invention of the steam rack? The electro-inferno of blazing hot processors running at umpteen Gigahertz will be cooled by vaporizing water under pressure. The resulting steam will then be harnessed to generate electricity or, maybe like the old days, run lines of machine tools. As the water gives up its heat and condenses, it will be channeled back into the sizzling electronic racks for another round.

Now we if could only figure out how to run electronic circuits on coal, both our computing and energy problems would be solved... although there is that small matter of environmental pollution.

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