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Power Consumption and the Future of Computing
mrdirkdiggler writes "ArsTechnica's Hannibal takes a look at how the power concerns that currently plague datacenters are shaping next-generation computing technologies at the levels of the microchip, the board-level interconnect, and the datacenter. In a nutshell, engineers are now willing to take on a lot more hardware overhead in their designs (thermal sensors, transistors that put components into sleep states, buffers and filters at the ends of links, etc.) in order to get maximum power efficiency. The article, which has lots of nice graphics to illustrate the main points, mostly focuses on the specific technologies that Intel has in the pipeline to address these issues."
Lots of errors in your suppositions.
DC/AC conversion? The bigger data centers can't use batteries - too many, too big of a hazard, etc. They use rotational UPS's. These stay AC all the way.
Additionally - power distribution is better at higher voltages. It's that current squared thing. More and more equipment is also going to higher voltage distribution on the boards with local DC/DC conversion at the load. For the exact same reason. Our center distributes at 208 volts.
The argument against a raised floor is bogus. That acts (and is necessary) not only for cabling, but also for air distribution. Heated air rises. Feeding cold air up from the floor to where it flows into the racks to be heated and then recovered at the ceiling is the most efficient way for air. The fact that the floor is not insulated is a non-issue. The whole room is being cooled. The temperature is the same on either side of the floor tiles.
And about the face to face and back to back layout of racks - every single one of our racks is already in that orientation for exactly that reason. We have hot aisles and cold aisles and the temperature difference between them is pretty marked.
The next wave is a move back to "water" cooling. Either plumbing liquid to each rack where in the rack it locally grabs heat from circulated air within the rack, or plumbing into the boxes themselves. This is simply because heat loads are going up and it gets harder (and louder) to pump enough air through a building to cool the more dense newer equipment. Plus people don't have to put on jackets to go out on the floor or yell to be heard in a big data center.
I've seen raised floor AC done right. Each rack was sealed, had a vent in the bottom and a vent into the ceiling. The AC pushed cold air into the subfloor, which was then sucked into the racks, with hot air rising into the ceiling. Where the AC pulled the hot air to be cooled again.
Also, 99% of UPS units don't convert AC to DC unless it's charging the batteries. Normally this would only be a trickle charge. If the UPS is providing power, you're in a critical situation anyways, I wouldn't worry about the fact that a UPS isn't particularly efficient, as you're probably spending 99% of your time not on UPS.
As for switching to telephone industry standard 48V power, you'd be converting it again to whatever the equipment wants, much of it 12V or less. 120VAC->12VDC is more efficient than 120VAC->48VDC->12VDC. In addition you run into the problem that 120VAC over 12gauge cable wastes less than half of the power that the same wattage of 48VDC would waste over the same diameter cable. So you'd have to use heavier gauge cable - payback isn't quick for that by any means.
You might be able to get away with it on a rack level, powering all the blades on 48V via rails to a couple of redundant power supplies somewhere in the rack. Either top or bottom, depending upon cooling and other requirements, though the middle might be an interesting choice, as it'd allow you to have half the wattage running over the rails on average(you'd have two runs instead of one).
You want to save power? I'd switch to feeding the racks/power supplies with 240V lines. Half the line resistance for the wattage.
I don't read AC A human right