DC Power Saves 15% Energy and Cost @ Data Center

Krishna Dagli writes "Engineers at the Lawrence Berkeley National Laboratory and about 20 technology vendors this month will wrap up a demonstration that they said shows DC power distribution in the data center can save up to 15 percent or more on energy consumption and cost. The proof-of-concept program, set up at Sun Microsystems' Newark, Calif., facility, offered a side-by-side comparison of a traditional AC power system and a 380-volt DC distribution system, running on both Intel-based servers and Sun systems."

Comments

Safety

[TimeTrav]

I, for one, would not be comfortable working around high power DC. Call me paranoid, but I rather enjoy my heart beating with its current interval. You can take all the precautions you want, but accidents do happen.

Re:Safety

[Engineering_bully]

You probably don't realize that most of the lighting and mechanical systems in your data center are already 277/480 VAC. That is the standard power configuration for a new commercial building (cuts down on conductor sizes). There is a dedicated transformer to create 120 VAC for all the plug loads.

In a properly designed DC system, your no more/less safe than your already are.

(Sorry for the repost - I finally remembered my login)

Re:Safety

[peragrin]

So you also failed electrical theory, as well.

DC is harmless unless it has a path to carry it. You can grab a 380 volt DC line and not feel a thing. now if you then touch a grounded object, or the return path you are dead. But you have to make the connection. AC is lethal at 220v. As others posted it does have the advantage of forcing the mucsles to spasm so you can let go of the wire, But still zaps you every time you touch the cable.

Go look up the history of Edison vs Westinghouse. Edison wanted DC power all around because it is inherently safer. a Broken AC wire can zap you, were as a broken DC wire can be touched with bare hands.

Re:Safety

[CaptainPuppydog]

If you happen to grab a DC power line this is especially dangerous, as an AC line with throw you off while a DC line will cause you to simply grab harder and you can't let go.

From http://www.andamooka.org/reader.pl?pgid=liecDCDC_3 , AC will tend to induce fibrillation of the heart, while DC will tend to 'freeze' it. A 'frozen' heart is more likely to regain a normal beat than a fibrillating (rapid, irregular beat) heart. Either way, not a 'Good Thing'.

Note to the wise: Wherever possible, always approach a circuit with the back of your hand. If it is DC, the muscle reaction in case of contact/shock will tend to pull your arm away. If it is AC, same thing will happen. Depending on the voltage present on the conductor, you may even feel the hairs on the back of your hand react to the field produced, i.e., they will 'stand up'.

CPD.

Re:Safety

[Anonymous Coward]

>So you also failed electrical theory, as well.

Yourself also?

ANY electrical path must be joined from source to drain or no power will flow. It doesn't matter if it is DC or AC. Period.

An AC path, however, has an easier to isolate ground because it works with simple transformers. A 1:1 transformer will allow you to grab a 220 volt line without being shocked, assuming you do not touch any path that leads back to the other side of the transformer. This is why in the ICU in hospitals you will find them being used: If a patients equipment shorts in a manner that the electricity reaches the patient, it will not shock the patient unless the patient grabs ahold of the equipment.

Unfortunately DC does not offer this sort of simplicity of isolation.

Edison was a sadistic nutbag that actually enjoyed electrocuting animals like cats, dogs, and elephants by joining them to an AC power path. His DC power was no less dangerous, the only reason it never electrocuted the animals was that the voltage was low enough skin (or fur) resistance did not allow enough current to pass through the animal's body to kill them. Furthermore, due to the low voltage/high current nature of his system, the amount of energy wasted through heating the conductors limited electricity runs to less than about 2 km.

The exact same ridiculousness in power cable AWG requirements can be seen in "modern" car stereo upgrades. People will run a 4 AWG cable to their subwoofer amplifier to power an "800 watt" 12 VDC amplifier. The same 800 watts can be generated from a 16 AWG cable hooked into a 120 VAC amplifier. The difference being that the car amplifiers are often unfused because fuses in the 100 - 200 Amp range are expensive, and circuit breaks even more so, and that 15 amp fuses and circuit breakers for home electricity are incredibly cheap. The unfused car system when shorted will burn the car down in no time. The fused circuit in houses when shorted will burn nothing down, and, when repaired, the wiring can even be reused.

Edison created a useless power system that never worked properly for anyone at all. He also enjoyed electrocuting animals for no apparent reason other than to hookwink customers. He also helped develop one of today's most popular capital punishments: The electric chair. Oh, and he stole credit for several inventions (not the least of which is the light bulb). All around, he's just not a cool guy.

So, basically, for Edison's idea to have worked, we'd all have 0000 AWG cables running to our homes, and we'd probably be melting several of them causing fires, not to mention that the DC power will cause the conductors to be damaged through electroplating. But, we wouldn't get shocked. Of course, the exact same benefits, along with the additional benefit of no electroplating, could be had by running the same conductors with the same voltage AC current at a frequency outside of 50 - 60 Hz.

Of course, at 50 - 60 Hz AC power is most dangerous. But then again, at the voltage levels required for modern electricity, the frequency makes very little difference.

I've always liked ...

[jc42]

... those claims of saving "up to 15 percent or more".

That pretty much covers the entire range of possibilities.

I often wonder why they didn't say something like "up to 50 percent or more" or "up to 99 percent or more". Those would be every bit as meaningful.

What's new about this?

[Flying pig]

DC buses have been used in military and industrial equipment since DC/DC converters were invented. (In fact, other former Cambridge undergraduates may remember the old 200V DC bus in the Cavendish labs, exposed contacts to the motors and all. Nostalgia...)

You can also store DC whereas you cannot store AC, meaning UPS always need an AC-DC followed by a DC-AC stage. Since we have had large FET power transistors it has been possible to make DC/DC conversion very efficient - especially since, if you were beginning again, you would not choose 50 or 60 Hz for best efficiency.

In fact, already the PC is using a DC bus to power small peripherals (USB) and it works surprisingly well.

I may be wrong about this, but it was Edison who accused DC power of being more dangerous ("Westinghoused") only to have AC adopted for the pleasant US custom of humanely frying criminals.

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[account_deleted]

Comment removed based on user account deletion

Re:Here, here!

[saider]

Copper losses are created by current and are described by the equation I^2 * R. So as you double your current, you quadruple your power losses.

Conversely, if you halve your current by boosting the voltage, you can reduce your transmission losses by 75%. Thats a pretty good reason to go with higher voltage. And since this is in the datacenter, you can train your people not to pee on the red wire.