DC voltage system

[sparky1978]

We are working with a client to design an efficent LEED building. Someone has suggested running a DC system for office equipment. This would include lights and laptops. Some receptacles would be located at various locations. The idea is to provide a transformer in a separate room and run a bus duct to supply the furniture for DC.

The thought is that by eliminating the individual transformers for lights and computers that it will decrease the energy dissapation in the building.

Obviously there is a concern for voltage drop and the avaliablity of this type of product. These receptacles would limit what could be connected and only laptobs would be able to be connected.

Has anyone heard of this type of design or concept?

 

[slavag]

Hi.
Please read this thread.
Intresting posts of Gunnar on this issue.
Regards.
Slava.

 

[slavag]

OOPS
thread238-202821

 

[itsmoked]

I'll never work..

I have four laptops and no two have the same DC requirement.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

I'll never work..

Well, maybe not never, but there will have to be standards developed first. There is some merit in the idea, but unless you want to saddle your client with a white elephant I think this should stay in the nifty ideas that don't fly category.

 

[alehman]

The idea is to provide a transformer in a separate room and run a bus duct to supply the furniture for DC.

I have a hard time believing this would be more efficient. Also, it's not very 'green' with respect to the additional materials required for construction. Where are you going to find office furniture and other equipment designed for DC power? Pre-wired office partitions are not designed for DC, to my knowledge.


Keith,
Why won't you work??

 

[itsmoked]

That's what I get for hacking back to contractions from strung out words. Lost a 't' during the melee..

Keith Cress
kcress -

http://www.flaminsystems.com

 

[stevenal]

Most laptop manufacturers have car adapters available, so the 12V DC cigarette lighter style receptacle is pretty universal. Not sure this any more efficient than using 120V AC adapters, though. And I understand the automotive companies are looking to change voltage, so the lifespan of this standard my be limited.

And how is DC powered lighting more efficient?

 

[davidbeach]

DC lighting - all electronic ballasts are switch mode power supplies and high frequency inverters, so if they can be supplied with DC the need for the SMPS is eliminated.

 

[slavag]

Hi.
DC lighting.. maybe only some emergency lighting.

About computers, We commisionned before few mounth SS.
We was installed UPS only becouse station computer and display.
All other staff on the DC. Lighting of course AC.
Actually, Im locking for computers with DC supply, display.. isn't problem
Regards.
Slava

 

[sparky1978]

Thanks for the feedback. Either way I need to give a report on why it will work or not work. Does anyone know of this being documented before or examples of it. Below is from a consultant I am working with. This is what he knows of these type of systems:

It is a well understood fact that there are significant losses in conversion of PV power to AC when all is said and done between the inverter the transformer, the diodes, etc there is a good 10% loss of efficiency. A high quality intelligent DC to DC converter probably has less than 2% losses. At night a high quality intelligent power supply, basically a rectifyer with a transformer and some electronics, is also quite efficient ,so it would take over when the solar goes down. We would need these to be located centrally in the building (or have multiples of them) so that the losses in the 12V wiring are small.



As for outlets we can use the new aircraft standard which is available for most if not all laptops, cellphones etc. We can then order our task lights with the same plugs which would make them difficult to steal. The task lights will be slightly cheaper as they do not require their own power supply.



Speaking of power supplies most of those used presently are quite dumb, they do not modulate their output dependent on demand, so their only fluctuation in energy use is due to the inductive effect in their transformers, a small amount. That alone could pay for the system in less than two years.



So here is what I think we could do. We could estimate the actual savings in a rough order of magnitude. From your end the additional work is the design of the system, the specification of the DC to DC converter, the AC to DC power supply and the specification of the 12V wiring and outlets. The client should decide whether to have the 12V outlets on the furniture system (which would require a bit of coordination) or directly on the raised floor in a monument or recessed pocket.



I do not think this is that difficult, we did a similar design for a building that unfortunately never got built, but at that time we did not have the airline standard. That has simplified things quite a bit.



Ideally, we can monitor this and keep a log of what the uses are and we could then estimate the savings. In addition, for those who worry about EMF apparently they believe DC is much better than AC (I do not subscribe at all to those worries, my feeling is that if EMF was such a danger the difference between the death rate of office workers today and 50 years ago would be statistically spectacular).


Any comments? Thanks.

 

[jimross]

Sounds a little like something Thomas Edison would come up with. I recommend that you stay with the Westinghouse method......

 

[rcw retired EE]

IEEE Industrial Applications Society (IAS) Transactions had a paper recently (2006 - present) by some Itlaian engineers that looked at powering everything in a large building with DC. I recall it was a pretty thorough analysis.

I've spent too much time looking for the article and can't find it.

Maybe you can locate it.

 

[Skogsgurra]

Sorry guys. You have got it wrong. It is not about feeding 12, 18 or whatever low voltage DC to the computers.

It is about feeding a voltage in the Urms*sqrt(2) voltage to the equipment. Computers, high efficiency lamps, incandescent lamps run off DC just as well as AC. There are installations using this technique in several places. Japan, France, Sweden are testing it. Intel is doing it big time. Google Annabelle Pratt or have a look at

http://www.energystar.gov/index.cfm?c=products.pr_esads_conf_media

.

This is not at all to ignore. You really have to have a more open mind

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Running dedicated servers on 350VDC as oposed to 120/208VAC is more efficient.
Running 12 VDC equipment off local transformers may not be so efficient. I did a layout for some low wattage 12 volt DC emergency lamps. The voltage drop on every section of every circuit was calculated to ensure compliance with the code requirements for maximum allowable voltage drop.
Try a calculation to determine the maximum distance you can send 1 amp at 12 volts on a pair of #14 AWG conductors without exceeding 3% voltage drop. Then do some extrapolation. Remember that 3 AWG sizes either doubles or halves the cross sectional area to a very close approximation. (So close that many don't know that it is an approximation and many text books use the approximation rather than the correct ratio.)

Bill
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"Why not the best?"
Jimmy Carter