Lies, damned lies, and VSD efficiency! 2

Well written article that I thought worthy of sharing with those who don't peruse this site provider, Drives and Controls UK magazine. I hope the direct link works.

http://www.drives.co.uk/features.asp?id=3

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[waross]

Thanks for sharing that with us Jeff.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[iop995]

Regarding VSD efficiency measurement / claim, I think major VSD manufacturers may push to setup a regional/international standard but maybe they (or part of them) are not so interested in such clear/correct mode.

 

[jraef]

It's been tried, and the outcome has been as you predicted for the most part. I can't remember the name of the organization, GAMBICA perhaps? Seems to me that nobody significant signed on, or at least nobody noticed on a large scale.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[jraef]

Ah, would that an edit function existed...

http://www.gambica.org.uk/web_image...GAMBICA_VSD_Guide_to_Measuring_Efficiency.pdf

Published in 2008, but few people noticed.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[ozmosis]

jraef
There is a performance standard for drives within the HVAC industry. This was recently released:

http://www.ahrinet.org/App_Content/...ndards pdfs/AHRI Standard 1210 (I-P)-2011.pdf

 

[iop995]

It's good any trial to define a standard but like article state, VSD efficiency it's a small part of overall system efficiency and main effort must be to know system structure / end-user requests, rules and laws and all other system components and interactions to develop operating system control that use VSD in such way to conduct at maxim system efficiency. VSD efficiency stated in datasheets may be good ammunition used by marketing and sales guys (like in all other technical products)...

 

[zdas04]

As a user of this magical equipment I get really nervous when people justify large capital expenditures based on "efficiency improvements" using VFD manufacturer's published numbers. As the article mentions, not all equipment is equal and some of the stuff that hurts the efficiency of given VFD results in real improvements to system efficiency (i.e., work done per unit of energy input). Mostly I use VFD equipment for applications with significantly varying load requirements (e.g., on a motor driving a wellhead compressor where the suction pressure, discharge pressure, and flow rate change many times per minute). If they save power costs I generally don't care since most of my applications move tens of thousands of dollars worth of product per day at a cost of dozens of dollars in power--small power savings at the cost of reduced throughput represent really poor economics. Whenever I can focus the VFD discussion on process improvements I can get traction, when it comes around to energy savings it seems that everyone has been burned by believing manufacturer's claims and the discussion gets ugly.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[jraef]

That's the way it should be in my opinion. I love VFDs and the application thereof, but I hate it when marketing trumps engineering. The big one is the "VFDs save energy because the power is reduced by the cube of the speed" and then compare a VFD operating a fan at reduced speed to a motor running across the line on a fan at full load. I try to tell people that's an erroneous comparison, very few people even listen let alone understand.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[LionelHutz]

But a VFD always saves power. The literature and hype tells me so.

If the input kW going into the drive is reduced then it's saving energy.

And Jeff, comparing the VFD energy savings to any other kind of process control method is just plain stupid and wrong.

Seriously though, interesting article pointing out that the real overall efficiency of the complete system is what matters.