Affinity Laws and CSV vs VFD.

[ByteMe]

I found this article very helpful in understanding pump curves.

Hope the link and this quote is allowed;

http://www.pump-magazine.com/pump_magazine/pump_articles/article_44/article_44.htm
Observations:

For friction-dominated systems (long pipes, flow transfer cases) VFD saves a very substantial amount of energy, and operates pumps reliably due to close proximity to BEP flow (100% in example shown)

Tried to fix link, added below.  Cary

Tried to fix link, added below.  Cary
For static-dominated systems (injection against constant pressure, lifting against constant head) the energy savings are substantially less, and the pump operates, surprisingly, substantially off-BEP position, not significantly different from a valved flow control case

For cases where both systems are present, an in-between scenario would result

So, in a average residential single household situation. The $2-$4 (I figured pump on a total of 3 hours a day) you would save in electricity per month would never pay the additional cost of the VFD over the VFD's lifespan.

Hope that helps someone else.

[Cary Austin]

Thanks ByteMe.  Here are a couple more examples from a few others who understand a VFD cannot save energy with most pumping applications.


http://www.pump-magazine.com/pump_magazine/pump_articles/article_44/article_44.htm

For static-dominated systems (injection against constant pressure, lifting against constant head) the energy savings are substantially less, and the pump operates, surprisingly, substantially off-BEP position, not significantly different from a valved flow control case.



http://files.engineering.com/download.aspx?folder=c3f30ccc-8fd9-412f-a269-0379249f4bea&file=20100212_VFD.ppt

—Invest in the mechanical engineering and specify correctly
—VFDs do not always save energy,
—VFDs provide a suitable solution to some pump operating conditions but should not be considered a panacea
—“You just can't ever beat the energy efficiency of running a properly sized pump at 100% BEP rated flow”.
—Mechanical engineers have a poor understanding of electric motors & VFDs and fail to communicate with process or electrical engineers




http://www.powerqualityanddrives.com/payback_analysis_vfd/

Since the affinity curve neglects the static head of the system as seen
by the pump, most applications will save between 1/2 and 1/3 of what is
determined by the affinity curve calculation.



http://www.cyclestopvalves.com/pdf/csv-vs-vfd_16.pdf

When backpressure increases to a certain level, the power drawn by the variable speed control condition is very close to that for a throttle valve.

[Cary Austin]

http://www.pump-magazine.com/pump_magazine/pump_articles/article_44/article_44.htm

For static-dominated systems (injection against constant pressure, lifting against constant head) the energy savings are substantially less, and the pump operates, surprisingly, substantially off-BEP position, not significantly different from a valved flow control case.


I don't know why this link would not work on your first post, so I just added it again here.