variable speed pumps
variable speed pumps
(OP)
I recently talked to a salesman and he said that the variable speeds units that control the electic power were very effective and didn't cost that much. The last variable speed pump I designed was in 1988 and it was a diaster. Could I have comments from other engineers with their opinions on the efffectiveness and desirablily of variable speed units?





RE: variable speed pumps
RE: variable speed pumps
RE: variable speed pumps
RE: variable speed pumps
Ver...
RE: variable speed pumps
The use of VFDs was proposed by a vendor, I had originaly done a more typical inlet throttling (control) valve approach.
Uncerainties include the system pressure drop clean/dirty, and I'm using much engineering judgement to estimate flows (first of a kind grass roots installation). Also the filter back cleaning cycle pulses will causes variations in flow maybe 5 to 10 times a minute.
My estimate of flow is certainly +- 100%, so it is quite possible fans will always operate at 50% turndown. I will have a bunch of process tricks to help out such as adjusting cleaning cycle, also I figure the level of vacuum is pretty self correcting with flow, finally I can always do a little manual inlet throttling.
I would be interested in any thoughts or comments from folks out there on this vfd application, fan types etc.
Thanks
SG
RE: variable speed pumps
RE: variable speed pumps
regarding VFD use with blowers...there have been problems with vibration of piping and silencers when VFDs are used with positive displacement blowers. The problems normally only occur a specific speeds, but this should be a major concern and be addressed in the spec. It can work as long as these issues are taken into about by the manufacturers of the blower and VFD.
RE: variable speed pumps
I am just working on a project that involves salesperson VFD applications. I calculated with respect to my project that the VFD's would add a cost of approximately 10,000 dollars per year to the evergy bills of the facility. This adds up to a PW of over 135,000 dollars based on the life of the facility.
The moral to my story at least is that there is a big difference in talking about VFD's and understanding their use through engineering. The salesperson swore I was wrong, but could not defend against my engineering. I see a lot of this out there.
VFD's serve as great tools when understood for the specific application. They are just a poor investment if no engineering is done in support of their application.
BobPE
RE: variable speed pumps
Don't forget the option of mechanical variation. They can be supplied to set up manually, or can have a little servo to provide logic controlled speed variation.
One of the advantages I see in this method is that you will definitely buy the whole package from the pump supplier and won't have interface issues between sources if there is a performance problem. Pump suppliers are fully competent and working on home territory in the area of the mechanical gear box, and motor selection is no more critical than the FSD case.
In contrast, you Variable Frequency Drive would require supply of very specific equipment from at least two sources, and possibly more: pump manufacturer, VFD manufacturer, Panel builder and, possibly, motor manufacturer to allow for VFD requirements. Your pump-man may claim to be happy to do the full package, but he is only doing it by subbing out and therefore putting more levels of interface between the buyer and the true source.
It does depend on the application and even I have accepted VFD for large cenrifugal pumps for potable water distribution, but such things as sludge pumps around a sewage treatment works may well be candidates for a mechanical solution.
As ever, there is no universal solution and if all goes well, thats fine. Unfortunately, my experience of problems arising where there is an extended contractual string has been to discover row upon row of perfectly matched sloping shoulders. And if there is any IT involvement... Oh don't let me start on that - the web-site authority would have to bar my access!