"I don't expect to convince you since I can only offer engineering principles, calculations, manufacturers literature, articles, research publications, and similar material while you offer your unsupported statements that valves save more energy than VFDs."
I was doing the math and my own research 20 years ago, when I was hyped up about VFD's like you are now. As you have already proven, there are many ways to doctor the math to make a VFD look really good. The math has not proven itself accurate with the many thousands of installations I have seen in real world applications.
I know that a VFD could be more economical if the head lowers to 200' or 115' instead of 231'. However, the well has a 231' pumping level, or the golf course sprinklers need 100 PSI form the booster pump no matter if running 1 sprinkler or all of them at once. The well is not going to make itself more shallow just to make a VFD look better. The sprinklers at the golf course are not going to give the coverage they should at 87 PSI to make a VFD more efficient, they need 100 PSI all the time.
If you want to add in another 14' of head from friction loss, then the pump now needs to deliver 1200 GPM at 245' of head. If you slow the pump down where it can only produce 200' of head, then the water is not even getting to the top of the well as the lift is 231'. The 14' of friction loss is going to be reduced as the flow rate is reduced. So the head can vary a little form 1200 GPM at 245' to 100 GPM at 231'. Other than that, you cannot reduce the head requirement just to make the power requirements of a VFD look better. If you are going to run a 1200 GPM pump at 240 GPM all the time, as per your example, then yes a VFD will save considerable energy. However, if that is all you are going to use, then replacing the 100 HP pump with a correctly sized 25 HP will cut the electric bill in half compared to using the VFD.
What I find in the field, is that most pumps are run at maximum capacity about 80 to 90% of the time, and the variable flow is only used when filling a spray tank or something else intermittent. This makes the electric bill increase for installing a VFD, after the math had already promised energy savings.
On the systems that I work with, if the system curve makes much difference, then somebody messed up and put in way too small of a pipe line. As per the ABB calculator, a reduction in head is really what makes a difference in power consumption, not the VFD. In the section labeled "head above an open valve", it should read, how much head can be reduced. Using pipe with less friction loss or going to a lower pressure irrigation system should be what the cash incentive is paid for. This will decrease the cost per gallon pumped, while decreasing the pump speed with a VFD increases the cost per gallon pumped.
"Efficiency will be reduced when a motor is operated on a bus with harmonic content. The harmonics present will increase the electrical losses which, in turn, decrease efficiency. This increase in losses will also result in an increase in motor temperature, which further reduces efficiency."
Then when transformers or line filters are added to reduce the harmonics, the input voltage is decreased and the amperage and heat increase even more.
I have been playing with the ABB calculator, and I find it to be as bad as the calculator for PG&E, that you already agreed was flawed. The ABB calculator also makes no provision for looking at the pump curve. How can you make a comparison if you don't know what the pump will do naturally? Considering the source, this calculator is designed to make a VFD look good no matter what.
I don't believe a Drive can be 98% efficient. I always see at least a 5% loss in pump output when I use a Drive. This usually causes more of a loss than the 7 PSI friction loss across a valve. This means at full flow there would be substantial savings for just pulling out the VFD.
I did calculate an actual savings of $800.00 per year when flow rates below the maximum are used for a majority of the time. This is no where near the $4,600.00 savings calculated by the ABB software. At $800.00 actual savings per year, the VFD would have to last many years to pay for itself. You might get a year or two of savings if the VFD last longer than it takes to payout, which is not likely.
If the flow required varies widely, even when the head remains constant, there are some energy savings by using a VFD. It is just never as much as exaggerated by the math or any Energy Savings Calculator concocted by VFD manufacturers. Even when a VFD can save $1,000.00 per year in energy, if you have to replace a $5,000.00 Drive every 5 years, you are not really saving anything. I know there are a few old drives out there but, very few last long enough to pay out. See the attachment below of an ABB drive that only lasted a couple of months. This is what I am used to seeing in the field, and why I replace VFD's with valves every chance I get.
Then lets not forget what started this thread, which was harmonics. Harmonics is "dirty power", which causes everything else on the same electric grid to become less efficient. I have even seen several installations where the air-conditioning for the VFD uses more power than the pump itself. How can your math or these calculators figure the losses elsewhere in the grid and add them back into the calculation? Harmonics are just one of many negative side effects of VFD control. Resonance frequencies, bearing currents, voltage spikes, RFI, nuisance trips, required technical assistance, and a several other problems go away when you eliminate a VFD.
Here is what you should learn from this;
1) Just adding the VFD without decreasing the head costs you more energy per gallon.
2) You should like Valves. Valves let you use the full range of the pumps capacity without any of the negative side effects of VFD.
3) You can save money using a Valve if you select a pump curve with a steep Brake Horse Power slope towards the shutoff point with NO loss of efficiency at your nominal operating point.
4) In high static head systems, which is most pump applications, it is more difficult to save energy with a VFD.
5) A savings calculator is available from the manufacturer of VFD's, which does not take into account the natural characteristics from the pumps curve.
I would like this to be my last post in response to you because I have better things to do than to prove the obvious. This was written so that a farmer could understand it but, it is technically accurate. It is just hard to see the truth through VFD colored glasses.
We could all be more green, if manufactures didn't try so hard to keep us in the red.
