Because they can see it reduces the amperage needed to spin the pump and motor, many people wrongly believe a VFD saves energy. In reality, reducing a pumps speed with a VFD greatly increases the kilowatts per gallon produced.
Let me put that another way. The more a VFD decreases the pumps speed and amperage, the more energy is used per gallon produced. So not only does a VFD NOT save energy, it actually WASTE energy in many ways. How many times and how many ways can I say this??
The biggest lie perpetuated in the pump industry is that VFD’s save energy. Kilowatts per production, is the only true measure of efficiency. Anytime you slow a pump down with a VFD, you are using more energy per gallon produced. A VFD also uses additionally energy itself, like any computer. The pulsing DC power coming from a VFD also reduces the efficiency of the pump/motor. So like in the case Boyce mentioned where the pump is always producing 300 GPM and working at full speed anyway, the VFD is still causing more energy to be used per gallon produced.
On top of that, to prevent harmonics caused by the VFD, every filter or reactor added produces heat and waste even more energy.
Even with all the new technology available, the most efficient way to pump a gallon of water is still with an old dumb pump and the old pressure tank only method. In this way the pump is working at it Best Efficiency Point (BEP) delivering maximum flow or the pump is off. The only way to improve on the efficiency of the old pressure tank only method is to reduce the cycling on/off by using the pump at maximum flow whenever possible.
Boyce has done an excellent job explaining all the grounding and filtering needed with VFD’s to reduce the harmonic problem. But the best way to eliminate harmonics is to eliminate the VFD. And if your goal is saving energy, you will want to do away with the VFD anyway. At maximum pump flow a VFD is only costing you about 5% to 8% extra energy, depending on how many filters you need. But if you run at really low flow a VFD can increase the energy cost per gallon by as much as 500%.
It also takes a lot of energy to mine, manufacture, transport, and install pumps, motors, and VFD’s. Considering the short life expectancy of VFD’s and the pump/motors they control, this causes even more energy loss.
Boyce also does a good job explaining a few of the problems associated with VFD’s. My question has always been, since VFD’s actually cause more energy to be used, how can they be worth any added expense and trouble?
Now having said all that I am not sure harmonics are the real problem with the light dimmer. As Boyce explained the Sub Drive uses a 1 PSI pressure switch instead of a pressure transducer. This switch causes the pump/motor to bounce from full speed to half speed about 45 times per minute. This amperage bounce can only be seen with an old analog type amp meter, by watching the needle bounce up and down. If the flickering lights correspond to the switch bouncing 45 times per minute, then the flicker is caused by loading and unloading of the power supplied (switch), not harmonics.
You can test this by opening up enough water to keep the pump at a lower pressure than the switch setting. This will keep the switch closed and not let it bounce on and off. If the lights don’t flicker when the pump is running at full speed/full flow, then the switch, not harmonics is your problem. If the lights still flicker, the filters might help.
I have helped several people switch out Franklin Sub Drives for a $130 VFD from Driveswarehouse.com. These standard drives can still ramp up the pump speed to 80 Hz as required with the ¾ pump on the 1.5HP motor. These standard drives also use a pressure transducer instead of the 1 PSI switch, so there is no pressure bouncing. (loading/unloading, which I believe is causing the lights to flicker) These standard drives are also able to convert single phase power to three phase, so you can utilize the three phase motor you got stuck with.
Oh and I guess I should mention that Sub Drives and conventional drives will both work with CSV’s.
With the Sub Drive you can use a CSV and a standard 40/60 switch to eliminate the 45 times per minute bounce caused by the “Sub Drive type switch”. I am still thinking this will solve the flicker problem.
With a conventional drive the CSV can eliminate the need for a pressure transducer. Start/stop the drive with the standard 40/60 pressure switch and let the CSV control the flow and pressure.
You fell for the VFD hype like so many others. Now you have to figure a way out of that energy wasting money pit.
Here are a couple of links to get you started on WHY VFD’s do not save energy, but everything you really need to know is on the pump curve. Study the Horsepower section of a pump curve and it will all start to make sense.
http://www.cyclestopvalves.com/vfd-energy_15.html
http://www.cyclestopvalves.com/vfd-energy_8.html
