Variable speed well pumps, booster pumps, and pool pumps are a scam. These pumps use computerized controllers, also known as Variable Frequency Drives or VFD's, and are designed to separate people from as much of their hard earned money as possible. Many government agencies, electric utility companies, engineers, manufacturers, suppliers, and installers are either part of the scam, or just caught up in the lies themselves.
Government agencies and power utilities want you to believe they are trying to help you save energy and money. Manufacturers, suppliers, and even some installers wish to sell you equipment that cost a lot and doesn't last very long. Many engineers want to vary the speed of the pump because it is easier, or they don't know how to properly design and size a pump system. Make no mistake about it, most are lying about VFD's to line their own pockets.
These Variable Speed type pumps do not save energy, and do not make pumps last longer. To the contrary, varying the speed of these type pumps can increase the energy used by as much as 500% per gallon produced. Likewise, varying the speed increases the heat in motors, causes excessive vibration, and shortens the life of motors from other undue stresses.
So how do these people get away with lying? As they say, the Devil is in the details. Read the fine print carefully. Comparing a VFD to the most inefficient pump system possible is the usual way to show it saves energy. Many articles will barely mention discontinuing the use of a dump valve, lowering the pressure required, or even installing a smaller pump in the system. Although these are the real reasons for the documented energy savings, the VFD added to the big pump wrongfully gets all the credit.
So called "energy saving calculators", especially for pool pumps, will not allow you to simulate turning the pump off. A pool pump only needs to run 6 to 8 hours a day. If you can't turn the pump off, of course a VFD is going to show $2,000 a year savings. But slowing the pump down with a VFD is not doing any good. At really low flow rates the skimmers don't skim, the vacuum won't vacuum, and the filter won't filter. Turning a standard pump off with a timer, instead of letting a VFD run it slowly all day, WILL save thousands of dollars a year.
Other so called "energy saving calculators" won't let you put in the head or pressure required. This way they can show tremendous energy savings when the pump speed is reduced by 90%. However, because the pump still has to produce head or pressure, the pump can only be slowed by 10%, which actually makes the pump use more energy than a properly sized pump without a VFD.
Still others will make a big deal about how the motor amps are reduced as the RPM is reduced with a VFD. However, they conveniently forget to mention that the flow is reduced 5 times faster than the amps, which makes the VFD cause 500% more energy use per gallon.
The Cycle Stop Valve is a good alternative to a VFD or big pressure tank. However, the pump industry will do anything they can to dissuade you from using a CSV. The CSV is a disruptive product. It really does make pumps last longer and use smaller pressure tanks. The CSV really does eliminate cycling and water hammer. The CSV really does save you money, which is why it is disruptive to the pump industry.
Don't let a fast talking salesperson force you into a money pit. Don't let an electric utility pay you an incentive to install a VFD. It will cost you many times that amount in frequent equipment (VFD/motor) replacement. Demand your installer or supplier to get you an original Cycle Stop Valve. The CSV is disruptive to the pump industry because, it may well be the last time you need spend any money on your water system.