Economical with the Truth: CSV vs VFD
Don't let the "fox guard the hen house"! It sounds foolish, but that is exactly what we are doing when we allow Pump and Drive manufacturers to design a pump system.
In many articles, Pump and Drive manufacturers preach of the efficiency and savings available with Variable Frequency Drives or VFD's. One author recently called this being "economical with the truth". "Economical with the truth" is just a nice way of saying they are lying.
For example, if you are pumping water, you want to focus on reducing the energy cost per gallon of water pumped, not focus on reducing the cost per hour to run the motor turning the pump. Using a VFD to lower the speed of a water pump, when the head cannot be decreased can easily reduce the efficiency of the whole pumping system, which increases the cost per gallon of water pumped.
The output voltage waveform of a VFD will increase the losses or energy used by the motor. Energy savings due to reducing the voltage can be very small. Then at maximum flow or BEP, the added energy required by the VFD device itself, along with the reduced efficiency of the motor running on the VFD's sub standard voltage wave form, will again increase the energy used per gallon. Installing a VFD can actually increase energy use.
The common and blatant use of the words "green" or "energy savings" to sell a product always needs to be considered in details. There is no more efficient means of pumping water than by using a properly sized pump running at BEP. Anytime you vary the pump speed, or run at maximum speed using a VFD, energy costs per gallon produced goes up, not down.
After you come to this realization, you may look at the tremendous marketing effort to sell VFD's in a completely different light. Notice that every Pump, Motor, and Electronics manufacturer and their brother, is heavily promoting VFD's. Countless before and after "studies" have been published. However, reading the fine print on these "studies", you can always find that a smaller pump was installed, use of a dump valve was discontinued, or the pressure required was decreased. These are the real reasons for the documented energy savings, yet the newly installed VFD falsely gets all the credit when authors are being "economical with the truth".
Many manufacturers have a "so called" energy saving calculator. These conveniently show the energy that can be saved for decreasing the head required and reducing the pumps speed. Although they usually fail to take into account that a certain amount of head must be maintained, the loss of motor efficiency due to the unstable voltage waveform, running a motor at partial load, and the "parasitic" losses of the VFD device itself. They tend to talk about the savings for matching the system curve, while promoting the "constant pressure" performance of their VFD. If people understood the difference between these two things, they would realize this is a "bait and switch" tactic. "System curves" and "constant pressure" are two different things.
Government agencies also want to be seen as "helping" by promoting energy saving devices. Some agencies help "verify" the "studies", and even offer cash incentives to purchase VFD's. This is much akin to taking credit for approving and providing drugs that cure one disease, while hiding or ignoring the fact that the side effects of the drug are worse than the original disease.
Although it is not the truth, it is easy to convince the layperson that reducing the speed of a pump will reduce energy consumption. Publications in the water industry have also fallen for this, and are constantly publishing articles that falsely claim energy savings. Publications also want to show they are "helping" by publishing articles that show people how to save energy. While trying to do good for the public at large, unknowingly printing articles with incorrect information, helps to codify the deceit and actually cost the consumer more in the long run.
Finally, the sheer number of manufacturers who promote VFD's, and the unbelievable amount of advertising dollars being spent, prove that manufacturers are benefiting from VFD's, not the consumer. You should ask yourself, would manufacturers spend so much advertising a product that would make their products last longer and save the consumer money? Manufacturers spend advertising money on what makes them the most profit, and saving the consumer money would be counter productive. Convincing you that saving energy means purchasing a product that is expensive, must be replaced as often as your cell phone, and actually shortens the life of pump/motors, is money in the bank for these manufacturers. Whether you realize it or not, "planned obsolescence" is the primary design requirement for most manufacturers. Known commonly as a "fluid system", products designed for a short life keeps the cash flowing "fluidly" for the manufacturers. Of course this cash comes from naive and unsuspecting customers who fall for any "energy saving" ruse.
Likewise, many of these same people are also "economical with the truth" about products that do save energy, make equipment last longer, and are generally good for the consumer and the environment. While promoting products designed to make money for the manufacturers, they also try to discredit products that would be good for the consumer and the environment.
A Cycle Stop Valve or CSV was designed to mimic the constant pressure performance of a VFD, eliminate the negative side effects of VFD's, and undo the planned obsolescence built in by the manufacturers. Many of these manufacturers even have a policy of terminating employees who mention Cycle Stop Valves as a viable alternative to VFD's. "Don't believe anything you hear, and only half of what you see." These words have never been more true than when dealing with manufacturers for pumps, motors, and electronic controls.
Do your own research. Don't take what manufacturers say as the truth. Or by the time you realize that Grandmother has really big teeth, it may be too late.