I don’t think the engineers are lazy. I think they have been convinced by the manufacturers of VSD’s, as well as many utilities and government entities, that a VSD will make any pump match any condition, and still save energy. Why bother doing the calculations when we can just match the pump to the maximum demand, then use a VSD to “save energy”, while making the pump match any demand from 100% flow to 0% flow?
I think a lot of facts like the loss of efficiency at partial load, and that head is reduced by the square of the speed, are being purposely omitted or ignorantly neglected. Purposely omitted by the manufacturers, government entities, and utilities, that want us to believe that a VSD always saves energy. The manufacturers benefit from tremendous sales, by being able to claim they produce a product that will help the world save energy. Government entities and utilities benefit from being able to claim, that they are helping the world by promoting or even mandating the use of products that “save energy”. Facts are being ignorantly neglected by engineers, plant operators, and the general public, because they believe that manufacturers, government entities, and utilities would not purposely deceive, to justify their existence or simple greed.
The fact that input power is reduced as the speed is reduced, makes it easy to dupe us into believing that a VSD saves energy. The average person sees the amps or watts being reduced as the speed is reduced, and thinks energy is being saved. Sadly, the energy use or electric bill actually increases because a VSD always increases the energy use per gallon produced. The owner in my case is still so convinced that a VSD will save energy, that I as the engineer am taking the blame for applying it incorrectly. There is so much propaganda on this subject that I am having a hard time convincing the owner, that a VSD will always increase the energy use per gallon produced, no matter how it is applied. My suggestion to go back to DOL controls and use a big tank which will save energy, is being met with resistence. Now a couple of other engineers have been brought in to reveal the error of my ways.
These other engineers are also of the mind that a VSD always saves energy, and are convincing the owner that I do not know what I am doing. I am sure that their attempt to “save energy” by “correctly” applying a VSD will also fail. By the time the owner is convinced that a VSD will not save energy, he will be too embarrassed to admit that I was correct, and I will have lost one of my best customers forever.
I believe that there are applications where VSD’s can “make a useful difference”. I do not believe that a VSD can save energy. What I have learned from this is, “all the people around the world that applies VSD equipment and measures clearly the energy cost savings are either mistaken” or outright lying.