I'm relatively new to the pool world and it seems everyone from my barber to the baker insists a variable speed pump is much more cost effective. However, given my simplistic reasoning, it doesn't make a lick of sense. Please help.
Assuming the purpose of pumping the water through a filter is to "clean" the water, then the volume of water pumped through the filter to clean it to a given level should be essentially the same regardless of how fast you put it through the filter. If you pump 1,000 gallons of water through the filter, it shouldn't matter too much if you pump it through in one hour or two hours (neglecting channeling, etc.) A centrifugal pump has a speed at which it is most efficient from an energy consumption standpoint. Therefore, with a variable speed pump, it - by definition - isn't always running at its peak efficiency. If you cut the volumetric flow in half, you have to run twice as long to get the same volume filtered. However you're now running less efficiently.
Why not have a single speed pump set to run at its most efficient point and keep life simple? What do I say to my barber and baker?