This post is partly a rant and partly me wanting honest answers from knowledgeable people here. I am ranting because I hate it when companies achieve a better product through better marketing, I hate this market speak and the mountains of BS that is hauled on the consumer as it trickles down the chain until they start raving to their friends about how great it is. People here "VFD" and think "Wow, that MUST be an awesome setup! It has a VFD! Those are so much more efficient!
I will be the first to admit here that I am fairly ignorant of pools, most of the people here know a lot more about them since they own and maintain their own. However, I do know a great deal about VFD motors and hydronic systems, and there is a great deal of marketing hype about these motors that makes me cringe when I hear it. I am trying to understand why a pool is a suitable application for a VFD.
First of all, people need to understand what, exactly, efficiency is, it is doing more work with less energy. A VFD is not efficient compared to a single speed pump, single speed pumps typically are a notch or two above a VFD when it comes to moving water with less electricity. All that a VFD does is let you slow the motor down so it uses less power and moves a LOT less water. A VFD also moves far less water for a given amount of electricity when it is slow compared to when it is running all out and especially compared to a single speed pump.
So if a VFD doesn't actually move your water with less electricity than why is it more efficient? I can shut off a normal pump and that is infinitely more "efficient" (to borrow the nonsensical marketspeak) than a VFD. I have maintained a friends pool for 4 years and we only run the pump 6 hours a day on a simple outdoor timer, what is so special about moving a little bit of water at all times? Most of the water won't actually run through the pump during these times of low use so you can't say it is being filtered. A little bit is being filtered all day so you really aren't filtering most of the water anyway and if you needed to, you could just turn a single speed pump all the way on.
So why would you want your pool's filtration system running at far lower capacity than it can run with but less electricity. From what I understand, (please correct me if I am wrong, I really do welcome it) most filters don't actually filter the water as well unless it hits a certain flow rate and pressure which it likely needs a pump running full speed to do optimally.
So what does running a filter all day do? You already have chlorine in the water, it is killing off anything that thinks of starting an ecosystem in your pool, sure the filter does trap particulate but I haven't seen a difference in water clarity between running a pump 24/7 and running it 6 hours a day, (as long as it is appropriately sized) so why do you need water pumping 24/7 even if it is just a little. Maybe some of the brighter people are remembering what they have learned about hydronics and that water flow is more efficient at lower velocities in your piping than at higher ones. Piping is cheap, why not just design your pool with larger pipes so the water moves with less friction and improves ANY systems efficiency? Maybe you WANT your water moving at a high velocity for some other reasons relating to how well it filters when there is more velocity. Well, if that is case, than why is running it at a low velocity with a VFD "efficient"?
Ok, so maybe some people here have a saltwater system and they need a water moving all the time because their fc levels will drop if there isn't flow. I thought you needed a decent amount of water flowing through your system anyway in order for these units to kick on in the first place, also, why not size them up a tiny bit so you can run the system for less time? Because it costs more? Not compared to a VFD upgrade!