Well, I'm probably not going to get much agreement on the reasons why I personally choose to use the variable flow (VF) settings on my Pentair VSF pump but here goes anyway (my full body armor is donned).
Some caveats first.
1. If I were currently utilizing a robot for cleaning instead of a suction-side cleaner, the following reasons for using VF settings would be "out-the-window". I plan to replace "Rita" with a Maytronics robot when she dies (requires a rebuild kit) or sooner and then I will revert to all variable speed (VS) settings instead of using some VF settings.
2. Like most here, I also do NOT subscribe to the "Pool Volume Turnover" myth. I run my pump on a daily basis just long enough to provide the proper amount of cleaning and chlorine production from my SWCG (11 hours in the summer and 8 hours in the winter). My total daily hours of pump usage, is based mostly due to the harsh summer environmental conditions in Arizona (desert, haboobs, brutal sun, etc.)
3. I currently reside in an area where my power company offers lower rates if I minimize my electricity use during "peak" hours of the day. So I run my pump on programmed schedules "around" those peak times in order to take advantage of the lower rates. If I did not have such an opportunity and used a robot instead of a suction-side cleaner, I would probably run my pump 24x7 on the lowest speed (VS) setting possible that would still satisfy the requirements of my SWCG.
- Why I find using a VF setting versus a VS setting works best for my particular requirements when in cleaning mode.
1. My suction side cleaner works best at a pump flow setting of 40gpm. When I say "works best", that means that the right front wheel of the cleaner turns at an optimum 13 RPM. This is with my Pool Cleaner/Skimmer Valve completely open to cleaner (pool skimmer completely closed) and Pool/Spa valve slightly open to Spa (spa skimmer). This is my "cleaning" schedule configuration.
2. I use another schedule for Pool Skimming Only (Pool Cleaner/Skimmer Valve completely closed to cleaner (pool skimmer completely open) and Pool/Spa Valve slightly open to Spa (skimmer). Here I use a VS setting (1500 RPM) because I am not trying to satisfy the flow requirements that are optimum for the suction-side cleaner.
3. The whole point of using a VF setting for my cleaning schedule is that it maintains that exact 40 GPM flow rate that works perfectly for my suction-side cleaner. As the filter "loads up" over time since the last backwash, that VF setting will continue to maintain that 40 GPM flow rate, no matter what.
Yes, the RPM WILL increase over time as the filter becomes dirtier. But I don't let it get ridiculous or out of hand. I always choose to backwash my filter when the filter pressure gauge is approximately 10 PSI over it's starting point. When the filter has just been backwashed, 40 GPM equals approximately 1950 RPM/450 watts. When it's dirty, 40 GPM equals approximately 2400 RPM/800 watts.
I realize my methodology here goes a bit against the grain of the common accepted thinking about using VF settings, but given my particular pool equipment, cleaning requirements and plumbing configurations, the method I have explained and adopted works perfectly for me and my pool. Like I said, when I convert to a robot, I plan to switch completely to a VS setting of approximately 1500 RPM or less and I realize that I will certainly most likely see some reduction in my monthly overall power consumption. The robot will be the key here for me. I am kind of holding out to see how the models that allow control by pool automation systems play out over time.
Fire away. lol..
