I am in the market for a variable speed pump. I have read through many pros and cons of single speed, dual speed, variable speed. I have decided to go with the variable speed. I am a water engineering PE and I enjoy the concept of optimizing my system (yes, playing with it) as well as saving electricity costs. I don't currently use a controller/timer (but I know I need one to optimize pump run time), so I thought would just try to use the controller on the VS pump for my modest control needs. I am interested in a low flow mode for regular operation (<40 GPM), a medium flow mode for heater operation (40 to 60 GPM), and a high flow manual mode for vacuum day (~full speed?). We use the heater only intermittently through the summer.
I have been looking at the Pentair Intelliflow and the Intelliflow VF. The reason I was very keen on the Intelliflow VF is because these pumps have very "flat" pump curves on the the low flow end, less than 40 GPM. Small changes in backpressure, say 2+ PSI, will change flow rate by TENS of GPM. This would seem to make flow regulation difficult through the cycle of a clean/dirtry sand filter. Which could easily vary 5 PSI from clean to dirty, between backwashes.
1. What is the experience of VS owners in dialing in a reasonably constant low flow rate (<40 GPM) if the only setting available is pump speed (RPM) rather than actual GPM? This assumes the VS owner also has a flow meter and actually can observe changes in flow as pressure changes.
2. Is the Intellieflow VF a solid/reliable unit? I read some comments on Amazon to avoid the VF drive in particular and just go with the Intelliflow.
3. Is there any other model/brand of VS pump I should consider that can calculate or measure flow and then control to flow rather than just speed?