Choosing a VS pump with flow control

[bjam]

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.

My questions:
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?

Many thanks.
Ben J.

 

[pooldv]

I have the 3hp intelliflo VS pump. I have found that the flow number is not important. It is easy enough to gauge a good flow rate to make the SWG happy, solar panels happy and skimmer/drain suction. My pump skimmed well and made chlorine at 900 rpm. But, as the filter clogged I started getting low flow errors. Bumped it to 1000 and it got better but still got an error occasionally. Bumped it to 1100 and it has been error free for a couple of years no matter how clogged the filter gets. And it only draws 150 watts at 1100 rpm!

After some trial and error I got mine all dialed in as follows,
Skimmers and SWG at 1100 rpm, 150 watts
Solartouch bumps the speed to 1950 rpm, 550 watts, for my solar panels
Brush pool to bottom drains 2500 rpm
Skimmers and waterfall 1500 rpm

I will definitely get another one when the time comes. You can see that I never get close to max rpm of 3450.

 

[Patrick_B]

Welcome to TFP!

1. I have a flow meter and yes it's easy to dial in, but you'll have to increase RPM as the filter gets dirty obviously.

2. I've only had my Pentair IF VS for a year now, but it's been flawless in every regard. I'd recommend it to anyone. It's very nice to have the option to tweak things. I like tinkering, and I like "extras" so it's been fun to have.

3. I'm not sure, but I haven't heard of one. I could have easily missed this however.

 

[jblizzle]

Everything I have read on the forum indicates skipping the VF and just get the VS. There is rarely a need to have a constant flow rate, it makes it more difficult to realize when you need to clean the filter, and if you are not paying attention to the filter getting dirty it can end up costing you a lot more in electricity as the pump automatically increases speed.

We generally recommend cleaning the filter with the pressure rises 20-25% over the clean pressure ... that is not obvious is the pump is increasing its speed.

 

[bjam]

I very much appreciate the three responses, and I look forward to maybe a few more that have direct experience with the Intelliflow VF.

Regarding the decision to backflush, it would seem that with either the VS or the VF one would need to pay attention to dP just as you would with a constant speed. This really isn't a concern for me--i check on the pool equipment every day or two. The literature also says the VF has a backflush alarm when it senses RPM increasing for a given flow rate.

From the responses, I hear the opinion that the VS is adequate and the VF is not an indespensible improvement. I would really like to hear testimony if the Pentair Intelliflow VF is problematic or not, or any more problematic than the VS. I would assume they are pretty much the same machine with some extra logic built into the VF. I don't know for sure how the VF monitors flow rate, but I have to assume it does NOT use a direct flow measurement or truly have a flow meter. I would guess it is calculating flow based on known Speed/RPM and Power/Watts using pump curves. Does anyone know for sure?

Also, are there any other manufactures that make a flow control pump?

 

[mas985]

I would guess it is calculating flow based on known Speed/RPM and Power/Watts using pump curves. Does anyone know for sure?

That is exactly how it is done. There is a direct relationship between flow rate, RPM and Watts for pumps so you can use a calibrated lookup table.

The issues that we hear about regarding the VF is that the pump will ramp up RPM when it encounters restriction (by design). By setting the flow rate as a constant (rather than RPM), as the filter gets dirty, the pump will ramp up RPM to compensate which also means that it will use more energy. With a VS, just the opposite is true. The RPM remains constant, GPM falls and so does power usage.

Also, some members have reported that on occasion when solar is triggered and the panels start to prime, the pump can alarm because it sees a rapid change in head loss so it thinks there is a blockage somewhere. There may be ways around this one though.


But the most compelling reason in my mind is that knowledge of GPM is really irrelevant. Since you are new to the site and you may not have heard this yet. We do not recommend setting run time by turnovers or flow rate (see Pool School - Determine Pump Run Time and pump run time study in my sig) so knowing or being able to the set the flow rate really doesn't buy you anything except maybe for the heater but even there, you could easily determine RPM necessary to keep the pressure switch in the heater closed by trial and error so even that is not very compelling. Same is true with an SWG. So to me at least, you are paying for something that is not really necessary and is less efficient than a VS (dirty filter example).

 

[chiefwej]

I too considered the VF pump, but after more research (much of it on this site), I decided on the VS series. I'm very happy that I did. But, I also added a flow meter to my system, just to appease that desire to fine tune things, and know how my speed settings and valve settings impact the flow rates. Just couldn't resist it. I seldom refer to the flow meter, but if you feel the need to monitor and set specific flow rates, it is a way to have the best of both options.