HP of Variable Speed Pumps Question

[SnHominid]

There's lots of good info on this site, but there's something I don't understand about hp and variable speed pumps.

If you run a vsp at low rpm, are you effectively running it at lower hp as well?

I have a small 9,000 gallon pool, and there seem to be very few options for things like vs or dual-speed pumps that are .75 hp (which is what I think I need). Would running a 1 or even 1.5 hp variable speed pump at only a low speed effectively be accomplishing the same thing as having that lower hp pump, but give me more options with timers, port sizes, etc.?

Thanks,
Eric

 

[Jimrahbe]

Eric,

VS pumps should be called variable horsepower pumps as that is what they really are.

I run my 3 HP IntelliFlo at about 1200 RPM and it only uses 170 Watts of power. My pump is an older one, the new ones are even more energy efficient.

In general, the larger the VS pump, the more water it can move at a lower RPM. So, a 3 HP pump can move more water at a lower RPM than a 1.5 HP VS pump.

I run my pump 24/7, most of the time at 1200 RPM, for less than $20 bucks a month. If I had a newer pump it would be less than $10 a month.

Thanks,

Jim R.

 

[SnHominid]

Thanks. If I'm understanding correctly--you can basically run your 3hp pool pump as a .5hp, 1.5hp, or 3hp pump.

So, as long as my filter/pipes can handle the speed I choose, it seems like it would be safe to install a VS pump that has something like 1.5hp or more, even though I'll never need anywhere near that upper limit to move water effectively through my 9000 gallon pool with no water features (for which I only need something like 20 gpm).

I assume I'll be able to set it at low rpm (1200 or so) for normal operation, and just bring it up a bit if I need to do so for things like the skimmer vacuum.

There are almost no dual speed or variable speed options at the level of .75 hp, so was thinking I would have to go with a single speed. But, despite the higher initial investment, it looks like a VSP might be an option after all, even with a small pool.

If there's anything I'm not understanding, let me know. Thanks again.

FYI: The pool is an Aquasport 52 pool (15'x24'x52" oval) I'm putting semi-in ground, and am running hard pipe underground about ten feet from/to the ground-level skimmer and return, so I don't think an above-ground pump is an option.

 

[Jimrahbe]

Eric,

When running at 1200 RPM, it is like running less than a 1/4 HP pump. At that speed, I still get plenty of water flow to turn on my saltwater system and skimming my pool.

Pipe size is really not an issue, as even running full speed, it is not going to hurt the pipes. But, silly to do, as the whole point of a VS pump is to only use the speed you need. So, in my case 1200 RPM normally, but I ramp it up to 2800 to run my waterfall wall. I also run at about 2000 RPM, when the wife and I are relaxing on the floats and want a lazy river effect.

Although, with the wind lately, the pool already has white caps.

Thanks,

Jim R.

 

[1poolman1]

Thanks. If I'm understanding correctly--you can basically run your 3hp pool pump as a .5hp, 1.5hp, or 3hp pump.

So, as long as my filter/pipes can handle the speed I choose, it seems like it would be safe to install a VS pump that has something like 1.5hp or more, even though I'll never need anywhere near that upper limit to move water effectively through my 9000 gallon pool with no water features (for which I only need something like 20 gpm).

I assume I'll be able to set it at low rpm (1200 or so) for normal operation, and just bring it up a bit if I need to do so for things like the skimmer vacuum.

There are almost no dual speed or variable speed options at the level of .75 hp, so was thinking I would have to go with a single speed. But, despite the higher initial investment, it looks like a VSP might be an option after all, even with a small pool.

If there's anything I'm not understanding, let me know. Thanks again.

FYI: The pool is an Aquasport 52 pool (15'x24'x52" oval) I'm putting semi-in ground, and am running hard pipe underground about ten feet from/to the ground-level skimmer and return, so I don't think an above-ground pump is an option.

The only hard number I have ever gotten from a manufacturer (Pentair) is that 2100rpm is the equivalent of 1/2 hp on their VSP.
For pool purposes, unless you have 2.5" plumbing or larger, 1.5hp is too much pump unless it is turned way down.

 

[Jimrahbe]

For pool purposes, unless you have 2.5" plumbing or larger, 1.5hp is too much pump unless it is turned way down.

Kind of the whole purpose of a VS pump.. Saying it is too much pump gives the impression that it won't work well which is just not true.

I have two rent house pools with 3 HP IntelliFlo pumps, and they work great. Obviously, I don't normally run them at full speed, but even if I had 4" pipes, it would be stupid to run the pumps at full speed.

That said, with 1.5" plumbing, running the pump at full speed, is not going to burst the pipes. Just not very energy efficient thing to do.

Thanks,

Jim R.

 

[1poolman1]

Kind of the whole purpose of a VS pump.. Saying it is too much pump gives the impression that it won't work well which is just not true.

I have two rent house pools with 3 HP IntelliFlo pumps, and they work great. Obviously, I don't normally run them at full speed, but even if I had 4" pipes, it would be stupid to run the pumps at full speed.

That said, with 1.5" plumbing, running the pump at full speed, is not going to burst the pipes. Just not very energy efficient thing to do.

Thanks,

Jim R.

Never said it wouldn't work. Said for pool purposes full output of 1.5hp is too much.

 

[SnHominid]

Never said it wouldn't work. Said for pool purposes full output of 1.5hp is too much.

I guess that's just another way to draw attention to my issue, which is to figure out if there is any problem with always running a high hp vs pump at a reduced speed. It might be a bit pointless to have the extra capacity, sure, but it doesn't seem like it would be harmful.

Thanks for helping me think through this.

 

[1poolman1]

For pool purposes, the maximum recommended flow for 1.5" pipe is 45gpm. For 2" its 80 -85 (depending on which chart you reference). At full speed, with 40' of head, a very common starting point for many pools, a 3hp Pentair VSP can, and will try to, move 160gpm. Their i2 will do 130gpm.
The energy wasted trying to shove so much water through those pipe sizes ends up as noise, excess filter pressure, damaged filters, channeling in sand filters, short filter cycles, un-needed high energy bills. At full speed a VSP will use the same energy as a single-speed motor of the same size. While a 420sq.ft. Pentair filter has a published flow rate of 150gpm, that water still enters and exits through 2" openings.
If a heater is involved, the high speed water can strip the copper from the heat exchanger, damage manifold water management systems

Running at lower speeds eliminates all that and reduces wear on the pump wear item, the shaft seal. No reason to not use slow speed. Many were set up to run 24/7 at a slow speed the majority of that time when these pumps first came on the market about 16 years ago and are still running today.