What's the Benefit to a Variable Speed Pump?

[jrglenni]

I know this question has been asked a bunch of times as I've done a lot of googling on it, but I have not been able to find the answer to my exact question. Basically, I am wondering If you have two pumps, one that is a variable speed and one that is a single speed, and they are the exact same efficiency, what would be the benefit of a variable speed pump?

Right now, we have a pump that we run 24/7 just to turn our pool over once per day. Either this fall or before opening it next spring, I plan on changing out all of the exist 1 1/2" flexible hose plumbing to 2" PVC and switching out the pump to something larger with a higher flow as we have a sand filter that can handle the flow, just the pump and plumbing aren't large enough to support it. If I got it to where I could turn the pool over in 8 hours, what would buying a variable speed pump gain me compared to a single speed, all efficiency and other considerations being equal? Running either one at full speed over night for 8 hours would produce the same results for the same cost, right? Is there some other big advantage that I am completely missing here?

 

[mknauss]

Re: What'd the Benefit to a Variable Speed Pump?

Welcome to the forum.

The 'turnover' process is a fallacy.

Read this - Pool School - Determine Pump Run Time

Variable speed pumps are really variable hp pumps. So you only run them at the RPM needed to do what you need, skim, filter, or create chlorine with a SWCG.

Take care.

 

[ride525]

Re: What'd the Benefit to a Variable Speed Pump?

Running the variable speed pump at a lower speed will save you a ton of electricity. And still give you the turnover you need. For instance, my Intelliflo pump runs most efficiently at 23 GPM, that's at about 1450 RPM, and about 250 watts for abotu 10 hours, so about 2.5 kwh. That compares to my old pump using almost 10 kwh running six hours a day. So, approximately a savings of 75% on pump usage.

 

[jrglenni]

Re: What'd the Benefit to a Variable Speed Pump?

So really it's just about pump efficiency then, correct? If you have a single speed pump that's just as efficient as a variable speed pump (not saying that they are in the real world, just trying to simplify the example and my question) at all variable pump speeds, you would just run it for less amount of time and in order to do what you are trying to accomplish. I.E. if a single speed pump does what you need to do as far as filtering, slimming, and circulating water in 4 hours, and the variable speed pump runs at the same efficiency but half the speed and does it in 8, then there isn't really much of a difference, correct?

That being said, running a variable speed pump at a lower rate for longer periods of time seems like it would do a better job of keeping the pool clean as the skimmer will be operating for longer periods. Stuff that falls in will be ore likely to get skimmed out sooner and won't collect as much before the next run time.

 

[jrglenni]

Actually I found this from the U.S. department of energy: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjB3O2D7c_VAhXHqFQKHVYYCtsQFgjmATAC&url=http%3A%2F%2Fwww.nrel.gov%2Fdocs%2Ffy12osti%2F54242.pdf&usg=AFQjCNGSO5tpbqlOne_vCaudpjtw-pXeYA

"Variable speed pumps utilize either Permanent Magnet Motors (PMM), which use permanent magnets to create a magnetic field between the rotor and the windings. This configuration is similar to the motors used in hybrid cars. Efficiencies are gained by the magnets working to spin the rotor, as opposed to a standard induction motor that requires additional electricity to induce the magnetic field into the rotor. The PMM motor design is much more energy efficient when compared to the standard induction motor, achieving efficiency ratings of 90% while the average single-speed pump will have efficiency ratings between 30% and 70%. PMM pumps can produce the same gpm flow rate as single-speed induction motors if needed; they simply run much more efficiently."

That clears things up... I always thought the big "energy" savings in the variable speed pumps were because you could run them at lower speeds, but I wondered how it would actually save energy when you wind up running them for longer. It sounds like it is really just in the design, and the mere fact that they are variable speed pumps means they have the higher efficiency of the PMM motors vs. the standard motors.

 

[Sk1dM4rk]

The answer is in the report you linked on page 1 in so many words.

"The majority of the savings is derived from a variable
speed pump’s ability to reduce the rpm of the motor, thus reducing energy use. A typical 1½-
horsepower pool pump draws about 2,000 watts and runs at 3,450 rpm. Reducing the pump
speed and flow has a tremendous impact on wattage draw due to the Pump Affinity Law. For
example, if you reduce the pump speed from 3,450 rpm to 2,400 rpm (30% reduction in speed)
the wattage drops from 2,000 watts to 593 watts (70% reduction in power)."

In addition to the power savings which is not linear, so even though you are running longer, it is still more cost-effective, there is also less noise pollution. I sometimes have to look in the basket to see dead bugs or grass clippings swirling to know that my pumps are operating.

I have 2 and run the one that runs my SWCG at 1700 rpm and the other at 1500 rpm. The SWCG, I found trough trial and error, needs 1700 to reliably operate the flow switch. The other one will keep prime at 1500 rpm and I never bothered to try lower. They have more than paid for themselves over the years.

Hope this helps.

 

[jrglenni]

Nice, I missed that part while skimming but that also explains a big part of the energy savings. I was always thinking that the the power consumption and output was linear. It all makes so much more sense now... Thanks for pointing that one out!

 

[JamesW]

Power savings are a cube factor. At half speed, the power is 1/8th (1/2)^3.

Therefore, even if you run twice as long, you use 1/4 the total energy.

Note that real world power is usually 1/6 to 1/8 at half speed.

 

[polyharmonic]

I used to have a single-speed pump. When it broke down I replaced it with Pentair Intelliflo VS 011018. I can tell you that the VS 011018 is much better for me.

1. The first and obvious advantage is the variable RPM (duh).
For normal overnight filtering, I have it set for 2900RPM for 4 hours and 1900RPM after that for 6 hours. A pool contractor programmed that in for me as the most efficient settings after he did a bunch of measurements and calculations. I also have settings for vacuuming, backwashing, for 3450RPM. Its great to be able to change to different RPMs for different functions and to be able to run your pump with max efficiency at different RPMs over the course of a day just for normal filtering.

2. The second is programmability. If you don't have a pool automation system, well the Pentair VS has one built-in. I am in fact using the built-in for my pump automation and not using a separate pool automation system.

3. Thirdly, the Pentair VS has built-in protection if your pump can't prime or is running dry and will shut-off. I believe my old simple 1-speed pump would just keep spinning and burn itself out as it doesn't have these sensors and protections.

For these reasons (and others I can't think of), I am very happy with my Pentair VS over my old 1-speed pump.

 

[chiefwej]

Great that you love your VS pump. If you want to protect it, you need to add surge protection. The number one cause of VS pump failures is power spikes. When you have a computer attached to high power motor, with very long wire feeding it, you can expect surges to be an issue.

I have two whole house type surge protectors. One larger one on my main service panel.
https://www.amazon.com/gp/product/B01AQAKRSS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
And a smaller one on the pool sub panel.
https://www.amazon.com/gp/product/B0052DMIUK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

A few months ago I bought them for $98 and $25. So, total cost $125 and one afternoon to protect my pool equipment and all my household electronics.

 

[tstex]

Just make sure you do not buy a Hayward EcoStar 3200 VSP or you will be in the pump fixing and replacement business, not to mention all the duress of worrying about when it will break next...it seems the Pentair Corp makes the best VSP, per the users on here. Do a google search in amazon for the ecostar 3200 and 1/2 of the reviews are 1-star...pump motors and the controller seem to fail w/in 9-18 months, which is the norm,,,don't buy Hayward !!!!!!

 

[chiefwej]

There is one more advantage of the VS pump, I haven't seen mentioned. Much better filtration of the water. Moving water through the filter slower with less force, provides for better filtration. I thought my filter worked better, but my neighbor with a sand filter says he saw a dramatic improvement in water quality, with the change to a VS pump. Slower flow and less pressure means you aren't pushing as much of the fine particles you hope to filter out through the filter and back into the pool.

 

[Nectarologist]

I have also been told VS pumps are much quieter so something to consider if your pump is within hearing distance from your pool. For me the added expense isn't worth it under the best scenario since I only run for 4 months a year. I mention since we're in a similar weather cycle.

 

[Plankton]

I have a Pentair Intelliflo VS pump. I have had it for about 3 years now. No issues, lower electricity bills and yes much quieter at lower speeds. When you start to ramp up the speed you can hear it, but at the lower speeds you don't even know it is there.

 

[JamesW]

One thing to remember about a variable speed pump on low speed is that the filter has to be kept clean.

If the filter gets dirty, the flow drops off to nothing pretty quickly. Big cartridge filters (420 sqft) are best, followed by 60 + sqft DE and sand is last. Sand should be at least 4.9 sqft.

Note: Just general suggestions, not definite rules.