Single speed pump vs. Variable speed pump

[JamesW]

if you do not then throttle your present pump after all you will save money.

In my opinion, throttling is almost never going to be a good choice.

If you want to reduce the power, replace the impeller with a smaller impeller.

 

[Jcciaschi]

I have a variable speed Hayward and I'll chime in here with some numbers.

Most variable speed motors will take 120v or 240v, alter it into DC, and then kick it back out as 3 phase. Why? 3 phase motors are more efficient than motors that run on single phase so immediately you gain efficiency. But there is more.

My pump allows me to set 3 speeds and I can choose RPM's anywhere from 100-3000 in increments of 20. I have the high speed set at 3000, the middle speed at 2000, and slow speed at 1000. The 3000 was easy as it is the fastest the motor will go. The 2000 is the speed where pressure will register about 1lb. I chose this speed due to back pressure and resistance. The more resistance the pump encounters the more amperage it will draw thus the lower the pressure the lower the amperage. At 1lb I know the pump is at its most efficient state of moving water. The slow speed is 1000 rpm. This was chosen as it works for my setup. I found I could run at 800 rpm when the filter was sparkling clean but if it got a little dirty the pump wasn't moving enough water to overcome the additional resistance and would airlock. So how much amperage do these speed draw?

The top of the pump had a display that shows speed, time, and amperage draw.
At 1000 rpm it draw about 76 watts
At 2000 rpm it draws around 320
At 3000 rpm it draws about 970 watts

As you can see, doubling the speed does not double the amperage so I use this to my advantage.

I have the pump set to run at 1000 rpm 20 hours a day. In the morning around 11 it runs at 2000 rpm for 2 hours and in the evening it runs at 3000 for about 2 hours. The 2000 rpm time was chosen as it is sunny on the pool at that time so it move around the water to take advantage of solar gain. The 3000 rpm time was chosen as that is when we usually swim and stir up the pool. I also went further and looked up the flow characteristics to ensure I was turning over the water enough with this plan. Thus far it has worked.

There is an added benefit of my current setup. I have found the pump running 24/7 just seems to keep the water clearer. I had a pool before with a single speed motor that would run for 8 hours a day and always had issues. Granted that was years ago in a different state, and many other variables so I could be wrong but I like the idea of water moving 24/7.

So how much does this pump cost to run? Simple math. We pay about .11/kw of power. 1000w = 1kw
970 watts x 2 hours = 1940
320 watts x 2 hours = 640
76 watts x 20 hours = 1520

Thus a 24 hour period uses 4100 watts or 4.1kw or .45 cents a day or roughly $13/month

A single speed running 8 hours a day (assuming the same wattage but again VS pumps are more efficient) would use:
970 x 8 = 7760 watts or 7.76kw or .85 cents a day or roughly $25/month

Hope this sheds some light on a variable speed VS a 2 speed VS a single speed.

 

[Yamo207]

I have a variable speed Hayward and I'll chime in here with some numbers.

Most variable speed motors will take 120v or 240v, alter it into DC, and then kick it back out as 3 phase. Why? 3 phase motors are more efficient than motors that run on single phase so immediately you gain efficiency. But there is more.

My pump allows me to set 3 speeds and I can choose RPM's anywhere from 100-3000 in increments of 20. I have the high speed set at 3000, the middle speed at 2000, and slow speed at 1000. The 3000 was easy as it is the fastest the motor will go. The 2000 is the speed where pressure will register about 1lb. I chose this speed due to back pressure and resistance. The more resistance the pump encounters the more amperage it will draw thus the lower the pressure the lower the amperage. At 1lb I know the pump is at its most efficient state of moving water. The slow speed is 1000 rpm. This was chosen as it works for my setup. I found I could run at 800 rpm when the filter was sparkling clean but if it got a little dirty the pump wasn't moving enough water to overcome the additional resistance and would airlock. So how much amperage do these speed draw?

The top of the pump had a display that shows speed, time, and amperage draw.
At 1000 rpm it draw about 76 watts
At 2000 rpm it draws around 320
At 3000 rpm it draws about 970 watts

As you can see, doubling the speed does not double the amperage so I use this to my advantage.

I have the pump set to run at 1000 rpm 20 hours a day. In the morning around 11 it runs at 2000 rpm for 2 hours and in the evening it runs at 3000 for about 2 hours. The 2000 rpm time was chosen as it is sunny on the pool at that time so it move around the water to take advantage of solar gain. The 3000 rpm time was chosen as that is when we usually swim and stir up the pool. I also went further and looked up the flow characteristics to ensure I was turning over the water enough with this plan. Thus far it has worked.

There is an added benefit of my current setup. I have found the pump running 24/7 just seems to keep the water clearer. I had a pool before with a single speed motor that would run for 8 hours a day and always had issues. Granted that was years ago in a different state, and many other variables so I could be wrong but I like the idea of water moving 24/7.

So how much does this pump cost to run? Simple math. We pay about .11/kw of power. 1000w = 1kw
970 watts x 2 hours = 1940
320 watts x 2 hours = 640
76 watts x 20 hours = 1520

Thus a 24 hour period uses 4100 watts or 4.1kw or .45 cents a day or roughly $13/month

A single speed running 8 hours a day (assuming the same wattage but again VS pumps are more efficient) would use:
970 x 8 = 7760 watts or 7.76kw or .85 cents a day or roughly $25/month

Hope this sheds some light on a variable speed VS a 2 speed VS a single speed.

What Hayward pump do you have? I've been looking at the Powerflow VS 300 but the controller doesn't look to be able to automate when it runs at each speed. The pump is so new I can't find much info on it online. Just curious, thanks

 

[Darin]

Throttling is a good choice if one does not have enough money to purchase a three phase motor and vfd to upgrade their existing pump to a variable speed system. It only takes a valve. This is the way we do it in the process industries It does save money and as long as i do not dead head the pump, the pump and motor are fine. Again this is a cost equation only. Electrical saving are realized when you throttle the wet end because the motor consumes less watts because it is doing less work. VS systems will always out perform efficiency speaking, no matter what pump it is on. Putting a smaller impeller is a cost that may never see a ROI.
Either way we should at least let people know that there is a way to save money, starting from throttling their existing pump, to purchasing an new VS pump and motor, or the biggest savings is to upgrade their own pump which is cheap to put seals in with a three phase motor and VFD. In the end everyone should go down to Harbor Freight and buy the cheap little AMP clamp for $14 dollars and see the savings for themselves.

 

[Randrx2]

I did a little experiment with my pump, but I am not sure if the results. I did not use a clamp or a flow meter, only the readings on the pump.

At 3450 RPM:
34 psi
2632 watts
88 GPM

At 1725 RPM:
8 psi
359 watts
44 GPM

At 3450 RPM with outlet throttled:
38 psi
1933 watts
44 GPM

So while there was some power reduction with the throttling, it was nowhere near the reduction from dropping the motor speed.

However, I would be curious to see the results in situations where the head pressure needs to be maintained.

 

[Darin]

I think it would be interesting to throttle your slow speed to say 25 or 30 gpm, measure the watts. Maybe you could run like that all the time and save even more depending on how your water responds.

 

[mas985]

However, I would be curious to see the results in situations where the head pressure needs to be maintained.

Those were given here:

Single speed pump vs. Variable speed pump

For those that haven't noticed the link to @mas985 (Mark's) article in my signature has been there for a LONG time. It's one of the best assemblies of fluid mechanics for pools I've seen anywhere. Sort of an pool fluid mechanics extraction from every relevant publication used to teach fluid...

www.troublefreepool.com

These were the results given for constant GPM:

Single speed pump vs. Variable speed pump

Hello. I could not find this topic in the deep end, so please let me know if it has been discussed before. When most people are changing out an older single or two-speed pump, the recommendation is to use a variable speed pump for the savings on electricity. The thought is that you will run...

www.troublefreepool.com

However, one thing to keep in mind is that the run-time for reduced flow rates will likely be more than those for higher flow rates depending on the task. We know that both circulation and skimming are flow rate dependent. So in fact, throttling may end up costing more than full speed.

 

[Randrx2]

Thanks Mark.

It looks like when a certain head pressure needs to be maintained for a desired flow rate, then throttling and VFD seem to break even. It might be said that throttling is the less expensive option, since there is no electrical loss at the VFD and there is no physical VFD cost.

However, for pools, since the head pressure is relatively low, the VFD option is the way to go. This can easily be seen in real world examples.

 

[mas985]

It looks like when a certain head pressure needs to be maintained for a desired flow rate, then throttling and VFD seem to break even. It might be said that throttling is the less expensive option, since there is no electrical loss at the VFD and there is no physical VFD cost.

The constant pressure example is really fictitious since you can never throttle to maintain a constant pressure because the pressure is much lower after the throttle. There is really no application where this would work so it is more of an intellectual exercise.

 

[Randrx2]

So the head pressure increase at the pump outlet is not felt through the rest of the system?

 

[mas985]

So the head pressure increase at the pump outlet is not felt through the rest of the system?

Nope. The total pressure seen by the pump is the sum of the pressure loss of each component in the pool plumbing. Every fitting, piece of equipment, throttling valve drops the pressure at that location by a specific amount until reaching the pool where the pressure is back to 0 PSIr.

 

[Jcciaschi]

What Hayward pump do you have? I've been looking at the Powerflow VS 300 but the controller doesn't look to be able to automate when it runs at each speed. The pump is so new I can't find much info on it online. Just curious, thanks

Not sure of the exact model but it was 4 years ago so it's not the one you are looking at. I think mine was only made for a short while as I remember when I tried to find YouTube videos there were none for my model pump but several videos for a similar pump with completely different programming. Just checked today and its a Max Flo VS

 

[mariane]

I want to preface my comment with: I know almost nothing about pumps and efficiency. My HVAC husband decided to get a SS pump since we only use it at most 6 months out of the year, usually run 24/7. He said the extra cost of a VS pump would not show a financial benefit to us for many years. Since SS will soon be "outlawed" we wouldn't have a choice when we need to replace it. So VS or 2 speed would have to happen.

 

[cfherrman]

At 3/4 hp running at a proper schedule it will take a few years for a vsp to equal the cost, but running your pump 24/7 I wouldn't be surprised if it's 1 year.

 

[Darin]

That is interesting. What is proper schedule? What climate do you live? Do you live in town vs. lining in the country (i.e. heavy pollen count and wind driven debris in the country). I do not believe the blanket statement of running the proper schedule works as you are comparing apples and oranges.
I have not seen a spreadsheet that demostrates using a VS set up does not have a ROI within a few years. Besides, the lower decible level itself is worth it at the slower speeds.

 

[thefloatqueen]

Deleted. Started my own thread since my response was long lol

 

[magiteck]

The VS pump is pushed heavily on TFP but for how cheap my electric is and me having a 7,500 gallon AGP, it would take several YEARS to recoup not even the entire cost of a VS pump. I know, I know — July 21st, 2021 VS pumps will be required for any new pools or replacement pumps -- that’s why I’m hurrying to get a good pump now. I’m looking towards getting a dual-speed. Seems like a nice medium. I currently have a single speed pump and ran it all the time the past two summers and my electric bills were not high at all. Yes my current pump is only .75 HP, but I ran it A LOT (by choice. Not because I “needed” to lol).

With a 1.5 HP pump, I would not run it as long. I guess what I’m saying is I’m not spending the extra money on a VS pump when it really doesn’t make sense for me to have one. I hope I don’t offend anyone here but I want what works best for my pool and my needs. With the shortage of equipment and price-hiking for pool stuff due to Covid, I cannot spend that kind of money on a pool pump. I still need to pay for installation, a new filter, unibead liner, cove, landscaping, etc.
I believe a 2-speed pump would be best for my needs. Agree to disagree!

I’m also planning on replacing my SS with a 2S this Summer. For the few months of a season we have, I calculated the break-even on the 2S upgrade even at 3-4 years. The VS would probably take me 10-15 years for a financial break-even.

More so than cost, though, I want the 2S because my current pump just moves sooo much water. I’d only have to run it a couple hours a day for filtration, but that’s not enough to keep the water visibly clean/skimmed.... or to keep it circulating while letting the sun “heat” it.

Ultimately I just want to be able to throw it on low speed, let it run all hours the sun is out, and not worry about it.

 

[PoolGate]

Don't forget to check out utility rebates on pool pumps. Many give $400 for a VSP.

 

[thefloatqueen]

I’m also planning on replacing my SS with a 2S this Summer. For the few months of a season we have, I calculated the break-even on the 2S upgrade even at 3-4 years. The VS would probably take me 10-15 years for a financial break-even.

More so than cost, though, I want the 2S because my current pump just moves sooo much water. I’d only have to run it a couple hours a day for filtration, but that’s not enough to keep the water visibly clean/skimmed.... or to keep it circulating while letting the sun “heat” it.

Ultimately I just want to be able to throw it on low speed, let it run all hours the sun is out, and not worry about it.

Glad you saw this before I deleted my comment. I started an entire new thread in the Above Ground Pools section. I’m glad I’m not alone in this one and someone else is on the same page. I am leaning towards 2-speed also. Variable-speed would be overkill for my situation in MY opinion. If I had lots of extra money, then sure, why not?! But I just want to get a quality product that suits my personal needs.

 

[thefloatqueen]

Don't forget to check out utility rebates on pool pumps. Many give $400 for a VSP.

My electric is extremely cheap lol. Who would be issuing these rebates? I know my electric company would laugh at me lol