Single Speed Pumps vs Variable Speed Pumps

[KCD]

It's been said that you can save money by switching your single speed pump with a variable speed one. According to this attached YouTube video, it ain't so. Has anyone on this board done the actual calculation to prove this? If so, please provide the detailed calculation (and the proof) showing the cost per gpm for each pump type (single speed vs variable speed).

 

[Rancho Cost-a-Lotta]

I tried to watch the video, but couldn't stand it any longer. This guy's talking about turnovers per day, algae caused by running pumps at low speed, and running his own VS pump at full speed for 6-8 hours per day. He's obviously not a TFP follower.

This chart was created by @PoolGate years ago and is my go to for demonstrating the potential cost savings of VS pumps. I routinely run my pump at speeds at around 1500 rpm for daily circulation. I do require higher speeds for short durations for vacuuming, running the spa, and using the suction cleaner. Since no two pools are alike, YMMV. For reference, a typical 2 hp pump can draw 2000 watts or more.

 

[Jimrahbe]

KCD,

I run my 3 HP VS pump, 24/7, mostly at 1200 RPM.. The cost to do that is about $15 bucks a month... I have been doing that for more than 10 years and my pump runs today just like it did when new.

And... my pump is over 10 years old.. New VS pumps are much more energy efficient..

Try that with your 1.5 HP pump, and tell me how it turns out for ya...

You need to find videos not made by total idiots...

Thanks,

Jim R.

 

[Newdude]

Have the YouTube guy explain this away. I'll wait.


The range of my 3 HP pump :

 

[Kaylee34]

I'll happily give the You Tube guy copies of my electric bills. The chart posted above is dead on point for my area. The dramatic decrease in usage when I replaced a 1hp single speed pump with a 3hp variable speed pump speaks for itself. Whatever nonsense someone posts on the internet is just that.

 

[KCD]

I tried to watch the video, but couldn't stand it any longer. This guy's talking about turnovers per day, algae caused by running pumps at low speed, and running his own VS pump at full speed for 6-8 hours per day. He's obviously not a TFP follower.

This chart was created by @PoolGate years ago and is my go to for demonstrating the potential cost savings of VS pumps. I routinely run my pump at speeds at around 1500 rpm for daily circulation. I do require higher speeds for short durations for vacuuming, running the spa, and using the suction cleaner. Since no two pools are alike, YMMV. For reference, a typical 2 hp pump can draw 2000 watts or more.

View attachment 586990

That chart tells you the cost per RPM. Cost per GPM is a better indicator to use when comparing single speed vs variable speed. My pump runs at 80 gpm with clean filters. Based on that I run it 4 hours to get a complete pool turnover. With only RPM, I don't know how long the pump should run for a pool turnover. Also,
knowing the RPM (instead of GPM) will not allow you to compare cost -- i.e., single speed vs variable.

This thread is not about whether the YouTube poster is a board member or whether you had a good experience with variable speed pumps. It's a call to show proof using math models, pump curves, empirical data, etc. that switching from single to variable speed can save money.

 

[Rancho Cost-a-Lotta]

Feel free to conduct your own research. I'll be looking forward to seeing it.

 

[KCD]

KCD,

I run my 3 HP VS pump, 24/7, mostly at 1200 RPM.. The cost to do that is about $15 bucks a month... I have been doing that for more than 10 years and my pump runs today just like it did when new.

And... my pump is over 10 years old.. New VS pumps are much more energy efficient..

Try that with your 1.5 HP pump, and tell me how it turns out for ya...

You need to find videos not made by total idiots...

Thanks,

Jim R.

KCD,

I run my 3 HP VS pump, 24/7, mostly at 1200 RPM.. The cost to do that is about $15 bucks a month... I have been doing that for more than 10 years and my pump runs today just like it did when new.

And... my pump is over 10 years old.. New VS pumps are much more energy efficient..

Try that with your 1.5 HP pump, and tell me how it turns out for ya...

You need to find videos not made by total idiots...

Thanks,

Jim R.

That's very disrespectful of you, given that you have no rational proof that they are idiots. I reported you for being disrespectful. I have broad background in pumps and fluid dynamics. This thread is a call for proof. What you provided is no proof at all -- NADA. Please post when you have the goods.


.

 

[KCD]

Feel free to conduct your own research. I'll be looking forward to seeing it.

This is part of my research. But I've just about concluded that it's not worth switching to a variable speed pump. This is from a scientific view. Economically, I would think that billions can be made by some by convincing people to switch.

 

[Rancho Cost-a-Lotta]

No one here is trying to convince you or anyone else to make the switch. I'm glad you've chosen a course so we can put this to rest.

Best wishes.

 

[Flying Tivo]

Based on that I run it 4 hours to get a complete pool turnover.

That piece of info is what is getting you deeper into the rabbit hole.

 

[Newdude]

This thread is not about whether the YouTube poster is a board member or whether you had a good experience with variable speed pumps. It's a call to show proof using math models, pump curves, empirical data, etc. that switching from single to variable speed can save money.

In the pics I posted above, it shows the power draw if my 3HP pump was a single speed (max RPM) and also how low I can dial it down being a VS pump while still satisfying my SWG flow switch. I can go lower but the SWG shuts off.

Picture proof a VS pump can vary from 35W to 2349W. How can you say that's not good enough ? If you care to dig into maths, the RPMs can be calculated into approximate GPM but this thread is about power savings.

Fact : my pump uses 98.6% less power at low RPM than full speed. It's so efficient I splurge allllll the way up to only 91.1% more efficient (210W) and still save serious bank. No two pumps are the same, but all will have similar ranges. A 2 speed for example is set a little higher on low speed, so its savings is in the 90% range and not the high 90s% range. But it still saves a metric truckload.

 

[Lake Placid]

That video is rubbish. He admits he runs his own pump like a single speed at 3450 rpm. Well duh lady there’s your problem. Flood your filter much? What’s an Infinity law? Oh does he mean Affinity Law? Just because something is on the internet doesn’t make it true or the speaker an expert.

 

[ajw22]

Here is data from my system…

1400 RPM 1 PSI 36 GPM 205 WATTS

1800 RPM 4 PSI 47 GPM 407 WATTS

2400 RPM 10 PSI 61 GPM 913 WATTS

2800 RPM 68 GPM 1406 WATTS

3400 RPM 80 GPM 2435 WATTS

Nothing on my pool needs more than 50 GPM of flow.

The sweet spot is around 1800 RPM pushing 47 GPM and using only around 400 watts. A SS pump cannot move water that efficiently.

 

[PoolStored]

That chart tells you the cost per RPM. Cost per GPM is a better indicator to use when comparing single speed vs variable speed. My pump runs at 80 gpm with clean filters. Based on that I run it 4 hours to get a complete pool turnover. With only RPM, I don't know how long the pump should run for a pool turnover. Also,
knowing the RPM (instead of GPM) will not allow you to compare cost -- i.e., single speed vs variable.

If your objective is to have the same gallons pumped, here is your comparison.

Typical 1hp single speed pump: (How Much Does My Pool Pump Cost to Run? - INYOPools.com - DIY Resources)
4 hours x 60 minutes x 80 gpm = 19,200 gallons.
The typical 1hp single speed pump will run at about 1720W (see reference, some run up to 3000W see reference)
a 1hp pump, @1720W, At .12/kWh, would result in spending $.83 per day, running 4 hours.
a 2hp pump, @2250W, at .12/kWh, would result in spending $1.08 per day, running 4 hours.

Superflo VSP (Pentair SuperFlo Bench Test (240V / 1.5" pipe))
1200RPM - 24 hours x 60 minutes x 12gpm = 17,280 gallons 179W
1500RPM - 24 hours x 60 minutes x 17gpm = 24,480 gallons 265W
179W, for 24 hours, at .12/kWh, would result in spending $.52 per day, running 24 hours.
265W, for 24 hours, at .12/kWh, would result in spending $.76 per day, running 24 hours.
To turn the equivalent 19,200 gallons as the single speed, it would cost around $.60 per day.

Where I think we differ from the rest of the pool industry is that we don't believe in turnover. Link-->Turnover of Pool Water - Further Reading

This study found: (https://consensus.fsu.edu/FBC/Pool-...4_study-efficiency_of_circulation_systems.pdf)

1. Dirt sinks to the bottom and chemicals stay in solution, whether the pump is running or not.
2. After skimming the surface, the pump pumps clean water, unless the dirt on the bottom is agitated.
3. Algae can form on the walls even if a pump is run 24 hours per day. In other words, running the circulation pump is not a substitute for proper physical and chemical maintenance of a pool.

We teach that you run your pump for a reason. Skimming, filtering, chemical distribution, vacuuming etc. As you can see form the study I linked, once you are skimmed, have proper chemical balance, and you vacuum debris, there is little reason to run a pump.

The reason we recommend running a VSP 24x7 is typically for salt water generator pools. This allows the cell to make chlorine at a constant rate throughout the day, maintaining FC. You can do that at very low speeds on a VSP, and at a low cost as demonstrated above. You can run a pump (VSP or not) fewer hours during the day with the cell on a higher % output, but that introduces swings in FC during the day and a higher monitor/maintenance requirement...and some accuracy on the output % to no go below minimum FC to kill algae.

I hope this helps you understand TFP and make an informed decision...

 

[pjt]

That's very disrespectful of you

Nothing was disrespectful, just straightforward and correct. I understand conflicting information is difficult sometimes.

you have no rational proof that they are idiots

We watched the video. That was all the proof we needed.

I've just about concluded that it's not worth switching to a variable speed pump.

A VSP will save you massive amounts of money. I can operate 24/7 for ~$5/month. During its service life, it will pay for itself many times over.

 

[Jimrahbe]

KCD,

I guess we will just have to agree to disagree about the requirement to be an idiot..

I agree that a VS pump is not for every pool owner. But a VS pump is a better and cheaper option for the majority of pool owners.

My pull-it out of my rear guess is that 99% of pool owners run their pumps much longer than 4 hours per day. The longer you run a single speed pump, the more cost effective it is to go with a VS pump.

Pools are different and people are different.. I could never run my system just 4 hours a day for several reasons.. I have a SWCG, and I need to run my pump long enough to generate the chlorine my pool needs. An extra benefit to running longer is that I'm skimming more. And.. I personally like the look of my pool when there is a little motion to the water. I like my pool to look alive, and not dead.

You seem to be caught up in the theory that VS pumps are just a way for businesses to make more money.. But for the majority of pool owners, a VS pump will save them money on their electrical bill.

Thanks,

Jim R.

 

[JamesW]

The person is using an example where the static head is 215 feet and the dynamic head is 5 feet.

In their example, the static head is 98% of the head loss.

For a pool system, the static head loss is zero and you only have dynamic head loss.



Static head loss does not change if you change the flow rate.

So, for their application, the head loss remains mostly constant and is not flow dependent.

For their application, the pump needs to be optimized for a very specific head loss and flow rate where virtually all head loss is static and the flow rate is either zero or very low.

For their system, you can basically ignore dynamic head loss.

For a pool, 100% of head loss is dynamic.

So, the use of a well pump analysis does not apply to a pool pump system.

If you have a pool that needs to have only one flow rate, then a single speed pump might be a reasonable choice.

For example, a commercial pool might be required to have 120 gpm by health code and they cannot slow the flow down.

In that case, a single speed pump that is chosen correctly might be a reasonable choice.

For a residential pool with no heater, you could probably get a small single speed pump that uses 200 watts if that would meet your exact needs.

One problem with that is they do not make single speed pool pumps that use 200 watts except for maybe a tiny Intex above ground pump.

Also, in systems with a heater, you will usually want to be able to vary the speed for heating.

I do understand the fact that buying a 3 hp pump and then using it to operate at low speeds seems wasteful and unnecessary.

If you could figure out the exact power single speed pump, it would be a better deal than getting a 3 hp variable speed pump.

For example, if you have a 3 hp pump and run it at 1500 rpm continuously at 175 watts and never change, then a single speed pump that runs at 1,500 rpm and 175 watts would be cheaper.

In practice, it would be almost impossible to be able to produce an exact pump for each individual pool that is optimized for the exact needs.

Also, most people want the ability to change speeds for different purposes.

In any case, below is the math involved for cost vs. flow.

For a pool system with zero static head, the power usage increases by a cube factor for the difference in rpm or flow.

So, if you double the flow, you use 8 times more power.

If you run at 60 gpm for 12 hours at 1,600 watts at $0.25 per kwh, that gives you 43,200 gallons filtered for $4.80 per day or $144.00 per month.

If you run at 30 gpm for 24 hours you filter the same 43,200 gallons at 200 watts for a total of $1.20 per day or $36.00 per month, which is 1/4th the cost.

 

[drsipe]

I don't want to dispute if a VSP is right for everyone, we all have to make our own decision on that, but I just want to post the information that I have and see if my assumptions are correct.

I live in PA and we can shop for our electric supplier. Currently I pay $0.0919 for the generation and $0.04608 for delivery, for a total of $0.13798 per kWh

Here is the page from my pump manual, I have a 1 HP Super Pump running at 230v.


So according to this, my pump consumes .75 kWh. So at $0.13798 per kWh, the cost of running the pump is $0.103485 per hour.

I run my pump for 8 hours a day, at a cost of $0.82788 per day. I run the pump for 8 hours to maintain chlorine from the chlorine generator.

Even though my swimming season is a little over 3 months, my pool is in service (pump running) for about 5 months. So that is about 150 days for a total cost of $124.182.

I've estimated that if I switch to a VSP, I Could drop to as little as $30 -$50 for the entire 5 months.

I'm asking the experts, if my math makes sense?

If my math is correct, I would save about $75 - $95 per year, and although that is a significant amount, I'm not sure it justifies replacing a perfectly working single speed pump with a VSP. My plan at this point is to wait till my pump fails and replace it with a VSP, unless one of the experts shows me a flaw in my math.

Thanks for any advice for any advice you can give.

 

[JamesW]

In the video, their example has one operating point.

In that case, a single speed pump can make sense.

Well pumps can also have variable flow requirements.

For example, a farmer that is irrigating crops might need different flow rates for different applications.

So, a well with a single operating point is different from a well that needs to provide different flows for different applications.

Also, a well pump with a large static head loss is significantly different from a pool with zero static head loss.

For a pool system, you generally want the ability to tune in the flow rate to meet your needs.

This is best achieved with a variable speed pump.

The main advantage of a 3 hp variable speed pump over a 1.5 hp variable speed is that the larger pump can run slower and it will be much quieter.