Single Speed Pumps vs Variable Speed Pumps

[KCD]

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.

How long do you run your pump per day for each flow rate? I'm calculating your numbers to get a comparison between your pump and mine.

 

[ajw22]

How long do you run your pump per day for each flow rate? I'm calculating your numbers to get a comparison between your pump and mine.

See below. Plus heater at 2800 RPM whenever heater is running on demand.

 

[KCD]

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...

It looks like you proved that switching to variable from single speed can save money. Thank you for you input. If I save $25 per month on utility cost, it would be about $300 per year. I don't usually like to switch if the payback time is more than 3 years. This means that, if the cost of variable speed pump + installation is more than $900, it might not work out. With the price of variable speed and labor these days, I may revisit this problem again when the single speed pump fails,

 

[PoolStored]

It looks like you proved that switching to variable from single speed can save money. Thank you for you input. If I save $25 per month on utility cost, it would be about $300 per year. I don't usually like to switch if the payback time is more than 3 years. This means that, if the cost of variable speed pump + installation is more than $900, it might not work out. With the price of variable speed and labor these days, I may revisit this problem again when the single speed pump fails,

I'm glad it helped you...

 

[KCD]

It looks like you proved that switching to variable from single speed can save money. Thank you for you input. If I save $25 per month on utility cost, it would be about $300 per year. I don't usually like to switch if the payback time is more than 3 years. This means that, if the cost of variable speed pump + installation is more than $900, it might not work out. With the price of variable speed and labor these days, I may revisit this problem again when the single speed pump fails,

I just dawned on me that the pool season is only about 5 months here, so the savings from converting to a variable speed pump would be more like $125 per year, not $300. It's unlikely now that I will ever convert.

 

[KCD]

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.

View attachment 587289

In my pool set up, the static head is not zero. The top of the filtration tank sits about 5 feet above the surface of the water and the head at the pump suction is about 10 feet. Under these conditions, speed 1 and speed 2, in your chart above, may not be enough to allow flow through the pump.

 

[JamesW]

In my pool set up, the static head is not zero.

If you pull from the pool and return to the pool, the static head is zero.

The only time you have static head is if you pull from a lower body of water and return to a higher body of water.

For example, pulling from a trough for an infinity edge and returning to the pool.

You can get static head on solar if you have a vacuum breaker that opens.

 

[JamesW]

If you need only a single flow, you can use a single speed pump if it is selected correctly.

The challenge is selecting the correct pump.

 

[Jimrahbe]

KCD,

In your case a single speed pump may be perfect for your pool.

But.. What I think you are overlooking is that operational cost is not the only reason that many people are buying VS pumps..

1. Many people, like me, have a SWCG, which has to run a long time to generate the amount of chlorine that our pools need. As you know from your own pool, running a single speed pump for a long time, is pretty expensive.

2. My pump is located about 8 feet from my head when I am in bed.. A single speed pump, would keep me awake at night. My 3 HP IntelliFlo is so quiet, at low RPMs, that when I first got it, I actually had to touch it, just to make sure it was running...

3. I have a pretty simple pool, but many here have spas, and various water features, that require different amounts of water flow depending on what is on or off. VS pumps allow the pool owner, or an automation system, to adjust the pump's output to match the flow requirement at that time.

4. And of course cost of operation is low for the majority of pool owners.

Thanks,

Jim R.

 

[KCD]

If you pull from the pool and return to the pool, the static head is zero.

The only time you have static head is if you pull from a lower body of water and return to a higher body of water.

For example, pulling from a trough for an infinity edge and returning to the pool.

You can get static head on solar if you have a vacuum breaker that opens.

There will be static head if it’s pumping to a higher elevation. In my setup, it pulls from the pool to a filtration tank at a higher elevation so there is static head even if the water is returned to the pool.

 

[JamesW]

If you have a closed loop, the static head loss on the return cancels the static head loss on the suction.

In other words, it might cost you to pull the water up, but the cost is recovered by the water going back down.

The net elevation change is zero.

 

[Jimrahbe]

I just dawned on me that the pool season is only about 5 months here

KCD,

A good point about being closed in the Winter..

But, at least half of pool owners live in places where we do not close our pools, during the winter months.. My pool runs 24/7/365, so it makes sense that I would see a much larger advantage to using a VS pump than you would.

Thanks,

Jim R.

 

[KCD]

If you have a closed loop, the static head loss on the return cancels the static head loss on the suction.

In other words, it might cost you to pull the water up, but the cost is recovered by the water going back down.

The net elevation change is zero.

What I was talking about is pump sizing: the size you need to overcome the static head to get the flow going. As I pointed out earlier, my setup is such that I may not be able use the lower flow rates on the variable speed pump because of the static head.

 

[KCD]

"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."

Based on this study, it looks like I can take my pump off the timer that is set to automatically run it 4 hrs per day. I use a solar-powered robotic skimmer (Betta) that does a good job skimming when pool is not used. I would just need to operate pump during chemical addition and when there are people in the pool.

 

[JamesW]

What I was talking about is pump sizing: the size you need to overcome the static head to get the flow going.

How high is the pump above the pool?

How much flow do you want or need?

 

[JamesW]

A pump like this can be a good choice.

 

[KCD]

If you have a closed loop, the static head loss on the return cancels the static head loss on the suction.

In other words, it might cost you to pull the water up, but the cost is recovered by the water going back down.

The net elevation change is zero.

I wouldn't say the net elevation change is zero. Net energy used here is zero. The static head is positive on the supply side but negative on the return side, so the energy used to overcome the static head is cancelled out.

 

[JamesW]

The static head is positive on the supply side but negative on the return side

Which results in zero "Net" Static Head.

If they exactly cancel out, then the pump feels zero static head.

During priming, you can get some minor static head on the suction side until the lines are full of water.

If you keep the lines full of water, then the static head is zero.

In any case, most pool systems can be considered and treated as having zero static head loss.

 

[KCD]

How high is the pump above the pool?

How much flow do you want or need?

The pump is about 2' higher than the pool but the top of the filtration tank is about 3' higher than the pump, which has to raise the water level to almost to the top of the tank before the water will start returning to the pool. I get about 80 gpm now but I think it's oversized since it can pump the pool volume (20,000) in about 4 hours. What size pump do you think I need for this application?

 

[JamesW]

What size pump do you think I need for this application?

What flow do you think you need and why?