Single Speed Pumps vs Variable Speed Pumps

[PoolStored]

So that is about 150 days for a total cost of $124.182.

A vsp running 8 hrs per day at 250W would be .28 with your electrical costs. 150 days would be $42. About an 80$ savings per year.

Your choice if it is worth it.

 

[Newdude]

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

It does. Single speed pumps also often push people into a higher tier if they calculated a yearly average and their ACs we're already chewing up the lower tiers during the summer.

But no matter the ROI on VS pumps or SWGs, it doesn't make the funds available to switch, or high enough on the priority list to make the available funds available to switch. So there is always that in play also.

 

[JamesW]

The basis of the person’s argument seems to be that there is some sort of sinister conspiracy between the government regulators, the pool pump manufacturers and the utility companies to make people to use more power for their pool filtration by forcing them to buy huge 3 hp pumps.

They use typical conspiracy theory logic, which is mostly speculation with specious arguments that never hold up to actual scientific scrutiny.

 

[ajw22]

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.

Your math makes sense.

For those of us with short pool seasons the payback for a VS pump can be greater then the useful life of the pump.

The VS pump runs less hours per year and should last for more years if well maintained. The economics really depend on how long the VS pump will last to recover the savings?

But then our government has outlawed most SS pumps over 1 HP anyway and limited our choices.

I never suggest someone replace a perfectly good SS pump and replace it with a VS pump.

 

[JamesW]

I have broad background in pumps and fluid dynamics.

Ok, so show what you know and post your logic and reasoning with the appropriate math and science.

 

[JamesW]

I do agree that the manufacturers have an incentive to sell more expensive pumps.

The cost for a pool pump has gotten to be ridiculous.

The cost is now $1,500.00, and up, which is excessive.

The manufacturers could create a line of single speed pumps running at 1,725 to 1,800 RPM or even 863 to 900 RPM that would meet the needs of probably 20% to 40% of simple systems and the power usage would be very low.

The pumps could be made and sold for probably about $500.00 with a reasonable profit.

The pumps would create the same flow at about the same power usage as a 3 hp vsp at low speed.

The main problem would be that you would have to be extremely good at choosing the correct pump because you have no ability to adjust the speed if it is not exactly right.

Also, if you want the ability to change speeds for different purposes, then a single speed pump would not be a good choice.

 

[JamesW]

The VSPs have a large "Idiot Index".

Basically, you have some plastic, a 3 phase motor and a drive.

Plastic = $10.00.
Motor Wholesale = $200.00
VFD Drive Wholesale = $200.00.
Manufacturing = $40.00 including parts like seals etc.
Manufacturer cost = $450.00 and sells for $900.00 to wholesale supplier. Profit = $450.00.
Wholesale Supplier buys for $900.00 and sells for $1,400.00. Profit = $500.00.
Retailer buys for $1,400.00 and sells for $1,800.00. Profit = $400.00.

 

[hexabc]

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.

Why do you insist on making a specific number of turnovers per day? Will it make the pool water more sanitary? Even if we accept that the filter can stop bacteria, how long you would need to wait until the bacteria is caught by the filter? And ultimately, it would need to be killed by chlorine. Which brings us to the point that chlorine IS present in the water all the time and kills bacteria on contact. The role of the filter is to remove small-sized dirt, pollen, etc, which is concentrated mostly on the surface (and is collected by the skimmers) or drops to the bottom (and is collected by a mechanical cleaner).
The water in my pool was never cleaner than after switching to a 3HP pump. I run it for 11 hours per day @1600 RPM using a little over 200W. Compared with my previous 1.5 HP Jandy single speed pump running @3450 RPM for 6 hours per day, I'm saving daily 5kWh of energy.

I have no idea why you insist that this is bad. I have a degree in electrical engineering and also 10-year practice as a control engineer in petrochemical industry, so I am qualified to have opinions in this area. Plus, you would be surprised to learn how many great experts are on this forum, I’m learning something new each time I log in.

 

[JamesW]

The manufacturers could create a line of single speed pumps running at 1,725 to 1,800 RPM or even 863 to 900 RPM that would meet the needs of probably 20% to 40% of simple systems and the power usage would be very low.

Why isn’t this done?

1) Because the pumps would be a lot less profitable.

It is a lot easier to demand $2,000.00 for a pump with giant motor and a fancy computer on top.

2) The regulations would have to be changed to accept these new single speed pumps.

3) The pumps would almost never be selected correctly to provide the right flow and the customers would flood the system with complaints of the pump not providing the enough flow.

This is why older single speed pumps were almost always oversized to provide way too much flow to avoid too little flow.

For a VSP, it is easy for the customer to adjust the flow to whatever they want, so there are no complaints and it requires virtually zero ability to select the right pump.

A service person can simply always use a 3 hp VSP and then dial it in as they like.

This requires no skill or ability to model out the system curve and figure out the correct pump based on performance curves and system curves, which is beyond most people's technical abilities.

Even if you have the ability, it takes too much time to do it correctly, which makes it unfeasible to do for most projects.

 

[JamesW]

For a simple pool with low electricity rates, a small single speed can be a good choice.

You save $1,000.00 on the purchase.

You might use 600 watts vs 200 watts.

400 watts (extra) for 12 hours a day is 4.8 kwh.

At 0.10 per KWH, that is $0.48 per day or $14.40 per month.

$1,000.00/$14.40 = 69 months payback.

That can be about 10 years for a 7 month season.

If the VSP only lasts 10 years, then you get zero benefit.

If you bought the single speed pump and invested the $1,000.00, the investment could double in value to $2,000.00 in the ten years, which makes the single speed pump a better choice.

For a single speed, you can replace the motor at ten years for about $350.00 vs. buying another VSP for $2,000.00.

 

[JamesW]

The manufacturers could create a line of single speed pumps running at 1,725 to 1,800 RPM or even 863 to 900 RPM that would meet the needs of probably 20% to 40% of simple systems and the power usage would be very low.

Assuming a simple system with low head loss, you could use a single speed 1,725 RPM pump and get a flow of 30 GPM for about 250 watts.

250 watts at 24 hours = 6 KWH per day.

At $0.20 per KWH, that is 1.20 per day or about $36.00 per month.

The main problem is that it gives you very little leeway on choosing the correct pump.

It would not work with a heater.

It would be susceptible to a filter getting dirty and reducing the flow too much.

A two speed pump is 1,725 rpm at low speed.

A waterfall pump is a single speed pump at 1,725 rpm.

A 1/4 hp (0.25 hp) single speed 1,725 rpm pump can do about 20 to 40 gpm at about 250 watts assuming a system curve of Curve C.

A 0.90 hp single speed 1,725 rpm pump can do about 40 to 70 GPM at about 900 watts assuming a system curve of Curve C.

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/pumps/waterfall/WaterFall_Specialty_Pump_English.pdf

WaterFall Specialty Pumps

The Pentair Waterfall Specialty Pool Water Features Pump has a closed impeller, low-head pump ideal for water features such as fountains, waterfalls and other special pool features.

www.pentair.com

 

[JamesW]

If you bought the single speed pump and invested the $1,000.00, the investment could double in value to $2,000.00 in the ten years,

Using the Rule of 72, we can calculate the interest rate as follows:

72 / Years to double = Interest rate

72 / 10 = 7.2%

Therefore, if a $1000 investment doubles in ten years, the approximate interest rate is 7.2% per year

Average annual S&P 500 return

25 years (1999-2023) = 7.18%.

 

[blackout]

I am not sure if the below qualifies as a math model or empirical, but it uses real world measured data from my system across three different scenarios, using the two speeds I use on my IntelliFlo VSF (24 and 65 GPM). In each of the scenarios, the mix of low and high speed is demonstrably cheaper than if it was at constant high speed. I also have an SWG, and thus I call out what I have determined as a minimum run time to enjoy sufficient chlorine in my pool.

I currently follow scenario 2 in my everyday pool management use case. I like the effect of running 24 hours a day. Payback period is probably like 2 years in this scenario. (Edit: my builder charged me $600 to upgrade to VSF back in 2019, so payback was like 1 season)

Scenario 3 could give me what I need for chlorination, and still be much cheaper with variable speed. Scenario 1 (1 turnover per day) has no basis in anything, and would not meet my chlorination needs at single speed, but I’ve provided it as another example for the OP to see that VSP would save money in turnovers per day target scenario as well. In Scenario 1, you may be able to get by with only 4 hours a day, but as the SWG degrades and/or when it gets hot and sunny, you may need to increase runtime and the cost savings would only increase.

 

[TinFoilHat]

All I can say is that my electric bill dropped about $30 per month when I put my VSP in and I run it for 12 hours each and every day, 1/2 of which is at low speed.

 

[Homebrewale]

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.

Your math makes sense but there is something missing that is hard to quantify and will be different for each person. It is the peace and quiet you get from running a VSP versus a single speed. I put a high value on the reduced noise from a VSP.

 

[Newdude]

I put a high value on the reduced noise from a VSP

Goodness I heard one today. I was getting tools and such out of the truck in a customers driveway and the neighbors pump was annoying from 200 ft away.

I just looked it up and it's for rent for the summer. Imagine paying this much per month and listening to an obnoxious pump ?

 

[Lake Placid]

Goodness I heard one today. I was getting tools and such out of the truck in a customers driveway and the neighbors pump was annoying from 200 ft away.

I just looked it up and it's for rent for the summer. Imagine paying this much and listening to an obnoxious pump ?

View attachment 587540

I’ve got an account at a multimillion dollar property….Bearings were failing in a motor I replaced because the HO ran the pump dry and destroyed the seals. Pump was screaming and I advised the property mgr it needed to be replaced asap. Instruction was run it until it fails…….this lasted 4 days until the HO had a get together around the pool and got to listen to the soothing music of pump bearings eating themselves. Immediately after that gathering I got the call that the pump needs to be replaced TODAY.

 

[JamesW]

Bearings were failing in a motor I replaced because the HO ran the pump dry and destroyed the seals.

this lasted 4 days until the HO had a get together around the pool and got to listen to the soothing music of pump bearings eating themselves.

LOL.

 

[JamesW]

If you had a single speed 1,725 RPM pump with the same impeller as an Intelliflo VSF, the pump would use about 350 to 375 watts and it could do about 40 to 43 gpm.

In my opinion, there is a market for a line of single speed 1,725 rpm pumps in the 200 watt (1/5th hp) to 900 watt (0.90 hp) range.

The pumps could retail for about $550.00.

For simple systems with low head loss, the choice could be better than a $1,500.00 to $2,000.00 VSP that you are going to run at low speed 24/7 anyway.

 

[Kaylee34]

When you throw energy rebates for VS pumps in the mix, the cost can be even less.

In my opinion, there is a market for a line of single speed 1,725 rpm pumps in the 200 watt (1/5th hp) to 900 watt (0.90 hp) range.

Full agreement! It's a shame they don't do this.