Replacing 2-speed 1.5 HP WhisperFlo with Intelliflo3 -- what horsepower?

[JChronis]

Hi, I've been reading this forum with great interest. Very educational. Time to ask my own question.

I'm having a new IntelliCenter control system installed and realized this was also the time to replace my inefficient two-speed pool pump. (I had no idea how much better efficiency I would have!)

My installer is quoting the Sta-rite Intelliflo3 VSF at 1.5 HP, but I see a lot of recommendations from you folks that sizing up to a 3.0 HP pump run at a lower RPM will be much more efficient at the same flow rate.

I believe you, it makes sense. But here's my paranoid (chemical engineering) question. What are the risks doing a straight-up replacement in an existing system? If the pump runs full speed due to a software bug or a user error, what might break?

I've currently got 2" PVC from the pump to my cartridge filter (Pentair 160301) and (I think) mostly 1.5" PVC from the filter to the pool.

Thanks

 

[HermanTX]

What is the model and hp of the current 2-speed pump?
I have 2" suction with 1.5" returns with a Pentair 3 hp VS pump so I see no reason for concern.

 

[Jimrahbe]

J,

I have two rent house pools that have 1.5" plumbing and 3 HP IntelliFlo pumps.. They work just fine..

A VS pump is really a variable Horse Power pump, you just adjust the speed of the pump to match the plumbing.. Even running at full speed, the filter pressure is still no where close to high enough to cause any failures. But, the whole point is to run them as slow as you can..

The key in my mind is that you can always turn a large VS pump down, you can't turn a small VS pump up..

The slower the pump can run and still move a lot of water, the more quiet they are. When new, I actually had to touch the pump, just to make sure it was still running...

In my case, my pumps run 24/7, mostly at about 1200 RPM.. This costs me less than $20 bucks a month. The pumps have been running 24/7 for over 10 years and operate just like they did when installed.. Newer IntelliFlo pumps are even more energy efficient...

I am a big believer in the "Bigger is always better, when it comes to VS pumps" theory..

Thanks,

Jim R.

 

[JamesW]

But here's my paranoid (chemical engineering) question. What are the risks doing a straight-up replacement in an existing system? If the pump runs full speed due to a software bug or a user error, what might break?

Your existing pump can produce as much pressure as the new 3 hp model pump.

So, there is no more risk than what you have now.

The pump allows the settings for maximum speed, pressure, flow etc. to make it safe.

85 feet is about 37 psi, which is below the ratings of all equipment.

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/pumps/whisperflo/manuals/whisperflo-pump-manual-english-spanish.pdf

WhisperFlo® High Performance Pump

Pentair WhisperFlo High Performance Pool Pump is perfect for your inground pool, delivering high water flow and quiet performance. Shop pool pumps here.

www.pentair.com

 

[JamesW]

The 1.5 hp can get to about 62 feet of head, which is about 27 psi.

Sell Sheet | IntelliFlo3 VSF Pool Pump

online.flippingbook.com

 

[JChronis]

Thanks. Very helpful.

 

[JamesW]

sizing up to a 3.0 HP pump run at a lower RPM will be much more efficient at the same flow rate.

The efficiency is not going to be a lot more for the same flow rate.

The main issue is that the noise will be a lot less.

To move the same flow on the same system, the efficiency depends on where the system curve crosses the pump performance curve and what the efficiency is at that point.

For example, the IntelliFlo3 has a maximum efficiency at 3,450 rpm of about 57% at 100 gpm and 72 feet of head loss.

The efficiency can go below 30%.

For the 1.5 HP model, the maximum efficiency is about 54% and that happens at about 76 GPM and about 47 feet of head loss.

So, you really need to know what flow you require for different applications as well as the head loss for that flow on your system and the pumps "Wire-to-Water" efficiency at that speed and operating point.

This is why the "WEF" numbers are worthless.

In any case, the power used at lower speeds is so low that the difference in actual power use is negligible.

So, basically, the bigger pump is probably not worth the extra cost strictly on an efficiency basis, but I would get the bigger pump in most cases for noise reduction, especially if the difference in cost is not a lot.







Wire to water efficiency is how much of the power used by the pump is actually transferred to the water to make the water move.

As the graph shows, more that 40% of the total power used by the pump is not doing any useful work.

 

[Jimrahbe]

more that 40% of the total power used by the pump is not doing any useful work.

Sounds a lot like me.....

Jim R.

 

[JamesW]

Sounds a lot like me.....

Jim R.

It is a lot of lost energy, but it happens to all pumps.

The actual efficiency will be in the 40 to 60% range for most pumps.

Trying to figure out what the actual efficiency is for any pump on any system is too much work for most people and virtually no one is going to figure out the actual efficiency for each different pump for their system.

For the 100+ different pumps someone could get, the efficiency will be different for each pump at each operating point.

If you had 4 operating points that you used, you would have 400 different efficiency levels (1 efficiency for each pump at each operating point.)

You would have to then look at the efficiency of each pump at each operating point and then multiply the efficiency by the amount of time that the pump runs at that speed.

You would then compare the total energy used by each pump by adding the power used at each Operating Point by the time at that speed.

Pump 1: Operating Point 1 power used x time + Operating Point 2 power used x time + Operating Point 3 power used x time + Operating Point 4 power used x time = total energy in kilowatt-hours.

Without doing the calculations, you cannot really say that one pump will be more efficient than a different pump for a specific system and how that system is operated.

As long as the system curve goes through the middle third of the pump performance curves, the efficiency should be above about 50%.

 

[JamesW]

For any purpose, the amount of power transferred to the water is the same.

For example, if you need 40 GPM for heating, the water might require 500 watts.

This is the same for any pump.

The difference depends on the pump efficiency at that operating point.

If a pump is 58% efficient, then the pump will use 862 watts to provide 500 watts to the water.

If a pump is 50% efficient, then the pump will use 1,000 watts to provide 500 watts to the water.

If the pump is 40% efficient, then the pump will use 1,250 watts to deliver 500 watts to the water.

 

[JamesW]

System A and C are typical Pool System curves and most pool pumps are designed to have their maximum efficiency in the range.

The A and C system curves go through the center third of the pump performance curves for all speeds.

So, the two pumps should be roughly the same efficiency for the same flow on a system.

The larger pump might be about 4% more efficient for most flows, but at low flows that use maybe 200 watts, the difference is not a big deal.

To deliver 116 watts to water, the bigger pump might use 200 watts (58% efficient) and the smaller pump might use about 215 watts (54% efficient).

15 watts at 24/7 for 30 days is 10.8 kilowatt-hours.

At $0.25 per kwh, that is $2.70 per month.

For 100 months, that is $270.00, but the smaller pump costs less and you can invest the difference, so the net present value of the savings is probably less than the difference in price.

The net present value of 100 monthly payments of $2.70 per month is about $190.00 at 4% interest.

In other words, if the smaller pump is $190.00 less and you loan that money to someone at 4% interest for 100 months, they would pay you $2.70 per month to pay off the loan.