Variable / 2 speed pumps worth it?

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1bordeaux

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May 27, 2009
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Hi

My trusty old Marlow pump is shot. 3/4 HP 115v.
According to all this pump curve info, I'm locked between 40 - 45 GPM based on est. head, 21,000 gallons, and 1 1/2" pipe.
National Grid electric costs a small fortune to run in upstate NY.
Do I go with an inexpensive 3/4HP or spring for a VF style pump and hope the usage data will truly save a heap on electric bills.
So many questions, so little time...

Thanks!
 
I have a two speed pump and run on low 12 hours a day. I only use high speed for vacuum and when I open the pool for maximum filtration. I think the problem is, and I am not sure, the first two speed pumps start at 1hp. This is what I have. If you need the gallons per minute that you state you may just go 1/2 hp and increase your hoses to 2''. There is a whole complicated area/calculation for head loss, GPM, ect.. but it confuses me a bit. Hey and I am a plumber!!.

Any way I cut my electric bill more then 1/2 of what it was using low speed.

This probably did not help you much, and hopefully someone can give you more info.

Mike
 
Welcome to TFP!

Yes, a two speed pump or a variable speed pump will save you a significant amount on electricity. My rule of thumb is that a two speed pump will usually save about 1/3 of the cost of running the pump and a variable speed will save 1/2, but actual savings can be more or less depending on how efficient your current pump is. If you know what running the pump costs you now, you can get an idea of how quickly a variable speed pump will pay back.
 
They are absolutely worth it, and for the above mentioned reasons. I am honestly looking forward to the day that I can give my 2 HP pump a funeral, just so I can put in a new 2 speed 3/4 HP.

Welcome to TFP by the way!
 
I'd love a two speed or variable, but I have solar heating and the installer said they prefer a large volume of water going through the panels rather than a small amount.

I specifically asked, because I thought it would make more sense to have slow flow and get hotter water from the panels, but apparently, in the world of solar heating pools, it's the other way around.
 
Yes, faster flow ensures faster heat transfer. The reason being that heat loss from the panels is proportional to the temperature of the water (radiation loss is T^4). So higher temp water will lose more heat and the net heat transfer will be less. Most panels will reach their peak efficiency around 1 GPM per 10 sq-ft of panel. This is usually much less than the flow rate of a single speed pump so a variable speed would allow you set the flow rate as low as possible but still keep efficiency near optimum.
 
My single-speed 1.5 hp WhisperFlo has a lot of years left, but is oversized. It's great for vacuuming and aggressive skimming and filtering, but it does one turnover in 4 hours by my math and power is expensive here. (I have a very simple, very low-head, all 2" system, including filter internals with pad 8' from pool.) Does anybody make an efficient, relatively inexpensive, low-volume single speed pump that would turn my 28K in, say, 18 hours? I am good with PVC and electric and I could install it in parallel with the big one quite easily and not have to spend $1000 on a variable. I've looked, but I couldn't find one.
 

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JasonLion said:
You can't use a single pump that is as low HP as a two speed pump is on low speed. If you did, it wouldn't be able to prime, backwash, or vacuum properly.
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That's why I would keep the 1.5 in parallel for backwashing and vacuuming. Priming is not a problem as existing pump is slightly below water level and self-primes, or rather, never has to prime unless water is a foot below skimmer. I'd set the second pump at the same level. I'd only use it for routine filtering.
 
Rangeball said:
What about the pentair WFE-2 or 3? Depends on the definition of inexpensive, I guess.
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Not a bad suggestion, and $350 beats $1000 for a variable. However, I pulled up the head curves for th model WFE-2 and it would cut my current 40 ft head @120gpm to only about 70gpm. That pump's manual also has the curve for the two-speed pumps which put out either 3/16 or 1/4 hp at low speed. I am not sure how to read that curve as flow would be zero at 40 ft of head. That might be true if it was lifting a column of water, but not in a system like mine with zero vertical lift. But I would think a 3/16hp or 1/4hp single speed would be about what I am looking for, essentially just splitting a two-speed pump over two machines. Theoretically this set-up could be more efficient than a two-speed or variable, as each impeller would be operating at its design RPM.

Here are the curves I am talking about: http://www.pentairpool.com/pdfs/WhisperFloOM.pdf Head curves are on page 9. I don't know how to pull one page out of a .pdf, sorry.
 
I serious doubt you have only 40 ft of head with 120 GPM. Head loss is dependent of the square of the flow rate so unless you have 4" plumbing, I doubt you have only 40' of head. What is your current filter pressure?

Also, why have two pumps when you can just replace the motor of your current pump with a two speed.
 
mas985 said:
I serious doubt you have only 40 ft of head with 120 GPM. Head loss is dependent of the square of the flow rate so unless you have 4" plumbing, I doubt you have only 40' of head. What is your current filter pressure?

Also, why have two pumps when you can just replace the motor of your current pump with a two speed.
Click to expand...

Pressure sits between 8 and 10. In warm-up mode, suction side is two 2" home runs (one is only 5'from pad) to two 2" skimmers and return is 2" to the main drain (an A&S feature is reverse main drain capability) plus a 2" run feeding three returns in shallow end (very short run). I think I did the Hydraulics 101 worksheet correctly.

I would like to look at the cost of your alternative (just a two speed motor). Thank you for the suggestion. Motor/pump supplier websites did not show me that possibility and I have not seen any discussion of motor upgrades on here. I would have paid close attention if I had.

I still think plumbing in a second pump could be done more cheaply, if I could find the right pump. I'd only need 1 3-way Jandy and one elbow on outlet side, and one elbow and one tee on inlet side and maybe six feet of 2" pipe. Plus one liquid tight assembly and a breaker.
 
Short answer: yes because you can pump at a lower rate which will cost you less electricity, and it will be much quieter. I don't know if the motor will last longer, but the impeller and housing should.

In my case, I have the Pentair Intelliflo that I bought to replace an old Hayward Ultraflow that was 1.75 HP uprated to 2HP.

My running cost is a bit more than 1/2 what it used to be (even though the Intelliflo is a 3 HP pump), but this is disregarding the much higher electrical use of my old pump at start up (14.9 amps at start up versus 9.5 amps running).

The neat thing with the Intelliflo is that it adjusts flow to head based on the time I input for running. Well, the neat thing is that I don't have to create a spreadsheet to figure out what speed to use when.

BIG benefit is that it is WAY quieter than my old pump. I could hear the Hayward over the 5ton heat pump, now I cannot. I'm very happy.
 
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