2 speed versus VS and figuring out pipe sizes

[Jay Laifman]

I looked for older threads on this first, but didn't find these answers.

I just went and spoke with three different local pool stores and got stupid answers - even my high school son who was with me couldn't believe the inability for any of them to answer questions.

Like everyone else, I need to go from a 2hp single speed to something more efficient. But, I want to do it smartly.

First, I first found a decent answer on this site that the reason a VS is better than a 2 speed is because you can set the GPM and it changes speed to maintain that speed. So you know that you are doing a full turnover in a given time. But for a 2 speed, that's all you have and your low speed only works if you have calculated the right hp to get the GPM so you can set the right duration. Although I also read on this site that for a residential pool, you don't need a full turn over.

Here are my questions based on those statements:
(1) If I were to take the time to do the calculations and get the right HP 2 speed for my pool, why isn't that as efficient as having a VS that gets to that rate anyway?
(2) Is it true that there is no magic requirement of one turnover a day?


Second, the two reasons I'm not wild about the VS are because I hear they still don't last very long and their price is so high. It seems to me that if I could get a $400 2 speed that is right for my pool, I'm way ahead of a $1,000 VS - even if I install it myself and lose the warranty. Then on this site I saw that someone referenced just buying a separate 2 speed motor and put it on my pump: 56Y Square Flange In-Ground Pool Pump Replacement Motors. At $200, I'd be even more ahead of the game (as long as I can map out the right hp). I had asked one of the shops I went to about this. The salesperson said that the pumps are different and more efficient on the VS.

(1) Is that true that the pumps are changed for VS?

Finally, I have a 23,000 gallon pool. The visible pipes into the pump are 2". But, I have no idea what is under the ground. The only think I know is that in the skimmer, there is a diverter valve that adjusts if the water into the pump is coming from the drain at the bottom or the skimmer. And the hole that goes from the diverter valve to the pump is 1.5". Does that mean I really just have a single 1.5" pipe?

Thanks for any advice!

 

[Isaac-1]

I wish I had more time to answer this now, but another thing to add to the 2 speed vs VS debate is if you have any equipment that may require minimum flow levels like a heater or SWG. Most of the time these will be happy with a 2 speed pump set on low, but some of the time depending on model and your plumbing setup they may have flow problem thanks to their flow sensors acting as safety cutoffs.

Otherwise there is no reason that you could not add a 2 speed motor to your existing single speed pump. If you can provide detailed model numbers and your overall setup we can help more. This includes adding a state to your location as location can effect advice we give.

 

[fields_g]

Yesterday, I replaced my single speed pump with a VS pump. After utility rebate, I only paid ~$250 (self installed). Many states have these programs. I don't know which "Oak Park" you live in, but here is a list of pump rebates per state.

I won't consider myself as knowledgeable as some people around here, but here is my crack at your questions:
1) VS pumps are usually built around PEM motors. They are said to be more energy efficient at any given RPM.
2) I seem to recall that the 1 turnover per day is a starting point. I think many people around here would tell you to adjust pump run-time up or down as needed to keep the pool clean. Higher RPM to get the skimmer(s) working well, lower speed for the rest of your filtering needs.

Other comments:
On my VS pump, I set the RPMs, not the GPM. For me to know the my GPM, I would either need to plumb a flow meter, or otherwise know the TDH of my pool system and look up the GPM value on my pump's TDH vs. RPM chart.
My pump also shows the wattage used. Here are a couple quick points: 3000rpm ~ 915w, 2400rpm ~570w, 1500rpm ~135w, 1000rpm ~70w, 600rpm ~28w. I find this to be an amazing range.

Hope you find an amazing price after rebate and can just put the whole dual vs VS debate aside.

 

[bobodaclown]

What's your KWH cost? The rule of thumb I use is if your electric cost is greater then $.25 KWH then look into a variable speed motor other wise look at using a 2-speed motor and run on low most of the time, high when your backwash or cleaning. With a two-speed on low moves 1/2 the water at 1/8 the cost or so.

Wet end of the pump is pretty bullet proof, change out the seal every few years, or at least catch it when starts to drip. When the shaft seal starts dripping, it eventually takes out the front bearing, front bearing starts making noise from lack of lubrication/friction, creates heat, that takes out the motor.

There is no magic turnover number. Pool School - Determine Pump Run Time

 

[gwegan]

Most pools without water features, a spa or solar will do great on a 2 speed pump. Even a spa or solar can work well on a 2 speed pump.

Total turnover every day is not needed and even if you ran the pump 24 7 that doesn't mean all the water will pass through the Skimmer, My water refuses to line up for cleaning in the filter and just laughs at me when I demand order.

 

[CJadamec]

Another note on VS pumps is pentair and hayward both offer pumps in the 650-700 range. VS pumps also include their own built in digital timer so you don't need a separate mechanical one any more.

 

[mas985]

Here are my questions based on those statements:
(1) If I were to take the time to do the calculations and get the right HP 2 speed for my pool, why isn't that as efficient as having a VS that gets to that rate anyway?
(2) Is it true that there is no magic requirement of one turnover a day?

1) Because a two speed motor uses a separate winding that is thinner than the main winding so you lose about 50% in efficiency. However, they still have pretty good efficiency and can save about 75% in energy over full speed. A VS will do up to 90% better at the lower speeds because it uses the main winding and a permanent magnet so there are less losses to deal with. However, not every pool will be able to operate at those lower speeds so your savings could be less. There have been many posts on this forum where members were very surprised to find out that they could not run at the most efficiency speeds and still have both their cleaners and skimmers work at the same time. Also, if you do the analysis, and I have a spreadsheet in my signature to do just that, you might find that the two speed is more cost effective over the life of the pump. It just depends on your energy costs, rebates, usage and ancillary equipment.

2) This is true. Please read this: Pool School - Determine Pump Run Time
Also read the pump run time study in my signature. Most pools can get away with 4 hours or less of run time independent of pool size.

(1) Is that true that the pumps are changed for VS?

No this is not true. The wet ends (i.e. pump) is exactly the same as other pumps in the pump line. For example the Intelliflo uses the Whisperflo wet end. So this means the wet end will have identical pumping efficiency. However, the motors are different and that is where the difference in energy efficiency comes from.

Finally, I have a 23,000 gallon pool. The visible pipes into the pump are 2". But, I have no idea what is under the ground. The only think I know is that in the skimmer, there is a diverter valve that adjusts if the water into the pump is coming from the drain at the bottom or the skimmer. And the hole that goes from the diverter valve to the pump is 1.5". Does that mean I really just have a single 1.5" pipe?

Probably yes.


Forgot to mention that you can get 2 speed motors with timers too: A.O. Smith Pool Motor Square Flange 2 HP Full Rate Dual Speed w/ Digital Controller - B2984T - INYOPools.com