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Thread: Variable Speed Opinions...

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    Variable Speed Opinions...

    Hi all, my local utility company here in AZ is offering a $200 rebate on the variable speed pumps/motors. Mine needs replacing soon and I was wondering what everyone's opinion on these pumps were. Are they worth the money? After the rebate, pump/motor, and install, I'm looking at about $1,000 - $1,200. Will I save boat loads of money on electricity? I'm trying to justify the expense when I can simply by a two speed 1.5HP for $400-$600 installed.

    Thanks in advance!
    26,000 Gallon Pool
    Triton II Filter - 74 gpm FFR - 4.91 sq/ft FA
    1 1/2 HP Pentair Motor & Pump - OLD
    2" lines

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    Mod Squad Bama Rambler's Avatar
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    Re: Variable Speed Opinions...

    It depends on your electric rates. If it's higher then about 24¢ per kwh the VS is usually worth it. Anything less than that the 2-speed usually wins out.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    mas985's Avatar
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    Re: Variable Speed Opinions...

    There are a lot of variables involved. It depends on the plumbing design, number of turnovers per day, the total cost of the pump install including any controllers and the energy costs.

    At $0.10/kwh, 1 turn per day (25% higher speed, 75% lower speed) and low head loss plumbing, break even between a VS pump @ $1200 vs a two speed at $600 is around 150 months of operation. After that the VS would be cheaper to operate but it might not last that long. Double the run time, halve the number of months.

    It also matters if the two speed needs to be sized for a spa (less efficient).
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Variable Speed Opinions...

    Thanks for the input. I checked my electric bill and our rates are .10kwh. We don't have a spa or a waterfall. I don't think a VS would make sense for us. A good 1.5HP 2-speed will do just fine and will be much cheaper in the long run. Unless my utility rates double sometime soon!

    Thanks again!
    26,000 Gallon Pool
    Triton II Filter - 74 gpm FFR - 4.91 sq/ft FA
    1 1/2 HP Pentair Motor & Pump - OLD
    2" lines

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    mas985's Avatar
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    Re: Variable Speed Opinions...

    Any reason why you wouldn't go smaller than a 1.5 HP. Doesn't seem like you need the HP.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Variable Speed Opinions...

    Well now that you bring it up, I'm only putting a 1.5HP motor/pump because that's what was there before. Do you think that's too much power for my 26,000 gallon pool?
    26,000 Gallon Pool
    Triton II Filter - 74 gpm FFR - 4.91 sq/ft FA
    1 1/2 HP Pentair Motor & Pump - OLD
    2" lines

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    Re: Variable Speed Opinions...

    Wow. Based on the "Pump Basics" in the Pool School, I'm way over powered. Our pool is 26,000 gallons, no spa, no water, just an automatic pool cleaner and a little spray nozzle that shoots water out. That's hardly on except when people are over. I'm think a 1HP would do me just fine. Any thoughts?

    Thanks all!
    26,000 Gallon Pool
    Triton II Filter - 74 gpm FFR - 4.91 sq/ft FA
    1 1/2 HP Pentair Motor & Pump - OLD
    2" lines

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    mas985's Avatar
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    Re: Variable Speed Opinions...

    I have a 1/2 HP pump my 20k pool so yes, I think 1.5 HP is way too big. Unless you need the flow rate for something, then the smallest pump possible will save energy. About the only thing that requires high flow rate in your set up would be your filter during backwash so you might check to see if there is any requirement before settling on a pump. But even a 1/2 HP pump can give you close to 70 GPM on backwash. To be safe though a 3/4 HP full rated two speed is probably reasonable.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Variable Speed Opinions...

    Thanks for the input Mark! I'll definitely drop the HP to save on electricity.
    26,000 Gallon Pool
    Triton II Filter - 74 gpm FFR - 4.91 sq/ft FA
    1 1/2 HP Pentair Motor & Pump - OLD
    2" lines

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    Re: Variable Speed Opinions...

    The variable speed rebate from SRP is a huge rip-off. You are required to buy from a specific list of retailers who simply don't compete against internet pricing. You are also required to have an approved tech go to your installed pump at your home/pool and program it for you at your expense. Out the-door price for all of this is well over a thousand dollars. (closer to $1500.00) The tech will most likely program it to operate as a 2-speed pump.

    Buying a 2-speed pump will cost you significantly less without any rebate. If you have APS, I believe you may have a rebate available for 2-speed.

    You can't properly size a pool pump (or motor) by simply knowing the gallons, matching the SFHP or any of the other rumors you may read. The proper way to do it would be to calculate your TDH, determine your desired GPM, then select a pump based on the pump curves supplied by pump manufacturers. With a little reading and an $8.00 vacuum gauge, you will be able to select the perfect pump to match your application. I suggest this: http://www.haywardnet.com/pdfs/Pump_filter_sizing.pdf But you should get your true readings and ignore "rule of thumb" nonsense. Look here at the end: http://www.poolplaza.com/pool-pump-sizing-2.shtml Connecting a vacuum gauge and pressure gauge is simple. Your pump is made with threaded plugged holes in it for this very purpose. You can even use the existing pressure gauge on your filter when your filter is freshly cleaned and ready to operate.

    Since you already have a functioning pool pump, you can save even more money by changing just the motor to a properly sized 2-speed motor instead of the entire pump, though it may be just as easy to buy a new pump and sell your old one to recoup the price difference.
    13,300 gallon pool
    2"Ø suction with Kreepy Krauly (1994-1999 model)
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    JasonLion's Avatar
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    Re: Variable Speed Opinions...

    Quote Originally Posted by DaveAZ
    Following their chart is both quite difficult and will almost always give you a drastically oversized pump. Their numbers are based on commercial pools. Residential pools don't need pumps anywhere near that large. Doing all that math is a real drag, very error prone, and ultimately pointless for most residential pools. Unless you have a gigantic pool, water features (fountain, waterfall, etc), very high electric rates, or 20 people swimming every day, you want a very small two speed pump.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    mas985's Avatar
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    Re: Variable Speed Opinions...

    Quote Originally Posted by DaveAZ
    The proper way to do it would be to calculate your TDH, determine your desired GPM, then select a pump based on the pump curves supplied by pump manufacturers.
    You need to be careful calculating TDH and then trying to apply that to a different pump. TDH is not only dependent on your plumbing, it is also dependent on the pump size. Downsizing a pump will reduce the TDH and visa versa. So when you put a new pump on your pool, the operating point (GPM & TDH) will change.

    The methods that Hayward and Poolplaza outline are usually not required to size a pump because in most cases, you will find that ALL pumps are too big for pools less than about 25000 gallons in size. This is the primary reason that two speed and variable speed pumps have become so popular.

    My general rule of thumb for sizing a pump for most residential pools is to go with the smallest pump possible unless you need the flow rate for a special purpose such as a spa, waterfall, etc or you have a very large pool. I get 70 GPM out of my 1/2 HP pump which is enough flow rate for a 30k pool and an 8 hour turnover.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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