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Thread: Pump sizing for the spa

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    Pump sizing for the spa

    Existing 1.5 HP motor kept dying about once a year (bearings every time), I've finally lost it and decided to replace it.

    The question is, was the pump sized correctly?

    Here's what I have so far:

    - Spa size is somewhere between 1100 and 1500 gallons;
    - Head is about 60ft, if I'm getting it right (10ft straight from the pump to the skimmer, 13ft straight from the pump to the drain, 7 jets, heater);
    - Filter is marked as "37.5 GPM public, 100GPM residential pools";
    - Plumbing is 1.5".

    Wanted to install a two-speed pump initially, considered SuperFlo 340043 and WhisperFlo 11522 to run them at low speed, but then looked at performance curves and got totally confused.

    First of all, it looks like neither of these pumps will work properly at low speed - 11522 curve starts at about 25ft, and 340043 curve starts at 20ft.
    Second, it looks like 11522 will overrun the filter, producing something about 100GPM at head of 60ft, and if it is, in fact, less, then oops.

    Reading the discussions, I see that IntelliFlo 11018 constantly pops up as a reasonable upgrade from WhisperFlo, and it looks like it can be programmed to match the rest of the equipment. Does this make sense?

    Since it's a chance to rework the plumbing, what measuring devices would I want to install to keep an eye on how well does the equipment perform? Flow meter? Ampere-meter?

    Since the high head requirement for spas is dictated by jets, would the filtering work correctly at lower speeds? How do I calculate/determine where is the go/no go threshold?

  2. Back To Top    #2
    Mod Squad jblizzle's Avatar
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    Re: Pump sizing for the spa

    Welcome to TFP!!!

    First, the head loss calcultion is not as easy as you assumed ... and it is variable depending on the flow rate. At the lower flow rates on low speed, the head loss is significantly less than at high speed ... so any pump will "work".

    Can you be more specific about what pump and filter you currently have? Like Make and Model.

    Is the current jet stength acceptible to you or would you want to change it?

    The Superflo is a smaller pump than the Whisperflo ... at the same HP, they move very different amounts of water. So with more information about the current setup, we can offer a suggestion on a suitable replacement.

    There is really no need to know the flow rate, but there are meters for that if you are interested.
    Jason, TFP Moderator
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    Re: Pump sizing for the spa

    Quote Originally Posted by jblizzle
    Welcome to TFP!!!

    First, the head loss calcultion is not as easy as you assumed ... and it is variable depending on the flow rate. At the lower flow rates on low speed, the head loss is significantly less than at high speed ... so any pump will "work".
    In other words, running 340043 at low speed will suffice for filtering?

    Quote Originally Posted by jblizzle
    Can you be more specific about what pump and filter you currently have? Like Make and Model.
    Filter: Sta-Rite Posi-Flo II PTM100
    Pump: Ultra-Flow of unknown model, the only marking I see is "Label #988719400"
    Motor: Emerson K63CXESE-4792, but there were other manufacturers' motors dying with exactly the same symptom: bad bearings.

    Quote Originally Posted by jblizzle
    Is the current jet stength acceptible to you or would you want to change it?
    Good as it is.

    Quote Originally Posted by jblizzle
    The Superflo is a smaller pump than the Whisperflo ... at the same HP, they move very different amounts of water. So with more information about the current setup, we can offer a suggestion on a suitable replacement.
    Two most important factors are, in no particular order: reliability and *total* cost of ownership (i.e. it's just fine if it costs more out of the pocket but breaks even before its life span is over).

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    Mod Squad jblizzle's Avatar
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    Re: Pump sizing for the spa

    Yes, low speed will always be fine for filtering. I will have to see if I can figure out the performances curves for the pump you have to determine if it is in the Superflo or Whisperflo class of pump to then recommend a similar pump on high speed.

    Do you get rebates for VS pumps? How much is your electricity? The VS pumps can be run at lower speeds for filtering to save more money on electricity than a 2-speed on low, but if your power is not expensive, you may never save enough power to offset the extra cost of the VS pump, especially if you do not get a rebate. Of course there is the advantage that you could dial in the amount of flow you want for the jets.
    Jason, TFP Moderator
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    Mod Squad jblizzle's Avatar
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    Re: Pump sizing for the spa

    Looks like that is an old Pentair Ultra-flow. Assuming the motor is a 1.5 full rated (with a 1.47 SF), I found a performace curve that put the old pump at 110 GPM @ 40 feet and 90 GPM @ 60 feet which puts it in the Whisperflo class of pumps

    It falls between the WFDS-4 (1HP FR) and the WFDS-6 (1.5HP FR) performance curves. Given the smaller filter (might consider increasing this) and plumbing, I think I would suggest the WFDS-4 (or -26 is identical). The performance curve is a little lower (100 GPM @ 40 feet and 77 @ 60 feet), but it will be cheaper to buy and run and likely should feel similar. You could adjust the spa jet size to change the feel and a larger filter would also increase the flow.

    For reference, the WFDS-6 (-28) does 123 GPM @ 40 feet and 100 GPM @ 60 feet

    Out of curiosity, what kind of pressures are you seeing on the filter? Given the limitation of the 1.5" plumbing, I am guessing you are operating at > 60 feet of head
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Pump sizing for the spa

    Quote Originally Posted by jblizzle
    Yes, low speed will always be fine for filtering. I will have to see if I can figure out the performances curves for the pump you have to determine if it is in the Superflo or Whisperflo class of pump to then recommend a similar pump on high speed.
    The idea was to run the pump on low speed for filtering (especially given the fact that filters are more effective at lower flow rates) and switch it on to high only when jets are needed.

    Quote Originally Posted by jblizzle
    Do you get rebates for VS pumps?
    Yep, "up to" $200. 11018 is about $150 more expensive than 340043, so it's worth it.

    Quote Originally Posted by jblizzle
    How much is your electricity?
    Somewhere between $0.06 and $0.30 per kWh, my electric company makes it very difficult to figure it out.

    Quote Originally Posted by jblizzle
    The VS pumps can be run at lower speeds for filtering to save more money on electricity than a 2-speed on low, but if your power is not expensive, you may never save enough power to offset the extra cost of the VS pump, especially if you do not get a rebate. Of course there is the advantage that you could dial in the amount of flow you want for the jets.
    ...plus the extra bells and whistles like remote monitoring - I wonder at what line these start?

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    Mod Squad jblizzle's Avatar
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    Re: Pump sizing for the spa

    The 340043 is a Superflo and a much smaller pump that you currently have.
    The 11522 is the WFDS-6 which is a little bigger than your current pump.
    The WFDS-4 I was suggsting is the 011486.

    But sounds like with the rebate, the Intellifo might be the way to go.
    Jason, TFP Moderator
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    Re: Pump sizing for the spa

    Quote Originally Posted by jblizzle
    Out of curiosity, what kind of pressures are you seeing on the filter? Given the limitation of the 1.5" plumbing, I am guessing you are operating at > 60 feet of head
    About 25-30 PSI.

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    Re: Pump sizing for the spa

    So you are running the floor and the skimmer ... both are run to the pump separately in 1.5" plumbing? Is the pad plumbing also all 1.5" or 2"? {I would suggest using 2" is you replace any}

    Regardless, the pressure is high like I expected. Likely your headloss is > 70 feet and your flow is < 70 GPM ... this is based on a tool developed by a member here ... it also points out the some of the data on Pentair's site is not correct in the curves.

    So, I would suggest the WFDS-6 might be a good comparable pump to what you have or the intelliflo if the prices are comparable.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Pump sizing for the spa

    Quote Originally Posted by jblizzle
    The 340043 is a Superflo and a much smaller pump that you currently have.
    /me sigh... Live, learn, die stupid Looked almost identical to me. Granted, I didn't think of finding performance curves for the current motor.

    Quote Originally Posted by jblizzle
    The 11522 is the WFDS-6 which is a little bigger than your current pump.
    The WFDS-4 I was suggsting is the 011486.

    But sounds like with the rebate, the Intellifo might be the way to go.
    ...especially coupled with the fact that it needs to run all year with ambient temperature ranges 32F-70F in the winter and 90F-120F in the summer

    Now, the question is - which IntelliFlo is the right one? I was initially considering 011018, but now that I'm looking, what's the tangible difference between IntelliFlo VF and XF? XF seems to be a newer design, has more features I care about (as in, remote control and monitoring) and is cheaper, but seems to be way overpowered, if their performance curves are correct (http://www.pentairpool.com/pdfs/intellifloxfBR.pdf)?

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    Re: Pump sizing for the spa

    Quote Originally Posted by jblizzle
    So you are running the floor and the skimmer ... both are run to the pump separately in 1.5" plumbing?
    Doesn't look like it. Drain goes to the skimmer, where a divider is used to control which part of water gets from the top and which from the bottom.

    Quote Originally Posted by jblizzle
    Is the pad plumbing also all 1.5" or 2"? {I would suggest using 2" is you replace any}
    I don't know what the pad is, so can't answer this question.

    Unfortunately, replacing any plumbing is out of question at this moment - previous owners poured all the available space with concrete, and I dread even to think how much it will cost to break it and then restore.

    Quote Originally Posted by jblizzle
    Regardless, the pressure is high like I expected.
    That would explain why motors kept dying, no?

    Quote Originally Posted by jblizzle
    Likely your headloss is > 70 feet and your flow is < 70 GPM ... this is based on a tool developed by a member here ... it also points out the some of the data on Pentair's site is not correct in the curves.
    Which one is incorrect?

    Quote Originally Posted by jblizzle
    So, I would suggest the WFDS-6 might be a good comparable pump to what you have or the intelliflo if the prices are comparable.
    IntelliFlo looks better and better.

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    Re: Pump sizing for the spa

    The high pressure has no influence on the life of the motor.
    A lot of the Pentair info is incorrect, I do not know what specficially. The data used in the tool tha Mark developed I think uses information obtained from 3rd party testing.

    The bearing should not go bad every year. They only go bad if they get wet, so ensure that the shaft seal is not leaking water at all and maybe you need to add some protection of the motor from the elements (like a motor cover or a roof over all the equipment).
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Pump sizing for the spa

    Quote Originally Posted by jblizzle
    The high pressure has no influence on the life of the motor.
    check
    Quote Originally Posted by jblizzle
    The bearing should not go bad every year. They only go bad if they get wet, so ensure that the shaft seal is not leaking water at all and maybe you need to add some protection of the motor from the elements (like a motor cover or a roof over all the equipment).
    Indeed, it rains pretty hard here, but there are two things that bother me as far as wet factor is concerned - one, there is a pool pump with 1HP motor that worked for 10+ years without skipping a beat, less than 10ft away, and two, if I remember it right, bearings were dying before the wet season was starting - but then again, it was getting extremely hot by that time, that may have contributed a lot. But then again, 10+ years for the other motor...

    Let's just leave this as a mystery - if this one dies within a year, then I'll be laughing hard

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    Re: Pump sizing for the spa

    We can fall back on the ol' ... things are not made like they used to be. There is another thread talking about pump life and someone mentioned the grease being used now may be cheap and contributing to the problem.
    Jason, TFP Moderator
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  15. Back To Top    #15

    Re: Pump sizing for the spa

    So, to summarize - which IntelliFlo?

    VF seems expensive. Granted, flow control is cool, but is it really worth that much?

    i1 looks like a "restricted" edition of VS, to satisfy California and Arizona compliance rules. No go.

    VS and XF look the same to the naked eye, feature wise, except that VS is an aging design, and XF, while newer and allegedly more efficient, seems pretty overpowered for this installation. Is it?

    Jason, thank you for your time, I really appreciate your help.

  16. Back To Top    #16
    Mod Squad jblizzle's Avatar
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    Re: Pump sizing for the spa

    Sounds like you got it. Get the cheapest of the VF, VS or XF. They are all overkill, but no other better options besides a two speed motor.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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