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Thread: Need technical pump help- Sizing, electrical use, etc.

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    Need technical pump help- Sizing, electrical use, etc.

    My 21,200 IG vinyl pool has this 1 hp above ground pool pump, the Pentair Dynamo.

    My filter is the Pac-fab (now Pentair) FNSP 36.

    I got pool stored several years ago with an overpriced AG pump that will not pull fully from my main drain.

    Although the pump seems to work adequately (I currently run it 24 hours but would like to get away from this) I'm wondering if an upgrade would both use less electricity and let me run it less for the same turnover. I'm considering this one, the Eliminator.

    All of the links have the flow charts, etc. My pool is 16' x 32' and slopes from the 3.5' shallow end to the 8' deep end. The skimmer line is about 1' below my pool deck and 20' from the pump. The main drain line is about 9' below my pool deck and 18' from the pump. All plumbing is 1.5". You can see the filter/pump area in the top left corner of this pic, with the vac hose plugged into the skimmer line and the main drain being centered below the diving board-




    If someone could work their pool pump calculating technical magic, that would be fantastic

    Thanks in advance

  2. Back To Top    #2
    mas985's Avatar
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    Rangeball,

    The best way to save electrical cost is with a two speed or multi-speed pump. At the lower speeds they use much less electricity but don't lose as much flow so you end up better off. I explain some of the benifits in this post post as well as how to pick the right pump.

    A couple of observations:

    Your filter is large enough to handle up to 90 GPM so that will probably not be a factor.
    Given the distance to the pool, I suspect you don't have too much head loss although 1.5" line will increase it some. Most AG pumps are on the low head side. This may still work for you since you are so close to the pool.

    First we need to determine what the performance of the current pump is and then we can look at options.

    And next some questions:

    Is the Dynamo a two speed pump and is that why you are running for 24 hours?
    What is the service factor of the pump? Should be on the label somewhere.
    What is the current filter pressure?
    Is the pump loud?
    Does the pump have trouble priming?
    Why the Elminator as a new pump? (there are more effficient choices but can be more $$)
    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

  3. Back To Top    #3
    Quote Originally Posted by mas985
    Rangeball,

    The best way to save electrical cost is with a two speed or multi-speed pump. At the lower speeds they use much less electricity but don't lose as much flow so you end up better off. I explain some of the benifits in this post post as well as how to pick the right pump.
    Thanks for jumping in. I was hoping you'd show up I'd read that post before, and in fact spent quite a bit of time re-reading it again after I posted this thread. Your quick factor/formulat (x3) for calculating head was very helpful. Using it I estimate my head to be right at 30.

    A couple of observations:

    Your filter is large enough to handle up to 90 GPM so that will probably not be a factor.
    That's what I was thinking. I actually could have probably gotten by with the next size down, but this is the one the pool store installed 5 years ago. It's still working great, so I don't plan to change it until it goes down.

    Given the distance to the pool, I suspect you don't have too much head loss although 1.5" line will increase it some. Most AG pumps are on the low head side. This may still work for you since you are so close to the pool.
    This is good to read, hopefully I am close to 30 on head loss, which gets greater flow with most pumps I've looked at.

    First we need to determine what the performance of the current pump is and then we can look at options.
    How do we do this?

    And next some questions:Is the Dynamo a two speed pump and is that why you are running for 24 hours?
    No, the pool came with the house when we bought it 13 years ago. I knew nothing about pools, and relied heavily on the pool store. They told me best be was to run 24 hours to avoid problems. I've always done it, but after finding pool forum awhile back have had the nagging urge to cut back on run time, but have hestitated given the sold me an AG pump. However, using your formula and 30 for head loss per the manufactures chart I should be getting 70 gpm which gives me a 5 hour turnover rate, or almost 5 turnovers a day. Probably adequate

    What is the service factor of the pump? Should be on the label somewhere.
    I'm not at home so will have to add this later. Is it something that's like to be in their tech stuff? I'll look at their site and see. Nope, not there.

    What is the current filter pressure?
    10 psi. This is what it runs at with a fresh start up. When it goes up by 10 I backwash, break the filter down and clean it (side note, I use to have to do this very frequently. Since going BBB, I do it at start up, once or so mid season, and at close.)

    Is the pump loud?
    I have nothing to compare it to. I would consider it loud, but I don't think it's from over working, if this is where you're headed.

    Does the pump have trouble priming?
    It's a gravity flow pump for AG pools. If I fill the pot making sure to allow water to also fill the skimmer line as much as possible, close the main drain line and turn it on, it usually has full prime within 30 seconds. Once running, I can slowly open the main drain and it will pull as well. If I try to prime with the main drain open and the skimmer line close, no go.

    Why the Elminator as a new pump? (there are more effficient choices but can be more $$)
    Mostly due to $$. My dad wants me to order him the chlorease SWG for his AG pool, and they had the best price for the new model. I noticed they sell pumps as well, so I checked them out. They say the eliminator is made by the #1 (whatever this means) pool equipment manufacturer and it's priced right at $260ish for the 3/4 hp model. Looking at this, I may even be ok with a 1/2 hp motor, although if I ever add anything (like a solar heater) I may be on the bubble as far as head goes, I don't know. I figure I'm spending about $90ish monthly to run my pump 24 hours daily. If I were to switch to 12 hrs and assuming no problems occured doing so, I'm at $45. If I can use less electricity with a more efficient, smaller or both motor and go to even perhaps 8 hours to get the same flow (looks to be a real possiblity as the eliminater 3/4 hp has 90 gpm at 30 head, 80 gpm at 40 and still 70 gmp at 50, where the dynamo does 70/50/20 at the same head), I figure I'm probably down below $30. I can live with this, and at the price of the eliminator it will pay for itself the first season (not computing simply running my current pump less time).
    When I looked at 2 speed pumps last year, I seem to recall the were considerably more $$, and although the payback would be greater, it would take quite a bit more time to realize it do to the higher cost.

  4. Back To Top    #4
    mas985's Avatar
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    The first thing you can try is to drop the run time to at least 10 hours. 2 turnovers should be more than enough. I only run my pump 1.5 turnovers and the pool is very clean.

    If you do decide on a new pump go with the lowest HP two speed pump you can find and you will save even more money by running on low speed most of the time. You will pay off the additional cost very quickly.

    To check efficiencies between the new pump and old, I need to compare the BHP of each pump against it's head curve which is why I needed the service factor of your old pump.

    I am not that familiar with AG pumps so I have to do some aproximations unless you know what the current draw of the pump is.
    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

  5. Back To Top    #5
    Quote Originally Posted by mas985
    The first thing you can try is to drop the run time to at least 10 hours. 2 turnovers should be more than enough. I only run my pump 1.5 turnovers and the pool is very clean.
    The one thing that is holding me back is that I assume 1/2 the stuff that hits the skimmer basket will end up on the bottom of the pool leading to more frequent vacuuming. Of course saving at least $45 monthly is very attractive. I have an outdoor intermatic timer I use for Christmas lights, I may hook it up and just see how it goes.

    If you do decide on a new pump go with the lowest HP two speed pump you can find and you will save even more money by running on low speed most of the time. You will pay off the additional cost very quickly.
    You think I'd be ok with a 1/2 hp motor? I'll look around and see what the price differences are.

    To check efficiencies between the new pump and old, I need to compare the BHP of each pump against it's head curve which is why I needed the service factor of your old pump.
    Ok, I'll add it later.

    I am not that familiar with AG pumps so I have to do some aproximations unless you know what the current draw of the pump is.
    12 amps is ringing a bell, but I can't find it anywhere on the pentair site. I may have gotten it off the motor label. If need be, I'll have my brother the union election put a gauge on it and get a real world number. I'll add this asap as well.

  6. Back To Top    #6
    What about this one-

    Pentair Whisper flow 3/4 hp 2 speed.

    It's only $100 more than the elinimator, has the same 60hz energy efficiency rating and I called them to verify that it is indeed the 2 speed version they are selling.

    Checking the charts, at the same head it produces the same gpm flow as the eliminator. I guess the question then is how much will the whisperflow save on electricity at low flow over the eliminator at high flow? Would I have to run the low flow longer to get the same turnover?

  7. Back To Top    #7
    Mark, I had occasion to stop by home so I took a look at my motor label. I saw nothing that says "service factor".

    What exactly should I be looking for? If I need to I'll call Pentair and ask their techs...

  8. Back To Top    #8
    Was doing some reading, and found this pump energy use calculator-

    http://www.pentairpool.com/pool_pump_calc/index.htm

    During the summer I pay .08618 per KWH (which is lower than the lowest input available on the calculator, so I used the lowest which is .10). Running my pump 24 hours at .10 gives me a monthly cost of $114 with about 5 turnovers. Going to 7 hours to get over 1 turnover daily drops the monthly cost to $33. Basically I'm wasting $81 monthly, which I will rectify post haste

    Plugging in a .75 hp motor only saves me $3.60 per month. At that rate it would take me 6 years to get payback on the eliminator pump, over 8 on the whisperflow.

    Assuming I'm understanding things correctly.

  9. Back To Top    #9
    mas985's Avatar
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    I think you have a good handle on things. The Whisperflow is a very good and efficient pump which will give you higher flow rates than you have now with probably nearly the same energy use as you current pump so you can decrease run time even further.

    However, the problem with their calculator is that it compares high efficiency pumps which your 1 HP is probably not. So going to a 3/4 HP high efficiency pump may give you much more flow for the energy consumption (GPM/Watt) than your current pump. This will allow you to save even more money that is not taken into account with their calculator. Not all 1 HP pumps are equal.

    I happen to have some data for the Whisperflow and modeled your plumbing (60 GPM @ 30 feet) as an approximation. THe 3/4 HP full rated Whisperflow will generate about 75 GPM at 45 feet of head. Head loss goes up with flow rates and the 3/4 HP Whisperflow is actually more powerful than your pump but may not draw much more energy.

    The 3/4 HP Whisperflow draws less than 1300 watts of power so for one turnover per day:

    4.7 hours/day x 1.3 kwh x 30 x $.08618 / kwh = $15.80/Month

    You can probably reduce than by another 30% with a two speed. Low speed uses about 500 watts but you need to double the run time.

    9.4 hours/day x 0.5 kwh x 30 x $.08618 / kwh = $12.15/Month

    Not much more saving but it can add up if you are doing two turnovers per day.

    BTW, the link to the Whisperflow is for a single speed pump. They do not have the two speed version.

    Check here for two speed pricing:

    http://www.poolplaza.com/C-WhisperFlo-Pump.html

    One more thing, I would stay away from 1/2 HP pumps in general since they tend to be the same motor as the 3/4 HP, just a higher service factor and lower load impeller which underloads the motor and the efficiency is not as good.
    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

  10. Back To Top    #10
    Quote Originally Posted by mas985
    I think you have a good handle on things. The Whisperflow is a very good and efficient pump which will give you higher flow rates than you have now with probably nearly the same energy use as you current pump so you can decrease run time even further.
    Thanks Mark. I put the timer on last night, and set it to run 7 hours from 9 pm to 4 am. So far so good

    However, the problem with their calculator is that it compares high efficiency pumps which your 1 HP is probably not. So going to a 3/4 HP high efficiency pump may give you much more flow for the energy consumption (GPM/Watt) than your current pump. This will allow you to save even more money that is not taken into account with their calculator. Not all 1 HP pumps are equal.
    I figured that when I was using it. I knew it wouldn't be exact but would give an approximation.

    I happen to have some data for the Whisperflow and modeled your plumbing (60 GPM @ 30 feet) as an approximation. THe 3/4 HP full rated Whisperflow will generate about 75 GPM at 45 feet of head. Head loss goes up with flow rates and the 3/4 HP Whisperflow is actually more powerful than your pump but may not draw much more energy.

    The 3/4 HP Whisperflow draws less than 1300 watts of power so for one turnover per day:

    4.7 hours/day x 1.3 kwh x 30 x $.08618 / kwh = $15.80/Month

    You can probably reduce than by another 30% with a two speed. Low speed uses about 500 watts but you need to double the run time.

    9.4 hours/day x 0.5 kwh x 30 x $.08618 / kwh = $12.15/Month

    Not much more saving but it can add up if you are doing two turnovers per day.
    Thanks for this. Looks like for one turn over it would take almost 7 years to get the additional cost of the 2 speed pump back in electricity savings. Almost 3.5 years at 2 turnovers. Sounds like a long time, but the pump should easily last this long and the initial investment is only about $150 more (from your link below compared to the eliminator in my first post), so why not.

    BTW, the link to the Whisperflow is for a single speed pump. They do not have the two speed version.

    Check here for two speed pricing:

    http://www.poolplaza.com/C-WhisperFlo-Pump.html
    I came to the same conclusion, no matter what the guy on the phone said. They clearly indicate the Pentair's model # that is for their single speed pumps. The good news is that the link you provided is the 2 speed, and only about $50 more than the other guy's one speed

    One more thing, I would stay away from 1/2 HP pumps in general since they tend to be the same motor as the 3/4 HP, just a higher service factor and lower load impeller which underloads the motor and the efficiency is not as good.
    Good to know.

    Mark, I really appreciate you taking the time to help me understand all of this. I think at this point I've decided to keep my current AG pump until it gives up the ghost, then replace with one of the two options discussed above, probably the 2 speed.

    Thanks a bunch

  11. Back To Top    #11
    Mark, one more question if you don't mind...

    When I was going through all the above, I had found something that said the max flow through a 1.5" line was 42 gpm. Since I have both a skimmer and main drain lines, each 1.5", I had assumed they would provide me with 84 gpm, the total flow of the two.

    However over the weekend it hit me; They merge into one 1.5" pipe right at the pump inlet.

    Does this knock me back down to the 42 gpm max?

  12. Back To Top    #12
    mas985's Avatar
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    There is no such thing as a maximum flow rate for PVC pipe. You will see many web sites with these limits as well as people on this forum talk about these limits but they are not absolute they are only recommendations. The pipe itself will cannot prevent flow rates to go higher. In fact, a lot of pools exceed the recommendations and most with 1.5" plumbing do without any ill effects. So you can pretty much ignore those limits.

    If you want to determine flow rates you need to find out your head loss via one of the methods described in the sticky.
    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

  13. Back To Top    #13
    Thanks, that satisfies me

    I'll quit worrying about it now

  14. Back To Top    #14
    Mark, I was looking at this stuff again today, and have questions if you don't mind.

    My filter has a max GPM of 90. The pentair 3/4 HP whisperflo at 30 head (per our calculations above for my pool) has 90 GPM flow. This puts me right on the border of too much for my filter.

    You said something above about dynamic head loss increasing as flow increases, but I don't see any way to adjust for this in the head loss calculations in your "lost your head" sticky. How do I figure what my head is likely to be so I can get a better idea of what the 3/4 hp whisperflow is likely to give me for GPM?

    If I simply install the 3/4 WF, is my filter pressure likely to increase? If yes, I guess this is where the calculation would handle the increase (3 * filter pressure) but I won't know FP until the pump is actually installed, a catch 22 or sorts...

  15. Back To Top    #15
    mas985's Avatar
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    With 1.5" plumbing, my guess is you probably have closer to 40' of head than 30'. 3 * filter PSI is pretty good for 2.5/2.0" plumbing while 4 * PSI is closer to 1.5" plumbing.

    A 3/4 HP Whisperflo is a more powerful pump so my guess from a head model I have and your original 10 PSI filter pressure is that the WF will have the following operational parameters with your plumbing:

    GPM 53 GPM @ 66 feet of head
    Filter PSI ~ 16 PSI

    This is pretty rough estimate because there are many unknowns and I am going by what pools I have modeled in the past. However, I don't think you will even get close to 90 GPM with the Whisperflo so I would not worry about that.

    BTW,

    Head loss changes by this formula:

    New Head Loss = Old Head Loss * (New GPM / Old GPM) ^ 1.852

    What you can do is plot this as a curve overlaying the pump's head curve and see where they intersect but I did that already for you above.

    Also, your plumbing is likely to between scenario A and B in the second sticky post so you can look that up if you need to.
    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

  16. Back To Top    #16
    Interesting.

    However, these new figures change everything we discussed above regarding turnover and potential energy savings.

    If I am at 30 for DHL with my current pump (using filter pressure * 3), I am getting 70 gpm or a turnover every 5 hours. At 90 gpm the WF is rated at with the same 30 DHL, I would turn the pool over in 4 hours, allowing for electrical savings, especially at 2 turnovers daily.

    However using the new adjusted figures if my DHL jumps to 66 if I install the 3/4 hp WF and the flow is only 53 GPM, my turnover rate is 6.6 hours, negating any potential energy savings and possibly costing me more to operate, as I doubt the WF is that much more efficient than the Dynamo I now have.

    Now I'm totally confused all over again...

  17. Back To Top    #17
    JasonLion's Avatar
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    Assuming I am following everything correctly, I believe that they key point is that you don't know your current total dynamic head and are just guessing. I believe mas985 said he though it was higher than your estimate. His more recent calculations are based on different assumptions about your current dynamic head and flow rate, so they can't be compared directly to your old numbers.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  18. Back To Top    #18
    Quote Originally Posted by mas985
    With 1.5" plumbing, my guess is you probably have closer to 40' of head than 30'. 3 * filter PSI is pretty good for 2.5/2.0" plumbing while 4 * PSI is closer to 1.5" plumbing.

    I had missed this.

    At 40 DHL my current 1 hp Dynamo flows at 50 gpm. Theoretically I need to measure it at some point. Which would be a turnover every 7 hours.

  19. Back To Top    #19
    JasonLion's Avatar
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    You can get a flow meter for under $100. See for example this site. You need to have a couple of feet (pipe diameter * 14) of horizontal (or vertical with a different model) pipe with no other fittings to install the meter.

    Pools should come with flow meters!
    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

  20. Back To Top    #20
    mas985's Avatar
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    Rangeball,

    Jason is correct in that without additional measurements it is pretty much guess work but I suspect that you are closer to 40 feet of head than 30 feet of head but again it is based on how other pools operate.

    From the pump curve, I read the Dynamo at about 45 GPM @ 40 ft. while the Whisperflo will be about 53 GPM @ 66 ft. and I believe that the Whisperflo draws less current than your current pump. So your total power savings is close to 20% which about as much as can expect when upgrading to a high efficiency pump.

    You will get much more benefit on low speed where the energy use is about 1/3 while flow rates are only 1/2.

    So at low speed with the Whisperflo, you are likely to save close to 50% over your current pump.
    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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