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Thread: Pool pump and dynamic head question

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    Pool pump and dynamic head question

    I am hopeful I have miss calculated the dynamic head of my pump system. I recently moved a solar heater from ground level up to the roof. I have an Intex pool with a 1500 gph pump/filter combo ( 25 gpm). We think it calculates to a 1/3 hp pump (110v x 2.1A x 0.001somthing). I have approximately 80' of 1.5" PVC pipe up to the heater and 80' return. There is a 20' rise from lowest point in the system to the highest. I calculated a head loss of 3.8/100 foot of pipe. 7.5/90 elbow of which I have 25 (yes way more than I should have but I moved the system and there was no real direct line to take). 1/foot of rise and 9.3 for the heater this is just a guess taken from a calculator site. This gives me a TDH of 223 which is off the scale of any of the pump flow charts I have looked at. Any help suggestions would be greatly appreciated.

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    Mod Squad jblizzle's Avatar
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    Re: Pool pump and dynamic head question

    Welcome to TFP!

    Calculating head loss is not straightforward and is generally not required. What exactly are you trying to figure out?

    If you are trying to see if your Intex pump is going to work for roof mounted solar, well I am surprised it worked with the solar on the ground those pumps are very weak and I doubt you are getting close to 25gpm.
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    Re: Pool pump and dynamic head question

    Totally agree that friction loss calculations are a pain! And I know zero about Intex pumps. I do, however, note one thing that will improve your calcs. The friction loss through a 90 is expressed as "equivalent feet of pipe". Engineering toolbox online has your 7.5 figure for equivalent length of pipe in feet, and the calculation is...

    7.5/100*3.8 = 0.3 ft of head loss
    (where 7.5 is the friction loss for a normal tight radius 90 elbow, expressed in equivalent length of pipe and 3.8 is the friction loss per 100 feet of 1 1/2" PVC pipe at 25 USGPM)

    Engineering Toolbox PVC fitting friction loss figures are higher than most other sources. You'll find more like 4 equivalent feet of pipe from other sources.

    Don't feel bad about 25 elbows - solar has to go around eaves, perhaps over roof hips, feed and collect from the array, etc. and often has lots of elbows. Reduce all you can, but don't sweat it, and use 45s where it makes sense and looks good (for example around the eaves).

    Now the pump - if it's 1/3 HP and is doing other work as well (circulation and filtration), I can't see how it will be enough. It is likely to be a very low-head pump as well. I have a 1/2 HP dedicated pump for solar, going to a heating array on a single story roof (around 10' lift) and it's decently matched with maybe 20% power to spare. The supplier recommended a 1/3 HP high-head. I went 1/2 HP because I want just enough head to do the job, but then highest flow the array could handle once the lift need was met and head loss from lift returned to zero.

    In a solar heating system, the pump is selected to have more than enough power to get the water up to the highest point. After the water passes the tipping point, and the return pipes refill, lift is negated and the work done for lift returns to zero (water is taken from the pool's water level and then returned to the same level, so no work is done for this purpose). In rooftop, this is what requires a bit more head from the pump. You also need extra power so you can throttle the flow. If you can't throttle, it's pure luck whether or not your vacuum release valve stays closed when the system is running, or pulls air due to the pull or suction created by the force of water going down the pipes back to the pool. The pressure at the tipping point must be high enough to keep positive pressure on the vacuum release valve, until the system shuts off.

    If it were me, I'd consider a dedicated pump or a booster pump. There are experts here that can tell you what's most likely to work for you. I'm new here and there's vastly more knowledgeable people here than me!

    Again, if it were me, and I was doing it as cheap as I could, I would try the existing pump by building the supply side of the piping, with maybe 8 or 10 feet of 1/2" or 3/4" at the end to simulate the panels or tubing. I'd use an elbow and point a foot or so of that pipe straight up, open ended. With the 1/3 HP doing all it's other coincident work, if I could shoot the water up a couple feet into the air beyond the end of the pipe, I'd reckon it might work and finish building. If it doesn't work, then I'd buy the dedicated or booster pump. Once the system fills, overcoming friction loss I think will be less than your 20' lift requirements. i.e. my bet is running will be less of a stretch for your 1/3 HP pump than the lift work. Sorry, but the farmer in me can't help at least trying to make do with what I already have. Downside is that even if it works, it will probably be pushing your 1/3 HP to the limit. But maybe deep down you'd way rather burn that one out and then be "forced" to buy a shiny new variable speed pump anyway??? Haha, food for thought. Have fun with your project!
    12k IG salt; glass beads in plaster; K-2006C, K-1766, CCL, and Aussie 4in1 (HTH); Pentair Eco800 1.2HP VS; Zodiac SWC 1.3 lb/day (25 g/hr); 25" filter recycled glass; OKU solar panels; 1/2 HP solar pump; Rebel (Warrior) pool cleaner; FlowViz; prior pool AG 10k | Read Before Posting to get the best possible advice | ... and this helped me a lot!: TFPC for Beginners

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    Re: Pool pump and dynamic head question

    Dynamic head takes into account the amount of water flowing. I'm assuming your pump can muscle the water up the 20' of rise. Once the pipe is full the elevation change is taken out of the equation (yes it takes energy to pump it up but for practical purposes you get that energy back when it falls back down). So a long story short. 1.5" pvc has a friction loss of 3.8 feet of head per 100 feet of length while moving 25gpm. When you add up all your pipe and fittings and heater you get the equivalent of 364 feet of pvc in your system. That gives you a dynamic head of 13.83 feet which is roughly 7psi on a gauge. None of these numbers take into account your filter restriction.
    Now take that roughly 14 feet of head and go into your pump chart and see what the flow rating is for that. If you are at or over 25 gpm you can still move that much water.


    All the fancy numbers aside since you have already done the plumbing just hook the pump up and turn it on. Measure the outlet pressure of the pump and that will give you the real world effective system head. Convert your discharge psi to feet of head (thank you google) go back to your pump chart and that is a rough estimate of how much water you are moving. Idealy you want that real world number to fall in the middle 1/2 of your pump curve. To far into the left and right 1/4 of the curve and your pump life will be shortened.
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    Re: Pool pump and dynamic head question

    Thanks for the help. I will have to replace the pump it can't push the water even up to the roof. If anyone has any recommendations for a pump I would love to hear them. Since I currently have a pump/filter combo I would need to replace with another.

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    Mod Squad jblizzle's Avatar
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    Re: Pool pump and dynamic head question

    1HP 2-speed Powerflo Matrix

    Might need high speed when running the solar, but can save money running on low speed when not running solar.

    What filter do you have? It might be too small for the larger pump.
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    Re: Pool pump and dynamic head question

    The filter is part of the pump. I have been browsing the sand filter pump combos. Not very many out there biggest one I have seen is 3/4 horse sand pro 75d. A local supply shop said they have a combination unit 3/4 horse with 26 feet of head for 480 CAD. Figure ill stop in there tomorrow and have a look. I cant figure out how much head the sand pro has no matter what i search on line. The data from the user manual online.
    SandPRO 75D (item 4711, 3/4 hp) NOTE: Requires 80 lbs (36.3 kg) not included
    Item U.S. Units Metric Units
    Pump Flow Rate 3,120 GPH 11.8 m3/hr
    Design Flow Rate 1,392 GPH 5.3 m3/hr
    MAX Operating Pressure 40 psi 2.75 Bar
    Filtration Area 1.16 ft2 0.11 m2
    Rated Voltage 110 V 110 V
    Sand Volume 80 lbs 36.3 kg

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    Re: Pool pump and dynamic head question

    Adding your pool info as a signature will help you get the best advice here. The experts will suggest economical solutions that are reliable and durable. To do this, go to Settings (scroll up, it's at the top right of the page). In Settings, scroll down a little and you'll see "Edit Signature" on the left hand side. Include pool volume in US gallons, equipment, etc.
    12k IG salt; glass beads in plaster; K-2006C, K-1766, CCL, and Aussie 4in1 (HTH); Pentair Eco800 1.2HP VS; Zodiac SWC 1.3 lb/day (25 g/hr); 25" filter recycled glass; OKU solar panels; 1/2 HP solar pump; Rebel (Warrior) pool cleaner; FlowViz; prior pool AG 10k | Read Before Posting to get the best possible advice | ... and this helped me a lot!: TFPC for Beginners

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    Mod Squad jblizzle's Avatar
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    Re: Pool pump and dynamic head question

    I am not a fan of the combo units ... You can get a better setup getting the pump and filter separate. You issue is that the tiny Intex pumps were never meant to run a solar system on the roof ... so you likely need to go to a "real" pool pump with more power.
    Jason, TFP Moderator
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    Re: Pool pump and dynamic head question

    I have given up on the combination units. I am now looking at pairing a Hayward 1 HP Power Flo Matrix with a Hayward 21 inch Sand Filter. Pool is 16 x 48 approximately 6000 gal.
    Intex 16x48

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    Mod Squad jblizzle's Avatar
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    Re: Pool pump and dynamic head question

    That would be a great setup ... and could easily handle a larger pool if you ever upgrade
    Jason, TFP Moderator
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