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Advice on a pump/plumbing circuit'

  1. Sep 3, 2007 #1

    DaveC426913

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    advice on a pump/plumbing "circuit'

    I have an above-ground pool with a 3/4hp pump - enough to operate the filter.

    I want to install a solar heating loop in the system. (passive array of water pipes that pass pool water and soak up heat). It has dozens of feet of pipe and a head of as much as 8 feet. Clearly, my 3/4hp pump will be inadequate to keep the same throughput.

    The obvious solution is to upgrade the pump, perhaps to a 1 1/4hp or whatever. But I have this other 3/4hp pump lying around doing nothing. It would easily drive the solar panel.

    My question: Seeing as there is noly one inlet and one outlet to the pool, how can I hook up both pumps? Do I hook them up in "series" or do I hook them up "in perallel"?

    If in series, I worry that one's through put is differnt thant he other, and one will either "suck the other dry" or overload it. If in parallel, so I'd have to have a Y-junction at inlet and outlet. But now I've got unfiltered water passing through my solar plumbing. So I could split off the solar plumbing after the filter - but now I'm back to series.

    Maybe I need a series circuit with some sort of bypass?


    Advice?
     
  2. jcsd
  3. Sep 3, 2007 #2

    turbo

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    Intuitively, I would install the pumps in series with a load (the heater array) located between them. In the case that you do not want to heat the water at times, you should install a bypass around the heater array and the new pump only use the one original pump to operate the filter.
     
    Last edited: Sep 3, 2007
  4. Sep 3, 2007 #3

    DaveC426913

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    Hm. I can see how putting a load between them would work in an electrical circuit. Does it have the same effect in a water circuit? I'd worry about the pump #1 "pushing" on pump #2 - or whatever the term is.

    Also, I think the heater array would go after the filter so that the heater is not at risk of fouling.
     
    Last edited: Sep 3, 2007
  5. Sep 3, 2007 #4

    turbo

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    Locating the heater after the filter is probably a good idea. I have not built a system with two pumps in series, Dave. It just seems intuitive that putting a load (head to overcome) between the two pumps would isolate them from one another a bit and allow them to share the load imposed by the heater. I could be 100% wrong about this, so it will be nice to hear the opinions of an engineer who works with pumps/hydraulics.
     
  6. Sep 3, 2007 #5

    russ_watters

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    Pumped water works just like an electrical circuit. If you put the two pumps in series it is like putting two batteries in series and the pressure is additive. In parallel, flow rate is additive (though the system resistance obviously makes that a little more complicated...). Anyway, if one gives you a good flow rate when you have less head loss, adding head loss would imply putting them in series to increase the pressure without increasing the flow.

    And don't worry about one pump sucking the other dry. They'd have to be vastly different in size for that to happen. You can look for pump curves on these pumps to help you figure this stuff out, too.

    Oh, and for location, yes, you want everything after the filter when you are pulling water from a pool.
     
  7. Sep 3, 2007 #6

    DaveC426913

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    Gee you know, as I work up the schematic, including the 4 way valve, another thought occurs to me. The four way valve has FILTER, WASTE, BACKWASH ans RECIRC (which simply bypasses the filter). I could possibly only run the heater when on recirc, bypassing the filter. One pump would suffice to run either filter or pump - just not simultaneously...Hmm. Only problem there is the manual switching every day. And that's not a small problem.
     
  8. Sep 3, 2007 #7

    DaveC426913

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    Hm. ?maybve I will do it. BTW, the pumps are quite similar.

    Everything except the first pump of course, The filter works by pressure, not by vacuum.


    So, it would be

    outlet > pump1 > 4-way switch > filter > pump2 > head > solar heater > fall > inlet

    Hm.
     
  9. Sep 3, 2007 #8

    DaveC426913

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    : slaps self on forehead :

    This other pump is a hottub pump.

    : slaps self on forehead again :

    It is the type of pump that is designed to heat water without need of a separate heater. (Frankly, I don't know how it does this - some sort of baffle system). It is so efficeint at doing so that it can heat a hottub to 104F and needs a circuit to shut it off so that the water temp doesn't go higher.

    I don't need the solar panel at all!
     
  10. Sep 3, 2007 #9
    The hot tub pump would have to have an electric heating element in it somewhere.
    It will cost a small fortune to heat a regular pool with a hot tub heater/pump combo.

    Since it is an above ground pool the easiest although maybe not the most aesthetic way is to run the piping for solar separately. Running them in close to the ladder will tend to hide them. You could also possibly get by with a much smaller pump for the solar this way. Do you have any specs with your solar panels?
     
  11. Sep 3, 2007 #10

    DaveC426913

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    I don't think so. I think it works by heat transfer and by friction.

    Depends on your assumptions. I only need to raise the temperature of the pool one or two degrees.
     
  12. Sep 3, 2007 #11
    You can do that by putting a solar blanket on it.
     
  13. Sep 3, 2007 #12

    DaveC426913

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    ahem.

    One or two more degrees. Than I get with the solar blanket. Which btw isn't very effective in the shade.
     
  14. Sep 3, 2007 #13
    Raising the temperature of that much water even 1 or 2 degrees electrically would still be costly. And then to maintain that temp.???
    You can easily estimate how much energy it would take to raise that volume of water 1deg. C using some math and some conversion calculators.

    I have worked with booster pumps on long pipelines before and my suggestion to you would filter>solar heater>2nd pump to keep pressure whereit needs to be. You can always put a dump gate(valve) on the 2nd pump as conditions change to get the optimum performance.

    I still agree with edward though that the solar blanket is the way to go, unless this is some kind of hobby/project and you like tinkering. (like me).

    Jim
     
  15. Sep 4, 2007 #14

    DaveC426913

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    My current pump runs many hours in a day. Another pump will be likewise.

    Apparently I'm not making myself clear. I have a solar blanket. It does its job as best it can. It is not quite enough.

    And yes, I tend to tinker.
     
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