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Evac Tube Array - Series or Parallel ?

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  • Evac Tube Array - Series or Parallel ?

    Hi all,

    My small space heating project at the cabin involves three X 20 Tube hot water panels which will heat a small 10 gallon electric hot water tank with a 1500 watt element for backup/assistance (Generator).
    From the tank, I have 2 wall radiators to dissipate heat into the room. This system augments an electric baseboard system and should help cut electricity costs.
    The combined BTU/hr rating of the H2O solar array is 7000 (on a nice sunny day).
    What is the rule of thumb when deciding whether to pipe the H2O panels in Series or Parallel ?
    (or does it even matter with a system this small???)

    Thanks
    veggie

  • #2
    Well, there are potential concerns with flow resistance and the pump capability which might argue for either series or parallel, depending on your pump.

    But I would first apply the following rule of thumb test:

    If one panel does not get the water hot enough for your intended use (at a very low flow rate) then put two panels in series.
    If one panel gives you hot enough water out, but cannot keep up with the usage, put the panels in parallel.

    Analogous to voltage and current when deciding whether to put PV panels in parallel or in series.

    If that rule does not give you a good answer, then look at other criteria such as flow rate and pressure.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      One bit if additional info....

      My insulated tubing is 3/4" and the estimated flow rate through the system is 3gmp


      Veggie

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      • #4
        Originally posted by veggie View Post
        One bit if additional info....

        My insulated tubing is 3/4" and the estimated flow rate through the system is 3gmp


        Veggie
        What is the dia. of the tubing in the panels and what is the panel length ?

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        • #5
          Pipe them parallel and install a ball valve on the outlet of the pump so that you can adjust the flow rate to the panels. You will only need about 1 gpm to the radiators to get a 20 degree delta t water temp through them.

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          • #6
            Originally posted by J.P.M. View Post
            What is the dia. of the tubing in the panels and what is the panel length ?
            The connections at the panel headers is 3/4 npt.
            These are evacuated tubes. (not copper tube panels).
            The panels are 20 tube units and the header is ~60" long.

            veggie

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            • #7
              For evacuated tube panels, the only flow resistance is in the manifold (header) and in the interconnecting pipes. The only remaining problem is that you still want to reduce the flow rate to the point where the output temperature is high enough to provide useful heat. What that temperature is depends on whether you have a pool system (low is OK), a space heating application (the needed temperature depends on the indoor radiator design) or domestic hot water (hot enough to meet your needs without supplemental heating if possible.)
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

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