guidance designing a drawback system

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  • badwithusernames
    Member
    • Jun 2020
    • 44

    guidance designing a drawback system

    I have some of the components for a drainback system, and would like to install it to preheat the water that feeds my modulating natural gas combi boiler. Is there anywhere that has info on needed pump sizes and speeds, recommended controllers, and general rules for pipe sizes/ layout to insure it works the best it can?
    What I have so far:
    2) 4'x6'6" SolarH2ot panels that I picked up new, but old stock.
    1) 50 gallon stainless indirect heater tank.
    I did pick up some extra Ironridge racking to mount it, and I have a spare Taco 007e pump. It's a 120V pump, but they're super efficient.
    Not looking to squeeze everything out of this system, just to make a dent in my gas usage.
    Thanks in advance.
    SD
  • J.P.M.
    Solar Fanatic
    • Aug 2013
    • 14925

    #2
    There are lots of good sources. Best source I know of that'll give correct, thorough and pretty much complete information on the design of solar thermal DHW systems and probably a lot more about solar energy you don't give a hoot about is Duffie & Beckman's "Solar Engineering of Thermal processes". Lots of things to consider you probably aren't aware of - probably too much for a forum post - but you won't go wrong by a read/study before you attempt a design.

    A close second in terms of usefulness: " Solar Thermal Engineering", by Peter J. Lunde, P.E. Lunde is more nuts/bolts about design but still very thorough.

    One more: "Solar Heating and Cooling", Jan Kreider and Frank Kreith. See chap. 6 on solar water heating in particular. Kreith is one of the world's best known heat transfer gurus and highly published. I've met with him in the past when I was in the process engineering business as well as at a couple of solar energy congresses.

    One thing of many: Depending on your location, without some planning, either a 50 gal. tank may be too small for A 50 ft.^2 of collector or a ~ 50 ft/^2 of net collector area may be too much collector for a 50 gal. tank.

    Another comment: Solar thermal and solar PV are different animals. Don't assume the same rules apply.

    Aside from all that, and FYI only, Duffie & Beckman also has one of the best and most concise primers (only 26 pages, chap. 23, but all meat) on the basics of PV design I've ever seen.
    Last edited by J.P.M.; 09-02-2020, 12:04 PM.

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    • badwithusernames
      Member
      • Jun 2020
      • 44

      #3
      Originally posted by J.P.M.

      One thing of many: Depending on your location, without some planning, either a 50 gal. tank may be too small for A 50 ft.^2 of collector or a ~ 50 ft/^2 of net collector area may be too much collector for a 50 gal. tank.

      Another comment: Solar thermal and solar PV are different animals. Don't assume the same rules apply.
      JPM, the point you make is exactly why I am looking for info.
      Finding all of the info that explores the relation between system volume/ pump volume/ location, etc is what I'm after. I'd rather read for several months before starting (and probably will) than rush into something that doesn't work right or has a catastrophic failure.
      Thank you for the suggestions, I am going now to look them up
      SD

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      • LucMan
        Solar Fanatic
        • Jul 2010
        • 624

        #4
        AETsolar ,they have multiple manuals for the design of solar thermal systems.

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        • J.P.M.
          Solar Fanatic
          • Aug 2013
          • 14925

          #5
          Originally posted by badwithusernames

          JPM, the point you make is exactly why I am looking for info.
          Finding all of the info that explores the relation between system volume/ pump volume/ location, etc is what I'm after. I'd rather read for several months before starting (and probably will) than rush into something that doesn't work right or has a catastrophic failure.
          Thank you for the suggestions, I am going now to look them up
          SD
          You're most welcome. Don't get discouraged by the perhaps daunting appearance of the technical stuff.
          It looks/reads like you might be in a similar place as I was ~45 yrs. ago before I got snagged by the solar bug.
          Simple math skills, common sense, the ability to think and persistence go a long way.
          None of this is rocket science - just somewhat convoluted at times.
          Holler back as your needs dictate.

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