Open Vented Primary Solar Circuit

Discussion in 'Plumbing and Central Heating' started by Axel, 5 Dec 2015.

  1. Axel

    Axel

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    Can anyone comment on the pros and cons of using an open vented primary solar circuit instead of a pressurised system (used where freezing presents no risk)?

    Thanks in advance..
     
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  3. PullerGas

    PullerGas

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    What, you want to install a Drain-Back system??
     
  4. Axel

    Axel

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    No, just using a header tank instead of an expansion vessel. System will work at lower pressure when hot. Means it will 'stagnate' earlier but also safer and lower spec components. No special filling process etc.
    Drain back is a closed system. I'm proposing an open vented one.
     
    Last edited: 5 Dec 2015
  5. PullerGas

    PullerGas

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    Drain Back doesn't need to be a closed system & rarely is. Most early thermal solar systems were Drain Back. Just ensure your system can accommodate the circulation pump head & monitor the water's glycol content closely.

    You've been educated by the beard stroking, tree hugging, tramps on the Navitron forum by the sounds of it??!!!
     
  6. PullerGas

    PullerGas

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  7. Axel

    Axel

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    Thanks Dick, looks good. Most of the info seems to be outside of UK.

    Just one thing I fail to understand: In a drainback system, when the pump is off (so there is no fluid in the collector), how does the temperature sensor at the collector measure that the collector temperature is high enough above the tank temperature if the collector is empty of fluid? Surely it could only measure the temperature of an empty pipe / collector housing and not the water that would be heated by it?
     
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  9. bernardgreen

    bernardgreen

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    Looking at http://www.solarconsultants.com/library/DrainbackRheemGL-30Man.pdf

    solar original.jpg

    It seems strange to put the hot water from the panel into the drain back tank before it gets to heat the water in the storage cylinder.

    This method of putting the solar heated fluid directly to heat the cylinder and then into the drain back tank would seem more efficient.

    solar modified.jpg

    Or is the drain back tank more than just a tank.
     
  10. PullerGas

    PullerGas

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    A fairly simple differential controller can be calibrated by adjusting the Pots to suit.
     
  11. Axel

    Axel

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    But how can the collector sensor sense the panel temperature if it is dry? It would only be sensing the temperature of the empty pipe / fitting connected to the pipe coming out of the panel?
     
  12. PullerGas

    PullerGas

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    Maybe just a thermistor sensing ambient at the panel, it can't be that complex. I'm sure if you route around you'll find a controls schematic on-line for a Drain-Back system.
     
  13. bernardgreen

    bernardgreen

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    It does not matter if it is wet or dry. If the metal work of the panel is hotter than the water in the store tank then pumping fluid through the panel will result in that fluid becoming hot enough to increase the temperature of the water in the store tank.
     
  14. DIYnot Local

    DIYnot Local

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    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

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