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Drainback Maintenance

notruck
notruck Member Posts: 3
in Solar

Sorry if this question has already been asked. I searched for quite a while and couldn't find what I was looking for.

I have an AET closed loop indirect system with drainback. The last time the loop was opened (about 5 years ago), it was refilled with water from a garden hose, so not demineralized water.

I thought I saw a post where someone (maybe @hot_rod) suggested flushing the system with some type of product, refilling with distilled water, and adding something to the water for some color to make viewing in the sight tube easier to see.

Anyone got any ideas?

Comments

  • hot_rod
    hot_rod Member Posts: 23,222

    do you know the quality of the original fill water? GPG of hardness for example.

    That first fill could be an indicator of how much if any scaling has occurred

    Just disassemble any component, like removing the pump motor from the volute would be an indication of scale deposited

    No harm in running a hydronic cleaner for a few days and refilling with low hardness water

    If it is only a few or a dozen gallons, buy water from Walmart, etc. That is typically RO water, most all the hardness stripped out

    Buy a hardness test kit to know for sure

    Solar thermal is low grade energy, so you want the best heat transfer possible to maximize the system potential

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    notruck
  • TBack
    TBack Member Posts: 21

    so I’m just finished my open drain back solar heater and in commissioning found that my Grindr’s 15-58 doesn’t seem to prime, I do have the check valve installed so as not to lose prime once initially started the pump is about 22” above the water line and the top of the pane is about 8ft above the pump. Tank is 4ft deeps 14’ long 2ft wide. Suction on the far side from the pump and heated water dumps in next to the pump. I have air vents and vacuum breakers at the top. My half inch tubes run a pitched horizontal with 1” reverse return supply/return. The 15-58 say 19ft heads 10’ should be a problem, maybe not enough flow? 17 1.3” copper at 32ft long?

    image.jpg

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,576

    Hi, Did you include a way to prime the pump? A T with a bibb that can be used to fill pump and nearby piping should do it. Where is the check valve installed? Best would be below the waterline in the pump's inlet.

    Yours, Larry

  • Kaos
    Kaos Member Posts: 175
    https://forum.heatinghelp.com/discussion/comment/1813478#Comment_1813478

    Where is your drainback tank? You want that above the pump intake so there is always some water and pressure there when the pump needs to start up.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,576

    Hi, It looks like the drainback tank is the large tank with the coils in it… lower than the pump.🤔

    Yours, Larry

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,576

    Hi, Been thinking about this, installing a check valve won't work, so as @Kaos essentially said, the inlet to the pump needs to be flooded. Is there a port lower down on the tank you can tie into… or can you drill and add a wall fitting? If not, taking the piping down over the side of the tank to the pump so it is under water level could work. That arrangement would need to be primed.
    Yours, Larry

  • hot_rod
    hot_rod Member Posts: 23,222

    you don’t want any check valves in a drainback.

    The water level needs to be above the pump when it is drained back

    Ive never used a vacuum breaker on the many drainback I have built. The water will drain down when the pump stops.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 23,222

    you don’t necessarily need a drainback tank if the piping and coils can hold all l the collector drainback water. At least below the freezing level

    This is how you typically get the pump below the water level in a coil in tank system, to give it some suction pressure some

    IMG_8747.jpeg

    pressure

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Kaos
    Kaos Member Posts: 175

    I think in the OP's case, it might be easier to use a small jet pump with a foot valve at the current location or a submersible pump in the tank. Submersible might be more power efficient if it needs to run continuously.

  • hot_rod
    hot_rod Member Posts: 23,222
    https://forum.heatinghelp.com/discussion/comment/1813601#Comment_1813601

    I've struggled to find any affordable submersible rated over 140F continuous operation. High lift low gpm is a common sump pump curve, not ideal for solar.

    Depending on array size to tank volume, 160F is fairly common with plate type collectors. Evac tubes can reach 180F or higher.

    For drainback you want high head, low flow. The high head is only needed for a minute or so to lift to the top of the collector. After that the pump is just overcoming piping resistance, the siphon is doing the work.

    The Grundfos 15-100 was a great drainback pump and at 1.1A, it would run on most of the new digital controllers with a 1amp relay. The Caleffi/ Resol control will actually modulate the pump speed. 100% for several minutes to establish the siphon, then adjust speed based on the ∆T.

    Or it can run two pumps, shown above, drop one off when the siphoin is going. On my system I paired a 15-58 with and Alpha, in series. Both will run for a minute or so, the 15-58 drops off, and the Alpha is the main pump running just 37W, or less depending on the speed selection.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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