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Drainback fill volume?

Orion_134
Orion_134 Member Posts: 35
I just bought a house with an indirect solar two-panel system that appears to have a tankless glycol drainback setup (northern VA). It is a 1983 setup with an 80 gal storage tank feeding a 20 year-old electric 60 gal (both showing signs of leaking). I've purchased a Richmond 120 gal solar/electric replacement and will be replacing both. I'm a handy diy, but am curious how to figure out how much glycol to put in the system once I install the new one? When running, I can hear the fluid sloshing down to about eye level on the second floor. Do I just calculate the footage (volume) above that point, and in the collector, and subtract that from whatever total volume I can pump into/drain from the loop? 

Comments

  • hot_rod
    hot_rod Member Posts: 16,557
    If it is a true drainback, installed properly to drain back, shouldn’t need any glycol. All the piping exposed to freezing should drain back.

    There should be a small tank somewhere with a site glass. Typically fill about 1/3 - 1/2 way up the site glass, the rest of the tank is the expansion space.

    If you could calculate the volume of the collectors and piping, that’s what needs to drainback

    Occasionally glycol is used if the piping is not sloped properly for extra protection.

    It’s a tough life for glycol as it flashes to steam when it hits a hot, dry absorber plate on start up

     Then the glycol turns acidic and destroys the components, flush and replace it every 5 years or so under conditions like that

    As old as it is it must have been installed well, maybe serviced regularly?

    Got some pics of the piping near the tank.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Orion_134
  • Orion_134
    Orion_134 Member Posts: 35

  • Orion_134
    Orion_134 Member Posts: 35
    edited March 9
    Maybe y'all can help me ID what I'm looking at. I'd also want to check the anode but wonder if I could even find one for this model...
  • hot_rod
    hot_rod Member Posts: 16,557
    The tank you have looks to be a stone or cement lined model. I don’t believe they have anode rods. I know the Vaughn brand of stone lined tanks doesn’t use an anode. Might be able to find a manual online

    The lower right is the solar pump and controller, relief and fill/ drain valve below. I don’t see an expansion or drainback tank?  Drainback tanks sometimes get mounted up higher, elsewhere in the building. Do you see those insulated lines anywhere else in the home?

    might be good to pump some air pressure in and see if you have leaks in the collector, or piping. Maybe drain that glycol and take a look.

    If the glycol is dark colored, harsh smelling, it needs to be flushed out.  Not knowing what type of fluid you have, see if you can recycle it. Your city or county may accept it. Quick lube places sometimes take it.

    Any indication of leaks at the collectors? Stained shingles for example?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Orion_134
  • Orion_134
    Orion_134 Member Posts: 35
    No leaks on the roof. I've been in the attic and the indirect loop has an almost direct path straight down through the attic into the basement. The system has been inspected every five years, but I'm unsure what maintenance is performed.

    As far as draining the glycol, that runs into the original question regarding replacing this entire setup in the near future: how much is *supposed* to be in it? I reckon I can just crack that lowest valve to get a sample of the fluid, but should I be worried about disturbing the pressure? Right now it's just under 10 psi.

    Thanks for the awesome responses BTW!
  • hot_rod
    hot_rod Member Posts: 16,557
    Good news that it holds pressure.

    The relief valve with the green tag, what is the pressure rating on it?

    It looks like a pressurized glycol system, not a drainback, as I don't see an additional tank, and glycol is not commonly used in drainback.

    Must work as piped, somehow even without and expansion tank. Be interesting to see how much the pressure gauge goes up when it is running.

    Guesstimate the distance that the collectors are above the tank. One story home? That will determine how much pressure you need on that gauge to fill the system to them top.

    Shouldn't make any noise when running, sounds like you have air in then loop.

    Does it work now, other than the noise?

    Pop the cover on the Goldline control, there is usually a manual switch in there to force the system on. If it is cold outside, no sun, you will feel cold coming down the return pipe.

    If it is sunny, and the tank is cold, it should start on its own. Force it on when the sun is in the collector and the return should feel warm in a few seconds if it is circulating properly.

    The Ford tank you have has a copper coil in the bottom for the solar glycol to circulate.

    I wonder that the Richmond tank you are considering has a coil inside, or it is just a storage tank?


    How much DHW do you need. With the electric element in the Richmond 120, you have a 60 gallon electric tank when the element is used, and there is no solar to harvest.


    How many collectors, what size? Is the glass covering clear or foggy? 39 years old? Hmmm

    A pic of a common drainback system
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Orion_134
    Orion_134 Member Posts: 35
    I know it turns on/off on its own and I can see the tank get up to 120-130° on a sunny day, but I do hear the fluid behind the second floor wall, so another ~10' to the collectors (three of them, unknown brand). I'll check the glass. The Richmond is Model #S120HE-1.

    Any thoughts on the rust ring going around the base of the Ford tank? 
  • hot_rod
    hot_rod Member Posts: 16,557
    Yeah, the tank is or was leaking. The fiberglass insulation acts like a large sponge and soaks up tiny leaks. For awhile!
    Regardless, at its age it has done well. Good chance the copper coil inside is covered in mineral scale also. the Richmond is in fact the correct tank, with the heat exchanger inside. Be aware that Ford beast could weigh 300lbs or more! Empty:)

    Since you have a repipe ahead of you, I would add an air purger and an expansion tank. You will quiet the system with an air purger, and the expansion tank will handle pressure fluctuations as the collectors warm, cools and stagnate.

    Since you are increasing the tank size, expect to see lower tank temperatures. There is a ratio between collector area and tank size for good operating temperatures 1.5 gallons per square foot of collector, 2 gallons in sunny SW regions.

    Either way you are harvesting X amount of solar energy. The larger tank will put the collectors in a lower operating temperature condition and raise efficiencies a bit.

    Here is a drawing of the best way to pipe a system like that.

    If you are interested I have a few solar pump modules I'd like to find a home for.

    Inside the insulated enclosure is all those components shown in the drawing, 3 speed pump, check valves, relief valve, air purger, expansion tank connection, fill and purge valves, temperature and pressure gauges. All high temperature components, not plumbing valves. Set up for 3/4 copper connections with compression style connectors. You could shop an expansion tank locally or online.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Orion_134
    Orion_134 Member Posts: 35
    edited March 9
    The pressure gauge remained at 8psi when turned on manually.

    I was planning to transfer over the pump/check valve/controller/gauges etc to the new tank in order to cut costs. I was going to replace the mixing valve to a Webster with a check valve. I know it's conflict of interest (since you're trying to offload stuff 😂) but what would be the advantage of updating to the package deal you're offering? Would the existing Goldline controller work with that pump? The obvious advantage is that I can plumb almost everything and just change over a few pipes right at the end and make the swap quicker (I'm also relocating it within my utility room. 
  • hot_rod
    hot_rod Member Posts: 16,557
    So the pressure that you put into the system is what lifts the glycol to the top of the collector, You want 12psi at least. Some installers will pressurize to 30 psi or more. The higher pressure it will increase the boiling temperature. So in the event of a power outrage, you don't flash to steam in the collectors. Be nice to be able to run 250- 300°f temperatures at the collector for some protection.

    You are missing a few key components on your system.

    You want check valves on both sides so you tank doesn't lose temperature back to the collectors at night. Air removal is important, air bubbles don't transfer heat well :)And they make noise.
    A solar rated pressure relief valve at least 300°, really all the components should be solar rated, 300°.
    Nice to have temperature gauges on both supply and return.
    Isolation valves to service the system without draining down.
    A multi speed pump to maximize the solar harvest.
    You want two hose connections, one to fill into, the other to purge the air out as you fill.
    Insulation around everything is nice so all the heat goes into the tank.

    These modules have a mounting bracket, two sheet metal screws to fasten it right onto the new tank. Solar pipes into the top, connections to the tank at bottom.

    This is probably a 1 hour install when everything is pre-built and the correct components in the correct location.

    No pressure on the pump station option, trying to make your life simpler and assure everything is piped properly.

    If you are putting two tanks in series again, the mixing valve should be on the second tank. Let the solar tank go as high as it can, then feed into the second tank. If the solar runs up to 150 or more on a hot sunny day, that flows into the second tank. The mix valve protects the HW to the building best on the second tank and maximizes what you can harvest and store.
    See attached graphic.

    Before you take it apart, fill and purge it with water, that flushes the old glycol out. Measure how much comes out is a bucket. T gives you an idea of how much glycol you will need to refill the system. Buy solar or HD (DowFrost HD) glycol, it has a higher temperature rating.

    One more tip, put the empty 5 gallon glycol bucket under the relief valve tube. If the valve discharges you don't lose 100 bucks worth of glycol.

    Here is a description of the solar station, a different brand, same features. Any controller can be used.


    https://www.caleffi.com/sites/default/files/file/28237_en.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    kcopp
  • Orion_134
    Orion_134 Member Posts: 35
    Message sent.
  • Orion_134
    Orion_134 Member Posts: 35
    If the lowest temperature ever recorded here is -18 F, would I be safe cutting the Dowfrost HD 50/50? Would that be with distilled water?
  • hot_rod
    hot_rod Member Posts: 16,557
    If you have glycol suppliers near you, they can blend the % you want, with DI water.

    Look at burst temperature for protection. If it slushes at -20, you probably don't have a lot of solar to harvest :)

    Looks like a 30% gets you down to that burst temperature. Don't cut it too close, no need to freeze a collector after all this work.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream