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    I have a tank plumbing question. I am helping my brother-in-law with his solar water heating system. It is a simple flat plate collector system with tank and recirc. pump. The controller’s output relay to the pump fails to operate on occasion resulting in cold showers and lots of complaining so I am replacing it.

    My question is about how the tank is plumbed and if performance is suffering as a result. Every drawing I have seen, including the piping diagram from our tank manufacturer shows the return to the collector going into the bottom of the tank with the piping back from the collector somewhere around the middle of the tank. Indeed, this tank has two large labels “To collector” and “From collector” plastered on the side of the tank. The return to the collector does go to the bottom of our tank. However, the hot water return “from collector”nipple in the middle of the tank is capped off. They have plumbed the hot water return from the collector into the bottom of the tank using the “to collector” nipple and used the drain valve fitting at the bottom to return water to the collector (which is less than a foot away from the inlet). At least they used a tee and kept the drain valve operational. This is not an indirect system tank so there is not a heat transfer coil inside.

    This seems like a possible “short circuit” to me where heated water could be taken back to the collector too soon and possibly prevent the full possible tank temperature to be realized. Or, maybe it doesn’t really matter? It just seems weird and they also didn’t install a mixing valve. So, either they have a lot of practical experience in plumbing solar tanks (I have none) and have empirically found this to be a better method or they didn’t know what they were doing. They’re a well known company around here but maybe they had a new employee that day?

    I would appreciate someone with experience to comment on the way this tank is plumbed as to possible performance issues.

    Thank you,
    Last edited by jvf; 03-07-2022, 05:01 PM.

  • #2
    maybe the installer was counting on the hot water rising to the top of the tank, for withdrawal and use. But with both at nearly the same level, that apparently is not happening. Ordinary water heaters have a "dip tube" that directs the incoming cold water to the bottom of the tank. Again, that's not happening here. You may have to experiment to see what works. is the water returning from the solar collector actually warm enough ?

    My thermal siphon tank connected to my masonry heater, is fed bottom & middle, and hot is withdrawn from the top
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    • #3
      Hi Mike,

      The system seems to work OK in that we’ve always seemed to have plenty of hot water throughout the day and (most importantly for the ladies) evening. I talked to the manuf and they said there weren’t any tubes inside other than the usual dip tube. The return water is plenty hot enough. So much so that I think it was a gross oversight not to install a mixing valve. Lately, we’re all imagining that production is down compared to last year. But, it’s been cloudy a lot lately.

      Then one sunny day, we had no hot water. That wasn’t anyone’s imagination. My father taught me to observe a process before making any changes (it’s tough keeping every engineer’s and mechanic’s itchy fingers at bay during this period). So, I started observing the system. Is it the sensors? Is it the pump? ,etc. Eventually I noticed that the controller was calling for heat but there was no voltage at the pump and traced the problem to the sticky relay. I could replace it but it’s an old unit and we can’t observe sensor temperatures so I got a newer one.

      Unfortunately, although I have been passing by the tank for a couple of years trying to understand its plumbing, I never paid any attention to the manual gauge the installer put n at the top of the tank and have no frame of reference for how hot it used to get. All I know is on a real good day now we hit 140 and once I saw 145. Usually we get up to 125. With a 120 gallon tank we can usually get by on the 125 degree days.

      So, is this normal? Might we still have a pump problem? I have no idea. Perhaps another question I might post is how hot do other people’s systems get with three collector plates? When I measured resistance, the old sensors seemed to indicate the correct temperature. The newer controller uses the Platinum type so I’ll have to change them as well. I’m going to recalculate expected heat rise vs. observed and see how close it looks. At first it seemed way low but there is quite a bit of thermal lag until the manual temperature gauge reaches max temperature a couple of hours after the system shuts off the pump. Perhaps re-plumbing the system to ‘normal’ might shorten this thermal lag. I didn’t want to outsmart myself by moving the return line only to find out that this unusual way actually is better for some reason. But, I don’t believe it is any better I just might not make any improvements if I move it.



      • #4
        Whoops! I forgot to mention that, as found, the controller was set to 165 max temp at the lower sensor and I've left it alone.


        • #5
          How is the tank doing now? It would be cool to see a follow-up post because I’ve got a similar problem, and I don’t know what to do about it. I am not a professional and can’t be sure about anything I do. I like when the job is done carefully and qualitatively, and that’s why I usually call the drain cleaning service in Anaheim. They always do a good job because they check and solve all the possible causes of a problem. Every time I cooperate with them, I can be sure that the job will be done properly, and I can be calm about the housing pipeline for the next year. And now I think I will call them too because I can do more harm than good to this system.
          Last edited by Metalltant; 07-25-2022, 01:44 PM.