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A very offbeat alternative solution to glycol water mix problems

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  • A very offbeat alternative solution to glycol water mix problems

    I thought there might be some interest in my somewhat offbeat solar thermal design as it eliminates issues with Glycol. I am also looking for some feedback on differential temp controllers as my design has caused me a problem.

    I will provide the short version now, and if anyone is interested in my design, and the journey to where I am now, I can expand on it.

    I obtained some flat panels on the cheap, and was detailing my design. Having researched solar thermal systems I identified one significant issue (for me at least) as being the choice of thermal fluid, with freezing/boiling and decomposition being interrelated issues. As a retired engineer from the petrochemical industry I decided there must be a better solution, and after investigation decided to try kerosine as my transfer fluid. Foreseen problems were leaks, and seal material incompatibilities which I dealt with. An unforseen problem was that due to it being capable of withstanding the panel static temperature of potentially up to 165C (i.e. if my tank hit the upper set point I could stop the pump with no concerns about boiling in the panels) the temperature sensors were able to see higher temperatures than they normally would.

    End result is that I have a system that works well (or at least did when the controller was working correctly), can withstand freezing conditions, does not boil/overpressure even in static sunny conditions, should never have thermal decomposition issues, is non corrosive, and which once the control glitches are ironed out should thus be able to run without any maintenance.

    My hope is that someone can point me in the direction of a reasonably cheap solution to my failed differential temperature controller, or, if not a complete kit (which is a cheap off the shelf chinese one), then at least equivalents to the failed sensors which are 3 wire DS18B20, where it turns out the sensor is only rated to 125C and the cable to 85C. I suspect at the panel end it might see up to 140C in reality (I don't forsee actually reaching 165C) and there the sensor is in a very short thermowell so it is just the sensor that sees the extreme temperature, and in the storage tank I can’t see me ever setting the protection thermostat, and thus the temperature that sensor will see, above 95C.

    Currently I am running the pump on a timer rather than on temperature control. Not as efficient but still gaining me energy.

  • #2
    See my post under the other thread you also posted this same information to.

    J.P.M.

    Comment


    • #3
      Originally posted by julianm1234 View Post
      I thought there might be some interest in my somewhat offbeat solar thermal design as it eliminates issues with Glycol. I am also looking for some feedback on differential temp controllers as my design has caused me a problem.

      I will provide the short version now, and if anyone is interested in my design, and the journey to where I am now, I can expand on it.

      I obtained some flat panels on the cheap, and was detailing my design. Having researched solar thermal systems I identified one significant issue (for me at least) as being the choice of thermal fluid, with freezing/boiling and decomposition being interrelated issues. As a retired engineer from the petrochemical industry I decided there must be a better solution, and after investigation decided to try kerosine as my transfer fluid. Foreseen problems were leaks, and seal material incompatibilities which I dealt with. An unforseen problem was that due to it being capable of withstanding the panel static temperature of potentially up to 165C (i.e. if my tank hit the upper set point I could stop the pump with no concerns about boiling in the panels) the temperature sensors were able to see higher temperatures than they normally would.

      End result is that I have a system that works well (or at least did when the controller was working correctly), can withstand freezing conditions, does not boil/overpressure even in static sunny conditions, should never have thermal decomposition issues, is non corrosive, and which once the control glitches are ironed out should thus be able to run without any maintenance.

      My hope is that someone can point me in the direction of a reasonably cheap solution to my failed differential temperature controller, or, if not a complete kit (which is a cheap off the shelf chinese one), then at least equivalents to the failed sensors which are 3 wire DS18B20, where it turns out the sensor is only rated to 125C and the cable to 85C. I suspect at the panel end it might see up to 140C in reality (I don't forsee actually reaching 165C) and there the sensor is in a very short thermowell so it is just the sensor that sees the extreme temperature, and in the storage tank I can’t see me ever setting the protection thermostat, and thus the temperature that sensor will see, above 95C.

      Currently I am running the pump on a timer rather than on temperature control. Not as efficient but still gaining me energy.
      Only 1 problem using kerosene for heat transfer fluid is that it is considered toxic to humans. Using it for domestic hot water would be a problem if the heat exchanger were to develop a leak and entered the domestic loop. A double wall HX would be required at minimum.
      A simple drainback system would work with just tap water, no worries of freezing, overtemp, or toxicity. Keep it simple.

      IMC instruments or Goldline are the controllers that I use and recommend.

      Comment


      • #4
        Originally posted by LucMan View Post

        Only 1 problem using kerosene for heat transfer fluid is that it is considered toxic to humans. Using it for domestic hot water would be a problem if the heat exchanger were to develop a leak and entered the domestic loop. A double wall HX would be required at minimum.
        A simple drainback system would work with just tap water, no worries of freezing, overtemp, or toxicity. Keep it simple.

        IMC instruments or Goldline are the controllers that I use and recommend.
        A valid point, and one which I should have covered in my design points.

        My thermal stores are the unpressurised type with a solar coil at the bottom, and a water coil at the top. The thermal store itself is filled with the treated heating circuit fluid. So I have the double hx as you suggest should be the case. Any leakage would be into the heating circuit fluid, and any concurrent leaks from the water coil would soon show up as continuous overflow liquid.

        As or the drawback system, yes it does provide a solution but requires you to have a system that is built without any chances of airlocks, and demands a greater pumping load. It would also require to be controlled from the overtemp limit switch on the thermal store as well as whatever you determine as the start finish times. I wanted to come up with an alternative that once the initial design issues are sorted, would be simpler to run and maintain. It remains to be seen i that is the case but I believe it is promising.

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