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Thread: Solar Thermal Temperature Control

  1. #1

    Default Solar Thermal Temperature Control

    Hello -
    I'm a DIY person trying to install a radiant floor heating system powered primarily by an evacuated tube solar collection system. The solar heat is a closed loop glycol based system with an 80 gallon storage tank. The heat will be transferred from the solar system to the radiant system via heat exchanger. I think I understand the radiant system pretty well, and the solar collector system is pretty straight forward. My question concerns controlling temperatures between the two systems. I'm trying to figure out the best way to keep my radiant system source temperature at 110 F, when the temp in the solar storage tank can vary from 110F (min temp at which the back-up electrical heat element turns on) to 180F (max temp set point of solar collector system). I've researched mixing and tempering valves, but they all seem to 'mix down' from a known hi temp source to a manually set lower temperature. Is there a tempering valve out there that will let me set it to 110 F, and mix hot and cold in proper proportion to maintain the temperature? If not, what other options are there?


  2. #2
    Plunger/TurdPuncher kingsotall's Avatar
    Join Date
    Aug 2008
    Flagstaff, AZ Sitting on an upside down 5 gallon bucket next to the GO 68HD


    Research variable speed injection. I don't know if its applicable with a storage tank application, though. (Typically a boiler is the heat source.)

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default temperature

    Mixing valves will not work, because they depend on incoming water to mix with the stored water. In your system you are using the same water over and over. The only "cool" water would be that returning from the radiant system, and that could range from cool to warm depending on the temperature of the floor and how long the system has run. You may have to control the solar portion so it does not overheat the water.

  4. #4
    Master Plumber master plumber mark's Avatar
    Join Date
    Feb 2005
    indianapolis indiana - land of the free, home of the brave....
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    Talking that is fun to figure out

    I would have to have some more info on your particualr system

    you can put a tempering valve on the potable side of the
    system to cool it down some before it goes into the
    heat registers... to cool it down...

    we attempted this a long time ago in colorado...

    the problem was always the same, you could not get

    a steady heat through the system due to the various

    temps every day... and the tempering valve woud jump up and down.

    one unit worked very well where they had a very large

    concrete storage tank buried in the yard that could handle the

    all incomming heat off the glycol panels...
    at any temp and it would even it out over the large
    tank of water... the tank had styrofoam about
    5 inches thick all around it for insualtion.

    the system worked pretty well, with very hot water always
    ready to go through the heat fins and you always had
    a large warm green spot out in the yard where the tank was ,
    even when their was a foot of snow on the ground.

    a great place for out-door grilling in the winter...

    most solar systems I have ever dealt with
    were always a pain


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