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Using the indirect loop as a high temp secondary loop

I'm installing a Triangle Tube Solo 110.  It's heating a radiant thin-slab and a dozen radiators.  There is no indirect tank.  I'm building a primary loop with four secondary loops.  One secondary loop is for the high temp radiators.  One secondary loop is an injection loop going to the radiant floor system loop.  Another secondary loop is the low temp input from the mod-con boiler.  I'm making the fourth secondary loop a high temp input from the indirect tank piping on the boiler.  That fourth loop will only come on when the radiators call for heat.  This way I still get ultra efficient output at lower temps when there is no need for radiator heat.  Is there going to be any problem with this?  I understand the boiler operates a little differently when it goes into a domestic hot water call for heat, but I don't see how that will hurt anything.

Comments

  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    I have to say

    I have no idea what you are talking about. Can you sketch it?
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Andruid_2
    Andruid_2 Member Posts: 38
    Sketch

    Sorry for the crudeness of my drawing.

    The whole idea of this is to get the efficienct burn of low temp supply water and still be able to satisfy a high temp demand when it is needed.  I don't want to set the output to what the radiators need because then I won't get a really efficient burn when just the radiant floor is needed.

    In my original post I talked about adding another set of closely spaced tees that I did not put in the drawing...they would have come from the indirect tank connections on the boiler.  The radiators would call for heat on the indirect tank aquastat connections on the boiler.

    After talking with someone today, I now know that I don't need the extra piping.  I can trick the same boiler pump to come on whether it's space heating or indirect tank heating that is being called for.  Now I'll have a boiler that can output two different temps for space heating depending on what is needed at the moment.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    I don't think you want to do this.

    in DHW the boiler immediately goes to high fire. I'd be concerned with cycling issues. You also lose all reset, which is counterproductive. You'd be better off running a higher reset curve for the radiators and mixing down continuously... at least then you'd only be at "radiator max temp" on design day, instead of every day. The rest of the time you'd just be between radiator max and desired radiant temp.



    Of course, the REAL great way to do this is to size the radiators for a temperature you can run the radiant at and drop the mixing. If your system flow rates are low enough you could drop 3 pumps and the mixing control muah ha ha.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Gordan
    Gordan Member Posts: 891
    edited September 2010
    Suggestion for the drawing

    Typically, an indirect is piped in with its own circulator directly to the boiler. There's no need for primary/secondary or closely spaced tees there. You could do the same with your radiators *if* you can ensure sufficient flow through the circuit.



    Here are some ways that people typically do multiple-temp systems. Boiler supply is controlled by outdoor reset, with the reset curve matching what the highest-temp emitter needs. Typically, with constant circulation, this will still allow you to condense a good part of the season. Then, you run the radiant loop one of three ways: 1) a thermostatic mixing valve set to a fixed temperature, that temperature being the design supply temp for the radiant loop; 2) a manually-set mixing valve that acts as what's called "proportional reset" - it mixes a fixed proportion of whatever temp the boiler supplies via outdoor reset, into the radiant loop supply; 3) an electrically-actuated mixing valve (or variable speed injection pump) that's controlled by an outdoor reset mixing control.



    Your idea *could* work if the radiators have a big enough thermal mass that you could just "recharge" them fairly quickly and then let them slowly cool down while you resume heating your radiant loop. But you lose the outdoor reset control for the radiators. That could still be ok... or not, depending on how much of your heat load is the radiators and how much is the radiant loop.
  • Gordan
    Gordan Member Posts: 891
    I probably started writing my reply before you started writing yours. :-)

    Of course, you have a much more concise way of putting things.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    my post-fu is strong

    hiyaaaaa!



    nice job explaining the mix options.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
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