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retro-radiant question?

Dave_22
Dave_22 Member Posts: 232
I have someone who wants some radiant tied into an existing BB system. It requires 20BTU/Sq.ft. First plan was to use heavy duty plates underfloor. When I run the #'s, I could not use plates and still be safe. It may not be as responsive, but they are looking to save $$. I guess I shouldn't be worried about low water temps anyway since this is a conventional boiler running at 180 degrees. Any thoughts out there???

Comments

  • don_79
    don_79 Member Posts: 3
    I dont know

    > I have someone who wants some radiant tied into

    > an existing BB system. It requires 20BTU/Sq.ft.

    > First plan was to use heavy duty plates

    > underfloor. When I run the #'s, I could not use

    > plates and still be safe. It may not be as

    > responsive, but they are looking to save $$. I

    > guess I shouldn't be worried about low water

    > temps anyway since this is a conventional boiler

    > running at 180 degrees. Any thoughts out there???



  • don_79
    don_79 Member Posts: 3
    I dont know

    > I have someone who wants some radiant tied into

    > an existing BB system. It requires 20BTU/Sq.ft.

    > First plan was to use heavy duty plates

    > underfloor. When I run the #'s, I could not use

    > plates and still be safe. It may not be as

    > responsive, but they are looking to save $$. I

    > guess I shouldn't be worried about low water

    > temps anyway since this is a conventional boiler

    > running at 180 degrees. Any thoughts out there???



  • don_79
    don_79 Member Posts: 3
    I dont know

    > I have someone who wants some radiant tied into

    > an existing BB system. It requires 20BTU/Sq.ft.

    > First plan was to use heavy duty plates

    > underfloor. When I run the #'s, I could not use

    > plates and still be safe. It may not be as

    > responsive, but they are looking to save $$. I

    > guess I shouldn't be worried about low water

    > temps anyway since this is a conventional boiler

    > running at 180 degrees. Any thoughts out there???



  • ScottMP
    ScottMP Member Posts: 5,884
    Dave

    Why can't you get 20 btu's per ft. out of plates ?? That seems a little odd to me. Aluminum plates would give you the best output for a underfloor installation. What is the problem ??

    What water temperature are you calculating at ?

    Scott

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  • Weezbo
    Weezbo Member Posts: 6,232
    well you certainly came to the right place....

    for any thoughts out there *~/:) We are Out there...:) i live in north pole Dave, and one can only surmise that you can indeed use plates at much lower temps than you may think. and use partial differential set point and modulating boiler and system by passes and or 4 way mixers both modulating and dummy with variable speed injection to put a sporty system together :)
  • hr
    hr Member Posts: 6,106
    Do you mean

    you could meet the load (20 BTU/ ft) without plates?

    Plenty of suspended tube jobs out there. I'd caution against running the tube right up to it's max temperature.

    A reset control on the boiler may be a good addition if you plan on running boiler temperatures to the suspended tube application.

    Possibly much of your heating season could be handled with a lower (reset) boiler temperature?

    Calc the entire house, room by room to see how the numbers work out.

    hot rod

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  • Dave_22
    Dave_22 Member Posts: 232
    Yes

    I'm sorry- I meant that the Slant Fins H/L program says it's do-able without plates at a water temp of 137 versus 118 with plates. I planned on using a P/S zone with a 3-way mixing valve. The boiler is running 180 now for the BB.
  • hr
    hr Member Posts: 6,106
    Close

    the Wirsbo design tables show a 20 btu/ ft output with an .5 r value floor covering needing @ 155° supply temperature. A bit higher than your figure. Still a safe operating temperature for the pex and the joist cavity components :)

    Pipe it PS and use injection mix or a thermostatic mix. I'd prefer the injection mix to allow boiler protection and outdoor reset on that zone.

    You didn't mention the load of that new zone? Watch the Cv of a 3 way thermostatic valve if you go that route. About 3 gpm max (30,000 btu/hr at 20° delta t)for a 3/4 thermostatic

    hot rod

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  • Dave_22
    Dave_22 Member Posts: 232
    load

    is only about 6,500 BTU/Hr.
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Are you sure you need 180 for BB

    I have seen very few systems that need that high of supply temp.
    Most come in about 160F, 150 average temp.
    As HR said calc all rooms, then measure bb and see what the necesary water temps are.

  • Dave_22
    Dave_22 Member Posts: 232


    That's what the system is running at right now. All I would be doing was adding 1 zone of radiant-I have no plans,or does the homeowner to re-design the rest of there system.
  • hr
    hr Member Posts: 6,106
    A boiler reset control

    would allow that system to seek out the ideal boiler operating temperature, and conserve some fuel. No sense in running 180 year 'round if 160 or so could do the job.

    If you go with boiler reset, use a plain 3 way non thermoststic valve and the radiant zone temperature will float along with the boiler reset temperature (proportional reset) It only works with single zone systems, however as it adjust temperature on flow rate, not temperature like a 3 way thermostatic.

    Basic boiler reset controls are fairly inexpensive. I like the tekmar 260 for a easy to use and install control.

    hot rod

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This discussion has been closed.