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How much for radiant heat

Discussion in 'Photovoltaics' started by Drew Cutter, Sep 9, 2005.

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  1. Drew Cutter

    Drew Cutter Guest

    Looking at doing two rooms in the house with solar radiant heat . Do I
    need fewer solar panels to do this then to power the whole house ? Can
    radiant heat be used to heat the whole house . The two rooms are on the
    first floor.
     
  2. Ecnerwal

    Ecnerwal Guest

    Depends if you do it smart or stupid. Smart is solar thermal collectors
    heating fluid that gets pumped around the floors (and/or a storage
    tank). Then all you need is a small solar electric panel (if you want it
    to be "all solar" or to work when the grid is out - otherwise just use
    the grid if you have it, it's cheaper) for the pumping. This is pretty
    efficient and cost effective. If you need backup heat it's easily
    arranged.

    Stupid is electric resistance heat driven by solar electric panels. This
    is the option for people who don't care how much it costs. Solar
    electric is very expensive. Solar thermal is not.
     
  3. Paul

    Paul Guest

    My first guess is yes, fewer panels for two rooms versus more rooms.
    You could heat the whole house, but you imply that it is two story.
    The upper floors are sometimes done with baseboard heaters that require
    higher temperatures. If you just heat the downstairs floor the temperature
    can be lower. The place at Tahoe ran 140F downstairs for the foundation
    and 180F for the upstairs baseboards. The 140F is in the range of lower cost
    flat plate solar thermal panels. The 180F is more in the range of evacuated
    tube
    collectors can can run $2000 per panel.
    Obviously, if you are heating the slab during the day as well as storing
    the
    heat in water tanks you can continue heating at night from the water tanks.
    But the water gets cooler as it is recirculated and the effectiveness is
    reduced. You would have to talk to someone that has done it. Nick Pine
    is a good source of info on this and sometimes posts here.
     
  4. Drew Cutter

    Drew Cutter Guest

    You gave sound advice. Any good source of info for further research ?
     
  5. Ecnerwal

    Ecnerwal Guest

  6. Drew Cutter

    Drew Cutter Guest

    This doesn't sound too bad , $$ wise. The ripping the floor up and
    putting concrete might be different.
     
  7. Ecnerwal

    Ecnerwal Guest

    It's obviously easier to put in when pouring a slab the first time. So
    much so that it's not a bad idea to consider putting tubing in any time
    you pour a slab, if there's the slightest chance you might ever want to
    heat the space the slab is under.

    If it's a floor on joists, you can run around in the basement or crawl
    space and attach the tubing (and aluminum heat spreaders, if you feel
    the need) to the underside without ripping up the floor (you might need
    to rip down the ceiling if the basement is finished).

    When retrofitting, there are multiple options to simply build up from
    the current floor, rather than "ripping it up", unless you have an
    inflexible need to keep the floor height exactly the same. Depending on
    the floor you have, you might also be able to cut grooves into the
    flooring to run tubing in, and build up only a tiny amount.

    But it's probably not the way to go if you were not planning to redo the
    floors - baseboard fin-tube units or radiators are much easier to add or
    retrofit than in-floor radiant is. I've seen some radiant installations
    in the walls (or extending into the lower part of the walls), but again,
    not very cost-effective if not planning to redo the walls.

    Often the first most cost-effective route (if you have no solar heat
    now) is to set up to heat your domestic hot water - you use that all
    year round, and it's easy to integrate. Hot air collectors for winter
    heat are often the next most cost-effective. This discussion is heading
    a bit off-topic for alt.solar.photovoltaic, might make more sense to
    move it to alt.solar.thermal
     
  8. Cosmopolite

    Cosmopolite Guest


    You may not have to rip up the floor. I will be doing this by laying
    down 1"x1" sleepers every 8", with .5" Kitec tubing between, foil on
    original floor, .5" ply, painted flat black on underside, over the
    sleepers and laminate flooring over that. The space will be a sort of
    space heating with hydronic as heat source. Foil and black paint to keep
    downward radiant losses at a minimum. I made a test panel and found
    that there was a large difference in temp. between the sleeper area and
    the " open" area, but I think this will be bridged on long term basis,
    test was short.


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  9. Drew Cutter

    Drew Cutter Guest

    Then your saying that you don't need to use concrete to lay the piping .
     
  10. Drew Cutter

    Drew Cutter Guest

    Wow . This is good news. Hate to be the person doing this for the family
    room. Very Tight crawl space. I was able to do it when i was 10. I
    think you just save a few dollars. I will direct the question on thermal
    newsgroup. Thanks.
     
  11. Cosmopolite

    Cosmopolite Guest

    No, you don't. Concrete is a better thermal mass, but I would not
    pour it over floor joists that were not designed for the weight and
    stiffness. I will use short pieces of lefover plastic strapping as
    clamps to hold the tubing down. ( 3" long, drill .06" holes close to
    each end and use short, large head nails )
     
  12. Guest

    Where are the sleepers and foil? The 0.5" tubing sounds too small for
    good flow, with too little heat exchange surface, and the black paint
    doesn't sound useful, unless you have sun in your basement, shining up.
    Don't bet on it. You might have better results with warm air or fin-tubes
    under the floor, and foil below that.
    Then again, IMO, radiant first floors don't fit well with solar heat,
    economically-speaking. Better to heat with a sunspace and some sort of
    mass or fin-tubes in the living space under the ceiling to both collect
    and distribute heat, with no rooftop hydronic panels.

    Nick
     
  13. Cosmopolite

    Cosmopolite Guest

    Ten feet to the south of my house is a two and half story house which
    blocks all direct sunlight. Fifty feet to the east is my garage which
    has the only clear southern exposure.
     
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