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Solar to heat in floor slab

Post in 'The Green Room' started by rombi, Feb 26, 2014.

  1. rombi

    rombi Member

    Joined:
    Dec 17, 2007
    Messages:
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    Loc:
    Green Bay Wi
    I am having a hard time figuring out where to start with solar and if there is any tax credits etc...
    What I want to do is use solar to heat my dog kennel. I have in-floor heat but the wood boiler eats too much wood to use it so I was thinking a simple solar plan to use the floor as a heat sink while the sun is shining would help a lot. It is all plumbed with pumps for the floor, I am thinking just running the solar into the floor to gain heat would hold it all night and cut down on my wood use. Maybe I am dreaming, anyway let me know what your thoughts are. I am very new to this idea and if it will be too much money with little gain in the Green Bay WI area then I will keep moving on with other ideas. I am looking for solar gain in the late fall and this time of the year when the sun is shining and a little more direct.
    thanks,
    Tom

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  2. GENECOP

    GENECOP Member

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    Ny
    Tom, everything I have seen appears to require to much square footage of panels to do any kind of effective heating....
  3. GaryGary

    GaryGary Feeling the Heat

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    SW Montana
    Hi,
    Is the floor slabe insulated? Around the perimeter? And/or underneath?

    Gary
  4. rombi

    rombi Member

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    Loc:
    Green Bay Wi
    yes the floor is insulated under and the perimeter. It is 800 sq ft of concrete.
  5. Ehouse

    Ehouse Minister of Fire

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    Loc:
    Upstate NY
    Be careful of over heating as well.
  6. Circus

    Circus Member

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    EC Wisconsin
    Fight the inclination to tie into existing systems. Figuring solar as a completely separate space heater will save on money and complexity. I suggest 120 to 200 sq. ft of vertical solar air and some sort of ceiling fan.
  7. GaryGary

    GaryGary Feeling the Heat

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    Loc:
    SW Montana
    Hi,
    There is a pretty detailed description of the solar collector direct to floor slab system here: http://greengateguesthouse.blogspot.com/search?q=Solar Sundays
    Its spread up over about 10 blog postings, but the link above should get you to them.
    Its a nice simple system.

    A rough rule of thumb is that 1 sqft of collector will get you about 800 BTU of heat over a reasonably sunny day -- so, a couple hundred sqft collector is good for about 160K BTU on a sunny day -- at 7000 BTU/lb of low moisture wood, that would be equivalent (roughly) to (160000 BTU) / (7000 BTU/lb) (0.6) = 38 lbs of wood in a 60% efficient wood burner.
    Or, about 2.2 gallons of propane burned in an 80% efficient furnace.
    Of course, not all days are sunny, and on days with part sun or thin overcast will be less -- all the way down to zero for thick overcast.

    If you build the collector yourself, the cost comes out to about $8 per sqft of collector for a good one with new materials -- an example here: http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm

    The insulation under and around the slab helps a lot.

    If you have the size and thickness of the slab and how hot you are willing to let it get, we can estimate how much heat it will hold, which would give an idea what collector size to use.

    Gary
  8. rombi

    rombi Member

    Joined:
    Dec 17, 2007
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    82
    Loc:
    Green Bay Wi
    5 inches thick and I could let the slab top out at 70 degrees ( I do not think it would get that warm) but if I could get the slab up to 50 to 55 that would be great.
    I know with the boiler now I run in about 120 degree water that returns around 90 to the boiler. I checked out the blog and that looks way above my skill level so I would have to have someone come in and help. If the hot air ones are that much easier maybe I will go that route. Just trying to reduce my wood demand and use the sun.
  9. rombi

    rombi Member

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    Loc:
    Green Bay Wi
    circus, is this something that I can buy or do I build them like I see on the internet. Looks like they are fairly easy to build, but do they work as well as one that I could buy?
  10. Circus

    Circus Member

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    I have no experience with store bought collectors. Mine were easy and cheap to build. They work like a charm. The hardest part was emotional, cutting big holes in my wall. Think of them as windows that don't have the usual heat loss at night or during cloudy days.

    Your insulated slab (thermal mass) is the perfect answer to the biggest drawback of solar hot air, temperature swings. Beats my 1500 water bottles.
    Last edited: Feb 27, 2014
  11. rombi

    rombi Member

    Joined:
    Dec 17, 2007
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    Loc:
    Green Bay Wi
    Floor is good but it is in a block building that has vermiculite (SP?) which I know has a low R value. What temps does your system blow in? Just wondering because it does not take a lot of warm air to heat this kennel. I do have a hanging heat exchanger that the wood boiler runs but I am looking at adding some more load to boiler in a panel radiator for an addition and heating the basement so taking some heat in the form of solar would help. I have no problems putting holes in the kennel, just depends on what size they have to be to get through the block.
  12. GaryGary

    GaryGary Feeling the Heat

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    Loc:
    SW Montana

    Solar air heating systems are much simpler.
    This is the one I use to heat my shop/barn: http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm
    Its a thermosyphon collector, so no fans or controllers.
    Total case back when I built it was $350 for 160 sf.
    It heats the shop well and gains about 130K BTU on a sunny day.

    It does require that you have a south facing wall with good sun exposure.

    Lots of other options for air collectors.
    I like the low thermal mass sunspace approach also -- especially if you can make good use of the added space: http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#LowMassSS

    Gary
  13. Circus

    Circus Member

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    Loc:
    EC Wisconsin
    Duct temperature is a poor indicator of performance. Air exits the collector whenever it's warmer than the room. In fact the cooler it runs the less heat you'll lose to the outdoors.
    Gary's design is useful for understanding design parameters, it helped me a lot. I suggest a flap on the lower vent to stop reverse thermal siphoning more effectively.
    As to your specifics, cut your losses first.
    Last edited: Feb 28, 2014
    woodgeek likes this.

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