Correct percentage of windows for solar?

Discussion in 'Homesteading Questions' started by cc-rider, Nov 28, 2005.

  1. cc-rider

    cc-rider Baroness of TisaWee Farm Supporter

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    I *thought* I read somewhere that if you were building a solar house, you wanted 12% of your square footage as glass/windows on the south side. Is that correct? Otherwise, you had too much or too little heat gain.

    For instance, a 1000 square foot house needs 120 square foot of windows on the south.... or the equivalent of a 10X12 window. Is that correct? Too simplistic?

    Thanks
    Chris (in Ohio)
     
  2. sisterpine

    sisterpine Goshen Farm Supporter

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    You know...I think that is what I read also. Cant put money on it but it sure sounds about right.
     

  3. mightybooboo

    mightybooboo Well-Known Member

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    SolarGary would know,if he doesnt see this thread,pm him,he is big on passive solar.

    BooBoo
     
  4. Gary in ohio

    Gary in ohio Well-Known Member Supporter

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    It also depends on where you live. If you live in the cold north lots of south facing windows on the south side of the house. If you live in the house lots of windows on the north side.
     
  5. SolarGary

    SolarGary Well-Known Member

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    Hi,

    As has been mentioned it depends on your climate. It also depends on how much thermal mass that your house has to absorb the heat. Lots of thermal mass means that the thermal mass absorbs the heat during the day, and keeps the house air from overheating, and it releases the heat during the evening when you need it.
    In a nutshell, for a climate like Ohio, you want the house elongated in the east-west direction, lots of windows on the south side, few windows on the north side, and a good amount of thermal mass (e.g. stone tile floors). You also want to be sure that the south facing windows have overhangs above them that block the high summer sun, but allow the low winter sun to get in.

    The above is kind of general -- if you want some more specific guidelines, try my site here:
    http://www.builditsolar.com/Projects/SolarHomes/solarhomes.htm
    There are some downloadable guidelines, and the Chrias book is quite good.

    If you get to the point of having a specific design in mind, the HEED software will let you simulate your design using an hour by hour weather file for your city. Its easy to use and free (what a combination!). It will tell you how much solar heating you are getting, and if you are going to have overheating problems. You can keep tinkering with the design until you like it. You can get to HEED at the link above.

    One thing to bear in mind is that while passive solar heating is a really, really good technology, the most important thing you can do to save energy and fossil fuel pollution is to design the house with very good insulation and build it tight -- this will make the solar passive heating work its best.

    Gary
     
  6. cc-rider

    cc-rider Baroness of TisaWee Farm Supporter

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    I'm trying to design it now and was thinking about the following.... would it work? Overkill? Not enough???

    I wanted to build the exterior walls using 2x8's for the sill and top of the studs (I don't know the correct terms). Then I would use 2X6's for the studs, on 12" centers, but alternating them (front edge of 2X8, back edge of 2X8, etc.) In essence, when you are done, you'd have a 2X8 wall that has a continuous opening in the center. Don't know if I can draw this or not:
    _______________
    | | | | | |
    _|__|__|__|__|__|

    You'd have 24" spacing on either "face". You could put a 4" layer of insulation between each stud on the face, and it would overlap the 4" layer of insulation on the opposite face. You wouldn't have any stud that went from interior to exterior to transmit cold, and you'd have 8" of insulation.

    Will this give you a sturdy-enough wall? I would think it would be as sturdy as a 2x6 wall (except I know 24" centers aren't too good). Wouldn't it be a bit better than that, though?

    I would think it would be VERY good insulation-wise. ????

    Chris
     
  7. raymilosh

    raymilosh Well-Known Member

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    Chris,
    Your idea about building the walls of the house such that there is no wood to conduct heat through is a good one. it sounds like you have a mind that naturally understands and is geared toward energy efficiency. I have read about folks doing exactly what you hve mentioned for the exact same reasons. Sorry I don't have a link. I also don't know if research has been done regarding whether or not the extra design and constuction time and the extra materials yield enough energy savings to be worth the effort. I hear that thicker walls...2x6 or wider construction IS worth the time and money. Like gary says, good insulation is definately where to concentrate your efforts.
    the solar gain and the wood heat in my house are both pretty modest, but the house keeps its heat inside (or outside) well because i paid attention to all the details of energy conservation.
    Very good windows and doors, good curtains, radiant barriers in the attic and crawlspace, proper sizing and orientation of south windows, proper mass, minimal east, west and north windows, thermal chimneys, open floor plan and the like are also definately worth understanding and incorporating into your plans.
    ray
     
  8. SolarGary

    SolarGary Well-Known Member

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    Hi,

    I think that your scheme would work, and I don't see why it would not be strong enough. It does use a fair amount of wood, and you would have to be careful to build it tight and seal well to prevent air infiltration (just like any normal stick wall).

    Some things along the same line you might be interested in:

    http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/NS/Calc.htm
    This online calculator gives the insulation value for real walls -- so you can get an idea how much it drops when you have studs that provide thermal bridges between the outside and the inside.

    SIPS are very good both on preventing thermal bridging and on preventing air infiltration.

    Foamed in place insulation (Polyurethane) is very good. It does not prevent the thermal bridging, but it essentially eliminates air infiltration, and has a high R value.

    Foam board sheating on the outside reduces some thermal bridging. You have to think about whether you can live with its low strength.

    There is a wall construction in which normal vertical studs are put up first, then 2 by 2 are run horizontally at about 2 ft intervals. Fiberglass insulation is used to fill the stud cavities. A mesh is stapled and glued over the 2by2's on the inside, and cellulose is blown into the area behind the mesh. This greatly reduces thermal bridging with much less wood. Can't remember the name of the wall -- might be the Moody wall?

    Gary
    www.BuildItSolar.com