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Thread: Solar heat storage in ICF walls?

  1. #1
    DIY Member Buffalobillpatrick's Avatar
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    Default Solar heat storage in ICF walls?

    In house planning stage, high altitude 8.800', cold Colorado climate, great solar available. Has anyone tried running pex in ICF walls before pour & using concrete for solar heat storage?

    Warming the ICF concrete with solar would reduce my gas bill somewhat.

    In my planned ICF walls & footers, there will be about 260,000 btus / 1* f heat storage available.

    Tying solar into my planned radiant floor system would be difficult with the high temperature cast iron boiler I have already bought.

    I realize that right now, solar is hard to justify cost-wise with gas rates being low.
    I would like to find a way to use solar cheaply.

    I don't like panels on roof, looks ,large hail, possible leaks, etc.
    Don't want passive windows, I've had them in past home, insulated curtains were PITA with the closing / opening, this needs to be automatic, again $$

    I will have a South facing wall with about 235ft2 am thinking of building verticle panels onto wall.

    I have used the DOE online RESCHECK to calculate my design heat load (32kbtu at -20*f). Had to SWAG some inputs like infiltration. R23 ICF walls are about 20% of load.

    Plans do inculde HRV, good windows, SPF ceilings, FPSF, well insulated radiant floors, etc.
    Last edited by Buffalobillpatrick; 02-14-2012 at 01:35 PM.

  2. #2
    In the trades Dana's Avatar
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    If you dump the solar heat into the concrete between the EPS layers in a hydronic solar approach you'll be losing more of that heat to the outdoors than would be going into heating the space. The whole "storage" concept isn't really applicable, given the ratio of insulation area to thermal mass you have in an ICF, compared to that of a well insulated tank fully inside of conditioned space. You'll get some performance improvement, but not nearly what you'd expect for the effort & expense.

    Thermal air panels (TAPs) mounted to or integrated into the south facing walls would deliver far more seasonal heat for a lower installed cost. It's not too tough to use snap-disc thermostats on the collector's heat exchanger metal to turn on blowers when the heat exchanger plate hits 110F and have it turn off when it drops to 90F, and put a line-voltage thermostat in series with the snap disc to keep it from overheating the place. With TAPs there are no freeze-up or leak issues to be concerned with too. In sunny high-altitude CO you should be able to offset at least 2-3 therms of natural gas (or 2+gallons of oil, or 3+ gallons of propane) per square foot of collector area per heating season with a decently designed active-blower TAP. If that's a couple hundred square feet of collector area it could knock off a a quarter to a third of your total heating fuel use. Additional gains from snow-reflected sun make vertical mounted collectors far more useful at altitude than in lower-dryer locations, and has the effect of less output when it's snowless/warmer out, which is generally what you would want.

  3. #3
    DIY Member Buffalobillpatrick's Avatar
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    As usual, great info Dana, thanks.

    There will be 2 bedrooms on that S. end of house. The truss design will have 3' of room above the ICF wall that I could use for in/out vents. That hot air would need to be moved to the rest of house with fans.

    I have 3x of those line voltage snap-switches, if I could remember where I put them, hehe

    The snow up there in Teller County melts off in the sun but hangs around in the shade. I could enhance ground reflection with white rocks.

  4. #4
    DIY Member Buffalobillpatrick's Avatar
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    I have a enough double pane 3' sliding glass door panels that I bought cheap 12 yrs ago.

    Trombe Wall ? Uninsulated 8" CMU surface bonded wall, painted black on outside & plastered on inside, no vents or windows?

    http://www.nmsea.org/Curriculum/Cour...s.htm#Indirect

    http://nmsea.org/lib/ThermalStorageWallDesignManual.pdf

    http://www.nrel.gov/docs/fy04osti/36277.pdf
    Last edited by Buffalobillpatrick; 02-15-2012 at 05:15 PM.

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