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Thread: Solar Heating?

  1. #1

    Solar Heating?

    I was curious what you guys and gals thought of this idea...a doozy I know...that is using the sun to heat water to help heat my house. I have a pretty good roof pitch and it is facing due south, so that gives me an area that is 52 feet long by 20 feet wide to put some collectors on.

    Now to save money I would like to make my own collectors out of framing lumber, pex tubing and whatnot. I think I could cobble something up that is inexpensive to build, but semi-effecient.

    Now my real question is, do you think this would work? Now I am not looking to get rid of my propane boiler, I know I would still need that, but like today, its bright and sunny out at 60 degrees. Yet tonight it will hit 40 degrees. It sure would be nice to heat water today and then cycle tonight in my radiant slab. The question is would the delay be too long for my floor to heat up to feel the difference?

    At the same time I know when it hits 30 below this winter my collectors won't due squat, hey this is Maine after all. But do you think it would be worth it to cobble something up for the other 3/4 of the year?

    The way I see it, I would have to have a circulating pump that comes on according to water temp. The coolant would have to by glycol as well in case of freezing on the roof. By the way my radiant fllor heat, boiler and the rest are tied into my domestic hot water via a storage tank.

    Now while I have everyone thinking of radiant floor heat, what about radiant floor cooling? We don't have AC's here, no need really, but it would be nice to keep things cool on the few nights is does get hot. I was thinking pumping cold water from my well through my slab would cool things down some. But then I am not so sure. Well water is 60 degrees all the time, won't my slab be about that same temp since it is resting on the ground as well?

    Just curious as to what you thought about this. As others are trying to do on here, I am not trying to be green as much as I am trying to be cheap and put my radiant floor heat to maximum use.
    I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"

  2. #2
    Join Date
    Oct 2006
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    I don't have much to say, to help you out, but, when I was a kid, my best buddy's dad made two flat coils of black rubber hose and put them on his South facing roof, they were about 12' in diameter each, hooked them up in parallel and then to the swimming pool. He had a shut off valve on each, they worked without a pump too. I know that in the first year, he more than recouped his time and money invested in natural gas to heat the pool, in fact, in August he would shut the system down, as it made the pool way too warm.

    Cheers!
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  3. #3
    Join Date
    Mar 2007
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    Travis,

    Just my couple of thoughts on this.....

    I have seen solar heaters for above ground swimming pools. The one I saw in use was out in the country about 20mi south of Buffalo, so it might be just a little bit warmer than Maine in the summer.

    Also if you were to make one, you would want to purge the water out of it with air, before it gets cold enough to freeze. One good freeze and your solar heater tubes would blow apart.
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  4. #4
    Join Date
    Dec 2006
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    535
    My mother's house has a system like this, basically just a couple of metal boxes with pipe inside, all painted black, and glass on the face. It kind of pre-heats the water going into the water heater, and a couple years ago they also tied it into a radiant system in an area where they were about to raise the level of the slab. Works pretty well for heating, what you describe "should" work ok for cooling too. One question though, what will you do with the well water if you need more for cooling than you use in a day? A similar cooling method I've heard of out here is to run large irrigation PVC about 12' below ground for several hundred feet, and then daylight the end and put a blower on the end near the house. Trick is sizing the volume to the cooling capacity of the ground, and the consumption at the house.

    BTW, if you want to try to tie a solar system into your existing radiant using some sort of heat exchanger, use propylene glycol instead of ethelene glycol - its not toxic and is even FDA approved for human consumption in small quantities, like in food coloring. That way you'd have fewer concerns about cross contamination IF you wanted to try to merge the systems.

  5. #5
    Join Date
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    Travis,

    Here's the key phrase in all this:

    "But then I am not so sure. Well water is 60 degrees all the time, won't my slab be about that same temp since it is resting on the ground as well?"

    No, your slab won't be the same temp, it's above the frost line. But if you have a nice, deep well, with lots of water down there, you've answered your own question. The only two questions left: what would it cost to run a pump summer and winter, so that slab stays at 60 degrees, both heating in the winter and cooling in the summer? And would the circulation mess up the water quality? If the answers to those two questions are 'not much' and 'no', it seems like using that water for heating and cooling is the best idea...

    Thanks,

    Bill

  6. #6
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    Here in Reno, when it gets hot, we also have low humidity. The Evaporative coolers are arguably the most efficient way of cooling in the summer.

    Basically a big fan that sucks hot, dry air through some pads that are soaked with water from a recirculating pump.

    We don't really need to turn it on until it gets above 90 degress, and then it's good enough to keep the house pretty comfortable.
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  7. #7
    Join Date
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    This would require some research but there are many sites dedicated to solar heating. My parents (Carlsbad, CA) finally took their water heater out as they never used it; solar was adequate for all their needs.

    Things like source water temperature, duration of solar acceptable weather, storage tank and recycling pump operation cost would factor in to your savings amount. That amount could then be laid against the cost of building and there's your 'return on investment' period.

    Example:

    $1000 to build.
    $40 per month savings for 6 months out of the year.
    25 months to pay back cost of build.
    4 years of 6 month periods -or so- to get your money out of it.
    After that, its gravy except for maintenance costs, if any.
    Any sufficiently advanced technology is indistinguishable from magic.
    - Arthur C. Clarke

  8. #8
    Join Date
    Dec 2006
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    I have built a few smaller ones and they work get for heating. You will want to use 3/4 copper pipe with sevral vertical peices. Has the water move across it it will heat it up. You will need a cirulation pump, temp sensor, antifrezze and maybe a small tank to store the water. The pump can be had cheap from a plumper( ask for ones the removed) they will be used but still enough power to pump low volumes to a small erea. I would make up on panel about three foot wide by six foot tall and play around with it to see what work best for your needs.

  9. #9
    Travis,
    Something else to consider is a material other than PEX - it is sensitive to UV and will break down with prolonged exposure.

    http://www.ppfahome.org/pex/faqpex.html

    "Can PEX be used for aboveground outdoor applications?

    No. PEX is designed for indoor and buried applications only and is not recommended for outdoor, aboveground use. Short exposures to sunlight are permissible, not to exceed 30 - 60 days. When storing PEX, it must be stored under cover, shielded from direct sunlight. "


    Just food for thought.

    Wes

  10. #10
    Quote Originally Posted by Wes Bischel View Post
    Travis,
    Something else to consider is a material other than PEX - it is sensitive to UV and will break down with prolonged exposure.

    http://www.ppfahome.org/pex/faqpex.html

    "Can PEX be used for aboveground outdoor applications?

    No. PEX is designed for indoor and buried applications only and is not recommended for outdoor, aboveground use. Short exposures to sunlight are permissible, not to exceed 30 - 60 days. When storing PEX, it must be stored under cover, shielded from direct sunlight. "


    Just food for thought.

    Wes
    That is interesting, I never thought about problems with above ground applications and UV resistance. I was thinking Pex because it expands 200X's its original diameter so if something froze it wouldn't break.
    I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"

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