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Another DIY solar water heating scheme

Post in 'The Green Room' started by GaryGary, Jun 21, 2012.

  1. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    This is the scheme I've been working on lately to do a DIY solar water heating system that is less work:
    http://www.builditsolar.com/Experimental/OffShelfDHW/OffShelfSolarDHW.htm

    It uses all off the shelf parts, so no collectors or tank to build. The collectors are pool heating collectors like the Fafco solar water heating system uses.
    A nice side benefit is that its both cheap and also qualifies for the federal tax credit as the collectors are SRCC certified.
    I'd say the jury is still out on what the year round performance might be in cooler climates, but the Fafco one appears to do pretty well. Also looking for ways to improve the collector performance in the winter.

    Any thoughts or suggestions (pro or con) would be very much appreciated.

    Gary

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  2. woodgeek

    woodgeek Minister of Fire

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    Very nifty. Despite all my naysaying about pro solar DHW on the east coast, I would love to do some DIY solar....I just want the projected output/$$ to be 'worthwhile' (or at least for a hobby, not miniscule). The flip side of the lousy winter resource out here is that unglazed collectors are a 'go' in terms of ROI--a glazed collector doesn't have many more BTUs to scavenge in December.

    On a related note...I looked at the solar attic concepts on your site, and figured that a big dumb (air) collector could work, until I realized that the shingles and sheathing added up to ~R-1.5, and this killed the delivery. A metal (and dark) roof would be perfect for a solar attic, but I no have. The lack of glazing was no problemo at least in the shoulder seasons. So, an unglazed pool heater sounds like it could work nicely (in principle).
  3. GaryGary

    GaryGary Feeling the Heat

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    I've had the same thought on my attic -- I have a nice section of roof that faces south at 45 degrees. It has the same problem with plywood sheathing and shingles, but when we reroof I may see if we can work out something that would work better for solar.

    Gary
  4. GaryGary

    GaryGary Feeling the Heat

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    On thinking about this a bit more, I think that a pool collector of the type described at the link above could work for space heating as well as domestic water heating if installed at a steep tilt (about 70 degrees?) with glazing. This would end up being very similar to the PEX tube collector I did and used for a couple years -- the logged temperatures never exceeded 230F, and this only for very short periods.

    Gary
  5. Seasoned Oak

    Seasoned Oak Minister of Fire

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    Be nice if you could incorporate SHW into a metal roof ,dark color. everything would be under the roof,those metal panels get pretty hot.
  6. GaryGary

    GaryGary Feeling the Heat

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    It does seem like metal roofs have a lot of potential for both solar air and water heating.

    You could do something like this one: http://www.builditsolar.com/Projects/SpaceHeating/RenwMagLargeRoofCollector.pdf and just leave the glazing off -- I think it would work well for SHW for three seasons.

    Gary
  7. tom in maine

    tom in maine Minister of Fire

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    Although hiding the collector under a metal roof seems to be a growing industry, the thermal performance is about 1/10 of what Gary shows with this unglazed system.
    The cost of burying the collector in the roof without glazing is very high and a whole roof might perform about as well as a couple glazed collectors.(I would hate to think about ever having a leak!)
    Of course, you cannot see it, but it will not work very well and will be horrible in cooler weather.

    Metal roofing companies love the concept. You can look up the performance at the SRCC (google it).
    The company that is making a system is New Dawn Solar.Compare it to any unglazed collector and then to any glazed flat plate.
    The numbers speak for themselves.

    Speaking of numbers, that's my 2 cents worth.
  8. dougstove

    dougstove Member

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    Hello;
    Nice project.
    I inherited 3 units of the 10' x 4' Fafco collector panels.
    Can you explain the water circulation?
    When you used rubber pipe and pipe clamps to hook together panels, how does the water flow?
    I have a 1 3/4" hole down the middle of the end tube, and then small perforations around the circumference; the end pieces appear to be double-walled pipe.
    I assume this double-space connects to the channels running through the flat panel?

    If I just connect together the panels, all the water is going to flow down the centre hole, not through the panel?
    Do you plug the centre hole?
    Do the Fafco couplers have some special arrangement?
    cheers, Doug
  9. dougstove

    dougstove Member

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    Sorry, just looked again more carefully.
    The double-walled, end-perforated section of the end pipes is on the final 1.5 cm or so.
    If I peer down the end pipes I can see the holes from the main 1 3/4" channel up into the collector panel.

    Does anyone know the function of the perforated end pieces? Some of the perforations are blocked with dirt.
    Doug
  10. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    Agree that the performance of the Dawn Solar collector leaves a lot to be desired: https://securedb.fsec.ucf.edu/srcc/coll_detail?srcc_id=2004009A

    But, I do think that metal roofs have some potential as solar air heating collectors. If the air path for the collector can be along the bottom surface of the metal roof, the heat transfer should be pretty good. Perhaps laying the metal roof on perlins spaced as far apart as possible to give the air direct contact with the bottom of the metal roof, and then using then boxing in the bottom side of the roof rafters with polyiso rigid insulation board (or sheet rock if requred for fire) would make a very inexpensive and very large collector.

    If some way could be devised to provide glazing over the metal roof -- maybe with something like the $1.50 per sf SunTuf corrugated polycarbonate glazing, this could be an efficient collector -- and it would still have a very low aesthic profile.

    Even though Randy's roof collector has no glazing, and it has to work through roof sheathing, it still provides some useful heat: http://www.builditsolar.com/Projects/SpaceHeating/AtticRafter/AtticRafter.htm

    And Rob's solar roof -- http://www.iwilltry.org/b/projects/solar-attic/

    You can get pretty good heat transfer through roofing and siding materials to heat air on the other side: http://www.builditsolar.com/Projects/LowTechCol/LowTechCollectorR2.pdf

    A metal roof that was manufactured with flow passages built into it might be a way to get a more efficient and not so expensive water heating scheme out of a standard looking roof at a low cost.

    So many unexplored possibilities out there!

    Gary
  11. woodgeek

    woodgeek Minister of Fire

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    This is exactly what I was thinking about/modeling. The glazing would not even need to be sealed...it would provide additional gain from reduced radiation losses, but still might not stagnate too hot in the summer....
  12. tom in maine

    tom in maine Minister of Fire

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    Once you try to glaze a metal roof, it is a different animal.
    I think if you are going that, then it makes most sense to seal it properly and get the most out of a
    glazing investment.
    Either way, it steps into a much better performance realm than unglazed.

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