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Thread: Small solar water heater prototype

  1. #1
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    Default Small solar water heater prototype

    I'd like opinions please. I know it's small and won't catch much sun, but it's a prototype and cost me less than $5. I'm just learning right now.


    1/2" CPVC painted with flat black grill paint, 1/2" Tees on the bottom, 3/4" - 1/2" Tees on the top. Hot water exits top left, cold in bottom right.

    The box is 2x4s with a 7/16" OSB back, painted black inside and a framed double pane window lid. The corrugated stuff is aluminum siding painted black grill paint.

    The pipe spacing is 2.5". It all works out to about 3sqft of collection. I plan to heat a small 1gal tank to learn.




    Do you see any obvious problems with this?
    Is the 3/4" CPVC top line reasonable? should it be the same 1/2" CPVC as the rest or larger than 3/4"?
    I was thinking it might work well to put a piece of 1/2" foam sheet I have behind the siding.
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  2. #2
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    Concept is good, Material choices are bad.
    CPVC will melt at the temperatures this could potentially operate at.
    CPVC will also be more of an insulator as the thermal properties you want for collection are not nearly as high as copper
    A better alternative would be copper piping with brazed joints or just solder them which would also work when using fittings.
    With using copper however the aluminum absorber will be a problem. It would be better to get some of the lightest gauge copper flashing in rolls you can find and form that around the copper pipes. Again solder this to the riser pipes.

    Increase the size of your tank to about 4.5 or 5 gallons. This will harvest more BTU's than a 1 gallon will.

  3. #3
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    "Concept is good, Material choices are bad.
    CPVC will melt at the temperatures this could potentially operate at.
    CPVC will also be more of an insulator as the thermal properties you want for collection are not nearly as high as copper"
    Alright, I'll keep a close eye on it and be ready to cover the glass. I have an infrared temp gun. I'll look up what the CPVC is rated for.

    "A better alternative would be copper piping with brazed joints or just solder them which would also work when using fittings."
    Very good sir. I've soldered copper before with good results. I read somewhere to use silver solder for solar water heaters. I'll get a working design and make my "Real" unit from copper.

    "With using copper however the aluminum absorber will be a problem. It would be better to get some of the lightest gauge copper flashing in rolls you can find and form that around the copper pipes. Again solder this to the riser pipes."
    Ouch, ok I'll look into this. The bond between the pipe and absorber should help heat transfer tremendously too..... on my "Real" unit.

    "Increase the size of your tank to about 4.5 or 5 gallons. This will harvest more BTU's than a 1 gallon will. "
    No kidding!!?? Hey it might work better than I expect eh? I have a 5gal metal can I will sacrifice then.

    Thank you for the opinions. At least the design is valid.

  4. #4
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    You might want to review the following resource.

    http://www.builditsolar.com/Projects...er_heating.htm
    --Ray
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  5. #5
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    Silver solder and brazing are basically the same thing.
    I would only silver solder the joints on the piping not the absorber to the tubes.
    Your design is good if you are only going to use one collector. If the plan is to build multiple collectors do a header/riser type collector. The only changes to your design is where you end the header tube with an elbow you would use a Tee. This would allow for parallel flow through multiple collectors. Your set up would mean they would be in series. In series each collector down the line from the first will harvest fewer and fewer BTU's, Due to higher operating temperatures in each successive collector.
    Ultimately you want to have a storage to collector ratio of about 1 1/2 gallons per square foot of collector. This is why I said to increase your storage to 4 1/2 -5 gallon.

  6. #6
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    Quote Originally Posted by raydias View Post
    You might want to review the following resource.

    http://www.builditsolar.com/Projects...er_heating.htm
    Thank you. I've looked at that site for hours There's some very good information in there; Low budget and fancy stuff too. I marveled at the 80 x 8ft (I think??) hot air collector!!



    "I would only silver solder the joints on the piping not the absorber to the tubes."
    I will do this exactly

    "......The only changes to your design is where you end the header tube with an elbow you would use a Tee. This would allow for parallel flow through multiple collectors. Your set up would mean they would be in series."
    Hmmm, I'm not sure I follow this, but I'll look into it. Multiple panels would be tough for me, for budget reasons. All panels would probably need to be the same size, which means the same glass, which is the most expensive material of the panel if we're talking larger than 4x4ft. Regardless I'm taking note of the advice in a file. I'll build as materials and money permit but this little guy is basically free and perfect to learn with.

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    Good article on building collectors
    The only concerns I have would be if moisture got between the aluminum and the copper. This may be alleviated by the silicone as it would be a dielectric insulator. Otherwise the aluminum will corrode very rapidly.
    Second concern would be using and fastening to a plywood back. I would prefer to see the absorber raised off the backing With a foil faced insulation and air space between. This would be a bit more time consuming but could be accomplished by assembling on a piece of sacrificial foam or homosote and fastening the two parts of the absorber together with pop rivets instead of staples.

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    Quote Originally Posted by Spiral_72 View Post
    Thank you. I've looked at that site for hours There's some very good information in there; Low budget and fancy stuff too. I marveled at the 80 x 8ft (I think??) hot air collector!!



    "I would only silver solder the joints on the piping not the absorber to the tubes."
    I will do this exactly

    "......The only changes to your design is where you end the header tube with an elbow you would use a Tee. This would allow for parallel flow through multiple collectors. Your set up would mean they would be in series."
    Hmmm, I'm not sure I follow this, but I'll look into it. Multiple panels would be tough for me, for budget reasons. All panels would probably need to be the same size, which means the same glass, which is the most expensive material of the panel if we're talking larger than 4x4ft. Regardless I'm taking note of the advice in a file. I'll build as materials and money permit but this little guy is basically free and perfect to learn with.
    If you are looking for cheap glass look into recycled sliding glass doors. Many times you can get them for free or very low cost on places like Craigs list. just build your panels to fit the glass you can get. For system size a general rule of thumb is about 15 square foot of collector per person if you are building for a domestic hot water system.

  9. #9
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    Just an update to let you know I didn't disappear. I have the box made, the window frame cut to size and 1/2" foil faced foam in the bottom. I tacked a cut piece of corrugated aluminum painted black over the foam.

    It's now time for assembling the pipe which will take me a couple days to get to. From there I'll need to get some bulkhead fittings for the metal 5g tank and connect the pieces together.



    Also FYI, that was an excellent suggestion about the door glass. I'm the proud owner of a single piece glass storm door. It appears to be double pane and I would guess 36"x80" but I haven't measured it. It's in an aluminum frame so I'm not sure what I'll do with, or if I'll use the frame. I'm figuring the door is a standard size, which should theoretically make it easy to build multiple panels of the same size.

  10. #10
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    I put my water heater to use this morning. It was filled with a starting temp of 75 degrees. It quickly rose to 140 degrees but it never moved water. I'm not sure why just yet, but I purged it of air several times. I had to make a run across town so I covered it for the best part of the day unfortunately. When I come back I hooked a small submersible pump to the cold water feed inside my 5gal metal pail to force flow. I never saw any signs of escaping air, so maybe I have something wrong.

    Regardless, I'll play with it some more later. I ain't gonna give up this easy!

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