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  • 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.
    Attached Files

  • #2
    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.
    NABCEP certified Technical Sales Professional

    [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

    [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

    [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

    Comment


    • #3
      "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.

      Comment


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

        http://www.builditsolar.com/Projects...er_heating.htm
        --Ray
        8xSV-X-195-LV - 22.80 Voc - 18.30 Vmp - 10.66 Imp - 11.55 Isc
        2xUL Solar 85w - 21.9 Voc - 17.9 Vmp - 4.84 Imp - 5.17 Isc
        1xUL Solar 120w - 21.9 Voc - 18.1 Vmp - 6.6 Imp - 6.8 Isc
        7xHF 15w - 23.57 Voc - 17.5 Vmp - 0.86 Imp - 1.15 Isc
        MorningStar MPPT 60 Charge Controller
        Midnite Classic 150 Charge Controller
        700ah used Gel batteries
        Xantrex PROWatts 600 PSW Inverter
        HF 1000/2000 MSW Watt Inverter

        Comment


        • #5
          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.
          NABCEP certified Technical Sales Professional

          [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

          [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

          [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

          Comment


          • #6
            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.

            Comment


            • #7
              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.
              NABCEP certified Technical Sales Professional

              [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

              [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

              [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

              Comment


              • #8
                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.
                NABCEP certified Technical Sales Professional

                [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

                [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

                [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

                Comment


                • #9
                  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.

                  Comment


                  • #10
                    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!

                    Comment


                    • #11
                      I noticed something interesting. I have 1/2" CPVC cold water supply from the bottom of the bucket feeding 1/2" CPVC parallel tube collector. The top line of the collector uses 3/4 to 1/2 CPVC reducing tees for a 3/4 hot water output line.

                      The bucket is 3ft over the bottom of the collector. The hot water line runs up about 16" and drops back into the bucket.

                      I poured water into the hot water pipe but could not fill it up. There were no leaks, so I reached my hand into the bucket and plugged the cold water supply..... was able to fill the HW pipe. So this tells me, the thermal expansion is pushing water back through the CW supply pipe!!

                      I'm wondering about turning the collector 180 degrees so the 3/4 line becomes supply and the 1/2 line becomes HW output in an effort to increase water head on the supply.... and decrease water head on the output (smaller pipe I.D. means less volume and less water head). This isn't how all the other collectors I've seen are built, but it's obviously not going to work how it is. The water just stays in the collector until it boils now. I have the "Thermo" part down, but the "Siphon" not so much

                      Comment


                      • #12
                        The hot water line runs up about 16" and drops back into the bucket.

                        Remember thermosyphon works by hot water rises and cold water sinks.
                        A chimney effect is required to get the hot water moving.
                        The HW tank has to be above the highest outlet of the collector with minimum fittings.
                        1/2" pipe is really small to expect thermosyphon to take place , increase the outlet & inlet to to 1" that may help and insulate the lines.

                        Comment


                        • #13
                          Hmmm, perhaps I did not explain myself very clearly. I'll try to post a picture of my setup in the morning, weather permitting.

                          The 16" rise on the hot water pipe is above the collector and the bucket, or about 4-1/2ft off the bottom of the collector.

                          The collector is sitting on the ground at an angle, propped against a table. On the table is my metal 5gal tank.

                          I'm surprised to hear, try 1" pipe, however maybe you are correct. For that I'll need to spend some money!

                          Comment


                          • #14
                            Alright it works. I was trying to lift the hot water above the water line and dump it over the lip of the bucket. I didn't realize you had to bore another hole in the side of the bucket to output the water AT the water line.

                            That sure puts a wrench in my idea of using this for the hot tub! Hopefully tomorrow I'll test it again with the output submerged to see if it still works.....


                            It really moves water man! It's pretty amazing the volume cycling through there with such a low temperature (90 degrees). I have it setup for tomorrow to take advantage of full sunshine.

                            Comment


                            • #15
                              One full day of sunshine. I started it at 10am this morning. The water was 56 degrees in an uninsulated metal bucket with the lid off. I rotated the collector every 45 minutes or so to track the sun.

                              By 3pm the water was 122 degrees, the top of the collector 130 degrees and the 122 degrees at the bottom. I saw that 6-8 degree temp differential all day.

                              The interesting thing is, I got the same flow all day long which leads me to think the volume is related to the temp differential across the collector..... and MAYBE a very tall collector would flow a higher volume. That's just a theory though.


                              SO, my little 16" x 28" CPVC collector heated 5gal of water 66 degrees in about 5hrs. If I insulate the bucket and lines it might do the same in 4hrs???

                              I'm going to play around with the design a bit to see what I can improve, then hopefully make a copper version.



                              Any thoughts or opinions or questions???? I still haven't posted a picture, sorry.

                              Comment

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