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  • Aluminum vs Copper

    What are the pros and cons, Aluminum fins vs Copper tube manifold in thermal panel domestic water heating in New Mexico? Thank You!

  • #2
    Not an expert but to my knowledge the biggest difference will be the fluid you use. Aluminum will require using glycol. The other main difference of course will be price. Copper is expensive.
    MSEE, PE

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    • #3
      Depends on the design, but being in NM or elsewhere doesn't matter much. It's pretty much the same all over.

      Best advice: buy a book on solar thermal heating. Best around is still Duffie & Beckman: "Solar Engineering of Thermal Processes"

      In the meantime:

      - Don't use dissimilar materials.
      - Copper will probably give longer service but cost more. Some of that cost difference will be mitigated by the thicker fin sections required for aluminum to get the same performance.
      - Believe me on this: The tube to fin attachment is critical. Clamping, no matter how tight is a poor performer. Gluing will not last. It's easier to get a metallurgical bond with copper (soldering, etc.).

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      • #4
        Aluminum is really difficult to work with. Unless you have skill with the stuff, I'd avoid it.

        I'm also making my own collectors, but I bought factory made 'thermal strips' with copper tube bonded to aluminum fins and with a semi-selective coating.
        It cost me less than using all copper.
        I bought the strips 9 years ago, when the price for collectors here in Portugal was simply ridiculous [1,000 euros, $1,200, each]. I'm only starting work now, and intend to follow though on the original plan, but today I could buy factory made collectors for only $500 each.
        The cost of building my own will be between $300 and $400.

        When I was doing my research, I found there were 2 factories making those strips, one in Canada and one in Norway. They send it out flat, in huge coils to collector panel builders, who cut to length and inflate the copper center tube with some sort of high pressure machine.

        I inquired with the factory, and they gave me a contact for a local shop that would sell me unrolled inflated strips cut to length and ready to assemble.
        That was 9 or 10 years ago so things may have changed.

        I still have to weld or braze all the copper tube ends to the headers.

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        • #5
          Thanks, I am buying new panels but wished to know the performance and durability between copper tubing vs aluminum fin factory panels using a glycol/water mix. I assume the copper is the more efficient absorber, but am clueless as to durability difference between copper and aluminum with a glycol mix as far as acidity damage. I am not familiar with the copper plus aluminum fin panels, only totally copper or totally aluminum.

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          • #6
            Originally posted by mark in Portugal View Post
            Aluminum is really difficult to work with. Unless you have skill with the stuff, I'd avoid it.

            I'm also making my own collectors, but I bought factory made 'thermal strips' with copper tube bonded to aluminum fins and with a semi-selective coating.
            It cost me less than using all copper.
            I bought the strips 9 years ago, when the price for collectors here in Portugal was simply ridiculous [1,000 euros, $1,200, each]. I'm only starting work now, and intend to follow though on the original plan, but today I could buy factory made collectors for only $500 each.
            The cost of building my own will be between $300 and $400.

            When I was doing my research, I found there were 2 factories making those strips, one in Canada and one in Norway. They send it out flat, in huge coils to collector panel builders, who cut to length and inflate the copper center tube with some sort of high pressure machine.

            I inquired with the factory, and they gave me a contact for a local shop that would sell me unrolled inflated strips cut to length and ready to assemble.
            That was 9 or 10 years ago so things may have changed.

            I still have to weld or braze all the copper tube ends to the headers.
            What is actually cold pressure welding can be a suitable joint with respect to heat transfer provided it stays durable over repeated thermal cycling. There is some research that suggests the copper may exhibit work hardening under differential expansion with AL.

            Getting the header joints leak tight may take some practice, especially if the tube is a non round section. I'd guess that the header could be a source of some leaks and PITA, particularly if the AL portion is heat joined to the header. Heat joining (soldering/brazing) to the headers may also upset the Co/Al cold weld for some distance down the tube.

            The surface coating of the AL may not be durable with respect to moisture/humidity.

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            • #7
              For performance, the manufacturers give numbers. Durability is harder to work out.
              Copper is less prone to corrosion; your glycol mix will protect either metal. if the price difference isn't great, I'd go for copper. Other factors are likely to be just as important though. Insulation, side and back material, quality of the coatings. Anything expecting to live 20+ years in the weather has to made to take a real beating.


              Regarding my build; I don't remember how the aluminum fins are bonded to the copper but I was impressed at the time [and I don't easily impress]. The strips are made to be welded to headers and I saw that being done at the small factory in Holland where I bought them. they were using mig.

              I have a cheapo tig attachment for my DC ark [stick] welder and i might give that a try. I'm very good with mild steel but gave limited experience with other metals.
              90 strips makes 180 joints; at the factory they added 2" little stubs to each end between the strips and headers, so 360 joints to weld.

              A friend of mine has a mig he hasn't used in a long time, I might borrow that. I need gas either way and that costs a lot here.

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              • #8
                1st choice copper fin with copper tubing.
                2nd choice aluminum fin with aluminum tubing.
                Not advisable aluminum fin with copper tubing.

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                • #9
                  Originally posted by mark in Portugal View Post
                  For performance, the manufacturers give numbers. Durability is harder to work out.
                  Copper is less prone to corrosion; your glycol mix will protect either metal. if the price difference isn't great, I'd go for copper. Other factors are likely to be just as important though. Insulation, side and back material, quality of the coatings. Anything expecting to live 20+ years in the weather has to made to take a real beating.


                  Regarding my build; I don't remember how the aluminum fins are bonded to the copper but I was impressed at the time [and I don't easily impress]. The strips are made to be welded to headers and I saw that being done at the small factory in Holland where I bought them. they were using mig.

                  I have a cheapo tig attachment for my DC ark [stick] welder and i might give that a try. I'm very good with mild steel but gave limited experience with other metals.
                  90 strips makes 180 joints; at the factory they added 2" little stubs to each end between the strips and headers, so 360 joints to weld.

                  A friend of mine has a mig he hasn't used in a long time, I might borrow that. I need gas either way and that costs a lot here.
                  Mark: You appear to have some solar knowledge. A little knowledge can be a dangerous thing. If you are even semi serious about solar thermal energy, NOMB or concern, and this isn't meant as a knock, but from what and how you write, it looks to me like you could benefit from a bit of knowledge as to how things work and what's available in the solar thermal world. More Do yourself a favor and do one or both of the following for starters:
                  :
                  1.) Acquire and read the Duffie and Beckman book. It's the solar thermal bible.

                  And/Or:

                  2.) Buy available solar flat plate collectors w/copper collector pates/fins and tubing and the rest of the required equipment and have it installed by reputable vendor. There are many decent products that will give a long service life.

                  Good luck.

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