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Best pipe material for solar heater  RSS feed

 
Luiz Eduardo Piá de Andrade
Posts: 23
Location: Curitiba, Brazil
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I'm planning on building a solar heater similar to this one (site in Portuguese, but the images are self-explanatory). I'd like to know which material would you recommend for that, taking into account that it must withstand the brazilian sun and high temperatures. The material should be safe (not leach chemicals such as BPA and dioxins), and as sustainable as possible.
 
Andrew Jackman
Posts: 28
Location: Salt Lake City, UT
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In Hawaii, with a solar hot water heater, we had PVC melt and sag because of the temperature of the water running through the system. In addition, PVC is usually not UV stabilized, and will become, at the very least, brittle in the sunlight. I would not use PVC in anything directly plumbed to the thermal collector.

In addition, I would like to mention that legionella is known to be a problem anyplace where water is left to stand at warm to high temperatures. Consequently, I recommend using a heat exchanger of some kind to prevent standing water in a system exposed to humans.
 
Luiz Eduardo Piá de Andrade
Posts: 23
Location: Curitiba, Brazil
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Yes, PVC is already out of the question. CPVC may work, but I'd need information from someone more knowledgeable than me on that.

I'd connect a pump (solar, possibly) to circle the water from the gas heater's storage tank (which we've had for a decade and have had no legionella problems thus far) to the solar heater and back. Do you think bacteria could be a problem in that system?
 
Andrew Jackman
Posts: 28
Location: Salt Lake City, UT
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I like that design. Direct exposure to sunlight is completely avoided and assembly looks easy.
 
Dean Howard
Posts: 126
Location: NE ARIZONA, Zone 5B, 7K feet, 24" rain
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CPVC may work, but I'd need information from someone more knowledgeable than me on that.


CPVC is able to withstand temperatures to 180F, and that makes it good for hot water, but a solar collector like you are showing could get much, much hotter. It's also brittle, meaning it will crack along it's length when frozen.

PEX can expand a number of times before breaking from freezing or fatigue (maybe 20 times). Neither is made for solar applications, though you may get by if the system isn't running near the breaking point.

Black poly tubing frequently used for drip irrigation is what is commonly used in the Frenchman's (Jean Paine? Payne?) compost pile heater...with temperatures getting no where near what you might expect from a roof-top solar unit. There is a good reason they use copper and other metal tubes, with anti-freeze, for a heat exchanger. They get very, berry, very, berry hot!
 
Luiz Eduardo Piá de Andrade
Posts: 23
Location: Curitiba, Brazil
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Dean Howard wrote:
CPVC may work, but I'd need information from someone more knowledgeable than me on that.


CPVC is able to withstand temperatures to 180F, and that makes it good for hot water, but a solar collector like you are showing could get much, much hotter. It's also brittle, meaning it will crack along it's length when frozen.

PEX can expand a number of times before breaking from freezing or fatigue (maybe 20 times). Neither is made for solar applications, though you may get by if the system isn't running near the breaking point.

Black poly tubing frequently used for drip irrigation is what is commonly used in the Frenchman's (Jean Paine? Payne?) compost pile heater...with temperatures getting no where near what you might expect from a roof-top solar unit. There is a good reason they use copper and other metal tubes, with anti-freeze, for a heat exchanger. They get very, berry, very, berry hot!


Freezing shouldn't be a problem, we get occasional frosts, but nothing so severe as to freeze things over. So basically you're saying PEX would be a good choice, but copper even better?
 
Rose Pinder
Posts: 410
Location: Otago, New Zealand
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Polypipe HDPE is rated to 120C (that's above boiling), and is what I've assumed is being used in Australasian examples of compost hot water systems. Not sure how that differs from PEX though.
 
Luiz Eduardo Piá de Andrade
Posts: 23
Location: Curitiba, Brazil
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Rose Pinder wrote:Polypipe HDPE is rated to 120C (that's above boiling), and is what I've assumed is being used in Australasian examples of compost hot water systems. Not sure how that differs from PEX though.


Good tip, I hadn't heard of HDPE before. A quick search yielded few useful results, it may be hard to find low diameter pipes, but I'll look into it.
 
Roy Hinkley
Posts: 264
Location: S. Ontario Canada
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Copper is a great conductor. I can't think of a better material for a collector.
 
Joe harrington
Posts: 5
hunting solar woodworking
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Roy Hinkley wrote:Copper is a great conductor. I can't think of a better material for a collector.


Also the copper will help prevent the growth of bad bacteria. CPVC will not work very well anyhow(Ask me how I know).
 
Juan Sebastian Estrada
Posts: 94
Location: Medellin, Colombia
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William already pointed you to builditsolar.com

There are tons of info and designs there, check them to see performance, materials so you can make a choice. Gary (the site owner) has done a lot of experiments with PEX and PEX-Al-PEX in comparison to copper, basically because even though copper is the material of choice in terms of conductivity it can be much more expensive.

The design that you linked to is not insulated but just an air exposed (unglazed) collector which is normally used for pools but not so useful for home water heating. You might want to look into glazed (where the collector itself is contained in a box with a glass or polycarbonate glazing to induce a greenhouse effect and retain the heat) collector designs which will be much more efficient. Having said this glazed collectors also get much hotter thus making the material selection more important. In any case the system should be of thermosyphon design so it will have water in the tubes at all times to cool them, otherwise the collector might stagnate and melt or seriously damage any plastic (e.g. cpvc) materials.
 
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