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Old 10-09-2008, 04:36 PM   #1 (permalink)
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PEX solar hot water collector

This is to try and entice more of you to check out EcoRenovator.

Experimental PEX Solar Hot Water Collector | EcoRenovator.org

Quote:
Over on BuildItSolar.com they have been experimenting with a new and much cheaper design for solar hot water collectors. The idea is to use PEX tubing with aluminum absorption plates instead of the traditional all copper design. With copper at such high prices these days this design provides a substancial cut in cost. This is not to mention its pretty darn easy to make yourself. How does the tune of around $150 for a 4′x8′ collector sound? Thats about 1/5 the price of a commercial collector!

Of course, there is a down side. The collectors efficiency is not quite on par with its copper cousin. The PEX collector operates at roughly 85% efficiency compared to the copper unit. Not a huge hit there, but there are also questions about the ability of the PEX to hold up to prolonged exposure to sunlight and stagnation temperatures (when water isn’t going through the collector). I guess time will tell.

In the mean time, check it out and let us know what you think here or discuss it on the forum.

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Old 10-09-2008, 06:37 PM   #2 (permalink)
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Great idea! Just what I've been wanting to do! Thanks for the tip!

I built my 24x36 shop to be passive solar heated. The long side faces due south, windows (south side only) are argon filled without heat reflective coating and are approximately 10% of floor square footage. Even in winter the inside temp is quite moderate without any additional heating source. Once I seal everything up, insulate and drywall I'm quite sure it will be downright comfortable in winter.

Passive solar really works! In the warm months the windows are shaded by the eaves and contribute only reflected light. The side benefit is it almost eliminates the need for lights in the daytime year round.

The next house we build will be passive solar heated, I'm sold!
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Old 10-09-2008, 07:57 PM   #3 (permalink)
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I've seen first hand what happens when you use pex on the hot side of a solar hot water collector, we used some to allow for some flex between the copper of the collector and the copper lines running to the house, about 3 months in to the system being up and running we got a call from the home owner saying the saw a blue stream of steam and water shooting 20 feet in the air, I collected some tools and went to check it out, the pex we used had melted, swelled and burst, sending a stream of boiling antifreeze/water mix shooting in to the air, if someone had been near it they would have been burned, maybe killed.
we figured that the one end of the panel with the pump controls had just enough shade that the pump didn't come on for a few minutes, while the rest of the panel got hot enough that the pex that was rated at over 280 degrees melted, normally in systems like this you have a temp release valve that opens at 260F to protect the pex that is in the concrete slab, and later systems instead of having a piece of pex to flex, they use radiator hose or hydrolec hose.
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Old 10-09-2008, 08:20 PM   #4 (permalink)
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So, as long as you design for the system, you should be alright?

Do you know what kind of PEX you used? It seems this PEX-AL-PEX can withstand higher temps and pressures.
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Old 10-09-2008, 09:42 PM   #5 (permalink)
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It was the type of pex that has a layer of aluminum between the layers of plastic, it's designed that way to keep oxygen from being absorbed by the fluid, leading to faster corrosion.
but yes, a well designed system shouldn't have that type of problem, and part of that good design should be to use tubing that can handle high temperatures, the a solar collector is collecting alot of energy, it should be designed to handle it without creating a danger.
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Old 10-10-2008, 01:37 AM   #6 (permalink)
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Interesting, but just what the f*** is PEX? Never heard of it before...
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Old 10-10-2008, 07:08 AM   #7 (permalink)
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PEX tubing is a form of flexible plastic tubing that is slowly replacing copper water lines in new house construction. Its much cheaper and easier to work with.

Cross-linked polyethylene - Wikipedia, the free encyclopedia
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Old 10-11-2008, 11:18 AM   #8 (permalink)
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PEX is cross-linked polyethylene.

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