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Thread: pex in solar radiant heat system

  1. #1
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    Default pex in solar radiant heat system

    Question
    I am running a solar powered radiant floor using pex.
    My pex says its rated at 100psi at 180f. how does it fail if temps go higher. Does it soften and blow out at swedged fittings? I have pex tubing starting maybe 30 feet from collectors (copper tubing to and from collectors), And the system runs at 10 psi. Could I be looking at problems if I have a power failure to pump? I have never read anything about pex failure at lower press with higher temps.

  2. #2
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    Follow the PEX temp limits!

    Why such hot water to the floor - my system is setup at 35

  3. #3
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    russ
    where did I say what temps I was running to the floor. I was asking what higher temps do to pex if press is kept low . I do not run anything near those higher temps. But what might happen if the pump doesn't run from power outage, then come on. Some very hot water might run through the pex for a short time. what would the pex do if temp were higher than rated at 180f. the specs say 100psi at 180f. ok fine, what about 240f at 10 psi. what happens? does the pex look like a Salvador dali painting?that was my question.

  4. #4
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    You didn't bother to explain what you were talking about then.

    Your panel's stagnation temp is well above 100

  5. #5
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    The pressure rating drops as the temp goes higher. Somewhere around 250-300 F it will get soft and deform and blow out.

  6. #6

    Default Pex

    Like Lucman said at the higher temps it will deform and blowout. What I have also seen is when constant hot temps even within guidelines is a hardening of the pipe. (constant flow of 150F-60PSI) It will then start to split at stress points. It is definitely worth protecting the pipe.
    Something else to consider is what the tubing is in. Concrete is only rated to 150F. And look at your floor coverings. Most wood should only get to 80F measured at the floor surface.

  7. #7
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    Thanks for the replys.
    I am going to change over my pex to the floor manifold to copper.
    Thus far the hottest the fluid has gotten from the panels is in the high 90s f. I aim for higher gpm/lower temps. My problem is what would happen if there was a power outage and panels would sagnate, its sure to happen. Then it sounds like there could be a big problem even if the temps reaching the pex was for a short time and press. I am running the radiant floor in my basement which is my shop, thus bare cement. Warmest the fluid has been comming out of the slab has been maybe 80 or so, Seems like there is about a 20 degree temp change from incomming to outgoing fluids.

    Russ I didn't try to russel any feathers, I value your opinions. My origionl question was more theoretical, just wonderin what happens to pex when fluid temps raise above 180f with low press.

  8. #8
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    No problem - As we bounce things around we all learn.

    Sometimes even relearning things as the original knowledge turns out to be faulty!

    Russ

  9. #9
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    That problem is solved by using a simple tempering or mixing valve to maintain a constant temp into the floor by mixing the cooler return water with the hot fluid from the collectors before entering the PEX and regardless of what the source temperature of water is will keep the floor from overheating. These are used in boiler situations where there is a radiant loop and radiators running off the same boiler the radiators may need 180 degree water but the floor radiant you only want 90 degree water.

    A good explanation is here with diagrams.
    http://www.radiantec.com/pdf/Install...ing_System.pdf

  10. #10
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    How does that help during a power outage and the collectors stagnate as my question asked. If there is no fluid pumping from a power outage to the pump there is no mixing, or am I missing somthing. Thats was my question, possible pex problems during stagnation. While the pump is running I am getting no where any temp that might be a concern. As I said in my post while the pump is running the max temp I ever reached was in the high 90s f.

    This brings me to another question. I have a press relief valve, one for a hot water tank in the system. I also have a about 5 gal pressure tank with 10 psi on the bladder.
    If the system stagnates how fast could the fluid pressure buildup? And should I find a relief valve set at a lower pressure. I am running the system at 10 psi and am using a 40/60 mix of propolyene glycol. The system, collectors, in floor tubing uses about 20 gal of fluid.
    Ideas

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