you should not have pex in line with collector temperature water. you can melt a hole in it and blow your fluid out. not much fun.

I'd say that is similar to what SRCC is discussing - PEX is OK with solar collectors that run at atmospheric pressures and similar low pressures. But use a pressure relief valve to make sure that you never get high (or even medium) pressures. High pressure and high temperature will be a problem. So will the few feet near the collector (so use copper there).

http://thermalproductsinc.com/wp-content/uploads/2010/07/SRCC-PEX-Policy-Drainback-Systems.pdf

If there is no possible way for the system to exceed 212 deg F then I might buy it... and that includes all failure routes including any potential failure to drain back.

Any flash or stagnation though and I don't care who allows it... I've seen a melt through occur, and raining superhot fluid down is not a place anyone ever wants to be. Maybe it was pressure, I don't know... but I wouldn't risk it.

There are some drainback configurations I might trust with this but there are many more I would not.

If the PEX is in the radiant floor, is it safe to assume there are lots of parts between the solar panels and the radiant floor? Such as a heat exchanger, manifold system, pressure relief valves, expansion tank, water storage tank etc? Unless the radiant floor tubing is hooked directly up to the solar panels, without any tempering system in between, then there might be a problem, but other than that, the PEX in the floor should be fine. How hot are you running the water through your PEX?

I have pex tubing maybe 30-40 feet from the collectors. I run copper tubing the 30 ft to make collector conections. Its a glycol system and runs at 10 psi. with a healthy expansion tank on return side. Normally the temps never get high enough to be a problem. But what would happen if there were a power outage and temps get to lets say as an example 250-260f. If the press stays at 10 psi what will happen. will the pex soften enough to blow or leak past a swedge fitting? turn into a Salvador Dali painting? This would be for a short period, untill return fluid runs the through collectors to cool system down. The collectors are hooked up to a slab radiant floor so a pretty big hear sink. fluid has never come out of the slab higher than 78-80f. Normal temps going is has been 80-95f I aim for higher volume lower temp for the system. Normally tems raise 20f at the collectors and lose 20f through the slab. So higher temp for short period, with lower press.
NRt ROB have you seen pex blow at lower press settings? You have me thinking about changing to all copper on my run to the slab.

No, definitely the blowout I saw was on a closed glycol system. I do believe it had a pressure relief valve but not near the collector.

but that said, I can see that MOST drainback configurations have failure possibilities that would prevent drainback, such as a leak filling the drainback resevoir. In any case like that I would definitely not consider using PEX in the collector circuit.

some drainback can't fail to drain back, and in those cases I imagine it's pretty safe to transition to pex away from the collectors at low pressures.

I am certified for 2 European packaged water heating solar systems and for one domestic solar panel company; none of the three allow "professionals" to use PEX on an part of the solar panel link for not-so-obvious reasons it appears. Note that the pressure rating goes down as the pressure goes up. When in doubt do the conservative thing.

jonr, this is a good find on the SRCC standard, but do you know of a manufacturer that allows it?

I would recommend copper for a DIY solar system (flexible stainless steel is common in current domestic hot water systems) and temperature control for PEX tubing in the envelope. There are two whole industries built on high water temperatures and pressure vessels; one is mechanical engineering and the other is insurance.

But hey, if Rosalinda says it OK...

I'm all for conservative design and sticking to manufacturers recommendations, but for the sake of discussion, you aren't going to get fluid temperatures over 230F at atmospheric pressures (because it would boil away). Looks like PEX is still good for 30+ psi at that temperature.

Note that no bladder is large enough to absorb the pressure that will be created once fluid starts to boil - only an atmospheric vent or low pressure relief valve would do that.

To all
First to Badger biolerMN Not sure what you mean in your last sentence to Rosalinda? I didn't see anything wrong with the statement. Is this somthing personal between you two and your voicing on my question? Nowhere did rosalinda say anything was ok.
Maybe I'm reading into your statement but WTF??
And I am convinced, I will change over my tubing to copper on the inlet side. I already have a popet valve in the system for over pressure.
Thanks for the help

Rosalinda said; "the PEX in the floor should be fine." Not O.K., I stand corrected.

Rosilinda is a new "expert" and I too like to have fun.

To my knowledge their is no PEX on the market rated for steam at any pressure. As for an expansion tank, the Germans actually promote a system that does change phase (I am considering it for a space heating solar application here in MN) and this would make the drainback system with its attendent limitations obsolete. I worked on a number of drainback solar systems in several states that were installed in the 70's and quickly gave up the ghost for a variety of reasons.

I have been doing solar thermal systems for over 30 years now. I would not recommend using pex for inlet or outlet piping to a solar array, just looking for a problem. Stagnation temperatures can approach 250F very easily. In fact I have seen old systems which were soldered using 50/50 which melts at 350, and there were plenty of leaks. If you are looking for a alternative choice for collector piping then try Solarflex by Omega.To take full advantage of the sun's energy , the solar should be allowed to produce temperatures as high as possible. Tempering the fluid should only be between the flooring pex and the thermal storage.

Morgan, nothing like taking what I said out of context. I said if the PEX is separated from the collectors by all of the items I mentioned, then it is fine to use in the floor with solar heated systems. At that point in the thread tandemsforus had not said where in the system the PEX was located, just that it was 30 feet from the collector. Reading and comprehending is also a skill.

Tandemsforus - yes it is personal - BadgerBoiler is irked that I could read and research, and then design, build and install a properly functioning radiant heating system without a professional to supervise, design and install the system. He also does not think I should share what I learned in the process since I do not carry any licenses for the 5 trades he feels must be involved in the process. I did get great advice on this board though, even some from BadgerBoiler, as I am sure you will.

PEX will melt at high enough heat, turning it to melted goo (a technical term). How high that heat and pressure need to be I leave to the professionals, but it should not be used on the collector side of the system, as you have gleaned from this thread. For folks who have large water storage/buffer tanks, I have read that they do use PEX from the tank to their manifold, in circumstances where the water in the tank never gets anywhere near boiling.

-Rosalinda

Reading Badger's post, he did not take anything from your original statements out of context. He simply stated his credentials and certifications, stated that based on the training he received to receive those certifications, PEX would not be allowed from the output of a solar panel. He then made a recommendation to use copper for this purpose. I agree with you that reading and comprehending is also a skill which is why I disagree that you stated that all of the items mentioned were required. Your original post stated "is it safe to assume there are lots of parts between the solar panels and the radiant floor? Such as a heat exchanger, manifold system, pressure relief valves, expansion tank, water storage tank etc?" This appears to be a question that has a list of suggested items to be located between the solar panels and the radiant floor, not a statement of a requirement. Even if it was interpreted to be a requirement, the original question was in regard to the temperature of the water. Can you explain to me how (other than standby losses) a manifold system, pressure relief valve, expansion tank or water storage tank will reduce the temperature of the water as seen by the PEX? The only item that will isolate the collector water from the PEX in the floor is the heat exchanger and that because there will be no power to operate the circulators if there is a power failure. You start your statement with "is it safe to assume". Having been reading this and other heating forums for over a year now, and from my own experience performing product safety evaluations, I can state categorically that it is NEVER safe to assume that anything was designed, specified or installed correctly. This is why Badger and the other professionals on this board will never make a statement like "you should be fine" or "that will be OK". They realize that any it is not possible to make a statement like that unless you have been involved in the design and/or installation of a project. They also realize that in today's litigious society, a statement like that can be taken to be a professional opinion and they can be held accountable if there is in fact a problem with an installation and they have made such a statement. Since Badger has been in the business for a while, I am sure he has either been involved with or knows of someone who has been involved in just such a law suit. This is also why when they give advice, they can be seen to be unwilling to help someone in need and it seems like they are only promoting the use of a “professional”. They realize that it is often not possible to provide the requested information without actually having hands-on access to the problem and if they provide advice, they may be held accountable. As for Badger, he has his good days, he has his bad days. Sometimes he even has “snarky” days (according to NRT.Rob in another post). Sometimes, he even makes a joke. However, the information he provides is always sound advice based on his wealth of knowledge.

OK boys and girls
Lets calm down here.
I asked a question amd appriate all the answers I recieve. If someont states an opinion as to what they feel is ok, I take it at that, an opinion no more no less. If they make a statement as fact then I am sure they can back it up as fact.
So lets not get into the he said she said thing. If you disagree just say so, and give an opinion as to why you disagree.
I come on this board to ask questions and learn. Its great for that. But when the inhouse fighting starts, its not a fun board to read.
Just MY opinion...

Copper....Copper copper copper
I suggest Copper,
Did I say copper.
Dan
Disclaimer, I do not sell copper!

I couldn't have said it better NH.

I have in fact been a contractor, distributor and manufacturer of hydronic heating equipment both here and in Canada. I have unfortunately been involved with the misapplication of sound technology and/or the poor installation of otherwise good products resulting in "property damage, personal injury" and most regretfully "death" as most installation manuals will state. Many of these unfortunate mishaps were the result of professional mistakes and many were caused by unqualified personnel both professionals and layman alike.

I work for lots of folks all over the North America from handy DIYers to engineers, mechanical and otherwise. They know each disipline has its own skill set and I help them decide which applies to their situation.

As to new "experts"; I poke fun to illustrate their ignorance lest some less experienced sole may be hurt by what they may say or leave out. It is one thing to venture out on your own behalf with "good reading and comprehension skills" and another to advise others on technical specifications you have only just discovered yourself.

I realize I am at times a bit sharp (and other times quite dull I'm sure) but always honest and never hide behind a noms de plume. Erasible yes, snarky maybe (that one hurts a little), but never smarmy.

At least you're not a curmudgeon.

Thank you, I think...heheheheee