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Solar Code: Minimum standards guideline.

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Mark Eatherton
Mark Eatherton Member Posts: 5,853
Greetings fellow Wallsters,



I had a meeting at the mountain home with 14 local high grade hydronic/solar thermal contractors who are concerned with the lack of standards as it pertains to solar thermal systems.



They are proposing putting together a set of minimum standard guidelines thru the local solar energy industries association (CoSEIA.org). I will kick this thread off with what I see as relevant areas that need to be concerned,and would solicit your input as it pertains to minimum standards of installation. For example, "Piping between solar collectors and mechanical package" Minimum pipe type should be type M copper tubing, side to maintain velocities as follows; Blah, blah, blah, ad solar nauseum, blah blah. I kid you not, these guys are coming across installations by alleged "qualified" contractors who are using PEX between the collectors and the mechanical room...



Having been involved with clean up of the last solar debacle in the late 70's, I DO NOT want to see a repeat of that mess, and will do whatever I can to help avoid it.



I told the group I would work with them to come up with a presentable document that we can then present to the AHJ's throughout Colorado (and the US and Canada for that matter) so that when they see someone doing something silly, like running PEX between collectors and mechanical room, that they can comfortably turn down the inspection and request corrections.



Please keep focused on THIS thread. If you have something UGLY to share, post it under a different heading, that way we keep this thread focused on the code issues we see that need to be addressed.



Many thanks to Dan and TLLM for giving us the forum in which we can present this information.



ME

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Comments

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Collector to Mechanical Package Piping:

    Need to address minimum pipe type, weights, soldering type, support, penetration sealing and insulation, etc.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited October 2009
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    Roof Mounting Details

    Minimum standard is usually dictated by the manufacturer, but additional caveats need to address proper orientation, height above potential snow loads to allow shedding, wind loading in certain locations (Boulder), anchoring, ability to withstand dead loads imparted etc.



    Avoiding dangerous collector snow "unloading" situations that might cause loss of life or property.



    Proper methods for sealing mounting hardware, piping penetrations etc.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Storage Considerations

    Gallon of storage to collector array aperture ratio, type of approved materials for drain back, closed loop, access for repair/service/replacement.



    Need for isolation and unions. Minimum insulation standards for near storage piping, and storage tank piping.



    Minimum piping types and weights.



    Antiscald temperature control between solar preheat and auxilliary, and between auxillary and loads.



    Recommended patterns for circulation return systems.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    "Solar Ready" rough in requirements.

    Minimum pipe type, weights and pressure test.



    Conduit for placement of control wiring.



    Minimum control wiring standards.



    Insulation weatherization.



    Backing details and on site documentation.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Interface into hydronic heating systems

    Recommended piping practices (variable speed vs. diverter, vs injection etc)



    Recommended emergency bypass piping procedures.



    Heat exchanger types, recommended locations as it pertains to storage tank height to avoid gravity thermosiphon conditions.



    Pump type and sizing procedures.



    Control interface to avoid carbon based BTU's displacing potential solar BTU's

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  • NRT_Rob
    NRT_Rob Member Posts: 1,013
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    this is a great idea

    but there are some issues. for example, do you really want to dictate storage volume? What if an application demands higher temperatures with a smaller array? What if you have a concrete slab you are charging instead of a tank of water?



    if you're going to do that, you probably need to be application specific. such as, storage to collector ratio for DHW, low temp space heating, high temp space heating separately.



    I would generally be leery about design questions and more keep it to execution, unless you can address truly universal design questions only, such as the existence of an expansion vessel.



    Fantastic project though mark!!!
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Fortunat
    Fortunat Member Posts: 103
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    Solar Code: Minimum Standards

    Mark,



    This is a good idea, but in practice it is a very challenging excercise. As Rob points out, so many of these things are installation specific that it would be hard to write a document that isn't so general as to be useless.



    With federal stimulus money creating demand for solar thermal projects on Schools and low income housing projects (which are typically built to spec), we've been having a tremendous struggle trying to get local Mech Engineering firms to write solar specifications that make sense. While well intentioned, most of the specs we have seen written are either just lifted from a single manufacturer, or else they are internally inconsistent, or sometimes just plain gibberish. We're in the middle of one project now where the engineer specified 350 sf of collector area with just an 80 Gallon tank and a miniscule little heat exchanger. Anyone who'se had their hands on a solar thermal system will tell you that this system will be leaning on the dump zone (and throwing away heat) pretty much all day long. As the installing contractor we know the system won't work as designed, but are powerless to change it unless we can convince the design engineer of the same.



    Anyway, in writing a solar code/guide, I think you could generate a pretty good list of things NOT to do, but the list of things that you should always do, is much more challenging.



    For example, I typically use something like 40l/h per m^2 (.016 GPM per sf) of collector area as a maximum design flow rate for the collector loop because that usually results in about a 10 deg C delta in the collector loop at mid day. But while I'm happy to write that into a 'best practices' manual, I'd hesitate to make it a requirement for an install. As you know, some systems are designed to operate with a much higher dT in the collector loop and it would be a mistake to cram that much flow through them.



    Anyway, I'm interested to see how this thread develops and excited by the idea, but frankly, I'm intimidated by the challenge.



    ~Fortunat
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Rob and Fortunat... If it were EASY...

    They'd call it PV (-....+) I can't take credit for that credo. It belongs to the group of contractors I am working with.



    Anytime someone takes on a task of putting together anything dealing with code issues, it is a gargantuan task, but it has to be done.



    Having already been through the process once or twice in my life, I am not intimidated by the process. As has been stated many times before, many brains/hands make small work of large tasks, hence I appreciate your and any other interested parties input.



    Remember, these are "GUIDELINES", not enacted codes. If some code bodies decide to adopt these guidelines as official enforceable code, then certain terms like "should" will be changed to "shall".



    Mechanical engineers, bless their hearts, are wont to overkill almost every mechanical system they design, and that is what they are being paid for. But most consumers don't involve an ME in the process, and subsequently, get a raw deal for their money.



    It is this groups intent to provide the AHJ's with some basic information to allow them the ability to discern right from rediculously wrong, and call certain practices into question (running PEX from the collectors to the mechanical package in the basement and not insulating pipes,) etc. And the AHJ's are asking for such guidelines because they really have absolutely no idea what they are looking at themselves...



    Thanks to everyone who participates in this process.



    ME

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  • EricAune
    EricAune Member Posts: 432
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    Perhaps a "Code of Ethics"

    Rather than an "Ordinance", maybe a signed code of ethics is a more tangible outcome.  I applaud you and the group for enduring each other and the arduous task ahead of you.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Code of Ethics...

    A code of ethics is a set of principles of conduct within an organization that guide decision making and behavior. The purpose of the code is to provide members and other interested persons with guidelines for making ethical choices in the conduct of their work. Professional integrity is the cornerstone of many employees' credibility. Member of an organization adopt a code of ethics to share a dedication to ethical behavior and adopt this code to declare the organiation's principles and standards of practice.



    What sanctions would be imposed if the code of ethics are violated, who would enforce them, and what is to keep the offender from doing business?



    Thanks for the input... I am sure some of the others will chime in, but it sounds as if one the Colorado organizations already has a C.O.E. that is being violated on a regular basis with no means of enforcement.



    ME

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  • EricAune
    EricAune Member Posts: 432
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    Great point

    Enforcement is the final goal, and your right..what would the punishment be.  I agree with what you are saying, I again applaud you and your drive for guidelines and accountability. 



    This is definitely an important topic, your influence will go a long way in getting the support needed from around the country (as I am sure you will need).

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  • Simply Rad
    Simply Rad Member Posts: 184
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    Guidelines

    I am part of the group Mark is speaking of and I too do not want to have a flash back to the 70s mistakes.  I wasn't installing then but I have seen alot of the relix.  I feel that we can and must come up with some guide lines, to the control the free for all.  This is suppose to be a green thing not a stimulus bonus for installers to jump into.  I know in our county the building inspectors have NO guidelines to follow to inspect a solar thermal system.  They are use to seeing PEX everywhere else in hydronic systems, so do you blame them for allowing PEX for solar.  No one has educated them and this is what Mark is taking about.  We can't change the world but when can alteast try to educate the installers, inspectors and architects.  Maybe instead of nit picking Mark's ideas we should be trying to work together to better OUR industry. 

    THe one thing I can not stand as of lately is the mechanical engineers design solar DHW.  Twice lately I have seen this design where instead of storing the solar energy in the form of potable water and preheating the DHW.  They are storing the energy in the form of heating water and pumping the solar energy into the domestic tank heat exchanger lines.  So they are not using the solar energy unless the solar tank is hot enough (167-180F)  to be used by the heating system suppling the DHW tank.  That is alot of wasted energy that is available and not being used.  And these are mechanical engineers....imagine what a new solar thermal installer could do???  

    Jeffrey
    Jeffrey Campbell
  • hot_rod
    hot_rod Member Posts: 22,244
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    IAMPO just

    updated their solar codebook. Someone from Denver had a handful of changes submitted that got passed. I sent in 6 changes, two or three got accepted. This would be enforceable by the local inspectors if they adopt the codebook.



    If it were easy they would call it PV.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Thanks HR...

    This is a good start by a recognized code authority. Not perfect by any means, but with recommended addendum's, it could be a winner.



    What parts did you recommend?



    ME

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  • Radman
    Radman Member Posts: 75
    edited November 2009
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    Here's an interesting point...

    Thanks to ME and all the wallies on this.  As another of this group, I have to say that the reason for the minumum guidelines are so we can keep the administrative authorities from making their own call.   Unfourtunately the permitting processes in some parts of our state are out of hand, while others are non-existent.   If a series of minimum guidelines are established, they can foucs on that and not worry about the things they cannot control or understand.  



     When educating a group of inspectors recently about thermal systems, the resounding comment fromt the inpsector group was "We don't care if it works, looks or doesn't look well crafted, or is designed properly.  We just want to determine it is safe to sign off on"   Tomorrow I meet with local area contractors and that AHJ, we'll see what comes up and I'll bounce it back here.For minumum guidelines, I think the basics are:



    Piping type & material

    Flashing penetrations 

    Lagging standards 

    MSDS requirements

    Emergency instructions

    Clearance for service, ie: no roofs with edge to edge collectors where you cannot access piping & connections without standing on the collectors like the PV guys do.

    Insulation minimums & types

    Sensor wire coatings for UV protection

    Insulation coatings for UV & animal protection

    Anti-scald valves on DHW supply out, and temperature protection to maximum temperature input rated appliances

    Snow-unloading.

    Basically what Mark already said, short of the design criteria which is a pandora's box. 



    If anyone needs motivation, here is a comment I recieved today from a "solar industry individual"  It got my shorts in a bunch that's for sure...



    "Solar thermal systems involve specific subsets of roofing, plumbing, mechanical and electrical knowledge that most roofers, plumbers, HVAC guys and electricians do not know. This is why I would support that people have a solar specific certification, either NABCEP or COSEIA."



    See that guys, you don't know any of this stuff anyway;-)

    Bo, aka Radman

    "If it were easy, they would have called it PV"

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  • Royboy
    Royboy Member Posts: 223
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    WI standards

    here's a link to the Wisconsin preapproval form for solar water heating system rebates. the "system requirements" section contains some of the sort of requirements you are talking about. they are pretty basic but do have things I don't particularly agree with, such as requiring antifreeze in drainbacks.



    http://www.focusonenergy.com/files/Document_Management_System/Renewables/solarhotwaterrewardpreapproval_applicationform.pdf
  • hot_rod
    hot_rod Member Posts: 22,244
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    SRCC- OG 300

    does cover quite a few of the requirements ME mentioned above.



    As for designs, on large jobs the system and storage really needs to be designed to the load, and location. "Where it's at and what you are asking it to do." Storage to array size can vary widely.



    Safety valves, components built to withstand high solar temperatures, the need for dump zones how and whys are all part of solar training.



    You would be amazed as to what passes for solar insulation sold to withstand higher solar temperatures, etc. We have been cycle testing some of the various pre-insulated solar flex tubing on the market, with bursts of 150C temperatures. When the solar market heats up all sorts of inferior products start entering the market.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Thanks RoyBoy...

    I have some other issues with the document, like "Drainback Systems: Solar system piping shall be in accordance with s. Comm 71and its references to s. Comm 82. All non-vertical piping must be copper

    with insulation rated to withstand over 180 degrees F. Vertical piping may be either copper, stainless steel or cross-linked polyethylene (Pex) (rated to at least

    200 degrees F at 100 pounds per square inch) with insulation rated to withstand 180 degrees F.



    I don't want PEX any where NEAR the solar loop. Because it WILL see temps over 300 degrees F if the panels are stagnating and someone starts using DHW... I've seen what happens to PEX under those conditions, and it is NOT pretty.



    But it is a start. Thanks for your contribution.



    ME

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Thanks Bo...

    Good luck in the peoples republic, and do please keep us posted. I'd come, but will be tied up in Montezuma commissioning our first all windows only heating system.



    Having people like yourself on this team will make it a much easier task. I have a call in to the ICC regarding a solar class at their annual educational meeting, If you see Sam D. at your meeting, tell him I said hey.



    ME.

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  • Radman
    Radman Member Posts: 75
    edited November 2009
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    Thanks Royboy, and yeah no PEx

    Thanks for that doc, it will help us along with delivering the basics to our AHJ.

    Seems like Y'all are pulling it together nicely out there.   Yeah, we all really need to keep informing everyone about the appropriate applications for PEx and why it doesn't belong in a solar thermal system.    I too have seen the disasters, and it is not pretty.  

    Hot Rod, you are scaring me.  I hope those failures are not on Caleffi's product?

    I have been enjoying using them for my smaller DHW systems.   What types of failures?   Tubing or fitting?   I suppose the double flare on some could be over-stressed during high temperature fluctuations.

    Keep us posted on that 4 sure.

    I am a little concerned over OG300 for AHJ adoption or for rebate/incentive qualification.  That has come up here and could really throw a wrench in some contractors business as far as material selection goes. (tanks, pump stations, etc) 

    Of course I do not worry because I use Viessmann and they are approved Jah!

    (said with bad German accent, think Heatmeister)



    Thank you for the props Mark, I appreciate it.   I was in the county, so I didn't see Sam, but know him well.   He is a good man, wise and fair and tough.   Good inspector.   A connection has been made in their office today, and a great colleague has agreed to help us get our whole leg in that door.  I am hopeful that this will continue.

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  • EricAune
    EricAune Member Posts: 432
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    Any updates?

    Hi Mark and crew,



    Awaiting the latest updates if you have any.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    A decision has been made....

    This is a great bunch of contractors, each and every one of them is a very consciencious contractor with an eye on quality and efficiency.



    What I think started the ball rolling, was complaints among themselves about less than scrupulous contractors that they were losing work to that really had no idea what they were doing (PEX between collectors and mech. rm.?) and were frustrated and wanted to do something about it.



    Sound familiar? I guess EVERY trade has it's low lifes and trunk slammers eh...



    The decision has been made to learn from each other, and raise THEIR bar, and forget about the alleged competition.



    Attrition (hopefully) will catch up to the schlockmeisters and put them to bed, and these guys will be like the sun, and continue to shine.



    So, essentially, they have decided to keep their nose in THEIR business, and out of other peoples business, and continue to be a drinking club with a hydronic problem :-)



    Personally, on the education front, I am still going to pursue putting an educational guide together for contractors and inspectors alike because there is a demand for it. There is also a major need for it as well.



    Unfortunately, the current executive director of the CoSEIA group has submitted her resignation, so what was a disorderly group has an opportunity to become even more so... I hope they get their act together before their Spring get together.



    SO, that is where it stands at present. I am still looking for photographs of bad and ugly installations that I can include in my presentations, as well as excellent looking installations so I can show the students the differences in good and bad installations, so feel free to share.



    Thanks for asking Eric.



    ME

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  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
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    COSEIA Certification

    It seems to me that the COSEIA tests and certification would suffice.



    The local building dept. should require this for solar installations just like they require a plumber's license for plumbing.

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  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
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  • Karl_Northwind
    Karl_Northwind Member Posts: 139
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    Solar Standards

    The Focus On Energy Standards are what has come out of 30 years of a real solar thermal industry in Wisconsin.  Not that there haven't been ups and downs, or black eyes.  But I can say that the standards on that application are more than enough to keep crap mostly off the market.  and as someone who has to clean up behind electricians, plumbers, and yes, sometimes mechanical contractors' solar installations, The dedicated solar thermal installer has a place in the inter-disciplinary world that overlaps the worlds of the plumber, electrician and pipe fitter.  Just remember that we have to uphold the highest standards of all of those trades in our own context.  at the same time.



    My solar thermal system kept my house from freezing today at -3F when my furnace quit.  I got it started again, but it was almost the excuse I needed to rip it out and go radiant.



    cheers,

    Karl  (full time solar thermal designer and installer)
  • Justin Topel
    Justin Topel Member Posts: 65
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    Mark...I am overjoyed to help

    Mark,



    I am in the exact same boat and feel that there should be something done about this very issue.  I see too many systems that are horrible to say the least.  Companies trying to cash in on the solar market without having any real idea what is going on.  From companies charge massacre rates to replace a "pump" when the solar controller was not even working, bray oil all over the basement, PEX everywhere, Sharkbites to compensate for lack of skill in soldering, and on and on.  I also spoke with COSEIA to discuss this very issue.  Unfortunately there is only one person who works there now it seems, but I expresed extreme frustration with systems that were installed to such a poor standard.  I told here about a particular job where everything was a mess.  She said she understood my frustration, but they do not want to become an enforcement agency.  I told her that was fine, but unless they do something more than what is currently going on..nobody is going to take them very seriously.  They need to step up to the plate a bit more to insure that certification means something besides this group paid their dues.  I told her that I would be happy to arrange for other installers to get together and come up with our own agreed solar code which would state that all of us would adhere the these agreed principles and standards.  The local inspectors have absolutely no idea what they are looking at.  In fact one city told me that they wanted me to pass their solar test.  I said OK, but do you guys have any idea how solar works or should be installed.  The nice lady said no, not really.  I then said so you want to give me test to make sure I know what I am doing, but yet you dont know what you are doing?  She smiled and said "Yeah, kind of messed up huh?"  Another think that is really scary is folks bolting panel hardware to trusses with crazy large fasteners.  A truss manufacturer told me they would allow no fastener over .250" and that is why Simpson's hardware is .248" diameter to stay under that.   I would be more than happy to help round up some folks who would be interested in forming a group who would sign on to an agreement that would hold us to a higher standard.  The nice lady at COSEIA stated that she would like for me to write a letter to the board telling them our desires.  She wanted to represent us, but needed letters from the represented stating their desires for the direction of COSEIA.  We also need to vote in some board members who are SHW reps.  It seems that it is all PV oriented....no pun intended.  I have no problem with PV, but a solar organization should represent all solar parties.  I am going to try and attach some pics as well as a CAD drawing I did for a system I recently fixed.  The homeowners hired the contractor with their home loan, the system did not work for over a year, and they were finally broke.  I rounded up some guys who helped me fix their system on the weekends.  They love solar again and cannot wait to expand.  If you can figure out the piping on the CAD drawing, you are an ace my friend.  It is funky.  Here are some of the lovely features.  The "drainback" piping drops into the basement before it make a 10' elevation climb into the top of the drainback tank, the pump is 1/2 horse rated for around 60' of head, the differential controller caught on fire from excessive pump relay requirements, home store insulation, was tied into the boiler system feeder (so much for drainback), PEX on the roof attached to the collectors, panels were leaking on the roof but who cares thats what the feeder is for right, holes in the roof for moved brackets without any sealant added, I gotta stop there so nobody thinks I am making this up.  If you need any additional pics, send me an email.  I look forward to helping you in any way I can to keep SHW systems on the side of high quality energy savings.  Sorry for the long post...I could go on a long time about this.  Oh by the way you have full permission to use these pics for your presentation.



    Mister T

    bethlehemsolar@gmail.com
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    that is U G L Y....

    Thanks for the photo.



    If you haven't yet, I would strongly suggest that you and your partner contact Eric Anderson at Low E and seek permission to join their drinking club with a solar/hydronic problem. Great group of guys to hang out with. WIlling to share their knowledge with people of like minds.



    Keep up the good work.



    ME

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  • Radman
    Radman Member Posts: 75
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    Something will be done

    Justin,

    First I must apologize to you, ME, HR, and all of the wallies that my involvement here is sporadic.   That being said, I do listen in and feel your pain, believe me.

    I was recently elected to the BOD of the very organization you speak of, and can not tell you how helpful your feedback is.   I will be contacting you directly, but for now please let it be know you have been heard.  

    I encourage all wallies to get involved in solar thermal, and also their local industry's associatons (if any).   The interest in thermal has really grown over the past few years, and will continue to grow if we build credibility.   Addressing the issues out there with regard to proper practices, etc is the place to start.  

    Again, thank you again for posting, this is great feedback.

    Radman

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Congratulations Bo...

    As you said, be careful what you wish for.



    You will do the organization and the industry a lot of good. I hope you don't get too frustrated in your efforts. You've got a lot of good backing behind you. You should do good things for OUR side of the solar industry.



    ME

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Bump to the top...

    With my most recent post regarding NABCEP, this thread deserves to be dragged back to the top.



    Here is a link to the OCG standards HR referenced.



    http://www.solar-rating.org/standards/OGDOCUMENTS/OG300DOCUMENT_20090203.pdf



    ME

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  • Royboy
    Royboy Member Posts: 223
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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    A gentle reminder as to why you shouldn't use PEX in a solar loop...

    As I was going through all of my slides, putting a presentation together for the CoSEIA folks, I came across a piece of PEX that I had intentionally installed in the solar loop to see if it could take the heat. It couldn't...



    Your milage may vary :-)



    ME

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  • D_Hatina
    D_Hatina Member Posts: 3
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    Pex always a problem?

    Mark, I can understand the inappropriateness of pex in a closed solar loop but why would it be a problem in drainback or open loops that don't see such high temps and pressures?

    Darren
  • hot_rod
    hot_rod Member Posts: 22,244
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    same temperatures in DB

    it possible for a collector to reach 325F or higher, even when empty of fluid, as in a shut down drainback condition.



    if the pump were to kick on, as the tank calls for heat, the fluid coming down from the collector will easily exceed the temperature limitations of pex.



    While some installers feel it is safe to run the cooler supply to the collector in pex, it's still a risk. Typically there is not that much piping in a residential collector circuit, it is not going to cost that much more to run copper, steel, stainless.



    Save the PEX for the potable and radiant side of the system.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
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    Atmospheric Drainback OK

    I have a few systems operating now for 25 years with polybutylene pipe in the collector loop. Since it's always zero or slightly negative pressure, there is literally never a possibility of any bursting or even leaks. The plastic must be kept at least 5 feet away from the the collector absorber plates, because they reach 350F.



    Note it's really hard to keep pex straight on those close to horizontal runs. It sags easily, and thus traps water which ruins your "drainbackability". A solution for that could be encasing the pipe/insulation assembly in downspout. Downspout is probably the best looking way to treat exterior pipes that are attached to the exterior of a house. Painted armaflex, unpaintable polyethylene insulation, or painted PVC or ABS all look like hack jobs when attached to the outside of a nice house.



    Pressurized and/or sealed drainback systems are starting to become the norm, thanks partly to Siggy's teachings. I'm still researching pex's capabilities in that type of system:

    http://www.heatinghelp.com/forum-thread/130091/Drain-back-with-evacuated-tubes

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