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Geothermal question

Tom HopkinsTom Hopkins Posts: 539Member
As a rule I always have an air scoop as well as an expansion tank. Even though the delta T of the systems normally shouldn't be that great to cause much expansion/contraction of the water, and the HDPE pipe (you are using geo-exchange rated HDPE pipe right?) does have some ability to expand under pressure, why run on the edge? Also the HDPE pipe is not an oxygen barrier material, and can get air in it over time. And the last thing you need after a few years are some airlocked loops, depending on how much flow you are using.
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Comments

  • Mike LampkinMike Lampkin Posts: 123Member
    Geothermal Question

    On a closed loop water to water heat pump,should there not be an expansion tank and air elimination device included on the earth loop side? I think so,since it is closed loop,but when I ask some of the geothermal companies, they say that it not required. There take on it is that the pipe in the earth becomes the expansion tank and that the fluid in the pipe has an oxygen scavenger so no air elimination is necessary,yet when I look at Siggy's drawings,he always shows this equipment.If it is not included would this not cause extra stress on the piping and equipment?What are other Geo companies doing?
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  • Mark EathertonMark Eatherton Posts: 476Member
    That industry has a LOT to learn from this industry....

    Remember, the people who really brought these systems to the forefront are a bunch of red clay farmers from Oklahoma. Farmers have my envy, because they MUST know a little bit about a LOT of different things, and be able to apply them. So, don't be tossing darts my way because of my farmer comment. It was meant as a term of endearment:-)

    We have been doing what the industry norm (THEIR industry, not ours) and have been keeping an eye on them for a while. Although we have not had any major pressure losses, nor have we had any air bound systems, one thing that I have noticed is that the cast iron pumps that they use on their closed loop non oxygen barrier systems look like crap after just a few years (failed loop pump replacements). And then there is the point of no pressure change thing, which with the way they do their dual pumps (push pull) a PONPC would probably thoroughly confuse the living crap out of the poor circulators... They wouldn't know whether they were coming or going:-) And then there's that whole minimum NPSH thing...

    I once asked one of their industry trainers how they dealt with the significant co-efficients of expansion on their PE tube to which he replied "Huh? What on EARTH are you talking about?" I explained to him that a typical 200 foot deep bore hole would experience an 8.8" growth differential, and he told me I was full of crap. (1.1" per 100' per 10 deg F difference, assuming 30 degree F minimum and 70 degree F maximum. Do the math, it's 8.8 "'s)

    For no more than the cost of a potable water expansion tank, and the cost of an air seperator and a few gauges, it could and would save time in the field troublshooting and diagnosing the systems. BTW, to the best of my knowledge, there are NO oxygen scavengers in ethyl or methyl alcohol. The systems operate at such a low operating temperature that the potential of diffusion is real low, but as we all know, ma nature dispises any indifferences in O2 content, and she WILL equalize it out, low temp or not.

    I think I have convinced my partner (hydronic) that in the future, it is worth the additional cost to include air seperation, expansion tank etc.

    And, then there's the limited access that they provide to COMMON replacement parts... Don't get me started :-(

    ME
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  • Mike LampkinMike Lampkin Posts: 123Member
    Thanks Geoff & Mark for the confirmation

    I will make sure and pass this info on to the Geo people that I have been dealing with.I will definitely be putting the expansion tank and air elimination on any new systems that they will be doing for me.You never know,I may get some converts.
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  • Mike LampkinMike Lampkin Posts: 123Member


    nm
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  • Mike LampkinMike Lampkin Posts: 123Member
    Congratulations Mark!

    Hey Mark!
    Congratulations on winning the Carlson/Holohan Award.You are extremely deserving of it and I couldn't think of a better person to receive it.
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  • Geo class

    Our instructor said "No 'spansion tank needed"! I damn near had to restrain my lead guy from taking over the class(G). Thermal expansion nuisance trip-outs & he was telling us no x-tnk was necessary??? They've since changed their recommendations and now suggest a 2-gallon potable tnk is best. Me? Boyle's Law & total system volume & overall D-T dictate our choice.
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  • Mark EathertonMark Eatherton Posts: 476Member
    Thanks Mike...

    I'm still pinching myself.

    ME
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  • semi-open flow centers

    We started using air separators & expansion tanks on our loops about 2 years ago, but have used these: QT flow center on the last couple projects, just about to start them this week but wondering what any of you thought of this approach. It's sort of a semi-open non-pressurized air separator, so no expansion tank needed.
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  • BryanBryan Posts: 259Member
    flow centers

    That is all I use. The systems are open and the flow center is the ex. tank. After 25 years in the geo business, I would never install another closed-pressurized loop. Don't get me started!!!! Bryan
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  • Mike LampkinMike Lampkin Posts: 123Member
    All-in-one Flow center

    Thank you very much for that info.It seems like a very well thought out product.
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  • Craig R BergmanCraig R Bergman Posts: 101Member
    100 Loops

    I have always had this question in the back of my mind. We were taught that you do not need an expansion tank or air eliminator on a closed loop GSHP. We have about one hundred systems out there (10 years is our oldest) and I have only had to "Juice" one of them.

    Take it for what you will...

    Bergy
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  • This is the second tank like this I've seen.

    why the heck would anyone want to use a non-pressurized system?

    seems like begging for air problems.

    Last one I saw specified cast iron pumps as well! for an open system..

    Not trying to be flip, I just don't get it. We like our pressure 'round these parts...
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  • BryanBryan Posts: 259Member
    pressure

    Ever see a pressurized system after several hours of operation at zero pressure? In someone else's words "it ain't pretty. Bryan
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  • Mark EathertonMark Eatherton Posts: 476Member
    What about NPSH requirements...

    Granted, its only around 3 PSI, but if the system is at zero, it's zero no?

    A LOT to learn from THIS industry...

    At least withthis tank method, both pumps will see the PONPC, or at least I think it would...

    ME
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  • Craig R BergmanCraig R Bergman Posts: 101Member
    Big difference

    In labor and materials between closed and open loops.

    See the attachment....

    Bergy
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  • BCBC Posts: 20Member


    I fabricated my own "open" flow center (though like many projects I do my parts cost was almost as much as the GT unit - I should have just bought one). So far it has worked great, no cavitation issues. Oxygen ingress is a concern, so I'm keeping a close eye on the pump (cast iron) and will replace with bronze if it ever becomes necessary. My loop fluid is a straight water/methanol mix.

    As far as nPSHR goes, from Siggy's book and other sources I've always understod the pressure to be an absolute pressure, not gauge, so you always start with 14.5psi or so even in an unpressurized system (less for Mark in CO!). I'm willing to be corrected on that if anyone has other info. Also, the level of the fluid in the tank is about 5 feet above my pump inlet so I get an extra couple of psi from that.

    I went with this setup primarily becaue it eliminated the need for a flush cart. This also necessitated the use of an indoor valved manifold for my ground loops so I could flush them individually using the loop pump. That worked fine, no air problems to date (6x600ft horizontal).

    I think a conventional expansion tank and air scoop would work just as well, too. I agree that the standard practice of using the loops as your expansion tank is ridiculous - sure it works 99% of the time, but why take the risk for $50 worth of additional parts? Also it means running the loop field static pressure as high as 60psi in the winter so the pressure doesn't drop too much in the summer. Sure all the components are rated for these pressures, but why stress things more than necessary?
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  • BCBC Posts: 20Member
    Craig,

    That does illustrate a drawback to my system described below - you do need more space and it is a pain to insulate the indoor manifold. Strictly speaking you only need valves on the outgoing loops (at least I got away with that) but you raise a valid point. In my case my basement is unfinished with dirt floors and virtually unlimited space, so it wasn't a concern.

    I don't think there's necessarily any need to couple an indoor manifold with an open flow center. With the right 3-way valve setup the open flow center could be used with an unvalved buried manifold and conventional flush cart. That would eliminate most of the benefits of the system, though.

    Probably the biggest benefit in my case was that I didn't need to do any fusion welding. Yes the parts cost was higher, but for a one-off install the savings over renting or buying a fusion setup, not to mention the required training made it a no-brainer. Obviously for a pro the economics would be a lot different.
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  • ?

    I've seen cars run without oil, and that's not pretty either... what does that have to do with anything?

    I've seen non pressurized systems get airbound too, that can not be pretty as well... and generally I would consider that much more likely than a pressurized system, once tested and comissioned, losing pressure without anyone noticing.
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  • BergyBergy Posts: 11Member
    BC

    A flush cart is the BEST thing to own... Ours will flush, up to, a six ton slinky AND it flushes our radiant systems in NO TIME AT ALL!!!

    Bergy
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  • BCBC Posts: 2Member
    yes

    If I was in the business (maybe I will be someday) I'd definitely have one! I actually had more trouble flushing my radiant loops than the ground loops, it would have been nice to have.
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  • BryanBryan Posts: 259Member
    and

    it takes two guys with strong backs to haul the d**n thing up and down the steps. Make sure you find a 20 amp circuit or the breaker trips and floods the tank and over it goes onto the new carpet. I will never use a closed loop, ever!
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  • BryanBryan Posts: 259Member
    hot

    fluid lubricated circulators need fluid, none available when the pressure drops.
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  • Craig R BergmanCraig R Bergman Posts: 101Member
    Too big

    Our flush cart is on the small side. It will flush up to a 5 ton slinkey so it's not very big, or heavy. (My previous post about flushing a 6 ton slinky was incorrect.)

    Bergy
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  • once again, a pressure drop in a pressurized system is not likely. there are thousands and thousands of pressurized systems installed every day and once they are filled, tested and commissioned, with a makeup valve installed for initial pressure issues, they don't just "lose pressure".

    So what is the benefit of an open system? I mean, beyond its superior air collecting ability and rustification ability ;)
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  • actact Posts: 2Member
    HDPE Pipe expansion, well grouting, ground thermal contact

    I do geo well installs and we go to great lengths to tightly grout the pipes in the ground and maximize thermal contact with the ground, so when I hear intentional expansion/contraction of the ground loops as your pressure regulator, I get a bit curious, whether this disrupts all that hard word we do to tightly pack/grout in the ground wells and maximize the thermal contact with the ground?



    Any opinions or experience with that?



    From my end, so far our experience is that w/ the non-pressurized, the startup of the system was much easier and more flexible. Finding, repairing leaks, flushing air, anti-freezing, etc.
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  • actact Posts: 2Member
    HDPE Pipe expansion, well grouting, ground thermal contact

    I do geo well installs and we go to great lengths to tightly grout the pipes in the ground and maximize thermal contact with the ground, so when I hear intentional expansion/contraction of the ground loops as your pressure regulator, I get a bit curious, whether this disrupts all that hard word we do to tightly pack/grout in the ground wells and maximize the thermal contact with the ground?



    Any opinions or experience with that?



    From my end, so far our experience is that w/ the non-pressurized, the startup of the system was much easier and more flexible. Finding, repairing leaks, flushing air, anti-freezing, etc.
    ·
This discussion has been closed.

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