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primary/secondary

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Glenn Sossin_2
Glenn Sossin_2 Member Posts: 592
Not sure why this didn't work. Will try again

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  • FRANK_24
    FRANK_24 Member Posts: 80
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    PRIMARY/SECONDARY...................

    After that, what comes next? There are many ways[I'm sure ] to install piping but which way is the preferred way? The attachment shows three 2,000,000 BTU boilers with indirect dhw and naturally building heat. Is my interpretation correct?
  • Brad White
    Brad White Member Posts: 2,398
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    May I suggest some things?

    Hi Frankie-

    1) The expansion tank is on the supply side of your circulators, whether the boiler or distribution loop. I would put the boiler circulators on the inlet sides especially if they have higher water pressure drops. Then you could keep the expansion tank where it is -even move it closer to the circulator inlets.

    2)The air separator location is fine as far as releasing air from the hottest water although I prefer it to be at the point of lowest pressure too. If a Spirovent or the new Taco type with the PALL rings it should not make a difference.

    3) Are these condensing boilers such as Aerco's or Hydrotherm KN's? Might I suggest a low loss header as a hydraulic separator instead? If you do have condensing boilers and the load is low, the bypassed water will go back at the supply temperature and quench the condensing.

    4) Are these conventional cast iron requiring return water protection? What you have would seem to protect them depending on the relative flow rates.

    5) What you show on the distribution side is not exactly P/S. The boiler loop flow should not affect the system-side flow if the flow rates are all balanced and steady-state. But drop off one of the boilers and its circulator the system side flow will be higher than the primary and that could force flow into the boiler circuit or more likely dilute your outgoing temperatures at the common tee set.

    6) How are you maintaining different temperatures between your domestic circuit and your heating circuit? Mixing valve? I know that no diagram can show everything, so I have to ask.

    7)The two parallel zones (heat and DHW) could affect one-another especially if one has more head than the other.

    In short, I see many variables changing which can affect the hydraulics.

    Let me know what your application is (condensing or non-condensing, variable speed pumping anywhere- pressure responsive or temperature responsive, etc.) and maybe I can sketch up someting for you. Others I am sure will have other ideas.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • [Deleted User]
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    What's your goal?

    Full ODR?

    Boiler protection?

    System protection?

    DHW priority?

    What's your heat source? Condensing, vs non condensing?

    Your intial concept drawing is close, but you could get rid of the check valve in the transfer loop, unless I'm not seeing everything. Also, make sure you have individual checks in the individual boilers, or you will have a circle jerk going on between the boilers, with very little energy making it out to the loads, until which time ALl boilers are on.

    There are also some fairly important rules as it pertains to the location of secondary tees and their relationship to other piping appurtenances. You want to have 5 times the primary pipe diameter of straight pipe before and after the secondatry tees in relation to elbows or other equipment. Also, be aware of thermosiphon ghost flow. If your space heating load is above your heat source, as drawn, when the boilers are hot doing DHW, you WILL have unwanted flow up to the system.

    John Siegenthaler has numerous articles on primary secondary in P&M magazine, which is available on line, and worth the price of admission (web site registration required).

    Just as an aside, I visited an orphan we inherited a long time ago this morning. The system is piped "perfect" primary secondary, which would mean thoeretically that NO flow should be going through the OFF boilers, and the boilers are significantly below the hot main primary, and guess what, all the off boilers were just as hot as the primary. One of them thar things that will make you step back and do a double take and say "HMMMmmmm..."

    Just when you think you know everything you need to know, life jumps up and shows you you don't really know squat...

    ME
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    Piping possibility??

    How about this ? Puts the expansion take in correct place. This also prevents you from drawing hot water past the heating zones on a DWH call.

    At 2,000,000 each I'm sure these are not condensing boilers. Never have worked with anything that large before, but I think this piping should be ok
  • hr
    hr Member Posts: 6,106
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    We need more details

    as the others mentioned.

    Keep in minds ALL boilers even cast iron and copper, run most efficiently with the lowest possible return temperatures.

    With non condensing equipment, however you need to be concerned with the return temperature and would be wise to use a stage control, like the tekmar, to watch all the temperatures, and be able to react, stage, exercise, data log, etc.

    Knowing how critical the secondary temperature requirements are is another piece of data needed. If all emitters "need" the same temperature, perhaps a parallel distribution piping would be in order.

    Search the Siegenthaler archives for multiple boiler piping both at pmmag and pmengineer.com (Jan 01, Sept 02)

    Or a copy of Siggys 2005 seminar tour handout booklet.

    Also John's own site www.hydronicpros.com

    hot rod

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  • Brad White
    Brad White Member Posts: 2,398
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    Condensing Boilers

    Glenn- these very well could be condensing boilers in that firing range or larger. Aerco Benchmark, Hydrotherm KN, Viessmann Vitocrossal, Buderus SB 615 and SB 765, Cleaver-Brooks Clearfire among others.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    large condensing

    Several old wiseman told me, keep your eyes and ears open and you will learn something everyday. I always enjoy learning and being exposed to new ideas and products. Thats why I enjoy reading the posts here.

    I don't normally get involved with systems of that magnitude. I will do some reading now. Thanks
  • FRANK_24
    FRANK_24 Member Posts: 80
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    THESE BOILERS

    SEE ATTACHMENT
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