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Primary secondary piping for boilers

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Bob Rohr, Jan 15, 2008.

  1. SteveJ

    SteveJ Member

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    So, there should be two circuits into the butffer tank:

    1. As drawn in the diagram, to charge the tank from the primary loop.
    2. (Not shown in diagram) Circulator reversed from that in diagram with a short dip tube, to extract heat from the tank to the primary loop.

    Correct?

    Then what is the general rule for sizing the primary circulator in relation to the secondary circulators?

    Thanks,
    Steve

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  2. Bob Rohr

    Bob Rohr Minister of Fire

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    Sure, you could have two loops into the buffer. What I find is any time my boiler exceeds 150 the buffer circ is running. As such the tank is always blended, not much stratification with the buffer tank circ running.

    On one hand I want the cooler water from the bottom of the tank to return to the primary loop and boiler to leverage delta t to the boiler and keep the efficiency up.

    However if the tank stratifies, for instance over night without the buffer circ running, in that case you would want to pull any heat loads off the top, warmest point. My buffer circ runs until that tank drops to 100F as my radiant floors can use temperature that low.

    If you have loads thay require higher temperatures, of course shut down the buffer at the lowest possible "useable" temperature.

    Whenever the buffer circ is off the boiler output would be going directly to the loads without "seeing" the buffer.

    Keep in mind under "ideal" conditions, at load, the boiler would be matched exactly to the load and the buffer becomes "unknown" to the system. The buffer is merely a parking space, either for excess btus, over heat protection, maybe solar storage input.

    You might consider the buffer as a "fixer" for the in-ability of solid fueled appliances to track close or exactly to the load. Different jobs require different size tanks to try to "nail" the perfect blend of not storing anymore then really needed, but enough to buffer all conditions, or perhaps offer some "non burn" times

    I can't say there is an ideal piping, size, or control configuration. It really needs to be sized and designed to the task you have in mind. I chose 500 gallons because it will buy me a days worth of heat, at design. It fit in the space nicely, and I don't mind switching to a mod con LP boiler back up.

    Others here want to burn hard and long and store more "time." For them more capacity may be better.

    Keep in mind more capacity = more standby loss. I feel there is an upper limit to realistic thermal storage, but it's a moving target :)

    Th primary loop circ is usually a low head, high GPM circ. It's ONLY lob it to move fluid around that circulator loop. It doesn't move any flow through secondary loops. Either the Grundfos 15-58 or Taco oo7 on speed 1 will usually be fine for that. To move 150,000 BTU at a 20Fdegree delta T you need to move 15 gpm. look for a circ to do that job at a low head, some of the DHW recirc pumps are great, but expensive as they are usually bronze or stainless volutes.

    hr
    Vizsla likes this.
  3. SteveJ

    SteveJ Member

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    master of sparks,

    Thanks for the detailed explanation...

    For a strictly off-grid house with power consumption at a premium, I think I like nofossil's approach over the primary/secondary approach. In nofossil's setup there is never more than one circulator on at a time and maybe a few zone values. With the primary/secondary setup, it appears that the primary pump is on 24/7 and there seams to be the same number of zone valves required and more circulators = more power consumption.

    Am I comparing apples to apples?

    What do you think is the ultimate off-grid setup?

    Thanks,
    Steve
  4. Bob Rohr

    Bob Rohr Minister of Fire

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    these off grid friends, Larry and Suzanne in northern California used greenhouse window operators connected to spring loaded ball valves to control the temperature of his gravity fed radiant wall heating system.

    Solar via PV powered circs to supply the wall radiant and DHW. Zero power consumption for heat and DHW. Very clever, and comfortable from a few years of experience. Small, about 1KW of PV power. They do have a back up generator with a homemade HX for heating the solar tank when it runs.

    hr

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  5. heaterman

    heaterman Minister of Fire

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    RE: Callefi

    Here's a project we did last year in a church. The hydraulic separator is the green and silver tank looking affair in the middle of all the pipes. We used this method of piping because flow requirements for the system are far different than the boilers that drive it.

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  6. Eric Johnson

    Eric Johnson Mod Emeritus

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    Nice looking job. Is that an expansion tank on the top?
  7. heaterman

    heaterman Minister of Fire

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    Yes it is. The old tank was more than adequate in capacity due to removing a 1,400 pound cast iron monster and replacing it with a couple small modulating condensers. Probably 40-50 gallons less system capacity now. It was an interesting job because all the old boys in the church were simply dumbfounded that those two dinky wall hung boilers were capable of heating 8,500 sq ft. They literally hovered in the boiler room while we were working and loudly proclaimed their disbelief. After this winter with a nice warm church and a 40%+ reduction in their fuel use.........let's just say that there was a conversion of a non-spiritual type going on there.

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  8. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    If that a structural caulking tube up top? :)

    Joe
  9. heaterman

    heaterman Minister of Fire

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    If that a structural caulking tube up top? smile

    Joe

    Yep. It's what we use to glue the boilers to the wall ;)
  10. zadwit

    zadwit New Member

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    Duplicate trimmed.... Gooserider
  11. zadwit

    zadwit New Member

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    I have an EKO-60 supplying 2 five hundred gallon propane tanks set side by side. My primary heat is currently a Burnham V-15 boiler (135, 000 BTU) feeding two radiant floor zones and one small base board radiator zone.
    I plan on running 1-1/2" pipe, galv. or copper from the EKO-60 to the propane tanks and return to the EKO-60 with same size pipe. There will be a small primary loop with a Danfos Tee to assure return water temp. Then I plan on "tee ing" off from the top of the propane tanks (where the hot water enters) and going to the Burnham boiler. I will need to install a flat palte heat exchanger between the propane tanks and the burnham boiler since the burnham side has glycol. We have to use glycol up here in North Pole, Alaska in case the power goes off or the system fails. It would cost too much to fill the propane tanks with 1000 gallons of glycol, so will use water.
    Some one told me to install two closely spaced "T's" on the inlet(return water) side of the burnham oil fired boiler. THis way, when the zones call for heat, the burnham circulator sucks the hot water thru the oil boiler to the zones. When the zones are not calling for heat, the hot water from the tanks circulates around the heat exchnager between the heat exchanger and the oil boiler(2 "Ts"). It seems to me that I need to connect the two circ pumps,( the ones that pump water from the tanks to the hx and from the hx to the oil boiler), to the same control that runs the oil boiler circ pumps. This means the honeywell aquastat on the oil boiler would have to power up 4 circ pumps. Is this too much? Do I need a switching relay?
    The EKO-60 has a large circ pump, grundfos UPS 26-99FC. I think it runs when the EKO-60 controller decides it needs to run.
    Does anyone see any major flaws with this setup? I am real close to plumbing this all in.
    Thanks in advance,
  12. Bob Rohr

    Bob Rohr Minister of Fire

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    I don't think so... but without seeing a drawing??

    Ideally a parallel, if not a true P/S as shown. As drawn here you would like to go directly from either boiler to the load. Without passing through storage or the unfired boiler. In your example (lower left drawing I think?) the oil boiler would need to be circulating for closely spaced tees to work. Not ideal in my mind, unless a tankless coil is used for dhw.

    Here are a couple rough drawings, although an additional 3 way zone valve could select from EKO or storage for a source. It gets to be a bit of piping work to cover all of your bases under any combination of 'players".

    hr

    Attached Files:

  13. zadwit

    zadwit New Member

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    I do have a DHW coil inside the Burnham oil fired boiler. I will try to attach a picture of a dwg. that was suggested to me as one way to plumb this all in. The hot water would leave the EKO and go to the storage tanks.A large "T" in the top of the storage tank would allow hot water to to be pulled from (A) the tank or(B) the EKO if it is producing hot water, to the flat plate heat exchanger. From the heat exchanger it would supply hot water to the return or inlet side of the oil fired boiler if and only if the oil boiler circulator is running sucking in hot water. Does this make sense? I realize it will not help much for domestic hot water. I could buy and install a superstor.
    1) Do I need to have another 1-1/2" female fitting in the storage tank, right next to where the hot water enters the tank, or will it work to install a large "T" so that hot water from the EKO can go either into the tank or directly to the hx?
    2)Should I install an aquastat on the storage tank so that it will "open" when the tanks cool down so that the circulator will not heat the tanks from the oil boiler?
    3)What do you think? Will this work?
    Thanks, Mark

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  14. zadwit

    zadwit New Member

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    Which is a better location for a danfos valve to maintain warm water return to the boiler? On the return side of the EKO-60 or on the supply side? I've seen both drawings.
    Thanks, Mark
  15. mouchey

    mouchey Member

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    I have a question? I am installing a dual fuel system with primary and 2ndary loop. I have an EKO 25 and a Munchkin condensing boiler with superstore indirect water tank. I am trying a 500gal propane tank for storage. Here's my concern is getting hot water from this storage tank makes me nervous. Does anyone have a recommendation of how to pipe a zone for the indirect water tank off the fossil fuel boiler so as not to use this storage tank water to wash or clean dishes? I have read a lot online here from NoFossil and others would love to know what you all think would really work. I am ready to do this install next week.
    Thanks,
    MJ
  16. Nofossil

    Nofossil Moderator Emeritus

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    Boiler and storage tank water is not potable water. Use an indirect tank (Superstor or equivalent) and/or heat exchangers to keep them separate.
  17. Gooserider

    Gooserider Mod Emeritus

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    What Nofossil said, with one minor possible exception -

    There is an outfit called Radiantec that does a radiant heating system that is primarily solar and gas DHW heater based, but can be used w/ a wood boiler & storage setup. Their system pulls supply water into the radiant plumbing, and gets DHW through it. The claim is that this gives greater efficiency by preheating the incoming water in the system before it gets to the main heat inputs, and also a small amount of "radiant cooling" in the off season.

    They claim to be fully approved by all the major plumbing codes, but it seems that Mass. is behind the times so I couldn't do their setup :mad: but it sounds good. They also have more conventional setups which I could use, and I've been considering them a little bit as their pricing looks pretty good...

    Not sure how they are reputation wise.

    Gooserider
  18. pybyr

    pybyr Minister of Fire

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    I'm sold on building my system around the primary/ secondary layout-- but some questions--

    first- so that I can draw some things up for feedback from you all, what's a good "HVAC diagram drawing for dummies" program, preferably one that's free and that'll run on either an Intel Mac or an ancient 33mHz pentium laptop

    second- are any of you familiar with TACO "twin tees":

    http://www.taco-hvac.com/en/products/LoadMatch<sup>®<_sup>+Twin-Tee<sup>®<_sup>+Fittings/products.html?current_category=118
    and
    http://www.taco-hvac.com/en/products/LoadMatch<sup>®<_sup>+Twin-Tee<sup>®<_sup>+Fittings/track_file.html?file_to_download_id=15084

    they look like an ingenious way to achieve the same effect as "closely spaced tees" only with less horizontal real estate in & occupied by the primary loop. Anyone aware of any drawbacks?
  19. kabbott

    kabbott Member

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    I don't no what software the experts use but I have played around with taco HSS.

    http://www.taco-hvac.com/en/products/ Taco Hydronic System Solution® (HSS)/products.html?current_category=84

    It will show head loss and auto select pump size and such and also has the twin tee's.
    many different types of emitters and buffer/storage tanks.

    edit::Hmmmm link didn't work, copy and paste.
  20. babalugatz

    babalugatz New Member

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    We installed a Radiantec system for a customer (upon her insistence & she supplied the product= NEVER an ideal situation for an installer). It uses potable hot water from a Polaris 75 gal. gas-fired/sealed comb. American Water Heater (95% eff they claim) & they recommend 3/4" pex tubing= a big pain-in-the-ass during install w/ kinking (it is a thinner walled tubing) & overkill as well.
    I'm not a big fan of this system in that there exists the possibility of stagnant water in some of the longer loops during warm months, when circ. pump(s) are off. They claim water will flow through all of the loops whenever there is a demand for hot water, but as we all know, no installation is going to be perfectly balanced. There are going to be loops with more tubing than others, and water is going to seek path of least resistance. Legionnaire's anyone? Too risky without installing a timer on all circ. pumps to operate them during off season...or Taco VS pumps that cycle every 3 days during non-use....
  21. Gooserider

    Gooserider Mod Emeritus

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    Thanks for the comments babalugatz... I'm not in a big rush on it, but I would love to do a solar house heat / DHW / pool heating setup at some point... I think we have an ideal setup for some sort of solar - (12/12 pitch roof, south facing, not to much shade, etc.) and I don't see solar electric being cost effective any time soon. However I could definitely put up a big water heating array, and (I think) take on a big chunk of the heating load... Not sure it would be worth trying to do a boiler as well, would probably want to do the system on pure solar for a while to see how it handled it...

    Now, according to Radiantec, they meet all the major codes, for whatever that's worth... It would be nice to believe that they have satisfied all the official types that there isn't any increased risk, no matter how unbalanced things are... However the combined system is not allowed under current Mass. codes so that isn't an option. I could do a heat-exchanger setup with the storage tank which would presumably cost me some efficiency for the extra pump, but would work pretty well I think.

    What do you think of that Polaris hot water heater? Our current conventional style (Rheem) natural gas water heater is presumably approaching end of life based on installation date, so I'm guessing we'll be needing to replace it within the next few years regardless.... I don't like some of what I've heard about tankless heaters, but a high efficiency condensing water heater sounds like a good deal - high efficiency, avoids the quirks and mechanical issues with tankless jobs, less of a safety issue than a conventional, etc...

    As to the tubing - I suspect that 2/3 of the house could be done with fairly small tubing, but that our living room which has a fairly small floor area, but has an essentially 2.5 stories tall cathedral ceiling (24' center height, and 3 BIG picture windows (2 at 6'x6' and a 6' half round) will need all the help it can get - our house is pretty, but not practical...

    Gooserider
  22. LeonMSPT

    LeonMSPT Minister of Fire

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    New oil fired hot water baseboard system is up and running great. Contractor left two valved T's at supply and return, and will be coming with the wood/coal boiler sometime in the next couple of weeks. He left a T'd valve at the supply and return on the boiler, and is going to pipe the wood/coal with 1 and 1/4 inch steel pipe with a circulator, air trap, and expansion tank. Says this way, the boiler remains hot at all times, better for it, and it give me some heat storage as well. Didn't have money for a "gassifier" and he wasn't sold on them anyway, without heat storage at least.

    Anyone used a set-up like this? Problems?

    Thanks in advance.
  23. joemeintzer

    joemeintzer New Member

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    Yes that is absolutely true if you're concerned about that type of thing. That work would fall under a pressure vessel code or power piping ASME B31.1 I wouldn't be overly concerned if you're doing it on your own equipment though I'll bet the warranty would be broken anyway.
  24. jimmie ray

    jimmie ray New Member

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    I think you could have too high a flow rate with a zone valve system, when only one zone is calling, and you sized the single pump for the capacity of all the zones - it becomes oversized for that one zone?
    But the most important reason to utilize pump zoning is that in the event of a pump failure, you still get heat to the other zones with the properly working pumps. That will keep the occupants happy until the pump is replaced, and hopefully even prevent frozen and burst pipes during severe cold conditions.
  25. heaterman

    heaterman Minister of Fire

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    You are absolutely correct. When a circ is sized to provide required flow to all zones simultaneously (design conditions) it stands to reason that flow will excessive when only one zone is calling. This can be solved in a couple ways. The first being to install a pressure differential bypass valve and bleed the excess energy created by the circ back into the return or by a far more preferable method which uses a variable speed circ that ramps up and down according to the load.

    Also very true is that a multiple circ system provides you with redundancy not achievable with zone valves.

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