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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. Bob Rohr

    Bob Rohr Minister of Fire

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    Here is what I consider an ideal piping

    It does use a lot of pumps, but those are cheap on e-bay. Look for 3 speed versions.

    Here are some features.

    Boiler protection is easily obtained, without bang bang control.

    The boiler can simultaneously provide heating and charge the buffer if the loads allow.

    Additional heat sources easily connect, solar or fossil fueled, perhaps electric boiler on off peak rates, as those become more common.

    Mix down temperatures could be a simple 3 way thermostatic, or a reset based control.

    You can pull energy from the buffer without ever flowing through the boiler, very important.

    Sorry if this ends up a double post.

    hr

    Attached Files:

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  2. Buck1200

    Buck1200 Member

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    Could you also accomplish the same by using a small buffer tank (albeit with quite a few tappings) in place of the yellow distribution loop? Seems like that would nix a circulator, right?

    Separate question: adding tappings to a pressurized tank would require the work of an ASME certified welder in order to remain legit. Is that true?
  3. tuolumne

    tuolumne New Member

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    H.R. - I know very little...it appears that charching the tank when no zones are calling would require pulling water through the primary loop pump. Is it a problem to pull water through an unpowered pump? When is the buffer's pump running? When the boiler is cold, does the primary pump pull water through the unpowered buffer pump? When I get my layout schematic done I'll post here to get some feedback. Basically it is a manifold supply and return system with zone valves for the radiators and injection mixing for the radiant floor. House gets priority, but a diverter causes extra hot water to simutaneously charge the tanks. This primary/secondary is a new concept for me. What if the buffer tank was in the primary loop, but zones could draw off water ahead of it if needed? That would be simple to accomplish if it is possible to pull water through a dead pump when the house is not calling.
  4. wdc1160

    wdc1160 New Member

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    I like the diagram. I wish you had inlcuded a legend for those of us who are plumbing impaired.
    Do you see any potential drawbacks from this design. 2 things I would point out to you.
    1. The method you are using to show the delta t protection needs elaboration. If you using a mix valve-- I have never seen this method used to display it. It also could change the scheme of the plumb, if you choose a 4 way valve- instead of 4
    2. Many member of this board believe if you choose to plumb the buffer in the way you have depicted it could be beneficial to reverse flows for a "storage phase" and "extraction phase"

    These two items are personal preference and also things that

    PS I am using a very similar configuration.

    What is a" bang bang control?"
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    Thanks, hot rod.
  6. Nofossil

    Nofossil Moderator Emeritus

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    Diagrams are good. I'm trying to wrap my head around the pros and cons of having a primary loop with its own circulator. I could also use an explanation of the device symbols. By the way - what did you use to make that pretty diagram?

    I thought my approach made sense, but it's a bit different. Here's what I'm doing:

    I essentially have a hot (supply) manifold and a cold (return) manifold that are shared by all heat sources and heat loads.

    Each heat source has a circ that draws from the return manifold. Heated water goes to the supply manifold.

    Each heat load has a zone valve that allows water to flow from the supply through the load to the return.

    When I add a radiant zone that needs cooler water, I plan on an additional circ and mixing valve for that zone as in your diagram. It will still be connected between the shared supply and return just like the other zones.

    So - pros and cons. Since I'm too cheap to buy a high-capacity mixing valve, I'm doing the bang-bang thing with a zone valve for input protection. I could add a mixing valve without changing anything else, though. I think one advantage of my scheme is that it has very nearly the irreducible minimum number of components. I could eliminate a circ by plumbing my heat sources in series, but I like to have each device plumbed so that it can be isolated independently.

    I've seen the loop approach many times, so I assume there's a benefit that justifies the extra circ(s). What am I missing?

    Attached Files:

  7. solarguy

    solarguy New Member

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    if you chose to install a primary/secondary piping configuration you are better off to use zone valves for your zoning needs instead of circulators. You will still have the primary circulator on your loop, the circulator on your wood boiler. The theory behind this statement is as follows:
    When you look at a pump curve, most small wet rotor circulators (Taco 007) will pump up to
    14 gallons per minute depending on the head. Most of the heat zones in an average home have less than a 20,000 btu heat loss which equates to 2 gallons a minute of flow. 1 gallon per minute @ 180 degress= 10,000 btus at a 20 degree delta. When you zone w/ circulators you could be pushing 5 times that water thru the loop than you actually need which results in more fuel consumption.

    Plumbers zone with circulators, heat men zone w/ zone valves:)
  8. Bob Rohr

    Bob Rohr Minister of Fire

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    Great comments and quotes. there are plenty of way to pipe these systems. all have pros and cons.

    A tank as the primary loop is an excellent option. it can act as the air purger, primary loop, and ad some “capacitence” to your system..I agree a certified welder might be the best way to modify a pressurized vessel.

    The primary loop pump needs to run for anything to happen really. None of the secondary loops will “communicate” without that loop circ spinning.

    The boiler return protection in this example is accomplished by a variable speed circulator. As the boiler temperature rises the circ spins faster. as it hits 140f or lower it would slow enough to allow the boiler to catch up. A lot less component cycling.

    Bang/ bang is a control the switches on off on off to provide control. variable speed eliminates cycling of components and better temperature regulation. The boiler output matches the flow through it with variable speed pumps. Just like the fans on the EKO and others that have variable speed controls.

    Any type of mixing valve uses pump energy. If in fact we are chasing the ultimate use of energy, be it wood or electrical, then design around the smallest possible circ pumps. the new ECM circulators hitting the market use about 40% less energy to get the job done.

    Nofossil has a good drawing. sometimes the pump will run at the top of it’s curve, sometimes off the bottom, and possibly right in the sweet spot. that is one problem with a single pump that sees various loads. if you size it to handle any or all loads together, when one small load calls it will be overpumping, inefficient, etc. A pressure activated bypass could help keep the pump on curve, but it also consumes pump energy.

    As drawn it would be hard to balance flow through high head zones and the wide open zones. The circuit with the least resistence will get most of the flow. Circuit setters could help, but overly complicate the system.

    Primary secondary systems need circs to work properly. you could add zone valves down stream of the circs for additional zones. There are a lot of small circs on the market, as well as 3 speed to dial in an almost exact flow rate at very small wire to water consumptions. we may even see a 1 watt pump on the market soon. laing also builds some very small flow circs.

    Hope this helps, it’s fun seeing and hearing of all the variations out there. The perfect one still eludes me, but the chase sure is fun..

    The drawings were done in John Sigenthalers HydroniCAD program. a great hydronic specific program. I'll label better next time.

    hr
  9. wdc1160

    wdc1160 New Member

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    You had like 100 questions to answer. Enough that this became a sticky link instead of a thread.

    I think that some of your solutions are unique. I am sure it is the first time I have seen some of the solutions you have posited.

    As an example I don't think I have seen someone choose a variable speed circ in leu of a mixing valve.

    In a previous thread we beat to death mixing valves and the reason for having them, I have no first hand experience failure from not using them, but try not to expereience alot of things people warn me about.

    So I will pass the warning to you, apparently low inlet temps can be real bad, be careful.

    My strategy(still brewing) for gasification is going to be mixing valve centeric ie I want to control the mix temp and flow 100%
    I think that can also be an efficient use of wood vs pump energy.

    I am still at the drawing board.

    Thank Bill
  10. solarguy

    solarguy New Member

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    >Primary secondary systems need circs to work properly. you could add zone valves down >stream of the circs for additional zones.


    Sorry Master, that is not a true statement. All you need is the primary circulator sized correctly for the load on the zones at peak demand.

    I say this based upon 35 years of hydronic experience.......
  11. Nofossil

    Nofossil Moderator Emeritus

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    Thanks for the detailed response. If I understand you correctly, the benefits of the primary / secondary approach are that the load on the pumps is more constant and the zones are easier to balance.

    I hadn't thought of either of those as problems. Here's my understanding. Please clarify if I don't quite have it right, and please excuse my insistent questioning. I'm trying to walk a fine line between learning and arguing, hopefully on the right side most of the time ;-)

    A circulator has a pressure / flow curve such that the less resistance, the more flow. This compensates to some degree for the varying number of zone valves that might be open - more zones, more flow. Manufacturers strive to make this curve as linear as possible, so that you will get close to twice the flow with two zone valves open as with one.

    Zone valves have a very small orifice so that the valve itself makes up a significant percentage of the head loss for each zone. In that way, the zones are close to balanced. There are no 'wide open' zones. Any zone that gets more flow will simply reach temp sooner and shut off.

    The circulator will pump less with fewer zones open, which will have the effect of increasing the boiler temp due to less flow. Wouldn't a variable speed pump increase its speed under those conditions, making it work even harder than the single speed? Does power consumption vary significantly with head loss? How would you define 'sweet spot' for a given circulator?

    Finally, I haven't seen a variable speed pump that's less than $300, even on eBay. The ECM pumps look to be in the $400-$500 range unless there are sources I haven't found. Would it be too much to ask you for rough-order-of-magnitude prices that folks could expect to pay for the more esoteric components? I've shied away from some approaches because of perceived cost. Love to find out I was wrong.

    For mine:
    Circ pumps: Taco 007IFC or Grundfos UPS15-58FC - about $50 on eBay, $75-100 in the real world
    Zone Valves: Honeywell Zone Valves - about $60 on eBay, about $80 in the real world
    3/4 Mixing valves (DHW): Honeywell AM101-1-C - about $50 on eBay
  12. slowzuki

    slowzuki Feeling the Heat

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    In a primary-secondary what he is saying is true, and what you say is true if you don't have any load shedding. He is talking about zone valves downstream on zones off the loop, not zone valves in the loop.

  13. Bob Rohr

    Bob Rohr Minister of Fire

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    In order to have a true primary secondary circuit you need closely spaced tees for the supply and return. properly installed there will be no flow to those secondary branches with just the primary loop pump running. That is the design intent of primary secondary piping. For some excellent reading on P/S check out Dan Holohans books "Pumping Away' and "Primary Secondary Made Easy" at heatinghelp.com. Also John Sigenthaler has quite few articles available at www.pmmag.com on primary secondary design and applications.

    The new small wet rotor circs we see hitting the market with variable speed have several modes.

    Some change there speed based on deltaP or change in pressure. In a zone valve system as zones close off the pump, electronically, senses this and reduces it's rpms accordingly. i have a 3 zone system in my shop and the circ runs from 17- 38 watts based on which zones are open.

    They can also work as a delta t or temperature difference mode. the Grundfos MixiMiser comes with two sensors. the control on the pump watches the two sensors and increases or decreases it's speed accordingly.

    I believe the new Wilo Stratos has the ability to work in either mode.

    Yeah, they are more $$ but with all the features and reduced power consumption I expect they will start showing up on more systems. Ii suspect price will drop as more manufacturers off this technology.

    Most pumps run most efficiently in the middle third of their pump curve. When you size a circ pick one that will operate your system in that middle range for best wire to water efficiency.

    hr
  14. wdc1160

    wdc1160 New Member

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    I will second nofo's statement.

    One of the things that is lost on the underinformed plumbers here are that we don't know enough to quantify how much wood,electric, material cost your saving us.
  15. slowzuki

    slowzuki Feeling the Heat

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    The last thing I will note is that a variable speed drive used instead of correctly sizing the pump is less efficient for fixed loads.
  16. solarguy

    solarguy New Member

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    aw, come on, I'm not an uninformed plumber.

    I agree with the 2 closely spaced tees. The intent is to create hydraulic jump to prevent the primary pump from pushing water thru the shell of the boiler or thru your zones if your zoning w/ circulators. The balance of your tees for your supplies & returns do not have to be closely spaced if you're zoning w/ zone valves. The only time we zone w/ circulators is for radiant manifolds, everything else gets zoned w/ zone valves. By doing this we feel we have better control to balance out the system for the proper gpm thru a zone.

    Everyone has an opinion on what method is best, it all boils down to whatever you feel the most comfortable in doing or whatever lifts your skirt.
  17. Eric Johnson

    Eric Johnson Mod Emeritus

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    Sorry, but no men wearing skirts allowed in the Boiler Room.

    Cussing and spitting on the floor is one thing, but the skirt business is where I draw the line.
  18. Gooserider

    Gooserider Mod Emeritus

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    Aye, and as 1/4 Scotts (Paternal Grandmother was a MacKenzie), (or more if the Scapa is flowing) I must ask what ye has against skirts? %-P

    Gooserider
  19. Eric Johnson

    Eric Johnson Mod Emeritus

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    They're only permitted when accompanied by bagpipes or when worn by Mel Gibson. Of course, anyone carrying a bottle of fine Highland scotch gets in no matter what they're wearing (or not wearing).
  20. Green DIY Guy

    Green DIY Guy New Member

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    The layout looks like there might be one un needed pump


    If I understand what I have been told you might be able to eliminate a pump and possibly consider placing the primary circulator on the supply going out, unless it's a heat issue with a wood boiler. I found great advice and plenty of layout examples here http://www.houseneeds.com/shop/heatingproducts/heatu/heatinguniversity.asp?stype=../../products.htm
    they answered my questions and help set up a "light weight " system using 3 speed pumps. Simple is better and extra pumps means more elec :O(
  21. Tony H

    Tony H New Member

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    Forest thanks for the link now I can read and learn so my input can be more than ........... What do you think of my new plumbing company
    Plumbers in skirts ( an all female crew) I think we might do quite well !
  22. Gooserider

    Gooserider Mod Emeritus

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    Sounds good to me - a good way to make "Plumbers Butt" a non-problem (much to the dissappointment of Duluth Trading Co.) ;-P

    Gooserider
  23. steam man

    steam man Minister of Fire

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  24. SteveJ

    SteveJ Member

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    hot rod,

    Thanks for the great post...

    How do you "pull energy from the buffer without ever flowing through the boiler"? In the diagram, the piping looks to be configured to only charge the buffer. How do you pull through the pump with the check valve?

    Please tell me what I am missing,
    Steve
  25. heaterman

    heaterman Minister of Fire

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    The Primary loop is the common denominator in the piping. The boiler itself is a secondary loop. Therefore, you can set up your control strategy to pick up heat from the highest temperature source. If the boiler would happen to be at a lower temp than the tank, the boiler circ would stop and the tank circ would come on dumping its heat into the primary loop.

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