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boiler, buffer, backup, DHW and loads

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Bob Rohr, Mar 2, 2013.

  1. Bob Rohr

    Bob Rohr Minister of Fire

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    I think this concept, designed by John Siegenthaler www.hydronicpros.com covers most of the functions that many want.

    The boiler is protected from low return temperature by a variable speed circ. I like this for high output boilers especially. Less cost and less pressure drop compared to large loading units, this could be an ECM pump for additional energy savings. Actually all the circs could be ECM which are mandated in Europe now for all heating pumps.

    I believe with a swing check, and generously sized boiler piping, the boiler would thermo-siphon for over-heat protection, remove any spring checks from the pump! It seems to work well in the loading units with a swing ck.

    The controls could be very simple. The wood boiler runs it's own pump P-1, all seem to have a relay output for that function. The load circ P-2 could be a brand with the logic built on, or run by an inexpensive solar differential control, just about all brands and models of solar controllers have variable speed functions built in nowadays.

    The buffer tank serves as a hydraulic separator and a fairly good air removal point for the boiler. as well as a dirt separation function.

    Boiler back up with a mod con has some buffer space for small micro zones. Loads could be removed from the tank with reset temperature controls MV-1.

    DHW is via a 30 plate HX. I have proven this method on my own system for a year now. I've found the Harwil Q8-N flow switch works perfectly and triggers at 1/2 gpm flow. Protect the DHW temperature with a listed 3 way thermostatic valve.

    DHW backup could be a small tankless gas or electric. if I were to buy a new mod con boiler I would use a brand with them DHW HX built in. So boiler back up and DHW from one unit. Really back up could be oil, gas, LP, electric, heat pump, any source you chose. Back up DHW could also be a small electric HW heater too.

    There are trade offs on any system design, this simple to plumb option shows a one tank concept that covers most options that customers want, with Caleffi components of course :)

    Thoughts, suggestions?

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  2. ewdudley

    ewdudley Minister of Fire

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    As usual, Siggy disregards maintenance of storage tank stratification as a goal when integrating DHW. A preferable design would be the European approach of putting a DHW coil in the top of the storage tank with an internal reverse chimney to guide spent DHW to the correct thermocline.

    Of course all-radiant all the time is nice because it makes integration of heating loads with storage foolproof. The choice of a motorized three-way seems extravagant with the price of temperature controlled ECM loop injection pumps coming down so nicely.

    I like the variable speed temperature controlled P2. Is it controlled only by return temperature? And if so is supply temperature an arbitrary function of P1 flow and instantaneous boiler heat output?

    Connecting the fossil fuel boiler directly to storage as a buffer and hydro separator works quite well, it seems that may are reluctant to take that approach.

    --ewd
  3. Bob Rohr

    Bob Rohr Minister of Fire

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    We have looked at DWH coils in the top of the tank. They add considerable cost and the ones we looked at had fairly low DHW output. Much too low for the typical US house hold, same with the early Euro designed tankless heaters that hit the US shores. Some of the brands tested had stainless steel corrugated coils and they pin holed from the treated water common in the US, cholorides or cholorine is not a common water treatment where those tanks come from :)

    The rest of the world is much more DHW consumption are. 2 gpm is plenty of DHW flow for a Euro family. In the US we need 5 gpm or more, some tubs have 7 gpm fillers!

    A heat exchanger with two "moving" flows is a better method from my experience, a coil in stagnate conditions will not transfer as well as a plate type HX and it is servicable when the HX is external. External HXers allow you to buy a fairly inexpensive "off the shelf" insulated tank, or former LP tank for the storage vessel.
  4. ewdudley

    ewdudley Minister of Fire

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    Pfft. My neck and collar cost $40 and the coil itself was $150 for a nominal 7 gpm 'tankless coil' [edit: actually it's labeled 5 gpm, from Diversified Heat Transfer]. Supplies shower and washing machine simultaneously and continuously. I set it up to supply preheat flow for an electric tank but it turned out it supplies plenty on its own.
  5. Armaton

    Armaton Member

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    Which coil do you have Eliot? Even tho I have my flatplate already, may be a better fit to put a coil in the top of my separator. Save a pump also.
  6. kuribo

    kuribo Feeling the Heat

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    How about the line of thermostatic boiler protection valves from Regulus? They make a line of three way thermostatic valves for boiler protection that have large Cv and very reasonable pricing. They make a 1-1/2" (Cv ~ 25) and 2" valve (Cv ~ 38) (TSV6, TSV8) that are priced around $100 and $120, respectively. They claim these are suitable for boilers up to 340,000BTU/hr output. That doesn't include shipping, but even with, seems it would be a lot cheaper and simpler option that the pumps, sensors, and controllers, never mind the electricity costs.
  7. kuribo

    kuribo Feeling the Heat

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    The only coils I could find were over $400 each. Can you provide a source for these at $150?
  8. ewdudley

    ewdudley Minister of Fire

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    Ebay and patience.
  9. kuribo

    kuribo Feeling the Heat

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    Ah....ok. Thank you.
  10. ewdudley

    ewdudley Minister of Fire

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    But now that you mention it, it took ten months to find and $30 per month electricity in the meantime for hot water. I've seen them new for less than $500 so looks like rewards of patience weren't so grand.
  11. kuribo

    kuribo Feeling the Heat

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    They don't look to complicated- wonder how hard it would be to make one...
  12. ewdudley

    ewdudley Minister of Fire

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    I needed one for DHW and another for hot tub. I moved one from my coal boiler to the buffer tank and got another like it so the mounting would be the same for both. It's a six hole 5.25 maybe 5.375 inch diameter bolt pattern that seems to be pretty common, with what looks to be plain old 4.00 inch pipe for a neck. The flange is about 6.5 inch OD.

    NexusTank.JPG
  13. lotawood

    lotawood Member

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    Will the P1 pump lower the head of P2 at all?
    I need to upgrade to a boiler protection valve. This approach looks better than a danafoss or termovar.
    A bumble bee is close to my gpm.
  14. ewdudley

    ewdudley Minister of Fire

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    At $190 an ECM Bumble Bee (model HEC-2) would be wonderful for a return temperature control application, but according to their sheet it only controls increasing-deltaT with increasing-flow, or increasing-temperature with increasing-flow. For return temperature control we need decreasing-temperature with increasing-flow, which it doesn't claim to do. It's possible they left it out of the documentation, or perhaps they've figured it out and have added the functionality in the meantime, or I maybe I've got it wrong, so might be worthwhile to research it further.

    It can be done correctly, inexpensively, and reliably with a PID controller and bang-bang injection. Such a two-pump solution is working well for me, one pump recirculates boiler supply to return, and another injects system return into the loop with a PID controller and bang-bang modulation.

    Return temperature control is accomplished by injecting into a boiler recirc loop with an injection pump under PID bang-bang control. With an 80 second cycle, 105 degF system return water, and a 160 degF return temperature setpoint I'm seeing a 10 degF swing in return temperature with boiler discharge temperature steady at 170 degF. Pumps were salvage, controller $40, relay with pedestal $12.

    Push a button and you can set the return temperature anywhere you want it. Since supply temperature follows return temperature, setting return temperature according to desired supply temperature can be used to avoid the two-laps-through storage problem where tanks fill with 160 degF water on the first lap and recirculate to 180 degF on the second lap. This is important for me during a couple weeks in January when there are zones that need 180 degF water to do the job. Again, these benefits could be achieved more efficiently and with little less complexity with a variable speed temperature controlled ECM pump if and when they become available economically with the correct operating modes for this application.

    (Then again as kuribo points out above, there are now affordable mixing valves with monster Cvs available. If and when there is an affordable ECM temperature control pump with an increasing-flow decreasing-temperature mode we could have a single pump solution with adjustable supply temperature, and be done with it.)

    There's a supply side sensor that kicks in a second pump when storage is hot and extra flow is required, and for fail-safe redundancy. Pump check valves are IFCs, but wouldn't have to be.




    boiler_recirc.001.jpg
  15. BoilerMan

    BoilerMan Minister of Fire

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    Good logic there, EW.

    Ebay and time is good at almost all things money saving.

    TS
  16. jebatty

    jebatty Minister of Fire

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    This is my arrangement with my Tarm and 1000 gal storage, and Deep Portage does nearly the same with a 4000 gal storage/hydraulic separator. At DP both a Wood Gun E500 and a Garn WHS 3200 charge the storage, but the storage is a "load" off a primary loop and a supply to the primary loop. Works extremely well.

    DP also is re-doing a Froling with a 1600 gal tank o operate as storage/hydraulic separator.
  17. lotawood

    lotawood Member

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    What would be an example of a variable speed setpoint circulator? That is P2 on the first post.

    Would the bumble bee, on a set point of 160 degrees, go slower under 160 and faster above 160. Or do I have it backwards?

    A PID sounds like a good alternative as well. I need to get one for another part of my system.
  18. ewdudley

    ewdudley Minister of Fire

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    The Bumble Bee is a variable speed setpoint (or deltaT) circulator, but reading the sheet on the Bumble Bee all I can see is 'direct acting' control, where if setpoint is 160 pump speed increases below 160 and decreases or stops above 160. It's hard to believe that they can't be configureed for 'reverse-acting' control but I'm not seeing it.

    Taco makes conventional motor '00' series variable speed units that do explicitly provide both direct and reverse acting control, but they don't offer the efficiency and wide range of precise flow rates available with an ECM pump like the Bumble Bee.

    http://www.taco-hvac.com/en/product...Circulator/products.html?current_category=193
  19. Blue Tornado

    Blue Tornado Guest

    Concerning the Taco Bumblebee HEC-2.

    In the instruction sheet at he bottom of page 5 is a diagram for the plumbing and sensor location as "boiler protection". It appears that using one bumblebee on boiler loop (as diagrammed in OP) and one for primary loop to storage (as diagrammed in OP) is an ideal alternative to a loading unit.

    Add a third to your shelf as backup and it is gold. At $200 per pump it is a close initial investment as a loading unit.
  20. ewdudley

    ewdudley Minister of Fire

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    The OP uses P2 as an injection pump into the boiler loop and requires a reverse-acting control, i.e., more injection causes lower return temperature to boiler. Again, I don't see that the HEC-2 offers reverse-acting control. Hopefully this is just a defect in the documentation, or the reverse-acting control will be available in future versions.

    Diagram No. 1b: Boiler Protection By-Pass on page 5 of the HEC-2 sheet shows ... well I'm not sure just what it shows. P1 sensor is labeled as 'Supply Sensor', but it's on the return port of the boiler, which should be our first clue that not a lot of thought has gone into this setup. P1 can run as fast as you please but if the other pump flow is too much or too cold then the whole scheme fails at providing return temperature protection to the boiler.
  21. lotawood

    lotawood Member

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    That is what I thought when I saw that.

    Blue tornado: I was aiming for something cheaper that a boiler protection valve. I read of a few people having problems. But I got to say that was more with a danafoss than a termovar. I have 1.5 inch pipe and the BPV get pricey or are not available.
  22. kuribo

    kuribo Feeling the Heat

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    Check out the Regulus 1-1/2" and 2" thermostatic three way valves. HIgh Cv and low prices. Simple solution.
  23. __dan

    __dan Feeling the Heat

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    The P2 variable speed injection pump could be a standard Taco IFC wet rotor circ and use an external three thermistor variable speed injection pump controller. Outside temp sensor (for reset), boiler HWS temp sensor (for target setpoint), and boiler return water temp sensor (for boiler low return temp protection). The (Tekmar) controller calculates target HWS setpoint but only enables and ramps up the circ after the boiler return thermistor reads return water above the protective low limit temp setpoint. Boiler return temp sensor is shown on the drawing.

    The ECM circ is very different internally, with internal sensors and inverter VFD. Not directly compatible with the Tekmar standard wet rotor circ controllers, but as the market matures I'm sure this functionality will be carried over to the ECM circ controllers.

    [​IMG]
  24. maple1

    maple1 Minister of Fire

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    Good lord, that wiring setup makes mine look not as bad as I thought it looked.
  25. kuribo

    kuribo Feeling the Heat

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    Simple enough....._g

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