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Boiler piping schematic with pressurized storage

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by tuolumne, Jan 24, 2008.

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  1. tuolumne

    tuolumne New Member

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    Here is my piping schematic. I finally figured out how to draw something where I could easily get it online. The circulator nearest the boiler will cycle water near the boiler until the danfoss opens at 140 degrees. At that point water will circulate through the twin 500 gallon storage tanks. If the house or DHW zones call, the primary loop circulator will start. The 3 way mixing valve diverts return water above the setpoint back to the zones. As a result, the reduced flow back to the boiler allows the boiler circulator to continue to charge the tanks with left over heat. If the boiler is off, the primary circulator will draw water off of the storage tanks. I just switched from a supply/return manifold scheme to the primary/secondary piping. Please let me know if I am missing anything glaring. Where do I need other items like checkvalves, isolation valves, drains etc. Thanks.

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  2. Nofossil

    Nofossil Moderator Emeritus

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    Nice looking schematic. What did you use to draw it?

    The three way valve has cold inlet on bottom, hot inlet on right, and mix out on left?
  3. tuolumne

    tuolumne New Member

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    Thanks nofossil, I drew it in AutoCAD LT and used the publish to we option for printing a jpg. Text is grainy. I hope to use this valve to shed water above the setpoint back to the supply manifold. I want two outlets and one inlet. Is a three way mixing valve the wrong product? I think what I want is a diverter valve. What I have is a Tekmar 712. Oops.
  4. Nofossil

    Nofossil Moderator Emeritus

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    I'm hoping someone with more plumbing experience than me will comment on this. My head hurts trying to figure out what happens to pressures at different points in the system with all of those pumps running in different combinations.

    To keep my head from exploding, I keep it simple by having only one pump running at any time. I'll have two when I have a radiant zone, but one will be contained within the zone just as you've drawn.

    Looks like you have flow in one direction for heating the tanks, and in the other for drawing from them. I think that's the way to go. You'd want to plumb them to promote maximum thermal stratification.
  5. solarguy

    solarguy New Member

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    I'd pipe the 2- 500 gallons in a reverse return configuration. This would ensure equal flow
    & equal heat distribution thru both tanks.
  6. tuolumne

    tuolumne New Member

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    Here is a version with the mixing valve gone. I would still like to charge the tanks during house demand if possible. I also changed the zone supply/returns to closely spaced tees which hopefully helps the primary pump not interfere with the secondary pumps. However, what does the charging pump do during this time? Will it tend to push water in series along with the primary pump, or will it send water into the tanks. When this pump is down, water will flow through the tanks in reverse, but when the charging pump is on, water will flow from red to blue as shown (I think). Where does a check valve or balancing valve belong in the system to insure proper flow direction. I'm starting to get dizzy with all the flip-flopping.

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  7. verne

    verne Member

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    what do you guys think of this pipeing scheme ? This is the first I have tryed to post pictures .

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  8. verne

    verne Member

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    Thats exciting something worked for me. I'm still learning the computer thing. Buy the time I type this post it will be on another topic.The tank is 1000 gal propane , expansion tank xtv 160, 80 gal. termavor mix valve. Taco 007 pump? 140' from boiler to boiler with 1" timesaver . Please ,any advice is greatly appreciated. Im starting to move some earth for my pole barn pad this weekend.I cant wait to get this project going
  9. Nofossil

    Nofossil Moderator Emeritus

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    2 suggestions: attach a higher resolution / larger image, and start a new thread for discussion on your system. I'd be glad to comment, but I can't see enough detail and I don't want to hijack the original thread.

    Thanks....
  10. Nofossil

    Nofossil Moderator Emeritus

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    This is simpler and better, I think. If you redraw it with the tanks placed vertically where the red vertical line is (at the left of the left tank) I think it's easier to understand: 2 loops, each with a circ. Both loops always flow clockwise. The left loop is boiler to tank and back. The right loop is tank to zones and back. Draw it so that there's a T at the top of the top tank and the bottom of the bottom tank, but exact same connections as you have shown.

    If the boiler circ is bigger than the secondary loop circ (and I think it should be), then the flow from that is split between going through the tank top-to-bottom and feeding the secondary circ. For instance, if the primary is 20 gpm and the secondary is 10 gpm, then you'd get 10 gpm going into the tank from the boiler. Boiler circ shuts off, tanks flow opposite direction at 10 gpm.

    You might need to add a bit of flow restriction to the secondary loop. Your heat load probably doesn't require a very high flow rate.
  11. verne

    verne Member

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    sorry wouldnt want to highjack a topic . maybe i should call it boiler piping schematic with pressurized storage#2
  12. tuolumne

    tuolumne New Member

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    OK, here is an identical schematic with the tanks moved for clarity. Are you suggesting that if pump A is larger than pump B, the tanks will always be charging even when pump be is circulating to the house zones?

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  13. Nofossil

    Nofossil Moderator Emeritus

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    I'm really hoping someone who knows what they're talking about will jump in so I can stop making this up as I go along......

    Yes, if A is bigger than B the tanks will charge all the time.

    There might actually be a slightly more elegant solution. Thinking out loud here:

    Going back to your first schematic, grab the mixing valve and make it a real mixing valve - hot and cold inlets, controlled outlet. Install the mixing valve to the left of the secondary pump inlet. Connect the cold water return line to the cold inlet of the mixing valve. With me so far?

    If you set the mixing valve for a temp of say 170 degrees, that would be plenty hot enough unless your 'typ' zones are marginal. If you did that, then the flow is balanced and the percentage of the boiler output that goes to the heat loads varies with demand. If the DHW is ice cold, then a high percentage of the boiler output would flow through the secondary loop. If only a single zone was calling for heat, then most of the boiler flow would be through the tanks.

    I think that would work, and I think it accomplishes what you were shooting for in the first schematic.
  14. tuolumne

    tuolumne New Member

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    I'll try to draw this up. My wall panels are sized for 140 degree supply water on the coldest day, so the whole primary loop need never be above 140. Do they make outdoor reset type mixing valves? In mild weather, I could run my storage all the way down to 100-110 probably. Is it even necessary to go the outdoor reset route? I can let the tanks run down anyway and a mixing valve wouldn't care.
  15. Nofossil

    Nofossil Moderator Emeritus

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    That's even better. At 140 degrees, the mixing valve would allow you to get the best of both worlds - heating storage to a high temp while returning relatively cold water to the boiler. I like it a lot.

    You could skip the outdoor reset, I think. Worst case is you run cooler water through your wall panels. If you put a few temp sensors on your tanks, you could get a really good sense of when you'd have to build another fire.

    This is more elegant than my approach in the sense that there's no sharp transition between heating with the tank vs. heating with the boiler. The boiler doesn't have to care at all about what's going on with the zones and vice versa.
  16. tuolumne

    tuolumne New Member

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    Thanks for getting me past that plumbers' block nofossil. Here is the simplified version, with a mixing valve to send 140 degree water through the primary loop. The varying amounts of return water diverted back to the zones will cause the boiler pump to charge the tanks all of the time. Back to some of the original questions...where do I need check valves, isolation valves, drains etc. Where in this scheme should I put tees for a future fossil fuel backup?

    I just thought of a small problem...I would still like the indirect DHW to get supply water as hot as possible. Also, I may be putting a hot water unit heater in the garage at some point, and when I want it on it will be with little notice and also need hot water. Just when I thought I could see bottom the water starts getting murky again.

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  17. Nofossil

    Nofossil Moderator Emeritus

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    You've sketched exactly what I was thinking. I'd make a drawing change to make it more intuitively obvious what's going on - I'd put the tanks one above the other, with the cold connection below the bottom tank. The tanks participate in both loops - te left loop with the boiler, and the right loop with the heat loads. If they 're drawn in the middle that way, it makes the two loops more obvious, and it also clarifies the thermal stratification. Ideally, you'll have a sharp thermocline that moves downward through the tanks in sequence as you put in heat, and moves back upwards as you withdraw it. I don't know how much you can avoid mixing, but commercial systems go to great lengths to promote stratification. Pipe fitting selection and location might be all you can do.

    Now that you've made the drawing change, move the expansion tank out of the way and stick a fossil fuel boiler in there with its own circ drawing from the cold return, so that it's in parallel with the tanks and the EKO.

    Both boiler circs need check valves. I'm hoping that the secondary circ won't suck water through the boiler(s). Probably the best approach is to plumb it so that it has an independent connection to the top storage tank.

    I like an isolation valve on each side of each boiler. Make sure you have a relief valve inside the isolation valve. Boilers have their own drain valves, You probably want isolation and drain valves on the tanks too.

    Perhaps you could move the DHW loop so that it straddles the mixing valve. I'd also consider if possible setting up a sidearm HX for the DHW, probably in the hot supply line just to the left of the top storage tank. That way, any time that either boiler is running, your DHW tank is getting superheated (you DO have a tempering valve, right?). The DHW circ will only run when the DHW tank drops below its setpoint. My DHW hasn't called for heat since October.

    If you're heating a remote load such as the garage hot water, use 1/2" pex. For intermittent loads, the loss from the slug of cold water that you have to push through can be a big deal.
  18. tuolumne

    tuolumne New Member

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    Regarding the superheated DHW...I have an 80 gallon tank that's about 6 feet tall, so locating above the boiler is not an option. Are you suggesting that a sidearm could be installed on this tank to thermosyphon hot water into the tank even when the tank is not calling (pump is not running for DHW zone)? I would probably have the tank thermostat set at 120, so as not to run the pump endlessly if my storage tanks are cooled off.
  19. Nofossil

    Nofossil Moderator Emeritus

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    Yeah - a sidearm is attached to the side of the DHW tank. An inner pipe connects the DHW inlet and outlet. The outer jacket is plumbed in series with your boiler output so that any time the boiler is running, hot water is flowing through it. The water in the DHW tank then thermosiphons as long as it's cooler than the boiler output. I think it's important to have the tees set up so that DHW demand doesn't just draw through the sidearm instead of the tank. Eric's the expert on this. There are a few sidearm threads.

    The benefit is that it keeps your DHW 'topped off' automatically. If you have 80 gallons at 180 degrees, that should last a good long time even if you have to mix it with 50 degree well water. I actually use two mixing valves in sequence to mix my hot water - well and preheated gets mixed to 115 (or as hig has the preheat coild supplies). The output of that gets mixed with DHW tank water to produce 118 degree hot water for the house. If my preheat coil is hot enough, I don't touch the DHW tank hardly at all.

    You probably want to have some circ inhibit aquastat that shuts down circulation in general when there's no useful heat. It might also illuminate an indicator in the living space that says 'build a fire, dummy'.
  20. Eric Johnson

    Eric Johnson Mod Emeritus

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    Isn't your tank thermometer your "build a fire, dummy" indicator, nofossil?

    Good description of the sidearm. You don't touch the inlet and outlets on your hot water heater (the pipes going into the top of the tank) when hooking up a sidearm. All you need to do is connect the sidearm to tees in the pressure relief valve outlet and the drain. That's it. Water enters and exits the tank the old fashioned way.

    The beauty of sidearms is their low cost and simplicity of operation and maintenance (no extra pump; no moving parts). Basically, you hook it up and forget about it.
  21. Nofossil

    Nofossil Moderator Emeritus

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    tuolumne, could you post the part number and source for the Danfoss thermic valve that you show?
  22. Bob Rohr

    Bob Rohr Minister of Fire

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    I'm not seeing a means to pull temperature from the buffer tanks without flowing through the boiler?

    hr
  23. Nofossil

    Nofossil Moderator Emeritus

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    When the boiler is cold, there's no flow in the left loop. Flow is from the top of the tanks through the mix valve through the secondary pump (the horizontal one) and out through the secondary loop. The return comes back to the mixing valve as needed and to the bottom of the tanks. I'm hoping it gets redrawn to make it easier to see - it takes a minute to realize that there are really two distinct loops.
  24. Donl

    Donl Feeling the Heat

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    With reference to Tuolumne's schematic, if Pump A is running and Pump B is not, will there be any flow through B? I guess a better way to phrase my question is how much resistance to flow does an idle pump present?
  25. Bob Rohr

    Bob Rohr Minister of Fire

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    What turns on pump "A"? Does it turn on with the 140f control on the EKO? If so what if the tanks are at 180F and the boiler hits 150F from a cold start?

    Also, depending on the flow pattern through that 3 way zone valve it LOOKS like the two pumps will be in series when the ZV flows straight though?

    Also what causes flow into the buffer tanks?

    Here is a picture of a typical 3 way zone valve, motor removed. The ports are A on the left, B on the right and AB out the bottom. Flow can be A to AB, or B to AB. There is no means for flow from A to B. I'm not seeing how that flow pattern fits your piping? Unless you have a 3 way with different flow patterns?

    Really your only primary secondary is where the zones take off. The boiler to buffer and to the right hand loop are not P/S. Only connection via closely spaced tees allows a true primary secondary.

    I still feel a true P/S with all the loads, buffers, boiler, and additional supplemental boilers, connected via closely spaced tees allows the most options. It allows boiler only to the loads, buffer only to the loads, boiler and buffer together to the loads, supplemental boiler to load only, or virtually any combination of loads and supplies to work smoothly and without having pumps in series.

    And of course you never want the supplemental boiler to flow through the unfired wood boiler, or really a hot buffer tank to flow through an unfired boiler as it will remove a portion of the energy and lose it to the room and the great outdoors via the flue. And probably you would not want to flow the supplemental boiler through the buffer tanks, Energy stores much better in the fuel, in the chemical form then it does in hot water. Unless you have the ability to load the buffer with an electric boiler on off peak KWH rates.

    hr
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