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Storage, Taco twin tee, and head-to-head circs

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Nofossil, Nov 4, 2013.

  1. Nofossil

    Nofossil Moderator Emeritus

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    A while back I remember some discussion about different approaches to getting proper flow direction into and out of storage in primary/secondary systems. There were approaches using 4-way valves, extra tees, double circulators with check valves, and a variety of variations.

    I've spent some time reading, researching, and thinking about this problem.

    My question for the collective wisdom of the forum: Is the approach shown below the simplest and least expensive way to get top-to-bottom flow through storage while charging and bottom-to-top flow while discharging in a primary/secondary loop system?

    [​IMG]

    The green blocks are Taco twin tees - necessary for the storage connection since flow can go either way through the storage loop. The two storage circs face in opposite directions and don't have flow checks. During charge (putting heat into storage), the top circ is active and pushes water from the primary loop into the top of storage and then backwards through the inactive lower circ. When drawing heat from storage, only the lower circ is active and flow through the storage loop is reversed.

    Any problems with this approach? Any better ways to do this?

    Thanks.....

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  2. maple1

    maple1 Minister of Fire

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    Likely some ignorance on my part (not being familair with a Taco Twin Tee) - but when discharging how does the storage water not just re-circulate itself to storage, or at least mix with cold zone return water, if the primary is always flowing CW?
  3. Nofossil

    Nofossil Moderator Emeritus

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    The Taco twin tee has two ports essentially on opposite sides of the main line, directly opposite each other. A vertical 'wall' prevents recirculation. As long as the primary flow rate is greater than the secondary flow rate, recirculation is prevented. I'll see if I can put together a sketch. It's a totally brilliant idea that I wish I'd thought of.
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  4. Nofossil

    Nofossil Moderator Emeritus

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    Here's a quick sketch (sorry for the size). The heavy red lines are the primary loop. The orange and blue lines are the secondary loop. The tee is shown in the center. The vertical baffle prevents recirculation of the water from the secondary loop. Neither the direction of the primary flow nor the secondary flow affects the operation of the tee. Very clever.

    [​IMG]
    Last edited: Nov 4, 2013
  5. Coal Reaper

    Coal Reaper Minister of Fire

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    i have tried and it is difficult to sketch a twin-tee. basically it is pulling water out of the primary loop at the temperature upstream of flow and injecting water at different temperate that goes downstream.
  6. maple1

    maple1 Minister of Fire

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    Just did some reading on the Taco site - a pretty neat & pretty simple item. I like simple.
  7. ewdudley

    ewdudley Minister of Fire

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    Perhaps just connect the boiler to one side of storage and load to the other:
    artflow_201311041756.png

    Also it's pretty easy to roll your own hydraulic separator from a small propane tank (e.g., 30 gallon or smaller) to take the place of the primary loop, which saves a pump and simplifies control of the storage-to-load pump.

    Storage-to-load can be run by an aquastat about a third of the way up from the bottom of the separator, on at 120 degF, off at 121 degF, or whatever desired return temperature to storage is.

    Meanwhile boiler just does its thing.
  8. Bob Rohr

    Bob Rohr Minister of Fire

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    Maybe something like this with a hydroseparator instead of the tees? A hydrosep keeps all the flows happy and provides the air and dirt removal function and a good spot to install the system control sensor. I'll noodle this some more but I think this works.

    Boiler return protection and loads omitted to keep the concept drawing simple.

    Attached Files:

  9. Nofossil

    Nofossil Moderator Emeritus

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    Thanks. I like the simplicity of the first (ewdudley) solution. However, I'm looking at a situation where there are multiple storage tanks that are far from the boiler (near the heat loads), so I don't think it will work in that case. I 'll ponder the Bob Rohr solution a bit.
  10. ewdudley

    ewdudley Minister of Fire

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    What problem does location of the storage tanks create, and how is it relevant?

    Oh, I see. You'd need two sets of lines all the way to storage to prevent short circuiting.

    Here's a hydraulic separator tank version.

    Additional heat source (e.g., fossil fuel boiler) can be connected to tank as well.

    Tank can be whatever size is convenient 10-30 gallon.

    artflow_201311042216.png
    Last edited: Nov 4, 2013
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  11. Nofossil

    Nofossil Moderator Emeritus

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    Excellent - thanks. I can see endless variations on this theme. One for the notebook. I've often used storage itself as a hydraulic separator, but I can see advantages to using a smaller tank for that purpose.
  12. jebatty

    jebatty Minister of Fire

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    It might be useful to separate the discussion into two parts, one for high temp and the other for low temp systems, because I don't think there is one simple solution to cover all systems. I don't see much advantage, if any, in the original proposal or the replies as related to a high temp system. Perhaps there are some insights into managing a high temp system with storage that merit a separate thread.

    I think any wood boiler system with storage that needs high temp water can be difficult to manage because the capacity of storage, unless very substantial, to provide the needed high temp water is quite limited. Essentially, the storage will mostly operate as a buffer to help even out the wood boiler operation to reduce idling. Also, high temp systems generally return quite hot water to the boiler or storage, which results in the coolest storage water being not less than the temp of the system return water. In a high temp system the boiler needs to operate more or less continuously to keep needed hot water available.

    After thinking more about the proposal and comments, as applied to a mid or low temp system, I may have some comments for consideration.
  13. Nofossil

    Nofossil Moderator Emeritus

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    I'm all ears.....

    It may be time to revisit the plumbing stickies on this forum and update them with additional options and detail. It seems to me that getting the right basic architecture is a really critical step and hard to correct once you go down a sub-optimal path. There are at least two important ideas here that weren't on the radar when I first started doing this - hydraulic separators and the Taco twin tee. Variable speed circulators are another factor.

    By the way - I noticed that I looked away for a few months and now you have more posts than me. I'll have to post a few times about that just to catch up ;-)
  14. jebatty

    jebatty Minister of Fire

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    ... slacker ;)
  15. ewdudley

    ewdudley Minister of Fire

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    A major advantage of the separator/buffer approach is that return temperature to storage can be minimized correctly with simple controls. (Of course if you're in an all-radiant all-the-time world it's simple, just draw from storage.)

    I use a Ranco aquastat that senses from a well about a third of the way up from the bottom. This time of year it activates drawing from storage when temperature falls below 89 degF and turns off on rise above 90 degF, running for a minute or so to draw about five gallons. As it gets cold out I work my way up to 119/120 degF. I have an indicator that shows when the Wilo Stratos load pump is running and when I notice that it is running nearly constantly it's time to raise the return temperature to storage a few degrees.

    I have a mix of baseboard and radiators, and yet we're able to do a good job of minimizing return temperature to storage and maximizing storage capacity.

    The kicker is that it was easy to set up my in-floor radiant loads to draw from the reservoir of 'spent' water in the bottom of the separator/buffer and return even lower temperatures to storage.
    Last edited: Nov 5, 2013
  16. jebatty

    jebatty Minister of Fire

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    ew, you're in a good situation with a mix of baseboard, radiators and in-floor, plus the knowledge to work such a system to the best advantage. The situation I am working with, and which many others have, is a single high temp system, in my case being baseboard plus water/air hx in two furnance plenums (plus a plate hx on dhw). I logged temps today, and I was able to make some flow adjustments to increase the delta-T between supply and return. I would like to achieve at least 140F maximum return temp, as that gives plenty of room to fire the Froling, meet demand and send excess to 1650 gallon storage tank without getting into the idling zone. The test will come with really cold weather and the need to push temps as high as possible to meet demand when the -30F winter days/nights arrive in MN.

    I'm starting another thread on the idea for a combo wood boiler and heat pump system. I haven't seen this discussed and intuitively it might make sense. Take a look.
  17. ewdudley

    ewdudley Minister of Fire

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    The Tarm reference designs make good use of a thermostatic mixing valve in a diverting configuration in high temp load situations. That might be something to try, although adding one might look pretty straightforward on paper it could be a major upheaval to work one into an existing system.

    More ideally you might want a motorized three-way valve configured as a diverter on the the return side with the right Tekmar control to make it do the right thing.
    Last edited: Nov 6, 2013
  18. Armaton

    Armaton Member

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    Jim, what temps do each of your WAHX, baseboards, and plate need. Looking at ew's design with the separator, seems that you could set aquastat to 140 degrees, and there would always be 140+ in the separator, even if each return to separator is mixed, the aquastat won't care untill it sees less than 140 then replenish untill it is satisfied. Granted a marriage of high and low temp emitters would seem to make this set up shine, but looks like it would work well for all high temp also. Just my 2 cents.

    Brandon
  19. jebatty

    jebatty Minister of Fire

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    I'm on a break due to deer hunting season. And waiting for colder weather and higher heat demand on the system. Then more tuning of flow rates.
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