Help with zone issue

Discussion in 'Boiler Forum' started by tom3holer, Apr 10, 2013.

  1. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    Hi,

    An issue has come up with how to rezone part of my home properly.


    Briefly I had an Alpine 150 installed in my home about a year ago. It was way oversized as the heat load ,not done by the plumber, came in at 60K. After showing him the numbers he agreed to replace it with an 80. He brought the boiler over yesterday and we discussed changing some things.

    There were 3 zones on the downstairs initally. All zones are fed with 007 circulators. I tied two of the 3 downstairs zone circulators to one thermostat and had very even temps in those rooms during the colder days. It was an attempt to unload the boiler more. Part of what my plumber is doing is to replumb those 2 zones as one. That has created differences on how to do it which leads to the question.

    Right now there is one line, a 28' run of 1" that splits and receives water from the 2 zones running each side of the house. One loop has 51' of bb and 41' of 3/4. The other has 42' of bb and 30' of 3/4. He wants to tie the two loops together where they split and eliminate the 28' 1" then feed it as a single long loop. I don't like the idea because if I shoot for a 20* D/T the last portion of the loop is going to be getting much cooler water and resulting, me thinks, in uneven heating. I want to keep it as is except feed the water to the 28' 1" and tie the two returns together making it 2 parallel loops abit with different head values. Put a circuit setter or something in the shorter loop to equalize the flow and it should work, I think. He sees my reasoning but not sure he agrees with it. What do those of you with far more experience than I think?

    Tom
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    To get even flow, you either need one continuous loop, or a valve to restrict the flow of the less restrictive loop. Or, just keep the two circulators, and activate them both at the same time as one zone.
  3. Dana

    Dana In the trades

    Messages:
    2,915
    Location:
    01609
    Jim has it right, but the tweaker-valve solution has more merit- put a ball-valve in series with the shorter section (==lower pumping head, higher flow) loop to be able to tweak the balance while running in parallel. It's fine to just split it off, running one pump. There isn't a huge difference in baseboard output between getting 1 gpm flow vs. 5gpm, and running two pumps roughly doubles the power use for no good purpose.

    If it seems well balanced room-to-room in it's current condition there could be a room-temp balance issue running them in series, since the AWT on one section would then be several degrees higher than the other, whereas now they're roughly equal.

    Depending on how many ells & tees are in each loop they may balance just fine in parallel even without the ball valve. The longer loop has (51 + 41=) 92', and the shorter loop has (42 + 28=) 70', so the shorter branch is only ~25% shorter than the longer higher-head branch, which raw terms isn't a huge difference in pumping head. The flows will differ, but the short branch won't be taking 2x the flow of the long branch. But add up the equivalent-lengths of all the fitting and add them in. Assuming it's all sweat copper & bronze, use this table for equivalent-feet.

    With a ball valve on the shorter equivalent-length branch that is naturally taking the higher flow, you then have the ability to drive some (or even all) of the flow into the longer branch. If you monitor the room temps and tweak the valve ~1/16 of a turn at a time giving the system a couple of hours to stabilize between tweaks you can probably come close to sweet-perfection in one weekend's worth of messing with it. Removing the handle of the ball-valve may be appropriate at that point to avoid accidental maladjustment, but tie it onto the pipe next to the valve keeping it handy since you may want some fine-tuning come winter when the heat loads are more pronounced.
  4. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    Thanks for the replies. I think I will put a ball valve in the shorter line and tweak it. Seems like the easiest thing to do. The plumber said he would be here Sat to do the installation of the 80.

    Dana, I tried to PM you the other day in response to your message but your mailbox was full.......you are Mr. Popular.

    Tom
  5. Dana

    Dana In the trades

    Messages:
    2,915
    Location:
    01609
    "Mr. Lazy" would be more appropriate- I hadn't cleared any of my received or sent PMs in awhile. (But I have now.)

    Here's wishing you a quick & painless boiler-swap!
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