Zone valve or its own circulator for an indirect water heater?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by gellfex, Jan 20, 2011.

  1. gellfex

    gellfex New Member

    Messages:
    56
    Location:
    NJ
    I'm at the tail end of a long "new heating system" story. The short is that I've got a W-M CGi 4E 90k btu boiler running 3 heat zones in my 1300 ft apt, plus a Phase III HL-36 indirect WH. Since I tacked the indirect onto the zone manifold that was built entirely out of 3/4 by the plumbers who installed the CGi, it's not getting enough flow for a speedy recovery, and the 4 way WH priority zone controller (Taco zvc404) installed means that the house gets cold while the heater struggles to get up to 130 after my wife runs a bath. (There's a tempering valve and I'd prefer to be able to run it 140 for more effective capacity)

    My plan is to rebuild the manifolds to give me 1" for the WH. The question is, since I'm tearing it back to the circulator flange anyway, should I tear it back to the boiler and install a 2nd circulator instead of just a 1" zone valve running on the current priority controller? Would it make any real difference, or would that be too much load on the CGi or a slow WH recovery if everything is calling at once and I'm no longer using the zone controller?

    Thanks for any opinions.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
    New England
    What temp do you run the boiler? Typically, when running a priority zone for the WH, it fires the boiler to max temp to quickly recover (rather than some lower temp that might be used for space heating). If you aren't setup to get high water temp, that would account for the slower recovery along with the smaller piping. Also, if you run a separate circulator, you can specify one specified by the WH for max flow, to minimize the time it takes. If the house gets appreciably cooler while reheating the tank, maybe it's time to think about some more insulation.
  3. gellfex

    gellfex New Member

    Messages:
    56
    Location:
    NJ
    Jim, don't get me started about insulation! This is a 100 yo brick tenement, with horsehair plaster walls either right on the brick or on lathe and furring. There's no place to insulate, and the windows are new. But we compensate by living in small space.

    That's interesting about the boiler temp, it's set to 180, and I don't think its set up to have the temp change when the WH calls. I can ask my supplier, but the aquastat is built into the unit. You'd have to have the thermostat line throw a relay to switch from that aquastat to an external one set to a higher temp. I bet it won't be necessary, since going 1" will nearly double the volume, but the point about a higher flow circulator is very interesting also. I have a table in the WH manual calling for a min of 7gpm, the Taco 007-F5 at the level head situation lists at 23. But that's presuming an open line not 3/4"! The table does specify in the conditions that supply temp is 200. Maybe that's part of the answer.
  4. Tom Sawyer

    Tom Sawyer In the Trades

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    3,236
    Location:
    Maine
    A zone valve will certainly work but, during times of high use, with other zones operating you may get reduced flow through the indirect coil. Truth is, circulators will give you more consistent flow and they cost less.
  5. hj

    hj Moderator & Master Plumber Staff Member

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    I have to question the validity of the diagnosis. The house should NOT "get colder" while the heater "the struggles to get up to 130 degrees" if the entire system is sized correctly. Both conditions should not occur simultaneously.
  6. gellfex

    gellfex New Member

    Messages:
    56
    Location:
    NJ
    I think perhaps both you and Tom missed the part about the multizone "priority" control valve that shuts down the other zones when the WH calls for heat. It shuts down the heating zones for however long it takes for the recovery. If the WH isn't getting the heat from the boiler fast enough due to it's improperly sized 3/4 feed, that can be quite some time. A 90k boiler should be enough to recover a 36 gal tank fairly quickly, if there's no other problems. It's those "other problems" I'm working on. Given all that, if you have another idea in a different direction, I'd love to hear it. I'm learning as I go, fixing a system the pro plumbers botched (long story having to do with the building's idiosyncrasies). The "heating specialist" at my very big local supplier is very knowledgeable and has helped, but has given me some bum steers too, which is why I'm gathering more info.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,183
    Location:
    New England
    The tank will list the head it generates, then you can look at the pump curves to decide what you need to meet the minimum 7gpm flow rate. With a 1" line, you can flow at a higher rate, but you may not be able to pull the heat from the boiler that fast, so it would be counter-productive - they both have to be within their limits. Also note, if you aren't running pure water (i.e., you needed antifreeze in it for some reason), that derates the heat transfer by about 20%.
  8. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,236
    Location:
    Maine
    I figured you had zone priority on the indirect. Make sure of a couple things before you pipe this thing. The indirect needs to be piped with whatever minimum size piping the manufacturer recommends. If it has 1" inlet and outlet then make sure that you pipe with 1" , do not reduce. As far as pump head goes, as long as the pump/indirect and piping are close together, pump head won't be an issue. A Taco 007 or equivalent Grundfos wiltol give all the head you need (that's what she said) Just for kicks though, if you can scrape up the bucks, take a look at Wilo VFD circulators. They instantantly and automatically adjust to maintain delta T whith variable load on the system piping. Amazing things, especially for radiant heat.
  9. gellfex

    gellfex New Member

    Messages:
    56
    Location:
    NJ
    Thanks for the comments.

    Like i said, I originally tacked this indirect onto a boiler system that had already been built with 3/4 zone manifolds, because it was the path of least resistance. Now I definitely am going to increase it's size to 1". The questions (including points raised by Jim) are what else to do.

    Whether to continue to use a zone valve and the priority controller, or add a new circulator just for the WH and get rid of the priority switch. The WH with it's 1" will still dominate the heat zones all running off a single 3/4, but it pointless?

    Whether to run the boiler hotter in addition, increasing from 180 to say, 200. Or alternatively, whether to rig a boiler temp increaser into the priority control, switching the boiler's aquastat to a secondary one set higher so just the WH runs on hotter water.

    I can't imagine that the taco 007's head http://www.taco-hvac.com/uploads/FileLibrary/101-029.pdf is really 23 gpm in practice on a 1" straight across from the boiler to WH, but it appears to be the least of the problems.
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,183
    Location:
    New England
    180 with full flow (the 1" line) should be okay, but a little slower than if it were 200. The spec sheets for the indirect often show the performance with multiple input temps for comparison.

    I have a mod-con, and my 'normal' heating water temp is only about 140. It rises to about 195 when the priority zone (the indirect) needs heat (that logic is built-into the boiler). Tommorrow night is is supposed to hit -10F, and I expect the logic will raise the supply temps on its own (outside reset control) to something higher than the 140-degrees.
  11. gellfex

    gellfex New Member

    Messages:
    56
    Location:
    NJ
    I wish I could have put in a condensing unit, but the basement location combined with nearby windows made it pretty problematic, not to mention the funky flue that I had to work with. But as noted earlier about insulation, the 85% efficient boiler is far from my weakest link!
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