Modcon with IHW Tweaking

Discussion in 'Boiler Forum' started by chris24, Jan 10, 2011.

  1. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    It would help if we could see pictures of the installation. Is that possible?
  2. mage182

    mage182 Member

    Messages:
    71
    Location:
    NY
  3. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    A few issues I see right away is the IWH tank is not properly piped. It should be 1" (if it is not now) and treated as another zone, not off the boiler piping. The Alpine 150 requires a flow of 11 gpm and the indirect requires 6 gpm. Is that pump for the Alliance a Taco 007? If so not big enough. It is hard to see the boiler secondary piping where it ties into the primary pipe. I am also concerned the ells on each side of the closely spaced tees are too close. You need a minimum of 8 pipe diameters before the tees and a minimum of 4 pipe diameters after. This all affects flow. The distance between the tees not to exceed 4 times the diameter of the primary pipe (not boiler secondary pipe).There should never be nothing between the tees.
    Last edited: Jun 10, 2011
  4. mage182

    mage182 Member

    Messages:
    71
    Location:
    NY
    I didn't pipe any of the things you mentioned as you can see by comparing the pics. I just redid what did not technically worked or looked terrible.

    This is directly out of the Burnham installation manual,

    [​IMG]

    Showing the tank piped as mine is. The connections on the tank are only 3/4" if that makes a difference. The length of the pipe between the closely spaced Ts is 4 inches so that is correct.

    The rest of it is not something that would easily be changed. It would require basically repiping the entire thing which I have no interest in doing. And paying another plumber (which I don't have) at least $1000 to redo isn't in the budget.
  5. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    As I stated it was hard to see the area of the piping where the boiler tied in.
    You are right the drawing is right out of the Burnham manual. But as you read the manual somewhere around page 39 dependent on date of the manual, it shows a table 12B. 12B states that an Alpine 150 should use drawing 32C or 32D for piping. The not recommended means not recommended piped to the boiler piping.
    As far as the piping to the indirect it should be piped in 1" to get the proper flow through the indirect for proper heat transfer from the boiler and also into the tank. Increase the piping to 1" right at the tank. The pump should probably be a Taco 0010 also.
    This would help resolve short cycling during production of hot water.
  6. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Performance may be enhanced by an upgrade to 1" but that is not a guarantee. Given the short distance and the maximum delta T of 35, the manual will allow the use of a UPS1558 or a 007 Taco (which you appear to have). Flow is determined by the size AND developed length.

    It appears also that you hired a good mechanic that didn't quite understand why but only how.

    The first drawing appears to be correct. It also appears that you have re-piped from the accepted primary/secondary to the direct pumps method, which is accepted by Burnham but not recommended because of the requirement for careful flow considerations...read experienced professionals only.

    If I had to guess, the pump on the primary pipe is bigger than the pump on the indirect. If that is the case, I would re-pipe to the original correct pipe schematic and switch the pumps (making sure the axis of the pump I level).

    The copper pan is a nice touch but will not stand up to acidic condensate.

    Careful of the DIY crowd, another "professional" is always your best bet.
  7. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    Your looking at a minimum of 14 ft head. How is a Taco 007 a good choice for this application? I believe it is primary/secondary but again it is hard to see from the picture.
  8. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    "How is a Taco 007 a good choice for this application?"

    I write, read and understand, condensing boiler installation manuals for a living. I believe this boiler has been repiped without the bypass.

    Over the past 25 years I have found qualified installers in 23 States and 7 Provinces, DIY on a ModCon is the road to misery.
  9. mage182

    mage182 Member

    Messages:
    71
    Location:
    NY
    I'm just going to post up the above references items from the manual for future reference.

    P.39 content:

    [​IMG]

    Table 12B:

    [​IMG]

    The feed side for the tank is 3/4" with a Taco 007. The return side is 1" (I'll assume because that was what was available at my house when the plumber did the install). Changing the feed side to 1" is not more than 30 mins worth of work and an easy fix. But since you're correct (as confirmed in 12B) that the tank should be piped as a zone, should I really bother buying a Taco 010 to replace the brand new 007 that I already have? Or is it feasible to just replace the feed like with 1" and leave the pump and just move the tank over to the extra spot on the manifold when I build the addition?

    The system is still P/S. All I did was move the feed side which was hanging 3' from the wall supported by almost nothing (including the pumps whose flange valves couldn't be closed because they hit the ceiling joists) over to the wall where it could be supported. I didn't touch the primary loop other than to fix the primary loop circ flange which was leaking.

    The primary pump is larger (I'll look up the model number tonight).

    Isn't that what the neutralizer is for? Or does that not neutralize as well as I've read? Most people I've talked to say not much condensate comes out anyway. If I see it starting to corrode I can fabricate the same item out of PVC. That was a fun project.


    Are we in in agreement that the system will function without breaking for a while until I start the addition at which time I can move the tank to the manifold and just cap off the connections on the primary loop when I have the new bathroom plumbed and the upstairs heating zone expanded?

    Thanks.
    Last edited: Jun 13, 2011
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    The amount of condensate depends entirely on the size of the boiler AND how much it is in condensing mode. If running condensing mode primarily, it can produce a lot of condensate! If, on the other hand, it is running full blast and not condensing, most of the moisture will be exhausted as a vapor. Some of this depends on the length of the vent pipes and where they run. SO, short answer, if you don't have a lot of condensate, your system is probably oversized...
  11. Dana

    Dana In the trades

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    It can still be grossly oversized, short cycling like crazy, and still return a lot of condensate if operating in the condensing region. It's the temperature of the return water, not the output rate (or output temp) of the burner that determines the amount of condensate. The more radiation you have, the lower the temp that still delivers the heat, and THAT will also increase the condensate volume (which is a good thing, efficiency-wise.)
  12. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
  13. Dana

    Dana In the trades

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    Has prayer proven successful in debugging hydronic systems? Any particular mantras, bhodisattvas, or saints work better than others? ;-)

    I like the "find a competent pro" approach much better. But I also like to measure stuff before/after as a sanity check, independent of the designer. To be sure "design by web-forum" only works in the simplest of systems, and when loads can be well-estimated by empirical data rather than heat loss calculation apriori.
  14. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    I am not sure I understand the moving the pumps or maybe I misunderstand what you are saying. The manual calls for a 0014 or a 26-99 on the boiler secondary pipe pumping into the boiler. The 007 could be used on the tank if the piping was change to a zone useing diagram 32C or 32D.

    Dana, isn't it both the supply and return water temp that determines the amount of condensation. You can have part of the boiler at a condensing temp and part of the boiler hotter than condensing temp. That would mean that only part of the boiler is condensing. This might happen when the return temp is getting closer to the high side of dew point where it is not going to condense.
  15. mage182

    mage182 Member

    Messages:
    71
    Location:
    NY
    The pump on the primary loop is in fact a Taco 0014. My two goals now are to switch the piping for the tank to use the extra zone I set up on the manifold before I move in, and to find a competent service professional using BadgerBoilerMN's recommendations to come and do the initial software configuration. Hopefully that same person would be available should I ever need service for the unit.
  16. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    The 0014 is actually on the secondary boiler piping. The close spaced tee's are always on the primary and the branches are secondary.
  17. Dana

    Dana In the trades

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    Boilers have counterflow heat exchangers- the output end of the HX is at the highest temp end of the gas flow, closest to the flame front. The hottest part of gas flame is on the order of 3000C and the bleeding edge section of the HX closest to the flame front is literally never condensing during a burn, independently of the flame size, even with 120F output water, since most of the gases are still well over the dew point of the exhuaust. But the MAJORITY of the fire-side to water-side of the heat exchange is happening in this section, since it has the highest delta-T from fire to water-side. Whether the output temp is 120F (50C)or whether it's 180F (~80C) the delta-T with the very hot gases of the exhaust isn't much different in percentage terms.

    But most of the surface area of the HX is cooler, where the gases of the fire side are already literally thousands of degrees cooler than where they entered the HX, but the delta-T across the HX to the water side is now much lower, and that temperature is governed most-predominantly by the return water temp. To the extent that the return water to output water delta-T is bounded, the amount of HX surface area that is below the dew point of the exhaust gases rises and falls with output temp, but the amount of condensation derived is still governed by primarily the return water temp. The size of the flame, and the output temp are only second-order effects.

    Below some firing level there isn't sufficient turbulence on the fire-side for good heat exchange in the low fire/water delta-T sections. Laminar flows create an insulating boundary layer that limits the amount of fire-side gas contacting the HX thus reducing the condensation. This is the technical reason why it's difficult to build a condensing boiler with more than about a 4:1 turndown ratio. At any given return water temp in the condensing zone the sweet-spot is usually somewhere in the lower 1/3 of the flame modulation, but not necessarily at the lowest. Cranking the flame lower than min-mod on most of them they run into laminar flow issues and efficiency falls off very rapidly with fire size as more of the gas volume then escapes without coming into direct contact with the cool end of the HX.

    An oversized boiler would be more likely to short cycle, but would deliver the heat at a lower flame modulation, with ever so slightly higher condensation for the same volume of exhuast gas BTUs. At any given return water temp it would still deliver about as much condensation as an appropriately sized boiler, but would be giving up more in fixed losses with every flue-purge & ignition cycles, delivering somewhat lower overall efficiency.
  18. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Ridiculously oversized...well, depending on the boiler, the minimum fire may well be 50% or more of the design load of the house - or radiation. If this the case and we are just making up numbers here since no proper manual 'J' heat loss was performed - the the boiler could certainly be "bumping off the bottom" while trying to heat a small zone. The boiler could be cycling while make DHW due to several reasons including lack of flow. This is all a bit complicated for the novice boiler installer and certainly not a DIY project no matter how many "plumbers" you go through.

    I advise my clients to find the local contractor that is factory certified for the condensing boiler you wish to buy. Short of this find local supplier or rep for any high efficiency boiler they intend to buy and make sure that you will have professional experienced support before the boiler is delivered. If you insist on buying a high efficiency boiler on the Internet make sure you will get the support you need from the people you gave your credit card number to.

    Taking advice from folks - however well intended - who have never installed a condensing boiler is a little risky.
  19. mage182

    mage182 Member

    Messages:
    71
    Location:
    NY
    Update

    Hey. I just wanted to give an update since I've made some changes, moved into my house, and am in the process of making observations.

    I finally found an HVAC guy that works with Modcons. He came over, helped me set up the boiler, and agreed that the tank should be piped as if it were a zone in 1". He said to try that before replacing the pump for the tank because it may not be necessary. I agreed to do that, track the number of cycles per day, the temp at the same time each day, and time some fire times for heating and IHW cycles.

    He set the max fan speed for heating to ~2500 (down from the max of 5500) due to oversizing and the max speed for the IHW to ~4000.

    A few weeks ago I repiped the pump for the tank so it is piped like a heating zone. It is done in 1" and I'm using the same Taco 007 as before.

    The HVAC guy asked me to take down numbers for a few weeks and call him back. If he doesn't think everything is working correctly he said he'll come back with a local Burnham rep he knows to look it over again and tweak.

    Observations

    It hasn't been that cold in NY until this week. I'm seeing heating cycle times around 10-11 mins.

    The count of cycles I have observed over the past 2 weeks suggests that the boiler is firing on average three times an hour. I'm not around enough to say if that is evenly distributed.

    While observing some cycles I found that sometimes the zone turns off before the boiler even reaches temp. This was on some of the warmer days a few weeks ago. Meaning if the temp is set at 130 by the ODR, the tstat is calling for heat, but then shuts off when the temp only reaches 120 because the zone is satisfied. Is this still considered short cycling?

    I am seeing what I would call short cycling on the IHW tank. The set temp for that is 170. But it will make that temp sometimes before the tank is satisified. Then the boiler will shut off as the water continues to circulate. Once the temp drops low enough it comes on again. Some have suggested placing a bigger pump on the IHW tank (Taco 010 or Grundfos equivalent), but will that really improve anything? I don't see how pumping the water through the coil faster will help heat the tank more efficiently?

    the office upstairs on it's own zone for now is the only room in the house with an old cast iron rad. That obviously stays warm a lot longer than the fin tube. Is that a better heating method than the fin tube? I have 50 feet of cast iron baseboard sections in my garage that I could swap out with the fin tube over the summer. But would it be worth it?
    Last edited: Jan 5, 2012
  20. Dana

    Dana In the trades

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    It's not considered short cycling unless the boiler's burn time is very short. It's the burn time that counts, since every ignition cycle and flue purge it "throws away" a fixed number of BTUs. If it's burning only 30 seconds and purging for 60 it's an efficiency-disaster. But if it's burning for 10 minutes you're in efficiency-heaven.

    The fact that it's not reaching the ODR temp at the output before the t-stat is satisfied is an indication that the reset curve might be too high- you may want to bump it down a notch or two.

    Pumping faster through the coil creates more turbulence for better heat transfer, and lowers the delta-T across the coil (and boiler), which may be the issue. The boiler may be turning down or shutting off before the tank is satisfied if the controls are trying to protect the boiler from the stresses of a delta-T greater than the boiler can tolerate. (I don't know if your boiler's controls do that or not.)

    Swapping out the fin tube for the cast iron baseboard rusting away in the garage is absolutely the right thing to do. Fin tube has very low thermal mass, and less predictable at low-temp (<125F) output, whereas cast iron baseboard usually has somewhat more water volume thermal mass, and substantially more thermal mass in the form of iron, and has a fairly linear output at low-low temps that will track reset curves better when the heat loads & water temps are quite low. Both factors make it better for use with a mod-con, since the higher mass keeps it from short-cycling at low output, and you can run lower reset curves without running into comfort issues at very low loads where the fin tube craps out, and the cast good keep working. It takes ~75lbs of cast iron to equal the thermal mass of a single gallon of water, but it takes 50' of 3/4" fin tube to equal one gallon. Weigh the cast iron, do the math. What's more, cast iron baseboard has that nice radiated-heat glow when it's cold out, whereas fin-tube's heat transfer is predominantly convection- it heats the air, whereas radiators & cast iron baseboards can heat the humans & pets directly via radiation- it's just plain more comfortable. I'd do it in a heartbeat if it were my house. (I'd even scrounge on Craigslist for lower cost replacement goods if there was a bunch of fin-tube to replace. It's quite expensive new, but it's often $10-20 foot, sometimes less, as private-sale surplus-used. )
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