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Problem on \"CO again\" post

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Comments

  • Jim I know this is what

    I am dealing with (excessive dilution air) and this afternoon will be making some temporary adjustments to see what I come up with. I know I have excessive dilution air (this is a problem more times than I can count).

    I also want to get the CO down to a safe level and then come back after some repairs to the chimney are made. The top of the chimney has some damage and the masons do not want to go up and repair it with wind chill factor of below zero.

    I am also having problems with the utility. They have informed me that Dept of Regulation states that no modifications can be made to gas equipment with out the approval of the local utility and a written letter with instructions from the equipment manufacturer. It goes on to state that the manufacturer must have a representative present when modifications are made. Finally said modifications must meet acceptable standards for such equipment.

    Oh well here we go again, not the first time I have run into this. When I was with the utility I could do just about anything and no one ever bothered me. I guess they have gotten smarter since I left.

    I will be blocking off the diverter and running some tests this afternoon. I will let you know how I make out.

    I put the thing about draft inducer or power venter in as that was the suggestion of the gas company to solve this problem.
  • An after thought

    for those who are following this post. I hope you see that this is not always just a simple screw down on something or adjust something. You have to know what you are doing and you need training and then lots of practice. I have found that sometimes there are no set rules but you have to go step by step and work until you find a solution. I have found there is always a solution it just takes time and experince to find it. I hope everyone is enjoying this problem I knew it would be a good one to post. I thank everyone for great input and suggestions. I also want to thank Rudy and Jim for being here to help us out. This sure is a great site to learn. Oh yeh, thanks Dan for letting us run these long threads.
  • jim sokolovic
    jim sokolovic Member Posts: 439
    Very interesting, but...

    isn't the purpose of the draft hood to minimise the effects of over-draft or down-draft? How is the stack temperature so high, if flue gasses are being prevented from entering the chimney? I haven't done alot of testing on atmospheric type boilers, so this is good learning stuff here!
  • Jim Davis
    Jim Davis Member Posts: 305
    Stack Temp

    The temperature is being measured below the drafthood at the outlet of the boiler not actually in the flue. If the temperature above the hood is below 275 degrees this is how you can tell more than 50% dilution air is being drawn in. As far as down-drafts hoods just keep the pilot lit and allow flue gases to come into the building, which prior to 100% safety shutoffs on the pilot was a good idea but not now. Special caps prevent down-drafts altogether.
  • Dale
    Dale Member Posts: 1,317
    Instead of lowering

    We had a furnace that was high CO and the final fix was to go to a smaller orifice and raise the pressure to 3.8" this seemed to pull in the extra primary air needed because of the higher gas velocity. Are you able to drill down through the top sheet metal flue collector to test between each section individually? I still wonder if you are having problem only over one burner. We will pull the mainifold out and connect a water hose to it to see if the streams from all the orifices go the same path.
  • jim sokolovic
    jim sokolovic Member Posts: 439
    I was assuming that ALL of the readings...

    were taken ABOVE the integral draft hood, in the pipe between the chimney and the hood, since Tim stated "Stack temp = 550 degrees net". I know it is very difficult to get consistent readings in the flue area (which is before the draft diverter) - because it is a large volume area with varying emmissions concentrations / temperatures and is usually not accessible with standard probes. Anyhow, besides fixing this problem (which we are all hanging onto our seats in anticipation for), is the moral of this epic that the installer needs to take super-critical draft readings to determine if a piece of equipment can be installed in what appears to be a suitable installation site?
  • Jim Davis
    Jim Davis Member Posts: 305
    Below hood

    There is a protocol for moving the probe around until the highest CO reading is measured in a round drafthood and in a rectangular hood a test is taken at every burner location.
    Draft is a critical measurement to determined if a chimney is functional, if there is adequate combustion air and if there is any interference to this flow from the environment. CO and/or Oxygen are the true indicators of venting and combustion air.
  • jim sokolovic
    jim sokolovic Member Posts: 439
    Thank you for the explanation, Jim...

    Just trying to make sure everyone is understanding where and how these readings are taken - I'm still thinking there is some confusion between the terms "stack" and "flue", though. I'm sure Timmie can confirm the specifics for us.
  • Stack vs Flue...

    versus breaching. I've always been under the impression that the connector between the combustion chamber and the relief hood was called the breaching, and that anything after that is consider flue, or stack.

    Timmie, Jim?

    ME
  • jim sokolovic
    jim sokolovic Member Posts: 439
    Sorry to make such a mess...

    out of this thread. The original subject is of great importance and interest, and now it has gotten so long that I bet many have stopped following it. I wanted to be sure where the measurements are being taken, to limit the confusion, not magnify it. Can we refer to the stack as the pipe above the draft hood, and the flue as the passageways between the combustion chamber and the hood (this can include the heat exchanger areas, but usually the combustion readings are taken in the pipe below the hood or the flue collector above the heat exchanger). I haven't heard the term "breaching" lately, but I guess it means accessable flue areas (for cleaning purposes)?
  • Jim Davis
    Jim Davis Member Posts: 305
    Flue. Stack, Breach

    Mark, you are correct by most understanding and definitions. The actual definition of the word breach is "break" which technically defines the hood itself. So we really measure before the breach rather than in it. The important part is knowing that combustion measurements are taken before dilution air-both hoods and barometrics.
  • Jim Sokolovic

    This particular Utica boiler has the drat hood built into the boiler so technicaly there is not what we would picture as a break or breach before the draft hood which would allow for taking readings. The procedure I am following is to place the probe inside and down into the heat exchanger before the dilution air pollutes the readings.

    This is the only way I know to do so on this package.
  • jim sokolovic
    jim sokolovic Member Posts: 439
    That's the way we do it here too...

    but when you provided the combustion, draft, and temperature readings you stated "stack temperature", so I wasn't sure if all the readings came from the same sampling area. I now assume that only the draft reading came from the area above the draft hood (which I firmly believe should be referred to as the "stack"), and your emmmissions and temperature readings came from some area below the draft hood (which I firmly believe should be referred to as the "flue"). I have no doubt that you, Jim Davis, and many of the other professionals here know the right way and location to take readings and evaluate the results - it is just a matter of terminology. In this case, I don't believe that I am nit-picking on this, if we are trying to teach and learn. Good luck fixing the problem!
  • Todays results

    I initially totally blocked off the draft hood opening the readings obtained:

    O2 14%
    CO2 4%
    -.06 draft
    stack temp 320 degrees (net)
    CO 37 PPM which is 115 air free

    I then removed the existing flue and placed a section of flue pipe with a Field Barometric MG-1. Totally blocked the draft hood. Now can take readings directly at the breach (right as flue pipe exits the boiler) before the barometric. I also drilled a hole after the barometric and plced a thermometer in the flue. Readings:

    O2 5.5%
    CO2 9%
    Draft -.02 after adjustment of barometric
    Stack temp before barometric 425 degrees (net)
    Stack temp after baromteric 350 degrees (net)
    30% excess air
    CO 35 ppm air free
    79% efficiency
    Draft over fire -.02 this was a little erratic because of boiler design.
    Draft after the barometric -.03

    Could not leave this per local code. They are coming back Monday to check progress on this job.

    Here is how I left the job: I partially blocked the draft hood (an old conversion burner trick) and set up the boiler with the instruments for these final readings which will allow me to leave it on for the weekend. I will be checking this every day until Monday when I argue with the utility.

    READINGS:

    O2 6.5%
    CO2 8.5%
    Draft -.02
    Stack 500 Degrees (net)
    Excess air 42%

    Co air free 120 PPM

    Efficiency 76.5%

    Some discussion about terms used:

    The term stack temperature is a term I have used for years which means a temperature taken before dilution air is introduced at the draft hood or barometric. On some design equipment you have to take multiple readings in all of the sections which are sometimes difficult to get at because of the draft hood location on many warm air furnaes and some boilers. The boilers with the draft hood vertically above the boiler are no problem. A hole drilled as close to the boiler exit point of products of combustion will give you accurate readings. I like to monitor draft at several locations just to see what affect changes have on draft. Draft remember is determining air being drawn into the combustion chamber to satisfy requirements for Primary, secondary and excess air.

    The term flue can mean the pipe leaving the building often also called the vent or chimney. It can also mean flue passages which are to me a part of the boiler or furnace.

    NFPA does not even list a definition for "Stack" I guess it is an old term carried over by some of us from oil burners. You know the "stack relay". It is also on some of the old "firefinders for determinng efficiency from Bacharach.
  • Jim Davis
    Jim Davis Member Posts: 305
    Just want to start back at the left

    Timmie, was this the first time you have made the barometric modification? Partially blocking a drafthood has less approval than anything I know, yet it is more accepted. I have seen older multi-section boilers with slide plates built into the rear draft hoods. Don't like fixed air adjustments in a variable pressure environment, but whatever it takes to make a job safe, even if temporary, sometimes has to be done.
  • No I had done it

    quite a few times in the past. The problem on this job was the "red tag" the gas company put on the job which brought them into the picture. Interesting when i was with the same company we did it numerous times to solve problems usually with a factory rep with us I might mention.

    I have done it many times on conversions that had a draft hood and we removed it and used a barometric instead to clean up some problems.
  • Here it is Jim Sokolovic

    for you.
  • Murph'_4
    Murph'_4 Member Posts: 209
    .sounds like a dog and pony show !!

    are they teaching the teacher? and tell me again ,what year was it that you invented the thermocouple ??!



    MJ
This discussion has been closed.