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Expertise wanted

realolman Member Posts: 513
Please take a look at the graph I made this morning of my oil boiler / heating system. ( on my computer the pictures don't display right. If you wait till they're done downloading , then hover your cursor over them, a zoom button will appear that will make them much better )

It is a Burnhan v74 with two zones. The green is pumped by a B&G series 100 and the blue by a B&G SLC 30. The purple is the stack temp, the red the boiler temp, the blue and green are the two zone returns. The black at the bottom is the outdoor temp. The two heavy lines in the center have nothing to do with temp, but indicate when a zone is calling for heat. If there is a line there, it's calling.

I think the stack temp is still too high, but what can be done about it? I have already downfired from a 1.1 to a .85... I'm gonna go down and put in a .65 this afternoon I think.

You can see the zone temp drops, how long the burner runs, how long it's off. What kind of load would you have to have on the thing to achieve a reasonable stack temp?
It is set with an analyzer 5.5% O 11.6% CO2 .03 draft

Any conclusions anyone can draw re: the temp drops of the zones, the quantity of baseboard, the match of the boiler to the heat loss... any thing at all would be appreciated. I would like to see what knowledgable people can glean from this info. I'm hoping it will interest someone enough to give it some thought.



  • Norm Harvey
    Norm Harvey Member Posts: 684

    I am using a laptop and I cant read any of the graphs, theyre choppy to me. So much so that I cant see any of the numbers.

    What IS the heat loss of the house?
    What is your pump pressure?
    What is the excess air reading on your analyzer?
    What is the CO reading on your analyzer?
    What is the smoke reading?

    What is the outside temp during the periods the graph represents?
    What is the inside temp?

    Those answers may help an analysis. Maybe on a desktop I could read the graph better.

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  • RJ_4
    RJ_4 Member Posts: 484
    High Stack Temp.

    I would check your flue design and your fresh air into boiler room. SELKIRK CO. has free trouble shooting info.
  • Norm...

    Hover your mouse cursor anywhere in the middle of the picture, then when the EXPAND button appears in the lower left hand part of the picture, move the cursor there and click on it and it will get easier to see.

  • How close are you

    to design temperature? What is the houses' heat loss compared to the boiler's Net rating? Is the boiler clean, or is there a lot of buildup around the pins?

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  • Weezbo
    Weezbo Member Posts: 6,232
    it seems that you could get alot more out of a lot less..*~/:)

    drop your low side down to 140 and the upper side to 165....

    i have to think that a smaller nozzel would also help. the stack seems high to me, you might have to run it so you get higher Co2 than an eleven.i also like the idea of making sure you have enough outside air available and that you set the barometric to curtail some of the stack loss.
  • realolman
    realolman Member Posts: 513

    I don't know why it displays so badly. It does the same thing on my desktop. It's something in the process of attaching it to this post and displaying it here. If you wait till it is done downloading and then hover your cursor over it, a button will appear that will make it much better.

    I think Beckett heat managers and those kinds of things work using the info available here. I was wondering if it was possible to determine things like: how well the boiler and the amount of radiation was matched to the heat loss load from the graphs... maybe some insights into the heat loss and the boiler size and efficiency. If it was working and matched wonderfully, what kinds of delta Ts, run times, etc. would you expect to see? If I was able to slow the pump down, or speed it up would I get longer run times? Beyond the stack temp, which I don't like, what would you say about this system?

  • realolman
    realolman Member Posts: 513
    I mean this respectfully

    I have read your posts and I know you are a knowlegeable person... I do not mean this to be a smart answer, so please don't be offended... but I guess that is I what I was asking you ... If I hooked this stuff up to your boiler, and it obtained these results, what would you think about your heating system? Again, I don't mean that to be a smart answer... That's what I want to know from guys like you.

    Can you tell from this info how close I am to design temp? Is it exhibiting characteristics indicating that the boilers rating is close to the house's heat loss? I guess those are the kinds of things I want to know if you can tell from this info.

    I think the the stack temp thing is looking hopeless. The boiler is clean. I even boiled the water side out with acid. I'm beginning to think that's just the way it is with this boiler. It just doesn't transfer enough heat into the water... Which is exactly the reason I started with all this sensor, computer, graphing stuff. I don't think I want to know what the stack temp would be with a 1.1 gph 140 psi nozzle at 180- 190° water.
  • zeke
    zeke Member Posts: 223

    Since your present duty cycle is about 7/13 at an outdoor temp of 20 then, it looks like your present "design" outdoor temp is about -30 using the .85 nozzle.[-{13/7*(80-20)-80]. If you go to a .65 nozzle, then you are probably looking at a "design" temp of -5.If you know the oil pressure, then you can get the oil flowrate and together with its heating value get the actual BTUH being put into the boiler. If you can get the flow rates in each of the loops together with their delta T's you can get the heat delivered and a simple ratio would give you overall boiler efficiency.
    If you want to increase the ON and OFF times you can reduce the differential in the boiler and/or lower the boiler setpoint temp and increase the hysteresis in the thermostats. But you have no control of the duty cycle which is governed by the outdoor temp for each nozzle size.
  • Slipping clutch syndrome with oversized engine...

    is what it looks like to me. Firstly, you could take all my personal knowledge as it pertains to oil fired boilers, and put it in the corner of your eye, and not know it is even there...

    That aside, a heat source is a heat source, and based on the presented information, it would appear that your heat source is a lot bigger than it needs to be. That, coupled with the slipping clutch (thermal efficiency or lack thereof) results in continuous short cycling, which is what I am seeing in your graphs.

    Interestingly enough, what you are seeing is TYPICAL of what I see in the field, even on systems that I know for a fact were properly sized. It has to do with the BANG BANG burner methodology. If you had the ability to modulate your burn size around the actual load, then the burn time would increase, the stack temps would decrease, and the net thermal efficiency, the point where the tires meet the road, would sky rocket. But I am comparing apples to oranges here, and that needs to be made clear. From what I understand, the modulating/condensing oil boilers are just around the corner.

    If this were a natural gas appliance, displacing it with a mod con would result in a fuel savings of around 40% right off the top.

    Understand also that the maker of the boiler is actuely aware of the consequences of high sulpher fuel gasses condensing, and the consequences of those actions, hence high flue gas temperatures. It is what it is...

  • realolman
    realolman Member Posts: 513

    Now yer talkin'
    That is the kind of thing I was trying to understand.

    By duty cycle do you mean 7 minutes of every 13 min the burner is on? I am very interested in your duty cycle formula... I'll have to try to digest that a bit more.

    The psi is 140 flow rate of 1.0057

    @ .65 @140 psi flow would be 0.769.

    The afg burner calls for 140 psi... would there be any problem with 100 or 120 psi?

    If I closed the valves to the radiation and fired the burner for a short time ( it would pop off before too long ) , knowing the BTU of the fuel, and how much water was in the boiler, if I recorded the peak boiler temp in this graph,would that not give me the efficiency of the boiler at getting the BTU from the oil into the water?

    I will have to get a different aquastat... mine has a fixed 10 deg diff. I think I will do that... I know when the water is "colder", the stack temp is lower as well.
  • realolman
    realolman Member Posts: 513

    So the heat source should not be capable of raising the water temp that rapidly... but that would not have any effect on the "off" cycle time... is that right?
  • Measurement system details

    Just curious on what type of system you were using to log all the temperature data simultaneously. PC based data acquisition with thermocouple probes? You seem to have a really efficient way to get all the temp info regarding a system at one time. I have done similar measurements on my system with 4 individual Fluke digital thermocouple thermometers, but it doesnt give the hard copy record vs. time of your method.
  • realolman
    realolman Member Posts: 513
    God bless you...

    I thought you'd never ask.

    I used a thing called a labjack that runs on a usb port. It's pretty easy to use. They also make them for ethernet.
    It has a some analog ports and a lot of digital I/O

    I bought a half dozen LM34 sensors, for about 2 bucks apiece, some 110v I/O solid state relays, and a thermocouple on ebay, and a thermocouple amplifier from simplecircuitboards.

    Because of a screw up on a 20 dollar item, I got to correspond with the owner / operator of simplecircuitboards. What a good guy! Gave me some hints that cleaned up the display of the sensors... I want to make sure I recommend him and his company highly. Go look at his site.

    From there on it was a matter of a whole bunch of programming in Visual Basic and the kindness, knowlege, and expertise of the people on this web site... which I appreciate greatly... and am still taking advantage of.

    Taking advantage is not a good phrase, but it's all I can think of... I really appreciate everything that I have learned on this site. I feel like I've gotten a college education since stumbling upon this site 4-5 months ago.

    I sound like I'm accepting an academy award or something... actually I kinda feel like it because you complimented my stuff. That'll keep me going another couple years.

    I hope to incorporate the duty cycle formula earlier in this thread. I think it would fit right in with this stuff recording burner run times... and was actually what I was trying to accomplish.

    Thanks again.
  • Steady state efficiency

    Very impressive system. I think I will look into one of those labjacks myself.

    By the way, you dont have to stop the boiler flow to calculate the efficiency. Given that you have the temperatures of the input air, the exhaust flue gas, the heat exchanger temperature and the flue gas analysis ( % O2 , CO2 etc.) you can calculate the steady state efficiency with the data you have during normal operation. Of course this doesnt take into account the standby losses like AFUE does, but it will give you a pretty good idea of its combustion and heat transfer efficiency.
  • sootmonkey
    sootmonkey Member Posts: 158
    Stack temps

    Realoilman....What can I say?....very impressive....I will tell you what I have done to try to lower the stack temps in my 1993 v73 Burnham. I have brushed it from the side and top with a steel brush, followed with a soft brush. I then removed the breast plate and brushed and vacked the exposed iron in the chamber area. I then heated the boiler up to or very near max operating temps and took a small garden sprayer and "washed" the pins from the side and top, and then through the "fire inspection port." I would like to think that at the time that I did that, that the last time the boiler was that clean, was when it left the factory. I fired the system at 140 psi .85x80A with some where between 11% and 11.5 % co2 and my stack temps were in the ball park of where yours are. I have tried many nozzle/pump combos, most of them being less than max fireing rate. I know that I have never seen less than 550 net stack. Just a monkey chewinn on a bannanna
  • McKern
    McKern Member Posts: 71

    Okay, so whenever your boiler fires it takes just under 2 minutes for your stack temps to stabilize. During that same time, your boiler temp is falling.

    Where's the sensor on your boiler? I would expect as soon as you fire your boiler, that the boiler temp would flatten. It would then accelerate upwards slowing at first with the peak slope when the stack temp stabilizes. Instead, your boiler temp is still falling when it fires for almost the full initial warm up period.

    Something's wacky... maybe the sensor placement, maybe my assumptions?

    I want something like this!! Very nice info!

  • I have a feeling that the boiler temperature continues to drop after firing begins because the return water temp is still dropping. There is a time lag until the casting starts rising in temp and begins transferring heat to the incoming colder water. Possibly the sensor is nearer the return end of the boiler?
  • realolman
    realolman Member Posts: 513
    thanks for the kind words

    The boiler sensor is strapped on the first inch or so of 1-1/4 " black iron pipe that leaves the boiler. it's still inside the jacket, and under insulation, but not down in the heart of things like the aquastat.

    Soot monkey, it sounds like you're saying that's as good as the stack temp gets with one of these boilers.
  • Theoretically speaking...

    if you are at or near design condition, your ON cycles should be substantially longer. In fact, if everything is sized exactly right, at design condition you are at a thermal equalibrium, whereby input equals output, so the boiler SHOULD be running 100% of the time.

    However, as I have stated before, even on systems that I know for a fact were correctly sized, I have yet to see more than a 50% duty cycle for a given hour at or near design conditions. Many internal gains are NOT taken into consideration on most heat loss calculations.

    My mod-con runs 100% of the time when it gets cold outside, but is modulated back to match the real time load.

  • Sounds like...

    A technology who's time to go has come...

    Poor thermal utilization, eh.

    EDIT: It would be EXTREMELY interesting to see the net thermal efficiency of this appliance. In other words, run water directly through the system with a flow meter on that side (mass) and monitior the delta T (gain) and monitor the input.

    Output divided by input = instantaneous efficiency.

    I do this with my natural gas mod con all the time and am seeing numbers between 98% (low burn) and 89% (high burn).

    I'm betting that the numbers from the typical oil boiler would not be nearly as impressive.


  • realolman
    realolman Member Posts: 513
    I wish I could understand

    why this is not right...

    Valves to radiation are closed. No flow.

    1.0 GPH nozzle @ 140 psi = 1.18 GPH

    Burner ran 5 min. 33 sec. used 1.18* 5.55/60 = 0.109 gal fuel X 140,000 = 15281 BTU

    15.9 gal water raised 77° F

    15.9 X 8.345 =132.69 lbs. X 77 = 10216

    10216 / 15281 = 0.6686 X 100 = 67% boiler efficiency

  • Dave_4
    Dave_4 Member Posts: 1,405
    I wonder if you would please explain

    some of the things you stated. They are very interesting, but I don't quite get them.

    Like the formula you showed including duty cycle... and the statement regarding having no control over the duty cycle... that it was governed by the nozzle size and the outdoor temp.

    In a way I can kinda get that... It's a specific temp outside... your house has a specific heat loss... the nozzle delivers a specific quantity of fuel.

    If you'd explain that formula and concept a little more, I for one would appreciate it.

This discussion has been closed.