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EKG decipher anyone?

josephny
josephny Member Posts: 270
edited January 26 in THE MAIN WALL
I have a house with a Burnham V84 (159MBTU), oil burner, 2 zone hot water.

I like to monitor data (even if I can't fully understand that data).

Below is a graph of:
1) Zone 1 temp
2) Zone 2 temp
3) Temp 2" from the boiler's exhaust pipe ("boiler temperature")
4) Each zone calling for heat (I call it "Heat Graph Binary")
5) Watts used in house (nothing else was switched on or off during the graphing sample)


I wonder what the double peak is around 11:30pm, 12:30am, 1:45am, and 4:30am.

On the zoomed in graph it shows that the tstat calls for heat at 1:35am and relinquishes the call at 1:52.

The boiler fires at 1:32 (time might be a few minutes out of sync) and then stops firing around 1:37, then fires again at 1:44 for several minutes.

I notice that this only happens when only 1 of the 2 zones calls for heat.

So I ran a little experiment and made both zones call for heat.

The third graph below is the result. It shows a continuous call for heat from both tstats starting approx 5am until 6:10am and the exhaust temp cycles a bunch of times by several degrees (seemingly indicating a cycling in the firing).

Something about oil-fired slightly older boilers would explain this?

Something in the way the Ecobees work? The zone valve wiring?



Zoomed:




Comments

  • Brent H.
    Brent H. Member Posts: 161
    Looks like cycling. If your zones can’t consume all the BTUs it is going to cycle. Your boiler has a fixed firing rate so it is always going to cycle except when the outside temp. is at design temp. (Assuming the boiler was sized correctly to begin with)
  • josephny
    josephny Member Posts: 270
    So it's probably as simple as the boiler is firing, reaches its upper safety limit, shuts itself down to cool off, then starts up again when it's safe?

    And this would be the stark difference between a fixed firing rate boiler and a modulating one, right?

    I found this earlier thread about Becket oil burners (and is fascinating):

    https://forum.heatinghelp.com/discussion/84738/Difference-Between-Beckett-Heads


    My V84 has a AFG70MDAQN

    Thank you.
  • pecmsg
    pecmsg Member Posts: 4,696
    edited January 27
    Those short cycles are going to kill that boiler!

    When only 1 or 2 zones are calling the load is too small. You need a smaller boiler, or a buffer tank sized so you'll get at least 15 minuets run time!
    STEVEusaPAethicalpaul
  • LRCCBJ
    LRCCBJ Member Posts: 58
    On your first graph, the boiler fires twice between 11:00 and 12:00. It then fires twice between 12:00 and 1:00. The zones are now satisfied until 1:30 where it fires twice before 2:00. It fires once at 3:15. It fires twice between 4:30 and 4:45.

    So, the boiler ran 9 cycles over five hours. This is NOT short cycling and no harm will occur to this boiler under this scenario.

    What you could do is to check on the differential for the high limit. If the differential can be extended to at least 20 degrees (and maybe even 30 degrees if the control will allow), the number of cycles can be dramatically reduced.
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 21,866
    The boiler fires at 1:32 (time might be a few minutes out of sync) and then stops firing around 1:37, then fires again at 1:44 for several minutes.

    I notice that this only happens when only 1 of the 2 zones calls for heat.


    Most would agree a 10 minute run cycle would be a good operating condition. A 3- 5 minute I would consider short cycling.
    Of course the size of the zones and heat load at any given time will drive the boiler operating condition.
    Small loads on mild days would probably be worse case cycling.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • josephny
    josephny Member Posts: 270
    I might be misunderstanding, so just to make sure, allow to clarify that I am referring to the double peak identified by the 2 arrows.

    This is occurring during a single period where the tstat calls for heat.

    I think the internal controls (sorry for the lack of the correct term) of the boiler shut down the firing of the boiler for those ~5 minutes.

    So, if I'm reading this graph correct, it says:

    1) 11:03 Tstat calls for heat and boiler starts firing
    2) 11:06 boiler exhaust temp starts to rise
    3) 11:12 boiler stops firing, probably because of boiler internal controls
    4) 11:16 boiler temp has dropped enough so boiler internal control make boiler fire again
    5) 11:21 boiler stops firing, probably because of boiler internal controls
    6) 11:27 Tstat stops calling for heat

    IF that is correct (give or take 1 minute in various places), then within a single 24 minute tstat call for heat the boiler fired for 9 minutes, stopped for 4 minutes, then fired again for 5 minutes.

    If this time-analysis is correct, then the boiler is short-cycling.

    Correct?



  • pedmec
    pedmec Member Posts: 932
    NO, for a warm day for a boiler to only fire twice in that time span is pretty normal. actually its really good because if your boiler was over sized i highly doubt you would even get a minute. a 9 minute run time is not bad. i'm assuming that's from a cold start as when the boiler recycled it was 4 minutes. You have an on/off system so once there is a demand that boiler is putting out the max amount it can. how much radiation is connected determines when the boiler will fire again and again. there are a lot of variables to look at when determining short cycling.
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 21,866
    Another important number to know would be the return temperature during or at the end of the cycle, regardless if it is a 6 or 9 minuter run, it needs to be warm enough to dry out the combustion chamber and all the venting. Above the fuels dewpoint.

    These electronic counters are handy for catching cycles.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Bob Harper
    Bob Harper Member Posts: 1,030
    The first EKG tracing shows an agonal ventricular rhythm with a Left Bundle Branch Block. Probably Electro-Mechanical Dissociation. The rest are asystole- toast.
    josephny
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,578
    edited January 28

    The first EKG tracing shows an agonal ventricular rhythm with a Left Bundle Branch Block. Probably Electro-Mechanical Dissociation. The rest are asystole- toast.

    Bob, I know. that you are the expert in venting systems, but in this comment you are stepping into another area entirely. Agonal rhythm is usually ventricular in origin. Occasional P waves and QRS complexes can be seen on the EKG. The complexes tend to be wide and bizarre in morphological appearance. Clinically, an agonal rhythm is regarded as asystole and should be treated equivalently, with resuscitation and administration of adrenaline.

    Don't you think?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    Bob Harper
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,578
    To make this easy to understand terms I like to put numbers to the situation.

    Let's say you have a design load of 100,000 BTUh at 0°F outdoor temp
    Let's say that you have 2 zones that require 50,000 BTHh Each
    Let's say that you have a boiler that can provide 125,000 BTUh. a little oversized but probably ok
    Let's say that this evening the temperature is only 52° outside and the temperature stays at 52° steady for this example. That is about 1/4 of the design requirement

    In any given four hour period one of the zones will require 12,500 BTUs times 4 hours of energy so 50,000 BTUs to maintain the zone temperature.

    So on a call for heat, 125,000 NET output turns on for heat in that one zone. The burner takes about 9 minutes to get to operating high limit temperature where the burner will stop firing, but the zone thermostat is still calling for heat. The radiators can only emmitt 50,000 BTU per hour so that 125,000 is overwhelming those radiators and the boiler gets hot fast (9 minutes). Then the burner stops and the circulator pump continues to move that high temperature water to the radiators. Eventually the radiators cool down about the boiler 10° to allow the burner to cycle on again. Since the boiler is no longer in the "Cold Start" condition it only takes 4 minutes for the burner to heat the water back to the high limit temperature. Then the same thing happens to the water because the circulator pump is still operating and sending the hot water from the boiler to the radiators and the boiler temperature starts to drop.

    Just before the boiler temperature drops to the point where the burner can fire again, the call for heat is satisfied and the thermostat turns off the burner and circulator pump control. Then the room continues to get warmer because the radiators are still hot. Eventually those radiators will cool off and the room temperature will drop over the next 4 hours. Let's look at the math.

    Boiler offers 125,000 BTUh for a total of 13 minutes. 125,000 divided by 60 minutes is 2,083 BTUs. Multiplying that number by 13 minutes is 27,083 BTU in that short period of time.

    The design load is 50,000 per hour and since we are at 52° we are at 25% of design so we only require 12,500 BTU per hour. Since we just put over 25,000 BTUs into that zone in the last 20 minutes, the next call for heat might be in about 2 hours. that is when we can start the process over again.


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • josephny
    josephny Member Posts: 270
    edited January 28
    Ed, that is a great explanation of what is happening -- thank you.

    I can see there is a huge of amount of information and knowledge behind what you wrote.

    But, now I can start the see the importance of a properly sized boiler (a topic frequently discussed here).

    While I am very interested in everything you wrote, one thing has a particularly practical importance: "the next call for heat might in about 2 hours."

    I wonder if we can look at this data (number of minutes firing, outdoor temp, how long between calls for heat, etc.) and figure out how energy efficient the house is?


  • hot_rod
    hot_rod Member Posts: 21,866

    The first EKG tracing shows an agonal ventricular rhythm with a Left Bundle Branch Block. Probably Electro-Mechanical Dissociation. The rest are asystole- toast.

    Bob, I know. that you are the expert in venting systems, but in this comment you are stepping into another area entirely. Agonal rhythm is usually ventricular in origin. Occasional P waves and QRS complexes can be seen on the EKG. The complexes tend to be wide and bizarre in morphological appearance. Clinically, an agonal rhythm is regarded as asystole and should be treated equivalently, with resuscitation and administration of adrenaline.

    Don't you think?
    Punching above my weight on this one. I’ll stick to the mechanical side.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • jesmed1
    jesmed1 Member Posts: 554
    edited January 28
    josephny said:


    I wonder if we can look at this data (number of minutes firing, outdoor temp, how long between calls for heat, etc.) and figure out how energy efficient the house is?

    Yes, you can. I've calculated our 4-unit condo building's heat loss a number of ways over the years, and I've found that taking data from an overnight period with NO thermostat setback and low but stable outdoor temperatures works well. Our boilers run long periods on (about 40 minutes) followed by, say, 3 hours off. So for one complete on/off cycle, our calculation might be:

    Boiler starts @ 2:00 am
    Boiler stops @ 2:40 am
    Tstat calls for heat again @ 5:00 am

    So, boiler run time = 40 minutes in a 3-hour period (180 minutes)
    40/180 = 0.22 duty cycle (boiler runs 22% of the time, on average)

    Our boiler burns 1.18 gph @ 85% efficiency, so 1.18 gph x 140,000 BTU/gal x 0.85 = 140,000 BTU/hr useable heat.

    Then for a 22% duty cycle, 0.22 x 140,000 BTU/hr = 30,900 BTU/hr average output.

    Since the thermostat calls for heat at the same temperature each time, we know that the building has lost an average 30,900 BTU/hr from the time of the first call to the time of the second call.

    Obviously that's based on a given outdoor temperature, but you can extrapolate to whatever design temperature you want fairly accurately. Say the outdoor temperature during the above data period was 20 degrees, with the thermostat set at 70. That's a delta T of 50. To find the expected heat loss at, say, a design temperature of 0 (and a resulting delta T of 70), take a simple ratio of the delta T's and multiply:

    70/50 x 30,900 BTU/hr = 43,260 BTU/hr expected heat loss at 0 degree design temp.

    This method only works if (1) you have no setback programmed into the thermostat, and (2) if there isn't significant auxiliary heating happening inside from cooking, etc, that can affect the thermostat, and (3) if the outdoor temperature isn't changing rapidly. Doing this at night also helps because it eliminates the variable of solar gain.

    Once you have a heat loss number, you can divide it by your square footage to get a BTU/hr/sq ft number. Here are some reference heat loss numbers for older houses for comparison.

    https://inspectusa.com/blog/typical-heating-cooling-loads-in-older-homes/
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,578
    edited January 30
    While I am very interested in everything you wrote, one thing has a particularly practical importance: "the next call for heat might in about 2 hours."

    I wonder if we can look at this data (number of minutes firing, outdoor temp, how long between calls for heat, etc.) and figure out how energy efficient the house is?
    Not to go too far off the cliff, The numbers I used were hypothetical and have no basis in fact whatsoever. Any resemblance to actual events are completely coincidental, The names have been changed to protect the innocent, No animals were harmed in the posting of this example, some assembly required, Batteries not included
    I just picked an arbitrary heat loss and an arbitrary boiler size to explain a point. The numbers of the 9 minute and 4 minute were taken from your chart to help you understand the point I was making. If I selected a boiler that was way over sized then the next call for heat might have been in three hours or 4 hours.

    You will need to make up your own spread sheet with your BTU Net from your boiler's rating plate or by actually clocking the meter to see what you use based on the gas meter, and clock the times the burner actually operates because the information of the temperature near the vent may not be as accurate as the actual on and off times of the gas valve. Measuring temperature has a delay from actual valve opening and closing. and will vary based on many conditions you have no control over.

    As far as how efficient your home is, that is going to be compared to what? How efficient it used to be before you replaced the window, or insulated the attic or weather stripped the door jams and soffits? Your home IS efficient based on old technology. It is not efficient based on state of the art building standards. So I guess you will just know what your actual load calculation is after knowing how much you spend on fuel at the end of the year, and comparing that usage to the weather information from the same time period.

    Hope my info helps and that you have fun calculating all your information. What you do with the information God only knows, but That information might come in handy at Starbucks where that info and $7.50 will get you a small taste of caffeine.



    PS: I like my coffee from 7-11

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics