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Munchkin modulation sequence...?

Plumbob
Plumbob Member Posts: 183
Before I bought a Munchkin, I thought the modulation feature was great: it would allow the flame to hold at the level needed to maintain the temperature, without ever going off.

Now I have read the Vision I manual, which is written in something that loosely resembles, but is not exactly, English. According to this manual, the Munchkin starts at low level, then goes up at one minute intervals until it is at the highest level. Then it stays there until the target temperature is reached, at which point it goes off.

Is this true, or is it just that the manual writing was outsourced? If true, what would be the point of that? Would it not be better to modulate down until a sustainable level is found (or hop between two levels such as to hold the temperature)? The delta-T and flow rate tell the control board all that is necessary to calculate the BTU needed, and if it doesn't know the flow rate, it can figure it out after a while.

Comments



  • Sounds like you're reading some sort of simplified explanation as to how the brain learns its "target" modulation rate over time and through various conditions (both indoor and outdoor).

    The graphs Mark Etherton posts (taken directly from the "brain" output) don't seem to show that sort of burner operation.
  • Plumbob
    Plumbob Member Posts: 183
    yes, probably

    > Sounds like you're reading some sort of

    > simplified explanation as to how the brain learns

    > its "target" modulation rate over time and


    You're probably right, but it's Munchkin's own documentation!

    > The graphs Mark Etherton posts

    > (taken directly from the "brain" output) don't

    > seem to show that sort of burner operation.


    How do I find these? I tried a search here but I am not really sure what keywords to use.
  • R. Kalia_5
    R. Kalia_5 Member Posts: 12
    relevant text

    > Sounds like you're reading some sort of

    > simplified explanation as to how the brain learns

    > its "target" modulation rate over time and

    > through various conditions (both indoor and

    > outdoor).


    Here's the relevant text. You can judge what it is a simplified explanation of.

    "...The Munchkin has a 6-step function programmed into the controller. (Note: this 6-step function cannot be changed.) When the Munchkin burner is activated, the burner output is regulated in one-minute intervals. As shown in the chart, Sec. 9. Fig. 9.2, Appendix, pg. 27. Note: these percentages are based on the rated maximum output. This feature helps the Munchkin from overshooting the heat set point and minimizes short cycling. As soon as the central heating is active (including pre-purge), step modulation begins. When in operation, the step will be increased. Once the heating demand is satisfied the step modulation will start from the beginning of its cycle."

    [The chart referred to is actually a table, and it gives the six steps in BTU/hr. I am not sure this information is relevant to the question, but for example, the six steps for the 140M are 56,000; 70,000; 84,000; 98,000; 119,000 and 140,000. Curiously, this model is supposed to modulate down to 47,000BTU (factor of 3) but the first step is 56,000 BTU. ]


  • Until recently, I had intentionally not studied the modulation schemes of various boilers, instead preferring to speculate. I long suggested that the Munchkin would be designed for use in typical American systems (read wall thermostats, zone valves, multiple pumps, etc.)

    That statement seems to support my assertion.

    The method described seems to be a quite reasonable way to achieve the goal. You should get nice, long calls for heat regardless of how many zones are calling. Remember, the boiler assumes that you are using digital thermostats--once they call you MUST raise the heat level--NOT just maintain.

    I would suspect that the boiler learns to modify the step sequence over time using outside temperature, return temperature and/or supply temp rise during a given step. Even if it doesn't the described sequence is reasonable for a system that can NEVER ASSUME MAINTENANCE.

    ------------------

    Contrast this with the Vitodens where the only explanation of burner logic is, "...non-mechanical, pneumatic modulating link between air and gas introduces the required amount of gas for correct combustion to meet the current heat demand." Obviously, this boiler ALWAYS ASSUMES MAINTENANCE.
  • Plumbob
    Plumbob Member Posts: 183


  • Plumbob
    Plumbob Member Posts: 183
    ??

    > The method described seems to be

    > a quite reasonable way to achieve the goal. You

    > should get nice, long calls for heat regardless

    > of how many zones are calling.


    I don't understand that. Within 6 minutes the boiler is on high fire and stays there until it goes off. Why should that give you particularly long calls for heat? (Short-cycling is already reduced by a minimum-on time, described elsewhere in the manual.)

    When (if) you cook, do you step the cooktop gas flame or electric element up to full in one-minute steps and leave it there until the pot boils over, then turn it off and start the whole process again? or do you find a medium heat setting where the cooking can continue at a stable rate?

    > Remember, the

    > boiler assumes that you are using digital

    > thermostats--once they call you MUST raise the

    > heat level--NOT just maintain.


    I don't understand that. When the thermostats are not calling for heat, the boiler is off and the water cools. When they are calling for heat, there is a water temperature determined by the reset curve, just as old-fashioned boilers have a water temperature set by an aquastat. The boiler's job is to heat the water to the target temperature (using high heat if needed) and then MAINTAIN the temperature (by cutting back on the heat but not going off).

    If it maintains the temperature by going in a predetermined way to full fire and then going off sharply, then rinse and repeat, is that much different from old-fahioned on/off boilers?


  • It won't make it to full fire if the supply temp called for by the reset curve is achieved along the way... From the exact sequence described, once supply temp hits the reset target (and provided there is still a call for heat), the burner will drop back down to minimum modulation and then resume the ramp-up sequence.

    While not described, I truly hope that during a single cycle the burner will learn to home in on the two closest modulation rates. Even if it's not that smart, the burner isn't going to shut down completely until all calls for heat are satisfied or the lowest firing rate results in supply temp higher than called for by the reset curve.

    Have you ever tried to perfectly regulate a pressure canner on an electric stove? (I do this for MANY loads EVERY year.) Even with the so-called "infinitely adjustable" electric burners it requires constant attention. With a nice gas range, it's quite a bit easier to home in on the exact setting. (I've used both for this and greatly prefer an instantly changing fire that I can see...)

    >>When the thermostats are not calling for heat, the boiler is off and the water cools.

    Right, BUT THE STRUCTURE COOLS AS WELL!!!!!!

    When you're concerned with temperature maintenance you NEVER want the structure to either increase or decrease in temperature unless the occupants desire. Perfection is impossible, but you can get close enough to "see" the solar cycle reflected over time (as retarded by your R-value and infiltration)...
  • Perfect Analogy

    "When (if) you cook, do you step the cooktop gas flame or electric element up to full in one-minute steps and leave it there until the pot boils over, then turn it off and start the whole process again? or do you find a medium heat setting where the cooking can continue at a stable rate?"

    PLEASE imagine this as compared to pressure (STEAM) canning on a stove. You want to maintain a certain pressure constantly--you want this pressure to correspond to the lowest possible temperature required to kill the nasties in a given food. If pressure (temp) is too low, you may not be assured of safety, if pressure (temp) is too high your food can turn to mush--literally!

    FROM THE STATEMENTS PROVIDED, the Muchkin is like an older electric stove with warm, low, medium, medium high and high settings (with an extra-high thrown in).

    The Vitodens, on the other hand is like a gas range with a completely variable dial--the only thing missing is the extremely sensitive "simmer" adjustment that usually takes up about a quarter of the total rotation yet only accounts for the bottom thirty-second or so of the fire. (Maybe they're working on that as I write.)

    When it comes time to pressure can, it's a royal pain in the **** to regulate the pressure (temperature) on an electric stove. You continually overshoot, then undershoot (quite rapidly if you're being picky). Even the so-called "infinite" electrics have this annoying lag time...

    With a gas range, you INSTANTLY change the RADIATION characteristics--you can see it and you can quite rapidly home in on the "perfect" setting.

    If the food you're canning is extremely durable (like vine dried purple hull peas) minor fluctuations in pressure (temperature) don't matter too much--but if it's whole tomatoes and you don't want juice...







  • R. Kalia_5
    R. Kalia_5 Member Posts: 12


    > It won't make it to full fire if the supply temp

    > called for by the reset curve is achieved along

    > the way...


    That's not what it says...

    > From the exact sequence described,

    > once supply temp hits the reset target (and

    > provided there is still a call for heat), the

    > burner will drop back down to minimum modulation

    > and then resume the ramp-up sequence.


    That is what it says (I was wrong to say it will go off), but why should it go all the way to minimum?

    > While

    > not described, I truly hope that _I_during a

    > single cycle_/I_ the burner will learn to home in

    > on the two closest modulation rates.


    That would be reasonable although that is not what it says. It is possible to simulate a continuous function with some discrete steps if it will just jump back and forth between the two closest rates (one above, one below).

    > Have you ever tried to perfectly

    > regulate a pressure canner on an electric stove?


    No, and I'm sure it is difficult, but it is made easier by NOT following mechanical rules like "increase the heat every minute, all the way to maximum, then go down to minimum and start all over". Modern microprocessors, IF intelligently programmed, can do process control much better than we can manually on stoves.


  • > From the exact sequence described,
    > once supply temp hits the reset target (and
    > provided there is still a call for heat), the
    > burner will drop back down to minimum modulation
    > and then resume the ramp-up sequence.

    Think about that for a moment and in context with a system that is already going--NOT from a cold start in a cold house.

    Say one small zone calls in moderate weather. Most likely the reset target will be hit quite rapidly and before the burner has made it to full fire.

    Now say a big (or a number of) zone(s) call for heat in cold weather. After ramping up for six minutes it will stay at full fire until the target is reached. Then (as described) it drops down to minimum modulation and starts ramping up again. Within a cycle or two, I'll bet that it starts hitting the target at lower than full fire.

    Remember--it's trying to prolong the call for heat as long as possible but it really doesn't know the inside temperature--it only knows "satisfied or not satisfied". With a decent reset curve the target will just be barely suitable to raise space temperature. Heat calls will be nice and long even if the burner is sort of pumping up and down.

    While not as elegant as the Vitodens (which appears capable of variable modulation in its range) it really does seem a reasonable way to control a digital system--some of that elegance is almost certain to be lost in the system itself when you connect a Vitodens. Remember: nearly (or is that every) Vitodens system I've seen posted here uses the low-loss header to decouple the boiler from the system itself. Good for the boiler, but IMHO not the best possible for system efficiency.
  • Plumbob
    Plumbob Member Posts: 183


    > Say one small zone

    > calls in moderate weather. Most likely the reset

    > target will be hit quite rapidly and before the

    > burner has made it to full fire.


    It doesn't say that. You're assuming that the process is reasonably designed, but there is no printed indication of that.

    >

    > Now say a big

    > (or a number of) zone(s) call for heat in cold

    > weather. After ramping up for six minutes it

    > will stay at full fire until the target is

    > reached. Then (as described) it drops down to

    > minimum modulation and starts ramping up again.

    > Within a cycle or two, I'll bet that it starts

    > hitting the target at lower than full

    > fire.


    It doesn't say that. You're assuming that the process is reasonably designed, but there is no printed indication of that.
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    How low can YOU go...

    The slow step up approach is a much more wise use of energy as opposed to starting at the top and working your way down. Although this may not make sense to some people, having spent 30+ years in mechanical rooms, watching the American technology of starting at the top and working your way down, the logic of starting at the bottoma nd working to the top has MANY advantages over the alternative.

    What actually happens is similar as is described. If the load exceeds the minimum burner output, it modulates upward until it approaches the variable set point (V-1 control assumed). If idle spped is more than the load, it has no option but to shut down to avoid overheating the system.

    Remember, it is virtually impossible to design a control logic that is capable of "seeing" all the dynamics that affect plant operation. All you can do is is get as close as you can to perfect thermal balance (input = heat loss).

    Twidling, fiddling and tweaking might get you close for the current situation, but will it cover the requirements at 2:00 AM when there is no solar gain, the wind is blowing at 10 MPH and there are no internal gains occuring?

    If and when someone comes out with a control that can take this, the thermal mass and insulation characteristic, changing weather conditions, night sky re-radiation, and ALL the other things that affect physical plant operation in to consideration, the American hydronic contractor will beat a path to their door... I guarantee it , or my name is not Orville Reddenbockerr:-)

    ME

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • R. Kalia_5
    R. Kalia_5 Member Posts: 12


    > The slow step up approach is a much more wise use

    > of energy as opposed to starting at the top and

    > working your way down.


    I wasn't questioning that, this is obviously better, although I understand that earlier Munchkin firmware started from high and went down.
  • Mark Hunt
    Mark Hunt Member Posts: 4,909
    Waaaaaaaahooooooooooo


    Gotta' tell ya' Kalia, you almost got me to drop Munchkins. ALMOST! (Less than 10 seconds)

    Then I realized that you have no freakin' idea about what you're saying or asking.

    I bet you piss your contractor off so much, he drops you as a customer.

    Good luck with your munchkin and your big mouth.



    Silver
  • Constantin
    Constantin Member Posts: 3,796
    The troll strikes again...

    ...in multiple threads, no less. I am duly impressed.

    R. Kalia asked a legitimate question. Your response had nothing to do with the topic on hand and was simply meant to hurt someones feelings. That's pretty pathetic. Why don't you go troll over at HVAC-Talk, they may like your high-school locker-room attitude better.


  • Hey Mark: how about posting one of your output graphs? I can't seem to find in the history, and as I recall such showed a very reasonable modulation scheme.

    You said: "Remember, it is virtually impossible to design a control logic that is capable of "seeing" all the dynamics that affect plant operation. All you can do is is get as close as you can to perfect thermal balance (input = heat loss)."

    I couldn't agree more, but the Vitodens does claim to do this (input - very small stack loss = nearly instant heat loss). Explicitely regarding the primary (boiler) loop when the low-loss header is used and implicitely in systems without the header and of proportional flow. Yet the price (or is it disbelief that such a thing is possible) seems to be keeping American hydronic contractors from "beating a path to their door".

    Watch for some fun stuff late this winter. While my data-logging ability won't be that of the Vision system, I'll have temp sensors on boiler (system) supply, boiler (system) return, and in the flue. Can only log every ten minutes, but it should make for some interesting comparisons as I have numerous indoor sensors (easily movable) as well as an outdoor sensor that will be right by the Vitoden's. Might be able to add a solar intensity sensor as well, but it's rather expensive and I gotta pay for the boiler first. Will attempt to set up tests in my "wild" radiant areas with radically different losses despite nearly identical construction. Will attempt to show just how much radiation automatically compensates for "...the thermal mass and insulation characteristic, changing weather conditions, night sky re-radiation,...".
  • munchkin-man
    munchkin-man Member Posts: 247
    The Munchkin does have variable modulation in its range

    The six minute step is simply to take a look at the return temp and monotor it so we do not over fire the Munchkin. This would be typical in buildings that have multiple zones of witch some of them are say a towel warmer or a bathroom zone with minimum btu requirement. We look at the return temp for only six minutes this is not a lot of time in hydronics.

    The control will target the set point through modulation and take six minutes to get there however if durring that climb the return water gets with in 20 derees of the supply it will start to moduate down and find the btu rate based on the return temp. It is that simple.
  • munchkin-man
    munchkin-man Member Posts: 247
    To all of our dedicated smart understanding customers

    Thank you for your continued support through professional comments and the use of our products. See you at the show's.
    Some poeple have way to much time on there hands.
  • From a person who does think too much...

    THANKS!

    As I kept speculating, manuals (understandably I might add) are often over-simplified and from every report/graph I HAD seen, the modulation seemed very reasonable and quite responsive. Just remember--I'm a freak when it comes to proportionality.
  • munchkin-man
    munchkin-man Member Posts: 247
    Thanks Mike

  • Plumbob
    Plumbob Member Posts: 183
    OK, thanks

    OK, thanks, that's all I needed to know. I wish this were made explicit in the manual though.
This discussion has been closed.