munchkin reset

mike terry_3

I contacted my local munchkin rep in an effort to be able to have reset on our companys munchkin boiler that is installed here at our shop.The munchkin takes care of the radiant slab in a new office addition.I was told by the rep that the munchkin had a modulating burner and reset would just be redundant.I disagree.The rep failed to call me back so that he might set up some kind of required training.Any how, if there is someone out there who would point me in the right direction,I feel that reset would really help some of the control problems Im having.
thanks Mike

Steve Wilson

Munchkin Reset

Please call John Sawyer @ HTP (508.763.8071)for help. He will get you the outdoor reset you need or will train you for Vision 1 certification.

Plumbob

> I was told by the rep that the munchkin had a

> modulating burner and reset would just be redundant.


Amazing, isn't it? So many hydronics "professionals" are just faking it.

Walt_4

confusion

I don't understand how outdoor reset helps a Munchkin if the Munchkin controls always modulate based on return temp. Why would it need to anticipate water temp when it can just btus until it sees the delta it is programmed for?

Mike T., Swampeast MO

Because it will modulate the burner only to achieve a FIXED supply temperature. VERY different than modulating a burner to achieve a reset "curve".

chuck shaw

actually

John is on Vacation untill Nov 1st.

Might be beter to try him then,

Chuck

Walt_4

Oh. I see. I thought is was trying to acheive a certain delta T (if that's the right term).

Thanks.

chuck shaw

with the reset

Walt,

The out door reset will change the boiler set point. For example, depending on climate and installation method, you might have a radiant system that would require 140*F water, when it is zero out doors. When it is 50* you might want the water to be 90*F. If you were to use the sensor, it would change the boiler set point to 90*F. The boiler may never come out of low fire. If you did not use the sensor, the setpoint would not change, and it would run at 140*F all the time.

The boiler will still look to maintain a 20* delta T accross the boiler, it takes into account the temperature of the water leaving the boiler, returning to the boiler, and the setpoint. The it adjust the firing rate accordingly to work towards the 20* delta T.

I hope this helps,

Chuck Shaw

Chuckles_2

how is this possible?

> The boiler will still look

> to maintain a 20* delta T accross the boiler, it

> takes into account the temperature of the water

> leaving the boiler, returning to the boiler, and

> the setpoint. The it adjust the firing rate

> accordingly to work towards the 20* delta T.


But you can't possibly maintain a 20F deltaT by adjusting the firing rate. The Munchkin has no control over the flow rate, and for a fixed flow rate, deltaT depends ONLY on the amount of heat loss in the radiation. On a warm day, deltaT must be low, on a cold day deltaT must be high. On a design day, maybe deltaT=20, but not on any other day.

As for as I can tell, the Munchkin adjusts the firing rate so as to maintain the supply setpoint. Thus the firing rate depends on the heat loss, and deltT varies with heat loss as well. DeltaT is not fixed.

Right? Or did I miss something?

Plumbob

or to put it more plainly

>Thus the firing

> rate depends on the heat loss, and deltT varies

> with heat loss as well. DeltaT is not fixed.


To say it more directly, the firing rate depends on the measured deltaT, and the steady state delta-T depends on the home's heat loss.

For example, if the set point (controlled by outdoor reset) is 110 but (at startup) the water is coming back at 70, the Munchkin will go on full fire, but when after a while the water is coming back at 103, the Munchkin will throttle back. The point is to put heat into the water at a rate that varies with the delta-T it measures---thus the output water will come out at the setpoint temperature and everything will reach a steady state without the burners going on and off.

The Munchkin can't do anything about the steady state delta-T; certainly it cannot achieve deltaT=20 at all times.

Mike Reavis_2

so you don't like the outdoor reset--don't forget about the warm

weather shut down. The are days where this is a real money saver.

mike

chuck shaw

Chuckels

Your right, I did take into account that people would size circulators according to instructions. I also took into account that the instructions would be followed, and the boilers would be piped primary/secondary.

This would give a very controlled flow through the boiler.

The logic in the computer, even if shooting for a set point of 180*, on a call for heat, will not jump right into high fire, rather, it will sense the incoming temperature, the outgoing temperature, and as long as the temp is climbing, it will hold a pretty steady firing rate. If the delta T through the boiler increases, or decreases, it will adjust the firing rate.

It looks to send water out, 20* warmer than it comes in, and adjusts accordingly.

That is why when people try to re-engineer the system, for a 30* delta, and use a smaller circulator then reccomended, it just doesnt work as well.

I hope this clears up what I may have been murky about.

Chuck

Mike T., Swampeast MO

Chuck

This is NOT a criticism, I'm just trying to understand something...

Say you have the Munchkin without the Vision 1 package and you're using a system with proportional flow control (TRVs). You've piped and pumped the boiler side as suggested.

With a fixed supply temperature delta-t in the proportional system side is going to vary wildly--in moderate weather the return temperature will be at or near ambient temperature. In this case I suppose you would recommend an outdoor temperature controlled mixing valve in the system side to send a variable amount of supply water back to the boiler return to keep boiler delta-t near 20°. Correct?

Now say you're using the Vision controls that allow inherent boiler reset. While it's quite possible to engineer your reset curve for reasonably constant delta-t regardless of the outside temp, that constant delta-t becomes a function of the radiation itself and may well be greatly different than 20°.

With the Vision controls is it still preferred to keep a 20° delta-t across the boiler? If so, do the Vision controls offer provision to operate a mixing valve to keep boiler delta-t near 20°. If not, what outboard controls are suggested?

Plumbob

still object

> The logic

> in the computer, even if shooting for a set point

> of 180*, on a call for heat, will not jump right

> into high fire, rather, it will sense the

> incoming temperature, the outgoing temperature,

> and as long as the temp is climbing, it will hold

> a pretty steady firing rate. If the delta T

> through the boiler increases, or decreases, it

> will adjust the firing rate.


That is completely reasonable; thanks for describing the process.

> It looks to send

> water out, 20* warmer than it comes in, and

> adjusts accordingly.


This is NOT reasonable, because then the setpoint will not hold. 20F on a design day is one thing, but 20F every day is another, and will cause the house to become a tropical rain forest!

Take for example the 80MBTU Munchkin. The manual calls for a circulator that pushes about 8gpm through the boiler. With 8gpm and deltaT=20F, the water will lose about 80,000 BTU/hr in its circuit though the radiation. This is just fine on a design day, but every day? No way. 20F is the maximum limit, not the everyday situation.

PS I do have a Munchkin in our home, and it does NOT have deltaT=20F at any time in this fall weather. It holds quite nicely at the setpoint (determined by outdoor reset), while deltaT varies with the weather.

For example, suppose the design day has 80 degree-days, the design water temp is 160F, and the design deltaT is 20F. Well, on a 25F day (40 ddays), Let's say the reset temp is 125F. The delta-T will be 10F (half of 20F, because the heat load is half). The Munchkin will soon figure out that it needs to fire at only 50% to heat the water to the setpoint of 125F.

Plumbob

The Munchkin requires P/S pumping, and thus it has a fixed flow rate determined by the boiler circulator. The deltaT we're talking about is the deltaT measured at the Munchkin, by the Munchkin.

You CANNOT have a particular deltaT (e.g. 20F), if the flow rate is fixed and the weather (heat load) varies.

With all due respect to Chuck Shaw, the Munchkin DOES NOT CONTROL deltaT. It looks at the deltaT, and uses it to determine its own firing rate. This way it just reaches, but does not exceed, the setpoint. Whereas an old-fashioned boiler would always be firing on full, and would soon exceed the setpoint and then go off, reducing efficiency

Guy_5

reset

To coin one of Chuck's phrases- think of it as a belt and suspenders:
Not only do you get the benefit of a modulating burner (firing rate), you also can add the option of the outdoor reset and modulating your operating temperature. Why deliver 200* water to baseboard on a 50* day in April, when 150* water will provide all of the necessary heat? At that point, the boiler will deliver the 150*, and as once the return water reaches 130*, the firing rate will drop.

Plumbob

>once the return water reaches 130*, the firing rate will drop.



There you go, that makes sense. It is not as if the Munchkin will try to maintain deltaT=20. But when deltaT>20, either on startup or all the time on a design day, it is on full fire. When deltaT drops to 20 and below, the firing rate will drop. The end result is to maintain the siupply water at the setpoint. That makes complete sense.