Heating Help

Modulating is it efficient?

Definitely a point for some discussion. Assumption here is that the system piping and duct work is compatible with the heating unit. A heat loss was done and system and heating unit are matched up.

When we look at say a 100,000 BTU boiler or furnace that fires on every call at full input is that efficient? Taking into consideration proper cycling rate.

If we however cause that system to modulate based on outdoor reset is it more efficient?

Now what about the combustion issue? When we fire at less than full input into a chamber designed for full input what is the trade off?

If we are firing at a lower input is excess air still the same?

What is the Stoichiometric (ideal or perfect)  Flame temperature for Natural Gas?

Is flame temperature affected by modulating?

Which has the bigger problem with the modulating concept as far as efficiency the boiler or the furnace?

Are there any charts or tables available for determining comparison of combustion analysis related to input on low fire versus high fire? Compared to Flue gas temperature on low fire and on high fire?

A lot of questions hopefully we can get some good discussion or maybe just get us thinking a little more about what is really happening with all this new equipment.

If we are firing at a lower input is excess air still the same?

I am not a professional, but I would love to know the answers to the
questions you posed. They seem important to me. I may well be naive
about this, but I would have assumed that boiler manufacturers would
have dealt with these issues, but the fact that you ask these questions
makes me question my assumptions.

Do you settle for manufacturer's claims, or do you want actual measurements?

On my mod|con boiler with outdoor reset, the manufacturer claims that the balance between the natural gas input and the air input is regulated. And it seems to be so in that the mixing area (before the mixture enters the combustion chamber -- heat exchanger) is a lot like an internal combustion engine carburettor. It does not need to evaporate the gas, of course, but the gas supplied depends on the air flow through a venturi, and the air flow blower is varied to do the modulation. So if it is designed right (I have no way of knowing this), it should always run at the proper ratio of gas to air.

I assume the way they do this is no secret, so any mod|com boilers can do much the same thing. I guess this assumption can be wrong.

"Is flame temperature affected by modulating?" I am not sure I understand your question. If you want the boiler to be modulating, you have to change the heat input to the thing. So you either change the flame temperature, or the amount of flame. I suspect it is hard to vary the temperature of the flame very much and still get good combustion, so I assume they just change the amount of flame. Is that not right?

I personally want to see some real

data on these efficiency claims.AFUE is not enough for me to get all excited and start turning all GREEN with envy.

A gas representative I was in the company of posed this question. Why if we are seeing all the rebates for higher efficiency do those systems when tracked for actual gas consumption based on degree day analysis not show some real changes in usage? What do you think could be the cause for this?

Does lower flame temperature affect efficiency?

In the last ten years

I had the good fortune to commission a wide variety of retro fits; CI to Vertomat and Rondomat, Dedietrichs, Laars, IBC etc - so I have a bit of data in the archives. The quick answer to your main question is: it depends. The very best results (consumption decreases) was accompanied by equipment change and operating parameters, eg. lowering design temps wherever possible. And there was the greatest challenge - popping in the latest modulating burner (or staged burner for that matter) with ODR without an operating change sometimes did not produce the expected xx% savings. My latest data is a WM CI boiler changeout in favour of a IBC condensing unit; emitters were baseboard and we added indirect DHW. Comparing annual consumption the client saved 35% during heating season but only >5% during the summer (DHW only). The apartment residents reported a more moderate heat delivery and the twice daily - no hot water syndrome disappeared. I noted in the firing logs (built in onboard the IBC control platform) that the burner reached 85% firing rate only when there was a call for heat from the indirects. I would think that even greater savings could be realised if the residents were slowly weaned off 125 deg hot water. I have all the data archived - so it will take a bit of time to retrieve. but I would think IBC still has the data too. hope this helps the discussion.

How about that maine system I was involved with...

... replacing two 84% AFUE Buderus 124X for one Vitodens 8-32. Besides being 2x over-sized, this supply-house designed system also had endemic issues with air entrapment on the upper floors, a very hot boiler room, and near-boiler piping that made my hair stand up straight. So there were a lot of issues besides swapping a proper boiler in a proper system for a proper condensing/modulating boiler.

But the customer saved 46% on the propane bill (despite rising LP prices that year) without any other changes to use. And, unlike years before, the house now heats very evenly, without noise, etc. Point being, that a 12% difference in AFUE doesn't  tell the whole story.  It's as good as any indication that there are significant penalties associated with oversizing single-stage systems that by definition will be oversized 97% of the year, even if they were properly sized in the first place! Modulation addresses that major issue (nameplate capacity vs. required input) for much of the year.

A high-mass system may be able to ameliorate some of the issues associated with single-step firing under non-design-day conditions (i.e. limit short cycling) but a better approach is to match the input to the heat loss. That's what modulation allows across a certain range of input capacities. With time, I expect boiler manufacturers to extend the modulation range of their gear to lower and lower input capacities. However, there are diminishing returns, especially for low-mass systems (i.e. less standby loss, less mass to heat, etc.), so it might make sense to cap the lower end of inputs at 15kBTU as most manufacturers do and to design the gear to handle the resultant short cycling during late spring and early fall/winter.

This experience is why I decided to abandon Ms. Vitola (who is almost properly sized) and retrofit a Vitodens, rather than fit a gas burner to Ms. Vitola. 

that is the right question....

I am interested to see what people have to say.

When it comes to combustion and turndown you have to make a sacrifice, how much of a sacrifice well that's debatable and seems to vary by manufacture. Another factor to consider is whether the appliance is condensing or non-condensing and its 
application.

 I would not go as far as to say that modulating appliances do not save money. I have seen to many projects in the field saving 30%-40% and sometimes more when switching from a non condensing low-hi-lo or on off appliance to a modulating condensing appliance. If that is what you are seeing I would consider looking at a different brand of modulating appliance or project design.

I have seen a chart, like many that shows the relationship between excess air, and condensing. Very enlightening.

Tim

Do you really think a fixed input appliance is more efficient? Viessmann's Lambda Pro system targets a constant 30% excess air. I have had combustion analyzers on many mod/cons and I've never seen more than 40% EA ever,so I assume the fan RPM/gas input model manufacturers use is pretty close in the real world

I am not saying

anything is more efficient than anything else, I am asking questions to get everyones input as to real world data.

When people state here and elsewhere savings as high as 50%, I always ask 50% of what. Was it an old oil or gas system that was either not being maintained or serviced.  There has to be some point of real reference or do we just take everyones word for it?

I have seen gas systems in my many years of service that had not had anyone touch them for 10 to 15 years. That was something that was sometimes promoted by gas suppliers for years. The truth was when you tested those units they were lucky to have 60% combustion efficiency.

I have tested a number of oil systems right after they were serviced and the tag read 78 or 80% efficiency and could only get 65% using three different testers.

Here are some figures on one Mod/Con which will go unnamed:

CO2 10.5%  O2  2.3% (10% excess air) 200° net stack 86% eff 100° net stack 88.% efficient CO 100 PPM air free.

CO2 8.8%  O2 5.3% (30% excess air)  200° net stack 85% eff  100° net stack  87% efficient CO 100 PPM air free.

There is very little change from one level of excess air and temperature to the other. Would perhaps one set of readings have been on low fire and the other on high fire?

Interesting thought Tim,,,

But if the heat is not lost up the chimney,, where is it going?
NG gives out a certain BTU perC/F or therm, if not wasted to higher stack temperatures (hence PVC use), does that not mean we are recovering more from the modulated flame?
Every M/C HX  may be too large 95% of the time,, but advanced burner technology & In/Out reset should make a huge difference.

How would one consistently alter the size of the HX to exactly match the flame at this "ideal" temperature?

Flame Temperature

Theoretical for Nat. gas 3600 Fº no excess air. Depending on exact composition of gas and excess air 1500 Fº to 2600 Fº.

Comparisons

In the industry we make technical comparisons but the customer only makes one, dollars.

Hmmmm...

As a start, I'd look at the different forms of heat transfer out there: radiant, convective, and conductive. A heat exchanger that is optimized for modulating boilers has to manage to scrub the flue gases just as effectively as when the burner is running on full-fire. I believe that is why we see a predominance of heat exchangers with very small openings for the flue gasses to pass through (i.e. a 1mm or less) in the condensing/modulating market. A radiant-dependent HX design wouldn't do as well for multiple input levels, IMO, since the flame luminosity is likely lower at low-fire than at high-fire. Not sure anyone does conductive HX, since that likely leads to CO, and other unwanted byproducts.

So, I would argue that a proper HX combined with modulation should yield higher efficiency (all things equal) in a furnace or a boiler since you're increasing the amount of surface area for a given amount of heat transfer. The charts that Viessmann has published re: Vitodens performance as a function of ΔT and firing rate seem to confirm that trend. However, the trick is for flue gases to have good contact with the HX surfaces, regardless of flue gas speed/rate.

Thus, I'd imagine that a very 'throaty' HX like the tubes typically found in the primary HXs of furnaces don't do as well at low-fire as at high fire since the flue gas flow at low firing rates may be a lot more laminar, thus insulating the hotter flues gases at the center of the tube. At higher firing rates, the turbulence caused by the inducer likely improves the HX performance. So the benefit of the HX surface area vs. required heat transfer may be negated by the lesser turbulence in the tube, leading to consistent AFUE performance across multiple firing rates or perhaps even a decline at low firing rates.  IIRC, Steve Ebels once tested a two-step furnace at both firing rates and found consistent AFUEs. 

Whether or not the burner has consistent combustion conditions at various input ratings is likely a function of design. IIRC, some current designs either meter the gas as a function of the air, while others meter the two completely independently. IMO, the independent solution is the better (tough likely more expensive) one, since it could allow you to account for changing caloric content in the natural gas, etc. in a way that a fixed ratio does not.

I noted with the many furnaces we just tore down at work that the secondary HX tends in condensing models have much narrower passages, sometimes with the addition of baffles, than in the primary heat exchangers. Perhaps not as sophisticated as some of the boiler heat exchangers, but clearly with the same aim: i.e. narrow passages scrub the flue gases more effectively than wide ones. Yet, on account of the lower modulation range of blower systems in furnaces and the lesser ability of air to transport heat (than water), I doubt that furnaces will offer the same wide range of inputs vs. boiler systems.

Other benefits

to modulation...when correctly sized, are much reduced starts and stops which in turn leads to better component reliability and seasonal efficiency. I don't intend this as an ad, but I've sold over 200,000 pieces of modulating Rinnai equipment over the last 20 years and when I first began living with the DV wall furnaces, I'd look at it operate and try to figure out, " now, why is it doing that?" My dv will start and stop on the t'stat in Sept and Oct, but by late Oct there is sufficient load to meet the 8,200 btu minimum fire. Last year the unit fired continuously from late Oct to March 24th. It simply modulated on the demand. It did not shut down in that period of time. It has done this for 12 years with no more than blowing off the fan blades and pcb area to keep dust off it. What, to me, is important is not how high a unit will fire but how low it will fire.Oversizing impacts the whole equation negatively.
What affect on efficiency does constant ignition have? The many propane companies who have installed these have said it is a dramatic reduction in usage for the customers as well as a dramatic increase in comfort. I can't offer the science you are looking for Tim, but this is my experience.

How about System benefits of modulation?

As far as I understand it, don't a lot of mod-con gas boilers expierience higher efficiencies at their lower modulation ranges?
There are other things to factor in too. Metal fatigue from constant expansion/contraction from short cycling. They say that cars would last much longer (as an example) if they were warm all the time instead of the constant start/stop of being turned on and off everyday.
There is something special about watching a mod-con fire at a nice low firing rate during a shoulder season knowing it's getting some nice efficiencies.
And even on a high temp load I think a modulating burner makes sense. How about the thermal expansion/contraction of your piping which flexes and puts pressure on 90's and joints as they expand & contract. This with a nice variable speed pump & outdoor reset (say in an apartment building) will reduce erosion and keep the pipes at a nice warm temperature to ensure just enough heat is given off.

combustion numbers

CO2 10.5%  O2  2.3% (10% excess air) 200° net stack 86% eff 100° net
stack 88.% efficient CO 100 PPM air free.



CO2 8.8%  O2 5.3% (30% excess air)  200° net stack 85% eff  100° net
stack  87% efficient CO 100 PPM air free.

These numbers do not surprise me when running a 180 setpoint,  it seems to me the differential is off a little and running a little rich compared to most Mod/Con boilers I am familiar with. As well as an elevated CO.

Excess air is more noticeable when running the boiler at lower temperatures according to the chart due to its affect on the boilers ability to condense.

eluv8 those figures are actually

the minimum and maximum readings allowed on a very popular MOD/CON.

I have requested from them what typical figures should be on low fire and high fire.

By the way 100 PPM for CO is not high for most MOD/CON that I have noticed in specs from manufacturers. Particularly on High fire you may see as high as 80 PPM to 125 or one manufacturer lists 135 PPM as a maximum. On Propane as high as 150 PPM. 

By the way I have invited my good friend

Jim Davis (NCI) to joins us in this discussion he may have some interesting insight to all of this. I hope he will be able to join us.

Lifecycle costs

Should we also be looking at life cycle costs?
Initial investment.
Maintenance
Replacement parts
Equipment life
I'm all in favor of energy efficiency.
But at what cost?

Lifecycle costs

Should we also be looking at life cycle costs?
Initial investment.
Maintenance
Replacement parts
Equipment life
I'm all in favor of energy efficiency.
But at what cost?

burky1957 yes we should but

would like to try to keep on target to the questions posed at the top of the post.

Thanks for the input and by the way each one of those could be an entire posting individually.

I would like to see

some figures posted here of actual combustion testing done on equipment at time of setup, then 6 months later or a year and get some comparison as to changes in efficiency as the units get older. Remember most of these require annual cleaning and testing. Anyone have such information?

Actually Tim,

I think ME had some data on his-own Munchkin unit he "purposely" left a few years to find-out exactly what you`re asking. Give him a shout.  ;-)  

Observations from a different perspective

Most of my observations are from Steam World (yea, I'm a Vapor Head), where the boiler temperature never changes regardless of firing rate and that modulation is base not on outdoor temperature but steam demand (as measured by gage pressure at the boiler).


Q: "When we look at say a 100,000 BTU boiler or furnace that fires on every call at full input is that efficient? Taking into consideration proper cycling rate."

Proper cycling rate is critical. Assuming we're load matched to EDR and the system is well balanced, firing the boiler at full such that it satisfies the Tstat as the boiler approaches pressure cycling, we're golden. I don't think we can get better than that. It rarely occurs but it sure is ideal. Given that combustion time, temperature and turbulence are important factors, as are the Temp diff across the heat exchanger and the heat exchanger material/thickness, we have the temp difference and turbulence working in favor of efficiency at full fire, as is the likelihood that excess air will be at its lowest.

Q: "If we however cause that system to modulate based on outdoor reset is it more efficient?"

N/A to steam unless working a vacuum subatmospheric system; I would say yes to HW if a) the HX provides proper turbulence b) air/ fuel mixture is constant, c) we are utilizing condensing technology and d) the returning water temp is low enough to allow substantial condensing.

Q: "Now what about the combustion issue? When we fire at less than full input into a chamber designed for full input what is the trade off?"

More time, less turbulence. HX design important here, i.e. water side flow rate, fireside surface area and gas passageway design. Some steam boilers with good modulating burners measure about the same efficiency regardless of firing rate. Mostly seen in some of the flexi water tube boilers like the Bryan. The old W-M MGB atmospherics (a tall, narrow boiler of low water content) claimed equal efficiency down to 20% firing. Perhaps somewhat a fictitious claim, but the unusual height and HX design might introduce enough added time for the gasses to transfer heat.

Q: "If we are firing at a lower input is excess air still the same?" Certainly not on an atmospheric with a draft hood!

Q: "Is flame temperature affected by modulating?" Educated guess here- I think the flame temperature is the same, only there's less of it. This still leaves the question of transfer characteristics thru the HX.

Q: "Which has the bigger problem with the modulating concept as far as efficiency the boiler or the furnace?" Dunno for sure but I think the boiler would have the bigger problem since the return water temp changes dramatically throughout the cycle and between cycles (and variable temp gain through the HX), whereas the furnace has a pretty predicable and low return temp.

So here's the flip side: On atmospheric steam with taller boilers (e.g. Peerless, W-M JS series, etc.), I have achieved excellent fuel savings per DD by introducing hi/lo firing even though the excess air has increased. The JS in particular develops quite a bit of excess air at a 45% firing rate. At this firing rate (which occurs when only one of two large zones is open) you can barely hear the burners, yet you can hear the steam rushing through the 6" outlet into the 8" header and through the 4" motorized globe valve. And this with a boiler steam pressure of less than 1# psig.

I can only assume that the benefit derives from the lack of short cycling (with the resulting steadiness of the steam drive and evenness of heat distribution) and the boiler design itself. It seems to me the where the excess air travels is of some importance. I recall reading some literature by Exhausto where they show one way excess air can envelop the flame, providing an insulating cushion of air between the hot combustion gasses and the HX surface. The greater the turbulence a design gives (like a tall boiler with rectangular "pins") the less likely that cushion is to develop in the worst possible place.

I use tools like this:

Combustion Efficiency and Excess Air

Reply from across the Atlantic (England)

Definitely a point for some discussion. Assumption here is that the system piping and duct work is compatible with the heating unit. A heat loss was done and system and heating unit are matched up.

When we look at say a 100,000 BTU boiler or furnace that fires on every call at full input is that efficient? Taking into consideration proper cycling rate.
- if any sort of burner fires at full rate every time, then it must waste a lot of energy overall, simply because it's using more energy MOST OF THE TIME than is actually required by the heating load.  Most boilers are over-sized anyway and need to be able to meet the maximum demand (ie. coldest predicted outside temperature) which is not the situation most of the time.

If we however cause that system to modulate based on outdoor reset is it more efficient?
- obviously!  In addition, there is the issue of type of boiler (conventional or condensing type).  If it's a high-efficiency condenser, then it's VERY unlikely that it will achieve maximum efficiency at full power.
- also VERY important to define your terms.  You have not stated exactly whether you are asking about a 'fully-modulating burner' setup or about weather compensation, or both. Burner modulation adjusts its RATE to match heat demand, with a modulation algorithm designed so that it slows down as it approaches a Flow setpoint and then maintains that Flow setpoint by burning at exactly the right rate.  Weather comp (aka
'outside temperature setback or reset') adjusts the Flow setpoint to match the heat-loss of the building and the furnace MUST be fully-modulating to achieve this.  The reality of most high-efficiency boiler designs is that they CANNOT achieve maximum efficiency at maximum temperature!  If the Flow setpoint exceeds (say) 75 degrees, it's most unlikely that the boiler will be able to condense AT ALL - the Return temperature will exceed 55 C degrees, above which condensation is physically impossible.  Most HE boiler control algorithms will prevent a delta-T of more than 20 degrees between Flow and Return, usually by throttling the burner to limit the increase in Flow temperature until the Return temperature catches up.  In a badly-designed system, you can get the situation where the Return temperature never rises enough and the boiler fails to reaches its setpoint.
 
Now what about the combustion issue? When we fire at less than full input into a chamber designed for full input what is the trade off?
- why would you design a furnace only to work at max output???

If we are firing at a lower input is excess air still the same? 
- with a zero-pressure governor, the fuel/air mix is close to stoichiometric.  Excess air is not present because the whole system is driven by the RPM of the combustion fan: increase fan revs = more airflow through the venturi = more gas pulled through governor = increased output at burner.

What is the Stoichiometric (ideal or perfect)  Flame temperature for Natural Gas?
This is well-documented all over the place but depends of calorific value (Wobbe number) of gas being used.

Is flame temperature affected by modulating?
- what's flame-temperature?  Sounds like a silly question but most burner-cap designs allow a wide range of gas/air mix pressures, so the flames can increase without much lift-off.  Temperature depends on measurement point but I imagine the temperature at the flame-tips doesn't change much.  OTOH, average combustion chamber temperature will vary a lot, according to burner modulation.  Trick of burner design is to achieve a good compromise between efficient combustion (high flame temperature) and acceptable NOx levels in the fluegas (lower temperature).

Which has the bigger problem with the modulating concept as far as efficiency the boiler or the furnace?
- don't understand the question!  (boiler, furnace = same thing?)

Are there any charts or tables available for determining comparison of combustion analysis related to input on low fire versus high fire? Compared to Flue gas temperature on low fire and on high fire?
- why should fluegas composition vary between low- and high-fire?  Ideally, it shouldn't!

A lot of questions hopefully we can get some good discussion or maybe just get us thinking a little more about what is really happening with all this new equipment

Reply from Dale Watterson

One more comment, my company is going to participate in the smart electric meter program where the appliance communicates with the electric meter to see what cost the load is based on time of day, night being cheapest usually. Anyway, I think eventually the pump/blowers will be maximized to run when the grid load is lowest. Perhaps not in our lifetimes but the young guys will see this. So, since gas or oil is a fixed time of day cost perhaps the cycling of the heating equipment will be maximized to the cost of the blowers/pumps. Always something to learn in our trade.
I numbered your bullets, hope that's OK
1. Heat loss, a very slippery topic since a lot of variability, let's say though that someone actually picks an input where the equipment runs 24X7 and keeps the house at 70 degrees at design, minus 10F here. In my 30 year career I only saw this once by the way.
2. The proper cycling rate is also interesting, I think Honeywell used to say 6 cycles per hour was correct for warm air, I think 4 cycles per hour for hot water and I always wanted 1 or 2 for steam, I think the efficiency suffers somewhat if we have full input and don't need it. I think the manufactures are saying this for warm air when the on/off condensing furnace is rated at 90 percent and the variable input at 94 percent or a little higher.
Since the warm air systems are the most common here I too always think of electrical load as well as gas and electric motors use more power at start up. I also know how little electricity is used by an ecm motor compared to a standard one, and that the ecm power requirement can be trimmed further is the heat rise can be kept up with reduced gas input because of lower load/higher outdoor temps.
3. Yes, given the problems with #1 it is more efficient although the spread varies.
4. I think the main trade off is slower response, I think the problem of combustion efficiency is fixed by a variable speed inducer motor that follows the gas input.
5. No, not in a major way if the inducer is variable speed also.
6. Good question, will need to look that up, I think 3500 degrees but will need to google it.
7. No, the flame temp. should not change, just the amount of heat. I have a tiny oxy acetylene jewelers torch that melts thin steel very nicely.
8. One problem we have seen is that there is a carbon monoxide spike when a step input valve changes input, it usually settles out with run time. I think the boiler has the bigger problem because the heat transfer is slower, sheet metal changes temp pretty fast compared to a boiler construction.
9. I think the low/high fire change over is affected by the step or variable method of input change. I am seeing more completely variable inputs, which I think are the best. I think the function of lowest possible flue temperature is really a direct result of heat transfer in the secondary heat exchanger, to me 90 degree flue temp is only 20 degrees above return air temp which mechanically is about as close as we can get.
　
Just a few thoughts Timmie, I'll be interested to see what others say, Take care, Dale
　

We have one customer

with an oversized W-M LGB on a large Broomell Vapor system. We hooked up the lo-hi-lo feature, with a Vaporstat to control it, and set it to drop at 3 ounces. The customer reported saving 40% on his gas consumption. Remember, this is an atmospheric with no way to control the secondary air.

40%. How much fuel could we save if we did this on every steam system out there?

All LGBs come with lo-hi-lo capability and most installers have no clue what to do with it, so they don't hook it up.

It HAS to be more efficient...

Modulating is it efficient?
Definitely a point for some discussion. Assumption here is that the system piping and duct work is compatible with the heating unit. A heat loss was done and system and heating unit are matched up.

When we look at say a 100,000 BTU boiler or furnace that fires on every call at full input is that efficient? Taking into consideration proper cycling rate.Driving tacks with sledge hammers has never been efficient. Nor has driving railroad spikes with upholstery hammers. THe biggest problem with fixed burn rate appliances, iks that they are only at their peak efficiency potential when they are running at 100% of their capacity, and theoretically, that only happens around 2 % of the time. In reality, the ACTUAL heat loss is typically 1/2 of the theoretical, so most appliances are oversized by a factor of 2. This causes a LOT of short cycling, which kills the efficiency of the appliance./b]

If we however cause that system to modulate based on outdoor reset is it more efficient?Outdoor reset has nothing to do with appliance efficiency. It has more to do with system efficiency. The problem I se with outdoor reset is the limitations of burners to be turned down. I had an off the record with a manufacturer about their ability to go even lower on their burner, and he said they had proven in the lab they they could go MUCH lower than they were, but certain quasi-governmental organizations did not recognize turn downs lower than what was being allowed, hence 20% minimums. This statement does not hold true for all appliances. It is a matter of burner design

Now what about the combustion issue? When we fire at less than full input into a chamber designed for full input what is the trade off?In my minds eye, there really shouldn't be any "issues" provided that all parameters surrounding the extraction of energy are in place, i.e. flow rate. When dealing with heat exchange surfaces, if the surface is capable of drawing off more heat than is being placed into the box, that equates to a higher fire to water efficiency in my minds eye. I am willing to listen to opinions to the contrary tho...

If we are firing at a lower input is excess air still the same?No, excess air has been very stable in every case of a modcon that I have looked at, within reason. Remember, this is a very tightly controlled combustion process, and with the introduction of the Lambda system, it will become even more efficient in eliminating excess air and associated waste. I believe that other than the ability to modulate, this is the one area that provides significant reductions in energy consumption.

What is the Stoichiometric (ideal or perfect) Flame temperature for Natural Gas?Beats me :-) What happens to the stoichiometric conditions if we inject pure oxygen into the process of combustion?

Is flame temperature affected by modulating?Again, I'm not sure, but I do know that I don't have the instrumentation available to determine it anyway. My thoughts are that modulation probably does allow for a lower flame temperature, but so long as all the other parameters are in line, what consequences are there?

Which has the bigger problem with the modulating concept as far as efficiency the boiler or the furnace?To my limited knowledge, full range 5:1 turn downs are not yet on the market for forced error furnasties, YET. My though is that it would be harder to maintain human comfort with a modulating furnace then a modulating boiler. It's not like people are standing right on top of the hydronic heat emitters, sensing different water temperatures. With forced error system, if you are anywhere NEAR a vent termination, anything less than 100 degree discharge is going to create a condition of cold skin surface, which is equated to discomfort.

Are there any charts or tables available for determining comparison of combustion analysis related to input on low fire versus high fire? Compared to Flue gas temperature on low fire and on high fire?None that I am aware of, but I do live in a laboratory, and have a good combustion analyzer, and a nice modcon boiler. Am recovering from one heck of a head/chest cold right now, but when I get better, I will run my system through the paces, and give you four or 5 points of data to analyze between the minimum and maximum burner capacities.

A lot of questions hopefully we can get some good discussion or maybe just get us thinking a little more about what is really happening with all this new equipment.In the last 10 or so years that I have been applying exclusively modcon equipment, I have not seen LESS than a 30% reduction in fuel consumption. The majority of these savings are coming from the shoulder (Spring and Fall) heating seasons. During the peak of heating demand is when I typically see the least amount of energy savings. I am sure others will echo that same sentiment.

Another interesting question would be energy savings in NON RESIDENTIAL or non SPACE HEATING systems. In other words, if I replace an 82% efficient copper fin tube boiler with state of the art direct heating modcon appliance in a restaurant setting, what kind of energy savings would I expect to se at a minimum?

Good questions Tim. thanks for asking.

ME

Test results

I intentionally cooled my home way down, open all doors, cranked all emmiters up, and tested at minimum RPM, and at roughly 800 RPM increments.

Ask away.

ME

Mark, let me look over those figures

and I will get back to you. Hope you are feeling better.

Looking at those

figures the one thing that stands out is at 1500 (low fire) excess air is 55.1 but the efficiency figure I come up with at that set of readings is 88%, the efficiency across the board stayed at between 87% to 89%. With that high a excess air the flame temperature would be cooled a little which may affect heat transfer but not enough to be a problem.

I agree with those figures pretty closely with two similar Mod/Con units I have tested. However they were brand new right out of the box. They were tested with room air at 70° F. Things change when air is brought directly from outdoors with no preheating before mixing with the gas. The heavier denser cold air gives higher O2/excess air in most cases. Concentric venting or preheating on these high efficiency units I have found really makes a difference. The good thing is that around 20° F and higher the figures even out. So it is only when air is down around zero that it would be a real problem as far as cooling the chamber and the gas flame.

By the way the Adiabatic Stoichiometric temperature is usually said to be between 3400° F and 3595° F. Adiabatic is a term used to describe combustion reaction in which all heat generated is retained in the products of combustion- none is lost to the flames surroundings. Stoichiometric is said to be perfect combustion with for gas 12.7% CO2 with zero excess air and 100% combustion efficiency. We are not there yet in fact far from it. It is rare by the way to find a flame temperature much above 3,250° F to 3,330° F. I believe Viessmann claims a little higher with the Vitodends 200 with Lamda Pro.

Very interesting Mark, so it would seem that from low to high fire there is not a lot of difference. It is also important to recognize that all of this is for boilers below 399,000 and furnaces below 150,000 BTU's.

So does modulation increase efficiency, I would say yes but it certainly depends on many other factors which have to be considered.

In talking to many manufacturers reps they tell me that the biggest problem with all of these units is improper installation probably caused by not reading the directions or not being properly trained.

A comparison to furnaces shows at the low end a much higher excess air so maybe a 10 to 15% drop in overall efficiency on low fire. On high fire the furnaces pretty much even out with the boilers I tested on high fire.

In comparison, et el.....

While I would have to double check my records on installs, the modcons I install seem to consistently see a drop in excess air at low fire versus high fire....I have not tested in the middle.  A drop in excess air at low fire would also permit easier condensing at low fire ( condensing threshold temp would be higher).....  which I would suspect may help overall seasonal efficiencies for most higher temp systems.  I suspect Mark's unit would work better for heavy cyclical loads such as laundry water heating, because as the input increases the ability to condense also increases.
Steamhead's input on a hi,low,hi steam boiler install is of interest too.  I have discussed this same type of installation with another installer and they did not see an improvement in fuel usage, but did see a great improvement in comfort.  However,  I suspect that STeamhead's boiler was a previous over sized install, where the other install was a new, properly sized install.  As to change in excess air on the LGB from high to low,  it actually does not do so bad, only about a 2% drop in combustion efficiency.  This is much better than other brands of boilers I have tested when using low fire. Pretty much every LGB I see, I pull the high wire wire and run at low fire only since nearly all are over sized.  
Using fuel usage changes from real world experience proves to be difficult to back up Modulating benefits. There are so many different factors going on.  If you are using a tight outdoor reset curve, how the system interacts with the structure I believe has a great impact on fuel usage.   Outdoor reset appears to reduce heat loss from the structure by greatly reducing stack effect air currents through a structure and the attendant air leakage.  This is why whenever I hear someone say "heat loss is heat loss" , I cringe.   It also tends to reduce overheating and under heating throughout the structure. 
With systems that use old cast iron or newer radiant wall panel emitters,  at lower water temps, the percentage or radiant output is increased versus air convection output.  Outdoor reset will keep the emitters cooler overall, increasing the seasonal percentage of radiant output.  This in return improves comfort at lower thermostat settings and reduces stack effect air leakage, both which reduce fuel usage. 
My longest term data re modulation of input involves small commercial space heating plant replacement installations where I have been using typical 80% efficiency on/off boilers in a step fired fashion, until recently.  These step fired heating plants have never delivered less than 30% reduction in fuel usage when compared to the previous 80% to 85% firing efficiency over sized, on/off boilers they replaced.   With step fired separate boilers,  excess air is obviously much more stable, since they are always running at full input.  However, outdoor reset, indoor feedback and other improvements are typically made at the same time.  Again, how much of this savings is due to "modulation" is a question.  It may be of interest that Burnham's data claims about a 10% improvement in fuel efficiency by step firing boilers, versus a single on/off.  It varies depending on the number of steps, however, going beyond 3 equally sized step fired boilers, the efficiency gains become very small in their tests.  This makes me think that a 3 to 1 modulation is where most gains can be achieved with typical consistent heat loads.

I guess the question is...

... can we find two Levittown or similar 'identical' homes in which to hang a Monitor MZ and another condensing boiler that also modulates? That's one way.

Another way is to hook up a BTU meter for a home and to compare a MZ-equipped home vs. one with a modulating, condensing boiler. Then compare how many BTUs go into the house vs. fuel use. See what the net difference is. Not too hard to do, a couple of thermowells, one or two flow meters, a WEL or similar data logger.

Going forward, I will be monitoring the fuel usage vs. the HDD in our home. I'm pretty convinced that we'll be saving fuel on account of the much lower standby losses associated with the Vitodens vs. a 30-odd gallon Vitola. I suppose a longer flue may help with allowing some pre-heating, but I think one grasps at straws when the return temperatures are in the mid-80's.

You're right

we didn't install that oversized LGB, we just hooked up the lo-hi-lo. It gets to 3 ounces quickly and runs on low fire for the better part of each cycle.

On a properly-sized steam boiler, the drop from high to low fire would only be just enough to shed the pickup factor. That's all you need to get a nice long burn without shutting off on pressure- even if the pressure is only a few ounces.

Tim, more information...

Interesting to see your theoretical efficiency numbers. The one number I recorded but did not report was the analyzers "Efficiency" numbers. Those numbers, that correlate with the readings taken were...

100%

100%

99.9%

99.7%

99.2%

98.8%

Per our friend Jim Davis, THIS is why we DON'T pay attention to that number,

But, I suspect my boiler is actually more thermally efficient than your calculations are showing. Tell you what I will do. Later today, I will hook the boilers computer to my PC and re-do all of these tests and show the actual fire to water efficiency and see how it compares to your theoretical numbers.

At one point, I did have the excess air lower on the bottom end, but it then made too much CO on the top end. Such is the nature of a negative pressure induction gas valve.

The other item I recorded but did not display was gas consumption. Those correlated numbers were;

11,600 btuH

21,101 btuH

28,730 btuH

43,941 btuH

49,800 btuH

62,250 btuH

Our natural gas is un-naturally derated to 830 btu/cu. foot by the utility. Guess they are worried about the pioneers hauling their own gas ranges and dryers up here from sea level in their Conestoga wagons... It comes off the well at 1,050.

As Ahnold Schwartzenegger said, "Ahl be bach"....

ME

I'm BAAAaaack..... It's not a tumah...

Greetings fellow flame heads.

As promised, I went back and re-evaluated the system, using the same parameters, while data logging the delta T's at the given test points. Of interest, when doing testing like this, it is nearly impossible to hit a point of  perfect equalibrium whereby the supply and return become dead nuts stable. Firstly, we are no where near design (OSA = 48 F) condition, so I am driving tacks with sledge hammers here, and the boiler keeps bouncing off the high limit setting. As my good friend Siggy would say, "It WOULD eventually hit a point of equalibirium, but where that point is going to be, and whether or not you can withstand those temepratures is a topic for another conversation on another day"...I suspect it would be out of the condensing mode when it did eventually hit equalibirium...

Ideally, in the "perfect" lab, I would have access to a very large stored volume of perfectly controlled water, and would run the boiler at a given RPM, until the supply temp stopped climbing, and then take a snap shot of that condition to assess "fire to water efficiency". Obvioulsy, I don't have that facility here. I will have it in Hydronicah, because I will have an Earth coupled heat exchanger that should have the ability to allow me to reach a point of stable equalibrium.

With all that said, I present you with the new findings.

Thanks again to Dave Davis of HTP for setting me up with this marvelous piece of equipment and the software to view it.

Enjoy!

Comments welcome.

ME

Quick question for Mark

What was the Supply and Return water temperatures?

Did the return water temperature remain stable during the test? 

If this is a condensing boiler operating below 130 on the return, it would be nice to see how much of an effect getting the excess air on low fire down would have on your efficiency.

Edit: Did anyone else hit the wrong X after looking at the pictures?

Cold, cold, cold.....

It never got over 100 degrees F on the supply. My system hits a point of stability within 2 minutes.

I could have data logged the S&R, but didn't think it was necessary or relevant.

I have two mass flow meters on my system. One on the hydronic side (2.5 GPM constantly) and one on the gas side. I did clock the meter and will post that information on Tim's post above.

This is a modcon boiler (Munchkin MC80).

Don't feel bad. I kept clicking on the wrong X as well...

ME

Mark my efficiency

numbers for what they are worth are taken from a chart I use for lack of anything better. It is set up with a 1023 BTU per cubic foot at .658 specific gravity. We really do need the manufacturers to release the figures from their testing in the lab under supposedly ideal conditions so we have a point of reference to work from. Also some accurate charts and tables would help.

I have found that using my five or six different testers it (my chart) is more accurate than the actual testers readings. As you know however real things we can look at are O2, CO, and net stack as far as combustion goes.

I have also found that you really have to test a various times and conditions and then try to average out your findings.

I have not seen any MOD/CONS I have tested that are much above 90% combustion efficiency.

Tim, regarding heat recovery...

I forgot to mention this, and I couldn't find my spare thermistor or I would have checked it, but my boiler has a 15' long concentric vertical counterflow vent, and there is another waste heat recovery heat exchanger that is built into the back of this boiler. http://www.giannoni.fr/Prod-ABSOLUT-CONDENS.html
I am certain that it is recovering waste heat out of the exhaust stream, but exactly how much I am not certain. In your calculations, you are probably using the Ambient air as the inlet temperatures to the appliance, when in reality, the appliance is pulling 100% outside air for combustion. What is the net effect of doing this?

The OSA was probably, heck, why guess.

at all RPM,s OSA= 45
What does this do to your efficiency calc's?

Do you need any additional information from me? This is at roughly 1 mile above S.L.

Thanks

ME

Mark,

I actually use a series of laboratory thermometers and strap on thermometers to measure various temperatures of both air and water along with surface temperatures of the actual boilers and furnaces to make some comparisons to jacket loss, along with piping and pickup. All not real state of the art but I have limited funds and do with what I have. It would be nice to have a setup like you have and live there to keep an eye on it.

I have three MOD/CON's that friends have in their homes that they let me play with. They are three different brands so I get a nice comparison and all three houses have similar set up and very close heat loss.

I did a lot of testing when with the gas company in conjunction with AGA back in the 90's on conventional equipment especially related to combustion air and dilution air temperatures and the use of barometrics on gas equipment with fixed draft hoods.

I have also done a lot of testing on warm air condensing units using secondary heat exchangers with conventional blowers. I have not had much opportunity to test furnaces with ECM blowers at this time. The number one problem with furnaces here in the northeast is insufficient return air by design. Many houses only have one return air opening and maybe two if you are lucky. This plays havoc with getting design efficiency out of these units. Much like putting a MOD/CON on a baseboard system and running it at 180 degrees and no ODR.

Thanks for all the good data, trying to get that from manufacturers is really tough.

Mark, how much more

efficient is the MC model versus the straight M version?

The conventional MC

is the same as the M except for its carbon composite water ways.

The MC Absolut Condense is around 2 points more efficient. To be honest with you, I am not really sure they are using the Absolut in their line or not. Suggest if you really want to know to contact HTP.

I know he brought a few over for field trials, but not sure if it ever caught on or not. May not be worth the extra Euro's...

Let me know what your thoughts are on my above numbers with the lower entering air temperature.

ME

Mark, if I remember

Chuck Shaw had mentioned to me they had done something with the Giannoni unit with a double exchanger to extract more BTU from the condensate, I never got a chance to follow up with him as he had left HTP by that time.

Give me some time to look over your figures and I will get back to you. I have some company coming over so I must leave Igor here in the lab for now.

Latent heat of condensation?

Tim, do your efficiency calculations take into account the efficiency gain from condensation? It seems your max efficiency numbers are topping out at  just below 90% which would be the case with ideal combustion and heat transfer, but not including the latent heat gain of condensation. This would possibly explain why Marks efficiency numbers are about 10% higher than yours (even though approaching 100% is unrealistic! ) which is the theoretical efficiency gain from complete condensation of the water vapor.

Mike your are

right on as my figures a purely looking at the fire. When you lower the input (Low Fire) the temperature of the products of combustion drop giving up more condensate assuming that the initial firing rate based on ODR was higher. This in turn with stabilization of the return water temp below around 130° or less will cause overall condensing to increase. All of this of course assumes that the installer set up the boiler parameters and outdoor air temperature reset curve correctly and is operating the system at it best input rate for outdoor demand.

The setting up of the gas valve/combustion air blower with a combustion analyzer is critical from the start. Failure to do this and maintain a stable flame environment causes many of the complaints and bad mouthing of equipment. It is typically not the equipment but the technician who is at fault.

Please do not take this the wrong way but many in the trade have a very difficult time with this new equipment. You have to sit down and read the manual cover to cover, sit in a factory training school, install and set up with someone who knows what they are doing, then do it your self with supervision and finally you are on your own (keep the tech center phone number handy).

How do professionals set reset curves?

I have a mod|con boiler which has three thermostat inputs. One is for the indirect-fired hot water heater, and the other two are one for each of my house heating zones.

The real issue is setting the curves on the two home heating zones. The defaults were way too hot for my house, so I now run the baseboard heating zone from 110F to 135F and that has been hot enough on the coldest day we had this winter (13.8F). I could lower the other end below 110F, but then the boiler short-cycles because the total heat load for that zone is so low that the boiler cannot modulate down far enough.

The downstairs zone has taken a lot of time to make right, and since that is the zone that takes the most heat, I have tried to get it to run almost continuously. I can do this at the warm end where I put 75F in in warm days (over 56F outdoors), and 120F at 0F. 14F is the design temperature where I live. I do not know if I have the cold end of the curve right, but it is OK, because it does not get cold enough, long enough, to be sure of anything.

I figured out the initial settings from my heat loss calculations (with the Slant/Fin program), and they would work (would work better than the defaults). But it seems to me that it would take a lot of nuisance trips by the contractor to get these right. In fact, I am still not sure of the very cold end because there are so few days anywhere near the design temperature. I think there were two this winter.

Do contractors usually make many trips to get this right? I do not see how they could afford the overhead of driving to the site, charting indoor and outdoor temperatures, looking at water temperatures and duty cycle on the circulators, etc. Setting the reset curve, if you know the values you want, takes less than a minute. Or do they set it what they think it should be based on the heat loss and hope for the best? I very much doubt most home-owners like tinkering with reset curves, if they even know they have them. I find it very interesting. When I did the heat loss for my house, it was necessary to make lots of assumptions. And these assumptions affect the outcome enough that, while they make good starting points, would not be really good for a final setting.

JD I am not sure we answered

your posting.

The setting of heating curves should be the responsibility of the contractor. If he he or she has done their homework it is fairly simple to do the reset curve for the customer. I would do a follow up once the heating season gets going with a phone call and then another call at the end of the first season.

I would if the customer is interested explain as best I can in layman's terms what the settings are all about.

Most contractors are not going to make multiple trips back to play with the settings.

This is why a lot of contractors find a boiler they like and are familiar with how to set up and then pretty much stick with that boiler.

From the service side we do not have that privilege and must be able to understand all of the heating equipment in order to properly service and adjust them. It means reading every manual there is.

Thank you.

As a customer, I agree that the contractor should set the reset curve(s) for a modulating boiler. I am not sure if a contractor would like a homeowner like me, one who read the entire installation manual for my boiler after he recommended the manufacturer (W-M) and model (Ultra 3), but before I even agreed with the proposed contract. And I also read John Siegenthaler's book. So I had a reading knowledge of how these things were designed to work, but no practical experience.

So I was surprised at their casual way of doing a heat loss, and then did one of my own.
Their design of the near-boiler piping was strictly according to the installation manual and the workmanship was excellent. (I had previous experience with this company before and had almost always been satisfied with their work.) They put all the required purge valves in, and so on. They flushed the system, it seems quite well, and so on. They then checked everywhere for leaks and found one slight one in a very difficult location and fixed it. They then started it all up to make sure everything worked. If they did a combustion test with instruments, I did not see them do it, but I could have been elsewhere.

But the reason for my initial question is that they set the reset curves to the factory defaults, and while this would have heated the house, it would have been quite inefficient and been as inappropriate as my non modulating old boiler. The main comfort problem would have been putting 80F water into my slab (radiant heating downstairs) at 70F outdoors and sloping up to 120F at 0F outdoors. (Design day around here is 14F). This resulted in severe overshoot from what would be right. I.e., I set the thermostat to 69F and it would overshoot to about 75 before the slab cooled down sufficiently after the thermostat was satisfied. I estimated the internal heat generation from appliances, etc., and looked at the heat-loss I calculated, and set the temperature, to 72F at 56F outdoors and 120F at -4F outdoors. This eliminated the overshoot in warm weather. On the coldest day, I had to change the other end from -4F to 0F for 120F water. That curve was pretty good, but the boiler, in spite of being the smallest they make, is somewhat oversized and will not modulate low enough, so it cycled more rapidly than I liked at the warm end. I raised the minimum to 75F and that is working quite well at warm outdoor temperatures, it can even run 24 hours a day and not get too hot or too cool inside. We have not had enough cold days to get the other end right (it may be right; I just do not know yet).

I would like to think that a professional could do this more quickly than I did, especially since at the time, my contracting company handled only W-M boilers (they have, since, added Peerless Purefire Boilers to their list), and should have been more familiar with the final setup. I think. It is clear to me that a contractor would not wish to make multiple visits to do this (unless a fussy customer were willing to pay an additional fee for the additional service).

I am not asking for criticism of my contractor; I imagine that would be as inappropriate as asking for what things cost here. The test, in my opinion, will be when they do the first year service. The Installation manual is quite specific as to what should be done, including disassembly of the heat exchanger and examining and cleaning it. doing a combustion analysis with instruments, and lots of little things. I wonder what I should do if they do not do all of it.

There is only one professional listed on this site anywhere near me, in case I choose to switch contractors for maintenance. I suppose if I am dissatisfied with their first annual service, I should first call the contractor, and if that does not resolve the issue, to call the one listed here and hope he is willing to work on W-M Ultra boilers.

JD it is a new world as far

as heating and cooling go. It behoves both contractor and homeowner to do their home work (literally), Failure on the part of both to properly set-up the system means inefficiency which obviously falls on the customer. In many cases it also means loss of comfort. We all must be diligent and if we choose to sell and purchase these high end products then get educated.

Speaking of curves with all of this new stuff we are all still on the learning curve.

We must ask questions and then hopefully working together we can answer them and learn and move on.

Many of the contractors who post here give this as the most important thing a homeowner can do, hire a good contractor who knows what they are doing and does it. You may pay a little more but it is truly worth it.The homeowner must insist on service after install as a part of the package and might I add be willing to pay for it.

I am not ready to complain yet.

I selected the best contractor I could, based on reputation and previous experience with the company who did some serious work for a building where I am partly responsible. They replaced all the previous duct work with all new insulated ducts (since it is a 200 year old building, and the ducts are in an uninsulated crawl space). That they did well. Later, we got cracks in some crappy heat exchangers, so they replaced those with new furnaces and zoned them. That they also did well. Since then, we have hired them to do the annual maintenance on the furnaces, electronic air cleaners, humidifiers, etc. Usually the technician who does the annual service is competent and diligent, but once in a while we get one who is pretty dim.

We have had experience with other contractors who did not seem to know what they were doing. So mainly based on that I selected the same contractor to replace my 55 year old GE oil burner (with a 30 year old Beckett burner) with the W-M Ultra 3 boiler. They also put in much more Slant/Fin in the upstairs zone so I could run lower water temperatures.

I had not expected to tell them what to do, though, as they said that they had already installed many W-M Ultra boilers already (mostly Series 2). And I chose to learn about this stuff just because I am interested in this stuff, not because I wanted to second-guess them. Their actual installation was just fine in terms of following the manufacturer's instructions.

At the time they installed my boiler, they handled only W-M boilers, mostly not the Ultra series. So I assumed they would be pretty familiar with them. I think my concern is that their maintenance department is not the same team(s) as the installation department. (It is a fairly large company.) My past experience with them is they do extremely well with installations. Their maintenance is rather different. They are quick in response to emergencies (if you have a service contract), but the routine maintenance does not seem to be the same people.

I guess what I hope is that whoever they send to do my annual maintenance next month is someone specifically trained on W-M Ultra boilers and not someone who knows only how to change oil burner nozzles and oil filters.

I am curious what happens to my warranty if I do switch to someone else to do the routine maintenance. I guess I will know in about a month, since the maintenance is scheduled for April 5.

First annual inspection on W-M Ultra 3.

I must say I am disappointed.

He did not follow the book on what to do on the first inspection. Actually, he did not even have the book, so I lent him mine. The very first thing to do is open the heat exchanger, inspect it and clean it if necessary. To do that, they seriously suggest having the gasket kit because it may need it and the boiler will not work without it. He did not have it. He said it was not necessary to do it even though the installation manual is very explicit about it, using lots of capital letters.

One of the next things to do was check the CO (less than 60 ppm) and CO2 (8.6% at high fire and 7.8% at low fire), but he did not have any instruments to measure those. It warns not to touch the throttle screw without those instruments. He did not know how to get it to go to high-fire and low-fire states. (Use push buttons on control panel.)

He was supposed to check and clean the ignition electrode, which he did not. He did not check the flue gas temperature. Nor did  he check the flame signal, the pressure relief valve , or the low water detector. He said they would reschedule when he could get a CO meter. Well, I hope it is calibrated and he knows how to use it.

So I guess the next step is to call the company and see what to do next. I get the impression that this technician was not fully trained on W-M Ultra boilers.

JD I am sorry you did not

get a very good result with your contractor. What is your location? I would like to connect you up with Weil-McLain and have them recommend someone.

I hope you did not have to pay for nothing being done?

I replied by e-mail...

I did not have to pay for the service call, since it is included in the cost of the installation. On the other hand, if I choose to go to another contractor, I cannot imagine they would want to do the job for free, since they did not make the profit on the initial sale.

I may have to eat that, though. Having a contractor whose abilities I trust is important to me.

First annual inspection on W-M Ultra 3.

Manufacture's Data

I wonder how much of this data has been done by the boiler manufacturers. In a early version of the Knight Mod-Con brochure they included a graph which showed the efficiency of their KBN boiler as a function of both the return water temperature from 50F to 160F, and also the boiler firing rate ranging from 20% to 100%. For some reason this graph is not in their latest publications.

Modcon efficiency graph

Here is a typical graph of efficiency vs return temp and firing rate for a modcon. It really shows how the efficiency increases above 90% as the return temp drops below the condensing threshold at 135F, especially at the lower firing rates. 

Confirms personal observations...

These beaut's really don't condense that much at full fire regardless of return water temperatures UNTIL the burner modulates back, and then, all of a sudden the heat exchanger surface is HUGE compared to the fire and load.

Oh sure, there is condensate dripping out at full fire and a return temp of below 135 degrees F, but it really doesn't start making a river until until the burner settles down.

ME

Thats right Mark, in fact

I notice with your figures stabilization starts to take place at around 3600 RPMS but that is also the lowest fire to water efficiency. The best is at the low end when maximum condensing could be occurring. So we gain two things, lower firing rate and higher heat transfer from condensate. I usually add 3% to 5% to all my calculated efficiency numbers so my 90% combustion average adding the condensing to the mix gives about 93% to 95%.

I have however had several units that had not been serviced in three or four years and I was getting combustion figures which would put them in the low 80's. Two of those had seen an increase in cost of operation from when they had been installed to three years later. After cleaning and servicing we got back up into the 90's.  

An interesting article....

http://www.aceee.org/energy/state/durkin_ashrae_journal.pdf

ME

Well this has been a very

interesting posting. I hope we have adequately covered the questions which I posed. There is an awful lot to all of this new technology and it requires a lot of study.

One unanswered question TIm....

What is the effect of the concentric heat recovery and preheat exchangers on the combustion numbers you generated?

Just curious...

thanks

ME

Mark I did not

really notice a difference until compared with direct feed of outside air when outdoor temps dropped below 20° F, excess air was increased and O2 went up and stack temp increased. As it dropped to around 10°F it started to climb even higher. I admit this was done by plan on a friends wall mounted boiler which I had told him I wanted to test when it got real cold. The night we did this test it got down to 7°F with a wind chill of below zero. This boiler had ODR and runs at a well set curve done by a local engineering firm here in RI.

All other testing at outdoor temps of 30°F or higher were very level in performance.

I would say if possible concentric venting is the way to go with all of this new stuff.

modulating more efficient ?

Let's see if this reply will make it.
Natural gas has a maximum flame temperature of 3590 degrees or 3600.  At stochiometric combustion-0% excess air or oxygen, it is producing 100% of its potential energy and converting it to useable energy.
At 3% O2(15% excess air) the flame temperature is about 3200 degrees.  This is about 5% less btus or 95% combustion efficiency.
At 6% O2(45% excess air) the flame temperature is about 2800 degrees.  This is about 10% less btus or 90% combustion efficiency.
Where do the btus go?  Nitrogen thieves!!  79% of air is nitrogen.  It becomes a heat sponge, absorbs heat and then does not give up any btus.
If an appliance is operating at 6% O2 it is releasing 90% of the btus in the fuel for transfer.  One would have to transfer 100% of this to be 90% efficient. 
I have seen many ModCon run at 3% O2 in most firing rates which is excellent.
However we come to the next problem of heat transfer.  Radiant energy releases 7 to 8 times more heat than convective energy.  The amount of heat released is determined by the temperature of a flame and its distance from the surface it is heating.  Anyone that is familiar with overhead radiant heaters knows that only objects within a certain distance get heated.  Imagine two campfires the same size.   One person is sitting within 3 feet of the fire and another person is five feet from the fire.  Both fires have the same energy but they are not transferring the same amount of heat to each person which in this case would be our heat exchanger.  Radiant energy is diffused elsewhere.  Therefore as flame modulate down their distance from the heat exchanger is increased.  I proved this fact 30 years ago with two pipe nipples and a couple of candles.  Anyone with my manual has seen the picture.
The next thing is convective heat transfer.  The flues gasses produced by the flame must scrub the remainder of the heat exchanger.  I will agree that ModCon designs are much more effective at doing this than furnaces and larger boilers and appliances.  But still there are some losses, but minimum.
When I read articles where someone states that typical flue temperature on water boiler are 250 degrees and on steam boilers they are 300 degrees, this person has very little experience on actual field operation, testing or performance.
I might mention that flue temperatures represent just a slightly lower temperature of the last pass in the heat exchanger.  If this is not at least higher than the return water passing across it,  the heat exchanger is being wasted.
ModCons would be 20-30% more efficient than an old boiler just because of their low mass.  Modulating burners do give high fictitious combustion analyzer calculations and unfortunately too many people today still think they are valid when in fact they are bogus over 90% of the time and the ten percent that are left are inaccurate 90% of the time.  Modulating equipment has a purpose when duct systems or piping systems may not be the best or when we are zoning.  It would be nice someday if someone actually put a single stage ModCon and a modulating ModCon on identical systems and actually measure how much fuel each used under equal conditions.  I am sure what the results will be but that still doesn't mean that there isnt a place for modulation but it will not be to save energy.
I think ModCon's are still one of the best things since sliced bread and hair spray no matter how they fire.

Radiant energy

Jim, It seems to me that radiant energy emitted from a source such as a candle,campfire or infrared heater would follow the inverse square law. The amount of radiant heat transfered would vary as the square of the distance. Double the distance and you get one fourth the heat. When the source is totally inclosed like the combustion chamber of a mod/con I can't see why all the radiant heat is not absorbed. There is no other place for it to go.

vary as the square of the distance

As distance from the (assumed point) heat source is increased, the amount absorbed per unit area does go up as the square of the distance. But the area of the load (in the case of a heat exchanger with the heat source with in it) also increases as the square of the distance. Thus, all the heat produced will be absorbed by the heat exchanger. This ignores that not quite all the heat source is surrounded by the heat exchanger. Some of it goes out the exhaust. You could close off the exhaust only in the case of something like electric heat, but then you would not bother with a heat exchanger.

Bob there is always the chimney

thats where the loss will be as combustion requires the introduction of oxygen and the release of the combustion products. They carry heat with them. In order to assure complete combustion a bit extra air is needed. The mod con can get the flue gases down in temp but not below the water temp. SO even with 90 degree F water temps warming a dwelling that is still at least 20 degrees above the target temperature. SO there is a guaranteed heat loss.

Where's the heat

I agree with you Charlie. I was referring to the RADIANT heat from the flame not the sensible or latent heat contained in the products of combustion.