Modulating is it efficient?

Mark Eatherton

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

Tim McElwain

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.

Mike Kusiak_2

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.

TomS

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.

Mike Kusiak_2

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. 

Mark Eatherton

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

Tim McElwain

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).

Tim McElwain

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.  

Jean-David Beyer

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.

Mark Eatherton

An interesting article....

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



ME

Tim McElwain

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.

Tim McElwain

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.

Mark Eatherton

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

Jean-David Beyer

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.

Tim McElwain

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.

Tim McElwain

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.

Jean-David Beyer

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.

Jim Davis_3

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.

bob_46

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.

Jean-David Beyer

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.

Jean-David Beyer

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.

Jean-David Beyer

First annual inspection on W-M Ultra 3.

Charlie from wmass

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.

Tim McElwain

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?

Jean-David Beyer

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.

bob_46

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.