Downfiring a 300,000 btu/hr American Standard Steam boiler?

Koan

Can one simply throttle back fuel supply by replacing the current gas valve, or is a combination of replacing the valve and burner assemble required? If I have missed the mark, how does one down-fire a burner? I have noticed in a Mapp gas torch that dialing back the gas too far makes the torch heat up a lot. Does the same thing happen if you down-fire a gas burner too far? Can you end up with combustion happening in the rail rather than outside of it? Is there a rule of thumb about how far you can normally "underfeed" a burner before problems arrise?

I am hoping to learn more about this. I understand it is necessary for a professional to do this work due to combustion analysis. I also understand doing nothing may be the best bet for now - or possibly until replacement.

I have an American Standard 3BN J2 boiler circa 1970. It has been examined by the best - @Steamhead . Pic of the nameplate below. He says I may have another ten years of service out of it, and obviously I do not plan on a replacement this year. It is not running yet this season as I have had all the radiators refinished and did a lot of neglected maintenance (the prior owner of the house was not aware maintenance was important). We have 399 sq ft of radiators and a boiler rated for 750 sq ft. Yup it is massively oversized. When the gas fires the meter clicks away like a playing card in the spokes of a bike. I assume I will get it up and running by the end of this weekend - the nights in Baltimore are getting a bit chilly.

I plan on clocking (counting ) the meter to verify the current firing rate to see if it is currently burning at or near its original capacity. For BGE customers the heat content is 1,050 Btu per cubic foot, so if at 300Mbtu/hr the 2 cu ft counter should go around in 25.2 sec. if it is firing at full rate. I am assuming this is the case for now.

I will attach pics of the boiler, burner, and gas valve assembly very soon.

Thank you

SWEI

The characteristics of the burner, the heat exchanger surface, the orifices, the flue, and gas pressure form a system of interdependent equations with multiple variables. Changing the firing rate from its design requires proper training, experience, and instrumentation. If the boiler is that far oversized, you will probably want look at making some controls changes once the lowest safe firing rate has been determined.

Koan

@SWEI
Like I said - I know this is not a DIY thing, but my mind is reeling trying to figure this out. I am not a pro like you all, but I learn fast and have a BS degree in Mechanical Engineering.

If you have the patience to explain I will be happy to listen, I really want to learn more about this. I won't endanger me or my family by trying this myself, but I do want to understand.

How is the minimum safe firing rate actually determined?
I assume one adjusts down the gas flow, matches the air, and measures combustion gas while observing the firing to "look" OK.

What controls would have to be changed?
Thanks!

SWEI

The combustion analyzer is set up, zeroed, and monitored as the appliance goes through light-off, burn, and shutdown. The behavior (dynamic) of O2/CO2 and CO readings during these three phases determines if there is a combustion problem and also indicates the cause. Adjustments are made until stable, complete combustion is documented.

After this, the firing rate can be lowered a bit (gas pressure adjusted or orifice changed, possibly both), tests are repeated, and adjustments are repeated, hopefully achieving good combustion at the new rate. Iterate until stable combustion is achieved at the lowest rate possible.

Tim McElwain

I will take some time tomorrow to address this posting. Right now I am exhausted after several days of being on my feet eight hours teaching.

Tinman

Just a couple things that may come up if you are going to de-rate the boiler. If you lower the gas pressure, it's possible you could have light off problems like delayed ignition. If you change the orifices and its a significant change, you could have flue gas condensation issues. I'm not saying either will happen, just that its possible.

Koan

@SWEI, @Stephen Minnich, @Tim McElwain Thank you all. I don't think it matters but our feed pressure is very low. I assume this only matters if you are increasing pressure not the other way around. Also the current system has a standing pilot that remains lit, and no flue damper... All very old school. I am very grateful for the education and you all sharing your gifts of knowledge.

@SWEI - I assume the only initial adjustments made on the existing setup are increasing or decreasing air openings to make sure the fuel/air mixture is not too lean or too rich. Is that correct?

@Stephen Minnich - I assume stack temp has to be above a certain point to prevent condensation. For natural gas is the minimum net stack temp about 330 deg f above room temp?

Thanks again!

EBEBRATT-Ed

If it is an atmospheric gas burner you would need to replace the gas orfice with a smaller one. the gas valve can stay as is.

That being said the firing rate must be high enough to keep the flue temperature from condensing, ignition and flame stability must be checked and Co2, O2 and Co must be checked.

It's adjustment and compromise

MilanD

I am new here so can someone correct me if I'm wrong: won't the lowering of gas flow and thus the amount of btus just take longer to boil the water on a boiler of the certain btu rating? Won't it just take longer to make steam, and in essence just burn off same amount of fuel, but take longer to do so?

We had a Weil Mclane LGB 11 at work, 1.3 million btu rating. Over the years, as burners would rot away, instead of replacing them, gas orifice was plugged and old rusted burner removed. By the time the boiler was finally replaced (we had the tech count rads and calculate edr and replaced it with an LGB 7), we were at about 2/3 of burners still in use at that time. It just took longer to heat the boiler than with all the burners.

This is a 1pipe 3 zone system on a 10,000 sq/ft building. We do have a nice big and new 50 gal condensate tank with the feeder motor. LGB 7 has, obviously, less steam volume, but the feeder keeps it filled and humming and it only makes up a little fresh water after few weeks of weekly blowdowns. I also think the positive of this setup is that it keeps the pressure down: each time the pump fills the evaporated water from the condensate tank, it lowers the op pressure. We heat everything on 7 oz of pressure, on a vaporstat pressure controller.

At any rate, I'm curious if anything will be gained by dialing down the flames. If anything, just remove a few burners and plug the orifices of the removed burners. We did this for at least 20 years on the LGB 11.

Koan

@MilanD brings up a good point, but I assume the having a boiler and burner rated for 750 EDR and 399 EDR of radiator area means I'm wasting fuel by making too much steam too fast and the burner cycling against the vaporstat.

From what little I understand, we are looking for 5-10% excess air above stoichiometric while keeping net stack temp high enough to prevent condensation.

What should the minimum stack temp be, and is that net above room temp or just gross stack temp??

I assume this results in approx 11% CO2. Leaning the a/f mixture out above stoichiometric 10:1 ratio by volume. So this would translate into 11:1 air to CH4 by volume. Cannot reduce the fuel below the 5% concentration lower firing limit or increase above the 15% upper firing limit or no joy at all.

So basically it is a trial and error process - Limit fuel, then adjust air to 5-10 % excess above the chemical optimum, measure CO2 trying to hit about 11% and O2 trying to hit about 2%, monitor the nastier gasses (CO) that show poor combustion (not sure what we do with this?) and measure net stack temp to make sure we can vaporize the H2O byproduct.

I guess the trick is to "know through experience" about how much you can limit the fuel for a given setup and adjust the air to get a sufficient stack temp and trade the stack temp vs the excess air.

Of course all this is sheer speculation on my part. That is why I am here asking for input from those who know this. Again my thanks.

SWEI

There's far more to this than adjusting air shutters. I'll defer to Tim, who teaches this stuff and does a great job of explaining.

On the controls side, I was suggesting PWM control of burn times (Tekmar 279, Heat-Timer, Eco-Steam) which has proven effective at taming oversized steamers.

Koan

@SWEI - I get that this is a combination of science and experience. I lack a bit of the science, and almost all the experience. I have to rely on good, knowledgeable, experienced people like you for help with that.

I mentioned limiting fuel first, then adjusting a/f mixture by adjusting air and measuring combustion gasses and stack temp. I don't think my post indicated that this was a simple solution of adjusting air shutters. I agree that just adjusting air shutters can only provide tuning for the existing setup, and I think doing that alone can only tweak what currently exists.

Thank you for the information about controls and Pulse Width Modulation - I was not even aware that could be an option, but it makes sense that it would work! Thanks for the hints on controls!

captainco

MilanD made the best comment in the fact that it will take longer to make the steam and use just as much gas if not more. Also dealing with the flue temperature. What most don't understand is the flue temperature is not the flue gas temperature but the mixed air temperature above the drafthood. If that drops below 275 degrees there will be condensation issues. The differential on the vaporstat should be set to the max to lengthen on and off time. De-rating can be a big mistake in this application.

John Mills_5

I was doing combustion analyzing training today, using a 2 burner 80% furnace. Burning beautifully for a 20 year old beast we removed. Tech partially covered the orifice for 1 burner making that flame a bit smaller. Instantly the CO produced went from almost nothing to dangerous. So as has been said, anytime playing with stuff like that, be sure to have it checked to be safe. Should have that relic checked anyway!

Tim McElwain

I agree with captainco who knows as much about all this as I do and then some. I am not a big fan of derating (downfiring) design equipment. In doing so it has been my experience that overall efficiency is affected. Many boiler engineering books will give some specs on reducing input to somewhere less than 10%. The simple way is too simply reduce gas pressure slightly and using a combustion analyzer see what happens to your readings. This should be done by someone who knows what they are doing.

As for typical numbers on the equipment we are talking about here 7.8% CO2, with 7.5% O2 will be about 50 % excess air and with a net stack temp of between 400 to 500 about 75% to 78% combustion efficiency.

Keep in mind it takes 1 btu to raise one pound of water one degree (F) up to 212 degrees water and then an additional 970 BTU's per pound to turn 212 degree water into 212 degree steam (latent heat of vaporization) . That being said that is why I am not a big fan of reducing input to steam boilers.

By the way adjusting primary air (air shutters) has very little to do with affecting efficiency other than the fact with gas we want a soft blue flame (no yellow), not roaring, not lifting and not floating around.

As always keep CO below 100 PPM air free. And last but certainly not least make sure your draft is adequate at all times (air for combustion) a negative .01, .02 .03 is satisfactory.

I hope this along with Jims comments answers the question you posed to me by e-mail. Jump in Jim if you think I missed anything.

Koan

@captainco Good insight and good information.
Thank you.

I disagree the efficiency would be indifferent or worse due to a slower heating rate. In fact, much of my reading suggests steam systems benefit from longer run times which is why temperature set backs do not work as well with steam systems. Though this may be anecdotal, it is repeated often in the steam section of this forum.

I assume the significant thermal capacitance (thermal mass) of the boiler itself should have some impact , and the fact that I simply cannot use all 300Mbtu/hr from the gas coming in. I realize these systems act in concert, but if I can only use 160Mbtu/hr of gas to heat 400 EDR of radiators, I am burning 140 cu ft per hour more gas than I can use. Assuming I could get down to 200Mbtu/hr and have efficient combustion, I would save 100cu ft per hr run time. as long as the burners would not need to run an extra 33% I should save fuel.

Of course this is all theory, and the only pragmatic solution may be to replace the whole system with a correctly sized boiler. But until then, if I can lower costs without huge expenditure, it is worth exploring.

Tim McElwain

MilanD
At any rate, I'm curious if anything will be gained by dialing down the flames. If anything, just remove a few burners and plug the orifices of the removed burners. We did this for at least 20 years on the LGB 11.

This is not a god idea and should really never be done as it changes the entire combustion process of the boiler or furnace. It also can result in high bills.

Koan

well - it was worth asking.

Thank you all for sharing your knowledge. I guess I was tying the set back issue to trying to keep a more steady lower usage rate. Any more comments are welcome and appreciated. It seemed to make sense. The higher usage is what I'm trying to avoid - and then there is the inadvertent CO issue.

Thank you all. I am disappointed but safer and better educated thanks to all of you. I enjoyed the conversation.

Just to clarify - @Tim McElwain you stated

"Many boiler engineering books will give some specs on reducing input to somewhere less than 10%."

Does this mean that with factory guidance a burner can often be safely de-rated by 10% by reducing pressure if it is a bit too much - so that there can be some safe tailoring to a specific application?

This I am asking for a future solution, to to tweak the current one.

Thanks again.

Koan

@Hatterasguy - ok - so at least I'm not crazy (at least in this instance). I did read this !
I do not yet know for sure as this is my first real heating season and the boiler isn't even up and running (soon though) - but I believe my system did cycle on pressure last year.

Please let me confirm I understand what you wrote.

1) down-firing means less combustion efficiency due to an increase in excess air - but at least that keeps stack temps up to prevent condensation.

2) says it all - longer run times even at slightly reduced combustion efficiency can mean higher system efficiency.

3) A steam system cycling on pressure is really inefficient from a system standpoint. It can easily happen on very oversized boilers or if one attempts to raise room temp too fast. If down-firing prevents a steam system cycling on pressure it can easily be helpful and lead to greater efficiency.

Do I have that right??
Still I know the best solution is to correctly size the boiler, and that will eventually happen, but for now I would like to do what I can if it makes sense.

Thanks!

MilanD

@Tim McElwain Thanks for the comment. I am not sure all the mechanics and physics behind it when taking out burners and plugging orifices. Someone in a comment above wrote about CO spiking. We didn't experience this. Although this was a large Weil-McLane LGB 11, in a dedicated boiler room with plenty of ventilation, and we never really measured it. I'm sure it's not as efficient with less burners as it takes longer to cook, so to speak. But isn't this exactly what you all are talking about doing here? Less flame for a slower burn - or a more of a 'simmer' like burn? As to flue temps and alike, I can't speak to it. And I am only writing this as this was what our old-timer heating guy did to keep the boiler going and it seem to have worked. He is now in his 80s and his dad operated one of the largest heating businesses here in town in the 30s, 40s and 50s. And for all I know, and what you are saying, he might have been wrong - but he limped that old LGB 11 along for 20 years before we were able to replace it. Coincidentally, the boiler distributor came out, measured radiators and we replaced the old LGB 11 with an LGB 7, which tells me the original LGB 11one was oversized to begin with and our less burners thing worked just fine.

@Hatterasguy - what does "cycling on pressure" mean? Always and quickly hitting the upper pressure limit and then short-cycling in it?

Again - I am not sure and can someone explain to me (maybe I should start a new thread on this): how bringing on the oversized boiler to make steam and then short-cycling it (as long as the thermostat is calling for heat) is bad? I see how it can perhaps produce too much steam head for the pipes to handle and this being an issue. Is this an issue @Koan ? So, if I understand this, you want to roll the water on 'simmer' so to speak, creating less of the steam intensity, and slowing down the volume of steam, right? In my analogous mind, this would be like taking a pot of water and moving it from a larger to a smaller burner. So, how can that be achieved with an oversized boiler if what we had done with our LGB 11 was not this exact same thing?

I'm new here, and I apologize if all these questions are irritating. This is a fascinating topic! Thanks everyone for letting me chime in.

captainco

One of my field experiences that I share in class is a hospital steam boiler that was well oversized for the load so it was de-rated. The way the boiler and controls were set up the boiler ran 24 hours a day, seven days a week. I told the hospital engineer that not only was this costing energy but it causes the boiler to require more maintenance.

So I helped him tune it up close to its normal firing rate as possible and then eliminated most of the modulation. The boiler was cycling on and off every 4 to 5 minutes.

Twelve months later the engineer called me to report that they had over a $100,000 reduction in gas usage and the boilers needed almost no maintenance.

Energy is transferred two ways in most heating equipment - Radiant Heat Transfer and Convective Heat Transfer.

Radiant Heat Transfer requires two basic elements: It must be Hot and then it must be in Line of Sight. Lowering gas pressure screws up both of these.

Convective Heat Transfer requires several elements also: It must be Hot, must be of a Mass to heat the whole heat exchanger and it must have Residence Time. All three of these are lessened when underfiring by adjusting gas pressure. I am pretty sure these are laws that man cannot violate.

captainco

I am pretty sure a hospital engineer has to do hospital energy audits every year. Burners heat heat exchangers not radiators. I can keep my car idling in the parking lot 24/7 but I doubt I will save gas.
This was one of hundreds of buildings this was done on over the years, each and everyone producing ten of thousands of dollars in savings. Boiler re-tubing was practically eliminated and burner motor failure was not even questioned or a problem. However maintenance was a major problem before these changes were made.

Working with a boiler repair company years ago, the owner wanted to know why sections kept failing and boilers needed constant re-tubing and repair, including the flues. After class he discovered 100% of the equipment that was failing was underfired and modulating.

Heat Transfer = Temperature, Mass, Line of Sight, Residence Time and Specific Heat Capacity of the Heat Exchanger.

The first type of equipment made that could maximize this at most firing rates is the Mod-Cons and those blow my mind. Other than that, any other equipment firing at less than their rating wasted the maximum amount of energy.

Koan

@MilanD
I am enjoying the conversation as well, it is great to learn more. My system runs on a vaporstat set to cut out at 12 oz of steam. As I recall, ( I was not in the house much of last year's heating season) any attempt to increase room temp more than a couple degrees would result in the vaporstat shutting down the boiler on the 12 oz. limit before the thermostat was satisfied. I will know more after this weekend when the beast is hopefully resurrected.
@Tim McElwain @captainco @Hatterasguy
I am humbled by your collective knowledge and experience. I appreciate you all engaging on this topic.
I will provide more facts as they become available. I have done a lot to get this boiler ready for service this year - more than I bargained for. I must have flushed easily ten pounds of solid gunk out of all the parts of this system including the pipes that had to be replaced.
Thank you all for sharing your knowledge.

Is it possible that while down firing is sub optimal from a combustion standpoint, it may in some situations like this one be more optimal in correcting for an oversized boiler cycling against its pressure limit?

I note that Smith makes an 8HE-4 boiler with two different ratings 175Mbtu/h input for 471 Sq ft EDR (radiator surface) and 210Mbtu/h input for 558 sq ft EDR. Same boiler, different burner (or just a different nozzle or orifice). The lower firing unit works at a 1% higher AFUE. Carlin makes EZ gas pro burners specifically for the Smith 8HE-4 at 157Mbtu/h and 175Mbtu/h. So to my naive eye it seems some tailoring is meant to occur. I understand that this is different than dialing back gas pressure, just noting that the differences exist fort the same boiler to tailor to different EDRs.

Koan

@captinco Mod Cons are all hydronic correct?? not steam

ChrisJ

Koan said:

@captinco Mod Cons are all hydronic correct?? not steam

Steam is hydronic.

Mod-cons typically are for hot water though, yes.

Koan

@ChrisJ
thank you for the clarification. Hydronic = hot water or steam
Mod cons are all hot water.

Would it be possible to have a mod con steam boiler??

ChrisJ

Hatterasguy said:

Koan said:

Would it be possible to have a mod con steam boiler??

You can get the "mod" to a limited degree.

You can never get the "con".

Sure you can.
You just need a really tall chimney and a restriction at the air inlet of the boiler.

I'm not sure what "really tall" is, but it sounds possible..
Unlikely, but possible.

Koan

@Hatterasguy , @ChrisJ
Is that because because the temps required to boil water are higher?

ChrisJ

Yes

captainco

Your boiler should not be running higher than 8 oz of pressure as a rule and the On/Off differential should be 7-1/5 oz. In other words it should almost go back to zero pressure before coming back on.
Most burners only fire efficiently at High Fire with minimum O2 @ 3-4% In the lower firing rates the O2 is 5-7% and sometimes even higher based on the burner design. We are making the same amount of BTU's no matter what. But there is something entering the equipment that steals the heat and that is the nitrogen thieves.

Flame Temp @ 3% O2 = 3200 degrees
Flame Temp @ 5% O2 = 2900 degrees
Flame Temp @ 7% O2 = 2650 degrees

Where did the temperature go? For every 1 O2, there are 4 N's. Those little N boogers stole the heat!!

On large equipment every @ O2 above 3% equals a 2% loss of efficiency. That equates to around $500 per percent per 1,000,000 btus or $50 per 100,000. Every 30 degrees your flue temperature is low is another 2%.

Example: Steam boiler 8 oz pressure power burner/3 pass
Ideal readings:
O2 - 3%
Flue Temp - 385 degrees(minimum)

O2 - 5%
Flue Temp - 355 degrees

O2 loss = 2 X 2 = 4%
Temp loss = 30/30 = 1 X 2 = 2%
Total: 6% loss @ $500 per % per million or $3000

SWEI

Koan said:

Would it be possible to have a mod con steam boiler??

Yes, in a vacuum system. @IgorZhadanovsky has proposed doing so in one of his papers.

ChrisJ

Are we talking an increase of O2, or an increase of air?

Koan

Hi All
what this seems to be leading to is that there may be value in down-firing, prticullarly is we are short-cycling, but several parameters must be very carefully monitored to prevent some really bad things such as death by CO, or condensation in the chimney due to low stack temps, or really inefficient combustion. It may also be that any tweaks could just not bear enough fruit.

What I assume would be better if possible would be to install a lower output burner assembly (gas valve and rail). But I figure this just may not be worth the expense. It seems the gas valve and rail configuration is more or less matched, so alteration to the gas valve pressure to lower output is "iffy" and requires absolute and careful combustion monitoring if done at all.
Does this make sense so far?

MilanD

It was interesting to listen to all this. Half the time I'm lost in all the ratios, co and O2 %... but here's a few more thoughts for @Koan and the rest of you:

1. Link below talks about Tekmar 279 controller. Looks like, if to save fuel, one needs to smart-up the boiler controls, esp. the oversized boiler. @SWEI mentioned it above. I think before monkeying around with derating boiler that was engineered to work a certain way, use the smart controls. That's why they are there. And it'll definitely be safer. Here's a forum talking about it with people's practical explanations on settings, and what it did for them http://forum.heatinghelp.com/discussion/135476/tekmar-297-steam-boiler-controller-share-your-settings Some of them talk of how this set-up waits to cycle the system.

2. Cycling on pressure: All we ever read about here and elsewhere, and know from practice, is that the pressure in the boiler needs to be as low as possible. Right? So, why not just make sure your venting is as good as it can be - use big-mouths everywhere you can on the main(s), and balance the radiators with the vents that are venting at the increasing rates the farther you go from the boiler. Then, go to the farthest radiator and when it gets hot, see what the pressure is at the boiler. That's enough steam. Then, make set-back on the vaporstat 0psi, and you are in business. Better yet, sit by the boiler and get a helper to sit by the radiator (you'll be warmer). Set the operating pressure to 1/2 pound, and when the pressure builds and shuts the boiler off, ask your helper if the rad is hot. I am quite curious if in fact the last rad would get hot before the pressure builds, even if boiler is oversized . If no, try to improve venting even more - put larger orifice vents everywhere and start the process over.

Once the steam gets to the last rad, set your vaporstat to that pressure, and then tinker with that setting, vents and the set-back to achieve as efficient air elimination from the system as you can. We all know there is no point in cooking water above 1 psi, and sometimes even 1 psi is too much. Low operating pressure will prevent you from cycling on as high of a pressure as the pressure will be very low, and should, in practice, only turn on to make more steam when the system is back to 0psi.

Another thought as to cycling on pressure: if the pressure is low and setback is back to 0 psi, even if it short-cycles (which is good as it's not as wasteful as overpressurising to 2-3-4 psi would be, for example), that new steam and it's latent heat won't be wasted. It's in the pipe, at ounces of pressure, on its way to the radiator, waiting for other steam to condensate, shrink 1,400 times and to take it's place and continue to give of its heat into the room as long as the thermostat calls for heat. If I'm not mistaken, waste comes from excess pressure. So, if you are at 6-7 oz, you are not wasting anything beyond what's needed to heat the room and that pipe to the rad will be hot and happy.

Now, you are still are cooking a larger pot to make steam, and burning more fuel to do so - but also creating more volume of steam in the process. 80% efficient is the same for 300 and 600k btu boiler, it's just that the 600k one is of a larger capacity and makes more steam by burning more fuel.

I am again going back to my small burner, large pot analogy and bring back that Tekmar controllers can help large boilers to be more efficient without the expense of replacing the boiler.

Last thought and question on derating: To make steam you need 212 btu + 970 btu per pound of water. Your oversized boiler has exactly the amount of energy in btu coming from burners to efficiently, at that volume of water, create steam. It's a bigger pot, so it'll create more steam with the amount of energy coming via burners. If you try to derate it, someone mentioned it can't be done more than 10%, and that it is quite technical. Analogous to it, I also mentioned that we had an LGB11 1.3 million BTU monster, that our old-timer heating man ran on 2/3 of burners (plugged orifices as the burners were rotting away). I also got a comment that this would be inefficient and waste energy. Well, if for that size of the boiler, less burners (in essence less BTUs coming in) wasted energy, how is derating the boiler any different? You are taking down the amount of energy coming in, all the same, whether you remove a burner or 5, or derate them all to burn less intensely.

So, to your question @Koan - If I were you, I'd look into Tekmar 279 and other gadgets that attach to it to make best use of the system you have, and make sure the vents are as open as your windows. If anything, call Tekmar and talk to someone there. They should be able to tell you exactly how to solve your problem and would be, I am sure, very happy to sell you one.

Good luck - and thank you everyone for such a stimulating mental exercise with this thread. Peace and Happy Thanksgiving!

Tim McElwain

As O2 is increased so is excess air which means a larger package up the stack and an increase in stack temperature.

The three "T's" we look at TIME, TEMPERATURE AND TURBULENCE all have an affect.

TIME - how long are the products of combustion allowed to stay in the heat exchanger? The longer the better as related to combustion testing otherwise the high velocity created will cause more heat to go up the stack.

TEMPERATURE - related to flame temperature and thus the actual temperature of the products of combustion in the heat exchanger again affecting heat transfer to make steam, heat water (forced hot water) or affect warm air temps on forced hot air.

TURBULENCE- this is related to the design of the heat exchanger but also to the draft device which actually affects all of these.

That is why using a barometric (automatic draft control) is better than a fixed draft hood.

After over 50 years in dealing with equipment in the basement and having installed over 3,500 gas conversion burners it is critical to have done a survey to determine heat loss, radiation EDR and duct loss on warm air or gravity warm air and also losses related to gravity hot water.

That should have created a system which was correctly sized. It was and is however the case that many times the systems were over fired (over sized). In attempting over the years to try and correct these mistakes and reducing inputs to equipment the process of reducing inputs especially to steam was not a good one. Firing equipment at its designed firing rate and doing a combustion analysis to accomplish that it is in my expert opinion thebetter way to go. With steam it is not a good idea to underfire. I have however been somewhat successful on forced hot water as long as I stayed with in the engineering specs on the boilers usually a 10% or less reduction in input accomplished by pressure adjustment in most cases. Power gas conversion burners single orifice actually made orifice size reduction and pressure adjustment the best combination. In all cases with conversions we used a double swing barometric which helped tremendously with accomplishing higher combustion efficiency results.

My follow up with every customer I ever did any kind of adjustments or analysis was to come back in a year and look at dollars saved. That to me is the true test of efficiency.

captainco

When you are adjusting air only the O2 and flue temperature have a 1% effect. However when you are adjusting fuel there is a 2% effect. On the boiler mentioned earlier the actual calculated combustion efficiency went down. I think it was in 1990 I discussed with an analyzer manufacturer how erroneous and bogus combustion analyzers calculations are for efficiency.

But you have to understand combustion to understand why they are bogus. What percent of fuel is actually sensible energy versus latent energy and how much do you lose if you don't condense. Next at what temperature do you have to burn natural gas to make 100% of the sensible heat available for transfer?(3600 degrees).

Why did a homeowner save 600 gallons of oil when we took his oversized oil furnace from 1.25 gal (de-rated) back to 2.00 gal?

As a national trainer I do not have room to make up stories that are untrue as they can be easily be disproven and in over 30 years that has never been done and that ain't cuz I is so smartz.

When I told a commercial appliance service tech I would help him tuned up some 2.5 million btu boilers at a nursing home but he needed to charge $600 each. They were slightly underfired. The nursing home engineer just about passed out but got approval. 12 months later he calls to say thank you for saving him over $27,000. I knew we undercharged but this was charity work. Almost took us 30 minutes to tune both boilers.

Maximum efficiency of non-condensing boiler - Hot water 180 degrees natural draft
O2 = 6%
Flue T = 450 degrees Net = 380 degrees

100% Starting point
- 14% Latent heat loss
- 6% O2
- 12.5% Temperature loss 380 degrees/30 degrees
- 32.5% Total loss or
-
67.5% efficiency.

Now check the combustion efficiency calculator and see how close it is! 79.5%???

I am only here to help and to teach not criticize. This is not meant to be an augument. I hope this is an educational and meaningful conversation. I am the least skilled person here when it comes to using hand tools. I bleed easily!!

We know what we know until we learn better. It is in our customers best interest to continue to seek the truth.

Steamhead

When I do the combustion test on Koan's boiler, I'm sure he'll share the printout with all of you.

Steamhead

captainco said:

I am pretty sure a hospital engineer has to do hospital energy audits every year. Burners heat heat exchangers not radiators. I can keep my car idling in the parking lot 24/7 but I doubt I will save gas.
This was one of hundreds of buildings this was done on over the years, each and everyone producing ten of thousands of dollars in savings. Boiler re-tubing was practically eliminated and burner motor failure was not even questioned or a problem. However maintenance was a major problem before these changes were made.

Working with a boiler repair company years ago, the owner wanted to know why sections kept failing and boilers needed constant re-tubing and repair, including the flues. After class he discovered 100% of the equipment that was failing was underfired and modulating.

How far down were they modulating, as a percentage of maximum input? Was the stack temp going too low?

Koan

@Steamhead
Right you are my friend! I wouldn't touch this without your help.

I assume you are still busy working out the kinks of boilers that didn't quite run right as heating season started. Besides, the last 3 radiators are still sitting in the living room waiting to be muscled up the stairs. I keep looking at them and wishing they would move by themselves.

Should have it all fired up by Sunday.

Lucky for me it has been a warm November. Hope all is well with you.
Kelly

captainco

hatterasguy, you are using a theoretical combustion efficiency chart, which by the way no one knows where it came from, as fact, and my facts as theory? I discovered way back in the 80's the efficiency charts are bogus as a $3 bill. As long as people continue to use them energy usage will stay high and possibly get higher. Today the charts calculate new furnaces to be 99.9% efficient.
We measure actual btus transferred and compare to fuel usage. Now most of what NCI does is air related but it doesn't matter. If the calculations aren't close for furnaces they won't be correct for boilers.

Tim McElwain

Keep in mind much of the efficiency on Mod/Cons has to do with smaller chambers and very direct heat transfer. I am not sure if present combustion analyzers really get it correct. I for one do not always follow the manufacturers recommendations to only touch the throttling screw. Sometimes a pressure adjustment is in order (I do not however recommend the run of the mill service tech touch the pressure screw unless you have been properly trained).

The concern here is that Koan has an oversized piece of equipment and should really be looking at replacing it.