modulating atmospheric gas boiler?

archibald tuttle

started this thought experiment in our thread about fine grained pressure control for steam.

now since atmospherics aren't set up for condensing, not as much attention has been paid to modulating them.

here (excepting our discussion of vapor steam) we're not talking about anything like modulating for condensing temperatures but modulating to keep very low steam pressure rather than short cycling.

so just thinking of the theory of it, most venturi induced combustion (if that is the right terminology) where there is no fan forced air or air gas mixture for combustion modulating the gas flow inherently modulates the air flow without other adjustment to allow for a range of btus -- see gas stove burner or gas grill.

so i'm assuming the same thing would work fine on an atmospheric boiler. I've encountered two stage gas valves before but they have something to do with startup as i recall and didn't modulate for temp or pressure control during the standard cycle. Maybe noone ever thought it worthwhile and by the time modulating became the fad, condensation was goal and you needed a heat exchanger designed for open flame steel or cast iron burners and cast iron heat exchangers didn't fill that bill.

but getting this steam right is pretty important, esp. on zoned systems. (my approach to zoned systems is generally get rid of the zoning, work carefully with individual air valves on rads and go home). But there still are relative load distinctions in coming back from setback and maybe in extremely cold outdoor temps, and just given the vagaries of the whole deal that make me think that modulating would be a way to cut system losses and keep steam up at low pressures rather than cycling.

Although my use is steam, I put this on the main wall because it could apply to modulating fire dependent on hydronic load as well.

brian

RobG

What about modulating condensing cast iron boilers? The HydroTherm KN boilers claim the their HX's can handle it.

JStar

@MarkS‌

archibald tuttle

Hatterasguy said:

I have a two stage gas valve on the 262K ECR.

i'll get the model of this boiler but part of my point is it was not delivered to run a two stage gas valve. so i'm wondering about the generic relationship of the common approach to atmospheric boilers, i.e. a manifold of gas jets into burner tubes that admit air adjacent to the jets to mix with gas and ignite along outlets in the burner tube, and a high low fire regime.

is it contraindicated to just turn down a boiler that was not delivered with that capacity. i can run comubstion on it at high and low fire to see what happens but my general impression of this technology when employed on stove burners and in grills is that the amount of air drawn in is related to the gas delivery through the jet so that you can, as a rule, turn the burner down and it will experience a reasonably proportional downturn in entrained air. just checking that i cam correctly comparing these technologies and anyone's experience on retrofitting to be able to low fire.

thanks,

brian

Jamie Hall

The key phrase in your last comment is "reasonably proportional". Reasonably proportional is not what is desired in a boiler. Just as a car engine will run over a remarkably wide range of mixtures, so will a stove or gas grille -- and the simple venturi will do very nicely. To get the sort of efficiency we are looking for, however, much tighter control of the mixture is desirable.

I will be interested in your results!

archibald tuttle

OK more info to chew on. was back by there yesterday (had to work on a Teledyne Endurance (the old blue with the cream covers) up the street (another story for another day). so i stopped in and got some dope on this big steamer. (not that kind of dope, not pipe dope, numbaahs).

So the boiler is a Burnham 500BN (i still haven't had enough panels off to count but this thing has gotta be at least 10 sections. long and low.)

it is rated 546,000 input 436,000 output and conveniently the rating tag includes this: minimum input of 182,000.

I'd say that is an indicator that the manufacturer thinks it can be turned down to that extent even though they didn't make any provision for it.

so now I need to think how i back into something like halving the input BTUs with a two stage gas valve. like a dope, i didn't get the model of the gas valve. will get that today and a picture, so maybe somebody can walk me through a two-stage substitute.

thanks,

brian

archibald tuttle

So I did some experimental work with the combustion tester and throttling the shutoff valve to get some empirical data on what i could accomplish.

As a refresher this is a 5008BN Burhham atmospheric steamer. Eight section 546,000 in 436,000 out by the label.

it has a broad draft hood and i took combustion readings in the exhaust stream across the hood above the draft opening which is a long flat rectangle and got pretty similar readings across. not sure if it would be best to drill a hold in the hood itself right above the fire chamber which i think would give non mixed results but in the 12" exhaust beyond the draft hood i'm going to be mixing in air from the room that was not part of the combustion mix so i think that would ske the sample. So maybe i should stay where i am, or drill a couple holes in the hood and check for similar readings from each end of the boiler. It would be way easier to drill holes instead of crouching behind the boiler. any advice on approach is appreciated.

no convenient manometer connections on the gas piping or gas valve so that i could take up and down stream pressures and maybe make some inference of btu in. when i see the burnham guys in chicago i'll ask if i can estimate btus from the pressure or maybe vaccuum on the burner side. (I know the forced draft units with manometer connections show vacuum on the downstream side of the gas valve, don't know if that would be the case for atmospherics).

Initial tests were giving me 7 % CO2 , 15 PPM CO, stack at 515 degrees and efficiencies around 71% so about 10% below the name plate which is 80% so there might be some ground to be gained right there but i digress.

on the 'modulating' front, i ran it with the gas valve flagged at a couple different levels. both cases the CO2 dropped. at the lowest firing rate I tried, it was down to like 4% the CO dropped even further to 10 PPM and the stack temp was about 430 degrees and the efficiency dropps to 69.5. and i wasn't really climbing out of the 5 or 6" range on steam.

turned it up just a little from there and I got CO2 back up to mid 5s to 6%. CO was pretty unchanged from 10 and the stack temp went up 10 dgress to around 440 and efficiency back up to 70.5 to 71 (the variations describe my varying results in testing across the width of the draft hood). and i was getting around 10" of steam pretty consistently over 15 minutes of firing.

All of this was without making any adjustment to the draft collars which I'm sure are as they were delivered from the factory, i.e. all the way open, probably 25 or 30 years ago on a guess but i might be only 15 years old, hard to tell unless you have more expertise on aging Burnham boilers by subtle trim or accessory changes.

I also tried steaming from relatively cool state at the lower firing rate and it took 15 minutes instead of 5 minutes to hit 3" of water which seems to begin serious steaming - although maybe it would at even lower pressures if i could keep it there but that would be ridiculously low fire and i'm not sure i'd get reliable lighting or that it would not get blown out with the drafts from the nearby air admittance vents. probably wouldn't blow out the entire bed in one fell swoop but i think also it would certainly fall below the minimum input on the manufactures plate of 182,000 although that is just a wild **** guess. (just realize, one way i could estimate BTUs is turn off the other gas appliances to be sure and monitor the rate of consumption at the meter, i'll see what the smallest reliable indication is on that)

So maybe when i speak about modulating, i don't really mean several stages but just chosing a lower firing rate. I haven't pulled off any burner tubes to see if the jets are pipe thread and changeable and imagine i could accomplish about the same thing by putting a regulator in the gas line upsteam of the valve. Not sure if one or the other is more desirable if both are options.

Of course I'm still intrigued by the idea of getting a two stage gas valve. don't know if the low stage would have a regulator so it could be adjusted or . . .

Then i could set the air regulators to go for higher efficiency at low fire (which would be the vastly predominate mode) but to insure free air and well controlled CO at high fire. find the best medium. although with low predominating so much it might be more sensible to give up on the stages and tune the hell out of it for a single lower fire rate and anticipate thermostat recoveries by 15 minutes and call it a day.

A few of these questions i hope to get answered in Chicago, but i figured i'd throw it out here because with what i learn on the wall i'm more likely to sound like i know what i'm talking about -- or talk like i know what i'm sounding about.

thanks,

brian

JStar

We retrofit a lot of 2-stage GCV's onto atmospheric boilers. Here's what I've found so far, after 12+ boilers running with this setup...

- The magic ratio seems to be 6:10 (Low fire to High Fire). At 60%, the boiler pumps out steam without a problem. All radiators stay warm/hot.

- We've been able to keep our stack temperatures above 350F in Low Fire mode on every boiler. Flue gas condensation has not been an issue. Going back on these boiler for maintenance shows no signs of condensation.

- The Excess Air on Low Fire is predictably higher, which will lower the combustion efficiency by a few points. However, the idea behind staging on an atmospheric boiler is to accept these losses and recoup the difference by using less fuel during cycles. If the fuel savings can outweigh the losses, it's successful.

- Staging is nearly essential for me on two-pipe steam systems. Something magical happens when you modulate an old vapor system. It's the best way to maintain super low pressures.

- I'm still collecting data on fuel usage compared to On/Off operation. We know that fuel is being saved, just not how much yet. The end of this season should provide us with a lot of needed information.

archibald tuttle

jstar,

do you have a favorite gas valve. this is a sizeable boiler so i would need 1" valve.

or at least one capable of passing half a million btu per hour on high fire.

is the low stage adjustable by a regulator to get your 60% setting or is that a facet of the Gas valve purchase.

thanks,

brian

SWEI

JStar said:

The Excess Air on Low Fire is predictably higher, which will lower the combustion efficiency by a few points. However, the idea behind staging on an atmospheric boiler is to accept these losses and recoup the difference by using less fuel during cycles. If the fuel savings can outweigh the losses, it's successful.

- Staging is nearly essential for me on two-pipe steam systems.

Great to see real data which confirms this. I believe the conventional cast iron boiler makers are missing a huge opportunity here by not offering two stage firing as a standard option (if not standard equipment) on all of their boilers -- steam and hot water. I suspect they could realize a measurable increase in AFUE as a result, which would carry some marketing power in the short term. Over the long term it would extend the useful life of their foundry operations.

JStar

SWEI said:

JStar said:

The Excess Air on Low Fire is predictably higher, which will lower the combustion efficiency by a few points. However, the idea behind staging on an atmospheric boiler is to accept these losses and recoup the difference by using less fuel during cycles. If the fuel savings can outweigh the losses, it's successful.

- Staging is nearly essential for me on two-pipe steam systems.

Great to see real data which confirms this. I believe the conventional cast iron boiler makers are missing a huge opportunity here by not offering two stage firing as a standard option (if not standard equipment) on all of their boilers -- steam and hot water. I suspect they could realize a measurable increase in AFUE as a result, which would carry some marketing power in the short term. Over the long term it would extend the useful life of their foundry operations.

I have yet to come across a system where our 2-stage GCV wasn't compatible. At least for steam. The manufacturers could easily switch to a 2-stage valve and leave the wiring open-ended for use with staging or not.

NYplumber

I looked into the Lochinvar Solution boiler. Not keen about the copper hx.

Looking for a wet base boiler with a conversion burner w/ lo-hi-lo and add a vent assist blower and barometric to vent it out the side of the home.

Initially was going to get a mod con, but now reconsidering.

Don_197

The solution is fine when correctly installed......with low return water protection........otherwise look at the Slant Fin Sentry......nice little boiler.

Don_197

Nowadays.......ModCon is the ONLY way to go.......and if you are looing to cheap out.....they can be had for around 3k. For hot water it just doesn't make any sense not to go ModCon. Someone that knows what they are doing can control these from their SmartPhone.

NYplumber

Don, the slantfin doesnt seem to have anything special pulling me towards it. Seen a dime a dozen good cast iron spark ignition boilers with odr controls.

As for mod cons, im unsure what your experience with them are, but my daily service work has shown that while they have the potential to pay for themselves and their repairs on larger homes and commercial applications, they just dont have the cost effective properties in three thousand sq ft and smaller homes. One repair offsets much of the savings. Cast iron boiler, buffer tank and odr. If you micro zone, things change. Typical one zone per floor, no need for the mod con.

ChrisJ

NYplumber said:

Don, the slantfin doesnt seem to have anything special pulling me towards it. Seen a dime a dozen good cast iron spark ignition boilers with odr controls.



As for mod cons, im unsure what your experience with them are, but my daily service work has shown that while they have the potential to pay for themselves and their repairs on larger homes and commercial applications, they just dont have the cost effective properties in three thousand sq ft and smaller homes. One repair offsets much of the savings. Cast iron boiler, buffer tank and odr. If you micro zone, things change. Typical one zone per floor, no need for the mod con.

Sounds like your opinion is save the money on the mod-con and put it towards insulation \ windows instead?

archibald tuttle

Don said:

Nowadays.......ModCon is the ONLY way to go.

modcons are cool technology and i believe its SWEI who has said that he is seeing over 50% of operation cycled with some condensing in baseboard applications with ODR. That has to depend on the amount of fin tube, more fins = more condensing.

And i would imagine it would mean convincing customers to give up setbacks to avoid high water temps during recovery. We could start a dozen more threads on the savings of setback regimes but even assuming they are low the savings from condensing 100% is 10% so if you have fin tube baseboard and heavy setback regime in modest size house i don't think the cost of condensing boiler justified.

and turning over a new leaf, at least for this thread i'll use a new post for a new subtopic in order to keep these novels below 5000 words.

archibald tuttle

NYplumber said:

I looked into the Lochinvar Solution boiler. Not keen about the copper hx.

unfortunately, my trip to Chicago was cut short or i would have spent some time looking at these boilers. I'm not familiar with the Solution but the Heatmaker (and to a degree the Paloma Pak as i recall but i only every saw one) pioneered copper heat exchangers and i still have them in service about 25 years down the pike.

the biggest problem was the earlier overtemp safeties without circulation proof controls tended to melt the exchanger.

the Mark II had a differential pressure safety on tappings across the circulator flange and that was bombproof.

Just put in my first endurance and see they went back to using solely temperature based heat exchanger protection. I resist change so i added a circulation safety that breaks the 24V to the gas valve on no circulation. I assume the heat exchanger is still copper but haven't had one apart.

I have to say the endurance seems like a nice little modulating package and improved on the buffer tank concept by removing the inserted coil and gasker which has been a failure area for heatmakers. And it modulates very nicely. And for Don who thinks that $3 K is cheaping out, this one cost me 50 bucks.

Can anyone give a little more of a description of operation resilience and pros and cons for the Solution?

brian

archibald tuttle

ChrisJ said:

Sounds like your opinion is save the money on the mod-con and put it towards insulation \ windows instead?

I'm all for that if the insulation and windows are carefully fitted (with insulation, condensing is bad as opposed to with modcons).

but I think you could expand this. i would put the money in emitters before i would put money in a modcon.

i think the industry has gone modcon crazy (and the government is pushing in that direction with all these purported demand reduction giveaways to gas customers. And there is no proof required that in any given installation setting and operating regime they actually reduce demand to any significant extent nevermind to an extent that actually justifies the costs of the program to other ratepayers. (Nor would i want any, that would only increase the bureaucracy, i just want them to get their regulations off our boilers. i can live with the notion of an independent safety watchdog. We need the same change with prescription drugs -- prove they are safe in an independently monitored process and leave efficaciousness to the market and we'll all be better off. )

icesailor

"" Sounds like your opinion is save the money on the mod-con and put it towards insulation \ windows instead? ""

Darn right. Take a 150,000 BTU uninsulated house and insulate and weather strip the heck out of it, and it gets down to 80,000 BTU's or less, that is a long term payback. For years and years. If you saved $500 per year in energy cost, that's $5,000 in ten years.

Even adding insulation and weather stripping to something already there has a rapid ROI. As I found out personally. And I've been involved with this.

When you buy a new car, they don't give you a choice of using the old engine out of your old car in the new one.

archibald tuttle

icesailor said:

"
When you buy a new car, they don't give you a choice of using the old engine out of your old car in the new one.

(is there some way besides quoting the whole post and then deleting the part you don't need to get an excerpt quote in this comment engine. I've tried selecting the text i want before clicking on quote but it always paste the entire post into the new comment. with most folks that wouldn't be a problem but if you every quote one of my posts you have to spend a half hour deleting the excess, unless there is some obvious way to get what you want and i'm missing it)

icesailor

not sure this metaphor works quite as well in this context. if i read you right you are saying that the modcon is the new car and -- metaphorically anyway -- you don't have a choice to use your old chassis, i.e. building envelope.

I agree the two can go hand in hand but since money isn't unlimited i don't buy new cars and i do put other engines in the ones i've got occasionally to keep them going. but I tend to look at insulation and emitters as the first thing to do.

i've got astronomical utility bills so better sealing windows were numero uno. i've tried blown in cellulose in about a third of the place. the rest of the walls on upper floors have really early fiberglas in them. but all of this does about nothing because the envelope around it is so damn leaky. but i'd really have to gut the houses from the outside or the inside to do anything about it.

And my emitters are these onetime 'space age' (for the 50s) silly steam convectors with virtually no mass. So there is no cast iron flywheel to convert to low temp hydronice.

I hate to say it, but in terms of ROI. i'm considering hot air for as much of the house as i can reach that way because it is way easier to get condensing out of hot air than anything else. Your return temps are like 70. When are you gonna see that in hydronic -- without heat pumping. The condensate literally pours out of one of those furnaces.

archibald tuttle

and back on the original subject (i'm quite glad of course that this thread has gone off in various directions and since i started it maybe i get to offer pardons for threadjacking. since i do it all the time myself, i'm noone to complain) I saw Robershaw and Burnham folks at the show in Chicago and I'm quite comfortable with the idea of putting a two-stage valve so i'm off to figure a location for combustion testing this particular Burnham because i want to tune the high stage carefully to reduce the excess free air on the low stage. It doesn't have an obvious location to get a mixed sample prior to the draft hood because it is a long boiler and the manifold that collects the exhausts is about 3 and half feet across and has the draft built right into it at the length. maybe i just need to drill several holes and average results across the length from several readings.

ChrisJ

icesailor said:

"" Sounds like your opinion is save the money on the mod-con and put it towards insulation \ windows instead? ""

Darn right. Take a 150,000 BTU uninsulated house and insulate and weather strip the heck out of it, and it gets down to 80,000 BTU's or less, that is a long term payback. For years and years. If you saved $500 per year in energy cost, that's $5,000 in ten years.

Even adding insulation and weather stripping to something already there has a rapid ROI. As I found out personally. And I've been involved with this.

When you buy a new car, they don't give you a choice of using the old engine out of your old car in the new one.

I agree,
Problem is, I like working on my steam system and hate working with insulation. So, like many I do what I like.

But, I will always agree that keeping the heat in is far more important than gaining a few % on the system's efficiency. A house built like a freezer (3.5" sprayfoam in walls, 8" sprayfoam in attic, new quality windows) will be cheaper to heat using a snowman and a conversion burner than a drafty uninsulated house with a 95% AFUE system.

JStar

archibald tuttle said:

and back on the original subject (i'm quite glad of course that this thread has gone off in various directions and since i started it maybe i get to offer pardons for threadjacking. since i do it all the time myself, i'm noone to complain) I saw Robershaw and Burnham folks at the show in Chicago and I'm quite comfortable with the idea of putting a two-stage valve so i'm off to figure a location for combustion testing this particular Burnham because i want to tune the high stage carefully to reduce the excess free air on the low stage. It doesn't have an obvious location to get a mixed sample prior to the draft hood because it is a long boiler and the manifold that collects the exhausts is about 3 and half feet across and has the draft built right into it at the length. maybe i just need to drill several holes and average results across the length from several readings.

It is always advised to take a sample from several locations in a boiler this size. You can drill holes in the draft hood or simply stick the CA probe on top of the boiler through the hood. On the Robertshaw GCV, there is no pressure adjustment of any kind, which bothers me, but we've yet to encounter a problem with it.

ttekushan_3

The Bryant Heat Tender modulated atmospheric gas boilers back in the '20's. Their trick was to modulate the secondary air with a damper system that was pneumatically operated by manifold gas pressure. The boiler had a belly pan sealing the base with dampers at the rear and doors at the front that allowed the primary air intake and manifold to sit outside the combustion chamber. Primary air shutters were outside the combustion area and were not modulated.

I maintained a B-Line gas boiler (1928-2012, R.I.P.) that had this and the analyzer showed 82-84% combustion efficiency at all firing levels. Unparalleled performance for a modestly sized residential boiler.

https://heatinghelp.com/heating-museum/bryant-pressure-tender-for-vapor-steam-systems/

Tim McElwain

Another modulating burner set up from the past was the Republic Gyroscopic gas conversion burner. It had a low setting and a hi setting and on steam systems could modulate between those settings based on pressuretrol setting.

Most of these still in operation today have been set to come on at high fire on every call as the control mechanism for low to high is no longer available.

archibald tuttle

OK, so i've widened my search for gas valves. Robertshaw tech tells me they do not make a dual stage on which either the high or low side are adjustable. In their valve the built in regulators are underneath the solenoids and cannot be accessed.

I don't know how you calculate the BTUs/gas pressure/pipe size /burner design - I've just been counting cubic feet per minute of operation on the gas meter as my surrogate. Current high fire is 8.75 cu ft. per minute x 1020 btus/cu ft. x 60 minutes = 543,150 (remarkably close to the nameplate 546,000).

My early tests of reduced fire were 7.25 cu ft. per minute or a little more than 80% fire. I'm thinking I could go down to 75% but 60% might be pushing it to keep up with the radiation.

The Robertshaw which is not adjustable delivers 1.5" W.C. and that is 60% fire. There is no manometer connection downstream of the existing gas valve so I haven't checked to see how close the current valve delivers to the high fire target of 3.5". But obviously the relationship is not linear as the pressure delivery to obtain 60% fire. is 43%. i guess i could play with some simultaneous equations and estimate what it would take to get to 75% fire, but realistically
this Honeywell seems to be the choice i have found.

It's adjustable with a range is .8 to 2" WC on the low side and 3 to 4.5" WC on the high side. seems pretty close to perfect but it has no integral pilot valve so I'd either have to leave the existing valve in and maybe just set the regulator wide open and add the two stage downstream, or I need an intermittent ignition pilot valve that I could put in a Tee .

I have the Johnson Controls G77x series pilot unit so I don't see a problem with it opening a separate pilot valve and proving the flame and then i'd have to intercept the signal to the main valve anyway with the dwyerstat control to switch stages, but the input to the dwyerstat would be the main valve connection on the G77 so it would not be energized unless pilot flame was proved.

But when i search for intermittent ignition pilot valve, i just get main gas valves with an integral intermittent ignition pilot valve. Thus I'm having trouble finding a standalone pilot valve.

Any help on this one?

thanks,

brian

JStar

Avoid a pilot safety valve and go for an upgrade to intermittent pilot. You'll then be able to find a GCV much easier.

archibald tuttle

joe,

i do have intermittent ignition already but the GCV that meets the two stage needs for this application does not have a separate pilot solenoid so i need a 24V pilot supply solenoid separate from the main valve.

brian

Tim McElwain

What are the valve numbers you have looked into?

archibald tuttle

Tim McElwain said:

What are the valve numbers you have looked into?

Honeywell V8944B1019
Robertshaw 700-064

archibald tuttle

The Robertshaw provides an intermittent pilot but offers no adjustment of the regulators. That is why I prefer the Honeywell but I will have to provide my own 24V pilot valve as there is no separate pilot tapping and solenoid.

archibald tuttle

PS -
for those with lower BTU requirements, White -Rodgers has great even more widely adjustable options but they only go up to 300,000 BTU high fire on nat. gas.

Tim McElwain

You are going to have to go to a commercial valve set up in order to meet the BTU you are looking for. Look into gas train with a CSD-1 set-up. Be ready to spend some money.

archibald tuttle

tim,

i like the honeywell commercial i already found. i bought one for $150 bucks. So now i just need a 24V pilot valve to go with it.

i'll look at the valve that is already on the boiler. maybe i can just max out the regulator or pull the regulator parts and eliminate the regulation function of the valve but keep it inline with the new two stage to perform the pilot and main safety function. but i thought, if a standalone 24V pilot valve is available that might be the slicker combination here or at least i would look for one. but the internet searches are hopeless because they keep bringing up main gas valves that have a pilot. i figured folks who know the industry may know if an independent 24V pilot is obtainable. Once I get some models I can pursue.

If it weren't the weekend i'd call a a few of the manufacturers to help me spec something but i thought folks out there may have seen or used one.

brian

SWEI

archibald tuttle said:

PS -
for those with lower BTU requirements, White -Rodgers has great even more widely adjustable options but they only go up to 300,000 BTU high fire on nat. gas.

That looks like the valve Rheem is using in their current two-stage furnaces. Easily adjustable at both levels (and quite compact as well.)