Question about derating a gas fired, atmospheric steam boiler. Again.

JohnNY

ethicalpaul said:

I think you know this, but you keep asking it, and no one is answering it, so I will answer it.

I stopped asking because I thought I might be losing my mind.

dopey27177

Through all of this I have seen or heard any one speak about draft and flue gas temperatures.
Can this 300% over sized boiler be de-rated 50% ? (ha ha). What will the draft be like?
Remember we are not talking about a fuel gun and draft induction. We are speaking about a gas fired atmospheric boiler.

Some one mentioned the old boilers being over sized. Remember the old boilers were sized the same way the new boilers are.

The only differences were the boiler sections were internals were wider causing steam to form slower. The metals were thicker requiring more fuel to make steam. All in all trying to de-rate a boiler 300% larger than what is needed and expect to good results and carbon monoxide in the building seems to me to be a bit fool hardy.

I think something got lost in this thread and was taken over by ego.

Jake

PC7060

JohnNY said:

So, with all due respect, you're an engineer and I'm just a lowly plumber and maybe you can explain this to me like I'm not the sharpest bulb in the tree.

"A longtime protegé of the steam heating industry expert Dan Holohan, John Cataneo is a member of the teaching staff at NYC’s Mechanics Institute as a fellow Steam And Hydronics course instructor."

Hardly a dim bulb (aka "sharpest bulb in the tree") or lowly plumber!

PS: There aren't any lowly plumbers, especially when the terlet wont work!

PMJ

dopey27177 said:

Through all of this I have seen or heard any one speak about draft and flue gas temperatures.
Can this 300% over sized boiler be de-rated 50% ? (ha ha). What will the draft be like?
Remember we are not talking about a fuel gun and draft induction. We are speaking about a gas fired atmospheric boiler.

Some one mentioned the old boilers being over sized. Remember the old boilers were sized the same way the new boilers are.

The only differences were the boiler sections were internals were wider causing steam to form slower. The metals were thicker requiring more fuel to make steam. All in all trying to de-rate a boiler 300% larger than what is needed and expect to good results and carbon monoxide in the building seems to me to be a bit fool hardy.

I think something got lost in this thread and was taken over by ego.

Jake

With all due respect Jake I can't agree that the original coal boilers were sized the same as the new ones should be. The reason being that the new ones run only at their maximum output and the coal fired ones were never intended to run there. It would be totally impractical with their pressure control systems to ever require being at "maximum" fire. The new ones run only there. Very big difference.

The only derating I ever get involved in is limiting run time. That way when the boiler fires it is always firing exactly as the manufacturer intended. By limiting any boiler to a maximum run time of 30 minutes per hour you have effectively cut its possible output into the structure by half. This approach is almost never considered around here. In this case the OP is saying that this boiler is so big that it will build pressure whenever it runs even from the get go into room temperature piping. At some amount of oversize this would certainly be so. Perhaps 300% will do that. Still, in this case I would like to know what that pressure is and what the time/pressure profile looks like from a cold start as things fill.

All I see here is a technical discussion I'm interested to continue any time and be wrong as surely will be required from time to time. Having no bruises proves only that one wasn't actually out on the field. Others apparently see an ego trip here, which is unfortunate.

ChrisJ

@PMJ from what I recall the Redflash boiler my friend had was rated for very close to the radiation it had installed as well as the oil burner that was in it.
I disagree with you on this.
It also had an automatic damper setup that was disconnected.

jumper

Is temporarily plugging half the burner holes that difficult or time consuming to do?
Then OP can check the draft and see how well modified steam maker works.

PMJ

ChrisJ said:

@PMJ from what I recall the Redflash boiler my friend had was rated for very close to the radiation it had installed as well as the oil burner that was in it.

I disagree with you on this.


It also had an automatic damper setup that was disconnected.

Disagreement works fine. 

I'll stay with my logic though. Even if the two boilers had the same max fire rating the coal one never ran on high and the replacement could only run there. However you wish to do the figuring I'd say that was not a match.

EBEBRATT-Ed

If a boiler was 2x the proper size and was de rated somewhat it would probably be workable. 3x isn't workable

The Steam Whisperer

I think derating options are limited with atmospherics.
We find nearly all the steamers we come across are about 60% oversized to the radiation, though we have come across a few as bad as yours.
On nearly every Weil LGB we maintain, we have them running on low fire only ( 1.2 inch WC at manifold), which is about 60% of high on most of the LGB's out there. We see an increase in excess air, so we lose a couple points in combustion efficiency, but I suspect that the longer heating cycles will balance that out so seasonal efficiency is about the same( somewhere in the mid-60% for most systems with typical 60% oversized radiators) On the Peerless 211A, where low (50%), mid (75%) and high fire gas trains were once available, we swap out the regulator spring so we can go down to 1.2 inches or greater at the manifold. We found going down below 1.0 ( 0.8inches = 50%), that the regulator can get sticky, so the set firing rate is not maintained. On the Peerless we seem to have greater combustion efficiency losses than the LGB.
I don't remember if the Weil EGH has a step opening gas valve like the Peerless 64, but if it does I would feel pretty comfortable running the boiler at the low fire starting input. System noise nearly always drops when we bring down the firing rate.
With the amount of excess air you end up with when just cutting the gas input on an atmospheric, I doubt you'll have problems with condensing from the flue gas. As the amount of excess air goes up, the condensing temperature point drops. Most modern atmospherics CI we've tested ( the exception being the more recent large Dunkirk atmospheric, ie. D249) are at about 50% excess air in stock trim. Older atmospherics.... typically with cast iron burners.... often run closer to 30% excess air, so they will condense at higher temps.
I suspect that at 300% input, you just can't get the velocities going into one pipe steam rads slow enough to allow the water to drain back out. The best possibility I can come up with is reduce input as much as possible ( low fire start gas pressure), big main vents to make sure the piping can eat up lots of capacity at start up, small air vents to slow the steam going into the rads so water can get out, and cycle the boiler at l ow pressure so it can't overwhelm the low radiator vent capacity. You may be able to fix the spitting vents, but I don't see much way around the short cycling.

Motorapido

The Steam Whisperer said:

I think derating options are limited with atmospherics.

I don't remember if the Weil EGH has a step opening gas valve like the Peerless 64, but if it does I would feel pretty comfortable running the boiler at the low fire starting input.

Hmm. So on my Peerless 64, which is about 2x oversize, you say there is a way to make the gas valve stay on the lower-rate of flow used when the gas valve first opens? Despite more Big Mouths than any human should own, a clean system and well balanced radiators, I cycle on pressure on my vaporstat setting of 8 ounces cut-out pressure. I've considered doing the timer method that works well for some, but is there a way for me to operate my Peerless 64 on the starting-state lower gas flow setting?

JohnNY

@The Steam Whisperer (Formerly Boilerpro) Good post. Thank you for your input.

The Steam Whisperer

"Hmm. So on my Peerless 64, which is about 2x oversize, you say there is a way to make the gas valve stay on the lower-rate of flow used when the gas valve first opens? Despite more Big Mouths than any human should own, a clean system and well balanced radiators, I cycle on pressure on my vaporstat setting of 8 ounces cut-out pressure. I've considered doing the timer method that works well for some, but is there a way for me to operate my Peerless 64 on the starting-state lower gas flow setting?"

If the change is possible, you'll need a professional to look into the changes necessary to ensure that everything is safe.

The Steam Whisperer

John, It seems no matter how many tricks we have, some things are just beyond getting them to work at some level of reasonably well. Extremely oversized atmospheric steamers seem to be one of those.