failure modes for large early 60's steamer

archibald tuttle

Got a 1960s vintage US Boiler Works (pictured in attached report page) steamer in a small (read impoverished) private school in Providence that has exhibited minor nuisance leakage - maybe press nipple or . . . - for maybe 5 or 6 years now or longer, don't know about earlier.



Basic question - if you don't want to read the novel below.



Convert to gas for btu savings, maintain and maybe add redundant low water safeties

or



New Boiler that they can't afford without diverting any and all money can raise for the foreseeable future that might othewise be devoted to conversion to hydronic or air furnace with air con (they don't currently have air conditioning and building is essentially unusable during summer vacation) and or envelope improvement, e.g. windows, insulation, etc.



Here's the novel:



Even if the eventual determination were to renew and repower the steam system, the obvious choice from my perspective would be to convert the existing for the time being to save on fuel cost while comparing options.



Real concern of the moment is what are possible/likely failure modes

for this (very) low pressure 60 year old steam boiler that has minor

leak that hasn't changed appreciably (if anything has lessened) over the

last 5 years. Should they be so concerned about failure of the existing

boiler as to ignore conversion (maybe $5000 expense which is likely to

be saved in 1 to 1.5 years fuel use) keep burning oil pro tem and expend

all efforts towards raising one to two hundred thousand dollar budget

to replace the boiler because of the risk of catastrophic failure?



So it boils down to concern about total loss to the boiler, not its day to day efficiency.



It's fired on low stage only at 6 GPH which is the smallest rated nozzle on the Carlin 800CRD low fire stage.



we don't even use the high fire as it can make a half pound of steam from a standing. i.e. room temp, start in less than a couple minutes on the low. fire stage.



I think it really should have an even lower firing rate and be converted to gas for the time being while the school sifts through its more expensive options of HVAC renewal. (The fan coil units are aged but usable, the old pneumatic vent and thermostat controls have long ceased working. I change a steam trap now and again as the thing limps along, but there is probably a major change in heating direction in their future but they need to consider what to do to buy some time to raise money for a revamp -- my guess is a away from steam because the return pipes are already springing leaks in the boiler room and that doesn't hazard reliability of the existing network, so I haven't recommended staying with steam, also because hydronic or hot air furnaces can take up less space but I'm sure since I'm on the steamer forum folks can try and talk us back off the ledge)



I am fairly sanguine about continuing with the old boiler as I have regularly babied along 90 year old boilers but all of these are household scale and that is why I'm asking for your observations since I'm out of my depth although I believe the ideas generally scale between residential and commercial scale boilers.



For the sake of due diligence the school engaged a consultant but I think his report is not particularly diligent or complete with regards to operating the existing boiler.



His response to possible failure modes was simply that you could have chronic or catastrophic failure without describing differnet modes of failure and their likelihood and/or preventability by safety control.  The only catastrophic failure I can imagine would require the failure of low water control leading to a catastrophic failure.



Maybe the word for the purpose of this analysis isn't catastrophic but instantaneous.  Are there any likely failure modes I'm not considering that rather than being the simple slight worsening of a leak would represent an overnight change from a boiler that could be operated to one that can't?



It is hard to estimate current rate of water loss, because even if they metered make up water, some is going to be lost around valve stems and unions and the like that are imperfect out in the piping and not attributable to the slight infirmities of the boiler, but if I had to guess I'd believe we weren't talking 3-5 gallons a day at its peak.  I haven't tried to perform some volumetric calculation to figure out what the actual capacity of the water jacket is, but its big so I don't believe that highest rate of loss we are talking is more than a couple% a day.



We did use an antileak additive and converted from pressuretrol to vaportrol operation yielding reduced head pressures. I don't know if the difference between 1/2 lb and 4 lbs would make noticeable change on nuisance leaks -  but the heat is just as effective in the building at 1/2 lbs. as it was at 4.  I do believe evident leakage is much reduced from that rate with these changes, but this is based on occasional observation and not scientific monitoring.



My inclination is to convert to gas, and maybe add an electronic as well as maintain the existing physical LWCO for redundancy although there is a custodian who checks water level visibily daily as well and the boiler isn't even run overnight but maybe one or two coldest nights of the winter. He comes in early and starts it before school.



But our consultant just says things like "we've been lucky" to date implying that the thing could drop dead at any minute. I don't blame the school head and parents on the building committee for being concerned when confronted with observations like that, but he doesn't discuss what in particular could happen. Rather just says the boiler is beyond its useful life.  That may be true in a way, but it was probably just as true 5 years ago and we haven't had a lick of trouble with the boiler itself. I just fear the building committee is being pushed to quickly replace the boiler rather than soberly consider what their longterm alternatives should be. This is occuring because of the cautious nature of the approach and not because of any conflict I'm aware of. The consultant doesn't sell or install steam boilers.  But the custodian found him much more sanguine about the existing plant when they met in person than in his report.  So I get this sense that it is necessary CYA because if you say go ahead and convert and run this thing and they only get 1/2 way through a season, your advice may still have been sound advice but are they going to come looking for you. It is kind of like defensive medicine, doesn't get the most practical real world answer.



So I've come to the well. I know no one can guarantee precisely what its likely life is,  but I'm more concerned what the likelihood of instantaneous non-repairable malfunction is. I believe if it is monitored and safety controls are tested and perhaps made even more redundant they shouldn't worry about converting to gas at maybe a 600,000 btu firing rate and running this boiler.



As I said, distribution control is virtually non-existant. I replace steam traps that freeze closed and block heat from getting to units because this symptom is an obvious alert of a problem,  but there isn't regular monitoring for traps that are stuck open although there isn't a plethora of steam in the returns. While fuel costs are an issue and good trap maintenance can help here, we're talking as much as 100% difference between Nat Gas and oil this season and the traps are difficult to access, weren't set up well for testing or element replacement. Maybe a full approach to them is also merited, or even just prophylactic element replacement, but the key concern i'm trying to address is how heating professionals familiar with large equipment such as this would approach a capital cost sensitive decision here, and whether you fault my recommendation for keeping the existing boiler running and converting to gas.



thanks for reading this novel,



Brian



PS -one last caveat. Of course a boiler this size is inspected annually in cooperation between the state and the school's insurance company. I believe they are mostly checking visible condition and the presence and operation of safety controls. Again, I have had residential buildings with higher BTU units subject to this kind of inspection.  This has been my experience. That said, we're not talking puddles of water on the floor or any obvious leak but I can find rust stains and dampness at one corner of the boiler under the jacket.  At least relative to the boiler itself are there inspection issues we're begging that i"m not thinking of?

Rod

Picture of Boiler

I blew the picture in the report up a bit.

archibald tuttle

thanks rod

i used to know everything there was to know about computer imagine but i feel like posting files on these boards I'm not good at.



brian

Greg Maxwell

Boiler Failure

The jobs that I have been involved on of this type have always been with the primary understanding that its a flip of the coin. That boiler yould last 5 years, or 5 minutes. The one thing that is for sure is that when it pukes, it wont be at a convienent time, and they are going to have to come up with the money in a real hurry. The best approach is the proactive one. I dont know if what the consultant came up with is the correct load or not, but that boiler is probably oversized, based on the fact that you are only running on low stage, and I am assuming that the building is heating properly. As far as BTU cost goes, be cautious in your approach, oil at 140,000btu, LP at 93,000, and natural around 100,000. There are alternatives in burner replacement for conversion down the road if you choose. Good luck

archibald tuttle

what is puke . . .

of course murphy will have it break at the most inconvenient time. that is a given that one has to assume as a possibility.



The problem is, if they are trying to be proactive, they would also consider alternative systems so they have to try to weigh the downside of sticking with their old equipment against the only near term choice being an expensive new boiler that is essentially a dedicated steam boiler iocking them into the old system -- at least by the level of expenditure apparently required.



So does "puke" mean a sudden much more significant leak. Have you experienced that kind of accelaration in an existing leak? I take it there isn't any non destructive way to ascertain the real condition of the boiler but having seen it unchanged or improved for 5 years I wonder at jumping to replace it.



So the real worry is what to do if that happens. I would think one bolt hole plan in case of failure would be to pull the steam traps pop in 3 or 4 low mass high efficiency hyrdronic boilers and run the existing units hydronic. Then they could, over time improve piping and distribution for the hydronic and abandon the old piping. 



That would be my idea for a safety valve against inconvenient puking.



That said, it may be that the estimates for a boiler replacement are too high because they are based on over sized boiler.  The building load is calced at about 1 million BTU's or 1.5 with ventilation load. The consultant estimated $150,000.



But even if they could go a bit smaller and got the nice deal form a plumber and supplier I still imagine they are talking close to 100 grand and I just don't see them making that level of commitment to an aging steam infrastructure. $50,000 I could see. i think 100 is right out.



so maybe to ask the question a different way, how bad of a safety valve is the idea of staging 3 or 4 boilers and converting to hydronic on the fly?  I've done this with 2 pipe radiator setups in residential situations and it worked fine.



brian

Steamhead

Without comparing heat-loss to radiation

you really can't make any kind of plan or arrive at a price. You need this info to proceed.



You got lucky on those residential jobs. But now you're working with a system that has already leaked from the returns in the boiler room. Knowing this, do you really want to jack up the operating pressure over ten times to run hot-water? I sure wouldn't! And how do you know the existing radiation would be adequate on hot-water?



How many lawyers are involved with that school?



For your cooling strategy, I would think mini-splits would be far easier to install than bulky ductwork. And has anyone tried more basic strategies to reduce heat gain, like painting the roof white?

Greg Maxwell

Steam Boiler

I agree with Steamhead, and would also add that "puke" is what you will find when you come in on the most inconvienent time of year. You will find that the boiler has leaked, maybe massively, and the LWCO may or may not have stopped the burner, but the feeder will continue to feed. There will be a LOT of water in your mechanical room. I have seen this happen in a commercial setting, and all the maintainence guy could do was hit the emergency switch, and run. If he has the wherewithall, he may be able to shut the supply off. That is worst case scenario.

With that said, I'd also like to add that a steam system such as this is an excellent delivery system. You need to do a load calc. on the building, install the correct size boiler, service the system, traps, pumps etc, and coose your fuel, then you will have a very efficient system for your application. Steam is efficient.

Mini splits would also be an excellent choice, you can use the heat pump function to get heating in the shoulder months, then the steam can take over.

archibald tuttle

mini-splits seem reasonable approach . . .

. . . and get that hydronic conversion will find the leaks. But if replacing the boiler is recommended at this age or because of symptoms, does that apply to the piping?  Then you aren't really looking at the cost of a boiler but of repiping steam. It's thoughts of that sort that make me think if there is any way to quantify the existing problem then they can assess the risk of running on current system.



IS there any protocol for  standing leak test, use air to pressurize system to operating pressue and monitor fluid loss over a certain period in order to effect any estimate of condition?



I don't disagree with the concept of mini-split heat pumps coupled with steam or hydronic, but mini might be a relative term. The building is divided into approx 12 classrooms/use areas, so taking the calculated load that would mean a system sized for about 80,000 btu per room.  Is that still mini split territory?



And here is another 64,000 dollar question though.  Could mini-splits, be used to provide for ventilation, ultimately keyed to CO2 sensing as that becomes more affordable to provide fresh air, which, even if not heated enough to provide heat at coldest times could still make some kind of room temp or outperform heat recovery ventilator. I suppose at the engineering spectacle end of this supposition, you could  use stale exhaust air flowing over the outdoor portion of the split in which case it would operating at those times as a heat pump and heat exchange ventilator.  Ideally, maybe, you could avoid that extra engineering, but the indoor and outdoor units could be installed proximately to facilitate such a plan. just blues sky here.



The possible need for ventilation is the stopper for a lot of full renewal plans(the school is used at much lower occupancy rate than original design, has had no working ventilation for years but loose windows and low occupancy seem to combine to create workable situation -- again that is empirically based. Evenutally, as against the whole energy consumption approach they will focus on tightening the envelope, but for right now, older windows are probably helping rather than hurting given all the operational requirements - this is a point on which I and the consultant agree ) .  Any major rework of the system will bring in the requirement for ventilation provision.



But there is no question in my mind that the existing fan coils could heat the building with hydronic supply (and could be serviced with modest priced home runs of pex that could obviate the concerns about higher pressure in the older piping) because they were sized for ventilation loads that are 50% higher than recirc loads. as mentioned above this raises the question of whether repiping to the existing units would trigger additional or replacement venting requirements. 



In the real world I would test the building air quality under normal use to see how much the lack of ventilation is pushing the point in regards to triggering this requirement. Obviously, I wouldn't recommend that the school avoid confronting it if they are borderline, but if they can demonstrate CO2 isn't an issue then I don't think trying to reuse existing equipment without confronting this problem is a bad medium term solution.



Looking at sticking with steam augmented with mini-splits isn't out of my mind.  But the estimates for boiler replacement, as I have mentioned, verge on prohibitive.



Partly because of my familiarity with smaller equipment and with ganging and staging of smaller equipment for large loads I wonder if this might be more cost effective and offer modest resilience given that operative failure for a single boiler wouldn't stop heating altogether.



I believe the supply piping would allow the load to be readily split approx. in half and then that could be in turn be serviced by ganging a couple 300-350,000 btu boilers.  Modest size, easier to move. much lower boiler water line could be established.  Given that the boiler room has a 5 foot lower floor it is remotely possible that condensate return pumps could be avoided. I'd have to do some more serious measuring.  seems likely that additional condensate storage might be necessary given the internal capacities of these smaller boilers. I like the simplicity of a gravity relationship for such storage.



So maybe I'm overthinking this and the engineering/piping for pairing and condensate storage, etc. just says bite the bullet and get a bigger boiler.  It is just seems to me that the scaling and relatively low number of units for these larger boilers really seems to push the cost envelope if the consultant is remotely close in his 150,000 dollar estimate for a 1.5 mill btu boiler. I'm just out of my depth on these big units whereas I feel like you could get 4 good sized residential units installed and ganged for a third of that.



If we were talking a 50,000 dollar expense, the doesn't have that anymore than they have 150 thou, but they could more readily raise or borrow it and I wouldn't think that they were getting over invested in steam. That would be a sensible medium term investment to protect against failure of existing boiler.



brian

Steamhead

Staging several steam boilers

You need to talk to Slant/Fin, they have been doing this for a long time. Ask for Larry Askew and tell him I sent you. Piping on these setups is VERY critical for proper operation, much more so than on a standard one-boiler system.



With that large of a staged setup you will still need a boiler-feed pump, since you need better control over when the water is fed to which boiler.



Not sure how far gone the pneumatics are, but they can be repaired- unless all the piping is shot.