upfire and downfire indications (prev. on the main wall)

archibald tuttle

moved over from the main wall because the questions are firing rate relative to steaming satisfaction.



have two steam boilers which I believe are giving opposite indications regarding suitability of firing.



Boiler One



In the first, even though it has slow response and might merit upfire, I'm concerned that the savings from shorter warm-up firing might not be offset by vaporstat satisfaction, if ya know what I mean. Partly because I haven't gotten the thing to hit the vaporstat. I don't really get it because the system is a tight two pipe. never needs water. even underfired like this I thought it would hit the vaporstat set at 2 oz, but no deal. It must be condensing as fast as it can make steam even when the system is hot. It's got a dozen modest volume convectors and two traditional rads. 2" mains, 1 or 3/4" convector piping. I haven't done an estimate of the volume of the system but it seems fairly small actually compared to full cast iron rad one pipe systems I manage so I'm surprised. Probably shouldn't be afraid to just slam it with another .4 or .5 GPH on the nozzle but when I metered and found out I was actually burning more like 2.0 GPH. It was last guestimated at around high 60s low 70s for efficiency, so thats about 185,000 BTU net which ought to make something like 150 or more lbs. of steam depending on losses per hour. Now I gotta put my noodle to whether that should be creating 2oz. or more in a system this size.



Bottom line I'll through a bigger nozzle at it and see what happens as a test case I guess but I'm wondering what I should be looking for.



Its an old triple pass coal conversion with an AFII mounted in the feed door. It's got a 1.35 nozzle but its actually consuming about 2 GPH so . It takes 25 minutes to get the whole house steamed up, and won't trip a vaporstat set for 2 ounces.



Seems to be a reasonable case for upfire, but I'm wondering if there are vaporstats with an 8 oz. range rather than 16 oz. This system operates just fine at what must be the 1 oz. or less range and how is a 16oz. control set near the bottom of its own range with a subtractive differential really going to do the job of saving me oil with a bigger nozzle by creating boiler cycles as opposed to constant run without a more sensitive control?



As an aside, there is an old hot water add-on to this boiler that I use to capture the hydronic heat from each cycle after steaming for a warm floor, so while I do have some stack losses during the long warm up cycle, I'm not just dumping the hydronic component into the basement after steam satisfiess the rads.



______



boiler 2. Behemoth with dual fire Carlin 800CRD. We never run on the second stage. It makes steam on the first stage with a 6.0 gallon nozzle from a dead stop in a minute. This seems to be a case for down firing but this system does hit the vaporstat with an 8 oz. setting and runs maybe minute on , two minutes off in typical circumstances where the building itself is not starting from a big setback.



The problem is that the low limit for the first stage is 5.5. So I guess that means we could get a bout a 10% throttleback, although I'd prefer to go to something like 4.5.



While a new oil burner is not in our future because a new non-steam gas heating system is in the medium term capital improvement plan, maybe a gas conversion that was 650 M to 750M would be a suitable choice if it wasn't too expensive. That seems to put me in the Midco 6700 or 6850 series, Powerflame JA or Carlin 301 Gas. I'm pricing these. If they are similar to the carlin residential approach you have a fairly easy time adjusting firing rates across a range so you try different firing rates and monitor results. This kind of goes to all the threads about oil vs. gas as well. currently gas with all the taxes and distribution charges is running about $1.50 per therm so that is half or less of oil. This application is slated to use 3000 gallons for the rest of the season so that means if the installation is $4500 or less that will payback in 3 months of the heating season or less.





But I guess the question is, forgetting which fuel, is there a cycle length/heatup optimum I should be aiming for in balancing the vaporstat trip against the gph input?



I am going to install hour meters on the existing set-up so I can really track what the hours of boiler call vs. hours of burner op is at the present 6.0 gallon nozzle so I have better than anecdotal information of guessing at it from the time I've spent in the boiler room.



thanx,

2B (or not 2B, you decide)

Charlie from wmass

The second boiler

needs to be set for the high low fire to get a much better utilization of your oil dollars. The first one If it is 25 minutes from cold to steam is pretty good. The volume is not what matters it is the condensing rate that matters. EDR is just the unit we use to measure condensing rate, at least indirectly. I would leave the conversion alone and just save up for a new boiler.

archibald tuttle

I'm with you on the dual fire but . . .

charlie,



thanks for the quick heads up.



of course I would prefer a dual fire setup to be working but when the lower stage makes steam in 60 seconds, but it is already fired at very close to the minimum nominal input for that stage, I'm not going to get effective two stage operation out of the existing burner (if I'm thinking right)  unless there are specs for using a smaller or less efficient fan so that the first stage can be significantly down-fired and then reinstitute the second stage.



I don't what these politenesses about not discussing price are all about. I hope we could discuss why we can't discuss price? It's fine if the standard is this isn't supposed to be a forum for selling stuff, or debasing sponsors or their pricing, but how can you make informed cost benefit decisions about heatings systems without discussing cost? Let me just say that the materials cost for a gas conversion would be paid back in a month and a half. at the current 100% premium I estimated for oil. The labor has to be negotiated but I still think we're talking payback in the current season.



I had suggested saving the pennies for the new system to this user, a small school with no extra money whatsoever, but when I look at oil prices I think they are spending the pennies they are supposed to be saving. And market forces are going to maintain the divide between oil and gas for the foreseeable future given that the dollar isn't going to magically strengthen and the influx of domestic NG. I'm not suggesting that this is a permanent reality, but I would think that if you have job with a one season payback, there is no excuse for not converting in the current environment given that we don't know how many seasons before they will have raised the capital to change the system.



Now, i know they're not going to get dual or modulating fire gas in that range, but they can get a gas burner that is capable of a number of different firing rates from well below to above the current operating firing rate so they won't be constrained from modest experimentation about the most efficient apparent rate.



2B (or not 2B, you decide)