upfire, downfire, and micro vapor sensing

archibald tuttle

Are there any vaporstat's with a 0-8 oz. range and finer differential?



I've got a 2 pipe residential steam system of convectors (late 1950s era piping and convectors with double pass coal conversion boiler, AFII gun in the door replacing shell burner at the floor).



Over the years with the old burner it was fired between 1.25 and 2.00. Right now it is at 1.35.



I have a couple smaller boilers I was going to use to make a dual boiler rather than dual fire approach. And then I considered just running the south rads with one and the north rads with the other. And then I decided I'm headed for hydronic radiant floor and walls in this joint in the long run anyway and the short run gains from all that work of repowering and repiping the boilers, if it was to be repurposed to hydronic with condensing boilers wasn't worth it.



So I went the modernization route and put the AF II at 1.35 in and that doesn't seem to have made a lick of difference in oil consumption.



It is slow to heat from a cool start, takes 25 minutes to get steam throughout. And once it's got steam it never hits the vaportrol/stat. I install a 0-16 oz. in place of the pressuretrol and the only way I can get it to shut off on steam is to turn the vaporstat to almost 0, which makes me wonder what the heck happens to a subtractive differential in that circumstance or why they even have 0 on the adjustment scale. when I do that, it never comes back on unless I go turn it back up to 2 oz., but if I leave it at 2 oz. it never turns off, so I can't really estimate how my shortcycling or other issues would be because there is no cycle (relative to vapor pressure). One other variable which I hadn't really thought about until we ran out of oil the other day and I ran the thing out of a 2 gallon can, and it was going through 2 gallons in an hour no problem on this 1.35 nozzle. Time for some hour meters to be added to the whole mess, one upstream and one downstream of the vaportrol although until I get a more sensitive vaporstat if one exists they are going to read the same. (I put a new pigtail on when I installed the vaporstat and had checked that there wasn't any blockage at the time so I don't believe the problem is lack of signal).



So my guess is that the theoretical solution here is to upfire. Now that always makes me nervous when the fire I have is readily heating the house and it's just a little slow to make steam.



Also, without a real baseline, it is hard to compare the results. So I would like to find a more sensitive vaporstat. because even if I upfired, I don't see any reason to be running more than a couple ounces. The system is tight as drum. Never needs water. Hits all the rads like gangbusters. Man do I admire the dead steamers who piped this.



Internal geometry of the boiler is making me think I might want to build a target wall nearer to the burner now that it is raised. (the old burner was in a shorter pit that would have been the ash bin for the coal). Although it has a nice double pass design for the exhaust so it's not a straight through thing and the stack temp doesn't seem off the charts. The exhaust comes down center passages above the fire box all the way back to the front of the boiler and then returns on the outside to the exit.



Got another boiler with an enormous 2-stage Carlin 800CRD burner that is in big need of down firing I think although this one is hitting the 8 oz. vaporstat so maybe I shouldn't worry about it. I will report back with some hour meter readings up and downstream of the vaportrol. Of course that won't tell me cycle length but my experience from just being around when its running is minute on 2 or 3 off.



It's got 6 GPM in the first stage -- we never fire the 2nd stage -never need it., the first stage makes steam from a dead stop in a minute and a half. I've never seen anything like it. The rating for this thing only goes down to 5.5 GPM on the first stage but I think if I was toying with it (this is the last year for this boiler anyway so I'm not thinking of getting a new or new used gun but maybe I shouldn't rule it out). If I got a much smaller two stage, I could repurpose it to my second location eventually.



Anyhow, it seems to me as I think about it that to derate this for lower firing the principal requirement would be a less efficient fan. Then we could maybe reinstitute the 2nd stage and fire it at 3 and 2.5 for a low end trial.



Or if that is too aggressive, 4.5 and 1.5 or something.



In both these cases I'm the 'circulatory' tech, not the burner side, but I try to factor burner technology and cost/benefit of improvements and approachs with the guys servicing the burner. But the guys working on them don't really even pull efficiencies. They just treat it as an art form with these old behemoths and if they are burning with a hint of smoke and making steam, that's the end of what they want to know about. The last nominal efficiency reading we had on the first boiler I mentioned was in the low 70s (noot the 1970s, but it was maybe the 1990s). But I wonder if the stack temp metric really accounts for the volume of exhaust on these systems. Maybe it is just a proportional reality. But also if one is factoring in the input btu's from a nominal nozzle and the nozzle is actually consuming 50% more than the nameplate rating where does that leave us?



Confused in Cincinnatti -- well actually Rhode Island but I like aliteration.



Brian

nicholas bonham-carter

aliteration

try reposting in the steam section, and do a search for "pressure" and you will find many people in your low pressure situation. my 55 rads does most of its work at 1-2 ounces!--nbc