pick up timer for finicky vaporstat or . . .

archibald tuttle

so i was on here a few weeks back talking about upfiring my boiler. bit the bullet when the nozzle clogged a couple weeks ago. Only went up 10% but also took a pressure washer to the inside of the boiler,old coal 3 pass behemoth. It didn't have thick soot, but a very regular 16th inch patina.



Don't know which did more because I did it at the same time but I cut my steaming the first rads from a dead cold start from about 25 minutes to 12 minutes and started hitting the vaporstat for the first time.



So I was pretty stoked and started trying to zone in on cycle length adjusting the vaporstat.  I ended up setting it for 5 oz. with a 3 oz. differential.  I was getting 3 or 4 minutes on to 2 or 3 off, seemed great.



then I got the no heat call. the vaporstat failed to pick up after a cycle. of course i was 30 miles away. sent my wife down to look at the thing and while I'm trying to explain to her how to look for which end of the vial the mercury is at to see if the vaporstat is made, she brushed the vaporstat and it tripped on.



So I set it up to 12 oz. and wasn't witnessing any trip offs and left it at that until I had a chance to break down the piping and make sure there wasn't any corrosion or obstructions. It looked clean on the vaporstat side of the siphon.  The orifice to the diaphragm looked fine. It was pretty close to level, might have been a half a degree out according to the hinky pendulum arrow in the control. And it was mounted on the siphon perpendicular so that expansion and contraction of the siphon coil was not transmitted to the operative direction of the vial.



in other words, i couldn't find anything wrong.  For obvious reasons I'd like to cut the set point back down and try to regulate cycles again, but I'm very concerned about not having the control pick up at the end of an off cycle.



I'm trying to conceive of a timer control that gets fired by the normally closed contact on the vaporstat and gets reset when the vaporstat picks up, but if the vaporstat doesn't reclose within say 15 minutes provides a parallel feed to fire the boiler as long as the vaporstat doesn't pick up.



So, I'm talking about some relatively elementary relay logic, I just have to sit down and draw out a circuit that does that and I could probably build it with some relays but I'm not particularly familiar with what's available for timers for an application like this and/or if there is some other similar control application so there might be a more ready made control for the application.



Presumably if it was just a fluke of gravity or a ghost in the machine pressure in the boiler cycled the vaporstat it might pick up operating again, but I see this boiler daily, so I don't really care if the circuit is self resetting or not.



Any ideas?



Thanks

Mike Kusiak_2

Vaporstat settings

Sounds lile your initial setttings were too close to the lower limits of the vaporastat to be repeatable. The indicated settings are notoriously inaccurate There is always some friction in the vaporstat mechanism, so setting the limits too low can result in erratic operation as you experienced. Why not try a compromise setting like 8oz with a 3 oz differential.



Do you really want to be cycling on the vaporstat so much? If you can run long constant cycles at low pressure by the thermostat without pressure cycling, it seems you would be much better off.

archibald tuttle

. . . to cycle or not to cycle that is the question

mike,



thanks for your quick response, here's mine.



I have tried going low end on the nozzle (1.35 in this case) and it did steam but only after about 25 minutes. Then it could maintain steaming and did heat the house. But my oil usage compared to the 'old days' when I was running 1.50 or more and a pressuretrol, i.e. steaming all the time the thermostat called, didn't seem better on a first blush run against degree days or averaged over winter months.



I do capture some of the heat during run up and run down because I've got some warm floors hooked up to an old heat exchanger on the boiler that made domestic hot water once upon a time, so I can use anticipatory thermostat cycles to make up for the long time to steam, but I didn't seem to be saving any oil.



So when the 1.35 gummed up after my keep fill oil company kept me empty a couple of times, it was time to try a bigger nozzle and cycling on the vaporstat.  I don't have useful gauging on this although I'm trying to fix that. What do your or anyone think of these (http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gage-Switches-Digital/SeriesDH3/ModelChart)

Dwyer WC Pressure controller, gauge and logger signal all in one.  (does this comment engine still not have a place to add links? I used to write them in html but what up with that, am I missing it? And how come I still have to answer an antispam question when I also have to sign in to post . . . but I digress). They cost about twice what the old mercury vaporstats did but they perform several functions that I think would be more expensive to buy separately.



So my understanding of the whole deal is that you want an aggressive enough fire to get steam up in 5 to 10 minutes, but that tends to be more fire than you need to keep up with the condensing rate, so that is why we install the vaporstate - because it has taken the oil industry forever to get with the idea of variable fire. Given that this is a behemoth coal burner with a lot of give insofar as draft, I thought of actually mounting 2 burners on the thing and just dropping one out with the vaporstat. Then I'd hopefully never lose steam, but in the meantime while I consider that plan I thought that if I could get some 4 minutes on 3 off kind of cycle going which seemed doable from my early experiments - excepting the foible that got this thread going - I could save oil by only steaming to the most minimal pressure I needed and always capturing virtually all the condensation with reduced thermostat overrun.



Maybe just straight running gives me slightly higher and constant pressure and therefore slightly hotter condensing point so I reach thermostat setpoint more quickly, so maybe the savings from vaporstat operation are illusory, but then why are vaporstats so popular. More to the point, why isn't there a variable setpoint controller that can take the 4 to 20 ma signal from one of the Dwyer pressure sensors linked above and vary the effective vaporstat setting compared to outdoor temp.  This is 2 pipe closed system and uses virtually no water ,but I don't know if this system is tight enough to hold vaccum although that would be doubly cool in that kind of control stragegy.



so, now that I know I can get a pressure logger at an moderately affordable price point, my plan is to turn up the original setpoint as you suggested to 8 oz. and see if I can hit that, but set the whole thing up with a logger that monitors thermostat call, boiler call downstream of the vaporstat, pressure and temp at the and temp outside every 15 seconds (if I was a real glutten for punishment I'd measure sunlight on the south side and wind and wind direction but how whacky can you get). Then I can try straight steaming and a couple vaporstat regimens and try to get an idea what is using the least boiler time for a given outdoor temperature and indoor result.



Another novel for the critics here at the wall. have at it.



brian

Mike Kusiak_2

Optimized system

Brian, it seems like you are on exactly the right track:



"So my understanding of the whole deal is that you want an aggressive

enough fire to get steam up in 5 to 10 minutes, but that tends to be

more fire than you need to keep up with the condensing rate, so that is

why we install the vaporstat."



Exactly as you say, you want the firing rate high enough to quickly fill the system with steam, but not so high as to greatly exceed the condensing rate. Quite a balancing act, made more difficult by the lack of available modulating burners.



So it really comes down to the question of is it better to run a slightly higher constant pressure, or to operate at a lower, but varying pressure by vaporstat cycling. My feeling is that constant relatively low pressure is more efficient.



If we consider the difference in efficiency between operating at a constant 12 oz pressure and a 4 oz pressure, I would argue that it is negligible. The difference in operating temperature between these two pressures is about 1.5 degrees or about 0.7% of the average condensing temperature. Certainly not enough to materially affect the combustion heat transfer efficiency of the boiler when you consider the flue temperatures are in the order of several hundred degrees minimum.



But if we look at how rapidly pressure cycling the boiler, especially an oil burner fired one affects efficiency, the results are more significant. It usually takes several minutes after the burner fires to establish proper draft and combustion conditions. During this initial firing time the burner is operating at a less than optimal state of combustion. Just when efficient steady state combustion is finally established, the pressure cycle ends and the burner shuts down, only to repeat the whole process again in a couple of minutes. Really not an efficient way to operate a boiler.



So I really believe that achieving low pressure operation by vaporstat cycling is counterproductive, compared to constant firing at a reasonable slightly higher pressure.

Steamhead

"old coal 3 pass behemoth"

Are there any bricks or baffles placed in the flue passes of this boiler? If not, you're losing a lot of heat up the chimney. Adding these requires a knowledgeable pro with test equipment, but can save you a lot of fuel- though not as much as a new MegaSteam.



Clogged nozzles are usually the result of poor oil filtration. Is there a filter on your oil line?

archibald tuttle

now you're getting into combustion engineering

which is my weakspot and I need to improve on both theory and practice here.



Given the forced draft in an oil burner (and the draft regulator) I thought that the change in draft between hot chimney and cold was on the margin of the operating draft provided by the squirrel cage. But, that doesn't mean it doesn't matter, maybe I'm not attributing enough importance, or maybe I'm just plain wrong about marginal change in operating characteristics. What about the use of delay fuel and the like to try to cut down on rich starts?



I thinking this way because the difference in temp at the rads between a 4 oz to 8 oz. cycle and a 12 oz. constant run is so small ,I feel like if I could get cycle lengths in the 5 to 6 minute range maybe with half or more of that off, my gut tells me I'd be saving oil.



But what the hell does my gut really know about it. And can I possibly be heating the house during the off part of the cycle. If I'm still condensing I'm heating and the condensing rate is the condensing rate. It seems like magic, free heat while the boiler is off.  But then where does energy from constant run at 12oz. go. Up the chimney? That is the idea that would get you doing this.  But maybe my condensing rate changes with pressure. I thought the rate was the rate but I have to reason that out a little. If I'm condensing less, that is a big difference as opposed to the small difference in rate.  Although I feel like the dead giants used to get condensing points down to 160 or something by using vaccuum so that the coal fired you banked in the evening could keep steaming all night.  So there is some threshold of energy input that isn't getting the job done, but if I'm operating at a lower pressured that lower threshold can get the job done.  I don't know, just wandering in the wilderness at this point and could stand to be educated in that regard.



The discussion of fire / no fire does tend to push me in the direction of just using two burners so is high fire/low fire which at least keeps traffic up in the chimeny.  I think two burners because dual fire is expensive and finicky in its own right and I got umpteen burners lieing around in my yard that will cost me nothing -- of course you get what you pay for . . . ).  The biggest issue seems like spacing.  The first conversion was in the cleanout door, but I moved the burner up to the feed door so it is closer to the underside of the boiler sections.  ideally, if I had been thinking about it when I made the  last year, I would have drilled two holes for burners instead of one, probably diagonally offset would work so the burner motor on one didn't interfere with the side mounted controls on the other. I think there is just enough space for that.   The opening is about 12 x 16. Might be time to make another plate.



The other possibilility is to alternate rather than run both at once which might be slightly more sane.  Run my warm up unit at 2 gallons and once I make pressure use the vaportrol to kick over to .85 or 1.0 and set a good sized differential so only really cold conditions will end up kicking it back into low, i.e. high fire, gear.



Brian



PS - and I'm thinking that if the big one is warm up you set your draft regulation against the smaller burner and let the bigger one just power a draft since it is more likely to be running of a cold start anyway.  . . . here though I defer to combustion wizards.



Thanks,



Brian

archibald tuttle

that goes for steamhead too . . .

They tell me the world's best boiler guy is only a state away from me but it ain't the time of year I can get him so that might be my off season approach. I do think that the issue is that I'm putting a good deal of heat up the chimney, which is why I'm busy trying to figure out how to reduce firing time. If this were baffled effectively it would no doubt help. On the other hand, I want to be sure to maintain the capability of cleaning the thing with my mine pressure wand.  I open the doors and 60 seconds later the thing is spotless and no dust, so I don't want to do anything that would inhibit that method, but, come to think of it, I could mount baffles to the clean out doors, because is where the exhaust gas turns for the third pass. I could event probably contrive a system that is adjustable so I could tune instead of opening and closing the boiler and adding or subtracting bricks.



Yah on the filter side, I've got an FB10 and an FB4 in line. But when they ran out of oil I took a real sock of water and gruesome crap the overwhelmed the drop capacity of even the FB 10.  And the filter at the pump wasn't even that bad but something got through to the nozzle. I wish these burners were all designed like waste oil burners where this wasn't a problem.  I just feel like you ought to be able to get approximately equivalent atomization by using compressed air the way the waste oil burners do and then it would handle any of the minisucle stuff that gets through the filter -- how I don't know.



I do throw water eater at the oil with some regularity but it is an outdoor tank.  Probably time to break down and put a Roth tank in the basement and be done with that headache.



Brian

Steamhead

Don't know about

"world's best boiler guy".. I just do my best. But thanks!



The stock FB-4 (or FB-anything) cartridge isn't so good. It doesn't filter down to as low a particle size as you need, and can bypass dirt if it gets clogged. But if you use a replacement cartridge like a General or Westwood that is made for the FB-4 housing, it works much better- about on par with the General 1A-25A or its various clones.



In your situation, you may need more capacity in your secondary filter than this setup can offer. It might be a good idea to go to a larger unit like a General 2A-700A or similar. The FB-10 could handle the larger stuff and also act as a sludge pot.



Cleaning the boiler should not be a problem. Simply remove the baffles and put them back when you're done.



If you wish, let's talk about looking this over when things slow down here. What are the results of the latest combustion test done on this thing?

Mike Kusiak_2

Conservation of energy

Remember, in the end the building need a certain amount of BTU's per hour to maintain the indoor temperature at the thermostat setpoint. There is no "magic" about it. The best you can do is to get the most BTU's generated from the fuel into the conditioned space as quick as possible.



There are really only three places for the BTU's to go. One is up the flue, which you try to minimize as much as you can by having the best combustion and heat transfer to the water in the boiler. Clean surfaces help, as well as baffling the large passages as Steamhead suggests to optimize heat transfer. You also want to minimize standby losses by limiting the amount of air going up the flue when the boiler is not firing.



Second, is heat losses to the unconditioned spaces like the basement. Insulating the boiler and piping is very important, as is proper venting, but there is another factor that is largely overlooked. That is the length of the the thermostat heating cycles. If the cycle time is too short, much of the cycle is spent heating the piping and driving out the air. Only after that does useful steam enter the radiators and actually heat the occupied space, so if the cycle is too short, a relatively lower percentage of the cycle time heats the conditioned space and more heats the basement. Thats why you sometimes see postings here " why is my basement so hot, but its cold upstairs". Usually turns out that the thermostat anticipator or cycles settings are wrong, causing thermostat short cycling and resulting in a cycle too short to actually get steam upstairs to fill the radiation.



The last place for heat to go is where you want it, into the radiators. Proper venting will insure that steam gets to the radiators and actually heats the living space. Unfortunately, this is the last place the steam gets to deliver the BTU's, so anything you can do to get the steam as quickly and easily as possible into the radiators will benefit efficiency.



So in the end, once you have done everything possible to optimize the whole process,  there is no "magic" to decrease fuel usage past that point. Trying to reduce the total firing time is fine, but in the end, you need a given amount of BTU's so you really can't reduce it to below what's actually required to meet your heat load.



Steamhead's suggestion to properly baffle the boiler passages will probably gain you much more efficiency than any attempt to reduce steam pressure further.

Have you ever had a combustion test done? The results might surprise you as to how much useful heat is actually going up the chimney. In your case, increasing the efficiency of the boiler itself is where the most significant savings could be realized.

Jamie Hall

A comment on finicky vapourstats...

Your settings should have worked.  (5 with a 3 differential).  However, there are two possibilities.



First, make sure the thing is really truly level, left to right, and can't move off level left to right as things heat up.  That is very critical.



Second, it may help to fit a snubber to the pigtail, just below the vapourstat.  This smooths out short duration pressure fluctuations without interfering with proper operation and sensing.

Mike Kusiak_2

Another possibility

Jamie, I completely agree with you that the vaporstat should have worked with his initial settings, but only if the vaporstat pressure calibration markings were truly accurate. Unfortunately, unless he set up the vaporstat with an accurate low pressure gauge, the actual cut-in and cut-out setpoints may have been nowhere near the indicated settings. Perhaps the actual resulting cut-in was below atmospheric pressure, which would explain why the vaporstat never reset after cut-out.



The questionable accuracy of the vaporstat calibration markings of the latest models has been well noted:



http://www.heatinghelp.com/forum-thread/128249/why-do-Honeywell-vaporstats-suck-so-badly

Jamie Hall

I keep forgetting

that these new-fangled microswitch things are much less sensitive to level... and do need calibration.  Senior moment, or something.



There is a way to handle it without a pressure gauge, though -- run the boiler to where it cycles off, then as it cools slowly raise the calibration until it cuts in.  Fiddly, but it should work.