Cycle rate for high fire, two stage gas valve

ratio

Well, I've mostly given up any desire for modulating the firing rate of my boiler, it's just too complicated & expensive for the benefits. So, I've set my sights on staging! My initial thought is to bang high fire in & out with a pressure switch, set somewhere in between the cut in & cut out pressures. I've drawn up a ladder diagram, based on the Dwyer control as seen here. (I seem to have lost the original thread)

Line four is the sole addition, and will be be nothing more than one pressure switch identical to the cut in & cut out switches. Will this simplistic control cause problems by cycling in and out of high fire too rapidly, or do I need a more sophisticated control such as a switch with adjustable hysteresis?

JStar

Typically, the wiring will remain exactly the same as factory spec's. When you install the 2-stage GCV, you will split the Main Valve control wire to go to the GCV as well as through the pressure controller, which feeds back to the 2-stage solenoid valve. You'll need a pressure controller with adjustments, so you can trigger low fire between 4 to 8 ounces or something to that effect.

vaporvac

My Honeywell Tstat is designed for staged-firing, although I have twinned boilers. The burners come on either high OR low fire depending on the differential between the current and desired temp, then maintain at low fire. They usually stay at low-fire except for nighttime set-back. It will still toggle on pressure settings, but once I'm steaming the Vsat rarely trips. I seem to recall you were over-sized, so I'm not sure how this would work for that situation.

ratio

I'll take a look at the factory schematic to see what it's doing. I'm just wondering, with basically no dead band between high & low, will I run into problems? This is a larger boiler, 3675 net ft², & for some reason I haven't dug into yet, she builds pressure quickly - IIRC that from a warm start in cold weather I'll hit the cutout in like five minutes. I'm working on surveying for EDR, maybe that'll shed some light on things.

Empire_2

It sounds like your second stage firing of the GV is rarely needed as you described. Unless you are coming out of a lo temp night set back, is the boiler by chance over sized? The recovery sounds exceptional and you may not even need the second stage........ My .02

Peace;
Mike T.

ratio

Well. I don't actually have two stages of firing- yet. I'm considering adding it, because even if my 3675 ft² is sized proper for design (which I suspect isn't the case), that still leaves the other 99% of the season.

I've looked at the MOD-U-PAC a little, while the schematics that I found don't agree with the control sequences that went along with them, they did tell me that second stage is controlled by a presssuretrol, which implies a certain amount of deadband is necessary, more so that will be available with a Dwyer 1823.

Empire_2

OK now you have me wondering.... Do you want mod or staged firing because of something you read or seen? Do you think it will absolutely apply to your current system and the pay off will be substantial? I am just trying to understand why you wish to stage or modulate, and what savings if and you expect to recoup by doing this,....With an existing boiler that is (if I am correct is an 80% sized for the home by other,..... Have you performed any calculations on the structure as it stands now, what and how much radiant base or emitters do you have, and was the boiler sized according to that or just installed according to the heat loss of the structure?
I can stage it a number of ways, but not something you do if it's not economically prudent, but we could if you want go with Maxitrol if you think you would like that rout.......


Peace;
Mike T.

ratio

Backstory: my parish school bldg, now leased to a charter school (who pays their bills & is therefore desirable). Original (~1950s) cast iron sectional replaced less than 10 years ago with Peerless 211A 8 section, so 3475 ft² of steam. Near boiler piping is ...adequate... by the fact that it heats without hammering, but not completely kosher. (I believe that's due to the 60" risers into the 8" drop header.) Sprung a leak in an underground condensate line a few years back & was running on makeup water when I got involved. The first leak was repaired, the second I signed for this morning. The tenant, bless them, has been turning the WWSD up & down to relieve overheating. The boiler, if it was sized at all, was probably sized for a fast Monday recovery as judged by how fast I build steam from a cold boiler - minutes, maybe tens of minutes. Steam traps are original to build, or addition, or replacement of enter.

The poor thing's been rode hard and put away wet. But, it's my baby now & I'm gonna make it work if it kills me. I'm quite sure that a little turndown on the firing rate will give a big payback in fuel, so I'm thinking about that now, but it's not next on the list - traps & orifices are, I think. I'm working on an EDR survey, but it appears that I'm going to have to do that myself too...

Whew, that's a few of the bigger items I'm trying to handle with this system. The church bldg itself, hot water piped "sucking towards", she's gonna have to wait another season or two!

Want more details, or did I scare you off? ^_^

Abracadabra

I just installed a 2-stage gas valve on a peerless 211a-7 boiler that was significantly oversized for the application. If your peerless does not already have a 2-stage gas valve installed, simply remove the gas pressure regulator and the first gas valve and replace both with a V4944. I wired in a vaporstat to open the stage 2 circuit when the vaporstat cutout hits. I setup the vaporstat for cutout at 12 and a diff of 8. I'll have to head back over there once colder weather hits to check out how it works. In addition to installing the 2-stage gas valve, I also removed 2 of the end burners. In additon to the work on the gas train of the boiler, main venting was also significantly increased. Adjust the low fire rate (stage 1) to not be less than the min. firing rate listed on the spec plate. for the 211a-7 i believe it was in the vicinity of ~660K with a max of ~1300K.

ratio

@Abracadabra, thanks for this! Seems like just the thing. I've been thinking about it all day. There isn't a minimum firing rate listed, but I think I could just aim for ~60% of high fire & tune it in with a combustion analyzer.

One question for you: I'm currently running on a built-up pressure control as I mentioned above, set to a cut in of 24 oz/in, & a cut out of 32 oz/in. To add the V4944 I'd have to add two more pressure switches, or a vaporstat. Do you think I should I just get two vaporstats & eliminate the built-up control?

Thanks again!

Abracadabra

ratio said:

@Abracadabra, thanks for this! Seems like just the thing. I've been thinking about it all day. There isn't a minimum firing rate listed, but I think I could just aim for ~60% of high fire & tune it in with a combustion analyzer.

One question for you: I'm currently running on a built-up pressure control as I mentioned above, set to a cut in of 24 oz/in, & a cut out of 32 oz/in. To add the V4944 I'd have to add two more pressure switches, or a vaporstat. Do you think I should I just get two vaporstats & eliminate the built-up control?

Thanks again!

Just add a vaporstat. Keep the pressure controls you have as a safety backup in case the vaporstat fails. Current version of the vaporstat from honeywell has a micro switch instead of a mercury switch and is prone to occassionally fail/stick. Do you have a pic of the rating plate for the peerless? Pretty sure they all have a "minimum" listed. Is there a space for minimum on the plate, but it's not stamped?

ratio

That's it. There's a blank for it, but nothing stamped there. I'll see if I can attach it, but I'm on mobile.

Ok, it worked.

ChrisJ

Interesting that it shows thermal efficiency and combustion efficiency.

Am I right in that's a total of 42.1% loss on a good day? Meaning a true efficiency of 57.9%?

JUGHNE

ChrisJ, you have to think positive! With your logic on those ratings wouldn't that be 157.9% efficient?

I wonder if thermal efficiency isn't more like an AFUE ratting.
And the combustion efficiency is steady state operation efficiency. I'm curious about the two ratings and hope there is more input on the subject.

The nameplate below has more info, perhaps minimum firing rate. It would be good to see the rest of it.

ChrisJ

JUGHNE said:

ChrisJ, you have to think positive! With your logic on those ratings wouldn't that be 157.9% efficient?

I wonder if thermal efficiency isn't more like an AFUE ratting.
And the combustion efficiency is steady state operation efficiency. I'm curious about the two ratings and hope there is more input on the subject.

The nameplate below has more info, perhaps minimum firing rate. It would be good to see the rest of it.

No?
Thermal efficiency isn't the same as combustion efficiency.

Combustion efficiency is the systems ability to convert fuel into heat.

Thermal efficiency is the boiler's ability to absorb that heat and stop it from going up the chimney.

I'm still thinking a true efficiency of 57.9%.

JUGHNE

So is it possible that a 2006 boiler could have an efficiency that low? I realize it is a commercial unit but.....


In the meantime hopefully Ratio can provide the lower metal nameplate.

ChrisJ

JUGHNE said:

So is it possible that a 2006 boiler could have an efficiency that low? I realize it is a commercial unit but.....


In the meantime hopefully Ratio can provide the lower metal nameplate.

According to Jim Davis and Tim, yes it is.
They both said my 82.9% AFUE rated unit's real efficiency was 69-78%.

ratio

ISTR that the lower plate just showed pilot locations for the various configurations, but I'll be on-site this weekend & will snap another pic.

What's the consensus on a barometric &/or a flue damper on a boiler this size? Operational efficiency is second only to reliability of the heating system.

Abracadabra

there are so many other things you can do to increase efficiency that will give you better returns than trying to install a barometric damper on an atmospheric boiler. I saw that @ChrisJ installed a barometric damper on his smaller residential boiler, I personally don't think it's worth the effort unless you are sure you've got all your other bases covered, ie. venting, air leakage around windows/doors, insulation both building and pipe, etc.

ratio

I'll keep that in mind, but you've got to understand that I'm a tinkerer... ^_^ Also, I don't look at ROI much, as this is mostly out of pocket anyway. Either 100% or 0% depending on how you look at it...

JStar

I have committed a certain acronym to memory that I use to decide what alterations to make, and when to make them. I call it the SEER rating for repairs.

S-afety
E-fficieny
E-conomy
R-eturn

Safety issues and repairs trump all others. A barometric damper is much safer than a standard draft hood.

The efficiency will rise up a bit - He who controls the air, controls the efficiency. A fixed-rate draft hood allows a very particular amount of dillution air into the mix at all times. The draft through the boiler can vary wildly throughout the winter. Control the air!

Economy and return - These are the bottom of the list for me, but not completely unimportant. Will a barometric damper save you enough money to justify its installation? Maybe. More importantly, for me, is the increase in safety. Better efficiency is just a perk.

ratio

Si, one "meh" & one "yes" WRT the barometric & damper. I'm sold! I'll stat researching then, but it's not gonna happen this season.

I did get a better pic of the lower plate, attached below. Doesn't show low fire.

Abracadabra

Just FYI, here's the plate on the boiler for the job I installed a 2-stage gas valve on. Looks like yours is a newer model. Not sure why they decided to stop including the min.btu input rate. I'd say a good min. btu rate would be 1/2 of max as shown on the pic of the tag of the boiler i've attached here.

ChrisJ

Abracadabra said:

Just FYI, here's the plate on the boiler for the job I installed a 2-stage gas valve on. Looks like yours is a newer model. Not sure why they decided to stop including the min.btu input rate. I'd say a good min. btu rate would be 1/2 of max as shown on the pic of the tag of the boiler i've attached here.

Holy smokes that's a big boiler!

ratio

Sounds like a good target. I've got a line on the valve, I'd imagine that I could have it here in the next week if I pull the trigger on Monday. Huh. I bet I could get this done in the next week or so if I wanted. Do you think I'd be well served to get this in this season, or wait until next summer? I've already got a floor cut coming in the next few weeks to repair what I'm hoping is the last underground leak.

ChrisJ

I swapped out my burner and drafthood during the coldest week last winter, we had a high of 18F and a low of -8F that week.

I did it because I wanted to see how it would perform.

My opinion is, do all you can now.