How to delay boiler from firing again right away after max op pressure is reached?

So here is something interesting to note today apropos building heat loss.

Given that it's something like 8 degrees outside today, with a wind chill of -5, I pulled the building out of 3 degree overnight set-back a little earlier in the morning, had it go from 66 to 68. It took about 45 minutes to get there (I wasn't here to monitor cycling, remote wifi tstat - but not bad). Tstat is Honeywell TH8320WF (sticker says TH, not RTH - this should matter, I think). Stat is set to its CPH pre-set '1' (for steam) heat under 'Heating Cycle Rate' (under system setup function 0240). I am not sure how this exactly works, but I can't manually set the number of cycles, it does this on its own. I have yet to figure out what exactly it's doing. It's not obvious.

The system is running off this one tstat and I mentioned it being in office space that, when rad is on, heats quite fast, sometimes faster than the rest of the building. It's generally set to 69 in the am (off 66 overnight set-back), and as the day progresses, I bump it to 71 and 72 at 2:45 and 3:45 (4 temp per day programming). This works well, for the most part, keeping everything comfortable. This morning I had it come to 71 at the end of that 66-68 bump (manually), and it's now holding at 71.

My plan is to, for now, add a TRV on this rad in the office with tstat, and set the TRV to shut off the rad where the room gets to 71, with the rest of the building being close behind. This is 2nd rad from the boiler, coincidentally, so it heats quickly, which makes it tricky to balance heat in the entire building while tstat is there - but, let's say I'm happy the way it is now. I can't move it elsewhere as I don't want to mess with either wires or people changing settings, or putting a lock box on it, which I guess I could do one or all of it, but am lazy for this kind of change right now (so am looking at Ecobee 3 and it's functions - more about that later). Instead (and this is why TRV valve may be a good alternative) I have a tall card board box next to the rad covering the rad and have been playing with where the box is - high-tech, I know, to balance this room's heat gain with each heating cycle. This works well, for the most part, except when someone closes the rad bc they may be too hot - or moves my box. That's another story I covered earlier and why I started this thread.

At any rate, being that's colder today, keeping tstat at 69 does not get the building warm enough on a day like today. I have it now on 71. Now the interesting part: tstat still shows 71, call is 71, and the system actually came on and cycled one cycle for about 30 minutes without tstat falling back to 70. This got all the rads hot (I just checked the last rad on this loop, hot beyond the comfortable touch), and tstat is holding on 71. One of the zones in the auditorium (also mentioned earlier in the thread) is completely off. I did not check if we had some cycling on pressure with this set-up (closed zone essentially makes the system oversized), but I am pretty sure we did not have more than a few cycles on pressure for this particular condition as is today: colder outdoor temp with windchill.

I am mostly amazed, the tstat actually cycled the boiler, without it falling from 71 to 70. I have not seen this happen prior to today, and we've had this tstat for the past year.

And, this kind of functioning, in addition to perhaps delaying immediate boiler refing on pressure rise/drop and thus cycling on steam is precisely what I was looking to achieve. So, on a colder day, with a wind chill of -5, tstat actually functioned where BTUs lost to building heat loss was replenished through a 30 min burn, without tstat moving the temperature...

Anyhow... I know, I'm OCD with this. I will now go and do something else for a few hours.

Thanks @Koan! I'll be giving this a read tonight after kids are in bed (barring any calls for no heat from my tenants... It's bound to happen - it's getting down to 6 tonight, and wind chill is supposed to be in minus double digits... last night I had air in couple of rads on one of the units that needed letting out... fun never stops.

Here's the video one more time.

https://youtu.be/rN-3CQcdXFQ

Hatterasguy said:

MilanD said:

I am not sure how this is achieved with 2 vaprostats. Are you saying it can be set-up to fire lower BTU and also higher BTU input based on some setting/parameter, or on higher and lower oz setting, based on some setting/parameter? If BTU input changes, this would make it 2 stage, no? How is this done?

You utilize a two stage gas valve. When the Vaporstat is below setpoint (8 oz), the 24V is closed to the gas valve and you get high fire. When the vaporstat trips at 8oz, the circuit opens and the boiler immediately goes to low fire (typically 60% of rating). At that point, the pressure would typically fall slowly. But, in your case, it could still climb even at 60%, so you'd need to use the Pressurtrol to shut the boiler down at about 1.5 psi.

It's an excellent addition for your setup as you have a boiler that is far too large when certain zones are closed.

@Hatterasguy

AWESOME!! After you mentioned this, I was thinking about it and the implication - this would be just amazing! As this is a bit above my pay grade, I'll contact our Midwest Mechanical that installed it, and talk to them about this set-up. This would be, I think, just amazing.

I'm wondering if this in combination with the time-delay refire after pressure buildup after and if the low-fire pressure rise cut-off, would significantly improve performance. You just opened another possibility that I'm going to ponder over.

Thank you so much! This is just amazing.

Got it. Thank you both!

Let me ask you the following: if on, say, 60% burn the steam pressure drops below 8 oz (or whatever that low fire pressure point is) but btu is now not sufficient to replace the heat loss, how does a full 100% firing happen again? What triggers it, how does the full burn come back again if it's needed? How does it oscilate between high and low burns?

Also, how much down do you set de-rol? Is this a trial-error type thing? Obviously, I get it can't go below the sticker minimum btu input so how is this honed in, and will this require combustion analysis? I am thinking this will be like turning down the burner on the stove, so no need to do combustion analysis (afterall, LGB 7 does have open burners and is not considered hi f), right?

I'll take pics of the gas valve setup on Monday. We have 2 of them on there already. If you can tell me what to get to replace, or if I can use what's there, that'll be great! I will also test vstat voltage. I was under the impression it was full 110-120... Didn't pay attention what it was when I replaced the trol with vstat. Thick, 14 gauge wires tho.

Thank you both @Gordo and @Hatterasguy !

So my original post did not upload in it's entirety. I need to retype all this again from memory....

Not giving up @SWEI ... No worries.

Here is where I'll need help with getting the low firing figured out, as far as wiring goes. I'm attaching the pics of gas valves and wiring that's on the boiler.

First off, I've replaced the older Hoffman 75 on 2.5 inch loop/zone with the BJ Big Mouth. Omg! Steam got there in no time flat. Wow.

Now, there is another wonky zone with 3 rads just before this vent. It's probably 45-50 ft to the last rad on the 2nd floor. It's on a 2 inch line that reduces to 1.5 and the 1.25 for the last 25 or so feet for the last run to the rad. To help it with venting even better, I'll be adding a tee with a 3/4" nipple and a Gordon 1 vent just before the rad. This should get that steam there rather fast, I gather. Perhaps 2 Gordon's on an antler. But I'll start with one.

Now to the "I need help with" part:

I get that I need another vaporstat. I will need to be told how to wire it in (if not by just replacing the trol that's there). If it's to be used as a high limit switch, can't I just use the trol that's there already diales down to 1.5 psi cut out?

Then, I will need to know how exactly to wire burner controls for the low burn.

Then, how do I set up the low burn, and what to set it to - how do I tell it to do 70%, 65%, 60%? What % should I set it to?

2 more questions, more as a "what would you do" kind of things.

Mark Stayton and @Hatterasguy both have shared with me the delay relay setup with a fairly cheap timer. I know this is different than the low burn setup, but I am not sure how better in terms of fuel consumption overall? So, could I ask for a show of hands, if this were your personal setup, what would you do? Timer or downfiring?

Which brings me to my last point: there was a thread about downfiring a 300k btu oversized boiler and expert advice was basically against it. How is LGB 7 different to allow it and this boiler wasn't? I'm mostly curious how some boilers can be and other cannot be down fired or derated? (And as I mentioned in my video, I get LGB 7 has a max and min btu input allowance and am wondering why it does and some other boilers do not.)

Here's that thread:
http://forum.heatinghelp.com/discussion/159797/downfiring-a-300-000-btu-hr-american-standard-steam-boiler

Along those lines, no one mentioned having to adjust anything associated with combustion, so I am assuming this will be a simple "simmer down" setup.

Thanks everyone. You have taught me so much!

@Hatterasguy

So I should forget the barometric damper and pwm setup and do just the straight downfire with the current setup? And this will work 99% of the time? Sounds simple enough. That's why I was asking about damper and combustion analysis. I am also of a belief that the simpler it can be, the better. I can live with a percent or two of efficiency loss at lower firing rate vs. cycling on pressure or firing delay.

Speaking of firing delay, if you had to choose for your setup, which one would you do: downfire or delay?

Second question: will I be able to do this downfire setup my self. I figure I'm a quick study, unless there are special tools I need that would be prohibitively expensive to get.

Then, can I use the pressuretrol or do I need to get the second vaporstat?

@SWEI

So I'm now thinking 2 pros with 2 opposing views.

Here's nkw my logic.

We are talking LGB 7 by Weil McLane. Sticker has max and min btu capability 780,000 btu and a min 380,000 (or there about, I don't have it off the top of my head right now - video above covers it). Says nothing about changing draft hood or anything as such. I will call the distributor here in town for clarification for sure as will also call the controls guy I know pretty well from the company that installed the current boiler in 2010. From what questions I asked and from what answers I got so far, it looks like the thing is engineered to do it under the curent setup without changing things other than what @Hatterasguy says too. Given I'm not a pro, I am gauging answers and educating myself so that my decision on what to do is made with confidence.

Again, it is interesting that we have 2 opposing views here from professionals in the field. One must be correct.

Now, my experience with our old LGB 11 and the slow removal of the burners done by our oldtime boiler man did not seem to affect either the combustion or the old boiler's performance other than taking longer to cook steam for the volume of water. But this also meant slowing down the steam head, no? Analogous to downfiring, less burners = less btu input. If anything, it actually improved performance of then greatly oversized LGB 11. We did not change the draft hood, and I tend to think it makes sense what @Hatterasguy says about the excess air.

That old timer boiler man, btw, is now well in his 80s and has learned with his dad who ran one of the largest HVAC outfit in Cincinnati from 1940s on. His dad started in the 20s. At that time in the 40s, he had 11 men on 11 trucks working full-time. Old timer who worked on our boiler is also a college trained man and was one of the guys who set up the trades track at a local HS here in the 60s, who then came back to HVAC work after his retirement from teaching for another 20 years. He was the man who brought back to life that old LGB 11 after it sat idle for 8 years while the building was empty. Only a few years ago did he finally hang it up for good. Body couldn't keep up with the mind.

Anyhow, that's my thinking. I will call and confirm with the distributor and the installer, and will then need diagrams on how to set up the 2-stage firing.

Thanks!

@Gordo @Hatterasguy

Can you point me to 2-stage firing diagram for the LGB 7?

Ok then. I'll need to sleep on this and then reread. My head is spinning right now, just like our gas meter.