Where is the savings in twinning boilers in this house?

Double D

Original installer removed an existing 300,000btu boiler and convinced the owner she would save on operating costs if she were to buy 2 boilers and stage one of them using outdoor temp control. For starters it would have been nice if the boilers had been sized and piped properly but that's not the case here. There are 7 radiators and 5 Gold Pin exchangers. I have not done a total EDR yet (due to several other issues which needed to be addressed first), but it appears one boiler would be close to all the house needs.

GW

You seem to have your opinions already in order. It’s yucky

JohnNY

Wow. That's full-on terrible. Thanks for sharing.

nicholas bonham-carter

In spite of his sophisticated attempt to use lead-lag boilers, he wasn’t very knowledgeable about the piping, even though I am sure there is a diagram in the instructions as to how it should be done!
I could see using two boilers each sized for one half the EDR and controlled with a Vaporstat, so when the pressure gets up to the set point of a few ounces, the lag one cuts out, leaving the lead to carry the load. A two stage thermostat is probably needed as well.
I think the system would function better with inside sensors instead of outside. Is this a Heatimer control- may be added later after this system started having problems?

GW

for my own knowledge- two smaller boilers work well? Does the half-size boiler make enough steam to keep the system happy? I thought a 'small boiler' would run forever and not heat up the entire system, running the fuel bills up. Just curious; i understand that a two-boiler job is different than one boiler that's too small.

Gordy

If I’m understanding correctly both boilers bring system to temp, and one drops out leaving the other to maintain temp.

Fred

Gordy said:

If I’m understanding correctly both boilers bring system to temp, and one drops out leaving the other to maintain temp.

I would say two boilers, of equal size and half the total requirement, if properly sized might do that in the shoulder season and maybe a little beyond but anywhere near design days, they will both run as if they were a single, properly sized boiler. I'm not even sure if a boiler rated at half the requirement would evenly maintain distribution of steam throughout the entire system design day or not ???

mikeg2015

I could see this work, but you need more like a 60/40 split.

So lets say you EDR is 600 (144,000 BTU). Conventional sizing says 191k BUT output so either 225k or 250k 82% eff) boiler. But you only need 175k input to match the load once heated fully. so a 175k plus a 100k.... assuming the header is sized well, I think you'd have a system that runs smooth, and has some redundancy. Plus you'd have some redundancy.

You could make the primary boiler standing pilot since it runs longer and you'd have heat in a power outage.

If you add TRV's you could subtract those radiators form the boiler #1 load and shift the size balance. You could put an indirect on the small boiler and then only have to run one smaller boiler in summer.

I would love to see if you could balance a system with an undersized boiler. I keep hearing that the system will never heat up and it uses more fuel. But why? From what I can tell, the vent rate will just slow.

EBEBRATT-Ed

Controlling two steam boilers and their respective water lines isn't the easiest thing to do. Makes any fuel savings by using 2 boilers not so hot. Consider this:

Idle boiler fills up with water because it is cooler it fills with condensed steam from the supply piping. So you need overflow traps to control the water lines $$$$$

Two boilers will never be under exactly the same steam pressure. Even a few ounces makes a difference. Gravity return condensate will enter the boiler under the lowest pressure. You cannot connect two steam boilers together below the water line (so you can't equalize the water connection) unless you use check valves (unless you don't care about the ASME Code) The reason is a leak in one boiler would cause a loss of water in the other boiler. So now you need check valves, maybe feed pumps and or motorized feed water valves $$$$$

And their are other issues

mikeg2015

Couldn't you just use a hartford loop on each boiler to keep the levels the same but prevent loos of water in one affecting the other. That and separate backup LWCO on each return.

I did realize that both would have to remain hot even if only one was steaming, so you'd have jacket losses on the idle boiler.

We had 2 boilers at a commercial building, but I can't remember how the water line was managed. It was an old hospital and it was renovated to add labs with huge makeup air requirements, but the labs were shut down. SO we needed up just rotating the boilers annually. I think the idle boiler just flooded up to the header.

nicholas bonham-carter

I think a Gifford loop might solve the inactive boiler filling up, and maybe the lead sized for building heat loss, and the lag sized for the difference between between total radiation EDR, and the lead boiler rating.
They could be piped into a large common header, with equalizer, and when the 2-stage thermostat AND the vaporstat allow, both will fire. When the pressure gets up to the few ounces of vaporstat cutout setting, or the second stage of the thermostat is satisfied, the lag will drop out.
This would probably work best on a vapor system.
I am being influenced by the Steam Whisperers experiments with using little or no pickup factor. This system gives you a pickup when you start heating, and does without in the shoulder seasons, —NBC

EBEBRATT-Ed

I am not saying it can't be done. It can but it's not simple as it seems.

Hydrotherm use to have a setup of modular steam boilers all piped together in one manifold. Code wise it was treated as 1 boiler because there were no valves between the boilers. No hartfor loops etc. never worked right.

Filling the idle boiler is from steam condensing in the cooler (idle) boiler more than the feed water issue. there are no piping methods to solve this other than an overflow trap

Double D

I may have spoken too soon in saying it appears one boiler would be close to all the house needs. The Gold pin heat exchangers come to more than just one boiler and the rads still need to be added to that. So glad I bought Dan's E.D.R. Ratings for "Every Darn Radiator. The exact Gold pin rads on the job are in the book.

@JohnNY
After looking the system over, the owner asked what I thought. I told her this is the kind of job you say "let me go to the truck and get a pencil". Then you drive away.

@nicholas bonham-carter
This is not a Heatimer control
I would prefer Vaporstat control

@GW
From what the owner tells me, the half size boiler keeps the system happy on 40+ degree days.

@Gordy
One boiler stays off as long as the outdoor temp is 40+ degrees.

@Fred
I have not seen the way this system operates on shoulder days but one boiler operating on design days is definitely not enough. The original call was, one of the 2 boilers is not running. Outdoor temp is single digit and stat not getting past 50deg.

@mikeg2015
Since the boilers are not that old, I will need to work them but I understand what you are saying. In addition to the poorly piped header, there are multiple system issues that need to be addressed. The system has had Many years of knucklheading done to it. Most if not all of the hammering the system does is due to the knuckleheading.

@EBEBRATT-ED
I would have never suggested 2 boilers in a house this size. Maybe Hi-Lo fire, maybe not. It would depend on what the owner was looking to do. One example would be the job I was on prior to this one. They have one steam boiler that heats the 1st floor and a second boiler that heats the 2nd & 3rd floor. (single home)
Due to all the system issues that need to be addressed, I will need to work with the boilers that are in place.

When the tops of the boilers were tied together, one boiler appeared to be having its steam condense in the other causing it to cycle off on low water while the other continued to fire. I needed to get some skim ports on those boilers ASAP, so I removed the 2" tie at the top and put in skim ports for each. Both boilers have cycled dead even on the water line since but I do see how it could be a problem. With the tops tied together, the steam collides in the header no matter which boiler is running.

ratio

Perhaps @vaporvac will chime in. She has twinned boilers that are working great, last I heard.

mikeg2015

nicholas bonham-carter said:

I am being influenced by the Steam Whisperers experiments with using little or no pickup factor. This system gives you a pickup when you start heating, and does without in the shoulder seasons, —NBC

Do you have links to these tests? I'm still trying to understand what problems there are.

For example if I had a modulating burner on my boiler and right now I cut it to match my EDR so pressure never rose, what happens? What if I dialed it back to match building heat loss. So it only made enough steam to partially heat the radiators. without cycling on and off?

I keep hearing that it will waste fuel because it runs so long. But if I run my boiler for 30 minutes per hour at design condition, it uses the same fuel as a boiler 1/2 that size running continuously.

nicholas bonham-carter

This may be a case for 2-pipe vacuum, wherein the lowered boiling point would enable longer burns with a smaller flame.
I’ll see if I can find the Steam Whisperer’s description of his experiments with this.—NBC

nicholas bonham-carter

I am amazed I found it so easily-not usually the case. Now I will have to reread it again so I can be certain I did not misremember anything!
Link below.—NBC


https://heatinghelp.com/systems-help-center/taking-another-look-at-steam-boiler-sizing-methods/

EBEBRATT-Ed

Like I said before. If you don't care about the boiler codes you can tie both boilers together below the water line to help keep the water lines the same. Some have probably done this. Highely illegal. Lose one boiler. loose two boilers

mikeg2015

EBEBRATT-Ed said:

Like I said before. If you don't care about the boiler codes you can tie both boilers together below the water line to help keep the water lines the same. Some have probably done this. Highely illegal. Lose one boiler. loose two boilers

Right, but couldn't you tie them with a double Hartford loop config? So its below the water line normally unless one boiler is low on water. Could actually share a secondary LWCO that kills power to both boilers.

mikeg2015

nicholas bonham-carter said:

This may be a case for 2-pipe vacuum, wherein the lowered boiling point would enable longer burns with a smaller flame.
I’ll see if I can find the Steam Whisperer’s description of his experiments with this.—NBC

nicholas bonham-carter said:

I am amazed I found it so easily-not usually the case. Now I will have to reread it again so I can be certain I did not misremember anything!
Link below.—NBC


https://heatinghelp.com/systems-help-center/taking-another-look-at-steam-boiler-sizing-methods/

I started reading this, and I feel like I could have wrote this myself. It answers all the issues I'm having in balancing my system without whistling vents. My boiler is simply too big, and I have the venting capacity low enough now that I could balance a much, much smaller boiler. I'm thinking getting DOE to match EDR and don't worry about pickup. My last 1-2 sections never get fully heated anyway as the vent closes first every time.

So in my case 172k BTU radiator capacity would put me at a 225k BTU input boiler as the nearest size going up slightly, but a leap of faith might have me go with a 200k. Building heat loss is around 90-120k depending on wind, sun, stack effect and because of building mass, it's really more a 36 hour average out OAT. I bet I could even get Maid of mist to make me some custom drilled size "#3" vents for even slower venting than the #4.

Downsize is it takes 15 minutes to head the main now on startup. It would take 22 minutes with the smaller boiler.

For now, I'll just have to increase venting rate just a little to keep it quiet but still balanced.

ratio

Don't forget that you can, in a manner of speaking, adjust the 'size' of the radiators via orifice plates.