Multiple steam boiler piping and controls

James Day_2

Have a project replacing one larger steam boiler with either 2 or 3 smaller steam boilers. For efficiency and ease of getting equipment in and out.

I see bunch of options of piping the boilers and not sure what is best option. Pipe each one separately and drop into main header, each one with a separate Hartford loop and tie returns in. Or using pumps and check valves on returns.

Any thoughts?

Thanks Jim

JStar

I always liked piping each boiler with its own near boiler piping, then sending each one into a main header. Keep it all gravity returns. Taco makes a staged relay that worked well for multiple boilers at a more affordable price than Tekmar or HeatTimer. I'll post links here to previous jobs if I find them.

JUGHNE

Do you have any pumps now?
And will the old and new water lines be close?

JStar

https://forum.heatinghelp.com/discussion/150480/twin-steam-boilers-4-stages-of-firing-rates#latest

https://forum.heatinghelp.com/discussion/148320/3-boiler-caravan-6-quot-header-kings-park-ny#latest

https://forum.heatinghelp.com/discussion/147862/another-twin-system-6-quot-drop-header#latest

https://forum.heatinghelp.com/discussion/147678/twin-boilers-one-pipe-steam-system#latest

https://forum.heatinghelp.com/discussion/147044/1930s-veco-vapor-system-boiler-change-and-system-upgrades#latest

James Day_2

No pumps on it now. It’s an old American standard steam boiler.

If you pipe the boilers separately with separate Hartford loops,
Why did you do with the equalizer on the header you tie the 2 systems into? Can’t see it from your pics JStar.

Thanks Jim

JStar

You still need to drip the header, and that's what the equalizer will do. It can drop right into a common wet return that returns to the boilers.

James Day_2

I meant what did you do. Not why lol. Fast typing. Appreciate the input

JStar

The main system header equalizer will drop down below the boilers' water line, then come up into the boiler hartford loops individually. The main system wet return comes up into the main header equalizer with a hartford loop (or Gifford loop!).

JStar

Here's the sketch.

You're essentially treating the bank of boilers as one unit.

nicholas bonham-carter

Is this a two-pipe system, or one pipe?
In spite of the drawing from most manufactures, for this twin boiler installation, I wonder if the boilers couldn’t both feed into a large common header, which could be welded. The boilers could be connected with drop headers to this common header, with one equalizer. Each would have its own Gifford loop connection to the wet return.
As long as there are swing joints between boiler and common header, the thermal stresses should not be a problem.
Now for the controls-one vaporstat (Mounted on the common header), could control the cutout of the lag boiler, and the cheap, useless supplied pressuretrols could be set high enough to prevent overpressuring when the customer allows the pigtail to get plugged.
Therefore, when the thermostat calls for heat, after a setback, both boilers would fire, until the vaporstat cuts the second one off. If you want to get more sophisticated, the lag boiler plus lead boiler, could be sized for the heat loss on design day (both firing), and the lead boiler could be sized for normal lower temps, where it could handle the load by itself.—NBC

JUGHNE

I am looking at a similar situation. This is one over sized steamer feeding 2 buildings butted together, zone valves used.
A 1 pipe that could be gravity return
The other 2 pipe that must be pumped return.

Was planning to use one boiler for the 1 pipe system and 2 for the 2 pipe system. Simple 2 boiler staging for the 2 pipe.

This system has been a not so good marriage since 1955.
Breaking up will be the best improvement.

Any zone valves in your project? Or even separate building areas with different temps or usage fed by their own main?

Is there any concern with water capacity of new boilers being perhaps less than old and slow water return causing feeder action.
If the old boiler is running IIRC there is a method of timing the return water back to the boiler. FWIW

RayWohlfarth

James I prefer using a boiler feed and separate pumps for each boiler. If you have an equalizing pipe between the two boilers, you could have issues with the water line. The old boilers got away with it because they were so large. A one ounce pressure difference can mean a 1 3/4" difference in the water levels. Check with the manufacturer because they may require a boiler feed unit. That is where the system makeup water is introduced. One of the other concerns with using modular steam is the control sequence. I like to bring both boilers on at the same time and then allow them to drop the firing rate once steam is established. If you only bring one on at a time, the nearest rads will be warm and the furthest cold. Just some thoughts from an old boiler guy

JUGHNE

Ray, is this where a F&T drip trap set just above the water line on each boiler draining into the wet return be useful. Excess water of idle boiler draining away.
It would usually drain into the feeder pump. But if there was no pump could it go into the return on the floor before HL's.?

RayWohlfarth

Yes it’s called the High Level Spill and part of Asme code

JUGHNE

Yes, but would it work dumping into the wet return?

nicholas bonham-carter

Wouldn’t the Gifford loop, (with its higher elevation), instead of the Hartford, keep the water from being pushed out into the wet returns?—NBC

RayWohlfarth

@JUGHNE i always use a boiler feed on all my jobs and feed the high level spills into a small condensate pump and pump into the boiler feed
@nicholas bonham-carter not sure if that would work Will do some research on that

JUGHNE

Could the spills just go into the feeder pump with the dry return or even teed into the vent pipe?

Most think cond/feeder pumps are a necessary evil, if gravity would work.

JStar

If all of the boilers are connected with a common gravity return, then their individual water levels will always be the same.

JStar

If you isolate each boiler with its own feed pump, then steam will condense in the boilers that are off and overfill, thus requiring high spill traps. By adding pumps, you've created a problem that didn't exist, then solved it with more parts that you don't necessarily need.

JUGHNE

So if 1 of 3 boilers are steaming pressure into a common header then the other 2 would have that same pressure above their water lines pushing down on the water in the idle boilers?

So if boiler #2 comes on line with different pressure will this still work?

JStar

Correct about the common pressure.

All pressure settings should/can be staged so that certain boilers only run if the system can't build enough pressure. If one boiler is kept off because the system pressure is high enough, then you don't need that boiler online anyway.

RayWohlfarth

@JUGHNE If the high level spills are high enough, I pipe them into the dry return.
@JStar That may not be the case. The pipes can equalize if both pressures are the same. If one is at a higher pressure, the levels will not equalize. Many of the smaller steam boilers have critical water levels and this could cause issues or carryover. When steam leaves the boiler, it fill all the pipes including the lag boiler. If there is no high level spill, the water level will keep rising. This could lead to banging pipes or if the water level is five feet above the pressure control, the control will think there is enough pressure if set at 2 psi and not start

JUGHNE

It seems if the idle boiler(s), being cooler, would condense the steam coming in then would gain water.

JStar

They will if they're not connected to a common return. But if all boiler returns are connected together, it acts like one boiler, and one water line. Any water that enters one boiler via condensation from the supply, enters all boilers through the return, and the level stays even, as if condensate were naturally returning from a gravity return in a single-boiler system.

Whenever I service multiple boilers with feed pumps (almost every commercial system), the idle boilers overfill and need to be blown down often (if they don't have high level drips). This is particularly a problem when one or more boilers are down for repairs and remain offline for hours or days without the supply valve being closed, or if lead/lag rotation is scheduled by days instead of hours.

Multi-boiler systems that are connected by their returns don't have this issue. Sometimes an isolation valve is installed between them, and someone will close it thinking the boilers should be separated, but that causes the overfill problem, and we get called for service.

EBEBRATT-Ed

You can't have high level spill traps unless you have condensate pups or boiler feed pumps. If you have gravity returns there is no way for the water to go, the only other option would be to dump the water on the floor or down the drain....not good

jumper

Isolate idle boilers. Really necessary in days of atmospheric burners.

vaporvac

When I designed my system with the help of the brilliant minds on this site, I paid close attention to Jstar's installations. In the end, I couldn't have been more thrilled. I'll find my old post that tracks the install, although there are many others that deal with precisely the questions you're asking. Mine is a 2-pipe Trane VaporVacuum system.

James Day_2

thanks for all the reply’s.

Going to be tackling this after the new year.

One last question. These will be 3 peerless ect-05 steam boilers.

Following there specs it shows 2” risers to a 3” header.

Then I would take 3-3” off those headers to my main system header.

Would 4” be sufficient for that? Or bump it up to 5” or 6”?

Thanks Jim

JStar

6" system header as a mininum. Normally, I would use a 4" header for the ECT05, but you'll have plenty of room for separation with the multiple headers.

James Day_2

Off that header 2” or 3” for equalizer ?

Thanks again.

JStar

3" system equalizer. Rule of thumb is no less than half the header size.

Henry

Why complicate things when you could install the same capacity and similar piping with a cast iron assembled boiler such as a Smith 19 or 28 depending on the size

jumper

Henry said:

Why complicate things when you could install the same capacity and similar piping with a cast iron assembled boiler such as a Smith 19 or 28 depending on the size

Yes it is more complicated but there are advantages. Also assembling on location is not common anymore.

Mike_Sheppard

Picture attached.

JUGHNE

Why not one big boiler.....you would have only 2 stages at best.
The 3 boilers could give you the possibility of up to 6 stages of fire if you wish.
We have discussed at length the necessity of oversized boilers for a few design days.
Also redundancy, 2 boilers would probably supply enough steam most of the time. Simpler interchangeable parts replacement with 3 boilers.
In the event of block failure replacement could be done without complete loss of heat in the building.