Multiple steam boiler piping concept

The Steam Whisperer

Been contemplating a piping set up for two boilers together as follows....full standard near boiler piping with header and equalizer and then coming off the header with a supply using a check valve in a horizontal run and then over to the common header of both boilers. Pumped return into each boiler would use a solenoid valve into each boiler, probably tripped by a water level control on the boiler. Each boiler would also get a vacuum breaker so on shut down, with the solenoid and check valve closed, the boiler wouldn't go into vacuum. This set up would allow one boiler to stay cold and eliminate the standby losses, while the other boiler heated the system, just like a well designed staged hot water boiler system. This would allow simple atmospheric models to be used quite efficiently, since the huge inefficiency of standby losses would be eliminated. I suspect, if referencing the data staged atmospheric hot water boilers, the fuel savings would be at least 7% to 10% and probably more like 20% over a single atmospheric due to the typical oversizing of most steam systems by around 60%. This would be in a multi zone system and the boilers would be staged based on the needs of the system. You could use simple pressure controls for staging, outdoor stats or 2 stage room thermostats ( 2 boilers) to stage each boiler if you have an orificed system to keep distribution even in the building. Overall the advantages would be pretty much the same as with staged hot water boilers... redundancy, a significant boost in efficiency, and very simple equipment ( no power burners).

EBEBRATT-Ed

Sounds good to me if the check valve holds. Similar to the set up used on high pressure boilers in tandem where a gate and a check valve (or usually a non return valve) is used in the supply from each boiler.

Using a condensate pump is ok usually a MM 150 pump control opens the boiler feed water valve and an end switch on the valve starts the pump. Or use dedicated pump for each boiler.

I have seen a few tandem set ups on this site and some violate ASME code because they pipe 2 boilers together below the water line which is frowned upon. It can be done with check valves which leak from the crud. Failure of 1 boiler could cause the water in the good boiler to be lost.

I would put an F &T on each boiler 2" above the NWL to act as an overflow trap

The Steam Whisperer

The check valves in the supply line are the only thing I'd see as unusual from typical multiple boiler installations. The code issues are perpetual since I have often seen that the inspectors don't know the difference between modular boiler and multiple boiler installations. The requirements are different. I've sort of forgotten where that line is myself. If the check valves hold, we shouldn't need an overflow trap. I suspect they'd be pretty reliable since there really shouldn't be any garbage getting up there, just dry steam. Of course there is belt and suspenders approach.

EBEBRATT-Ed

Your right if the check valves hold you shouldn't get any condensation in the idle boiler.

As far as modular Hydrotherm used to make modular steam (I don't remember any others.) There were no valves between the boilers so code wise it was considered 1 boiler and they could get away with a minimum of controls. They didn't work very well. Connected together on the steam and return side water backed out of the operating boilers as soon as they started building steam always tripping low water and the idle boilers filling with condensed steam.

What your doing should work in my opinion, you could always leave a couple of plugged tees for the overflow trap and add it if needed

Jamie Hall

I like the idea -- and you are a far better steam man than I could ever hope to be! …

but...

I'm a little concerned about the check or non-return valves. Ive not had really good luck with valves on saturated steam lines, unless they are full port plug or ball valves -- but those don't operate as non-return or check valves by themselves. I wonder if, at the expense of some complexity (which I hate!) if you might need to use a motorized full port valve, opening on a signal from the boiler that it (the boiler) is up to steam...

The Steam Whisperer

Slantfin still has their modular steam boilers. I've installed 3 of them with 2 modules with common supplies and returns and once the water was cleaned up they worked quite well. I've got 2 galaxy set ups and one Intrepid. I"ve found that the Galaxy atmospherics produce exceptional quality steam, even with the little 2 1/2 inch tapping. The flow of steam in the boiler is much different than typical boilers. After it moves through the port connectors, it takes a turn down the very wide end section which probably kills velocity allowing water to drop out and then hits an inclined plane which probably further drys out the steam and then reaches the exit tapping.

EBEBRATT-Ed

Your right. I forgot about Slantfin. For some reason they are not represented well in my area, Hardly ever see any of there boilers

RayWohlfarth

@The Steam Whisperer (Formerly Boilerpro) I have designed many modular steam systems. We used the Triad vertical firetube boilers and had great success. Some of the lessons I learned are:
The check valves in the supply do work but have a tendacy to leak through. @EBEBRATT-Ed was right. ASME suggest using a high level spill trap about 2" above the normal water line. I believe the check valves help the boilers meet the International Energy Code of isolating the idle boiler.

I have found you are better to bring both or all boilers on at same time and once you get steam pressure, you could stage them back. If you start only one boiler, the rads furthest away will not heat. I explain it it is like an airplane taking off.

I prefer using one boiler feed pump per boiler rather than a solenoid on each boiler. The modular boilers cycle so quickly the solenoids fail after a few years.

I typically see savings of 15-22% by using modular steam boilers.
Good luck Ray

The Steam Whisperer

Ray....Any advice on whose check valves and what configuration? Since you do seem to get leakage through the check valves ( I suspect you also use vacuum breakers on the boilers), then the spill traps make sense. I have seen installation after installation without spill traps and unless they are firing both boilers fairly regularly and are high water content ( I.E. Kewanees, Pacifics) overfilled boilers are a problem.

I've seen that same problem with start up on large single zone two pipe systems with our outdoor reset mod steam boilers with the system converted to supply valve orifices. However, we've found so far that running only 1/3 to 1/2 of the orificed radiator capacity is all that is needed to get the system moving. Generally for these larger systems, we use orifices designed for a 3 psi pressure drop on the design day with the radiators at about 60% capacity ( since the radiators are nearly always 60% oversized for design load). In addition, these systems typically were originally vacuum systems, so the pipes are a bit smaller, but this is made up for with the much lower volume of steam moving through the system (lower pressure drop) with the orificed radiators. Essentially the orifices eliminate the extra boiler capacity needed for pickup and all you're left with is the piping loss and a radiator load designed for the current building heat loss. I end up sizing steam boilers for these systems the same way as I do for hot water systems... based on historic fuel usage plus a small safety margin to cover the losses of the piping system.

RayWohlfarth

@The Steam Whisperer (Formerly Boilerpro) I like to install a swing check on the hozizontal piping to the header. The old boilers never used the high level spills as water level was not as crucial. The thing to be careful of is a 1 ounce pressure differential between the boilers will mean a water level difference of almost a couple of inches. I would be a bit hesitant sizing it according to heat loss as the boilers closet to the boiler will heat and the furthest ones might not
Good luck

The Steam Whisperer

That what I was thinking a simple swing check.

The "magic" is in the orifices to restrict the steam flow into the radiators so it wants to head down the mains. A typical radiator orifice size is 3/16inch of an inch or smaller for a 3 psi drop so it helps alot. We even have a system with about 1800 EDR in a big home where the orifices are sized at a 1/2 psi drop and it heats nearly all year round with only a 225,000 input boiler. It doesn't even need any more capacity for startup.

JUGHNE

Do you vent your steams in addition to the vent provided by the cond/feeder pump.
I have done orifices and it seems like asking a lot to vent a lot of air thru the orifices and the main thru the EOM F&T traps, if any.
The main air vents at the EOM have speeded the flow of steam to the ends pretty quickly.

The Steam Whisperer

I've done it both ways. I suspect getting the biggest venting you can on the mains is still the best way to go. Typical F&
T's vent very little air, so some big cross over traps would probably be very helpful. However, if the system is orificed, then we downsize the boiler capacity to the heating needs of the "virtually" downsized radiators. This make the steam cycles much longer, so venting air is not nearly as big an issue. On our best systems, we are running the boiler on outdoor reset so the boiler output modulates with the outdoor temp. With this setup, we've been told that the boiler will run for weeks without cycling, so air venting and system pick up loads become almost nonexistant events for most of the heating season.

JUGHNE

Sounds like a coal fire in January.

The Steam Whisperer

Yep, you get the idea.