Vertical main steam flow is down

havocman

The engineer overseeing a historic renovation states this system will work. It is a bit unconventional in my limited system design experience and I would like to know if anyone has some input. We are replacing the old steam boiler that was in the basement serving a single pipe gravity return system and relocating it to the second floor. A 2 1/2" main will send steam 20 or so feet down to the basement and tie into the original 3 1/2'' horizontal main loop run, at the end of which will be a thermostatic trap that will dump the condensate into a receiver/pump. The condensate will then be pumped up to the second floor boiler room into a boiler feed assembly. Peerless 63-06, 287.5 input MBH, 746 sq. ft. steam net.
How well will steam travel in this design? What are the red flags here? Would an F&T trap at the end of the main be a better design? What about flash steam? Should there be a drip and trap at the bottom of the vertical main?

Steamhead

Why are you moving the boiler in the first place? Seems like an awful lot of work.

I'd make the 2-1/2" drop main 3". Also drip the bottom of it with an F&T trap instead of sending the condensate into the existing steam main. Use an F&T trap at the end of the existing steam main since it will handle condensate better than a thermostatic type. And vent the heck out of that main- the small vent in an F&T trap won't be nearly enough to distribute steam quickly.

Jamie Hall

And be sure to control the pump as a boiler feed pump -- not a condensate return pump -- and dump any makeup water called for into the condensate return tank, not the boiler.

A boiler feed pump is controlled by the water level in the boiler.

JUGHNE

What type of construction of the 2nd floor that the boiler would sit on?

havocman

Thanks all...did a bit of research myself since posting and with your responses as well the F&T seems like the way to go. I will install a second drip at the bottom of the riser.
I failed to mention that a boiler feed pump and receiver will be installed near to the boiler on the second floor; so the pumped return from the basement will enter the receiver of the boiler feed. This was designed by the engineer. Reminds me of the 60's game called mouse trap.
The house is historical and was damaged by Sandy, so the powers that be have decided to place NOTHING below the flood line. Beats me - plenty of potential flooding from the second floor now with all that water up there. Ah, the great minds that have devised our administrative protocols! Who am I, but a humble mechanic, to question such wisdom.
The floor below the boiler was shored up by the general contractor, and we are to install a non-combustible base made of one layer of fire treated sheathing upon which will be a layer of 8" block held in place with steel angles.
The original design was to convert the system to hot water using the antique one pipe column type radiators (can't replace them, they're part of the history). Needless to say, on my first site visit during the preliminary walk through I kindly pointed out why those awesome radiators were not candidates for such a conversion. Hence the system was converted right back to steam.

Steamhead

Why not put the boiler-feed pump in the basement? It can pump right up to the boiler, eliminating the condensate pump.

havocman

I don't believe there is a functional reason for this, and even my supply house questioned it. It must have something to do with the higher cost of the feed unit and the regulations requiring any device over a certain dollar amount to be kept out of the flood waters. Will verify, now I'm curious if I'm correct on that.