Condensing steam boilers

Brad White_184

Steam as a medium is, (unless under a severe vacuum), well above the dewpoint of flue gasses. Most flue gasses have a dewpoint of between 128 and 130 degrees F. Steam as you know is at least 212 degrees F at conception.

Still, you can get steam boilers of 85% or better AFUE, especially the oil-fired Burnham Megasteam and other 3-pass designs. Not bad!

The key is proper sizing and application. The best boiler improperly applied is a boiler defeated or at least diminished.

Bob_109

Condensing steam boilers

We're planning on replacing a steam boiler in a two-pipe system in a small apartment building. Boiler size will be about 2000 MBH. Does anyone make a condensing boiler that size? (I realize I may be ahead of current practical technology and reasonable cost.)

Steamhead (in transit)

Bob, make sure

the boiler you install has low-high-low firing. This has been known to save over 30% on fuel consumption.

If this is a 2-pipe system with traps, it's probably Vapor. Control it with two Vaporstats: one set at 2-3 ounces for the shift from high to low and back, the other set a bit higher as the operating limit. Set your CSD-1 manual-reset Pressuretrol at 2 pounds or so.

If parts of the building don't heat well on ounces, find the problem and fix it. Don't raise the pressure to compensate.

Your customer will love you for this.

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Brad White_184

Good catch. Frank

I missed the size aspect at 2000 MBH. Low-High-Low, absolutely. Wish they had modulating in that size..

ttekushan_3

and don't forget

that industry does have the option of using condensing economizers on very large, very high pressure, and very hot boiler systems! Unfortunately, we can't get those on the scale found on heating systems we encounter. One of those cost/benefit/payback things.

-Terry

ttekushan_3

Steamhead--

I've had a run of suitable LGB's to hi-lo fire via vaporstat. I updated all of them. My favorite is a system I balanced, etc. last year- a formerly problematic system with heat balance problems.

The building's a 4 floor 1917 Tudor style apartment building that has 26 apartments and sits on a corner lot, actually turning the corner with parking behind. Since the building is divided into three sections separated by firewalls, it has a downfeed single pipe steam system with a single riser that heads into the upper roof area. EDR approx 6000.

Everything heats quietly and evenly at 5 ounces, 2 ounce subtractive diff. I think this is pretty good since the system is inadvertently operating as a snowmelt system for the upper roof. The insulation has been chewed off the the horizontal runs in the roof, radiantly heating at least one top floor apartment. I heard that the roofers didn't think they'd be able to keep the old access doors to this area from leaking so they sealed them off and roofed right over them. Oy. Things should be better next year once we figure a good way to get in there to solve the problem. In the meantime that building has the longest, most dangerous icicles in town!

-Terry

tim smith

Regarding burner operation

I would think full mod might be a good idea on this size of boiler. Not as much cycling and can do a better job w/ o2 trim etc. Just a thought, Tim