Steam

todd s

I'm looking at a steam boiler replacement for a 3-story building with thermostatic radiator vents on 22 radiators. Is it correct that pressure will need to be maintained constantly in the building in case some rads need heat? The t-stat is located on 2nd floor and about dead center of the building. Beautiful ornate rads, vents made by MMA. I measured it up but haven't calclated EDR yet. The main has large handwheel valves, 3 actually that don't appear to have any purpose nowadays, why would they have been used? Any tips would be appreciated. Thanks Todd

Steamhead

TRVs

serve as limiters. You are correct that the boiler needs some sort of automatic control such as a thermostat or outdoor-reset system to fire it according to the building's needs. TRVs then limit the heat going to areas where it's not needed.

The boiler must be sized to the radiation. This is because on a cold night all the TRVs will likely be open. Do not simply get the same size boiler as what's there, since the old one may be oversized. Use a 50% pick-up factor rather than the usual 33%.

Those valves on the steam mains serve to isolate parts of the system for servicing while keeping the heat on elsewhere. It would be a good idea to make sure they are working.

Measure the length and diameter of each steam main. From this info we can determine what vents each main needs. Proper main venting speeds up steam distribution, saving fuel.

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tp tunstall

MMA

the valves are MMA or macon controls. look it up under www.maconcontrols.com

todd s

Steam mains

Length, is that just horizontal measurement or up each riser as well? My lost art book is on loan and I won't get to see it for another week. I have suggested re-insulating the mains and the building manager wants that done as well. If mains get re-insulated should I reduce pickup or stay with 50%.

Unknown

My two cents

Insulate, for sure. That changes the system characteristics so greatly, that you almost need to re-evaluate the system, after. It's AMAZING how much better it will perform.

Bare pipe uses FIVE TIMES the steam that insulated pipe uses, after it warms up.

On the 50%. I have used TRVs a LOT. I always wished I'd used a smaller pickup factor with TRVs than 33%. I don't dare to, but I think 50% is a lot.

Only when you start the system from setback, or in the shoulder seasons, is the piping absolutely cold and every TRV wide open. Other times, there are some TRVs throttled partly shut, and the mains are partly warm. Those times, the boiler never runs long enough to get out of condenseing mode, which is bad for the boiler metal, and worse for the chimney.

But I'm afraid to undersize the pickup factor, because the cost to run goes up very fast when you cross the line, into undersized.

Steam has evolved into choices that balance constant run time of old days, with start/stop of modern boilers.

I pick 33% pick-up factor with one-pipe and TRV vent valves, and insulated mains. And proper near boiler piping and sizing. And venting. And clean water. And clear returns.......


Noel

Steamhead

Measuring Steam Mains

For the vents located at the ends of the steam mains, just measure the horizontal portion. If you find you have trouble getting steam to the tops of the risers, you can measure and vent these as well.

BTW- Noel's right about the 50% pickup being a bit much sometimes. But you can always down-fire a boiler that's a bit big, whereas you can't increase the fire in a boiler that's too small without major problems.

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Mad Dog

The boys are right!

As steamhead said, the trv is merely a limiter. I learned the hard way several years ago that a TRV WILL NOT hold back the steam IF there is constant steam available in the supply side. The system needs to cycle on and off long enough for the pressure to drop and vacuum to break insidfe a 2 pipe radiator...learned the hardway..just one of the beatin's ya gert 'long the road to steam supremacy - we all got our scars. Mad Dog

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