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Temperamental heating

Tommi68
Tommi68 Member Posts: 47
in Strictly Steam

Time for another quiz of the great minds.
I have a large institutional building that has trouble getting heat to an upper floor. The system is two pipe steam with vacuum return. At the end of a common pipe run of 300’ with dozens of risers, the last riser goes from the basement to the second floor through an inaccessible brick chase in an exterior wall. The pipe in the riser chase is uninsulated.
During cold days, the steam does not reach the upper floor, and the risers upstream seem to lose heat. Do I have a problem with condensate backing up from the last riser? I’ll open the access panels tomorrow, but I feel the end of line trap is a simple thermostatic trap.
What else could I look for? I recall previous years having cold rads that seem to fail as they are upstream of the end of line trap.

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,780

    Could be a bad steam trap that has failed closed. What kind of pressure are you running at the boiler?

  • 109A_5
    109A_5 Member Posts: 1,885

    Pipe pitch, broken, dilapidated straps that were securing the proper pipe pitch.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    Tommi68
  • Tommi68
    Tommi68 Member Posts: 47
    https://forum.heatinghelp.com/discussion/comment/1825669#Comment_1825669

    Steam traps were unearthed and serviced in March. Most of our pipe runs are under finished floors or behind brick walls. It is a struggle to prove the need to expose them. Usually, only leaks get demolition to expose the pipes, maintenance issues take many seasons to warrant demolition. I have suspected the trap is insufficient to handle the condensate load created by the uninsulated riser. Sagging pipes are a strong possibility as well.
    We try to run the header at 2-3psi but need 5-6 to get enough volume through the PRV station to heat the entire building on cold days.

  • Jamie Hall
    Jamie Hall Member Posts: 25,213

    How is the steam main to that last riser, and that riser, vented? Crossover trap? To what? and where is that vented? How is condensate handled from that section of steam main and that riser? Wet return?

    Aside from the obvious noted above — pipe pitch and the like — remember that basics are basics, and apply to any steam system. As our fearless leader likes to remind us, the air has to get out somewhere. The condensate has to get out somewhere. All so the steam can get in. A vacuum system — which is a remarkably poorly defined term, by the way, doesn't change that. It just changes the pressure differentials involved.

    You mention a PRV — pressure reducing valve? Why? When operating at partial opening on saturated steam, they can really cause odd problems…

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Tommi68
    Tommi68 Member Posts: 47

    The steam main at the last riser is 3" at a T, with 1-1/2" rising to the upper floors and a 1-1/2" pipe dropping into a cooling loop. The cooling loop reduces to 1/2" before reaching the cross over trap, a 1/2" thermostatic trap. There is no venting on our systems until condensate returns to the receiver/vacuum pump. The returns are all dry as we receive district steam from across campus and pump condensate back to the boiler plant.

    My primary concern is that the room at the top of this riser does not receive steam of cold days. Today is 1'c and the steam is reaching the top floor. It was not heating when the outside was -5 recently. Is the uninsulated vertical riser robbing steam with excess condensation? The pipe chase is brick, in an exterior wall.

  • Jamie Hall
    Jamie Hall Member Posts: 25,213

    Somewhat oddly, your hypothesis that it is something about the uninsulated vertical riser may be correct. It usually isn't a problem, but depending on just how that riser (and the radiator) is vented and condensate is returned from it may be the problem.

    Steam may not be able to move into the riser fast enough to get to the top on colder days — losing most of it in trying to heat the riser (we often forget that the velocity of the steam front has less to do with how fast the venting is and a lot more to do with how cold the pipe is and how fast it loses heat!

    Or at least make it to the top within the cycle on time of the system. Or is it always on?

    Another possibility is if the venting and condensate return line (lines?) or any traps are also in the cold area. They can freeze, believe it or not!

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Tommi68exqheat
  • Intplm.
    Intplm. Member Posts: 2,292

    "Inaccessible brick chase in an exterior wall"? It might be time to install an access panel and look inside.

    Including the very good information above, insulation, and any other unknowns should be corrected in that space.

    Tommi68
  • 109A_5
    109A_5 Member Posts: 1,885

    Did it ever work ??? If so, what changed ?

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Tommi68
    Tommi68 Member Posts: 47

    It presumably worked for the first 80+ years. During my 20 years here, the third floor room and spaces upstream have struggled in cold weather.

    What has changed is not certain, but the pipe run was abated, reinsulated and hangers added/changed 20 yrs ago. The crossover trap does not appear to be correct and has a braided flex hose connection to the condensate line. This has only been revealed one year ago with access holes being cut into the finished floor of the basement room with the area main pipe run.

    I need to create a supporting argument for more access holes and an upgrade to the steam trap…

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