Steam overheating and banging

MikeMarino

We have an 8 story building in Boston that we have been asked to look at banging and overheating in one of the condo units.  It is a two-pipe steam system.  Although we are not long time steam experts we said we would look into the issues since we handle the other HVAC systems in the building.  We found the boiler operating at approx. 2 1/2lbs of pressure.  After consulting with a few other professionals we decided to lower this to 3/4lbs.  We instructed all the unit owners that had their radiator valves in the off position to open them up all the way.  We also reduced the heating curve (run time) on the heat timer control.  Our client was extremely happy when the water hammer stopped in her unit however the house was still 85 degrees!  She shut two or three of the radiator valves but the hammering started right away.  I have a meeting with her this afternoon and I am not sure how to proceed.

Install thermostatic valves?

Inspect/replace traps?

Check for improper pitched pipes?

Let the knowledge fly!

nicholas bonham-carter

Boston baked condos

Have you checked the traps for functionality on this system? Closing the valves should not affect the Rest of the system on a 2-pipe system.

What is controlling the system-complicated boiler control, or thermostat in some bad location?

Is everyone overheated or just a few? How is the air escaping as steam rises?

Post some pictures of the radiators and valves,as well as the boiler and supply piping.--nbc

MikeMarino

Steam overheating and banging

Another contractor had been working in the unit and said he replaced all the traps.  A heat timer control in the boiler room is controlling the heating sequence for the entire building.  We have dialed down the run time two adjustments on the curve.  There are other tenants who are experiencing the same problems but we haven't been able to meet with them.  In regards to the air escaping I am not sure how that is happening there are no vents on the radiators but I don't believe you need them on a two pipe system.  I can try to get some pictures of the existing systems and post them.

Jamie Hall

Is there any other control

for boiler run time than the heat timer?



Some of what you are describing sounds suspiciously to me as though the boiler is running longer -- or possibly more often -- than necessary.  Specifically, the comment that the building was still overheating, but the system was quiet.  That makes me think that fundamentally the system is working well, but that it doesn't need to work as much.



Therefore... is there anywhere in the building that might be a suitable location for a plain old vanilla thermostat?



I might add that part of the problem with TRVs -- or just shutting off radiators -- is that they (obviously) reduce the size of the radiation being fed.  If just a few are off at a time -- say ten percent of the system -- on a system which is sized to have all of them on, then you are only ten percent oversized.  Not to bad.  If, however, you have two thirds of them off at a time, then your boiler is three times the size needed at that time.  This is not going to be good... even if you don't get annoying noises, your efficiency will suffer.

BurningRod

Water Hammer

When were the traps replaced and what were they replaced with? If you have banging, you have water hammer. 

c.t.kay

Overheating

Survey the building radiation, size the orifice plates and install TRVs.

Call Woody Tunstall at 413 594 8695.

nicholas bonham-carter

8 floor condo

I would get the steam distribution problems solved before putting on the trv's. Chances are that if the radiators are in rooms which have not been down-sized so as to leave a big radiator in a small room, the radiation was correctly chosen for the area.

I wonder why the banging occurs when the radiator valves are closed.

1.lower pressure with a vaporstat, verified with a low-pressure gauge on the same pigtail.

2.ample main venting (maybe risers too).

3.a trustworthy boiler control system, with sensors in cooler areas (maybe even a thermostat with averaging remotes, and the controls locked up.

4.finally, if any areas overheat, then put trv's (or metering valves/orifices) on.--nbc

michael_43

HT control

It sounds more like a control problem than a trap issue. Make sure the control is in calibration and check the heat established setting. Most over heating with a steam control is not having the "steam established" set properly.