Large system, cold rooms

Tommi68

Hi group, I am looking for tips to track down possible solutions for cold radiators in a large, institutional building. Our building is 100+ yrs old, has a two pipe, vacuum return system to an off-site, central steam plant. The problem (seemingly) is at the end of branch, on the 2nd and 3rd floors. The apparent lower points of the immediate branch are getting steam, but the 2nd floor rad gets warm, not hot and two rads above are cold. If I disconnect the supply from the lower rad, I can drain water, and occasionally steam rises to the loose fitting.
What is the first places I should look? Do people use compressed air to check for pipe connectedness? All of my pipes are behind plaster.

I am left to figure this out, our trades can not find the problem or a solution, so they added electric heat.

Jamie Hall

Other smarter guys will chime in -- but if you can drain water from a steam supply pipe -- ever -- there is a pitch problem. The water, what little there is of it, should all drain freely back to the boiler.or a drip to a wet return. But certainly not stay anywhere near the radiator.

Now the question is... why. Well, water runs down hill -- so somewhere in the supply line to those radiators there is a low point where water is pooling. Start tracing pipes...

Steamhead

If that's a vacuum-return system, it has traps. I bet a bad trap is causing this.

@Tommi68 , where are you located? We might know someone who can help.

Tommi68

Thanks Steamhead, I am in Toronto, Ont.
The traps in my building were subject to a steam trap survey by Spirax Sarco. Any identified traps were replaced, I have also replaced any trap on a non operating rad to remove this as a possibility.

mattmia2

Tommi68 said:

Thanks Steamhead, I am in Toronto, Ont.
The traps in my building were subject to a steam trap survey by Spirax Sarco. Any identified traps were replaced, I have also replaced any trap on a non operating rad to remove this as a possibility.

The bad trap generally isn't in the radiator that isn't heating, it is in another radiator that is letting steam in to the returns that is preventing the radiators that won't heat from being able to vent. Steam in the returns will also destroy the vacuum pump.

Water pooling in the supply will condense the steam before it gets to the radiators.

How is this system controlled, are there zone valves somewhere? Are there valves on each radiator?

It is possible there isn't enough steam being supplied to the system as well. Will these heat if other closer radiators are shut off?

Tommi68

Our supply is not a problem, we have never lacked for steam during the coldest days. We do regulate individual rads, and close zones manually based on demand. Every rad has a manual control valve and steam trap.

The lowest of the problem rads (2nd floor) can heat, but does not heat completely, and goes cold overnight. The rads above this one (3rd floor) have not heated in years...

How do I test for plugged pipes? A 3rd floor rad did show up completely plugged with sediment two years ago.

Traps not trapping may still be the case here.

mattmia2

Plugged pipes would be tested with a hose and see if you can flush water through. It usually doesn't happen without a precipitating event of some sort like the system flooding. It is possible but the least likely cause.

Tommi68

It was amazing to see a radiator on the 3rd floor be plugged with muck. Also a happy day to be able to use one of the 'spare' rads during the cleaning.

Jamie Hall

This is two pipe? Do the problem children share a return? First thing I's check is the traps, then I'd make sure that if the do share a return the return has no sags which can trap water...

Ironman

Crack open the union at the supply valve of the problem rad(s). If you get steam at that point, then the trap is not opening or the return line is clogged.

mattmia2

Ironman said:

Crack open the union at the supply valve of the problem rad(s). If you get steam at that point, then the trap is not opening or the return line is clogged.

Or it can't vent through the return because water is trapped somewhere or the trap is closed by steam from the other side.

Tommi68

Thanks for the help. The steam is back on and the trap was failed closed, contrary to the Spirax steam trap audit!