old steam system

Howard_5

I have been assisting a local contractor fix an old ammonia converted steam system in a large commercial building. The converted system has 4 boxed coils stacked on top of each other (2 on 2)heated with steam. In this coil room is a 20ft. vertically hung wooden spoke wheel(from the old ammonia system)in front of the coils that moves the heat upstairs through grates. The contractor was working in the building this past summer and noticed the return lines near the coils were all leaking so they were replaced. The system worked before and now the complaint is insufficient heat. I saw the new piping and instructed the contractor to re-pipe the returns toward the boiler(most were pitched back to the coils causing blockage and water hammer. the re-piping was finished yesterday with limited success. When the coils fill with steam they get nice and hot but once the wheel is on the coils cool rapidly. The contractor cracked open a return pipe union near the base of the coils and water and steam flowed. However, once the wheel was on the steam and water stopped. With the return piping replaced back as close to the original(pre-summer) I'm not sure what to try next.

Barbarossa

Coil

How are you controling the steam into the coils? and some pix's might help and encourage others to reply.

Howard_5

There's a 6" feeder to 3" valve and then reduced to 3" to the coils. The contractor will get in/out temperatures today to see if there's a problem with the valve. As he said though they're both too hot to touch so not sure how much loss there is.

Barbarossa

Coil

This is difficult to visualize from the narrative. Thus the request for pictures; there are many knowledgeable people on the wall who can assist if they have the right info. My first thought was so much coil cooling that the condensate was being held up due to partial pressure in the coil. I really am groping based on the information presented.

Barbarossa

steam boiler

pixs

Howard_5

steam boiler

I have posted some of the pictures. I thought I had one of the wheel but guess not. I can hopefully describe a bit more-the wheel spins a lot of air(cold air)over the coils in photos and up through the floor grates. The 6"steam main travels to a 3" valve(full open) and then into a 3" pipe that enters both top sides of these top coils. The steam travels down the coils and right to left in rows-there are no elbows at the end of each coil row so the steam ends at the right end of each copper coil row. The condensate travels down the coils in to the return, back to the condensate receiving tank at the boiler some 60 ft away. The wheel and coils are in one large 90% enclosed room. It's very cold to stand in the room as the wheel turns-it reminds me of a spoked water wheel the way it slowly turns. There is a switch to control wheel speed and even at a very slow speed the coils cool where they never did before the re-piping. If there's pressure built up in the coils I'm not sure how to relieve it. I've never seen a system like this in 30 years so hence the questions.

Steamhead (in transit)

The return lines were changed

so we will probably find the trouble there.

You say the coil return lines go to a condensate tank. Are there traps in these lines? If so, where are they located?

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Christian Egli_2

A conversation piece

I have no idea what a conversion from ammonia to steam might be but it certainly sounds most exciting. Having one such plenum chamber beats the home forced air furnace any day. Hot stuff.

By coincidence, I just very recently had something to do in a building with such impressive rooms with the giant fans that can suck you up whole, including your car. What an impressive way to do things.

Of course, steam heat is always impressive.

Here's what I think is happening (just a hunch from the limited clues). It's an air venting problem.

The system with the built-in rust holes was doing the trick precisely because of the holes. We know also that your superfan is also quite capable of condensing most if not all of the live steam that can get to it, even a 3 inch valve is no match for a 20 ft fan...

We've got the boiler producing one cloud of steam that shoves it's way down the main towards your plenum chamber and into the return pipes up to the trap and no further. The rest of the downstream piping should only contain atmospheric air (perhaps even subatmospheric air if there ever was a vacuumizer there) and liquid condensate. The atmospheric conditions were perfectly met with the built in rust holes... . It doesn't seem like there was any major steam leaking through those old rust holes and this may have been because the traps work just fine or - more probably - because your big fan has so much cooling power, not much of the lumbering steam cloud makes it past the small finned heat exchanger.

All an all a cool situation. Here's what's happening now.

The rust holes that connect to the atmosphere are no longer there, and this has uncovered the fact that the whole system is not properly vented further down the return lines as it should be (I note you mention nothing of the conditions at the boiler return point of the condensate lines)

Now, our previous cloud of steam has to bully its way to the plenum since the air in front of it no longer scrambles out of the way. What happens? It all depends on localized pressures. Let's guess your boiler is set at 7PSI, this means your steam cloud can go a good way squeezing down the wad of loitering air, far enough it seems to give you some heat you can feel in the coils. Cool, it seems everything is cool indeed.

Next you start up the fan and the steam cooling power comes into play. Note how the cooling fan has no effect on air. Air is useless, it does nothing, hot or cold it is still a waste of space. Note also how the cold air shower on the bit of steam we have there makes it shrivel: localized steam pressure is entirely dependent on local cooling rate, but this is not a problem in a properly air evacuated system, the collapsing part of the steam cloud turns into a localized vacuum that calls for an immediate replenishment of steam freshly delivered from the boiler. This is the magic of steam heat.

But

Your current system is no longer properly air evacuated, thus, when the cooling fan is turned on, the steam cloud collapses, but now, it is the wad of pressurized air that springs back - it detected a weakness in the steam pressure game and no fresh deliveries from the boiler can be made. So, as long as the air is not out, and as long as the fan is powerful enough to cause a localized steam collapse, the front line on the steam cloud might back up enough for there to be no heat available at the plenum coils. Inside the pipes, all you have is hot air - and that's not quite as great as steam as we all know.

Double trap - double jeopardy.

To see if this scenario is plausible, investigate the air path along the returns. It seems you have thermostatic traps at the plenum coils, this means there must not be no other traps (either mechanical devices or air vents or condensate puddles or tramp steam from a leaky trap elsewhere) of any kind in this path to an open hole to the atmosphere, possibly back at the boiler.

It would seem also, that your test cracking the union on one return line, (possibly on only one coil?) did not provide enough air venting.

If there is no easy fix to provide an alternate air path to the atmosphere that is as effective as the previous rust holes were, you could install a new, air-only return line that runs like sewer line vents. This line would depart at the coils, and travel through a thermostatic trap to an open hole somewhere else beyond the plenum chamber. If necessary, this line must drip (without trap) to the floor or into the other return line.

Check the pitch of the coils themselves, they may have moved with all the pipe fiddling.

And yeah, check if the valves are open.

Anyways,

What exactly do you mean by ammonia? was this system originally cooled with an ammonia chiller? How is it doing the cooling thing today? More pictures of the ammonia part?

I hope this helps.

I include a picture taken from inside a plenum chamber. The shelves are all steam coils, you can see the steam lines, and the dual return, the water only ones with the float trap and the air only ones with the thermostatic traps. Both lines are separate. This takes care of preparing the entry of steam in the grandest fashion possible, like rolling out the red carpet at the Oscars.

Howard_5

Thanks, well described. I agree the holes in the vent were both good and bad. Other than piping a separate air-only line, which I'm not sure how to explain to the contractor, how else can we emulate the old leaking returns? We have a return line of 60' to work with(returns to a condensate receiving tank pre-boiler).