Improving One-Pipe Steam
Most one-pipe steam systems can be improved with a modest scope of work. The change may not be dramatic, but your customer will see improvement, and the paybacks are good.
The One-Pipe Workscope
This All Works Together
Let’s work backwards through the workscope. The final work-item is thermostatic radiator valves. When one-pipe TRVs work, they work very well. But they need very low steam pressure. One manufacturer states that their one-pipe TRV won’t work above 1½ PSI. So before TRVs can be installed, the pressure must be lowered.
But there’s a reason people resort to high steam pressure: it can work as a quick-fix for heat complaints, because it pushes air out of the system.
So before you can lower the pressure, you have to cure the problem that made somebody turn up the pressure in the first place : air binding. In order to let the air out, you have to install master vents onto the mains and risers.
But master vents can squirt water if the boiler is making wet steam. So first you have to make dry steam.
To lower the steam pressure, you also have to make less steam. So you have to enable modulation and maximize turndown. Ideally you should also derate & install a low-range pressuretrol.
Summary of the Workscope
That covers the general workscope for one-pipe steam. To recap, here's a summary:
- Enable modulation, maximize turndown, derate, install a low-range pressure control, and lower the steam pressure.
- Make dry steam by limiting high fire, cleaning the boiler water, installing anode bars, and lowering the waterline.
- Let the air out of the system by Installing master vents onto the mains and risers.
- Where overheating persists, try out thermostatic radiator valves.
Or to put it another way:
Walk the Building
Bidding the one-pipe worksope means leaving the boiler room. Here’s the best way to collect the information you’ll need to price the job.
Go to the Roof
First, go to the roof. This makes it easy to see what shape the building is, which you’ll need to know in order to trace the steam mains.
Is the building U-shaped? H-shaped? Make a simple sketch of the building outline. Also show where the chimney, elevator bulkhead, and vent stacks are. These building components go straight down to the basement, so showing them in your sketch makes it easier to stay oriented while you’re tracing the mains.
Top-Floor Apartments
After you’re done on the roof, go into apartments on the top two floors. Check for several things:
- Are all the risers exposed, or just the direct-heat risers (in the bathrooms and kitchens?)
- If the risers are exposed, do they all have vents? Or do just the direct-heat risers have vents?
- Is the system one-pipe or two-pipe?
- What kind of heaters do they have, radiators or convectors?
- If they have radiators, are they exposed?
- What kind of radiator vents do they have, fast or slow? Are there signs of water leaking from them? Are they installed low (as they should be), or high?
Walk The Basement
After the apartments, go to the basement. Trace out the steam mains, starting from the boiler room and going out to the end of each main. Draw the mains onto the sketch you made on the roof. Use a red pen to make your drawing easier to read. (It’s a good idea to also bring a blue pen, in case you want to draw returns.)
Collect the information you need to price main line vents. How many spots should be vented? What’s the size & length of the mains being vented? How will you pipe each vent connection?
You can also look for additional workscopes. Is there buried return piping? Are any of the steam mains back-pitched, or slumping, or piped into a gull-wing at an elbow? Are there loop-seals without blowoffs? Are there drip-traps that should be piped better?
Alert your customer to such conditions, using your judgment about the problem’s severity. Not every backpitch needs to be addressed, but if you hear a steam main hammer, or see one that's likely to, tell your customer you can fix it. Not every buried pipe is leaking yet, but it will before too long. And maybe the drip-traps are fine, but without test-valves in place, who knows? If it’s been awhile since the traps were replaced, price replacing them with float-only traps.
Check for signs of water leaking from vents. Lots of water indicates wet steam, which will require comprehensive dry-steam measures.
While you’re tracing out the mains, constantly ask yourself two questions: How does the air get out? How does the water get out? This is how you troubleshoot systems, and how you find biddable work.
You can also count the riser connections. This is the easiest way to do your riser venting takeoff. Be careful to count direct-heat risers (such as in kitchen & bathroom risers) separately from risers that supply radiators. Direct-heat risers usually have small takeoff piping, often smaller than the riser itself.
Boiler Room
After walking the entire basement, you can focus on the boiler.
Can the burner modulate? If it does step-modulation, is there a Low-High-Low pressuretrol? Is modulation bypassed? Does the burner need a high-fire limit control added so that it can modulate while operating at limited fire?
Get the burner serial number and UL number, so that you can confirm its turndown capability
Will it be easy to get detergent into the boiler? If not, where can a detergent port be added? Is there a manhole, or at least a hand-hole large enough for adding anode bars? Is there a skim drain, or a good tapping to install one?
If there are buried returns, is there a water meter? If there is, is anyone logging the water use? (If not, give them a log form.)
You can do the walk-through in about an hour. You’ll then be able to price out the four parts of the one-pipe workscope: make less steam, make dry steam, let the air out, try some TRVs.