Boilers & Hydronics

You Don’t Need a Weatherman

You Do Need Knowledge of the Quirks of Older Heating Systems

December 16, 2013
Trans

I was chatting with an engineer the other day. She called to ask me some questions about old steam-heating systems, particularly those of the New York City variety. She was putting together a paper on what to watch out for if you were considering an energy management system (EMS) for an older building with either one- or two-pipe steam heat.

Dan Holohan
Dan Holohan

She mentioned that there were lots of case studies available on newer buildings, mostly provided by the folks selling the EMS packages, but there wasn’t any scientific research that she knew of on older, steam-heated buildings. You know, the sort where they had two identical buildings, each with the same problems, and they put an EMS in one but not in the other. I told her that I didn’t think two such buildings existed (exact same problems?) and knew of no unbiased research.

She told me that she knew of one where they installed the EMS, watched it for a while, and then turned it off to see what would happen.

“And what happened?” I asked.

“They saw a 3°F difference in temperature. Up in some spots, down in others.”

And that made us both wonder if the EMS was worth what it costs to install and maintain. I mean, wouldn’t the money be better spent doing basic maintenance on the system, air vents, steam traps, pipe insulation, and other stuff like that?

Where the Thermister Goes

There’s an old device that’s been around longer than I have that manages steam systems in NYC apartment buildings. It works like this: You set the control to sense the outdoor temperature, and you place a thermister on a pipe that’s going to tell the control when steam has filled the pipe to that point, which is supposed to indicate that steam is everywhere in the system. The control will then begin a countdown-to-shutoff cycle, based on the current outdoor temperature.

So, let’s say it’s 40˚ outside. The burner comes on and the boiler makes steam. The steam travels down the pipe and heats the thermister. At that point, the control may decide to run the burner for another 20 minutes because it’s 40˚ outside, which is chilly, but it’s not freezing. On a colder day, the control will run the burner longer. Make sense?

OK, let’s introduce people into the mix. Who’s going to pick the spot for the thermister? Probably the person installing the control, right? We don’t know who that person is, and we have no idea if he understands the workings of a steam system. But what I do know is that once the thermister gets placed, it also gets forgotten. Try to find it and you’ll see what I mean.

Suppose it’s near the end of the longest steam main. That seems like a grand place to put it. I mean, if steam gets to that point it should be everywhere else, right? But what if the main vents are clogged with debris and aren’t letting the air escape ahead of the steam? That happens every day, and where there is air, steam will not go. So the end of the main stays cooler than the thermister’s trigger point and the burner runs on and on and on. The boiler is burning lots of fuel and the tenants are cold. Happens every day, and the price of a new main vent will solve it, but who’s noticing this?

Now, let’s install an EMS in the building. It will tell us that we’re burning a lot of fuel, which we already know. It might even tell us that some tenants are too hot and others are too cold. We get that news as a computerized report, or perhaps through a Web app, which we access from our iPad anywhere in the world. It will tell us what we could find out by walking to the end of the pipe and looking at that clogged main vent, or by talking to the tenants.

I’ve seen thermisters installed on wet-return lines, which will never reach the temperature of steam because those pipes are always filled with liquid water. I’ve seen thermisters installed on sewage lines, which probably won’t get that hot either. Why did the guy do that? Because he could.

I once saw a thermister installed on a cold-water pipe. Hey, a pipe is a pipe, right? And I even saw one installed on the gas main.

“Why did you move that thermister to the gas main?” I asked.

“We’re trying to save gas,” the superintendent explained.

Supers can be so creative.

Modern Electronics and Monitoring

Nowadays, everything is about electronics, monitoring, and knowing what’s going on in the building — and catching people opening windows in the winter so the landlord can toss them out. EMS packages are smart and sexy, but I don’t think they’re the answer to the problems we see in older buildings heated with steam. I think they should be the last step, and only if you think it’s worth it at that point.

For instance, consider a two-pipe steam riser in an apartment building. It goes up, say, 20 stories. The steam supply is on the right; the condensate return is on the left; the radiators are the rungs of the “ladder,” and at the outlet of each radiator we have a thermostatic radiator trap. That’s typical.

OK, one day the trap that serves the radiator on the first floor fails in the open position, sending steam into the condensate return line, which is way too small to handle steam. We now have steam pressure in both the supply and the return lines, and this happens before the air can move through the radiators on the 19 floors above the failed radiator trap and exit the system through the vent on the boiler feed-pump’s receiver. Keep in mind that where there is air, steam will not go.

Now let’s bring in the people again. The guy with the bad trap will always have heat. Everyone above him will be cold. They’ll call you; the guy on the first floor won’t. He’s happy.

A knucklehead shows up and installs one-pipe steam air vents on all the two-pipe steam radiators. That allows air to escape the radiators so the steam can enter. The radiators get hot and the tenants praise the knucklehead.

But now the condensate won’t drain from the radiators because there’s steam pressure in the return from the failed trap on the first floor. The water builds up within the radiators, and gurgles and squirts from the brand-new air vents. The boiler goes off on low water. The boiler feed pump comes on and does what we’re paying it to do.

Later, when the boiler finally shuts down, the water comes cascading from the radiators and overflows the feed-pump’s receiver, leaving the super with a big mess and the building owner with a need for expensive water-treatment chemicals.

And you say you want an EMS? I’d fix the traps first. I’d also make sure all the main vents are the right size and in the right place. I’d check the near-boiler piping to see if the boiler can produce dry steam. I’d make sure the asbestos that came off the pipes gets replaced with fiberglass so the steam doesn’t die on its way to the farthest radiators. Without insulation, the boiler will run a lot longer and that inspires tenants to open windows. The EMS can let you know that the tenants are doing that, but you could also learn that on your own by stepping outside and looking up.

Unless you get an older steam system working as it should be working, sensors and software will just let you know that something is wrong.

Which you already know.

The Lovely Marianne asked me about the weather the other day. I clicked on The Weather Channel app on my iPad, but then a novel thought struck me. I put down the iPad, opened the door, and stepped outside. I looked up and got hit in the face with rain. “It’s raining,” I shouted. “Thanks!” she shouted back.

Point being, you don’t need a weatherman to know which way the wind blows. When it comes to older heating systems, what you do need is knowledge of the quirks of those systems and a willingness to care for those old systems.

That’s not sexy. But it is smart.

Publication date: 12/16/2013

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