Dan Holohans Heating Help Newsletters Page 3
The trouble with motorized zone valves on steam systems
A gravity-return steam system uses a combination of two forces to put the returning condensate back into the boiler. First, there's the steam pressure that's leftover at the end of the mains. Now, this pressure will never be as great as the pressure that's inside the boiler because as steam travels through the pipes it loses some of its energy to friction. What you wind up with at the end of the main depends on the size of the pipes and the boiler's load. This has all been figured out years before you were born by the Dead Men.
The other force that works to put the returning condensate back into the boiler is gravity. Gravity combines with the leftover steam pressure at the end of the main to create a force that's greater than the pressure inside the boiler. The Dead Men allowed enough vertical space between the end of the lowest steam main and the boiler's water line to give the returning condensate a place to stack up. That's what most folks in the business call, "Dimension A." Gravity takes over and the condensate slides back into the boiler. It's all very simple, and it has been for years.
But now, someone shows up and adds their motorized zone valves to piping that's leaving the steam boiler. They figure that this will be a neat way to save fuel dollars. They're wrong, but you've met people who are wrong before, haven't you? Some of them can be very convincing!
Anyway, these valves will work beautifully - as long as they never close. As soon as one or more does close, however, that "leftover" steam pressure that you were depending on to put the condensate back into the boiler disappears. Now, all you have going for you is gravity, and that's not enough to put the returning condensate back into the boiler. So the condensate backs up into the main and lies there, waiting for that evil motorized valve to reopen.
And when Mr. Valve does reopen, Mr. Steam comes raging through, meeting Mr. Condensate and sending him rocketing toward the end of the main where he lands with enough force to knock the building off its foundation.
Perhaps you've heard this noise?
But this isn't the only problem. Keep in mind you have a burner on that boiler that's sized to provide steam for the entire building. When any motorized zone valve shuts, the firing rate doesn't change, does it? Suddenly, you have more steam volume than the pipes can handle. Too much steam volume means the steam will move at a higher velocity, and at the higher the velocity, the faster the steam will suck water out of the boiler. That, of course, leads to water hammer in the zones that are calling for heat.
Perhaps you've heard THAT noise? Oh, that's a BIG noise!
But wait, there's more. As the water goes flying into the pipes, the boiler begins to drop into a low-water condition. Bound to happen, right? The burner shuts off, but before the condensate can return, the automatic water feeder kicks in and adds water to a system that doesn't really need more water. When the condensate finally returns from the system, the boiler floods.
You blame the automatic water feeder for this. The feeder is absolutely innocent - but also convenient.
What's next? Oh, someone decides to install a check valve in the wet return. That person figures that a check valve will keep the water from backing out of the boiler. On the day that the check valve goes in, the water stops backing out of the boiler. Problem solved?
Nope. It's really just beginning. Now the condensate can get back into the boiler because there's not enough pressure to open the check valve. The water hammer continues its psychotic banging whenever any zone valve opens. What to do? What to do?
You install an expensive boiler-feed pump. And in doing so, you also opened the system's returns to atmosphere by hooking them up to the boiler-feed pump's vented receiver. Steam vomits into the boiler room from the vent. Yikes!
You decide to install one huge master trap at the inlet to the boiler-feed pump to keep the steam from spewing forth from the vent. This has never once worked in the history of Heating, but don't let that stop you. Maybe it will work for you because you're so good-looking.
The master trap allows steam to work its way into the formerly wet returns. Now, you have more water hammer than you had before. Worse yet, whenever all the zone valves close on a boiler that's filled with steam, a vacuum forms inside the boiler. This causes the water that's in your new boiler-feed pump to flow into the boiler and flood it.
The automatic water feeder gets blamed again. It's innocent, but what the heck?
You should never get yourself into these situations with gravity-return steam systems and motorized zone valves in the first place. But if you do, know that a half-inch line, run from one side of the zone valve (across the TOP, not the bottom of the valve) will bleed some steam pressure into the mains. It just might get you off the hook.
Like to learn more?
Spend more time at www.HeatingHelp.com. We get into some pretty steamy discussions on the Wall. And check out my books on steam heating in the Books & More section. There are four that will help you look very smart on that next steam job:
"The Lost Art of Steam Heating"
"The Lost Art of Steam Heating Companion"
"A Pocketful of Steam Problems - with solutions!"
"The Golden Rules of Hydronic Heating"
Hey, why shouldn't YOU be the one with the answers? Sometimes, your best tools are made of paper. Arm yourself with the best books you can find and use them to your advantage. Hey, that's why I wrote 'em!
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Thanks for all that you do for us.
More Heating Help
The trick to sizing steam piping
They built the place in the 1930s and heated it with steam. It's always been a commercial building - part office, part factory. They heat the offices with one-pipe steam radiators and the factory with steam unit heaters nowadays, but it wasn't always that way. There was once a time when they heated the factor with pipe coils.
The coils ran back and forth on this pockmarked brick wall. There must have been a couple of hundred feet of pipe in that coil, but they were gone now. The pipe coils had started to leak at the joints and it no longer made sense to fix them. They now heated the place with unit heaters that hung from the ceiling.
Unlike the one-pipe radiators in the offices, the old pipe coils in the factory worked as two-pipe units. It's not unusual to find this mixture of one- and two-pipe steam in older buildings. The two types of systems can work well together - if you follow a few rules.
The Dead Men didn't use steam traps with the old pipe coils. They didn't need steam traps because those coils drained into a gravity wet return. The Dead Men knew enough to use traps when any heater drained into a dry return on a two-pipe steam system, or when any heater drained into an atmospheric return on a system with a condensate- or boiler-feed pump. They knew that steam traps are there to keep the steam from winding up in a place where it doesn't belong. If they were draining into a gravity return, they knew that the steam would have nowhere to go once it left the heater. And that's why they didn't use traps. They also knew that if they DID use steam traps where they weren't required they'd wind up with big problems. If you trap a gravity-return line, for instance, you'll probably back water up into the heating equipment, create water hammer, cause the boiler to go off on low-water or, if there's an automatic feeder, cause the boiler to flood.
The Dead Men knew they'd have to use air vents, though. Here, they put the vents at the outside of the pipe coils. They realized that if steam was to get into the heater, the air had to get out first. They were really good at venting air in the old days.
In this factory, the Dead Men supplied the steam from an overhead main and let it flow back and forth through the horizontal pipe coils. The steam condensed as it went, carrying the condensate along to the gravity wet return and back to the boiler.
The trick with this system was to make sure the coil was higher than the system's "Dimension A." In a gravity return system, that's the vertical space between the center of the gauge glass and the bottom of the lowest horizontal, steam-carrying pipe. On this job, that would be the air vent at the bottom of the pipe coil. "Dimension A" should be at least 28 inches.
When the unit heaters went in, the installer ran new dry returns. He put an air vent and a float &thermostatic trap at the outlet of each heater and ran the returns back to the boiler. He knew that he needed traps because he had switched from wet to dry returns. Without the traps, steam would have zipped from the return of one unit heater to the return of the next. That would have led to air-binding problems. He knew this.
The problem, though, was that whenever the unit heaters were working, the people in the office were miserably cold. No one knew why.
It turns out the installer had sized the piping to the unit heater to be the same size as the hole in the unit heater. That might work with a hot water system, but it won't work with steam. You have to look in old catalogs to appreciate why.
During the Steam Era, unit heater manufacturers went to great pains to show the installer what size the piping had to be. For instance, if you look in a 1954 unit heater catalog you'll see these specifications for a 260,000 BTUH heater:
The heater's inlet and outlet are both 2-1/2".
The main supplying steam to the heater has to be at least 3".
The horizontal runout between the main and the riser to the heater has to be at least 3-1/2" (4" nowadays).
The riser from the horizontal runout to the heater has to be at least 3".
The steam trap has to be 1-1/4".
Piped this way, the pressure drop through the piping to this unit will be two ounces per 100 feet of equivalent length. That was a piping standard for steam heating systems in the old days. It's what allowed the Dead Men to run their systems at such low pressures. In 1954, the unit heater manufacturer went to great pains to explain the reasoning behind pipe sizing. They wanted their unit heaters to work well with the other types of radiation they knew the Dead Men would use on a typical one- or two-pipe steam heating system.
Not so nowadays. If you look in a current catalog you'll find these specifications:
The heater's inlet and outlet are both 1-1/2" (perfect for hot water, not so good for steam).
There are not other piping specifications (you're on your own).
Assuming you size the pipe to be the same size as the hole in the unit heater, your pressure drop through the piping leading to the unit heater will now be two pounds per 100 feet instead of two ounces per hundred feet. Big change, eh?
The trouble nowadays is that most unit heater manufacturers are building their equipment for hot water, but still rating them for steam. Will they work on steam? Yep. But you need higher pressure to make them work at their rated capacity.
Steam pipe sizing is very subtle. You can get just about any steam load you'd like through any size pipe if you have enough pressure. Look at what they manage to do with 3/4" pipe and 125 psig in the typical dry-cleaning shop. But in a steam heating system, the boiler pressure should ideally be less than 2 psig if you expect things to work well and economically.
Here's what happened in that commercial building I was telling you about.
Whenever they cranked up the boiler pressure to overcome the pressure drop of that undersized unit heater piping, all the quick vents on the office radiators would snap shut and refuse to open again. If they lowered the pressure at the boiler, they would get heat in the office, but not in the factory. That's because steam air vents and steam system pressure are married to each other. And pipe size has everything to do with system pressure.
What did they wind up doing? They repiped the heaters, of course. This time, though, instead of basing it on the size of the hole in the unit heater, they looked in my book, "The Lost Art of Steam Heating" and found the right sizes.
That job works really well now. And that's a good feeling!
It's so simple to do it right the first time
All you need is the right information. The right reference books can make you shine on problem jobs that have everyone else scratching their head. Why shouldn't you be the one with the answers?
Read every day.
And More Heating Help
The Golden Rules of Hydronic Heating
That's the title of one of our most popular books. "Golden Rules" is a little handbook that contains all sorts of hard-to-find charts, tables, conversion formulas and rules of thumb, which, when properly applied, can help you face tough steam- and hot-water heating challenges. Also in the booklet, and briefly stated, are these seventeen truths. These are The Golden Rules of Hydronic Heating, upon which I shall now briefly elaborate:
There's more to life than combustion. Don't be a flamehead!
Ever notice how most of us head for the boiler room first? I figure this is a vestige left over the days when we all lived in caves. You feel safe when you can get underground and build a fire, right? The trouble with being a flamehead, though, is that the answer to your problem often lies out there in the building. More likely than not, it has something to do with the piping. So get out of the boiler room and poke around. See the system, not just the symptoms.
If you can't find the time to do it right, you'll never find the time to do it twice.
Think about this Golden Rule the next time you're tempted to take a shortcut. Manufacturers print those instructions for a reason, and if you choose to ignore them, you're probably going to get a callback or two...or three. Got time for callbacks?
Never do work for your relatives, your church or your synagogue. These jobs will never work.
You know why?
1. You do these jobs for free, or for next to no money, and
2. You're working for the people who are most likely to break your chops and drive you nuts when the slightest thing goes wrong. And by the way, this is the reason why most heating professionals have the worst imaginable heating systems in their own homes and offices.
On most days, the urge to oversize is greater than the sex drive.
Like the first Golden Rule, this one is also genetic. Most heating professionals are born with this recessive gene that mutates and expands like microwave popcorn whenever it's time to do a heat loss calculation or size a boiler, burner or circulator.
Just when you think you've got it all figured out...you don't.
Most of us learn everything we need to know during the first five years we're in the business. The next five years, we spend believing we know it all, and telling anyone who will listen how smart we are, and what an idiot the boss is. If we stick around beyond ten years, however, we begin to realize we're actually as dumb as rocks.
Mother Nature makes no allowances for ignorance or budgets.
You have my permission to quote this one the next time you're speaking to the board members of a cooperative apartment building.
The problem and the solution are rarely in the same room. Get out of the boiler room and be nosey.
This is especially true of steam heating systems. Steam likes to play a slight-of-hand game with you. It sends you running one way when the real cause of the problem is the other way. If you hear a noise on the second floor, look in the basement for the answer. If the condensate isn't returning to the boiler, wander out into the piping system because that's probably where you'll find your answer. Again, look to the system, not just the symptoms.
The best tools a troubleshooter can carry are a very bright flashlight and a very open mind.
Do you ever figure out what's wrong with the job before you even get there? You make up your mind while you're still in your truck, and then you set out to prove you're right, even though you may be wrong. Bright flashlights can help you look, but only if you're willing to see.
High pressure goes to low pressure...always.
This is what makes steam flow from the boiler to the radiators. It's also what makes hot water turn this way or that every time it encounters a tee. If there's not enough pressure difference between two points, the fluid or gas (whether it's steam or hot air) won't move, and you'll wind up with a no-heat call.
One in-coming phone call will always generate a minimum of five out-going phone calls.
If you'd actually like to accomplish something during the course of a day, never pick up the telephone, especially if you're on your way out the door. Touch that phone and you will never see the light of day.
When troubleshooting, always round up the usual suspects: air, dirt and improper piping.
I was thinking about some of the nasty and spooky jobs I've visited over the years. The cause of the problem in nearly every case was air, dirt or improper piping. Most of these nightmares could have been avoided if the installer had read the directions, remembered that air is everywhere, and flushed the system before starting it up. It is so easy to stay out of trouble, it really is.
You can have it good. You can have it fast. You can have it cheap. Pick two.
This is my all-time favorite Golden Rule. So much truth to it!
The Laws of Physics will always override the Laws of Economics.
However, the Laws of Economics will usually prevail in the short run.
If you bleed a radiator and you don't get any air, it ain't an air problem. Stop bleeding!
Open a hole in a closed hydronic system and water will flow from it. Let it flow long enough and you will drag hot water up from the boiler. This does not mean you solved your problem, unless, of course, you plan to leave the hole open permanently. If you don't get air, it ain't an air problem. This is one of life's great truths.
When you do something stupid in heating, you will always be rewarded in a small way. This leads you to do other stupid things.
If you keep bleeding the radiator, it will get hot eventually. That's your reward for being dopey. In a similar way, when you raise the steam pressure, you'll compress the air that's trapped in the pipes. The steam will appear to move a bit further down the line. That's your reward! You'll feel so good that you'll raise the pressure even higher, along with the fuel bills. The system won't work any better, but you'll be smiling like the village idiot.
When it comes to steam heating, if it makes sense, don't do it!
For instance, if you want the steam to move more quickly lower the pressure, don't raise it. It works because it doesn't make sense. So crank it down!
The two correct questions to any heating question you will ever be asked:
1. It depends.
Let me get back to you, okay?
Number One, when properly delivered, makes you appear sincere. Number Two, which is to be used only when Number One fails, gets you out of the neighborhood.
That's the fun stuff, you can get at the meatier part of this little handbook by treating yourself to a copy the next time you visit www.HeatingHelp.com. You'll find it in the Books & More section.
And Still More Heating Help
Why a radiator is not "heat"
I once looked at a problem job in an office building on Long Island. It can get pretty windy here on the Isle of Long. This building had a wide driveway that passed under the first floor to a parking lot out in the back. The wind barreled down that driveway like a runaway train and made the concrete that formed the building's first floor colder than outer space.
"The people who work in that first-floor office are freezing to death," the guy in charge told me.
"I'm not surprised," I said. "This is a terrific great example of radiant cooling."
"I think we need more heat," he said.
"I think you're right."
"It won't be hard to do, though," he continued. "We have 1-1/4" commercial fin-tube radiation running around the perimeter. There's room in the cabinet to add a second tier of fin-tube. That will double the heat in every room."
"How do you figure that," I asked.
"Well, there will be twice as much fin-tube in each room," he said. "That's twice as much heat."
"What is heat?" I asked.
"What is heat?" I repeated.
"What are you talking about? Is this a trick question?"
"Nope," I said. "It's just something we need to talk about. Is fin-tube radiation heat? Or does it have the ability to give off heat."
"Oh, I see what you're getting at," he said. "Okay, it has the ability to give off heat. I think you're picking nits, though. With twice as much ability to give off heat, we'll give off twice as much heat, okay?"
"How do you figure that?" I asked.
"You're a wise guy, aren't you?"
"Nope, just curious. Are you going to change the size of the pipes leading to the fin-tube?"
"Nah, I can't get at those pipes. They're all behind the walls."
"Are you going to raise the temperature of the boiler water?"
"I hadn't planned on it. We're already running at 200 degrees," he said.
"So if you're delivering the same flow rate at the same temperature to the fin-tube, how can you double the amount of heat that comes off it? Without increasing the flow rate or the temperature, you're going to be delivering the same amount of heat as you've always delivered. Twice as much fin-tube will just mean you'll give it up faster to the air in the room."
"Well, that will make a difference, won't it?" he asked.
"Figure it out. Let's say you now have a 1-1/4" supply line to the existing fin-tube."
"That's what I do have."
"Okay, you can get, under normal conditions, about 14 gallons per minute through that line. Each GPM represents about 10,000 Btu, so that means you can deliver about 140,000 Btu to that zone."
"Okay," he said.
"Now let's split the flow rate in two when it gets to the fin-tube because that's exactly what you'll be doing when you add that second tier of fin-tube inside the cabinet. And that's also assuming you balance the flow between the two tiers because if you don't, the water will go into whatever place it's easiest to get into."
"Now how much water should flow through each tier of fin-tube, assuming they're in balance."
He hesitated a bit and then said, "Fourteen gallons per minute," he said,
"Through each one!"
"Think about what you're saying." I said. "You're delivering 14 GPM to the fin-tube through the 1-1/4" supply main."
"So how can it suddenly turn into 28 GPM when it hits the fin-tube?"
"Because there's twice as much space in the pipe?"
"But the fin-tube is connected to, and it's getting its supply from, the 1-1/4" pipe," I said. "The pump is only delivering 14 GPM. When that flow hits the two tiers of fin-tube, it will split in half. Each tier will get about 7 GPM, assuming everything is in balance. You'll be delivering about 70,000 BTUH to each tier, not 280,000 BTUH." His eyes were getting wider.
"I'm starting to see what you mean," he said.
"If we could figure out a way to suddenly double the quantity of heat you're delivering to the building in the middle of the zone we'd really be onto something, wouldn't we? We could make a fortune selling something like that."
"So I guess doubling the amount of fin-tube won't help us here, will it?" he said.
"Not unless we increase the size of the pipe that's carrying the water. And not unless we check to see if the boiler can also deliver the additional heat."
The next time you're troubleshooting
Ask yourself, "If I were heat, could I make it to the people?" And then take a look at the size of the pipes. Look, too, at how close together the diverter tees are (if you have them on that system), and ask yourself, "If I were heat, which way would I go?" And while you're at it, look at that extremely long loop of baseboard radiation and wonder, "If I were heat, wouldn't I have gotten off somewhere up the line? Maybe that's why the radiator is lukewarm?"
If you want to be a good heating troubleshooter, you have to "think" like heat.
When I write a book
I try to make it as visual as possible so that you might be able to see in your mind's eye what I see in mine. I think of the piping system as the "train" that the heat travels on from the boiler to the radiators. I find that when I imagine little BTUs riding the train the troubleshooting just gets easier. Give it a try; turn your next problem job into a cartoon. Have some fun with it. Every problem job presents an opportunity to learn more.
I mentioned radiant cooling in the beginning of this story. That's the feeling you get when you're standing on or near cold concrete. This has always been something to consider in construction because it can lead to a feeling called, "Cold 70." That's the way you feel when there's a big difference between the temperature of the air in a room and the temperature of the surfaces in the room.
You can read more (a LOT more!) about this in my book, "Hydronic Radiant Heating." I also have a chapter in that book about radiant cooling, which is becoming widespread in Europe for commercial construction. The Europeans have managed to reduce the operating cost of air-conditioning dramatically by using the phenomenon of "Cold 70" to their advantage. Fascinating stuff!
You can order "Hydronic Radiant Heating" through the Books & More section of www.HeatingHelp.com.