New job, Steam Boiler FAQ's

JR811

Like my title states, I recently started a new job as a maintenance mechanic for a school district. I have 8 years of HVAC experience, but have not worked with heating systems in 5 years. For the past 5 years I've been working with large centrifugal chiller plants and building automation, but now brought in to a position where I was asked to modernize a school system with their automation system and get their plants up running. In my short time of being here I've been thrown immediately in to solving issues with a big steam boiler that has been constantly over heating a very old building within our organization. Like I said it's been some time since I've worked on any sort of Hydronic or Steam system, primarily in residential applications so I have a good idea of the theory and operation of a heating system, but from what my foreman tells me about the operation of this system, is completely foreign to me. I'll add in that my foreman does not come from an HVAC background, but knows the quirks and nuances of our buildings...but that doesn't necessarily mean it's correct.

1. Our steam boiler is controlled through a BMS system, when the sensor in this building calls for heat, 2 Johnson Controls Actuators wired in tandem open and close the Steam Isolation Valve and send steam to the radiators. One of the issues we were having is that it was constantly sending steam through the building due to the isolation valve not seating. I found the actuators that controlled the valve were not wired properly at all and corrected that. What was happening was the Master/Slave dampers were not wired to work as such, only relying on the master damper to open and close the valve. now wired properly and adjusting the standing voltage it now is configured that it is using motorized power to keep the valve shut and prevent steam from passing through. We are still getting high temps in this building, my foreman believes there is still steam weeping through but I don't think so and for 2 reasons. 1 the radiators have been ice cold since correcting the issue, based on trend analysis the boiler has not been called for heat the past 36 hours since correcting the issue.

2. The other issue and this opens up another question because it's where I'm not certain in my theories. The temperature sensor for this building is mounted on the wall of the Chimney, it will always read high because of the flue gas temps radiating through that wall. Which brings me to that other question, even when the building is not calling for heat, the boiler will run every 5-10 minutes to build up pressure in the vessel, then trips on pressuretrol due to the steam isolation valve being closed since the controller is not calling for heat...since this is a PLC controlled system it may be different, but based on the operations and theory I know from residential steam, the boiler isn't going to turn on and create steam unless the thermostat calls for it to. My foreman says this is normal this is what the boiler does it will always generate steam pressure, it's questionable to me but since the boiler is firing all the time creating 5-6PSI of pressure, it is constantly sending flue gasses up in to the chimney, thus giving a false reading to the PLC temperature sensor saying the heat in the building is x amount of degrees. With everything I'm telling you at the moment, my foreman still thinks that steam is passing through the isolation valve, despite all the radiators being ice cold...but I'm confident these high temp readings we're getting are due to the sensor being mounted on the same wall in front of the Chimney.

Since correcting the issue with the Actuator on the valve, looking at a trend analysis of the boiler it has been doing it's thing of running for a few minutes and tripping on pressure, but not running for prolonged periods of time which would be from a true call for heat. I'm also keeping in mind finding the politically correct way to address this issue with my foreman, because while he may understand the nuances of the building and how to combat them, his theories seem off and I think there's a way we can permanently fix both issues I mentioned.

For further info, this sensor is on the 2nd floor the building, and the first floor of the building being cold has always been an issue from what they tell me (which makes sense as heat rises). This is also a 15 PSI boiler with a 7275 SqFt. Rating. Thank you in advance for all the help.

ratio

Sounds like you've got your hands full with the steam system, and maybe other things too.

To start with, pick yourself up a copy of TLAoSHR. After that, I'd validate the pressure it's operating at—sounds high to me, but IDK. With electronic controls, I don't see any reason to run with steam up all the time, the system should be able to coordinate steaming with the valves & whatnot. You should be able to realize some savings by that.

How much makeup water are you using? Keep an eye on that, add a water meter if you can.

A cheap thermal imager is a good investment.

JR811

I have the other Steam book Dan wrote, I probably should read it again

In this short time, I don't see why we need to keep any operating pressure. This Boiler is in that grey area of too large for a residential application, too small to be a "commercial boiler" nor would operating it require me to have a license since it doesn't fit in that criteria. The building it serves is maybe 7000 sqft, it's a small mansion if it were a home. It's not like we're operating a building with square footage in the 6 or 7 figure range or a sky scraper or a steam turbine where you need to have constant steam pressure.

If it were to call for heat with no standing pressure it could generate 5-6 PSI in a short amount of time and as we know once the radiators are warm, they stay warm for a while. It's a small enough building that I think it can operate fine like that.

JUGHNE

I have 3 old school houses, all over 1M btu steamer, 2 of them had standing pressure with zone valves that leaked by.
They all got rewired to fire only upon a call for heat. This prevented overheating of building and especially boiler room and adjacent areas.
Also the pressure was set as low as the controls allowed.
Down from that 5-7 PSI to 2-3.
This helped everything and existing dripping leaks on flanges and valves nearly stopped.

Jamie Hall

Your building and the main place I care for are almost exactly the same size at 7000 square feet. The pressure you are maintaining is much too high, unless you have some air handlers or coils somewhere in there. If all you have is radiation, then you don't need anything more than 2 psi -- and probably less. The main place I care for operates just fine, thank you, on 2 to 3 ounces...

However... your steam isolation valves. Are they full port valves? That is really important. If the are reduced port, or worse, globes, then you do need the higher pressure just to get steam past them -- and you are losing a lot of energy at the valve, even if the are "open". And for that matter, why do they exist at all? Was this place connected to district steam heat at one time, perhaps?

How is the radiation piped? I would assume in a building that size it would be two pipe... I hope... but which is it? If it is two pipe, what are your radiator valves and traps? And, perhaps critically important, are the traps working properly? And if it is two pipe, how are the mains vented? Vents or crossover traps? and the returns -- how are they vented?

What is the total EDR of all the connected radiation? Frankly, a boiler rated at 7000 plus square feet sounds to me like massive overkill and I would expect some really serious cycle timing and control problems.

If it were mine to play with -- and the foreman were amenable, which he may not be -- I'd try finding a more normal place for a thermostat (mounting it on a wall with a flue behind it is pretty dubious) and control the boiler in the conventional way with the thermostat, and leave the isolation valves open wide. If some rooms are too warm, and it really is two pipe and the venting is adequate, just turn down the valves a bit in those rooms.

JR811

It's a Globe style valve, which explains the higher pressure.

To my knowledge this building was once connected to a hot water system in a central plant. 10 years ago they upgraded the central plant and this building was retrofitted with Steam. If I were to guess, it's a 2 pipe steam system because the radiators remained the same. I'm not at work right now to take a full look but that is another good point I should look in to, adjusting the valves at each radiator.

I guess that answers one of my questions that it isn't abnormal for Steam Boilers to operate with a standing pressure, but we've all come to agreement in this thread it's overkill for a building this size to need it.

I like the idea of re-wiring the controls to only fire the boiler upon calling for heat. It only takes minutes for the boiler to generate the desired pressure and it will make all parties happy in the building. Currently the complaints are the first floor is always cold, 2nd floor is constantly baking.

The issue of moving the temp sensor off the Chimney is the sensible solution but like you said, our foreman is not going to bend on that. My best solution there would be to just leave the old sensor on the wall as a decoy and wire in a new one elsewhere and not tell them about it

Truth is this old lady of a building has the most simplified system in our entire district and we're investing too much time combatting issues due to overkill when we don't need to. We have quite a mix of HVAC equipment across the entire district that needs attention but we are investing our time reinventing the wheel of a system that doesn't need to be.

Jamie Hall

If those things are globe valves, then yes you do need the higher pressure at the boiler. Most of the pressure will disappear across the valve, as will a good chunk of your heating dollars -- at a guess, without actually measuring on site -- could be as much as 10 to 20 percent. I truly think this is the first time I've said this on the Wall -- don't' reduce that boiler pressure! Futher, depending on exactly where you have condensate drips in relation to those valves, you may find that you do, in fact, need to keep the pressure up and not try to go from a cold start. Experiment with it, but if you find you get water hammer or that it takes a long time for the mains beyond the valves to get hot after a start, you're going to have to go back to maintaining pressure and temperature.

More money.

Gsmith

If you don't need to close the valves to isolate the mains for some reason, take them out put in spool pieces , reduce the pressure, balance radiator inlets valves to the heat needs of each space ( making sure it's a two pipe system) and move the thermostat. I'd be surprised if the fuel savings will not provide less than a one year payback.

JUGHNE

"Spool Pieces"... are they what I envision?
Flanges with short pipe to replace those valves or any manual valve?
I have imagined them, but never seen one, wondered if they existed.

Gsmith

Yes, exactly, many are pre fabbed to fit exact valve flange to flange distance. Or use a straight pipe, threaded with a union or Dresser style couplings. Can be made up with two threaded flanges and a custom size field cut threaded piece of pipe.

JUGHNE

Thank you.
Another question for flanges: in another posting someone with a steam main had a flanged connection. The entire piping need to be about one inch longer. Is there a flange with the gasket surface on both sides that could be slipped between the existing flanges. Like a "sandwich filler"?

Steamhead

@JR811 , where is this building located?

Gsmith

@jjugne, yes, metal pieces in various thicknesses with flange bolt holes, sometimes called flange fillers.

JR811

So just an update on the issue. We've looked at every possible scenario with this boiler, it seems to be the disc that opens and closes the valve is warped. When the boiler is off for an extended period of time, the valve is able to seat without issue. When the boiler runs constantly and the valve gets hot, it will not seat all the way.

My belief is the disc gets warped so when in the "seated" position the disc is reshaped, constantly allowing steam through even when the building does not call for heat. We're in the process of ordering a re-build kit to replace the internals of the valve.

Jamie Hall

It would be better to replace the thing with a full port ball...

JR811

i agree, but as a school district there's only a finite amount of money.