Location of main vent

Abracadabra

Does it matter exactly where a main vent is located on a 1-pipe steam system?







ie. right after the last riser off the main or at the end of the dry return before it turns down?  I'm thinking that it shouldn't as long as the main is vented properly.

nicholas bonham-carter

vent location

i think the vent should always be on the dry return, otherwise you may have the remaining air in the dry return expanding and upsetting the steam distribution. [could be your problem with the cold apt.]

if you have some sort of tekmar/heattimer outdoor reset control, then the steam arrival sensor can be placed on the dry return, if it is vented.--nbc

Dave in QCA

on a One Pipe system

When you say the dry return, I think you are talking about the long end of the steam main where it loops around for considerable distance after the last steam takeoff and probably returns back to the boiler room where it drops and becomes a wet return.



In this case, the main vent can be located anywhere that is preferably 2 feet or more after the last takeoff.  If you install it near the last steam takeoff, you will put less heat into that dry main, which is probably all lost to unheated space anyway.  However, if you put the vent at the point where the main drops, it will probably be in a location that is closer or perhaps in the boiler room, and there are advantages of having all of the apparatus in a central location.  Also, if you desire the extra heat that is lost to the basement space, thereby making it warmer, that is a consideration too.

Abracadabra

main vent

nbc,  the main vent is already actually at the end of the dry return.  I was thinking of moving it closer to the beginning of the main return so that the main vent closes up quicker, pushing steam up the riser earlier to that cold apt, instead of waiting for steam to fill a useless volume of pipe.

Abracadabra

main vent

Dave,







Exactly.  I'm talking about the end of the main that has been reduced down and is supposed to only really be handling condensate return back to the boiler.  I'd like to have this main vent close up quicker so that I can start pushing steam up the risers earlier, instead of waiting for the steam to loop back around and heat up the vent.  It shouldn't really matter if I've left unvented air in that dry return, does it?  I'm not worried about having all the main vents in the same place.  There's already some main vents for some branch mains already thought the basements, I'm more concerned about trying to push steam up risers sooner.

Dave in QCA

It will work fine

There is not need to run steam down that dry return section of your main.   It will still handle the condensate just fine even if there is still air in the pipe.  Your desire to get the main vent to close earlier is fine and it may help you out some.  The main difference is you won't be heating up that section of pipe, that is what causes your delay in closing the vent.  No reason to heat up a pipe that does not need to carry steam.

crash2009

Just before the drop

I like the main vent installed just before the drop to the wet return.  This gives us a couple advantages over installing just after the last rad.  Please correct me if this doesn't make sense.

1 Having the vent at the end of the main takes the steam to the end.  Steam to the end encourages the condensate to go there as well.  You might not need that condensate back in a hurry but I do.  And, Don't we need that pressure to push the contents of the wet return up and over the Hartford to the equalizer? 

2 After the main vents cool off, and start to allow cold air back in the mains, I would rather that cold be in the boiler room rather than 2 feet from the coldest takeoff in the building. 

 

Dave in QCA

More discussion

Crash, first, I have to say that I too prefer the vents to be at the end of the line.  That's where mine are and since my mains loop around the basement and end back at the boiler room, I like having the vents in the same room where everything else is.  Also, while I don't heat the basement to living temperatures, I do like to have it moderately comfortable for doing laundry, etc.



My previous comments on this thread were merely repeating what I have heard one or more of the pros on here state. 



Here is my thinking on it.   Vents located after the last riser or lateral connection on the main will work just fine, not better, not worse.  They will save needless heating of return piping in the basement, unless you prefer to have it heated.  I think its kind of a tossup.

As far as function, the condensate is going to flow down hill unless there is some kind of pressure difference impedeing it; in this case there would not be.  So the condensate will be laying in the bottom of the pipe, rolling slowly down hill.  It will do this whether there is steam above the condensate or air above the condensate, it would make no difference.  As far as pressure and returning the condensate to the boiler, etc., the last section of the pipe that still has air in it will be at exactly the same pressure as the portion of the main containing steam.  So, the condensate really won't know the difference.  The pressure that returns the condensate through the hartford loop is actually the column of water that would begin to stack up.  Of course, there is the dimension A issue that accounts for pressure drop over the lenght of the main assuming that the boiler pressure is 2 psi.  Whatever the pressure is in the rest of the system, it will be the same in the section of the pipe that is filled with air. 



When the boiler shuts off and the system sucks in a big breath of cool air, replacing every single cubic inch of steam, it probably won't make a lot of difference is that 212 degree steam is replaced with 72 degree air from the boiler room or 60 degree air from the storage room.



I am still inclined to believe that the best thing for the system is to keep the air out and let the system fall into a deap vacuum.   But that is another subject, for further experiments and study at a later date.

crash2009

Dave,

Abracadabra has the vents at the end of the line allready.  He was thinking about moving them to near the last riser, so that he could save a little steam to heat the building with.  I thought that changing the vents location was a bad idea for the reasons listed above (correct or not, could we discuss that at another time?) and...I think he has something else going on.  If you are unable to spare enough steam to fill the main, how are you going to heat the building?  We are told to fill the mains first, and fast.  I think his place is heating the radiators before the mains, and it's huge, and it's full of renters, access is difficult.  If you can't fill the mains how are you going to fill the risers.  I think he needs more main venting.  

Abracadabra, How many cubic feet of air do you have in the mains?

How many, and what type of main vents do you have?

 

nicholas bonham-carter

Where to put them

I like to be able to study the operation of all of my 6 dry returns in the same area, so that is the main reason for my venting location.

You are right that the pressure would be the same whether vented half-way along or at the end, but I think the cold air in the unvented portion could expand with the heat, and perhaps mix with the steam going into the riser of the last takeoff. I haven't arrived at this theory after extensive thought, just gut reaction/intuition.

I would love to have an ir camera to study the progress of steam in the pipes, and maybe when the children are off the payroll, I will get one (cameras will be really cheap by then, hanging next to the checkout at the supermarket!!!)--NBC

Abracadabra

layout of mains

attached is a layout of the mains.







up until this morning, the main vents were as follows:

V1 = 3 Gorton #2

V2 = 1 Gorton #1

V3 = 1 Gorton #1

This afternoon, I had an idea.  Somewhere on the wall, or maybe Gerry and Steve's "Balancing Steam Systems" I remember reading that you can't vent any faster than what an open pipe will vent. I pulled all the vents off at V1 and left that location completely open. V2 and V3 venting was reduced to a single Gorton C.  My intent was to completely slow down the steam running to V2 and V3 and to coax it towards V1.  Let me repeat, V1 completely open, no vents.  just an open end of a 3/4" pipe. Boiler started up and once it started steaming, I started a stopwatch. It took 12 minutes to get a negligible amount of steam to start coming out of the open end of the 3/4" pipe.  This seems like an extremely long time for steam to get there.  Anyone else think so?  

crash2009

You likely need 13 Gorton 2's

I just did the math.  If I have calculated correctly, and you have measured correctly, I calculate 13.789 cubic feet in your mains.  It doesn't surprise me that it takes 12 minutes to get steam out of the open hole.  Mine pushes the air out at about one foot per minute @ a half ounce. 



Now if we use Steamheads calculations from a couple days ago and vent the main using the one ounce scale from the handbook, you would need about 13 Gorton 2's.  Four and a half Gorton 2's is the max on a 3/4" antler.  Where you put them, I don't know what is best.  You will probably have to break down the math for all the mains and install them proportionally.



Sounds like a lot huh?  NBC's got 20, I have 8 in this little place.  13 might just get you started.  Here is a nice little video and some pictures.



http://www.gwgillplumbingandheating.com/webapp/GetPage?pid=415

Abracadabra

13 gorton #2s

That's exactly what I don't want to do.  I don't want to put any gorton #2s on those short mains because those apartments are overheating, and the apartments fed by the V1 branch aren't getting enough steam. I'm leaving the Gorton C's on V3 and V2 for now with 3 gorton #2 and a gorton #1 at the V1 location.  It's a bit warm in Chicago right now and unit temps are gonna be a bit skewed for now.

nicholas bonham-carter

Lots of G-2's

Yes I have a lot, added in stages until the back-pressure during the venting phase went down as low as it would go (>1 ounce).

Just remember that the vents are allowing the steam to arrive as quickly, and as simultaneously as possible. Once the steam has filled the mains, the vents no longer have any influence on the volume of steam going down the line. Therefore, why not vent all the mains as quickly as possible, and then let the Hoffman 40's allow the steam to enter the risers and takeoffs more slowly. If you have some tall risers then you can increase the radiator venting for those areas at the top.--nbc

Abracadabra

...

I don't want to add more G2s to the sections getting overheated, because the steam starts to rise up into the risers before it's finished filling the long main. Even with that main vent completely off, steam is starting to cheat up the risers and by the time the long main has filled the overheated units risers have steam halfway up. 

Dave in QCA

Oooooops!

I think I got lost in the theoretical debate instead of focusing on the main problem.   I am in complete agreement with Crash.

The location of this vent is not causing your distribution problems.

Moving the vent location is not going to solve the distribution problems.

I prefer my vents at the end of the main too.

I believe that the effect of moving the vent would be between zero and an imperceptable difference.

crash2009

Gorton C as a main vent

Thats the same as going elephant hunting with a peashooter.  The whole idea behind having enough main vents is to fill the main with steam instead of air. Then all the risers at the same time begin to fill.  You will have eliminated your hot spots.  By the way, you need more than 13.  I just noticed the 12' X 5" connected to B (must be boiler) there's another foot and a half.  You got more air in that 12 foot pipe than most homeowners have in their whole system.  



You have a fantastic system, put the pedal to the metal, and rock it.



Here are 3 videos that might help you visualise



http://www.youtube.com/watch?feature=endscreen&v=HSp7K_C6IDg&NR=1



http://www.youtube.com/watch?v=l_CfD0h1LEE&feature=endscreen&NR=1



http://www.youtube.com/watch?v=8lFDcgxy-WM&feature=related











I will leave you to draw your own conclusions as to what is going on inside your system.

Dave in QCA

That Argumentative Dave.....

I really don't mean to be argumentative... really!

But, I'm going to throw out something a bit different.   Crash, my numbers for volume in the mains probably agree with yours.  Dividing the shared mains equally, I come up with 7.36 cu ft for V1, 3.92 cu ft for V2, and 2.43 cu ft for V3.   Using the approach that Gill and Pajek describe in their publication, Balancing Steam Systems Using a Vent Capacity Chart, in which they theorize that 3 minutes (after the boiler begins to steam) is a reasonable time to vent the mains, I come up with the following.  V1  needs 2 G2s, (but since this is a problem vent, throw in an extra G2 for good measure).  V2 needs 1 G2 + 1 G1, V3 needs 1 G2.



On other observations, I would guess that while it was taking 12 minutes for the steam to arrive at V1 (and I assume that the clock began at the point the boiler began to steam) that steam was already going into the radiators near the boiler.  Once steam enters the radiators, they are going to condense and consume a great deal of the steam, resulting in longer times for the steam to get to the end of the main.



Also, I have read back through the posts by ABRACADABRA, and I am now a bit confused.  You have indicated that you have even steam distribution.  That the steam arrives at the radiators at pretty much the same time and that they all get hot all the way across.  You indicate that you have even heat, but that one of the units is cold inspite of the fact that its radiators properly heat.  Is this really correct?   If it is, then we are all pounding our heads against that wall trying to solve a steam problem that doens't exist.  It must be cold air infiltration or some structurual issue that causes the unit to be cold.



However, you have also indicated that the colder the weather gets, the more even the unit temps become, this would indicate that there may well be balance issues under partial steaming conditions which occur in mild weather.



An important observation would be to compare the % of each radiator to get hot in a partial steam cycle.  For example, at a given cycle where the rads might heat 24% of the way across, do they all heat 24%.  This is really critical. 



Also, I have searched through the various threads that you have running, and I can't find whether the mains in the basement are insulated.  It is critical that they are.



What are you using for a control and how many cycles per hour are your running?



Does the steam arrive at each radiator at the same time, or within a minute?  If not, how much difference is there, and where are the last radiators to get steam located?



Where in Chicago are you located, and have you considered getting BoilerPro over to give you a hand?  He is the best and he is the one who wrote the articals on slow radiator venting.  In your system, with its great disparity in steam main length and volume, this approach may be vital.



You indicate that you have already replaced radiator vents, what did you install?



BTW, I'm located in the Quad Cities, on the opposite side of the state.

crash2009

Boilerpro?

I was just thinking the same thing Dave.  I think Abracadabra was thinking the same way, before you and I.  This may be the reason he asked this question in the first place. 

The math (cubic feet of air) says we need  (lets just round it off to 15).  If we install 5 at each end of main, that probably won't work.  I agree that the vents should be spread out.  The million dollar question is where.  Boilerpro is probably looking at this diagram right now laughing, and wondering if us 4 eggheads will ever figure it out  

My guess is that additional venting stations need to be installed.  

Dave in QCA

Entertainment

Crash,  Do you suppose that this whole Heatinghelp.com thing is just a twisted ruse that Dan fabricated with conspiratory help from the noted professionals, where the novices try to solve problems and thereby provide endless hours of entertainment?

I can just hear 'em talking at their jobsite, as they are throwin that 5 foot pipe wrench around, "hey did you see what that idiot Dave in QCA said yesterday?"  Then they all chuckle.... or perhaps all fall on the floor laughing!

Abracadabra

more info

Ok guys, her goes.. some more info

Let me start by saying I'm not totally a newbie.  I've balanced a couple of other large apartment buildings and I have a general idea of what I'm doing, but of course I don't have the years of experience many of the pros here have, so I haven't seen too many different situations....  As I'm sure many of you know, there's always that one job that confounds you.







I was at this building today for some other stuff and the boiler started a cycle.  I figured I'd follow the steam along the main to see how fast it moves and see where and if it slows down.  There was a lot of running between basements and 1st floor apartments.  Before I get to that, please note the attachment.  It's basically the steam main layout I've posted before, with some key points marked in.  The LR radiator of the cold apartment that is fed off the main that is all the way at the right on my diagram (marked as LR) just before the reducer between the 18' 3" main and the 14' 2" main.  The DR radiator takeoff is at the corner where the 11' 2" main and the 30' 2" main elbow.  Got it? ok... moving on. With 4 Gorton #2 at V1 the steam was flying down the 4" main to the right. The V2 and V3 vents were left at Gorton Cs.  Yeah, yeah, I know... more venting, but I really really want to push the steam to the right.  I doubt there's any chance at all I'll be overheating the apartments all the way on the right based on what's been going on. So the steam is moving along the pipe at a nice clip.  Of course, all times are started once steam starts flowing out of the header at the boiler. Steam gets to the LR radiators takeoff in 3:30 after steaming starts, and pretty much grinds to a crawl after that. It takes another 4 minutes to get to the DR takeoff and then another 4 minutes to get to V1. The return drip leg where the return goes from a 2" dry return to a 1-1/4" wet return gets very hot before steam gets there from the condensate. Hot enough where the 3/4" antler I have setup gets hot enough to not be able to hold onto.  There's about 1150 EDR of condensate returning thru that 1-1/4" wet return.  Again, I'm right at the limit of what that return line is supposed to handle. All this hot condensate is making the pipe extremely hot, but no steam at V1. I will be back there on Monday to measure with a laser thermometer but I'm guessing it's in the 175-190 range from my calibrated fingers. I seem to remember that Gortons have a tendency to close up early or too soon?  Is it possible the vents are closing up due to being heated from the condensate return?  The vents get hot to the touch, but there's no steam. I have 3 Mepco 3/4" 2E traps.  I'm thinking of replacing the Gortons with the 3 Mepcos.  a Gorton 2 will do 1.1cfm while a mepco 2E will do 1.53, so 3 mepcos will replace 4 gorton 2s.  Maybe I can get a longer delay before closing on the mepcos?

I am considering cutting into the 2" main between the 2 bath takeoffs and installing some heavy venting there with a 2x2x1 tee and a mega menorah.





Dave, see my replies below to your comments:

" I would guess that while it was taking 12 minutes for the steam to arrive at V1 (and I assume that the clock began at the point the boiler began to steam) that steam was already going into the radiators near the boiler."  Yes.. steam is probably entering radiators above and near the boiler.  There's 19 units, each with 4 radiators per unit. 76 radiators. There's no way I can run to each radiator and check the first section to see if steam is getting to it at the same time.  I have checked radiators in first floors of 5 units spread out across the building. The radiators start getting steam at about the same time except for the BR and DR radiators of the cold unit, which get steam about 1 minute later than the same unit's LR radiator.  

"It must be cold air infiltration or some structurual issue that causes the unit to be cold." This is always the first thing I check.  Storms windows closed, leaks around windows and doors checks. Radiator pipe holes in floor plugged. I've even resorted to installing window film. If you check one of my other posts, where I attached a graph of temps, you'll see that the dropoff of temperature in this cold unit is the same slope as the other hot units, so heat loss is similiar across the units.  

"However, you have also indicated that the colder the weather gets, the more even the unit temps become, this would indicate that there may well be balance issues under partial steaming conditions which occur in mild weather." Yep.  I'm still leaning towards a venting problem.

"An important observation would be to compare the % of each radiator to get hot in a partial steam cycle. For example, at a given cycle where the rads might heat 24% of the way across, do they all heat 24%. " I would have to guess at this, but I don't believe this is the case.  Near rads 25% hot (2 sections on a 8 section) far rads would be 11% hot (2 sections on a 18 section) and in fact, today 42 degree weather, in the same cold unit the first floor LR radiator got very hot all the way across, the DR radiator had 2 last sections lukewarm.

"Also, I have searched through the various threads that you have running, and I can't find whether the mains in the basement are insulated. It is critical that they are."  Yes, all mains are insulated with the exception of the main that runs thru the basement apartment. The basement apartment has radiators and is a occupied living space.  Problem is going to be trying to find 3-1/2" pipe insulation.  I haven't found a supplier.  I have to wrap the pipe in 1/2' fiberglass pipe wrap and then use 4" insulation around that.

"What are you using for a control and how many cycles per hour are your running?" Using this: http://www.rdcontrolsystems.com/steam-200-series.php Daytime temp set to 70, evening temp set to 69, morning and evening boost set to 71

"Does the steam arrive at each radiator at the same time, or within a minute? If not, how much difference is there, and where are the last radiators to get steam located?"  Again, with ~80 radiators a bit difficult to tell, but from radiators in the middle of the building to the LR radiator in the cold unit, I'd say steam starts showing up into the first section within less than a minute of each other. The radiator that has steam show up late is the DR radiator in the cold unit.  Won't show up for about 2 minutes after it shows up at the LR radiator in the same unit.

"Where in Chicago are you located, and have you considered getting BoilerPro over to give you a hand? He is the best and he is the one who wrote the articals on slow radiator venting. In your system, with its great disparity in steam main length and volume, this approach may be vital." On the northside, about 5000N and 2000W (near Foster and Damen).  I actually emailed Dave to do a combustion analysis, but I haven't contacted him for this balancing problem, since it seemed he was a bit backed up. 

"You indicate that you have already replaced radiator vents, what did you install?" I replaced all vents initially with Maid-O-Mist vents. All close in 2nd and 3rd floor large radiators got #6, smaller rads got #5. Close in 1st floor large rads got #5, small rads got #4.  I figured up one size for the higher up rads to vent the riser.  Furthest out 3rd  floor very large and very cold rads got #C, smaller bedroom rads got #6, bath gets #5, 2nd floor big rads got #6 and BR and bath #5. Cold 1st floor got C in LR and DR, #6 in BR and #5 in bath.  I actually created a chart to use when I went thru and replaced the vents.  Since these problems, I have downsized a bunch of the close-in #6 to #5 and #5 to the cheapo chinese Watts SV, since according to Gerry and Steve's BSS it's like a #4.5 in cfm. 

Thanks again for everyone's help.  I know it is not said enough, but I truly appreciate everyone's input!

crash2009

Fast condensate

It's late.  I am not sure I read this right.  Did you say the condensate gets to V1 before the steam does?  If so where is it coming from?  Above or below?

crash2009

WARNING offensive remarks ahead

I don't know how to say this without sounding rude and insulting so I am going to apologise first and just spit it out.



  I am still not believing what my eyes are reading.  Something doesn't sound right.  Are you saying that the condensate is backing up the wet return at V1?  and This is overheating the main vents, causing them to close prematurely?  and This premature closing of the vents, stops the steam dead in its tracks at the takeoff to LR?  and This whole process takes only 3 minutes and thirty seconds?  



Back in the boiler room, How does the condensate get into the boiler.  Is it pumped or gravity or what?  Have you ever mapped/diagramed the wet returns?  How well is the boiler piped?

Dave in QCA

A combination factors I think

Abracadabra,

Thanks for posting all of the information and observations.  It is helpful.  I am not sure how you are going to resolve the problems in your building, but I suspect that it is going to take either on site consultation from a pro, such as boilerpro, or some trial and error on your part.



It appears to me that the problems are caused by a combination of factors.  I believe that those factors are, 1) pressure drop on your long main because of its great distance from the boiler, and 2)  the pressure drop problem is compounded by radiator venting that is too agressive for this system. 



You have an unusual piping setup, the end of main #1 is twice as far from the boiler as main #3, almost twice as far as main #2.   When you get to a main that is 187 feet from the boiler, it is going to show more than the usual pressure drop.  According to TLOSH pg. 23,  Large systems are often designed for a pressure drop of 8 oz.  Your system is obviously designed on the edge, so while we don't know what the pressure drop actually is, and I am not a mechanical engineer and don't know how to figure it, I think it's safe to assume that it is a major factor here.  You indicated that it took 12 minutes to get steam to the end of Main #1 when you were venting through an open 3/4 pipe, and then, there was not a lot of steam blowing out.   This indicates that the steam is being consumed elsewhere.  Fast vented radiators will compete for the steam, and those at a disadvantage will end up losing the battle. 



A few months ago, I wrote a piece, that attempted to describe what happens when radiators are vented too fast.   But first, I must say that your choice of vents seems to follow the book.  If your system consisted of main 2 & 3, you'd probably not have a problem.   It is when that very long main is added on that the problems appear.  That fact that the LR radiator in the cold apartment fully heats before the DR radiator only 2-3 sections hot indicates that there is too much rad venting somewhere.  I bet the DR radiator won't heat much faster than it does if you were venting it through an open 1/8" hole.  There just isn't any extra steam left until the rest of the system comes up to temp, then there is plenty, and it moves on into this rad.



Here is the cut and paste post .........

Your idea that if you get the air out of the radiators real fast, they will heat longer makes sense at first, but you have to remember that your boiler makes steam at a certain rate. That rate is not nearly fast enough to fill all of your radiators with steam in a few minutes. It takes a while. If you over vent your radiators, your system will end up with severe balance problems. Here's why.



With a properly vented main, the steam comes rolling down that pipe from the boiler. You want big vents on the main because you want the path of least resistance to be to the end of the main. You want the steam to get all the way to the end before it starts to enter the radiators and heat them up. That way you will get even heat. On a cycle in moderate weather, your radiators may only heat half way across. And that is what you want. It is critical that they all heat about the same amount. If you have one that gets hot all the way across, and others that only heat about a fourth of the way, or don't heat at all, you have obvious problems.



To achieve even steam distribution, there are two parts. The first part is fast venting in the mains. The second of slow venting of the radiators. If you have TOO fast venting on your radiators, the steam will start to enter some of the radiators before it gets to the end of the main, no matter how big and fast your main vents are. That is an obvious problem, right? But that's only the beginning. To get a clear concept of what goes on in a radiator that gets steam real fast, you have to do a little visualizing.



Imagine you have a radiator that is connected to a 10 psi steam supply line. It is up to pressure. There is a very large boiler that has the capacity to maintain 10 psi. The radiator valve is shut tight, and the radiator is cold. There is a very ample FAST vent on the radiator, and a pressure / vacuum gauge to let you know what is going on. OK, now turn on the steam valve. Open it all the way. Steam is rushing into this stone cold radiator, and even though it is able to quickly push out most of the air though the vent, the radiator has hundreds of pounds of cold cast iron. It is beginning to get warm, but no means up to temperature. Now, shut of the steam valve very quickly and also put a piece of tape of the port on the vent. Steam condenses and shrinks to water. The compound gauge is now going to suddenly show that there is a very strong vacuum in the radiator. And this phenomenon, in very subtle pressure differences, so small that they are almost undetectable, is what will happen in a system where the radiators are vented too fast. You will almost certainly set up a situation where some of the radiators get steam too fast, and as a result, they start to suck all of the steam that the boiler can produce, leaving nothing for the other radiators in the system. Sometimes it may be only one radiator left cold. It may always be the same one, or sometimes the steam is fickle and it will randomly change which radiator is left cold.



Small radiator vents will cause a slight increase in the pressure, perhaps an ounce, maybe less. Just enough so that the steam is slowed down and kept orderly. A little bit of steam, going nice and easy into each one of your radiators. Each one getting its fair share. The slow vent prevents any one radiator, or little gang of radiators from getting loopy from too much steam and turning into a belligerent HOG that takes over your system and sucks all of the steam that it can get, leaving other radiators cold and hungry. Slow venting your radiators does not cause steam to be lost or energy to be wasted. It does however, force your radiators to be considerate and fair, and to share the steam equally with all of the other radiators on the playground.



The question remains..... how do you fix the problem in your building?

Well, at risk of committing Venting Heresy, the way I would approach the problem is as follows:  I'd use Hoffman #40 vents throughout with the following exceptions, LR radiators (I assume they are significantly larger) use your MOM#5 and in the bathrooms, use your MOM#4.  Oooops, I forgot to include the mains, so I'm editing it in now.  Vent #1 I'd use 3 Gorton #2, Vent #2, 1 G2 and 1 G1, Vent #1, 1 G2.  With this arrangement, you probably will not have to do any special accounting for the distance from the boiler.  The rads will be venting so slow that the mains will vent fast, and it will not take 12 minutes to get steam to the end of #1.



Perhaps someone else has posted other theories while I have been typing....



Also, I must post a disclaimer, I am not a pro.  My experience is operating a large high pressure institutional steam system and school systems with about 20 years experience.  Low pressure residential heating systems are a whole different animal, and I am still learning.

Abracadabra

new venting station

any ideas or comments regarding my thoughts that the G2 are sealing up too quick based on just convection from the pipe heating the vents?







Tomorrow I will be installing a venting station just after the DR takeoff.

With regards to you comment about the pressure drop, couldn't I measure that myself by comparing the gauge at the boiler with a gauge at V1?  When V1 just starts to move and showing pressure the difference would be what's shown at the boiler.  No?

Mike Kusiak_2

Another thought

How does the high firing rate compare to the installed EDR? Are you generating enough steam with a suitable pickup factor to quickly fill the system with steam?



I dont know how feasible it would be to increase the initial high firing rate and the let it switch to the present lower rate when pressure starts to build. It is interesting to note that you have significant pressure at the boiler while at the end of the long main you have an open 3/4 inch pipe. Perhaps it is just not possible to run this system at the current pressure levels without loss of balance?

crash2009

Convection heat and Antler gauge

re- convection heat closing vents early, G2 is known to close at a lower temp than steam.  I don't know what temp that is.  I don't think you should have heat there.  The condensate from the last cycle should be gone or at least cooled off.  My antlers are right beside the boiler, they cool off between cycles, and don't get hot until the steam comes back down the main.  

Have you tested V1 with a manometer, to see what the condensate is doing during a burn? 

re- pressure gauge on antler.  Yes it will show you a difference.  As you know, not alot till after the vents close.

Steamhead

Something else going on here

Check the pitch of main 1, maybe there is a small water pocket that is slowing the steam but isn't big enough to cause banging.



Check the return from main 1, see if something else ties into the return before it drops below the waterline.

Abracadabra

more reponses

crash, regarding the early closing on the G2s, I'm not worried about from the previous cycle.  I think the G2s are closing up when the current cycle starts and the condensate heats up the antler.  Because there's so much condensate (1200ish EDR) flowing into a 1-1/4" wet return, that pipe heats up within 3-4 minutes of the condensate flowing thru it and that heat transfers to the antler.











Mike,  HB Smith 28A-S-5 is rated at 3646 sqft. Connected EDR is 3250 sqft.  I've clocked the meter and burner is firing at 1.375MBtu at high fire 745K at lo fire.  Vaporstat kicks burner to lo fire at 12 oz and back up to hi fire at 4oz.  It cycles back and forth from lo to high in about 5 minutes ish?  I don't recall exact timing on the lo-high cycles. I can't fire the burner any higher than it already is.

Steamhead, how small a puddle can a puddle be and not create water hammer?The main between the LR rad that heats up ok and the DR rad that doesn't is a 2" line. I'm assuming a 1/2" puddle of cold water would create hammer? No?

Any ideas on using the Mepcos instead of the G2s?

Steamhead

Short answer is

"it depends". Any puddle is supposed to be able to create water hammer, but I've run into a few that didn't. Check your pitch to be sure.



And make sure your return from that main drops below the waterline before it ties onto anything else. Otherwise you could have air coming at those vents from two directions.

Abracadabra

i'll check the level

Ok.  I'll check the level. Will be a pita, because all the mains are insulated.  Can I just check the level of the main from outside the insulation? 







The dry return from the main drops straight into the wet return. Goes no where else.

Mike Kusiak_2

Another thought on pressure

 I remember your video where the gauge was indicating about 4oz pressure but the vent 3/4" pipe was still open. It seems that the pressure drop in the long main is about 4 oz. Now you say that the low pressure cut-in is also about 4oz. Perhaps these are related?



If the pressure drops to 4 oz before the burner switches back to high fire then at that point there may be no steam at all at the end of the main. Its just a thought but maybe you can increase the cut in pressure to 6-8 oz so there would still be some residual pressure at the end of the main at all times.



If low fire is 745 k BTU in, at 80% efficiency steam output is 596k , but the radiators can condense 780k, so there is not enough steam at low fire to maintain pressure. Since the end of the main has the least pressure to start with, this is where the rads will be starved for steam. If this makes sense, maybe increasing the low fire rate to the equilibrium steam generation rate of 780 k BTU (975 k BTU input)  would make a difference in maintaining balance?

crash2009

More suggestions

Rod came up with this measuring device to help check the pitch of a main covered with insulation.  Here is the link that explains how it operates.  http://www.heatinghelp.com/forum-thread/135808/Tilting-Main-Lines-Short-Cycling



Steamhead found the words that I was looking for.  The wet return shouldn't get hot enough to bother the vents at V1.  What is causing them to get hot?  As you say 1.25" is borderline.  What else is not quite right in that area?  I think you found the symptom, the problem might be more evasive.  Follow the wet return to find the source of heat. 



EDIT I did this rough sketch to try to explain what I have been trying to spit out for 2 days.  Is it possible that the hot condensate from the wet return of V2 (or some other wet return), is being pushed the wrong direction, towards the venting station at V1.

Abracadabra

checking pipe pitch

crash,







Thanks!  That give me an idea to do something similiar without all the rest of the "jig".  I can just clamp a 3" sinker nail to each end of my 8' and 4' levels.

Quick ASCII art:

=|=======|=

If that makes sense, so that the nail will poke thru the insulation to the pipe.

Regarding your drawing, my main layout on this building is not exactly like you have it there.  Where you have V2 is actually a tee. The V3 branch starts there with a  back to back 45, so there's no way that condensate from the V2 branch can run into the V3 branch.

I'll be moving the V3 vent closer to the bath/DR runouts today.  I'll have some pics to post later tonight I hope. 

Dave in QCA

You may be on to something...

Mike, this may be a part of the problem indeed!  While, I certainly hesitate to suggest that the solution may be to turn up the pressure.... in this case I think that it would be well worth the time to change the setting on the low fire cutout up to 8 oz and observe what happens. 

Abracadabra

additional vent station added to Main #1

Pics of a 2nd vent station added to the main vented by V1.



I have 2 G2s and 1 G1 at this station. The original V1 station has 2 G2s and 1 Mepco 2E.  Up until this new station gets hit with steam, The main is being vented by 4 G2s, 1 G1, and 1 Mepco 2E. Pressure at boiler is now hardly hitting 1 oz until all main vents are closed up. This should be about 6.26 CFM. Wisps of steam arrive at the new vent station at about 4:15 after boiler starts steaming. I ran a cycle with my "manual" vent 1" ball valve seen in pics, wide open to test.  With ball valve closed vents heat up at 4:30ish.  So a 15 second difference with the pipe full open.  I am not really getting any appreciable amount of steam until about 20 minutes into the cycle. I think the steam is getting eaten up somewhere else.  It's almost like the main is not insulated, but it is.  



I am beginning to think that MOM #5 and #6 that I used on the radiators off main #2 and main #3 are helping to vent those mains too fast. I'm starting to think that I need to vent all the radiators off main #2 and main #3 with #4s.  I believe Dave mentioned Hoffman #40. The total venting of main #3 is 2.395 CFM. Total venting of main #2 is 2.395.  Total venting on main #1 is 9.36 CFM (3.08 radiators + 6.26CFM) 



By the way, this system used to run on a pressuretrol setting of 3.5PSI and 2/3 of the building used to use the double hung heat control method.

Abracadabra

increasing vaporstat cutout/cutin

Dave and Mike,







I saw these posts this morning about turning up the vaporstat at bit to get more pressure. Vaporstat is now at 13 cut out and 7 cut in.  I'll let it run for a few days like that and see what change that makes.

Dave in QCA

Excellent work!

Great job on adding the new venting station.  It has also let you observe the steam flow and/or lack of it. 

As you know, when a cool radiator get's a big gulp of steam as a result of fast venting, it can cause it to get real piggy and suck in even more steam until the rad is fully heated.  I am pretty sure this is where your steam is going.

I had suggested Hoffman #40 because it is a good old workhorse of a vent.  It is quiet and about as reliable as vents come.  It's slow, but not quite as slow as the MOM #4.  My thinking is that the MOM #4 might be too slow for the largest radiators, even the close radiators, but then if you have some #4, it would be worth a try.



At 1 oz of back pressure:

The venting rate of a Hoffman is 0.042 cfm.

MOM #4 is 0.028, about 2/3 of the Hoffman #40

MOM #5 is 0.100

MOM #6 is 0.150

MOM #C is 0.283