Option discussion for oversized 1 pipe steam boiler

dabrakeman

I will give just a quick background here. There is additional background in an earlier post last year: https://forum.heatinghelp.com/discussion/166807/2-stage-gas-valve-setup#latest .

I have a one pipe steam system with Weil McClean EG-65 that is not facing any serious problems but I am trying to see what I can do to try to get a little better gas use efficiency due to it being significantly oversize. The calculations have been done and reviewed on previous discussions on this forum and I am anywhere from 33% to nearly 50% oversized depending upon whether a few radiators are shutoff or not. The main venting capacity is quite good, pipes are insulated, pigtail is clean and system is balanced throughout the house. Only real issue is very cold days short cycling a bit on pressure or just cycling off on pressure. Typically pressure is

1) Downfire the burner
2) block one or two of the burners (10-20% overall reduction)
3) Get a 2-stage gas valve and vaporstat and have the gas valve reduce gas flow based upon sensing pressure rise via the vaporstat
4) Alter the thermostat cycle time in some manner (I.e. what would be best setup for an oversized boiler condition?)
5) Unisulate some of my pipes in the basement. I didn't see any efficiency improvement when I went and insulated everything (gas use per heating degree day) in the first place 4 years ago. Basement and some of the floors on the first story just got a bit cooler. I had insulated all my returns as well at the time...

Of course welcome to additions to the list. Right now I have a heating guy suggesting I do #2 (block a couple burners). He wasn't willing to do the 2-stage setup anyway (says if not recommended by manufacturere then he could be liable...). Seems to me blocking vents wouldn't be too different in that regard but valid point is that it is easily reversible.

I wonder about thermostat possibilities. Most of the time when I know my boiler is starting to build pressure my thermostat is already reading the target temperature... why does it keep calling for heat?


I will apologize if I don't answer responses right away tonight since I have a function. Will plan on spending some time tomorrow though. Appreciate anyones input.

dabrakeman

Thermostat btw is a Honeywell model 3900 set on steam/gravity and with the default Smart Response Technology "on".

Fred

Check the gas valve on that EG-65. If my memory serves me right, I believe that boiler came with a 2 stage gas valve. It may just need to be wired and a vaporstat added to function.

Jamie Hall

First off... let's be sure you really do have a problem. If the steam cycle is long enough -- let's say coming back from a mild setback, for instance, does the burner cycle on pressure? And, if so, what are the pressure settings, and what is the actual duty cycle (that is how many seconds (or minutes) on, then how many minutes (seconds) off?

There are -- no surprise! -- divergent opinions on what the duty cycle should be -- or even if the burner should cycle at all. If the boiler were by some minor miracle exactly sized to the radiation, it would come up to some low pressure -- on the order of a few ounces to perhaps a half a pound -- and just sit there. It might take a remarkably long time to get there. If the boiler is reasonably oversized -- say for example that the EDR corresponds to the radiation so there is a 33% pickup factor -- one would expect the duty cycle have an on time about 3 times as long as the off time. What this is doing is effectively modulating the boiler to 3/4 of its full capacity. There is a slight loss in overall efficiency in doing this, but so long as the off time is short enough that the boiler never really cools -- less than a minute or two, in my view the loss is negligible (others differ). You are using the vapourstat as a modulating control; hopefully you also have a pressurestat as a safety device also.

Now. If the off and on times become comparable, or the off time is significantly longer than the on time, then it is time to think about down firing the boiler -- if it can be done. Not all can. That's your options 1 and 2. If a two stage gas valve is applicable to your burner, that too is an option, using -- as you mention -- two vapourstats for control.

Uninsulating the pipes will do little to help, and will reduce efficiency since the boiler has to run longer to get heat where it's needed.

dabrakeman

@Fred - On an earlier discussion last October you had contacted a Weil Mclein rep and they said no, one was not available. Below is your post:

Sent question to a Weil Rep, this is his response:

"Thanks for submitting your question about the Weil-McLain EG-65-S-PIDN - 157K BTU - 83.0% AFUE - Steam Gas Boiler - Chimney Vent. Please see our response below.

Q. Does this unit come with a two stage gas valve either standard or as an option? If it is an option, what gas valve is used?

A. Wouldn't be an option, Fred, I apologize. See attached for the valve that comes along.


I know there is a 2 stage for the EG75 but apparently they don't suggest one on the 65 ????

dabrakeman

@Jamie:
Yes, if the cycle is long enough due to cold or mild setback it will cycle on pressure. On just a cold day or maybe a 1 degree setback it may not cycle at all but it will seem to run a long time with the radiators 100% full, the thermostat already reading the target pressure and pressure build from the normal <0.5psi to almost 3psi before shutoff. It seems to me half the issue would be resolved if it would just shutoff when the thermostat actually hits target since the rooms do of course continue to heat even after the boiler shuts off. Result is usually an overshoot of about a degree. Also would like it to kick off at a lower pressure than 2.5-3psi but I can't seem to get it set up to do so with my current pressuretrol (I do not have a vaporstat).

I would agree when it does short cycle (and this is usually just one or maybe two cycles) the off time is shot, probably <5 minutes or so. The initial cycle can be over an hour long and all radiators are normally full after about 35-40 minutes from point boiler start producing steam.

Overall in normal constant stat winter heating I would say off time is as long as on time but I really have not accurately tracked that.

PMJ

The main enemies of efficiency are pressure and air, not size of boiler or length of cycles. Developing measureable pressure requires filling the system with steam - hence the overshoot you observe. Overshoots are particularly bad as they result in longer off periods to the next call where the entire system cools and fills with air.

Significant improvement can be achieved through control such that a boiler (even a big one) runs spaced cycles that are long enough to heat but not long enough to fill and make pressure. Unfortunately and sadly such control is not commercially available.

dabrakeman

If I "could" limit the overshoot then wouldn't it shorten the on cycle and the amount of time I am producing inefficient steam under pressure and likely shorten the idle time between cycles? You don't think there is any way to accomplish this via the thermostat? Intuitively it just sounds like some kind of programming logic in the thermostat.

PMJ

Actually I think the old fashioned anticipator likely did the best job of that. There are various thermostats claiming to do various things with cycles but you don't really ever get to see the logic they use.

I started there but ended up building my own control. Once you see how little radiator fill(and therefore barely measurable pressure) is actually required to heat under most conditions you realize that you simply must control run times to the conditions somehow.

Jamie Hall

Your target pressure is much too high. If the gauge is even remotely accurate. You will be much happier with a vapourstat. Yes, they are expensive, but worth it. Get one to supplement your pressuretrol -- which will become a safety -- and a low pressure gauge so that you can check calibration. You mention a normal pressure of about 0.5 psi -- check that with your nice new low pressure gauge, and observe the pressure on a long run. It should -- if your main venting is adequate -- rise to a certain level (typically around 4 ounces to 8 ounces) and then hold relatively constant for a while -- then start to rise again. Note that relatively constant pressure, and set the vapourstat to cutout perhaps 2 or 3 ounces per square inch higher. Set the differential so that it cuts back in at perhaps 2 or 3 ounces.

The result will be that the system does fill with steam -- but never actually empties and fills with air (which, as @PMJ points out, does hurt efficiency). This may well help with the overshoot.

On the overshoot. The 3900 shouldn't do that, although it is not as adjustable in that regard as the old T87s. It may be a problem with thermostat placement -- be sure that it is in a room which is being directly heated by the radiation, or which communicates freely with such a space (such as a big archway) -- and that the radiation in that room is on.

If the overshoot really bothers you, first get an accurate thermometer and place it next to the thermostat to see if it's real. Remember that the thermostat readout does not show decimal degrees -- and you may find that it doesn't round off, either, but "jumps". That is, anything from say 68 to 69 will read 68, and then at 69.1 it will jump to reading 69. The actual internal thermal switch, however, is sensitive to decimal degrees -- and the combination can give an illusion of a one degree overshoot which isn't really there.

PMJ

I think the presence overshoots is most easily determined by the length of calls vs time between calls. Perfectly even heat would be a never ending call. The longer it takes to satisfy the call(provided the temperature is never falling) then the closer you are to adding heat at the rate of the current demand. If I satisfy the call quickly - that is add heat at a rate which moves the room temp from cut in to cut out quickly, then things simply can't stop on a dime at the cutout temp. There will be an overshoot and a longer off period with a larger variation in radiator temperature. I found this unpleasant and unnecessary.

dabrakeman

Jamie, I do have a low pressure gage (3psi) so pretty confident in my pressure readings. It makes sense though that controlling the cutoff pressure better with a vaporstat vs just with the pressuretrol may be a good initial approach. It is kind of expensive including installation but probably worth it (looking at the Honeywell L408J1017).

Nonetheless, it still seems that I should be able to get a little better control with the pressuretrol that I have, better at least than cutting out at 2.5-3psi when it is set on 1psi. I have verified the pigtail is not blocked (although the liquid was ink black) and even tried tweaking the tiny hex head screw below the dial clockwise in minute increments. Doing such it seems where I am is the best I can do because if I go any further on the screw the boiler shuts off immediately after turning on. I could try to play with that more but wondering if the pressuretrol itself is just a bit screwed up. Of course the pressuretrols seem just as expensive as the vaporstats so your logic of just using it as is as a backup makes sense over trying to get anew pressuretrol.

Thermostat is in a heated room on interior wall. I had placed a thermometer next to it last year and if anything the thermometers read slightly higher temperature 0.5-1.0F than the stat. I just assumed there is some cool air always inside the walls, even interior. Overshoots based upon thermometer readings are greater in peripheral rooms than shown on the stat.

Fred

dabrakeman said:

@Fred - On an earlier discussion last October you had contacted a Weil Mclein rep and they said no, one was not available. Below is your post:

Sent question to a Weil Rep, this is his response:

"Thanks for submitting your question about the Weil-McLain EG-65-S-PIDN - 157K BTU - 83.0% AFUE - Steam Gas Boiler - Chimney Vent. Please see our response below.

Q. Does this unit come with a two stage gas valve either standard or as an option? If it is an option, what gas valve is used?

A. Wouldn't be an option, Fred, I apologize. See attached for the valve that comes along.


I know there is a 2 stage for the EG75 but apparently they don't suggest one on the 65 ????

My apologies! Old age blurs the memory!

dabrakeman

@Fred
With the hundreds of users you help it's pretty understandable. I only need to focus pretty much on one user.

dabrakeman

@PMJ:
My point is simply that as overshoot increases the time between calls will increase. So, could I reduce overshoot by having a lower swing temperature on the stat?

dabrakeman

So, back to the list:

1) Downfire the burner
2) block one or two of the burners (10-20% overall reduction)
3) Get a 2-stage gas valve and vaporstat and have the gas valve reduce gas flow based upon sensing pressure rise via the vaporstat
4) Alter the thermostat cycle time in some manner (I.e. what would be best setup for an oversized boiler condition?)
5) Uninsulate some of my pipes in the basement. I didn't see any efficiency improvement when I went and insulated everything (gas use per heating degree day) in the first place 4 years ago. Basement and some of the floors on the first story just got a bit cooler. I had insulated all my returns as well at the time.
6) Get vaporstat for finer control on pressure cutoff

Any thoughts on whether to block any burners or downfire?

Fred

I would have someone downfire and do a combustion test before I blocked any burner tubes. While not immediately obvious, it is a known risk that uneven heating across the cast iron block can, over time, create some hairline fractures.

PMJ

> @dabrakeman said:
> @PMJ:
> My point is simply that as overshoot increases the time between calls will increase. So, could I reduce overshoot by having a lower swing temperature on the stat?

The quick answer is yes you can....some. The problem is the delay between when rads get steam and the resulting warmed air gets the stat to react. The needed amount of steam has been supplied well before the stat knows about it making it a poor control without anticipating software. I gave up working on it from that end and set about controlling and evening out the amount of steam I supplied. A control like Ecosteam burns a set amount of steam based on an ongoing analysis of what is needed. What is needed never fills the system or creates any pressure. There are many ways to approach this but a PLC control is needed.

Jamie Hall

"well before the stat knows about it making it a poor control without anticipating software." Yes... except the bit about software. The same result can be -- and is -- achieved remarkably well with an anticipator in thermostat. Take a look at the innards of an old, mercury, T87... maybe not as perfect as a well written program for a PLC, particularly one which can also take into account outside conditions (temperature, wind, solar gain, cloud cover...). But with a little patience, it's quite remarkable how close one can get. And not all of us have either the patience or the expertise of @PMJ!

dabrakeman

I don't think I can change a swing temperature on the CT3600 Honeywell stat. Only choice would be to go to the next system setting which is from gravity/steam (1) to hot water (3). I believe the 1 and 3 are cycles per hour. Intuitively 2 seems like it would be good but not available.

PMJ

> @Jamie Hall said:
> "well before the stat knows about it making it a poor control without anticipating software." Yes... except the bit about software. The same result can be -- and is -- achieved remarkably well with an anticipator in thermostat. Take a look at the innards of an old, mercury, T87... maybe not as perfect as a well written program for a PLC, particularly one which can also take into account outside conditions (temperature, wind, solar gain, cloud cover...). But with a little patience, it's quite remarkable how close one can get. And not all of us have either the patience or the expertise of @PMJ!

I quite agree that the T87 is quite good. I had one. But that is also the bad news ... that we don't have something clearly better after all this time.

The level of expertise required for work on a $100. PLC is not so great. I just make a plug now and then hoping someone will plunge in. The work is quite rewarding if you love steam heat.

dabrakeman

I think what I am going to do is do a few things slowly one step at a time. Not mentioned here in this discussion but discussed earlier is the placement of my mains which are at the end of my returns rather than the end of the mains. Getting that changed right now so want to evaluate its impact alone before doing anything else. I do expect it to increase my delivery rate to the radiators but don't expect it to change much with regards to the pressure cycling issue.

Probably sometime in early December I will start experimenting with the cycle time. If it solves or improves my issue, great. If not then sometime in January I will invest in the vaporstat which will truncate the long cycles via pressure control. If that doesn't seem sufficient then in February I can look into means of downfiring.

PMJ

@dabrakeman , controlling cycles on/off times yields the same result as downfiring - at far less cost and far fewer combustion related worries.

Jamie Hall

PMJ said:

@dabrakeman , controlling cycles on/off times yields the same result as downfiring - at far less cost and far fewer combustion related worries.

Totally agree!

dabrakeman

Thus the order of attack. Thanks all.

BTW, does anyone know of a thermostat that allows 2 cycles per hour?

dabrakeman

...or I could just try one with a swing option of something less than +/-1deg. (i.e. =/-0.5)

Steamhead

dabrakeman said:

I don't think I can change a swing temperature on the CT3600 Honeywell stat. Only choice would be to go to the next system setting which is from gravity/steam (1) to hot water (3). I believe the 1 and 3 are cycles per hour. Intuitively 2 seems like it would be good but not available.

If the system responds quickly, setting this to 3 will work well.

ethicalpaul

> Not mentioned here in this discussion but discussed earlier is the placement of my mains which are at the end of my returns rather than the end of the mains.

Do you mean “...placement of my main _vents_ which are at the end of my returns...” ?

That’s where mine is too but it’s only about 10 feet in my case, but it still bothers me

Jamie Hall

Cheer up. In the system Cedric powers, the main vent is at the boiler where the dry returns come back (the mains vent into the dry returns through crossover traps). It really doesn't matter where the main vents are, so long as they are beyond the last radiator runout.

ChrisJ

Jamie Hall said:

Cheer up. In the system Cedric powers, the main vent is at the boiler where the dry returns come back (the mains vent into the dry returns through crossover traps). It really doesn't matter where the main vents are, so long as they are beyond the last radiator runout.

I had considered moving mine to the end of the dry returns.
The problem is, every little bit of extra pipe means more friction losses. So, I didn't move them.

Fred

dabrakeman said:

Thus the order of attack. Thanks all.

BTW, does anyone know of a thermostat that allows 2 cycles per hour?

A lot of the Honeywell tstats have a "2" setting. I have the model RTH-7000 series. No WiFi though.

PMJ

@ChrisJ said

"I had considered moving mine to the end of the dry returns.
The problem is, every little bit of extra pipe means more friction losses. So, I didn't move them."


Generally I don't hear much concern about the lost effort and time required to overcome this air friction around here. But you are exactly right...it truly is there and I am convinced very much a loss.

Maybe the lack of interest has to do with the unhappy place where the road leads...to the realization that the vast majority of the friction comes from removing air that open vented systems just let back in each and every cycle; over and over again.

dabrakeman

Often the unhappiness of placing the main vents at the end of the mains is the location of the end of the mains. In my case one is in a very unappealing crawlspace but I am going to do it anyway.

I have a north main and a south main on my system. From the moment I start producing steam it makes it to the ends of both mains in about 3min:30sec. It takes two to three times as long before my main vents are all closed. Seems like a lot of time where I am filling dry returns with steam and getting just a little steam out toward the radiators. I have 1.23CFM (1 Gorton #2 and 1 Ventrite 75) of vent on the North and 2.32CFM on the South (2 gorton #2's and a Ventrite 75). I have one section on the South of dry return that is 38ft of 1 1/2" pipe. I haven't begun to total all the other pipe that is the least resistance pathway back to the mains but it seems I should be able to quicken my time to fill radiators. Am I wrong assuming that once the main vents close if at the ends of the mains then the elast path of resistance becomes the radiators? Any reason the steam would want to continue to fill the dry returns?

I am probably going to ask someone else/younger to crawl in the crawlspace and tackle that 100 year old fitting though.

Jamie Hall

Now you know why crossover traps were -- and are -- popular! Wear a bunny suit and goggles and a mask and crawlspaces aren't so bad...

But more seriously -- clearly you are not speaking about dry returns, but continuations of steam mains. A dry return should never, ever, have steam in it, since it should be separated from any steam by traps. Vents are placed on dry returns to vent the air coming through the traps (including crossovers, if used) from the radiators. Vents on steam mains are placed to vent the air in the steam mains -- unless there are crossover traps.

Some one pipe steam systems are parallel flow, and there the steam main does continue back around to the boiler and the condensate empties there. Other parallel flow systems have drips at the ends of the steam mains and return condensate via wet returns. In either of those, the best place for the main vents is on the steam main just beyond the last radiator runout.

ChrisJ

dabrakeman said:

Often the unhappiness of placing the main vents at the end of the mains is the location of the end of the mains. In my case one is in a very unappealing crawlspace but I am going to do it anyway.

I have a north main and a south main on my system. From the moment I start producing steam it makes it to the ends of both mains in about 3min:30sec. It takes two to three times as long before my main vents are all closed. Seems like a lot of time where I am filling dry returns with steam and getting just a little steam out toward the radiators. I have 1.23CFM (1 Gorton #2 and 1 Ventrite 75) of vent on the North and 2.32CFM on the South (2 gorton #2's and a Ventrite 75). I have one section on the South of dry return that is 38ft of 1 1/2" pipe. I haven't begun to total all the other pipe that is the least resistance pathway back to the mains but it seems I should be able to quicken my time to fill radiators. Am I wrong assuming that once the main vents close if at the ends of the mains then the elast path of resistance becomes the radiators? Any reason the steam would want to continue to fill the dry returns?

I am probably going to ask someone else/younger to crawl in the crawlspace and tackle that 100 year old fitting though.

Most of my main vents are jammed in a crawl space as well.
It is what it is........

In my situation, them being in a cold location allows them to re-open faster though which helps me in extremely cold whether when my system only shuts down for 4-6 minutes at a time.

Plenty of 1 pipe systems have the main vents at the end of the dry returns. It's up to you if you want to try it out. It won't hurt anything and might work just fine.

PMJ said:

@ChrisJ said

"I had considered moving mine to the end of the dry returns.
The problem is, every little bit of extra pipe means more friction losses. So, I didn't move them."


Generally I don't hear much concern about the lost effort and time required to overcome this air friction around here. But you are exactly right...it truly is there and I am convinced very much a loss.

Maybe the lack of interest has to do with the unhappy place where the road leads...to the realization that the vast majority of the friction comes from removing air that open vented systems just let back in each and every cycle; over and over again.

Maybe it's just one of the many necessary evils and or compromises we have to deal with in life.

If you can ever prove to me that TRVs will work on a single pipe vacuum system as well as some how balancing improperly sized radiators I'll convert mine over. But in my mind, it cannot work so I'll never waste my time with it. I'm sure you would never waste your time doing something you're convinced wouldn't work, would you? Especially if someone who never worked on a similar system was the only one telling you differently?

The air is the thing I'm exploiting to control my system and you want me to get rid of it.

@PMJ If you want to try and explain your hypothesis again, let's move to another thread though. I don't want to send this one off course.

PMJ

@chrisj,

I'm sorry you seem to have taken my comment personally.

I merely agreed with you that moving air creates a friction loss. Way back when I started my work and listened to all that air going in and out it all the time it seemed really wasteful to me. It is, so I don't do it anymore.

I'm always happy to kick around the technical aspects of any of this with anyone interested on any thread. I'm not a one pipe expert. It is not my hypothesis. Keeping the air out is a very old idea.

dabrakeman

@Jamie Hall
The return I am talking about definitely is well above water line. My system has drip legs from every radiator feed which return the condensate back to the boiler. On the South loop most feed into this "long return" that starts at the end of the South main and continues back to the boiler. It T's into a vertical near the boiler the top of which is where the main vents are located. Maybe steam is not supposed to be going in, but I am quite sure that it is. For one, how else would the main vent close? By putting the main vent at the end of the actual main I believe I can prevent this.

Jamie Hall

A lot of systems did have the steam main loop back to the boiler like that. Strictly speaking, it's still a steam main -- not a return. But that's OK. And yes, putting your main vents right after the last radiator runout will make a small difference.

dabrakeman

Anyone have any good ideas of how to get this plug out? I was able to get the south line main vents moved but cannot get this fitting out on the north line. Have tried penetrating fluid, hammer tapping the plug, hammering the end of the two foot pipe wrench and even putting a 5 foot extension on thee pipe wrench with the pipe supported. Intuitively fluid plus hammering with high shock loading on the wrench would be the most likely but had worked on it for about 5 hours with no success. I am concerned about using any kind of flame since it is a very enclosed area (and very dry with lots of wood...).

At this point would it be the best approach to have someone come in and just cut it out and replace the entire step down and elbow or do you think I should let them try to free it up or have them try to shatter it?

dabrakeman

This one had to get cut off, then drilled out then segment cut to get the plug out. But, now both of the main vents are moved to ideal locations.

Picking up this post the following year: I am saving over 2 minutes run time per cycle having my vents at end of mains now instead of end of returns (main extensions)

dabrakeman

This was actually completed Nov 2019. Will share data later.