Two pipe trane steam system that is short cycling

Roma

I have an oil fired Peerless TW-5 steam boiler that keeps short cycling after the steam reaches the convector units. The vaporstat with a mercury switch keeps shutting off the boiler and restarting it. I originally had it set at 9oz Main and 5oz Diff. The system would run for about 45 seconds then shut off for about 25 seconds and constantly repeat until eventually the thermostat was satisfied. I changed my vaporstat settings to 12oz Main and 8oz Diff as I read on a past wall post for proper Steam settings. Now the system runs for about 2 minutes & 15 seconds then off for about 40 seconds. I was told that the short cycling is probably because the boiler is oversized. Any thoughts. I'm in Yonkers, NY.

Roma

Also, my oil boiler man suggested using a much smaller nozzle to downfire the 5 section boiler. He suggested trying to get it into the 0.75GPH Range. It currently has a 150 nozzle. However, if I am understanding the previous posts about downfiring a boiler it's not recommended because efficiency becomes very bad. Any other way around the short cycling without wasting more oil?

Jamie Hall

You were told correctly. The boiler is about half again as big as it needs to be. If this really is a Trane vapour system, I'd be inclined to put the vapourstat settings back where you had them -- which is where they belong for a vapour system -- but various people have suggested putting a time delay in to delay the refiring of the boiler by two or three minutes. Exactly how to do that depends on how your system is wired.

Roma

Is the concept of the time delay to allow the convectors to absorb or distribute the heat to the house longer instead of short cycling on and off before there is a need for the boiler to kick on? Also my convectors are the ones built into the wall in a metal box and then plastered over. Openning vent on top and opening on bottom. House is a 1936 tudor about 2700 sq ft with 2 convectors in the attic as well. Also you said "the boiler is about half as big as it needs to be", I am confused so you think it could be undersized not oversized?

Roma

nicholas bonham-carter

Has this short cycling been going on for a long time?
Is a one pipe or two pipe system? When does the short cycling begin in the heating cycle? Is your thermostat set up for steam?
Probably the air is not escaping easily enough, although the boiler may be oversized, but that would be an unknown, without measuring the radiators, and comparing that EDR value to the boiler rating plate. Give us some more information about this, and we can see what can be done.—NBC

Roma

This is a two pipe oil fired steam system with 22 trane covector boxes. The thermostat is set for steam. The boiler will run for 10 minutes or so to get the steam all the,way through both mains when the thermostat calls for heat. Then after the convectors get steam hot the vaporstat keeps going off on pressure. One main with a 3/4" has tapping has 4 gorton # 2's . The other main with a 1/2 taping has 2 gorton # 2's. Both returns have 2 hoffman 75's on them. All the vents are located at the end of the main, which because that's where the tappings were. And yes the short cycling has been happening for a long time. Water is treated as well.

Roma

I will attach some pictures

Roma

clammy

Where are u located maybe you need a pro to take a look Peace and good luck clammy

clammy

How old are your main vents ,it sounds like your vents are not working properly ,have you cleaned the pig tail on your vaporstat and do you have a low pressure gauge so you can be sure your vaporstat is set properly . If your main vents are over 10 years old replace ,I would suggest using some Barnes and jones big mouth larger vent capacity and cheaper then Gorton as for vent capacity. Do your convector have traps on them or no trap and orificed inlets which is common to trane convectors as I have ran into ? The few trane systems I have worked on where vacuume systems and I was able to leave them vacuume systems by installing Hoffmann 76 valves . Has anyone done a edr on your convectors so they could match your load minus 20 % if no traps due to not wanting steam in your dry return . Have you checked your system for any crossover traps one bad crossover trap can pressurize your dry return and all but stop steam distrubition being no pressure differential . Downsizing the nozzle to a .85 will not correct it will only take longer for it to start short cycling ,from the pics I know the boiler has been in place a long time but even so the near boiler piping is not looking to good which is key to proper operation of 2 pipe convectors systems without proper near boiler piping there will always be issues .if you have traps then you better start looking for bad traps or crossovers . Hope it give you some insight being this is not a new issue correct Peace and good luck clammy

Jamie Hall

That should have been half again as big as it should be -- in other words, oversized by a factor of about 1.5.

And the idea of the time delay is mostly aesthetic -- in my view, although others may differ. Some people are bothered by the burner cutting off and then immediately refiring.

Roma

So the shrt cycling may just have to be something I live with then because of the oversized boiler

acwagner

Do you only have convectors or is it a mix of cast iron radiators and convectors?

dopey27177

You no longer have a 2 pipe vapor system.
All the locations where Gorton vents were installed used to have crossover traps.

Te crossover traps caused the system air to to vent from one main air release valve,

Do you still have steam traps on the convectors or are there radiator vent valves there.

In these old systems the radiators are larger than a plain two pipe steam system because the system operated in a vacuum as low as 16" HG. The steam temperature was about 160 degrees not the 212 degrees that you are operating in a pressurized system.

Try what your oil guy said. Instead of a ,75 nozzle use a 1,00 nozzle. The boiler efficiency does not get lower. You only burn less fuel over a longer time.

I would not worry about your pressure setting now, whats important now is stop theshort cycling.

acwagner

Sorry, I overlooked you mentioned in an early post they are all convectors.

I use a timer relay. They work well with cast iron radiators because the they have large thermal mass that continues giving off heat after steam delivery stops. So, using a timer to delay refiring does not interrupt heat delivery to the rooms, if you set it up right. With low mass convectors that might not be as effective.

Downfiring may be an option, but they can only be downfired so much. The first step would be to actually calculate what your radiator EDR is compared to the boiler output.

dopey27177

sorry about the cutoff.
Hit the wrong key.
Your Trane system used to be a vapor vacuum system originally with a coal fired boiler. Coal fired boilers made steam slower and as the fire cooed down a vacuum was formed in the piping system.

Can not write the whole operation because it will take a lot of words.

If you have a lot of money to spare and want to restore the system look on Dan's site for qualified contractors.

Jake

Roma

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Roma

To answer Jake (dopey27177). I spoke with Bob (clammy) this morning for a while. He recommended trying a few things.
1. Fire up the system and to check both sides of all the convectors by touch to see if there is a temperature diffence between the supply and trap side (to check for a bad trap).
2. He also said to check and see if the vents are working.
3. Also I explained that the two dry returns are connected with a balancing line to each other as well as to the large Trane Direct Return Trap. He said the returns should never be connected above the water line in today's systems. So I am going to open the union and cap both sides so they work independantly.
4. Also recommended using a ball valve on dry returns and openning it to make sure steam is not getting through.
I am going to do some testing. Wish me luck.

Roma

NO LUCK EVEN MORE CONFUSED AFTER TESTING

Jamie Hall

Um... well, have to disagree with @clammy … on a vapour system, even today, unless it has really been mangled, you can -- and probably should -- connect the dry returns above the water line. Be that as it may, however, the dry returns -- connected or not -- need at least as much main venting as the steam mains do, particularly if the steam mains are vented with crossover traps -- but even if they aren't. Put simply, those dry returns are the only path for venting for the radiation, and if they aren't adequately vented... no or poor heat.

Roma

I have 4 Gorton # 2's on one main, 2 Gorton # 2's on the other main, 2 Hoffman 75's on both returns, both returns are connected above with a balancing line. I took the vent's off and blew through them they are working.

I openned a plug on that line to see if any steam would come out and it did not. It also did not alleviate the short cycling. I left the plug out during the entire run. The returns did not get too hot it seemed like 115 to 120 degrees with the infared thermometer.

All of the convectors were very hot on both the supply and trap side of their pipes. It was hard to tell a difference temperature wise between the two different sides.

Still confused.

PMJ

@Roma, I'm still not clear here. Are all the convectors hot and heating the space ok? If so then is your only issue the short cycling after all is filled up and heating?

If so, to me this is a classic case. Two pipe system, big boiler, all convectors heating ok. Only problem is that the big boiler fills things too fast, makes pressure and bounces off the pressure device during the natural lag period( everyone has this) until the thermostat sees the change. The more oversize the boiler the more pressure and quick cycles you can get.

But don't despair, you just need to pace this boiler a little with a timer and the problem will go away. No more quick cycles because the timer won't allow them. Runs more efficiently because the pressure is much much lower. Vaporstat becomes a safety device only because your system will get the whole job done well below any pressure settings on it. Even at the simplest control level it would be dramatically better than what you have now for under $100 in material.

No off the shelf equipment exists for this simple and inexpensive fix. Apparently contractors won't/aren't doing it for anyone either. Homeowners on this site have done it themselves with excellent results. If you are interested to do it yourself there is help available. This is exactly the problem I had with my oversize boiler and two pipe system many years ago.

If there really are other problems beside the short pressure cycles you mention let us know.

Jamie Hall

Why the confusion? It sounds as though the system is working just as it should (pity about the main vents vs. the crossover traps which were there once -- cost a bundle for no gain -- but that's the way it often is).

Your boiler is oversize, and no amount of venting is going to fix that. If it can be downfired, as Jake and @acwagner suggested, that will help, but that must be done with the assistance of a really good tech to set up the burner, and only if is within the firing range of the burner and boiler combination.

Roma

It seems my main problem is the oversized boiler. I am going to have my boiler guy try to downfire it this week. Thank you for everyone's help.

Roma

I used to have a trane convector edr chart booklet anyone know where to find one

Roma

what was the boiler timer you were talking about

PMJ

@Roma ,

I was talking about adding a timer to your control assuming the following:
1.That you have a 2 pipe system where steam reaches all convectors at about the same time (reasonably balanced), and all convectors are heating their spaces appropriately.
2. That you have a boiler feeding this system that has significant extra capacity and does not need to run nearly all the time to heat on the coldest(design) days.
3. That your complaint is simply that on a call for heat your big boiler fills your system ,builds pressure, and cycles a few times on pressure before your thermostat is satisfied.

If these things are true then I am suggesting approaching a solution to excess pressure cycling from the control side of things rather than making expensive hardware changes. From my own experience with my own two pipe system with "oversize" boiler I will say that control changes can give you a much more satisfying result than any hardware changes will at a much lower cost. Not only do I have no interest in reducing the size of my big boiler, from what I have learned about all this if and when I do need to replace mine I will "oversize" again.

The difficulty in this is that no off the shelf device currently exists for this. Those of us who are doing it have done so on our own. I can't really explain why residential steam got stuck in this place with nothing available commercially beyond decades old controls. I can say that with even a little more control sophistication dramatic improvement is possible for very little cost especially in two pipe, and boiler size makes little difference.

If you are able to do things on your own and are interested in pursuing this type of solution in more detail let me know. There are some of us out here doing it who can help.

Roma

I noticed last night that my trane convectors seemed to be gargling for a bit at the end of the heating cycle. Is this normal?
I still have the pressure set at 12oz main, 8oz differnential which would make it cut out at 12oz and back in at 4oz. My boiler man still hadn't had the chance to come over and downfire the boiler.

Roma

January 16, 2020.
Frank my boiler man came and downfired the boiler from a 1.50 nozzle to a 1.00 nozzle. The short cycling stopped altogeither at the present settings of 12oz main & 8oz differential cut in at 4oz. The system ran for about an hour heating from 68 degrees to 73 degrees. Going to see how this works.

exqheat

We can help. I tame over sized boilers. ( most are over-sized due to poor measurement and fear of a no heat call or low heat call.) I would check the specs for that boiler as to the fire nozzle size. If the fire is too small the heat does not heat the exchanger, but simply goes up the chimney. That will waste oil.
john

Jamie Hall

Roma said:

January 16, 2020.
Frank my boiler man came and downfired the boiler from a 1.50 nozzle to a 1.00 nozzle. The short cycling stopped altogeither at the present settings of 12oz main & 8oz differential cut in at 4oz. The system ran for about an hour heating from 68 degrees to 73 degrees. Going to see how this works.

Good show. I'm a little surprised that the boiler could be downfired that far, but if it checks out OK, that's just about the amount of oversize I would have expected from your initial post.

PMJ

Jamie Hall said:

Roma said:

January 16, 2020.
Frank my boiler man came and downfired the boiler from a 1.50 nozzle to a 1.00 nozzle. The short cycling stopped altogeither at the present settings of 12oz main & 8oz differential cut in at 4oz. The system ran for about an hour heating from 68 degrees to 73 degrees. Going to see how this works.

Good show. I'm a little surprised that the boiler could be downfired that far, but if it checks out OK, that's just about the amount of oversize I would have expected from your initial post.

exqheat said:

We can help. I tame over sized boilers. ( most are over-sized due to poor measurement and fear of a no heat call or low heat call.) I would check the specs for that boiler as to the fire nozzle size. If the fire is too small the heat does not heat the exchanger, but simply goes up the chimney. That will waste oil.
john

Great. Add new worries about combustion and burner efficiency for one new single speed which will be "better".

A control based approach would come with with no such worries and an easy way of choosing any net capacity in the entire range just by turning knobs. It would come with the ability to very easily adjust more precisely to each particular case.

It is a real shame @Roma that no standard device exists for this as simple as it is that contractors could be comfortable installing. I know you really don't have as an option what I suggest so please don't be offended by my remarks. I write this as part of an ongoing discussion here, however one-sided. The preoccupation here that boiler capacity and its impact on pressure short cycling can only be adjusted with hardware changes is truly quite remarkable. This market has not accepted anything new in decades.

Jamie Hall

Now wait a minute. Reality check time here. Altering the firing rate of a boiler, within the limits established by the manufacturer's testing, is a long established and completely valid approach to matching the power input to the required output.

Not only is this accepted standard practice for heating boilers, but you do exactly the same thing when you press the accelerator pedal in your car. You don't control the relative time the engine is developing full power vs. no power; you control the power output.

I have flown airplanes where you control the power with an on/off switch (some World War I biplanes) and trust me -- it's a **** compared with a throttle.

The objective of all of our work in this regard is to match power supplied to power required. If it can be done by altering the continuous power supplied, I would hope we can agree that that is the best approach.

PMJ

@Jamie Hall , where are you reading that I said downfiring was not an accepted practice? What I said was as a "solution" to pressure short cycling it is less effective than a control solution. I also merely highlighted yours and others concerns about potential problems with downfiring. And, I do complain that finding the "correct" single boiler output size, achieved by either a different boiler or downfired is the only thing ever offered as a solution for pressure short cycling. Control is never talked about. I am trying to change that...obviously without any success whatsoever.

The steam required per hour is a moving target determined by demand from the outside. The conventional wisdom always speaks of the demand as fixed...as you do again here. The "power" ,as you put it, required to meet the current outside demand is not determined by the installed EDR. It is a fact that the original coal fired systems used only a portion of the installed EDR even on design day. The amount of steam condensed per hour through the same area of filled radiation actually can change a lot. So nothing magical happens by matching a one speed boiler's output to any particular percentage of EDR. If you go small enough you won't pressure stop as much or maybe not at all. But your boiler doesn't suddenly start producing the correct amount of steam per hour for all demands because it is a certain size. A boiler with a control like Ecosteam does however. It matches what is supplied in a given hour quite closely to what is actually needed for the current outside demand. It also does so digitally on/off with a fixed speed boiler of pretty much any size. The result is far more even and satisfying heat.

It is well past time to start steering some of the money and effort that goes into hardware changes into an interest in controls instead. Homeowners like the OP here would be much better served. It might slow or maybe even reverse the steady demise of residential steam heat.

Jamie Hall

Oh dear. Well, I'll use (or recommend) whatever I think will work best in any given situation -- controls, downfiring, rebuilding, whatever... and I have, at one time or another, recommended all of them.

PMJ

Jamie Hall said:

Oh dear. Well, I'll use (or recommend) whatever I think will work best in any given situation -- controls, downfiring, rebuilding, whatever... and I have, at one time or another, recommended all of them.

Well, you haven't and can't recommend a residential control that isn't several decades old because there isn't one and that is my point. I think for residential steam to have any chance going forward that needs to change. Clearly you don't.

It never takes that long for us to clarify our disagreement which I think is good for all those reading.

dopey27177

Do want your system to operate in a vacuum?

I found a check valve you can put between the vent and the system.

Once you get rid of the excessive amounts of vent valves you can use one or more CVs, hopefully you will be able to get back to one vent valve.

See attached

Jake