Cycle Times - Help?

JohnLaPlante

Hi all,



Attached are some pics of my system.  Weil EGH-85, 350K.



About a month ago, I thought I was having problems with my system (the system would short cycle), so I called a local HVAC company who has worked on our boiler for the past 4 years...mostly just routine maintenance, adding corrosion inhibitor, etc.  I told them that the system would get to 2.5# and then shut off.  I thought this was a problem (I knew nothing about steam), so the tech set it to 5#.  I thought this was OK until I started reading here. 



So this morning I watched my system and made some adjustments...here's what I found.  NOTE:  It is 0F outside right now, which is just about the coldest it ever gets here (NE Ohio).



7:28am - TSTAT 60F, set to 66F

7:30 - return vent (see pics of vents) starts hissing

7:33 - return vent stops, pressure reads 1.5#

7:39 - supply vent starts slight whisper

7:46 - pressure 3#

7:51 - pressure 4.5#, all rads filled, heating

7:51 - cut out, high pressure



So at this point I made a change to my pressuretrol based on reading here...I set it to 1 with a differential of 1...so here's what happens:



7:54 - pressure 2.5#, supply vent still whispering

8:00 - pressure 0, all vents quiet, cut in

8:02 - pressure 2#, cut out

8:04 - pressure 0, cut in

8:06 - pressure 2#, cut out

8:09 - pressure 0, cut in



This cycle continued...2 minutes steaming to fill the piping, 3 minutes to condense all steam



I worried that this seemed excessive, so I changed the differential to 2 just to put a little more steam in the pipes, so now I'm seeing



8:41 - pressure 0.5#, cut in

8:44 - pressure 3#, cut out

8:48 - pressure 0.5#, cut in

8:52, pressure 3#, cut out



So my cycle time is now 3-4 minutes on, 4 minutes off. It has now reached the 66F setpoint, so there is no call for heat at the moment.  It took about 2 hours to bring the house (3800 sq ft) up to 66F from 60F.  We also have a small electric strip heater that heats part of the first floor, but nothing else. 



Is this normal operation?  I'm just not liking that the boiler is cycling on and off so much.  I don't remember it cycling this much in the past, but I don't know that I ever paid attention that much. 



Thanks all...this really is a great site.



John

Mike Kusiak_2

Cycling

The cycle times you posted are normal given the fact that you have a boiler that is oversized compared to the amount of radiation you have. The boiler is producing more steam than the radiators can condense, so the pressure rises to the cutout setpoint. Then when the condensing catches up, the cutin pressure is reached and the cycle repeats.



The only real solutions are to add more radiators so the system can accept more steam, or reduce the size of the boiler so that it produces less.

BobC

Questions

John.



That's a good sized house so i assume your steam mains are pretty long. You show two Hoffman 75 main air vents in one picture, you may need a more venting so your not using your gas to compress the air in the steam mains. Also 3PSI is the highest pressure those air vents should ever see, most residential boilers run at less than 2PSI, mine runs at 12 oz.



Your near boiler piping may not be optimal, do you have a hartford loop? Does the water in the gauge glass move up and down much?



How long are the steam mains and what size pipe?

How long (from a cool start) does it take each main vent to get hot?

Is this single pipe steam?

Are all the radiator vents working and what kind of vents are they?



Your boiler may be oversized, and that can lead to short cycling. The only way to determine that is to measure all the radiators to see how many sq ft of radiation (EDR) you have. Try printing out this form and figure out what your total EDR is - http://www.usboiler.burnham.com/contractors/tool-box-sizing The EGH-85 is rated at 875 sq ft of steam so your radiators would add up to something close to that in a perfect world.



Compare the near boiler piping to that shown in the installation manual to see what the installer might have missed.



Bob

Rod

Insulation

Hi John-  Just from what I can see in your pictures you seem to be missing a lot of insulation. Lack of insulation turns your piping into one big radiator which means that the steam is condensing all through the piping and not just in the radiators where you want it. With proper insulation your pressure won't drop as quickly. Here's a good link on this subject.

http://www.heatinghelp.com/article/11/Hot-Tech-Tips/300/Why-you-should-insulate-steam-pipes

The only insulation my system was lacking was on the near boiler piping and when I did added insulation to just that section I was surprised how much of a noticeable difference it made.

- Rod

Mark N

Bullheaded T"s

You have 2 bullheaded t's right in your supply piping, They shouldn't be used fix them or have them fixed. Do a radiation survey to seen how many sqft of radiation your have . Compare to the output of the boiler.

jimmythegreek

boiler size

I have a commercial 4 story building about 12,000 sq ft and 40 or so rads.  I have the same boiler and it has never short cycled and I run at less than a pound but have 4 gorton #2s  for main vents.  How many rads do you have and how many sections roughly.  (ie sq ft of radiation) You near boiler piping is kinda bad as previously stated, and that boiler is probably way oversized for your application.  You may be able to change the orifices on the gas supply branch B4 it reaches the burners, but thats a hunch never tried it. 

brian_44

That's a pretty big setback...

If you're going from 60 to 66 every AM, that's a pretty radical setback. I think it's recommended to go no more than 4-5 degrees at the most. Since your boiler sounds to be oversized, a radical setback like that is even more counter productive.



We do a setback of 2 degrees (63-65) mostly because of little ones in the house. If I had my way, we'd go 3 or 4 degrees, but no more than 4.

JohnLaPlante

@Bob - Answers!!

Hi Bob, thank you so much for your response!  I have spent the last day or so on suggestions and "lookups" from the great people here...so here goes!



1.  Please see the attached picture for some insulation I added to the near boiler piping.  It's not pretty, but how does it look?



2.  We have a 2-story house (3 including the basement).  10 of the rads are fed directly from mains in the basement, but 2 are fed from a branch off of one of the rads on the second story, so I can't get to those mains to measure.  So when you say "mains", what do you mean?  Just the part of the piping that feeds the branches?  If so, then there is just about 80 feet of that.  The branch piping would be on top of that.



3.  This is 2-pipe steam.



4.  Regarding the vents on the rads themselves.  While I was calculating EDR, I found that 11 out of the 12 radiators had a small plug where the vent would go (see the picture below).  However, one of the rads had what looked like a bell-shaped vent (again, see pic below).  Not sure if this matters, but this rad is in the room we use for exercise equipment, and the rad is almost completely shut down (so as to minimize the sweat factor).  Could this be contributing to my venting problem?  This rad is about the furthest away from the boiler, which may be why it is there.



5.  I calculated my EDR, and I have 662.5 sq ft of radiation.  Multiplied by the 1.33 factor I've read about here gets me to 881...so my 875 boiler seems to be correct.  So it looks like maybe I do have a venting problem which is causing the short cycling...am I on the right track?



Thanks, Bob...your responses are so great!



John

JohnLaPlante

@Rod - Thoughts?

Rod, thanks for your post...can you take a look above at what I installed yesterday and let me know your thoughts?  It's not a professional insulation installation by any means, but maybe it will work?

JohnLaPlante

???

Hi Mark, I'm sorry to say that I don't know exactly what you're talking about...are you talking about the way the vents are connected?  Or on the near boiler piping?



When looking at the vent picture above, the closest vent to you is actually on the RETURN side of the system.  The fartest away (on the silver insulated piping) is on the SUPPLY side.  Those are the only 2 vents I have in the basement.



So I'm not sure about what Bullhead Ts you're talking about...but thanks for your response!!

JohnLaPlante

Jimmy - Answers

Hi Jimmy - thanks so much for your post!



I have 12 total steam rads, 662.5 sq feet of radiation.  I also made some additions to my near-boiler piping with some batt insulation...how does it look in your opinion?

JohnLaPlante

Setback?

Hi Brian, I guess I never really thought about that.  I'll have to do a little more research...I'll search here for setback, but are there any other resources you can point me to?

Mark N

Bullhead T

John



I'm talking about your near boiler piping. Both risers from your boiler go to a bullheaded T at the equalizer/system takeoff. This piping is incorrect. Both risers should connect to the header then the takeoffs for the mains then the equalizer. You say you have 662sqft of radiation, then you should have a boiler that can supply that not 875sqft. The 875sqft EDR rating of your boiler is its net output. Take that number multiply by 240, that will give you the net output in BTUs then multiply that number by 1.33. That is the gross output of your boiler , also know as DOE heating capacity.

crash2009

Thanks for your help Mark

http://www.heatinghelp.com/forum-thread/134484/No-Pressure-Problem-Solved

http://www.heatinghelp.com/forum-thread/134161/I-have-a-WM-EG55-with-377-EDRplease do not reply

http://www.heatinghelp.com/forum-thread/132580/Pressureplease do not reply

JohnLaPlante

THANK YOU!

Mark, thanks...I have a steam guy coming out next week, so I'll talk to him about your recommendation.  Appreciated!!!

BobC

Insulation doesn't have to be pretty

John,



Insulation doesn't have to be pretty, it just has to keep the heat in; pretty can come later. When you have time start doing the same to all the piping you can reach in the basement.



You really want to keep the pressure down on these systems, 1.5 to 2 PSI is all you need. More pressure just makes the gas company happier. Also consider cutting that setback down to 3-4 degrees, so you don't have to bring everything up so much.



The steam mains are the large (2-2.5-3") pipes that feed steam to all the radiator takeoff pipes (1-1.25-1.5). Let us know about how long each of those large main pipes is. If the total length is 80 ft and it looks like it might be 2-1/2" pipe (about 9" in circumference) then you have about 2.7 cubic feet of air to expel from the mains alone; you want to vent those mains quickly. The existing Hoffman 75 air vents are too small for that, if the mains are roughly the same length you probably need a Gorton #2 on each return. The Hoffmans are rated at 0.75cfm while the Gorton's are rated at 1.7cfm - both at 2oz of pressure. The Gorton #2's are large vents so you may have to use a slightly shorter nipple below the vent to accomodate them, measure the room you have to work with before buying anything.



Since yours is a 2 pipe system radiator vents are not used, except for that single radiator - is that one radiator piped as a one pipe? Are there any steam traps and are they working? The high pressure may have damaged them.



Once you have all the piping insulated your pickup factor will shrink even more; your boiler will be capable of producing even more steam than you can use. In fact that boiler rating is NET which means it has already discounted the 1.33 pickup factor. Even if it produces more steam than you can use, with correct venting and insulated pipes, all that heat will be upstairs keeping you warm and cutting the fuel bills.



Most of us have boilers that are capable of producing more steam than we need, especially on "normal" days, if everything were perfect then the boiler would run almost all the time on a design day.



My own boiler is too large, on a zero degree day the thermostat calls for heat about once every 45 minutes. It fires for about 6 minutes to make steam and 2-3 times more (cycles on pressure) for about 60 seconds each. I'll fix that when the boiler has to be replaced and hopefully that won't be for a while yet.



Once everything is working correctly you might be able to get a technician to lower the firing rate of the boiler so you aren't producing so much steam.



Bob

Mike Kusiak_2

Boiler sizing

As Bob and Mark have already mentioned, the 1.33 pickup and piping factor is already included in the net boiler rating of 875 sq ft. Actually your boiler can produce 1163 sq ft of steam, ( 875 x 1.33 ) but you only have 662 sq.ft of radiation attached. So it can produce almost twice as much steam as the radiators can accept. This explains why the boiler runs about a 50% duty cycle on pressure. It needs to run only half the time to supply all the steam the radiators can condense.



I believe you mentioned that radiators may have been removed and some electric heaters have been installed. If the radiators were reinstalled, it would go a long way to match the steam capability of your present boiler, which would reduce the short cycling. You might discuss that possibility with the steam pro when he comes.



As other have mentioned, the near boiler piping is far from ideal, but replacing it at this time will not address the cycling issue. Rather the present piping would contribute to wet steam and water hammer, which you don't mention as current problems.



Probably the most effective thing to do now would be to check and improve the venting, to make sure that all air leaves the system during a cycle. If air is left trapped in the radiators, it reduces their ability to accept steam and effectively makes the boiler even more oversized than it presently is.

Rod

Two Pipe Steam System

Hi John- Mike is giving you good advice. Just get the venting straightened out and tackle the boiler piping, boiler size etc. later down the line. (when it gets warmer!)



You are very lucky in that you have a two pipe steam system. They are far more "tweekable" than a one pipe system and having a one pipe system myself I'm rather envious. I'm attaching several pictures /diagrams which maybe of help to you.

One picture is a blow up of your boiler piping with the bullheaded tees circled. These are frowned upon as the steam flow is disturbed as it bashes into the tee and is deflected in both directions.

I've attached a diagram of a typical 2 pipe steam system. A diagram of a two pipe system is like a ladder with one side of the ladder being the Steam Main and the other side of the ladder being the Return Main.

Note end of the steam main- One configuration option is that the Steam Main has a Main Vent at the end which allows the air to escape and also a Drip Line which ducts the condensate back to the boiler via the Wet Return. (It would appear from you pictures that this maybe your system's configuration - let us know if it is)

 Another option is there is not vent or drip line at the end of the steam main but there is a cross over pipe (shown in the drawing as a dotted green line and with F&T trap) which allows the air and the condensate to escape to the Return Main and via the Return Main, the air to a Main Vent and condensate back to the boiler via the drip line on the return main to the Wet Return. The F&T Trap (Float & Thermostatic) allows air and condensate (water) through but closes when steam reaches it.

Radiators- Note in the diagram they are like the rungs on a ladder and are connected to both the Steam Main and the Return Main.  Two pipe radiators may or may not have a trap connected to the lower outlet pipe of the radiator. The type without traps have orifices on the inlet valve which limit the amount of steam that can enter the radiator.

The trap allows air and condensate (water) to pass through but closes when steam reaches it. I've attached a diagram of a steam trap. You didn't mention whether your two pipe system did or don't have traps. Do you have traps? If you do, one of the things you will need to do is check whether your traps, radiator and F&T (if you have one) are in working order. We'll save that for another post! Rebuild parts are available for most traps (even very old ones)

As I understand it you have one radiator with a steam vent. This is unusual as on a two pipe system normally the air from the radiators escapes through the radiator trap and into the Return Main and then out of the Return Main via the Main Vent on the Return Main.



So picture this- ALL the air in the radiators is escaping the system through the Main Vent on the Return Main. If there isn't a dripline on the Steam Main and a crossover pipe instead, added to the volume of air from ALL the radiators is ALL the air escaping from the Steam Main!  This is why having large capacity vent(s) on the Return Main is SO important! Otherwise the steam backs up and the pressure control shuts off the boiler, causing short cycling. If there is a drip line on the Steam Main it is important to have a large Main Vent(s) there too as this takes care of the Steam Main's air rather than it going through the radiator and to the Return Vent.

Sorry to be so long winded but hopefully this helped fill in any blanks you had in understanding what is going on in the system. It took me a while to put the pieces together when I started out.

- Rod

JohnLaPlante

Rod - Traps

Hi Rod, thanks so much!  I spent an hour yesterday diagramming my system...I'll digitize and post tonight.  Thanks so much for your pictures and description...I have a much better feel for why my return main vents much more than my supply main.  But I still think I need more venting.



Here is what two of my rads look like...are those traps?  I have never noticed them before.  How can you tell if they're working?



Thanks, Rod.  Really appreciate the help!!

Dave in QCA

Boiler Sizing Explained another way...

Mike, I may be splitting hairs here, but I'm going to offer another perspective of boiler sizing.



Boilers do not produce square feet of steem.  A Sq Ft, is a 2 dimensional measurement.  If steam was measure by the foot, it would be cubic feet, but it is not measured that way.  The EDR rating of a boiler indicates the size of the system that the boiler is capable of properly heating in which the total surface area of the radiation is measured in sq ft.  You can't really say that a boiler with a net rating 875 sq ft actually produces 1163 sq ft of team.  You could say that a boiler with a net rating of 875 sq ft could heat radition totaling 1163 sq ft, if there was no piping, and if there were no pickup factor figured in. 



Calculation firing rate, or BTU input of a properly sized boiler for a hypothetical 875 sq ft system would be as follows.  (this assumes 80% efficiency)

875 sq ft x 240 BTU/sq ft x 1.34 piping and pickup x 1 BTU input/.8 BTU Gross Output =  351,750 BTU Input



For John's 662 EDR system:

662 sq ft x 240 BTU/sq ft x 1.34 piping and pickup x 1 BTU input/.8 BTU Gross Output = 266,124 BTU Input



We do agree that the first order of priorities is to address the inadequate venting as well as trapping issues that may exist.

Dave in QCA

Mouat Vapor System

John, You have a Mouat Vapor system.  You don't have thermostatic traps on the radiators, you have Mouat vented vapor seals.  This system is intended to run at a pressure fo 3 oz or less.  Here are 2 links to information on this system.

http://www.heatinghelp.com/files/articles/1391/52.pdf

http://www.heatinghelp.com/files/articles/1376/541.pdf

JohnLaPlante

Dave - Thanks!

I appreciate those links...I will get to reading!  More posts to follow...this is turning into kinda a cool hobby...:)

JohnLaPlante

So...In Other Words...

... I am paying for 30% more fuel that I really should be if my boiler was sized correctly?

Dave in QCA

Mouat System Follow-up

John, What a fantastic system!



In the original Mouat installation, all venting would have been on the return line via the special Mouat vent.  The main would have been vented through the radiators.  However, with gas firing, this is not adequate, so at sometime in the past, your 2 Hoffman 75 vents were installed; one for the steam main and one for the return line.  Current perspectives on venting recognizes the advantages of getting the air out of the steam main as quickly as possible, so that the steam will begin entering all of your radiators at the same time.  I don't think you have stated what the diameter of your steam main is, but just guessing, I would say that 2 Gorton #2 vents would be in order.  They would be equal to 4.5 Hoffman vents.  Your return line vent is all stained and the sheet metal above it sure indicates that this vent has been blowing steam.  If your system is running at the proper pressure, you will never even see steam in this pipe, but a good vent is insurance that if steam does make its way into the return piping, it will not be exhausted into your basement.  The Hoffman 75 is completely adequate for venting your return lines because of the mass and condensing ability of the radiators.  Steam goes barrelling down the main very quickly when the boiler starts, and the faster that the air in the main can be vented, the better the system will work.  However, once the steam enters the radiators, it creeps very slowly, because there is so much iron to be heated up, and the steam can't move any faster than it can heat the radiator. 



As a side note: (I am currently venting my return lines through a vent rated .55 cf at 1 oz.  I have about 1280 sq ft of connected radiation, and am firing at 600,000 BTU. Pressure at my boiler never exceeds 2 oz until the rads are all heated and the traps begin to close.  When I was venting the returns faster, I was getting uneven distribution.) 



To repair your obviously leaking Hoffman 75, I would recommend removing it and soaking it about 5 minutes in liquid Lime Away cleaner.  Flush it with water and repeat.  That should make it work just fine unless it has mechanically failed.  Some folks on the wall will recommend vinegar, which is fine.  Lime Away contains a very mild acid that works very quickly on lime deposits, but does not attack the metal.



I am sure that some of the pros who are familiar with the Mouat systems will jump in here.  There advice should be considered gospel.



Dave

JohnLaPlante

Dave, thanks!

I just re-read your post...you said 3 oz or less?  Do you think I have damaged something by operating at such a high pressure?



So...I'm thinking I need a Vaporstat to run at such a low pressure...I don't think my Pressuretrol is that sensitive...am I thinking correctly?



Also, do you think I can fix the hoffman 75s or should I have my plumbing guy replace the vents with new?



Also also, it doesn't look like those mouat vented vapor seals have any way to fail...or do they?  Could they have damaged with the high pressure?



Thanks, Dave.

Dave in QCA

Reply

John, since there are no moving parts in the Mouat return fittins, you can't damage them by high pressure.  The only thing that can go wrong is that the pin hole that vents the air can get clogged up.  Perhaps, this is the reason that one of your rads has an air vent installed.  By the way, that air vent is very old and this was done some time ago.

Your Hoffmans may be able to be cleaned with Lime Away or vinegar.  The Hoffman 75 is fine for the return lines, but you probably need large vents on your steam mains.  Just guessing from the size of your system that 2 Gorton #2 would be in order, perhaps 3.

Dave in QCA

Not really....

Because, remember your original complaint was related to cycle times.  You are not burning gas when the boiler shuts off.  However, it would be better if the boiler was properly sized.  Any way you can add back those missing radiators?



Also, have you clocked your gas meter to see exactly how much gas this boiler is burning?  It might be over firing, i.e., exceeding the manufacturer's rating plate.

Mike Kusiak_2

Oversize boiler

Dave clarified what I was trying to say. I was a bit sloppy in my explanation, but what I was attempting to get across is that the radiation you have can only accept and condense a certain amount of steam. If the boiler is capable of generating more steam than the radiators can condense, the pressure will rise and the pressuretrol will shut off the burner. The relative on and off times ( duty cycle ) will adjust itself so that the average amount of steam produced during cycling will equal the condensing capacity of the radiators.



So theoretically you don't use any more fuel than a properly sized boiler would under the same conditions. In the real world, however, the cycling of the oversize boiler is less efficient than a continuous burn of a properly size one. So while you will not use 30% more fuel, there is some loss of efficiency, and if possible you would like to minimize the cycling as much as you can by matching the boiler output to the installed radiation.

Dave in QCA

Tipping Hat to Mike

Very well stated.  I agree completely.

JohnLaPlante

Missing Radiators...

...funny you should ask!



We are just beginning a kitchen remodel, so I think I will try to add some more radiators to the house to get that EDR closer to 875.  Know of anywhere to purchase some new Mouat radiators?  LOL...I doubt there are any new ones available anywhere.