Tips for Improving Short Cycling?

AdmiralYoda

I've been giving my steam boiler some love this winter and now that it's getting colder out my boiler is short cycling.  It does this just about every time the thermostat calls for heat when it's colder than 25 degrees out.  

I have an EDR of 219 and my 37 year old boiler is 40% oversized.

I've insulated the mains and run-outs, added main vents, and added larger and more appropriately sized radiator vents.  All radiators hear up quickly and evenly.

My boiler also doesn't have a header.  It has two risers and each one goes to one of my two mains.  I intend to repipe this correctly in the spring.

Any tips on reducing short cycling?  

Btw..my pressuretrol is set to 1.5psi with a 1psi differential.

ethicalpaul

Insulating your pipes made the short cycling "worse" but it's good anyway because it's previously wasted heat you are now putting into your living space.

Main venting is great to do, good job there.

Lower your pressuretrol to .5 cut-in. Shorter cycling is better than burning gas for nothing.

Have you explored options for plugging a couple burners? Don't do it without a tech who can competently analyze your combustion.

Finally, you can put a low pressure switch on a delay relay so that when your pressure hits, say, 1psi, your boiler is shut down for some amount of time (like 10 minutes). This gives your radiators time to give off their heat, lengthening the burn cycles rather than burning fuel for nothing. This will also take the cycling off of your pressuretrol, which isn't meant to be a moderating control.

EBEBRATT-Ed

Not much you can do. Raising the pressure control setting will reduce cycling a little.......but don't be tempted to do that it's the wrong way to go. Don't remember if your on gas or oil but you might be able to down fire the burner but that must be confirmed with a combustion test.

Some advocate a timer system to reduce cycling

ethicalpaul

Here's a switch: https://www.ebay.com/itm/DWYER-1823-20-PRESSURE-SWITCH/254230363560?hash=item3b314f7da8:g:DCgAAOSw8Ahc2ar1

Here's a delay relay: https://www.amazon.com/GRT8-A1-Maxmartt-Electronic-DC12-240V-Certificate/dp/B07YQYJGLJ/ref=sr_1_13?dchild=1&keywords=grt8-b1&qid=1608226725&s=hi&sr=1-13

AdmiralYoda

Thanks guys!  It's a gas burner and the steam system is a single pipe counterflow setup.

Does having proper piping at the boiler improve things?  I intend to repipe to a true dual riser and oversized header in the spring.

The delay relay does sound interesting....I'll look into that.

PMJ

I recommend not ever letting your boiler ever run long enough to develop pressure in the first place so it can't possibly short cycle. Control both the burn time and the wait time between burns with a Macromatic TR-6512U and effectively reduce the size of your boiler. See images attached. T1 is burn time and T2 is wait time. Independently adjustable to whatever cycle and net BTU/hr scheme you want. You simply wire it in series with your thermostat.

The only situation in which this won't yield excellent results with an oversize boiler is in systems that are badly unbalanced where some areas never get steam without pressure. Good balance is key for any system to achieve comfort and efficiency. Poorly balanced systems will always be problematic.

ethicalpaul

Oh it's a gas power burner? Then yeah a tech with a combustion analyzer should be able to see if it can be derated (and still have proper combustion and chimney temp, etc)

I don't think your near boiler piping is going to be affecting your pressure TOO much. In fact, if it were improved and your steam were dryer, you might find you get to pressure even faster which would decrease your cycle time more.

AdmiralYoda

Wow, thanks @PMJ!!

That doohickey looks pretty cool!  My system is very well balanced so I might look into this!

PMJ

AdmiralYoda said:

Wow, thanks @PMJ!!

That doohickey looks pretty cool!  My system is very well balanced so I might look into this!

Others have done it with good results. A simple an inexpensive way to avoid all pressure if there is no need for it which in a well balanced system there never is.

AdmiralYoda

The only potential issue I see is if I have the timing scheme dialed in during a cold month....say to only turn on for x minutes then off for x minutes, it may not work as well for mild month.

For example, today it's around 20 degrees and my boiler is coming on a couple times an hour.  The water is already hot and it doesn't take long to make steam.

On a mild month the heat might only come on a few times per DAY and the boiler might be stone cold.  So it will take longer to heat the boiler up and make steam.  In this example it will just take the thermostat longer to be satisfied since it might take a couple cycles on the timer before the water really heats up.

PMJ

AdmiralYoda said:

The only potential issue I see is if I have the timing scheme dialed in during a cold month....say to only turn on for x minutes then off for x minutes, it may not work as well for mild month.

For example, today it's around 20 degrees and my boiler is coming on a couple times an hour.  The water is already hot and it doesn't take long to make steam.

On a mild month the heat might only come on a few times per DAY and the boiler might be stone cold.  So it will take longer to heat the boiler up and make steam.  In this example it will just take the thermostat longer to be satisfied since it might take a couple cycles on the timer before the water really heats up.

You are absolutely correct. At this basic simple level you need to set a scheme that contains enough burn time per hour to cover a cold day. If you don't want to change anything this setting may still cause some pressure on a warm day. On an actual dead cold start the system takes longer to get going.

The solution to this which is how I run now is to install a remote temperature switch on the feed pipe of the last radiator to get steam in your system. Run every burn until that switch is satisfied. From there run the T1 timer to get to a fill level. When the switch opens up initiate the T2 timer to set the start of the next burn. This way every burn achieves the same fill level regardless of how warm/cold the start is. These cycles also then adjust themselves as the weather changes.

The wiring is more complicated(I do it with a PLC), but it can be done.

acwagner

I've used a timer like @PMJ recommends for a few years now. My experience has been with some trial and error you can get a single on/off time setting to work for pretty much any condition. I forget my exact settings, but it's something like 20-ish minute burn followed by 12 minute dwell.

It does require that your system is relatively balanced, though.

AdmiralYoda

@acwagner thanks!  Any estimate on fuel savings?

Jamie Hall

I wonder what's wrong with Cedric? He almost never cycles on pressure, but doesn't have a timer or anything. Just a vapourstat. Must be doing something wrong here...

acwagner

@AdmiralYoda I don't.

The main advantage is it gives you more control on the boiler operation beyond the thermostat and pressurtrol. I originally put my timer on because I did temperature setbacks and wanted to be able to recover without shortcycling. I also didn't like the huge temperature overshooting that occurred even during a normal heat cycle, and my thermostat didn't have a built in way to address that.

PMJ

Jamie Hall said:

I wonder what's wrong with Cedric? He almost never cycles on pressure, but doesn't have a timer or anything. Just a vapourstat. Must be doing something wrong here...

I thought you said Cedric barely gets it done on a design day with wind. Surely not much oversized then if at all so no surprise you have no short cycling. Nothing wrong with that I know of.

This solution is for those of us significantly oversized. I'm of a mind that oversized is not only very manageable but actually an advantage. When I have to replace mine I'll do oversize again.

AdmiralYoda

@acwagner thankfully I don't overshoot at a steady thermostat setting, but I sure do on a setback!  This is the reason I just keep it at a certain temperature.

Another thing I'm after is reducing wear and tear on the old boiler.  I'm not financially ready to replace it so I'm trying to be as gentle as possible.  That means keeping the pressure as low as I can and still produce heat.

The Steam Whisperer

My first question is what is causing it to short cycle... the pressure control, the low water control, or the thermostat?

AdmiralYoda

@The Steam Whisperer it's the pressuretrol.  I'm 40% oversized.  I'm pretty sure the previous owners removed a radiator or two 40+ years ago and when they replaced the boiler in 1983 they probably replaced the original boiler to the house circa 1899.  It was a coal to oil conversion.

They added a gas line when they installed the boiler 37 years ago.

My water only bounces about a 1/2" in the site glass, maybe 3/4" max.  Everything heats evenly, just builds pressure before the thermostat is happy.

Jamie Hall

Pay attention to @PMJ 's solution. For a boiler that oversized, it is a very good way to make it happier.

PMJ

So here is what oversized looks like. Attached is a shot of my system status screen this evening. Data collection was reset 3 days ago. Weather is mild - average outdoor temp 35degF. You can see the total burn time is 21% of total time. If it were 0degF outside it would double the demand and burn % would be 42%. I really haven't seen more than 55% ever and it hits the minus teens here.

When this shot was taken the last burn was 34 minutes ago. It was an 11 minute burn and the tsat was satisfied on minute 17 of the following wait. We are at 17 minutes after that or 34 minutes since the last burn ended. The heat switch centrally located in the main is still hot but the remote rad switch is not. The system is sitting at -4.8 minutes Hg vacuum - a nice place to start the next call which will be shortly. The system has been calling for heat 57% of the total time and the single vent has had the system open to the atmosphere at total of 10% of the elapsed time. Not much air handling required. The average call has been 60 minutes long. Mild weather stuff.

PC7060

Funny, had a similar problem as you steam heads with my old hot water boiler.  Way over sized with 2” pipe dumping return water directly into boiler. Used a very similar approach to solve the problem. 

Designed and built this microcontroller with thermocouples to run pump for 15 seconds on then 120s off. The program adjusted run and dwell time based on return water temp. 

 

AdmiralYoda

Wow....and I thought I was a tinkerer!

The Steam Whisperer

You could just the thermostat for shorter cylces.... then you won't get the short cycling of the pressuretrol usually. If you are set for 1 cycle per hour , bump it up to 2.

PMJ

The Steam Whisperer said:

You could just the thermostat for shorter cylces.... then you won't get the short cycling of the pressuretrol usually. If you are set for 1 cycle per hour , bump it up to 2.

No one really knows what the algorithm being used in these things is. The people writing the instructions don't. Sometimes it works out, sometimes it doesn't. With the timer I suggested above you actually take control of the burns and waits directly. There is little cost to this and no downside.

People with big boilers know all to well that they should have shorter run times than the standard control provides. In my example above my tstat was being satisfied 17 minutes into the wait time after the previous burn for goodness sake, and not on just that one cycle. This is how fast an oversize boiler puts steam out there. There is a real need here for a controlled wait because of the natural response delay in these systems. The more oversize the boiler the bigger the need. The good news is that the solution is actually quite simple and inexpensive. All this angst over boiler size then simply goes away.

Big boilers need some real serious slowing down to get anything close to even heat. By the time the tstat (or worse) the pressuretrol reacts to a burn, it is way too late if you have an oversize boiler and want to put a stop to the heat roller coaster.

dabrakeman

@PMJ Maybe I am underthinking this but I would want a device in series between my thermostat and boiler where upon initial stat call for heat its timer would start and once it reached say 35 minutes it would open the circuit shutting down the boiler for a set amount of time, say 15 minutes. If after that 15 minutes the stat is still calling for heat it would reclose the circuit the boiler would come on and if it isn't calling for heat the boiler would not come on. Seems this is all that would be necessary to overcome the vast majority of oversize boiler issue. Mainly just for recoveries. Is this what the Macromatic TR-6512U is capable of or am I misunderstanding it?

PMJ

@dabrakeman , no misunderstanding - you have stated the operation quite correctly. This is exactly what you can do with the TR-6512U. On first time T1 and off time T2 both independently adjustable to suit any combination you wish.

SteamingatMohawk

I don't know anything about other steam systems, but mine has a HB Smith boiler with a Hydrolevel CG400 series CycleGard 1090 LWCO and a new Hydrolevel VXT with the digital readout.

What I like about the Cyclegard is the device has an "intermittent level test" which basically tests the LWCO function every 10 minutes for 90 seconds (aside there are other choices for time and duration). This device essentially lets the boiler stop firing for a short time every 10 minutes. It helps with pressure going up too much, accomplishing what many on HH try to do without home-made complexity and it is a commercial device, so there is no personal liability for a home grown situation that may cause problems in the system at some time in the future. Check it out at Supply House.

My steam system is in a 90+ year old rental, so I am alert to creating liability that I create that has no-one other than me designing, installing and maintaining it.

Don't get me wrong, I like the McGyver ideas, it's just not necessarily a great idea from a liability point of view, especially in a rental.

Having been a member for 2 years now, I am continually amazed by the skills of many of the folks on HH and have learned a lot from HH and some side consultations with other members.

PC7060

@SteamingatMohawk  - “Don't get me wrong, I like the McGyver ideas, it's just not necessarily a great idea from a liability point of view, especially in a rental.”

It is certainly important to ensure systems fail in a safe manner. Both @PMJ  method and the the micro controller I described operate on the low voltage Thermostat line outside of the boiler with no impact to to safe operation of the boiler controls (eg. fail safe)

pecmsg

With 37 years of short cycling start planning on its replacement. Find a contractor that knows what there doing. Get the exact EDR# you need. After this season replace it as well as the piping issues.

SteamingatMohawk

@pecmsg Teach me something. How does short cycling affect boiler life? I would think Hydrolevel wouldn't have the "intermittent level test" function in it's LWCO devices if there was a significant adverse effect on life.

pecmsg

@SteamingatMohawk ANY "system" needs X amount of run time to stabilize combustion. Generally 15 minuets, then your at the rated efficiency's. Less then that the #'s are unknown. Constant movement of metal shortens it life.

EdTheHeaterMan

SteamingatMohawk said:

@pecmsg Teach me something. How does short cycling affect boiler life? I would think Hydrolevel wouldn't have the "intermittent level test" function in it's LWCO devices if there was a significant adverse effect on life.

Really? Anything made by a human or by nature for that matter wants to break down to its most basic state. Some faster than others. I believe it is called Entropy.
...so, to your point. If I invent a gizmo that will last 10,000 cycles, on average ...and you cycle it one time a year, in theory, it will last 10,000 years. Now if you cycle it 20 times an hour, then it won't last a year.

So you have a 37-year-old system that has short cycled for its entire life, how inefficient is that? For the energy savings alone it's time to upgrade to a more efficient boiler.

I liked to tell that to customers that asked "Why did that part fail?" When I answered "Entropy" the conversation would stall for a moment and I could change course to the solution and away from the purposeless conjecture of why does anything in this world fail, Why are we even here on earth? What is the purpose of life? and who is Aristotle anyway?

Back to your query. Each cycle of anything man-made places it one step closer to failure. The Cast iron will outlast the contacts on the thermostat in most cases, but everything we make that cycles will eventually fail. BTW, Do you still have your first car?

AdmiralYoda

Woah.  And to think that for the first 24 years of the boilers life the pressure cut in was at 4 psi and had little to no maintenance, antique radiator vents, no main vents and leaking radiators.

Then I got ahold of it and reduced the operating pressure and installed somewhat better radiator vents.

Fast forward 13 years and I've finally installed proper main vents and appropriately sized radiator vents.  Fixed the leaking radiators and started using Rectorseal 8-way.

@New England SteamWorks does the annual maintenance and said the boiler is in amazing shape for its age and is squeeky clean. 

It's time is coming, but not yet.

pecmsg

The biggest issue with waiting is its on the Boilers terms and generally its not at a convent time!

The Dice are in your hands.

PMJ

pecmsg said:

@SteamingatMohawk ANY "system" needs X amount of run time to stabilize combustion. Generally 15 minuets, then your at the rated efficiency's. Less then that the #'s are unknown. Constant movement of metal shortens it life.

I would argue that a larger temperature range of change in the boiler cycle is worse than more cycles through a significantly smaller total change. Longer burn times and longer off periods cycle the boiler through a significantly wider range of temperature each time. This is also where vacuum operation is key. Few today can really appreciate how much warmer the boiler and the entire delivery system stays between cycles when it is in vacuum between burns.

Beyond this I think those who are worried about too many cycles and boiler life need to give us some definition of what length of cycle is too short and or how many per day is too many. For those of us with big boilers like mine, on an average day anything more than 25% net burn time per hour will overheat the place. That is 15 minutes total. If I am allowed to break that into even two pieces those are 7.5 minute burns. For a couple months now with temps in the 30's my average burn is a single digit number and I am doing about 30 of them a day - or 1.23 cycles per hour. If anyone thinks that is abusive please advise.

Just for the record my average burn has been less than 10 minutes for 25 years now, and this on a boiler that already had 38 years of use on it when I took over. I'm guessing I have put 4-5000 cycles on it each of my seasons. I guess I have a really early warning system already installed to know when it is giving up - it won't hold vacuum anymore.

AdmiralYoda

@pecmsg I 100% agree with you but it could have 20 days or 20 years of additional service life.

Maybe a poor analogy but it's like having an older car that is still very functional and operating perfectly.  Then replacing it with a new one because "something will probably go wrong in the future".

In the spring I plan on repiping the near boiler piping and one of the wacky mains just because I can and it might add a wee bit of efficiency.  

Maybe in a couple years I'll put an appropriately sized boiler for my 219 sqft of EDR.  

We have a new wood stove that is more than capable of heating the house.  If the boiler ever fails catastrophicly with no warning signs, I have a backup.

SteamingatMohawk

@EDTheHeaterMan I am quite familiar with the concept of Entropy in your frame of reference. During my working days we used that term in jest many times.

That being said, I fully understand the non-infinite life cycle of physical things whether it be mechanical, electrical, chemical or otherwise.

Appropriate maintenance on equipment can prolong it's life. Too little and too much can create their own problems.

Safety devices and operational controls all have their limitations. Poor chemistry and corrosion due to air can compromise the pressure boundary.

I take your tongue in cheek humor as offered, but you have not commented on the design of my LWCO to cycle every 10 minutes. An 11-1/2 minute pause in firing doesn't put much thermal stress on the system. In my mind, I tend to think doing a setback over night or during the day causes a more significant thermal cycle on the system compared to the LWCO tests. Remember the test only does anything while there is demand for heat, even though the LWCO still cycles when there is no demand. I have a recollection the newer LWCO can be selectable to only test when heat is demanded, mine cycles regardless of call for heat.

There are many modes of failure in a complex system. For many systems most components are available or have superseding replacements, so that the system can continue to operate. Even a leaking heat exchanger may be able to be replaced years later.

The decision on any replacement is the cost/benefit analysis of repair versus wholesale boiler replacement.

SteamCoffee

READ AND LIVE THIS QUOTE.........

PMJ said:

I recommend not ever letting your boiler ever run long enough to develop pressure in the first place so it can't possibly short cycle. Control both the burn time and the wait time between burns with a Macromatic TR-6512U and effectively reduce the size of your boiler. See images attached. T1 is burn time and T2 is wait time. Independently adjustable to whatever cycle and net BTU/hr scheme you want. You simply wire it in series with your thermostat.

The only situation in which this won't yield excellent results with an oversize boiler is in systems that are badly unbalanced where some areas never get steam without pressure. Good balance is key for any system to achieve comfort and efficiency. Poorly balanced systems will always be problematic.

Dooverdixon

Im late to the party here but i have recently implemented @PMJ 's macromatic t1/t2 setup because my boiler was 50% oversized and would cycle on pressure during almost all heating cycles. I've bought a vaporstat, tons of main venting, new radiator vents (the main symptom was screaming vents). This was the ONLY thing that help and it helped immensely. My house is currently under construction so getting the settings dialed has been a bit of a challenge, but im 100% sold on this method. Right now im using an 8 minute burn with a 10 minute cool down and I do not build more than a few ounces of pressure on the gauge and the vents (save 1) are quiet.

He was also super helpful in helping me install this setup. For some reason there is some pushback on this site from some folks on this idea, but it really does work and works well. It also costs $100 to implement vs who knows how much to have a tech come try and downfire your burner.

SteamingatMohawk

Correction to my December 19 post, the pause is 1-1/2 minutes, not what looks like 11-1/2 minutes. My typo.

The Macromatic time delay relay mentioned above is very similar to the intermittent test function in my LWCO. It's just not adjustable, but that's not the main purpose of the LWCO.

I guess I agree putting a time delay relay in series with the tstat is a good way to control the burn rate of oversized boilers, which seem to be very common these days. It's especially good with the large range of on and off times available in the unit mentioned.

I also believe it is probably better to cycle on an accessory device than a safety device and maybe cheaper in the long run.