Timer to Minimize Short Cycling on Oversized Boiler I

swassbac

I have a fairly complex and large 1890 steam system - see this post for more details: https://forum.heatinghelp.com/discussion/187115/1890-steam-system-looking-for-st-louis-area-expert-and-or-advice/p1. Water hammer issues brought me to this forum and those (thankfully!) seem to be resolved after draining and extra flushing the boiler two weeks ago. The next item on my list is short cycling.

The boiler is likely way oversized even at low fire (450k BTU) and although I’d like to avoid replacing the 2015 boiler, I do want to calculate the actual need since some of the in-duct radiators seem to have LOTS of surface area compared to traditional radiators. I opened up the ductwork for the easiest to reach one (below is a pic of one that is approximately 40" x 36" x 7.5") but it will take some work to get access to all of them to measure the sizes, # of sections, etc.


After the thermostat initially calls for heat, it runs 10-25 minutes (depending on whether it has run recently or been cool for a while – seems like it takes about 8 mins to produce steam when it has been off for 24 hours). At that point, it shuts off based on pressure. The thermostat is still calling for heat (I have a couple degree set back to make sure the thermostat isn’t causing any cycling) and the low water shutoff is not being tripped. I have the cut in set to .5 with a differential of 1 and have played around with increasing the cut in and/or increasing the differential and it did not seem to affect the short cycle timing.

At the point the boiler turns off for the 1st time, the radiators are all mostly hot (the thermostat is already showing the house temp is rising – I have 3 temperature sensors around the house that are averaged by the thermostat) and the pressure only seems to get to that point once most of the radiator vents have stopped venting. From that point, the system will cycle shutting off ~2 minutes and running 1-3 minutes until the thermostat is satisfied with the heat.

From reading We Got Steam Heat, the one thing that stands out is the main vents in the basement. 4 of them look pretty rusted and I have only heard two of them vent so I am going to replace those 4 with Gorden #1s since I am not sure which ones are working or partially working. For the one long main section (40’ of 4” pipe) there are NO vents so I was also planning on adding a vent to each end – that pipe is only vented by a couple of small radiator vents – that is all that is serviced by that pipe. I think before the kitchen was remodeled ~20 years ago, that pipe used to provide steam to additional radiators that have since been removed.

As much as I think the main venting needs to be fixed/expanded and is going to help get steam to those radiators at the end of the 40’ run, I am not sure how much it is going to help with cycling after the system is hot and the vents are closed. I am hopefully though because I do still hear some venting even after the initial cycle so I have to believe more or better venting with lengthen the time that it takes for the pressuretrol to trip.
Short of replacing the boiler, I think what I really need to do is add a timer so that once the system is filled with steam and hot, the system waits 5-10 minutes before allowing the burners to fire. My concern was I didn’t want to wait 5-10 minutes after I call for heat for the boiler to start. I like the idea of pressure switch attached to a timer that was mentioned in this post which seems to solve that issue (https://forum.heatinghelp.com/discussion/comment/1678404).

My boiler being 45-50% oversized it tends to short cycle on pressure during a heating cycle. I don't use setbacks...just 66F and forget it.
I installed a low pressure gauge 0-15oz and noticed that the pressure slowly climbs to 6oz and then takes off rather fast from there until the Pressuretrol kicks in. At 6oz my radiators are full of steam and pretty darn hot.
So rather than let the boiler short cycle I installed an adjustable pressure switch that I set to about 8oz. When the pressure hits 8oz it kicks in an adjustable timer that interrupts the call for heat. This lets the radiators give some of their warmth to the house and often times the thermostat is satisfied during this pause period.
I have the timer set for 5 minutes. After this has passed if the thermostat is still calling for heat the boiler will fire up and the cycle will continue.

It's essentially a soft pressure limit. So far its been working great. Previously the radiators would get scorching hot and overshoot the thermostat by the time it was satisfied. This kind of tames the beast.

My main goal of this whole thing was:
1. Maybe save some fuel costs.
2. Less cycling of the boiler which I would hope may increase its operational life.
3. It operates at a lower pressure which hopefully will also help its lifespan.

Has anyone had experience with this type of setup and can provide the link to what switch and timer they would recommend to insert this delay after pressure initially begins to rise? I messaged the original poster of this comment but haven’t yet had a response.

Thanks in advance – this forum and Dan’s book have dramatically increased my steam knowledge in the last few weeks.

Jamie Hall

If the boiler really is seriously oversized -- and your cycle timings suggest that it is, though not as badly as some we've seen -- and you want to space out the cycles (longer off and longer on), a timer is a good way to do it. @PMJ and some others have had good success with that approach.

Note that it will not save you fuel, and the last thing you want is for the boiler to cool between cycles while the thermostat is calling

ethicalpaul

Your description doesn't sound too bad. Here is my advice:

1. I know you are using a setback for testing purposes, but how about in real life? Do you need one? If not, get rid of it and run a constant setting (or minimize the setback as much as you can stand). You are in better shape than some since you aren't seeing the cycling until some or all of your radiator vents close. By minimizing setback, you might find the thermostat is satisfied without cycling at all.

2. Get the main venting in order. It sounds like you are on track for this. Good main venting will help even more, but admittedly won't affect your situation after all the vents are closed.

3. I do run the exact timer you describe. You might see my yapping about it in that thread, I didn't go look. I use a Dwyer Series 1800 pressure switch (credit to @ChrisJ who taught me about this switch and also the Magnahelic gauges) which comes in different versions for different pressure ranges. I think the one I settled on was adjustable between 5 and 20 inches of water column. I recommend buying one used or NOS on ebay for about $20. In fact I'm looking at one on my desk right now model 1823-10, I can't remember which range that is but if you can't find one I'll sell you this one.

Then, you need a timer. You can use something like a timed relay, or one like this: https://www.amazon.com/gp/product/B07Q2F95QH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

There are a ton of different versions of this timer so make sure you get the right one. You want one that will open a switch for a set delay when an input is set. You wire up the pressure switch to the input of the delay timer, so when the pressure switch closes, it opens up the relay and starts the timer. Then after the timer expires, it will close the relay switch. Just wire your "call for heat" thermostat line in series with this relay switch so that the timer relay makes it as if your thermostat was satisfied. Then the damper will close and everything.

I have my timer at 10 minutes. My boiler is well-sized so it only triggers when coming back from a few degree setback (keep in mind, it activates at only 15 inches of water column or so). I did it mostly for experiment's sake, but also because I just couldn't stand burning fuel while my radiators were fully hot. There's no point to building pressure while the radiators are hot. I know Jamie just said it won't save fuel but different people have different opinions Let the radiators radiate some of that heat away was my thinking. My boiler cools down must be a couple degrees in 10 minutes if that.

Jamie Hall

The reason I say that it won't save fuel is this: it takes a power of N BTUh to keep a structure at a certain temperature with certain outside conditions. It takes M gallons/cubic feet/Kw per hour to provide that N BTUh. Nowhere in that relationship does the cycle timing of the power source appear.

Sorry...

Now that is not to say that the cycle timing does not have an effect; it does. The direction of the effect (more fuel per unit power out or less fuel per unit power out) is the subject of considerable debate, and is subject to a very large number of variables. It is also lacking in hard reproducible data, which makes it more fun. In any event, the effect is not likely to be large.

My own feeling is that for steam the optimum off portion of the cycle should be as long as possible without the boiler stopping producing steam, although at a lower rate than when the burner is firing -- the objective being that that way there is no loss in reheating the water and the boiler metal back to steam production. Others disagree with me, and that's fine. The considerations for either hot water or hot air heat are very different.

EBEBRATT-Ed

@swassbac

Sounds like your on the right track to me. Those indirects are huge!!

I am wondering if the indirects are taking in outside air as that is how some of those systems were designed.

If they are that may be a place for some energy conservation.

I am wondering how much of your system is standing radiation and what portion is indirects?

ethicalpaul

Thanks for that explanation Jamie. I guess the steam in the system at the higher PSI has more heat energy in it which will of course get released into the house. I feel you must be right and yet it bothers me to have the radiators full and the fire still burning.

Jamie Hall

It does seem a little odd at first... but consider: start with boiler maybe warm -- no call for heat for the past half hour or so. Thermostat calls. Burner fires -- but the radiators don't begin to warm up for a while (hopefully quickly, but there's always a lag) and they take time to warm up. Meanwhile the burner is humming along. Now in an ideal world the steam production matches the condensing... let's suppose that that's so. Now eventually the burner quite and, perhaps 30 seconds later, steam production ends as the boiler metal cools. But... the radiators are nice and hot, and continue to give off heat. What is the balance between the heat added while the boiler was coming up to steam -- no radiation to the structure -- and the heat added to the structure by the radiators with no heat added to the boiler?

We need more research! But this is why I like to keep the off part of a cycling boiler as short as possible -- to avoid that loss of heat bringing the boiler up to steaming.

PMJ

ethicalpaul said:

Thanks for that explanation Jamie. I guess the steam in the system at the higher PSI has more heat energy in it which will of course get released into the house. I feel you must be right and yet it bothers me to have the radiators full and the fire still burning.

I agree that eliminating small amounts of pressure won't result in large savings. I do believe that a pressurized system overshoots, and that increased average delta T causes higher overall loss to the outside for a given setpoint which must be replaced. So pressure is a negative on the cost side, though a relatively small one if the pressure is low.

I have argued for years that main benefit of the timer approach with big boilers is comfort through what can be dramatically more even heat. Building system pressure requires significantly fuller radiators that would be required steady state to meet the heat loss - the condition they would have had to have been with the original continuous fire. So going into and out of significant pressure results in a roller coaster that to most like @ethicalpaul states here is quite annoying. You know that your radiators are already more full than they need to be to do the job but your boiler is still firing away.

The timer approach works best when you stop the burns well short of full radiators and pressure developing in the first place, using one of several methods, and then timing a wait before the next burn. Unfortunately, especially with one pipe systems as I think this one is, if it is not really well balanced some radiators will not get steam at all without pressure. In that case it is still better to initiate a timed wait after some minimal pressure trip happens as others have done here. But the best result is running without any pressure trips at all as those who have achieved it will attest.

swassbac

ethicalpaul said:

I know you are using a setback for testing purposes, but how about in real life? Do you need one?

I probably have the terminology wrong, I have set the "Heat Differential Temperature" on the ecobee controlling the boiler to 2 degrees to ensure I don't call for heat if the temp just drops .5 or 1 degree - the temps in the house are fine with that much of a spread. The smart thermostat is pretty critical to my setup since I also have a furnace and have my home automation system switch over from furnace and boiler depending upon predicted temperature swings. For instance it's been in the 30s all week but yesterday was in the 60s so the system switched over to the furnace for that day and then switched back to boiler when the temps starting dropping. I also use this to turn on air vents to pump in cold air to my equipment room in the basement when the temps in that room start climbing and the boiler is running. I could also setup a relay to handle the timer but would rather that be a stand-alone device separate from the home automation system

Thanks for the timer advice - that looks like exactly what I need. Once I get the venting addressed assuming the short cycling continues, I'll go ahead and pick it up - looks like there are plenty on ebay.

swassbac

EBEBRATT-Ed said:

I am wondering if the indirects are taking in outside air as that is how some of those systems were designed.

It may well have originally pulled air from the outside. The ducting goes under the foundation so I suspect it was also used to circulate cool air through the house in the summer. Currently the only air intakes I have found are both in the basement with ventilation fans attached to temp sensors on the pipes that kick on once steam is hitting the radiators.

EBEBRATT-Ed said:

I am wondering how much of your system is standing radiation and what portion is indirects?

There are currently 9 radiators above the basement level and ~5-7 (it's hard to tell with the amount of ductwork) in duct units that are connected. There are two in duct ones that have been shut off due to slow leaks. I am trying to determine if they are repairable and hope to get them powered back up. There are also 3 in duct ones below the dining room that were disconnected many years ago and likely will never been re-connected (I'd probably put some coils in the duct feeding the dining room if I wanted to add heat back there).

ethicalpaul

I probably have the terminology wrong, I have set the "Heat Differential Temperature" on the ecobee controlling the boiler to 2 degrees to ensure I don't call for heat if the temp just drops .5 or 1 degree - the temps in the house are fine with that much of a spread.

Yes, I call that "swing" but it has many names. That should be fine. I was referring to a setback of like 5 degrees or more that some people like to do at night for example.

swassbac

ethicalpaul said:

I was referring to a setback of like 5 degrees or more that some people like to do at night for example.

OK, then we actually do set back as well, we drop the temp 4 degrees at night which we find comfortable and assume saves us a little gas overnight. When we had the hammering issues, I would set it to raise the temp several degrees before night and then setback even more which allowed us to make it through most of the night before the boiler (and hammering) started in the morning.

ethicalpaul

It might save a little, and if it's for your comfort I certainly won't blame you, I set mine back a few degrees also.

During the daytime does it short cycle, like from noon to evening? Make a note of how it behaves during those non-setback-recovery times and see if it improves after your main venting improvements.

reggi

ethicalpaul said:

<Snip> Then, you need a timer. You can use something like a timed relay, or one like this: https://www.amazon.com/gp/product/B07Q2F95QH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 There are a ton of different versions of this timer so make sure you get the right one. You want one that will open a switch for a set delay when an input is set. You wire up the pressure switch to the input of the delay timer, so when the pressure switch closes, it opens up the relay and starts the timer. Then after the timer expires, it will close the relay switch. Just wire your "call for heat" thermostat line in series with this relay switch so that the timer relay makes it as if your thermostat was satisfied. Then the damper will close and everything. I have my timer at 10 minutes. My boiler is well-sized so it only triggers when coming back from a few degree setback (keep in mind, it activates at only 15 inches of water column or so). I did it mostly for experiment's sake, but also because I just couldn't stand burning fuel while my radiators were full

Wonderful ! ( I'm assuming this thread is about these steam system controls? If not I could move this post to start a follow up thread..lmk..
Amazing... Just recently my mid 60's Natural Gas Steamer has begun to increase its Water Column from 4 inches water column to a bit over 10" water column at which point my mid 80's Merc vstat shuts it down until the pressure drops to around 2 oz of water psi and turns on perhaps a few times until the thermostat is satisfied..
I have some ideas but they will require warmer weather proceed with as I've been using steamaster the past few years and this year did quite a bit of skimming though I believe I have rust debris on the water side bottom of boiler that is dancing around when it fires up after sitting for a couple of hours.. nothing big to drain with but 3/4 full port ball valve off the rear and LWCO 67 on the front..no skin port but I have a 3/4 on the back to Tee'd to the pop and 1/2 " 4/5th of the way up on the side...
Really no place to get a wand in and at closing in at 60 yo I'm not sure how hard I want to hit it... 175k in 150k out off the top of my head..
And it's a Vapor , Vacuum, Pressure System pretty much 80% original maybe more..
Which gets me to the timer oh @PMJ I've read his words but but I get lost in his explanation..I guess I just read your post @ethicalpaul and Bank there it was 90% ready to go in somewhat simpler terms (PJM) nothing against you.. just the way my brain could hold with something or start jumping lines..
As the extreme cold weather recently I saw my highest natural gas consumption EVER

well going on 50 years.. and I stood there and watched that vstat sitting steady then rise ,cut ,fall, fire and repeat..If I was there I'd cut the power for five minutes or so..it would have to build pressure again but I'm in 7-8 inch of vacuum by then and it's like a instant boil and steam follows momentarily..I usually hear the vaporstat plate pop to the opposite direction.. from pressure to vacuum or vice versa..
But anyway I think that's exactly what I've been looking for and just wanted to let either or both of you know I might have a question or 2 and just wanted to give some back ground.. appreciate your work 

swassbac

@ethicalpaul

One more question - is there a low pressure gauge I could install that would allow me to see the actual pressure to make it easier to adjust and tweak the pressure sensor switch and/or pressuretrol going forward? Searching around I see lots of gauges that are higher pressure. Not sure if any are pass through or whether you can leave one on a T and still get a good reading or if that is a good idea. Thoughts?

ethicalpaul

Dwyer the same company that makes the switch makes a fantastic line of gauges called Magnahelic. Again look on ebay for used or new old stock. 

swassbac

Thanks. I am a thinking a Dwyer photohelic combination gauge/switch (like https://www.ebay.com/itm/272112827797) could work and eliminate a separate pressure switch. I see some on this forum have used these as a DIY vaporstat but I would just be using it in addition to the pressuretrol with a timer to introduce a wait time before allowing the burners to relight.

veteransteamhvac

There are two 0-5psi guages available at Supply Warehouse. A Bluefin: https://www.supplyhouse.com/Bluefin-GLP25-5-BM-2-5-Steel-Low-Pressure-Gauge-Bottom-Mount-w-Brass-Internals-0-5-PSI and a Winters: https://www.supplyhouse.com/Winters-Instruments-PLP305-2-1-2-PLP-Steel-Low-Pressure-Gauge-1-4-Bottom-NPT-w-Brass-Internals-0-5-PSI

I have the Winters and it's fine. The Bluefin is only $20.

SteamingatMohawk

Without boring you with the calculations, 1 cubic foot of steam at different pressures contains different amounts of BTUs.

Yes there is a difference, because even though the BTU/lb stays essentially the same (0.2% increase), the cu ft/lb gets smaller, making the "energy density" get larger.

Raw Data from Crane Technical Per 410

SteamingatMohawk

Any low pressure gauge that cannot handle 30psig, needs to have an isolation valve so it does not see pressure when not being used or it is not to be permanently installed.

Read the caution on the label on the Bluefin about not going above full range pressure. Unfortunately it's hard to read.

There are Magnahelics that can handle 30psig, that's why @ethicalpaul suggested Dwyer.

ethicalpaul

They all handle 15 psi. I leave my low pressure gauges open…my boiler never goes over a psi so I sure don’t need a valve that is good up to 30 except for that one that never moves

Motorapido

Hey, ethicalpaul, check your heating help message inbox. I've got a question for you.

swassbac

ethicalpaul said:

You wire up the pressure switch to the input of the delay timer, so when the pressure switch closes, it opens up the relay and starts the timer. Then after the timer expires, it will close the relay switch. Just wire your "call for heat" thermostat line in series with this relay switch so that the timer relay makes it as if your thermostat was satisfied. Then the damper will close and everything.

ethicalpaul,
I think I am going to get this Dwyer A3150 (up to ~5.5 PSI) Photohelic Gauge/Switch (so I can see the pressure and switch setpoints on the same device and can get it for $30 on ebay) and pair it with that relay timer you linked to on Amazon (the single SPDT version).

Here is the relay timer schematic:


Does this wiring diagram look correct?


If so, the last thing I need to figure is how to mount the relay timer.

Thanks for all your help!

ethicalpaul

I didn't hook mine into the thermostat like that. The only thing I had hooked into the thermostat was the relay timer (the common and NC connections I put in series with the thermostat)

I used a separate power supply for the timer relay, not the boiler power. I think I went with 12v. Different relays have different power requirements.

I used a DIN rail power supply to go with the DIN rail relay. Here is the stuff: https://www.amazon.com/s?k=din+mount+power+supply&amp;crid=2AR7E347PGB6Y&amp;sprefix=din+mount+power+supply,aps,104&amp;ref=nb_sb_noss_1

The photohelic is cool, but it does require its own power which I didn't care for.

I think that 5.5psi is a much higher range than you would want. The photohelic comes in ranges like 0-35 inches of water column which is much more appropriate I think.

PMJ

This solution is surely much better than the straight on/off result of the standard pressure based control. Those doing this have arrived at the rather obvious conclusion that a system pressurized to a measurable amount is already so full of steam that they know the boiler doesn't need to run again for a while, but unfortunately their standard control doesn't. It surely is a big improvement, and it is an easy way to eliminate the worry about a boiler being "too big".

But as food for thought look at the wiring diagram and consider for a moment what if the pressure switch was a remote temperature switch instead providing a signal when steam had reached the last radiator in the system to get steam. If the timer were a delay off type it could then be used to set an amount of partial system fill closer to what is actually needed to heat ongoing, which in well balanced systems is well short of what will generate any pressure. Then, when the temp switch opened again the switch will reset and if the call is still in progress you would get another firing, and refill to the same (no pressure) amount.

I have found that a second adjustable timer with an additional hold past when the temperature switch opens is very useful to provide additional control of the spread between firings. The pressure based timer can be extended as long as you want obviously, but I prefer never to let my radiators get so full and hot as would happen with pressure in the first place. The most even heat comes from well balanced systems that never show any pressure. Using an actual temperature sensor in the field also allows the actual conditions and rate of condensation to affect the spacing of the firings - some actual real time adjustment in the control.

When you do very much of this a simple PLC platform makes it all a lot easier to try things. Timers, combinations, order of operation, even schedules become just keystrokes on a computer. Though they run many years a backup on hand for only $100 isn't crazy. Or, one simple bypass switch around the whole thing can take you right back to where you were with the standard control in a pinch. That switch should be installed anyway.

swassbac

ethicalpaul said:

I didn't hook mine into the thermostat like that. The only thing I had hooked into the thermostat was the relay timer (the common and NC connections I put in series with the thermostat)

I used a separate power supply for the timer relay, not the boiler power. I think I went with 12v. Different relays have different power requirements.

I used a DIN rail power supply to go with the DIN rail relay. Here is the stuff: https://www.amazon.com/s?k=din+mount+power+supply&amp;crid=2AR7E347PGB6Y&amp;sprefix=din+mount+power+supply,aps,104&amp;ref=nb_sb_noss_1

The photohelic is cool, but it does require its own power which I didn't care for.

I think that 5.5psi is a much higher range than you would want. The photohelic comes in ranges like 0-35 inches of water column which is much more appropriate I think.

I didn't realize the photohelic requires power but since I need power for the relay, I don't think that is a big deal. After looking at it, they both can use line voltage so I updated the diagram to pull from that which I think is cleaner and cheaper than adding a separate transformer.

The reason I wanted a gauge to go to 5+ psi is that I am still getting a cutoff even with the differential maxed. Although I don't need anything more than 1.5 or so psi for the switch, I am also going to use the gauge to help me debug how things look as I turn on more radiators, add more venting, etc.

I didn't realize the relay just mounts on a DIN rail - I have plenty of rails hanging around. Thanks again.

swassbac

PMJ said:

But as food for thought look at the wiring diagram and consider for a moment what if the pressure switch was a remote temperature switch instead providing a signal when steam had reached the last radiator in the system to get steam.

I love the idea of a remote temp sensors and it would be easy for me to add since I have miles of CAT6 run through this place so I could pull off a pair for a sensor run back to my home automation controller or I could find a wireless version.

For wireless, I use switchbot IFTTT temp sensors (although I'd use something different for radiator sensing) around my home now and am 100% behind programmable control and am doing that today for a lot of other things (like switching my HVAC system from boiler to furnace in shoulder temps). Another example is my computer room in the basement gets warm when the boiler is running all day (little by little I am adding more insulation and closing up holes in the old ductwork but that is a long process...), so I have a ventilation fan that I kick on and dumps in cold air from outside when the boiler is running and temperatures in that room gets above 75 degrees.

Thanks - you have given me more to ponder.