Time delay for 1 pipe steam

Dooverdixon

Good evening,

I think im ready to try to use a timer based method to control my oversized boiler and help minimize the cycling on pressure. I know that @PMJ has put a lot of time and effort into this control option'; it would be great if he could weigh in!

My boiler is oversized by about 50%. I know its generating too much steam too quickly because the rads are always whistling. I've added a bunch of main venting as well as a vaporstat set to cut out at 0.5 psi and back in right before zero. Once its up to temp and pressure it cycles quite a bit on pressure. The off cycle is only long enough for the system to depressurize (i dont think the rads are taking more steam). I feel like it would be beneficial to my system to keep it from firing back back up for 5 or 10 mins after it cycles off on pressure.

Any suggestions on the best device for this task (adjustable would be preferable) and how to wire it up to do the desired task?

Thank you!

nicholas bonham-carter

You should probably confirm that the vaporstat is cutting out the boiler, and not some other safety device.
Is your main venting capacious enough to let the air out at less than 2 ounces?
Are you using setbacks?
Can you put on a two-stage gas valve?—NBC

SteamCrazy

I'm Not sure but isn't that cut-in & cut-out settings to low??? If not can someone explain why it wouldn't be. I thought cut-in should never be less then .5 psi 

Jamie Hall

SteamCrazy said:

I'm Not sure but isn't that cut-in & cut-out settings to low??? If not can someone explain why it wouldn't be. I thought cut-in should never be less then .5 psi 

No, with a vapourstat the cutin can be much lower. Just not less than zero, of course.

The pressure drop you are seeing, @Dooverdixon , is from the steam condensing., and it will be remarkably quick.

My other question is this: have you confirmed the venting capacity? It's not guess work. You must have a low pressure gauge. On a cool start, the pressure should rise very slightly as steam is being produced, but then should level off at perhaps a few ounces until all the radiators are satisfied. Then it should rise again, at which point your vapourstat should shut off the boiler. If you do not have that nearly constant plateau, you do not have adequate main venting.

@PMJ has all the answers on timers, and I'm sure he'll tell you what to do.

Dooverdixon

nicholas bonham-carter said:

You should probably confirm that the vaporstat is cutting out the boiler, and not some other safety device.
Is your main venting capacious enough to let the air out at less than 2 ounces?
Are you using setbacks?
Can you put on a two-stage gas valve?—NBC

I'm pretty confident that the vapor stat is cutting off the boiler, its quite predictable to watch gauge and happens at exactly the same pressures.

I've done the math on the length of pipe (35 and 40 ft of 3") and think im pretty close on main venting. I have 1 gordon #2 and 1 hoffman 40 on each leg. I'll probably buy one more big gordon and slap it on just to be safe.

I keep the house 1 degree colder at night.

Not sure 2 stage gas valve. Its an older dukirk model boiler, can this sort of thing be added retroactively?

@Jamie Hall

My other question is this: have you confirmed the venting capacity? It's not guess work. You must have a low pressure gauge. On a cool start, the pressure should rise very slightly as steam is being produced, but then should level off at perhaps a few ounces until all the radiators are satisfied. Then it should rise again, at which point your vapourstat should shut off the boiler. If you do not have that nearly constant plateau, you do not have adequate main venting.

What you are describing is EXACTLY how my system work, except as soon as the first time the vaporstat kills the system on pressure, it starts cycling on pressure for quite some time until thermostat is satisfied. These cycles are usually 30 seconds off and 45 or so seconds on.

Maybe this is acceptable? but it seems more efficient to make the boiler stay off for 5 minutes or so after the vaporstat kills the system to dissipate more heat and steam given that my huge boiler can make more so quickly??

Jamie Hall

Let us just say that there are differences of opinion on the matter of time delay on refiring. My own opinion is that the behaviour you are seeing is quite acceptable -- though it would be nice if the boiler could be downfired some (hence the inquiry about a two stage gas valve) -- and has the benefit -- to my mind -- that the boiler never cools below steaming level, and thus does not need to be heated back up. However, others differ, and I'm sure they will tell you exactly what to do.

PMJ

The thing is, the goal is really to put steam into the system at the same rate as is needed to satisfy the current demand, which is dramatically different from day to day. The end of the plateau which @Jamie Hall quite accurately describes occurs when everything is already full of steam. The pressure rises from there at which point a pressure device cuts off the supply of steam. The problem with that is by that point you are already putting heat into the rooms at well past the rate of the demand. The radiators are already way fuller than they need to be for the conditions. It is a roller coaster of heat that doesn't need to be so.

It is very true that the vast majority of calls can be satisfied by a well sized boiler pushing steam into a well balanced system while still in the plateau and at very low (ounces) of pressure. But as the boiler gets more and more oversized, and there are many out there, satisfaction does not occur while still in the plateau and several bounces off the pressure device occur before satisfaction. This situation gets even worse in setback recoveries unless of course you just give them up which is the usual advice here.

My point is simply that using a timer to space burns totaling a design day burn rate per hour will eliminate any need to ever fill the system all the way up and ever pass the end of the plateau...no matter what size the boiler is. All that angst just goes away. The installation of a delay off/ delay on timer where both segments are adjustable allows the user to go all the way from where the system is now with no effect to a firing cycle per hour rate and max hourly burn rate of his choosing simply twisting two knobs.

This is the simplest level of this kind of control. It requires a reasonably well balanced system to begin with. Systems which currently rely on pressure to push steam to some places will not be happy with this as those last areas which currently do not get steam until pressure arrives may not get it at all. All radiators need to get steam easily at plateau pressures and approximately at the same time.

@Dooverdixon, if this sounds like you then I am happy to help. @Jamie Hall accuses me of having all the answers. I don't know that anyone has them all and I surely don't claim to. I do have some.

Dooverdixon

@PMJ Interesting. I was under the impression that there was a way to use a delay to tell the system "ok, you have started to cycle on pressure, take a 10 minute break before starting back up." Your idea sounds different than that, but i'm interested. I will say that my system pretty well balanced. All the rads get steam at a consistent rate and none require pressure to make it happen (if anything they all get too much pressure and whistle, which is what im ultimately trying to fix). This is why i have the vaporstat set to kick off at 0.5 psi. Anything past this level just gives more loud whistling and not much additional heat.

Can you give me more info about your timer option? For what its worth i just recently upgraded to a ecobee (renovators lost my honeywell). It doenst allow CPH, but i have it set to have a 10 min minimum run time.

@Jamie Hall Thank you for your comment as well. lots of input and options here. Just out of curiosity how big of a deal is the retrofit for a 2 stage gas valve. Does this require a combustion analysis after retrofit?

Jamie Hall

On the two stage burner -- it depends. Some boilers can be retrofitted with them, some can't -- and I'm not qualified to say. Hopefully someone who is will chime in... or you could message @Tim McElwain , who surely will know. The retrofit would require a second vapourstat, to tell the burner when to stage. And yes indeed, a combustion analysis would certainly be required -- for both firing stages.

PMJ

Dooverdixon said:

@PMJ Interesting. I was under the impression that there was a way to use a delay to tell the system "ok, you have started to cycle on pressure, take a 10 minute break before starting back up." Your idea sounds different than that, but i'm interested. I will say that my system pretty well balanced. All the rads get steam at a consistent rate and none require pressure to make it happen (if anything they all get too much pressure and whistle, which is what im ultimately trying to fix). This is why i have the vaporstat set to kick off at 0.5 psi. Anything past this level just gives more loud whistling and not much additional heat.

Can you give me more info about your timer option? For what its worth i just recently upgraded to a ecobee (renovators lost my honeywell). It doenst allow CPH, but i have it set to have a 10 min minimum run time.

@Jamie Hall Thank you for your comment as well. lots of input and options here. Just out of curiosity how big of a deal is the retrofit for a 2 stage gas valve. Does this require a combustion analysis after retrofit?

@Dooverdixon , you can do what you say. It is slightly more complicated wiring because it involves the vaportstat separately whereas what I am suggesting is just in series in the hot call wire from the Tsat to all the boiler controls. Secondly, I just don't see the point to ever allow the system to go to the pressure in the first place. It isn't needed for heating and just overfills everything.

But I'm happy to approach any way you wish. There is more than one way to do this.

He is a link to a Macromatic timer on/off adjustable timer.
https://www.macromatic.com/literature/catalog/time-delay-relays/?#page=22 I think you would want the TR-54128-16 or-17. They are about $75. It can be done for even less though.

Dooverdixon

@PMJ For 75 bucks I'm willing to give either way a shot and see if it helps.  I like your idea because If successful it will probably help solve my loud rad vent issue as well???

 Can you give me a rundown of how your idea works and how to set it up?  I'll order the device asap.  

PMJ

Dooverdixon said:

@PMJ For 75 bucks I'm willing to give either way a shot and see if it helps.  I like your idea because If successful it will probably help solve my loud rad vent issue as well???

 Can you give me a rundown of how your idea works and how to set it up?  I'll order the device asap.  

First, do I understand correctly that your heating is pretty even and it is toward the end of cycles when radiators are quite full and pressure starts building that you have the whistling you complain about? Your open vented system does have a lot of air to remove every cycle no matter what. An oversized boiler pushes it out faster and necessarily will make more noise. Is the worst of it at the pressure end of the cycle just before the vaporstat cuts out?

What I propose is a timer which simply prevents any single burn long enough to ever get to that pressure point and yet provides enough total burn time per hour to heat on design day.

Estimate for me what total actual burn time per hour you think your boiler would run on the coldest days you get. For instance my boiler doesn't need to run more than 30 minutes per hour at -20F outside to maintain heat. The start off point will be to design a burn/wait combination that assures that this minimum burn time per hour is covered so that you will still be heated on very cold days without touching anything. It is easy to overshoot the burn time some and back down from there with the two knobs. Once this thing is installed it is easy to dial in whatever works best for you anywhere in the range from not enough heat to right back to what you have now.

Fizz

I have single pipe system which would shut on pressure of 11/2 lbs, and overshoot t-stat; I switched from old merc t-stat to emerson non-programmable 70 seriese, removed red clip and now pressure in system never gets above 2 oz. Once t-stat is satisfied(set at 71), it stays at 71 and cycles 2-3 per hr. Both problems solved. Guess I was lucky.

Dooverdixon

@PMJ

To answer your first question, yes. the heat is pretty even with the exception of the top floor which has just been insulated an now runs pretty hot (maybe 8 degrees more than the rest of the house). Using different sized vents has not really helped because the rads are simply too big now ( they cannot be removed). Im thinking of adding a TRV to the biggest rad on that floor, but i will do this later.

The whistling definitely gets substantially worse at the end of the pressure cycle (although is starts as the system begins to build pressure (after "plateau" is obtained).

I just purchased the timer you recommended. I'll have to wait until there's actually some cold days to give you an accurate guess of how long the requires burn time is. I have Ecobee data from a date that was cold, but it just gives me "call for heat" which lasted most of the night (4 hours). But the system would have been cycling on pressure during that time so this doesn't really help right? How did you determine this number?

PMJ

@Dooverdixon , your situation sounds very good for this.

If the arrival time of the steam from burner start at all the rads is similar - like within 1-2 minutes of each other you are good to go. Then we just start about limiting the burns such that pressure high enough to trip the vaporstat never happens.

It is not necessary to know very accurately the cold day total hourly run minutes. Approximating it just helps get an idea where we need to be on the cycles. But yes, on a cold day you would time the actual run minutes of the boiler during an hour with the burner actually on. Our cycles need to be set to exceed this cold day hourly burn time.

When you get this timer set up you will just begin with a warm start burn time that stops just short of when you build pressure and whistle now and then making the boiler wait longer than it does in the off mode of the short cycles you have now. We just start breaking the required burn time to heat into a few more pieces and spread things out a little thereby avoiding all the pressure. Just by twisting the knobs you can go right back to where you are now if you wish too.


Also, did you get a base for the plug in module? I forgot to mention that. Pretty sure you need the 11 pin base.