PMJ plc system

Sure.

Inputs are remote make/break temp sensor on remote radiator feed pipe, analog pressure sensor on boiler header, outdoor temp sensor. Outputs gas valve, single remote solenoid vent.

On call for heat boiler runs continuously until a make on the remote temp sensor AND pressure sensor shows all system vacuum is gone which then starts a timer whose preset is adjusted by the outdoor temperature. That timer is about 2 minutes in moderate weather and 5 minutes + in single digits. So no matter how long it has been since the boiler last ran, it will run until the same approximately a 1/3-1/2 radiator fill is achieved. After that, if a call stays in progress the boiler waits until the remote temp sensor opens again PLUS a set timer of 4 minutes that I haven't changed in years. At that point the boiler will fire again with the stopping point controlled the same as above.The vent opens during the burn as soon as the pressure sensor shows any positive pressure and lets leaked in air out for what is about the last few minutes of the burn depending. Cycling will continue this way as long as the call is still active. Calls get longer and longer as demand increases. Vacuum increases as demand increases.

I can attach charts but in mild weather burns will be 6-7 minutes separated by waits of 20 minutes and calls will be satisfied in a burn or two. As demand increases - say single digits - vacuum and automatic timer adjustments will extend the burns to 12-13 minutes and waits will be18 minutes or so. Burns per hour always close to 2. No two burns/waits are exactly the same.

Recently at single digits outside I looked at a 12 hour chart that showed 22 burns and 4 tstat satisfactions. The tstat was satisfied a total of 66 minutes in 12 hours never for more than 20 minutes and the system was calling for heat all the rest of the time. Radiator condition 1/2 -2/3 full and very constant - tough to tell that they were changing at all. I don't know exactly what the remote temp switch trip point is but guessing about 180F. This is exactly the performance I want where the occupants really have no idea anything is happening.

Hope this is what you were looking for. Happy to share any of it.

For the record I studied the Ecosteam approach along the way and even bought surplus equipment from MarkS.

It has always been on the feed pipe. My description above isn't quite accurate. The fill level isn't always exactly the same. By having it just before the radiator the timer adjustment does vary the fill level. The important thing is that the boiler always does a straight run to the point radiators start filling no matter what. We all know that the time required for that varies a lot depending on off time especially in mild weather and I wanted to eliminate any possibility of lost time for that reheat.

@PMJ My present curiosity is the compound pressure transducer used to measure the system pressure. Not finding one in the range I would expect for best performance.

Any custom interfacing to match the pressure transducer's range to the PLC's A to D input range & resolution ?

is this the boiler with the jbweld at the top of a section or was that someone else's 1950's bryant?

@ChrisJ , Attached is a chart from today when it was 35 degrees. The call was satisfied 12 times or basically once and hour. The waits of around 30 minutes are when the tstat had been satisfied and for about 15 minutes each time. Following these longer satisfied waits the boiler fired and did a full burn of 8 minutes or so followed by normal 17 minute waits with the call still in progress. Notice then that several times the boiler fired for a second time in the same call but that the call was satisfied very early during the second burn. The red burn line will go flat either when steam reaches the remote radiator or the the burn stops because the call was satisfied. If the burn was only 2.5 minutes no new steam had yet reached the radiators. The reason I am pointing this out is that at those times then the calls were satisfied some 20 minutes after the boiler had been off. That is because in a vacuum system a lot of steam is still in the mains when the boiler goes off and still keeps travelling into the radiators. So all that time the temp in the room is still rising slowly even though the boiler had been off the whole time. This is the same phenomenon that everyone accepts as valid logic as a coal fire burns down but don't accept it when the fire goes out suddenly. Actually the two situations are very much the same. And when you consider it happening many times in a single day I think it adds up to more total benefit than one time per day with a coal fire. The plain fact is that a lot of steam that you already produced actually gets delivered to the radiators that never would be without the vacuum.

i am sure there is a thread here with 800 comments that explains this, but you have a 1 pipe system, right?

what keeps the radiator vents from pulling in air when it is under vacuum? do they seal with enough force to not open under a slight vacuum?

other than that you are doing what is difficult to do, making an electric check valve with a very low cracking force. I bet @ChrisJ could make such a check valve. think large area and relatively light valve/ball/flapper so the ounce per in^2 or so pressing on it develops a fair bit of force over that area.

There's one small joker in the deck… the mass of the boiler and its heat capacity. In the old coal fired — or earlier oil fired boilers, such as Cedric's predecessor — the mass of the boiler was… large. To put it mildly. Modern boilers — even a commercial 80 series Weil-McClain such as Cedric — are a lot smaller and a lot lighter.

Once the fire is shut off in an oil boiler (the situation is more complex in a coal boiler, as the fire does not "shut off" abruptly) the only heat available to evaporate water and create steam — at any pressure — is the heat stored in the mass of the boiler (unless you lower the pressure to a point where heat can flow from the surrounding space into the boiler and thence into vaporizing the water).

The specific heat of iron is about 0.12 BTU/lb.F.. Thus if you have a 500 pound boiler with a mean material temperature of 250 F you can extract about 65,000 BTU from it. About a third of that will be extracted by steaming after the burner shuts off but before the system pressure drops to atmospheric, regardless of the control strategy.

In the case of a system which does not drop into a vacuum, the remaining heat is lost to the surrounding space if the boiler is allowed to continue cooling. A similar amount of heat is required to raise the boiler to the point where it will start to steam from a cold start. Depending on how one defines "efficiency" in a heating system — a very slippery concept — that may be seen as loss and a reduction in efficiency. In a system which is sealed that heat appears in the target space instead.

Don't get too hung up on that it's just the residual heat in the boiler. Most of the steam that keeps moving to the rads is already in the mains when the boiler goes off. Keeping that moving is the big thing. Open vented air fills the radiators not more steam from the mains. This is where the big difference is. Much more steam actually gets to the radiators, and much of that occurring with the boiler off.

It's been a thing here for a while that this must only be about boiler residual heat. It is really about never ending flow and all the steam that is already in the mains when the flame goes out. Radiators stay a lot warmer a lot longer because the steam stays flowing that doesn't open vented. I showed flir photos of this a while back. The benefit is cumulative cycle after cycle.

With system pressures like @PMJ documented, the boiler iron and all the water in the boiler has to drop below 200 degrees Fahrenheit before the steam flow stops completely and the steam flow starts at a lower temperature than your typical boilers. So I can see the radiators maintaining a more uniform temperature enhancing comfort. I'd like to see this graph with the boiler water temperature also. Maybe with this cycle rate shown it never truly stops steaming.

Finally someone is giving this chart some real thought. When new burns start you can see that even 18 minutes after the boiler has been off steam is still condensing and dropping the pressure at a rate not so different than it was when the boiler first went off. So there is still significant steam coming from somewhere. Where is it condensing? Mostly in the radiators. Yes it is increasingly less dense steam and yes the latent heat it is giving up is less, but not that much. Besides, what this really needs to be compared to is if those 18 minutes were spent filling the radiators (and mains) with air instead. The result isn't close.

I'm adding new steam for 12 minutes every 30 minutes and in the living space it is very difficult to tell anything is happening at all because nothing is changing. Radiators are always about the same.

Seems to me pretty obvious that if there is flow there is pressure drop so there is an A dimension. It is also clear that it is quite small. My transducers confirm this, though I have never felt the need to increase the resolution to see it more precisely, or even spend lots of time on calibration. The reading is very close to the dial vacuum gage on the header and I did switch the transducers once to see if the difference remained the same which it did. But then I already knew the pressure in the dry return remains lower always just by feeling radiator feed pipes.

But while the subject is up, the more important thing about pressure differences is actually the unmeasurable ones radiator to radiator due to sun, wind etc. which causes different condensation rates on different sides of the house and upstairs vs downstairs. An amazing amount of balancing occurs because of this that again does not if you fill with air. I admit, I would have said the improvement I have seen in balance was not possible until I experienced it myself.

Nothing occurs to me that scale changes the physics, but that doesn't prove there isn't something. I'm open to learning what those are.

My curiosity purely from a controls perspective, what brand and model of PLC are you using?