PMJ plc system

ChrisJ

@PMJ

If possible would you be willing to refresh my memory on how your plc system is programmed? I tried it a few times but it was a good 14 years ago so maybe me memory is off.

ChrisJ

*12 years sorry.

PMJ

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.

Jamie Hall

I can see how your system would be reasonably applicable, @PMJ , in situations where the radiation is seriously oversized (not so much the boiler), which appears to be your situation. There is also the subjective benefit — which could be quite real — that the radiation will stay in a more or less steady state. This would be particularly true with newer, relatively low mass radiation, I would think, and could be very attractive to many homeowners.

Have you been able to make any measured assessment on the overall thermal efficiency (tank to structure — I'm not interested in boiler efficiency by combustion test)? I am a little concerned, perhaps without reason, by the relatively short boiler run times — but it is likely that I am influenced by my own system, which has a high mass, relatively high water volume commercial boiler which simply takes time to start producing any significantly warm vapuur, never mind any steam.