IFM transducer as operating limit

Lard

I finally had time to install the IFM transducer/controller unit and a delay-on timer as an operating limit.  I have it programmed normally closed hysteresis—cut-out 1PSI, cut-in 0.2PSI and the timer set to 30 minutes. The timer simply breaks the thermostat call for heat, thus closing the makeup air dampers and killing the burner.  The two pressuretrols are unaffected by this change and remain in their original circuit as safeties.

So far, it is behaving quite well but will obviously need some tinkering. The graph is showing minutes of heat request and testing began on the third firing around 18:00.  Once 1psi was hit, the transducer 24vdc output went low, then at 0.2psi it went high, triggering the 24vdc timer which then closed its contacts for the 24vac thermostat call 30 minutes later, only firing the burner once the radiation has had time to release heat. Hopefully this tames the beast a bit!

acwagner

Very nice. I had to look up your older postings to get context on the system.

Does the 1psi system pressure correspond to full radiators or some other condition?

I would offer from my own experience doing something similar that you want to make sure that you keep the dwell time short enough so during "design day" conditions the radiators are still supplied with enough steam to meet full radiator demand.

ethicalpaul

I’m going to implement the same thing but with a Dwyer pressure switch at maybe 2 inches of water and maybe a 10 minute delay. 

It would take my system a long time to get to 1 psi but it does start to get a few inches of pressure once all the radiator vents close

Lard

Thanks for the insight

For context, this sensor is an IFM PN7007, -14.7 to 14.7 PSI range in 0.1 increments, fully programmable setpoints, debounce, etc. with a very accurate sensing element. IFM makes more sensitive units that can be used for ounces with the same options, but for this installation that was not needed.
I salvaged a bunch of Siemens Sirius 24v timers from some lightly-used machining coolant chillers we scrapped at work that can be set from 30ms to 300 hours.
The boiler is a W-M 1180 with a Gordon-Piatt gas gun, comically oversized, piped wrong, and generally abused the past ten years. This feeds a sizable single-pipe system in a church with a few two-pipe, air vent setups on the largest radiation.

I timed out how long it took to (mostly) fill the radiators from a 62-degree to 65-degree bump and have tried the half-hour dwell manually on a 10-degree day last year. The pressure rides around 0.1 during main venting, then to 0.3-0.5 during radiator venting, then rapidly spikes once the radiation mostly fills up.  There is 1700 surplus EDR so short cycling then begins in earnest. 

 I have a gaggle of temp controllers, so one may get added to the radiation and can always do a countdown burn setup as used by @PMJ rather than using pressure. I need to get a box and DIN rail to mount the timer and 0.5A breaker currently in use so I plan to leave some extra space for future logic.

ethicalpaul

Thanks for all that detail, sounds great.

I do like a pressure-based trigger rather than a straight timer, because the pressure-based one removes a lot of variables for you.

Like, how warm are the radiators currently? How warm is the area the radiators are in? How warm is the boiler? Its piping?

All those questions are removed for a pressure-based trigger, but with a straight timer, how does the timer know if the system had to come back from a cold start? It doesn't.

Lard

It did well on this morning’s request as the building begins the slow warmup for Sunday (64 today, 65 tomorrow morning, 66 Saturday night, 68 5am Sunday). One obvious change is that the overshoot is gone and it runs shorter cycles more often (more even heat instead of big swings). 

Of bigger concern, there is a trend of increased water consumption I noticed when looking at the burn time meter (the water meter has the same interface). I noticed quite a bit of gurgling/spitting last night, so it may just be from wet steam as the 8-way degunks things in combination with the terrible piping job. The pH has definitely crept up the past few weeks. I blew out 20 gallons of crud from the mud leg last night, the pH was 10.3 (still high) this morning and the sample was quite turbid. Probably time to do the planned dump, wand, and recharge. 

 I ran a camera through the collector box over all 11 sections (Through the rear flue cover) this morning and saw nothing of concern and all is dry below. The returns are all OK too. Fingers crossed....

acwagner

I agree using pressure as a trigger is superior to using only a timer. The only time pressure becomes a problem is if the water line in the boiler easily becomes unsteady and leads to false pressure readings. So you probably need some buffer on the pressure trigger settings.

The increased water usage is strange, but, as you said, it may be coincidental to the new controls. The only thing I could think of is with short burns and more even heat, areas of the system that maybe didn't get as much steam before now get more. All tiny leaks add up over time.