End of Burn shutdown control

[afblue]

So my system is up and running, a few stats on it are: Paxo 25 with OEM RK-2001UA controller. 830-850gal Unpressurized storage. Radiant heat manifold with individual actuators, Tekmar 356 Injection mixing outdoor reset. I am firing it now and the system is performing pretty much amazing, but I havent come up with a control scheme yet to tell the boiler to shut down when the burn cycle is over. I would like to be able to load it with wood at night and shut down when its burned its cycle into storage in the middle of the night. But I have waken most mornings to the blower still running when the fire burned out long before. Only a few random times the RK displaying "FUEL" and the blower is off, I think that fact that it has storage that it keeps circulating from throws off the logic in the RK and its not going to operate the way I wish I could. I read last year of some people using a exhaust probe but I cant find reference to it again. Or would another option be a timer like the older Garns, and just test how long the burn is and use a simple 120V timer switch?

 

[ewdudley]

Here's a couple ways to shut down the draft fan:

https://www.hearth.com/econtent/index.php/forums/viewthread/80962/

You can shut down just the draft fan or shut down the whole control if it's safe to turn off the boiler-to-storage circ at the same time as the draft fan.

 

[Hunderliggur]

I have the Paxo 40 with a similar issue. I have the circulator set to start at 170 and off at 165. When my storage is over 170 the circulator cannot shut off since the boiler sees >170. Add to that the boiler control and unreliable FUEL blower off. I know some people use twist timers (set for 6 hours which is 50% longer than a fuel load). I was thinking of that AND a safety circulator control. A temperature control on the output output of the boiler. If temp >195, power the circulator (even if the twist time is off). Means dual power leads to the circulator but I don't see that as a problem perse. The 80962 thread gives some good ideas.

Just ordered a couple of Kiln control PID with thermocouple from http://www.ebay.com/itm/Mini-Dual-D...ultDomain_0&hash=item1c1fcf34d0#ht_1527wt_905 at $38 each including shipping. One for fan&circulator; one for overtemp circulator on. We'll see how they work. 5A relay output is plenty for my circulator and fan.

 

[ewdudley]

I was thinking of that AND a safety circulator control. A temperature control on the output output of the boiler. If temp >195, power the circulator (even if the twist time is off). Means dual power leads to the circulator but I don't see that as a problem perse.

Exactly. I stayed away from the circulator part of the problem to keep things simple, and I was being a bit lazy.

Plus what you need to do depends on the situation. On my boiler I can shut everything off without worrying about it because I have thermo siphon to storage built in, but in other cases it would be better to have a fail-safe mechanism for keeping the circulator running if supply temperature is high, just as you describe.

Just ordered a couple of Kiln control PID ... One for fan&circulator; one for overtemp circulator on. We'll see how they work. 5A relay output is plenty for my circulator and fan.

It's only a $40 controller, so you can afford to be fairly cavalier, but the service life of relay contacts drops off exponentially as you approach and/or exceed the amperage rating, especially when switching inductive motor loads. At $13 apiece a couple RIB relays wouldn't cost very much to save wear on the controller relays.

--ewd

 

[jebatty]

it would be better to have a fail-safe mechanism for keeping the circulator running if supply temperature is high

Tarm deals with this in a simple way, use of an overheat aquastat to switch on a zone. Use an additional aquastat to switch on the circulator if supply temperature is high.

 

[stee6043]

I've been extremely pleased with my ultra simple timer setup. I bought a run-of-the-mill timer from Home Depot and simply inserted into the fan circuit like many others have done here. Set the timer for 4-5 hours for the last load of the night and presto....happy burning.

I do still have the circ issue you've identified. But I usually go down and throw the switch on my EKO manually in the morning before I go to work. Usually my tanks will be 175-180 top to bottom at this point so I don't feel too bad about letting the circ run for a few hours after the burn finished overnight.

 

[EffectaBoilerUser (USA)]

Glad to hear your Paxo system is up and running.

I used to have an EKO40 before purchasing my effecta lambda 35 and have also helped many EKO users with this same issue.

I'm assuming you have not changed the settings on the RK2001 U controller since you installed the Paxo.

If this is true than I believe a majority of your problem is that the "Fb" setting on the controller is set for too long of a time.

The Fb setting is the amount of time (in minutes) from the last rise in temperature of the boiler water until the fan shuts off.

I normally tell everyone to set the Fb setting to 35 minutes. Thus, with the Fb set to 35 minutes, once the controller has registered the final increase

in temperature (indicating that the wood fuel has all been consumed) the fan will shut off 35 minutes from this point.

This setting worked 95% of the time with my EKO40 boiler.

Brian

 

[ewdudley]

I'm assuming you have not changed the settings on the RK2001 U controller since you installed the Paxo.

If this is true than I believe a majority of your problem is that the "Fb" setting on the controller is set for too long of a time.

The Fb setting is the amount of time (in minutes) from the last rise in temperature of the boiler water until the fan shuts off.

I normally tell everyone to set the Fb setting to 35 minutes. Thus, with the Fb set to 35 minutes, once the controller has registered the final increase

in temperature (indicating that the wood fuel has all been consumed) the fan will shut off 35 minutes from this point.

Factory setting for Fb parameter is 30 minutes. If Fb had anything to do with the problem then lengthening the Fb time to 35 minutes would aggravate the situation.

The actual problem is that when the tanks are charged, the circ and the fan run until the RK2001UA senses that supply temperature is below the supply temperature setpoint minus hysteresis for Fb minutes, which could be many hours, assuming of course that the RK2001UA hasn't halted and caught fire itself in the meantime.

This is pointless controller logic because in this circumstance boiler supply temperature has no bearing on whether of not the fuel supply has been depleted. Flue or firebox temperature, however, can be correlated to the fact of ongoing combustion.

 

[rkusek]

I'm assuming you have not changed the settings on the RK2001 U controller since you installed the Paxo.

If this is true than I believe a majority of your problem is that the "Fb" setting on the controller is set for too long of a time.

The Fb setting is the amount of time (in minutes) from the last rise in temperature of the boiler water until the fan shuts off.

I normally tell everyone to set the Fb setting to 35 minutes. Thus, with the Fb set to 35 minutes, once the controller has registered the final increase

in temperature (indicating that the wood fuel has all been consumed) the fan will shut off 35 minutes from this point.

Factory setting for Fb parameter is 30 minutes. If Fb had anything to do with the problem then lengthening the Fb time to 35 minutes would aggravate the situation.

The actual problem is that when the tanks are charged, the circ and the fan run until the RK2001UA senses that supply temperature is below the supply temperature setpoint minus hysteresis for Fb minutes, which could be many hours, assuming of course that the RK2001UA hasn't halted and caught fire itself in the meantime.

This is pointless controller logic because in this circumstance boiler supply temperature has no bearing on whether of not the fuel supply has been depleted. Flue or firebox temperature, however, can be correlated to the fact of ongoing combustion.

I actually had my FB set much higher last year 60 or 90 minutes I believe when running without storage. I came upon a couple instances where whole firebox was full of charred wood and wood gas because the EKO hit the FUEL shutoff after 30 minutes probably due to bridging (had a few big pieces). That is when I changed the pump setting to not come on until 165 and shut off at 160. Quite a bit of huffing and puffing to work off that load of charred wood. The higher pump setting made a night & day difference on the entire operation. I could probably go back to the 30 minute setting now.

I guess I will have to experiment with the storage this year. I still need to buy some kind of differential controller that will power the storage charge circ (ie. shut off when tank return is higher then boiler output temp). I have a P/S loop so my plan is to only run the storage draw circ when the boiler circ is OFF and an aquastat on the primary loop asks for hot water. Without the differential controller I can see where the boiler would never shut off and basically cool the storage. I always wanted a flue temp measurement anyway. Looks like that controller on Ebay may be he ticket.

 

[jebatty]

The relatively "easy" shutdown control is at actual end of burn vs shutdown caused by an episode of bridging or idling. I am not aware after 4 full seasons of burning with the Tarm that it has ever shutdown prematurely as might be cause by a bridging or typical idling episode, which suggests that the Tarm approach of a shutdown sensor in the smokebox set at 90-100C or so actually works as intended. Other locations may work also. It seems to me that a flue location can work but also can be problematical depending on siting of the sensor, especially in non-end of burn potential shutdown situations, because a flue has the possibility of being cooled by ambient conditions not related to wood yet to burn.

Regardless of a shutdown control, I think it is important not to overload the boiler for the purpose of periodic re-firing after idling to sustain long heat output. The better procedure would be to only load wood that is likely to be burned in a continuous burn process. That requires sufficient demand and/or sufficient storage to absorb the btu's produced by the burn. The result also is increased efficiency and cleaner burning.

 

[Duetech]

As this is an "end of burn shut down control" thread I was wondering if maybe a shut down probe/sensor could be more accurately (temperature responsive) placed in the secondary airways close enough to the refractory but not too close and far enough away from the direct input of the incoming entry air to sense the cooling airways of or near the refractory. Obviously there would have to be the "bypass" concerns for start up but I think the place the gasifier is going to exhibit the most sudden temperature change that reliably reflects the boiler is out of fuel or the fire has died is in the secondary airways or secondary refractory. Units that are indoors should be more readily regulated in a reliable manner while some of the newer OWB gassers might pose more of a challenge but I still think that each system will have a sweet spot that would give dependable shut down information and system component safety even if the outdoor units might be more radical. I don't think I have never heard of anyone trying to control boiler intake air based on secodary air channel temperatures. Any thoughts?

 

[steam man]

I would think you can use a timer for fan shutdown but also use something like a solar differential controller between the boiler and the storage. Have it shutdown when no extra heat is generated but have the controller set to cycle the circ in a high temp situation. I believe mine does that on my evacuated tube setup. I'll have to check it out and let you know.

Mike