post-burn shut down systems?

[pybyr]

Hello all--

On my Econoburn 150, once it is turned on, the blower will continue to run until it is manually shut off. Similarly, at the end of a burn, while the "main" circulator from the boiler to the load will shut off when the boiler drops below about 150, the "near" circulator will come back on below 150, and remain running until the boiler is shut off.

I'd originally thought of using a temperature switch, placed in the flue, as I mention in this prior thread-
https://www.hearth.com/talk/threads/20728/
with a temporary bypass timer to actuate at the beginning of the burn to allow the boiler to get going

but I'm interested in other ideas, or suggestions on pros and cons of the temp-switch approach

What do other boiler makes, or other folks' installations use to accomplish this function? I've heard mention of timers, but I don't yet have a good sense of the estimated times, which seem to vary a lot based on wood type and size, heat demand, and weather. And I am concerned about the effect on the boiler if the timer times out too early with a bed of coals in the firebox.

Some have mentioned O2 sensors, but I am assuming that those would be expensive and fiddly. I am looking for reliable and simple.

Looking forward to input from the collective Boiler Room brain...

Thanks!

 

[603doug]

I want to set up a similar switch, the fan comes on and only shuts down when up to temp would like to have it switch off say when the water dropped to 120 f. That way if the fire goes out during the day the fan will not keep eating up the "ole" electricity

 

[Piker]

pybyr,

I am questioning why your blower stays on until you manually shut it off. The mechanical aquastat that should be mounted on the supply side of the boiler should shut the blower off when the high limit is reached.

A timer with a relay to turn on your near boiler circ and turn your boiler off is the ticket. Keeping that near boiler circ running will prevent steam from being produced if you short change the timer and still have a fire in the box. And... if plumbed properly, will not affect flow through your storage tanks as the near boiler circ will only be running water in and out of the boiler. Pics on my website if you are interested. Check the products page. Pretty simple build for the do-it-yourselfer with some electrial experience.

I don't have any of my customers using this method yet, but I have been testing it extensively here at Hillside, and plan on putting it out there this season for some folks. It also works well for people who don't want to use thermal storage, don't want to oversize their boiler, and are willing to let their fossil fuel take over when they can't keep a fire going at night. They can run the wood boiler for a set period of time (granted this is kind of a guessing game) and then shut it down leaving a coal bed while the fossil boiler takes over. When they go to start the boiler again, there's a coal bed waiting to just throw a few logs in and have at it.

It's probably not for everyone, but it does work, and it's relatively inexpensive. Compared to a fully automatic system that is.

cheers

 

[Piker]

I am sorry... "post burn shut down"

totally wasn't paying attention... I understand your blower issue now totally...
sheesh... need to read everything before opening mouth.

cheers

 

[Nofossil]

I do it with a computer..... wait, that sounds a little twisted. Let me try again......

My controller manges that function, but anything you can do with a computer can be done with relays.

How about this: Use a timer relay that's 'set' by an aquastat in the boiler outlet, and stays set for 45 minutes or so after the aquastat goes cold. Add a manual pushbutton to set it when you start the boiler.

 

[mtnmizer]

My EBW 150 is plumbed parallel to
a lp boiler and I've noticed that when the load has burned out, the blower
will continue to run on high because the water temp will not fall low enough
to shut off. This is because the LP boiler will feed the wood boiler. When
I have to to manually shut it off and closed
one of the iso valves on the main circ. pump. Not an ideal situation.

I'm thinking maybe a spring check valve on the return line might stop the
LP boiler from feeding the wood boiler or maybe a zone valve? Or take out
the parallel hookup and go to closely spaced tee's? I'm thinking that the
primary loop is making a low pressure signal at the WB return and starting
the flow..

The main blower can be controled by the aquastat lead either as Piker states via
a timer which looks easy enough or some other sensor.

On the other hand Ol man winter gave a shot of zeroish temps tonight and the EBW is humming
along nicely @175 degrees on a half a load of fir/pine chunks .

 

[pybyr]

I do it with a computer..... wait, that sounds a little twisted. Let me try again......

My controller manges that function, but anything you can do with a computer can be done with relays.

How about this: Use a timer relay that's 'set' by an aquastat in the boiler outlet, and stays set for 45 minutes or so after the aquastat goes cold. Add a manual pushbutton to set it when you start the boiler.

Thanks NoFo- I'll ponder that- although the boiler contains enough water that it seems to hold temp quite a while even after the fire is out.

That's why I was thinking of trying to track flue temp.

The NoFo control system must somehow track rate of change of water exit temp to detect when the fire has hit the fast downhill slide to out?

 

[pybyr]

I am sorry... "post burn shut down"

totally wasn't paying attention... I understand your blower issue now totally...
sheesh... need to read everything before opening mouth.

cheers

No need to apologize- and I find your idea of cutting the fan but keeping the "near" circ going to be an intriguing idea if I ever decide to set the thing up to try to hold live coals between burns. Thank you for sharing the ideas.

The control side of these systems is both intriguing, and at moments, bewildering, because there are so many aspects one might track and control and cross-integrate for the most efficient and convenient operation, especially with storage.

 

[Piker]

I am sorry... "post burn shut down"

totally wasn't paying attention... I understand your blower issue now totally...
sheesh... need to read everything before opening mouth.

cheers

No need to apologize- and I find your idea of cutting the fan but keeping the "near" circ going to be an intriguing idea if I ever decide to set the thing up to try to hold live coals between burns. Thank you for sharing the ideas.

The control side of these systems is both intriguing, and at moments, bewildering, because there are so many aspects one might track and control and cross-integrate for the most efficient and convenient operation, especially with storage.

Indeed... when it comes to controls, you can spend just about as much as you can imagine. The more automated, the more expensive. It seems like the timer with near boiler circ control is easy enough for folks to understand how to use, and low cost enough to be fairly practical... especially on the Econoburn. It's not quite as adaptable to systems that use return line tempering with a valve unless you plumb another loop with a boiler circ on it... at which point the price goes up a bit.

cheers

 

[flyingcow]

Stack temp, I think you're on to something. That's how the unit I have is set up. In a another topic it was noted that with storage, the fan would shut off at 90c, without it was set at 60c.

 

[Nofossil]

Fan and circulator control are and should be separate issues. You want the fan to shut down when there's no more fuel to be burned, and you want the circulator to run when there's heat to be moved to some useful destination. The two don't always coincide.

I use flue temp to detect when a fire has started, combustion chamber to detect when the fire is out, and outlet water temp to manage the circulator. The reason I don't use flue temp for fire-out detection is that it drops pretty low before the fire is really out.

Here's a 'death of a fire' graph:

At the left end, we're already down to coals. Secondary combustion is down to around 700 degrees, and flue is around 350. Over the next hour or so, the coals settle and burn out. Around 3:00 the fan shuts off. The circulator continues to run intermittently, and the recirc valve opens to try and get the water hot enough to heat storage. the 'tank zone valve' signal shows when heat is going to storage.

Eventually, the fire is done and there's no more useful heat. During this die-out phase, I'll circulate water down to 130 degrees - I figure the fire is out so there's no real condensation risk.

The glitch at around 4:30 is missing data - the database goes down for nightly backup.

Bottom line - flue temp drops so slowly towards the end of a fire that it's tough to figure out when the fire is really done.

 

[Piker]

Fan and circulator control are and should be separate issues. You want the fan to shut down when there's no more fuel to be burned, and you want the circulator to run when there's heat to be moved to some useful destination. The two don't always coincide.

That is true most of the time. The circ that I am talking about turning on and off doesn't move heat anywhere... it's purpose is the same as a tempering valve that most of the offshore gassers use. It only moves water through the boiler, and not the rest of the system. The idea is actually to short change the timer a bit to leave a coal bed in the boiler for the next firing. Not many people want to start their boilers from scratch once, let alone twice per day. Leaving a coal bed without worry of producing steam is the key.

It is convievable that you could use a stack temp sensor inplace of the timer. Just adjust the stack temp sensor to a point where you know there would still be a generous coal bed left in the firbox, and as soon as the sensor shuts the boiler down, the relay would kick the circ on. This would actually take the guess work out of how long to set the timer, though it's going to cost a little more money.

I think I would like to build one of my timer units with a stack sensor in place of the timer for testing... I think it's a viable alternative... anyone have a favorite stack sensor they recommend?

cheers

 

[Nofossil]

I think I would like to build one of my timer units with a stack sensor in place of the timer for testing... I think it's a viable alternative... anyone have a favorite stack sensor they recommend?

cheers

See my post above about the difficulty of picking a flue temp that represents 'out'. For flue temp, I think the only viable choice is a jacketed thermocouple. They're not too expensive, but they require additional electronics to create a usable signal. There are some really cheap PID controllers on eBay that take thermocouples as a direct input.

 

[Piker]

I think I would like to build one of my timer units with a stack sensor in place of the timer for testing... I think it's a viable alternative... anyone have a favorite stack sensor they recommend?

cheers

See my post above about the difficulty of picking a flue temp that represents 'out'. For flue temp, I think the only viable choice is a jacketed thermocouple. They're not too expensive, but they require additional electronics to create a usable signal. There are some really cheap PID controllers on eBay that take thermocouples as a direct input.

I don't have alot of experience in tracking stack temps... looking at your graph now I see what what you mean about figuring what temps represent 'out.' I don't understand what the big valleys are from in the stack temp line. It seems like it would be easier to detect the point at which there is only a coal bed left but not really any gasification going on... but looking at your graph, now I wonder.

Without modifying the boiler itself, I can't think of a good way to measure combustion chamber temps. There would have to be a hole put in somwhere wouldn't there? How do you do it?

cheers

 

[Nofossil]

I don't have alot of experience in tracking stack temps... looking at your graph now I see what what you mean about figuring what temps represent 'out.' I don't understand what the big valleys are from in the stack temp line. It seems like it would be easier to detect the point at which there is only a coal bed left but not really any gasification going on... but looking at your graph, now I wonder.

The stack temp is the lowest line - multiply the scale value by 10 to get the actual temp. The line with te dips is the boiler inlet. Dips show a slug of incoming cold water when a zone calls for heat.

Without modifying the boiler itself, I can't think of a good way to measure combustion chamber temps. There would have to be a hole put in somwhere wouldn't there? How do you do it?

cheers

I drilled a 1/8" hole in the door flange. On the EKO, the flange protrudes from the water jacket about 3/4", so there's a place you can get through. I used a 1/8" diameter jacketed probe, and bent it so that it runs in along the wall of the secondary chamber. Here's a photo:

 

[Piker]

sorry... must be color blind

cheers

 

[pybyr]

NoFo- which variable is it that you use to shut the combustion blower down? Is it the secondary chamber temp that you're monitoring via thermocouple?? And do you then (after cutting the blower) continue to run a circulator so that hot spots don't develop in the boiler?

PS- and it's OT re this thread, but seeing your new refractory, I'd be interested in hearing how you arrived at it and what you find in terms of what it gives you over a "U" shape- (or in my case, a slightly sloped but rough-surfaced lower refractory that came with my Econoburn.

 

[Nofossil]

NoFo- which variable is it that you use to shut the combustion blower down? Is it the secondary chamber temp that you're monitoring via thermocouple?? And do you then (after cutting the blower) continue to run a circulator so that hot spots don't develop in the boiler?

PS- and it's OT re this thread, but seeing your new refractory, I'd be interested in hearing how you arrived at it and what you find in terms of what it gives you over a "U" shape- (or in my case, a slightly sloped but rough-surfaced lower refractory that came with my Econoburn.

I use secondary combustion temp to decide when to shut down the fan. I run the circulator as needed, and it will typically run many times after the fire is basically out. The few remaining coals and the refractory give up heat to the water jacket for quite some time.

The combustion labyrinth gives me about 50 degrees cooler stack temps and seems to give me cleaner / less sooty deposits in the lower chamber as well as quicker 'time-to-combustion'. Unfortunately, the labyrinth in the photo has been transformed partially into gravel by this time, so I'm running a simpler configuration - basically, remove the horizontal shelf and that's what I'm running now.

 

[jebatty]

Fan and circulator control are and should be separate issues. You want the fan to shut down when there’s no more fuel to be burned, and you want the circulator to run when there’s heat to be moved to some useful destination. The two don’t always coincide.

This has perplexed me for some time but I think, at least for the Tarm, I now have it solved satisfactorily. My setup has two circs, the first on the Tarm (Grundfos 15-58) controlled by a differential controller, measuring boiler output vs storage return. When boiler output is +16F over storage return, this circ comes "on." The second circ (Taco 007) is controlled by an aquastat on the boiler output and turns "on" at 180F with an 8F differential. This adds additional flow when boiler output is sufficient. The aquastat turns the 007 "off" at 172F boiler output.

My problem, which I previously handled with a timer to shut the system down, is caused by the Termovar. If post-burn boiler temp remains greater than +10F over storage return (example: boiler 160F and storage return less than 150F), the differential controller keeps the boiler circ "on" and the Termovar recirculates the boiler circ output (160F Termovar boiler return protection) so that it will run near endlessly because boiler temp will remain more than +10F over storage return. I would set the timer to shut down, say, after 8 hours of "burn" time.

The solution uses the unused lo-limit terminal on the Tarm controller. Months ago someone posted the following:

I wired a 110vac relay ... to #11 on the Tarm Strip, to the aquastat that controls the circulator. I played with the settings and found 90* works well enough. I don’t have the problem of my storage tank discharging back into the boiler anymore.
The low limit shuts off the circ as the fire dies out. So far its been working great!

... which I also now have done. I set the lo-limit at 95C, though. The lo-limit terminal on start-up energizes the relay coil and trips the relay to "on," providing power to the circs, subject to the differential controller and aquastat control described above. When the firebox sensor on post-burn reaches 95C (203F), the lo-limit activates and the coil is de-energized, tripping the relay to "off" and cutting power to both circs. In addition, power to the draft fan also is cut and the draft fan goes "off." At firebox temp of 95C burn-out has been realized.

If before the lo-limit activates, either of the other controllers sense conditions to turn off their respective circs, that still happens. For example, if boiler 170F and storage return greater than 160F, the differential controller turns the boiler circ "off." The storage circ may continue to run so long as boiler output is above 172F as burn-out approaches, but that is a minor issue because the draft fan will be on and burn-out will progress until the lo-limit activates. This allows any final heat output from the boiler to be sent to storage to prevent any over heat condition.

 

[Fred61]

I have the Ekoster 2 controller on my unit. It has the low fuel shut-down feature but I can't seem to set the temp above 60*C (140* F) and by the time the temp is at that point, the coals are gone. Sometime in the future I will address the problem but for now re-plumbing my new storage is priority and then major construction work on my house. I think I have taken some of the sensitivity out of the overheat issue. I am plumbing my overheat loop through a coil in the bottom of my storage tank which I believe will absorb the over-temp. If the fan or primary circ. shut down with enough coals to cause overheat, the overheat aquastat will take over and put the heat into my storage where I can make use of it, since I only heat from storage. I haven't yet decided what the min.- max. settings will be on my overheat aquastat. The Ekoster 2 only allows a maximum temperature of 80*C.

 

[jebatty]

80C on overheat seems quite low. Mine is set at 210F (100C). With the setup I now have, on overheat power is cut to the Automag and the 007 circ turns "on," accomplishing what you are doing, that is, circulating through storage to take the excess heat. The Automag operates a gravity overheat loop which also will be charged by the 007, but if the power is out, gravity alone should relieve the excess heat.

 

[Fred61]

80*C is the max temp of my controller. The overheat circuit is completely seperate and is presently set at slightly over 200*F and is presently being pumped to a Modine heater. In a couple weeks, when I shut down my system to connect my new storage, that circuit will be directed to the coil in the bottom of my tank. I don't think my set-up will thermosyphon. I wish I could make it happen. This is the circuit that I will be adding the inverter to.