Wood Stove Monitoring

Hi Everyone,

I live in a log cabin in rural Vermont. It's -1F outside but we are warm from our soapstone wood stove. We were warmed in July when we were gathering firewood also..

It takes some management to keep the temperature close to 72 or so which we would prefer. I wish we could do these things better:

  • Remember to stoke the stove before the fire gets too far down and is harder to get a new load of wood burning well
  • Remember to turn the stove draft down as we approach a good temperature without too much overshoot
  • Consider the outdoor temperature and the current indoor temperature as a factor in needed heat output
  • Monitor the firebox temperature where wood is burning
  • Monitor the output flue gas temperature to warn of low-temp creosote formation condition
  • Monitor the output flue gas temperature for a sudden high temperature indicative of a chimney fire, sound an alarm
  • Later add servo control of stove draft.

I have thermocouple flue gas temperature working (Example HERE)

So this looks like 2 Thermocouples and 2 DS18B20s to measure temperature, some code and an LCD display and alarm.

Has anyone seen a project like this? Pointers? Suggestions??

Thanks!

My suggestion would be to set up some sensors and collect data over a few days to determine the correlation (if any) between the measured data and the actions that you need to take.

For example, maintaining a suitable flue-gas temperature may prevent you from keeping the room temperature as low as you would like. Or it may require the inconvenience of applying smaller fuel top-ups more frequently.

Is there any value in also measuring fire-box temperature?

Does the likelihood of a chimney fire justify computer monitoring?

I have a solid fuel stove but I burn smokeless coal. The thing I love about it is that there is no electrical item connected to it. :slight_smile: Also, for all I know, coal may burn with less variation in output levels.

...R

maintaining a suitable flue-gas temperature may prevent you from keeping the room temperature as low as you would like. Or it may require the inconvenience of applying smaller fuel top-ups more frequently

Yes, one of the challenges is managing the woodstove when the outdoor temperature is above 30F or so. I plan to do monitoring and evolve the controls behavior over time. Fortunately my desk/computer/worktable is 2 feet from the stove. That's also nice as I have a place to keep my coffee mug warm.

Is there any value in also measuring fire-box temperature?

I have observed that the firebox (mass of soapstone) has a very long time constant compared to flue temperature which is quickly affected by the fire/damper etc. The heating of the house is mostly from the exterior of the stove. So there is an interesting PID application issue here. Hmmm...

Does the likelihood of a chimney fire justify computer monitoring?

I think so. But IF better control means there is not enough creosote formation to allow a chimney fire maybe it's not needed. But I don't LIKE Chimney Fires!

Update: I am finding some online projects for woodstove control/monitoring. Some ideas to use for sure.

I would offer that any sort of fresh air controls would be greatly enhanced by a linear control valve.

I have dealt with these over the the years and would be happy to show you how to turn an ordinary ball valve into a linear valve. $5 enhancement of the valve itself.

you would have to figure how to connect it.

if you want something more home-grown, I can show you how to make one from scratch with some soup cans.

generacally speaking, a damper used for air will allow about 80% of the flow at less than 20% opening.

you will want a means to set trip points, gains, dlay tiems etc; probably a switch or two and/or a pot.
maybe a shield that integrates such with a 1602 LCD makes sense!?

Hi,
@dave-in-nj

I would offer that any sort of fresh air controls would be greatly enhanced by a linear control valve.

That's very interesting. Yes, I'd like information on doing this... The existing input air control on this stove ("Mansfield" by NHC in Morrisville, VT) has a sliding 'valve' that attempts some kind of alt.linearity control in that it's leading edge is "V" shaped. I don't know if it's better to servo control this sliding 'valve' or retrofit some other valve such as you suggest.

Any photos of the ones you are talking about?

@wgOz

you will want a means to set trip points, gains, delay times etc;

Hmmm.. In the beginning I'll probably keep multiple versions of the code with these parameters. Maybe it would be good to have options that have been tuned for outdoor temperatures of 45 down to -20 F like we get here.

I have not thought about a 'product' level device with user hand controls, at all. Hmmm. Again..

Actually the "Hmmm...??" point in the Engineering Design Process is very familiar to me!

I have not seen a Vee shaped flow control on a wood stove, but that is exactly what you can do for a ball valve.
we used to bend some metal, brass or thin sheet and fill in the voilds with epoxy.

Hi Dave,

Now that I look at it closely it is pretty cool.. the shapes of the slider and the base make it easy to make fine adjustments on the "low air" end of the range..

There is some nonlinear relationship of rotation / horizontal movement to air volume (and added factors of draft etc). But I think I can approximate it. Air volume would be closely related to short term heat input, I think.

I'll try disengaging the front-handle (which has a little friction) and try moving it with a servo.. Well, maybe try with a large servo first.. Hmmm.

If this works I can implement a chimney-fire-shutdown option...

Hi,
OK, moving forward on the OTHER Thermocouple project: A controller for a 3-zone 240V Kiln I will use for "Warm Glass". I will put up a separate project for that soon..

I have the main chassis laid out, cable entrances for high power 240V, mounting for the RoboRED (UNO) and Thermocouple amplifiers, etc etc. I have 2 thermocouples working with shared SO and CK lines. Example code for that is HERE The wood panel shown here will go on the right wall of the metal controller chassis:


The code link also shows this wired...

I am getting to put my money where my mouth has been about Common Ground Point, Optical Isoalation and All That. We'll see how stable stuff is when it's switching 5000 watts at 240V every few seconds in a PID loop. The chassis looks like this:

Any suggestions welcome!

Hi, Update: The Kiln Controller is coming along well; I have integrated the Thermocouple measurement, A good Menu system on LCD with Analog Button keyboard and putting a box together.

I've done something similar with a 2kW heating element and a nano/max6675 shield.

Worked fine

regards

Allan

I'll be following this project with interest.

I am planning on a waste oil burning water heater controller using much of the same principals you have outlined.

Hi Everyone,

*** UPDATE *** Page with this project is here:

http://arduino-info.wikispaces.com/Project-GlassKilnController

If anyone wants to see early code just email me…