OWB controls

[H-Ranch]

I've been pondering about the air controls for my OWB for a while (and maybe even mentioned it on other threads already.) My thought is to have a multi-stage controller that will do the following:

1. Open the damper solenoid when the water temperature falls below 145F. I think in many instances this will allow enough air to burn without replacing all of the hot air in the fire chamber with cold air.
3. Turn on the fan when the water temperature falls below 140F. This would add air to the fire in the instances where natural draft was not enough to keep up or was needed to start idle coals.
5. Turn off the fan and close the damper solenoid when the water temperature falls below 135F. This would indicate that the fire was out or the wood was low and would allow the system to idle without continuing to blow cold air into the fire chamber thus further cooling the water.
7. Turn off the fan and close the damper solenoid when the water temperature reaches 150F. This means the water is up to operating temperature and no additional air is required.

I could add another aquastat to my system to control the damper solenoid and fan separately which would also give me a spare if one died. It would still require a third control to turn everything off at the lower limit though. The absolute tempetures may require some experimentation, but that is how I think I may be able to improve the system. Currently I use a single Johnson Contols A419 digital aquastat. I have it set so the damper solenoid opens/fan comes on at 145F and the damper solenoit closes/fan goes off at 150F.

Does anyone use this type of system? Or have something better? Thanks for your input.

View attachment 270235

 

[Stihl310]

I use an aquastat on mine, the easiest way to possibly do what you want is to utilize your existing controls and then place "snap acting" thermostat controls in to do what you want.

One snap disc could cut power under 135, and one could control the action of the fan at 140 degrees. Basically you could run your controller and at 145 it would send signal to the damper to open and power to the snap disc, once the snap disc hit 140 it would allow power from the controller to pass through to the fan. One more snap disc could be set to cut power to either the controller or intermediatly between the co triller and the damper/fan load.

There's a ton of ways to do it, but in my opinion simple is the name of the game. No reason to overcomplicate things, especially something that keeps your house warm all winter. The nice thing is also, if something malfunctions all you would need to do is bypass the snap stats and you'd be back up and running.

 

[NC4AB]

I've been doing something similar using a RANCO two stage temperature controller with my Hardy H2.

Basic operation:

Damper solenoid opens at 160F, closes when the water temp gets above 170F

Fan comes on if the water temperature falls below 150F, turns off at 160F.

The RANCO has a 0-10v temperature output that is use to monitor the temperature with a readout and datalogger.

I ran the 24vac control voltage for the circulator pump through a SNAP-Disc thermostat that kills the pump if the water temperature drops below 110F.

I've been happy with it for the past 6 years.

 

[loadthestove]

.

One snap disc could cut power under 135, .

Sorry just had to ask this.if power is shut off a 135 how do you get stove back up to tempature so power will come back on.

Dont want to sound like a smart @$# ,a few years back i had a homebuilt owb and set it up basically like stihl said I was real pround of my work until I tried to get the stupid thing running after a few hours of checking and rechecking I realized I had to bypass the snap disc until stove was up and running.Felt like a complete idiot once I figured out my problem

 

[Stihl310]

Sorry just had to ask this.if power is shut off a 135 how do you get stove back up to tempature so power will come back on.

Dont want to sound like a smart @$# ,a few years back i had a homebuilt owb and set it up basically like stihl said I was real pround of my work until I tried to get the stupid thing running after a few hours of checking and rechecking I realized I had to bypass the snap disc until stove was up and running.Felt like a complete idiot once I figured out my problem

Bypass switch would probably be the easiest. There are certainly fancier ways of doing it, just trying to think of the easiest. Bypass in parallel should clear it up I would think??

I still would like to hook up a plc, but I keep telling myself, " keep it simple stupid". I like how mines setup right now, I could basically have total control failure and still limp the unit along until I got it fixed, if nothing else just to keep the water above freezing point.

 

[Butch(OH)]

We have a 4400 Woodmaster for this being season 6. I have always thought that the forced draft system on it was geared more towards big chunks of wet snow covered wood. You have promted me here. Since I am off for three days and can watch it close I am going to unhook the fan and see what it does with draft only. We burn only well seasoned split wood that is stored under roof.

 

[Stihl310]

We have a 4400 Woodmaster for this being season 6. I have always thought that the forced draft system on it was geared more towards big chunks of wet snow covered wood. You have promted me here. Since I am off for three days and can watch it close I am going to unhook the fan and see what it does with draft only. We burn only well seasoned split wood that is stored under roof.

I tried this on my homemade unit, unfortunately the inlet hole off the blower is either too small or too constricted by the fan blades to allow for enough air flow. With my fan off I just can't supply enough oxygen to keep her going. When I build my next one I'll have most of these issues tweaked and hopefully be runnig much more efficiently.

 

[russhd1997]

I've been pondering about the air controls for my OWB for a while (and maybe even mentioned it on other threads already.) My thought is to have a multi-stage controller that will do the following:

1. Open the damper solenoid when the water temperature falls below 145F. I think in many instances this will allow enough air to burn without replacing all of the hot air in the fire chamber with cold air.
3. Turn on the fan when the water temperature falls below 140F. This would add air to the fire in the instances where natural draft was not enough to keep up or was needed to start idle coals.
5. Turn off the fan and close the damper solenoid when the water temperature falls below 135F. This would indicate that the fire was out or the wood was low and would allow the system to idle without continuing to blow cold air into the fire chamber thus further cooling the water.
7. Turn off the fan and close the damper solenoid when the water temperature reaches 150F. This means the water is up to operating temperature and no additional air is required.

I could add another aquastat to my system to control the damper solenoid and fan separately which would also give me a spare if one died. It would still require a third control to turn everything off at the lower limit though. The absolute tempetures may require some experimentation, but that is how I think I may be able to improve the system. Currently I use a single Johnson Contols A419 digital aquastat. I have it set so the damper solenoid opens/fan comes on at 145F and the damper solenoit closes/fan goes off at 150F.

Does anyone use this type of system? Or have something better? Thanks for your input.

View attachment 270235

Why do you want it to run so cold? I have mine set at the factory default setting of on at 175 and off at 185. My oil burner kicks on at 140 if the OWB goes below that.

I have watched it on cold days when there is a big demand and have seen it in the 160's before it gets hot enough to start climbing.

My OWB is a Central so no blower just a fresh air damper. One less thing to go wrong but a little slow to recover at times. It is the source of heat and domestic hot water for 2 houses with it. I don't like the cold shower complaints!

 

[H-Ranch]

Sorry just had to ask this.if power is shut off a 135 how do you get stove back up to tempature so power will come back on.

Dont want to sound like a smart @$# ,a few years back i had a homebuilt owb and set it up basically like stihl said I was real pround of my work until I tried to get the stupid thing running after a few hours of checking and rechecking I realized I had to bypass the snap disc until stove was up and running.Felt like a complete idiot once I figured out my problem

Ha! Great point that I missed in my strategy - a bypass switch is definitely required. I can see me running around like you wondering why I can't get it going. :msp_confused:

Just one more reason to post it on AS first... somebody has already been there and done that!

 

[H-Ranch]

Why do you want it to run so cold? I have mine set at the factory default setting of on at 175 and off at 185. My oil burner kicks on at 140 if the OWB goes below that.

I have been running it for 3 years set at 150 and haven't used any propane to heat the house. I always plan on raising the set point during the very coldest days, but just haven't needed to. I don't use it for heating domestic water (yet) so that may be one reason I can get by with a lower temperature.

 

[Butch(OH)]

This morning I cut into the fan motor wire and installed a switch so tha I can easily turn the fan on if need be. Been running on draft only all day. Will be able to tell in the AM if ther eis a substantial differance in wood usage. It does produce more smoke than it did with the fan draft and of course takes longer to reach cutoff temps. OP talked about programming the fan. It would be easy to do and cheap actualy. I purchased a programable controller, relay and K-couple temp sensor on Ebay last fall for my parts washerfor like $40 inculding shipping direct from China. Works pefectly and very easy to program

I am thinking along same lines, natural draft open attemp X, fan cut in if it drops say 5 more to X, fan cut back out when it rises to draft open temp? Here is one suited to this type app for $25. I have made 20 purchases direct from China and Hong Kong with no troubles, shipping is about a week usualy.

220V Digital Temperature Controller Whit Sensor 2 10A Relay 2500W | eBay

 

[H-Ranch]

This morning I cut into the fan motor wire and installed a switch so tha I can easily turn the fan on if need be. Been running on draft only all day. Will be able to tell in the AM if ther eis a substantial differance in wood usage. It does produce more smoke than it did with the fan draft and of course takes longer to reach cutoff temps. OP talked about programming the fan. It would be easy to do and cheap actualy. I purchased a programable controller, relay and K-couple temp sensor on Ebay last fall for my parts washerfor like $40 inculding shipping direct from China. Works pefectly and very easy to program

I am thinking along same lines, natural draft open attemp X, fan cut in if it drops say 5 more to X, fan cut back out when it rises to draft open temp?

For sure there is something to be said for keeping it simple, but you can always default to draft only/single controller/single snap disc thermostat/whatever base system you start with.

I had one other thought too since you're talking programmable contoller. Say the temperture dropped low enough for the fan to kick on - so it does and it gets the fire started again. Is there any reason for it to continue to feed air or can it revert back to natural draft again? I'm thinking after 5 minutes it should be enough to continue to burn naturally and not replace the warm air being created by the fire with the cold outside air with a force feed from the fan. I suppose a multi-speed or variable fan could help in this case also.

You've got me inspired now too so I may just put a switch in-line for my fan tomorrow. Thanks for your feedback and legwork on this.

 

[Stihl310]

I may at some point try hooking labview up to my OWB, the only issue then is having a fulltime pc dedicated to running it. However, the control options are truly limitless with it. You could log data and actually prove put what would be the most efficient use of fan/damper combination.

The issue that worries me is not having a ups backup in the event I'd lose power.

 

[NC4AB]

I have my data logging program running in the back ground of my main PC, and the reasoning for the two stage control was to minimize the exhaust stack temperature. I played around with lowering the water temperature set points until the stove went out a couple of times during the day under low load conditions and then I bumped the temperatures up 5F and left it. Been running it this way for 6 years.

I burn softwood slabs heating a ~2000 sq foot well insulated house plus heating the Domestic Hot Water. The damper only mode (natural draft) works under just about all heating conditions, the only time I see the fan motor kick on is when one of the kids takes a 30 minute shower. My Hardy H2 only has 100 gallons of water storage, if it had more thermal mass I doubt the fan would ever come on.

 

[H-Ranch]

Butch(OH) thread about using draft only on 4400 Woodmaster:
http://www.arboristsite.com/firewood-heating-wood-burning-equipment/220005.htm