Boiler controls

mike_belben · January 10, 2022, 01:29:35 AM

I was hoping you guys could enlighten me on what components your OWBs have for controlling the fire and water temp. Im sure there is a lot of variety but in general i have an interest in how they cycle and sequence events.

Im getting close to success on my outdoor hydronic stove build and am starting to consider controls.

beenthere · January 10, 2022, 01:53:48 AM

My indoor boiler unit had an Erie damper operator controlled by an aquastat, safety relief valve, and pressure-temperature gauge. (all 110v)
Worked very well for 40 years. Closed system so no rusting in the boiler ~~when~~ after O2 was driven off (by heating water) if/when fresh water introduced.

Pumps distributed the water when thermostats called for heat.

Dave Shepard · January 10, 2022, 02:22:59 AM

The basics of my 6048 is a damper controlled by an auqastat. Very basic. 10° differential on/off. Mine is a dual fuel capable of gas or oil backup, do there is more junk for that.

Dave Shepard · January 10, 2022, 02:47:44 AM

I just got my replacement oil burner going last week. My plumber took all the fancy junk off the Becket burner and hooked it to a simple aquastat, a Honeywell 4009A, iirc. Just need a well tapped into your water jacket. You could use something like that to open a damper solenoid. The Central Boiler is part #4184. About $30. Just run power to the damper, and run it through the auqastat. No additiinal power, circuit boards, or anything else to fail.

Hilltop366 · January 10, 2022, 04:15:06 AM

I'm not sure but other than gravity feed I think I have the most basic control system on my indoor wood boiler, it is all 110v no 24v needed. It has a standard 110v aquastat for low temp cutoff for the circulator and a 110v thermostat to control the circulator and a 110v overheat aquastat that turns on the circulator if the boiler reaches a set temp (set at 200° f). The two aquastats could probably be purchased as a single unit duel unit.

I would get a basic mechanical aquastats over the electronic ones.

The draft control is a Samson hydraulic draft regulator, it uses no power and is variable depending on water temp. Opens/closes slowly as water temp changes verses a electric draft control that is on/off (open/closed). I think Danfoss makes one too.

The one thing that I don't have is a "automatic open" heat dump to prevent over heating during a power failure. That is usually a normally closed 24v motorized valve that opens when the power is cut and allows the boiler to thermosiphon. I use a backup battery/ inverter to run the system but I have to do this manually. The only thing I'm running is the 110v circulator which is less than 1 amp. A 200w inverter will start and run it.

With a outdoor "open to atmosphere" boiler they seem to have all of this plus a heat exchanger to have a closed system in the house. I guess if it was a totally open system you would not need a expansion tank or pressure/temp relief valve.

PoginyHill · January 10, 2022, 07:12:15 AM

ClassicEdge series use a PLC to control everything. A single fan is used with two dampers connected to separate step motors. One is primary air, the other is secondary air. When the low setpoint is reached, the fan turns on and the step motor opens the primary damper. A furnace RTD measures firebox temp. At a lower setpoint (mine is 550F), the secondary air damper starts to open. It "steps" open from the lower firebox temp to fully open at the high firebox setpoint - mine is 750F. Fully open for my unit is actually 68%, but can be adjusted. Burns pretty clean, so opening further is just more excess air - no contribution to combustion. The primary damper "fully open" is 85%.

A more efficient control, but more expensive, would be to measure Oxygen in the stack and control the secondary air to a target Oxygen content, like 6-8% or so.
Another way to control things would be two fans (primary and secondary) on variable speed and use that to control air rather than dampers. A simple open/shut damper would probably be needed to control air from natural draft if you have an idle setting.

Lots of options regarding how to control wood burning combustion.

Jdock · January 10, 2022, 08:30:48 AM

The simplest system is a 110v aquastat controlling a plunger type solenoid for the draft and a n/o solenoid for the circulation pump. This works pretty good for a simple loop. For adding to an existing furnace the thermostat can trigger the circulation pump and the aquastat just controls the draft to maintain water temperature. Either way a nice feature is a float switch controlling a valve to a water supply to keep from running low. Amazon sells the Taco 009 circulation pump for around 100$ and the Honeywell aquastat is about 30$.

Jdock · January 10, 2022, 08:41:22 AM

I recently rebuilt a Hardy owb that had been frozen and overfired, pretty much destroyed all the controls. They use a forced air draft but a simple shutter works as well, just doesn't heat as quickly. Automation direct has the relays for cheap.

Southside · January 10, 2022, 10:11:59 AM

I had high and low water temp aquastats for the blower, blower door, and circulators. Very low tech and worked like a charm.

scsmith42 · January 10, 2022, 10:36:42 AM

Watching.

mike_belben · January 10, 2022, 12:24:28 PM

thank you boys. youre all gentleman and scholars and i am very appreciative of how much spam ad sifting youve just saved me to get just a fraction of that overall big picture. ive read every word and am digesting it slowly.

i didnt know about damper solenoids. i guess they are a mechanical arm that magnetically pulls open and is spring loaded shut? how much stroke? what voltage are they?

it sounds like some boilers stoke up with a forced fan draft and a damper.. while others just open an inlet air supply and come up naturally. is that correct? what are the ups and downs of each that i may not be considering from lack of experience?

do OWBs tend to have stack dampers or just inlet dampers?

Hilltop366 · January 10, 2022, 12:30:52 PM

Quote from: mike_belben on January 10, 2022, 12:24:28 PMi didnt know about damper solenoids. i guess they are a mechanical arm that magnetically pulls open and is spring loaded shut? how much stroke? what voltage are they?

The electric dampers I have seen (indoor wood boilers) are motorized with a 24v motor, same motor as a honeywell motorized zone valve.

Southside · January 10, 2022, 12:54:46 PM

I had an intake and stack damper as the goal was for the fire to run out of oxygen when not calling for heat. When the time came, add O2 and whoosh, she made heat.

mike_belben · January 10, 2022, 01:41:02 PM

Add 02 by blower or just open both dampers up?

mike_belben · January 10, 2022, 01:42:11 PM

How many gallons are these things are are the tanks all integrated in direct contact with the firebox or are any if them modular where the water tank is not in flame and is replaceable independant of the firebox and vice versa?

Southside · January 10, 2022, 03:00:16 PM

The one I built was a down draft style so it needed a blower. Water volume was 200 gallons ish from what I remember and I had surface contact everywhere possible, main chamber, secondary chamber, and an exchanger in the stack.

Dave Shepard · January 10, 2022, 04:28:36 PM

My 6048 is 397 gallons. I'll get pics of the solenoid in a bit.

mike_belben · January 10, 2022, 04:49:52 PM

wow these things are monsters. man thats a lotta steel.

Corley5 · January 10, 2022, 04:53:16 PM

I'm in no way recommending them as a place to purchase only as a resource to see what's used. Solenoids for the forced draft dampers/doors are pictured as well as draft motors, aquastats etc. Shop for parts. I got a replacement blower for considerably less elsewhere. It's a good place to take a look if you haven't already.
https://outdoorboiler.com/

Our Heatmors have Honeywell mechanical aquastats and they work great. The Heatmaster SS has a digital one and it's never had an issue but the readout is smoked and it needs to be replaced. It's from the control being over the firebox door. A design flaw on the boiler manufacturer's part.
The Heatmaster holds 200 gallons of water. The Heatmors I think are 130 with a rubber expansion bladder on top. They're all direct contact firebox to water. The Heatmaster has water tubes that go across the top of the firebox to increase surface area. No dampers in the stacks, just air tight. When the draft is off the fire dies to nothing and comes to life with the forced air. The KISS principle is in full effect with OWBs

PoginyHill · January 10, 2022, 05:07:01 PM

My Central Boiler has the blower on the inlet. Dampers are between the blower and the furnace. Other furnaces use a blower on the exhaust (Induced Draft Fan or ID fan). But if the fire doesn't burn hot and clean, any ID fan may clog with creosote.

A step motor allows for mid positions between open and shut. A solenoid damper is either fully open or shut.

Mine has a water capacity of about 300 gals.

Dave Shepard · January 10, 2022, 06:00:14 PM

I'm using a 4006A, not a 4009A aquastat. 120v. The 4184 draft door solenoid is also 120v. The solenoids are $30, and the aquastat is $100, but they are bulletproof and dead simple. I bet they can be salvaged, along with the well, off of many old boilers. I reused mine off my old boiler.
I ran my circulator continuously from the owb to the heat exchanger, but an aquastat would work to switch the circulator on and off.

mike_belben · January 10, 2022, 11:06:56 PM

i have an aquastat or two already.

i just went through about 4 revisions of trying to turn a stove i made previously into a hydronic hot water rig to heat the camper by putting the radiator in the underbelly plumbing service area. i proved that concept out with an electric heater under there and it was great, warm floors and pipes.. finally did get the stove to where i was sending hot water to a radiator but by the time i got it doing that the thing was pretty delicate. i built that stove to heat an interior space on a 5 gallon bucket of waste vegetable oil and sawdust per day so it was about maximizing the length of the fire path and extracting maximum BTUs in a modified rocket stove fashion. it was a tremendous success in that regard.. btu extraction. i got 550 firebox temp and 75f stack temp which i would call total BS on if i didnt actually do it myself. the water reservoir and internal water coil are extracting almost all of the temp.

but alas, this unit makes a poor boiler. or maybe a fickle one. to make it stay in the sweet spot is a lot of babysitting, and it required a coil of water through the interior of the firebox which was all too happy to make steam so it has to be pumped before then.. but once the water changes out of the coil it drops back down in temp and the btu of the fire is so small (literally less than a handful of fuel per 10 minutes) that it cant recover the water temp unless the pump shuts off a while.. and turns on.. and shuts off.. i dont want the constant startup loads eating pumps and drawing double the current of continuous flow.. but my water is too far from the flame to stay up to temp on even a throttled continuous flow.

so i started on a new firebox today that has fuel efficiency as the last concept and rapid heating a small water tank as the primary. it is nothing like a conventional OWB at all but im confident itll work well. its more like a cross between a hot water heater, and an on demand water heater fired by sawdust and oil... but where the flame rate is constant and never turns off. temp regulation will probably require two loads. one is the primary radiator and when that stops calling for heat the other device gets the flow. like a dump load except its not energy dumped, its energy stored. truthfully it would be good if the thing made the place too hot and we had to open windows. thats the only way to deal with camper condensate in winter. they are a swamp inside with no means to dehumidify besides opening a window and letting it draft out all the heat.

i personally like the idea of a high temp tank and a low temp tank to manage this constant flame rate unit. i can slow down the fuel feed auger infinitely variable but its a manual knob change and not something that will have a controller or remote adjusting. since there is no ashes to my fuel there is no option to start and stop... it wont smolder. its either flaming or its out out and that would occur every few minutes without the auger continually crumbling in more, like a pellet stove. relighting is manual unless i were to rig up some propane gun into the burn tube.. so i dont want the thing going out unless the high temp safety cuts it off. then its a manual reset.

in the future i will do a big old OWB to heat much larger spaces and that will be a lot more conventional. for now im just trying to get a picture of the various methods and parts available. and it was mostly related to the unit that i have abandoned. well.. not abandoned but decided to leave it as an indoor stove and not a hydronic boiler. i think this new revision is going to be very simple and work really well. or so i hope. its flippin cold in here.

hedgerow · January 11, 2022, 09:18:02 AM

Quote from: mike_belben on January 10, 2022, 04:49:52 PM
wow these things are monsters. man thats a lotta steel.

Mike my Garn batch burns into 2000 gallons of water. Then I used that stored heated water to heat my shop and house. You could set your stove up to heat water in a storage tank and then use the storage to heat the camper.

PoginyHill · January 11, 2022, 10:34:32 AM

Mike,
I'm guessing your heat load is normally variable? Are you looking to control the firing rate based on heat load? If you're feeding a mash of sawdust and oil with a variable speed auger, the auger speed should vary with heat load (which is hard to measure directly) or temp deviation from a setpoint. With a PLC, you can match that temp deviation with a signal to the auger drive. For air, whatever mix of fuel and air work well that ratio should be maintained throughout. I'm guessing you don't have secondary air in this set-up (sounds like a pellet stove type arrangement).
Sounds like a fun project.

Hilltop366 · January 11, 2022, 10:41:47 AM

Quote from: mike_belben on January 10, 2022, 11:06:56 PMit cant recover the water temp unless the pump shuts off a while.. and turns on.. and shuts off.

My wood boiler is about 40 gal so it always cycles on and off anywhere from 10 to 30 min depending on floor temp (concrete in floor) and fire size , the basic Grundfos circulator pump is over 20 years old no issues yet.