Automating The Most Analog Of HVAC Equipment

Burning wood, while not a perfect heating solution, has a number of advantages over more modern heating appliances. It’s a renewable resource, doesn’t add carbon to the atmosphere over geologic time scales like fossil fuels do, can be harvested locally using simple tools, and it doesn’t require any modern infrastructure to support it. That being said, wood stoves aren’t something that are very high-tech and don’t lend themselves particularly well to automation as a result, at least with the exception of this wood stove from [jotulf45v2].

While this doesn’t automate the loading or direct control of a modern pellet stove, it does help [jotulf45v2] know when the best times are for loading more wood into the stove and helps keep the stove in the right temperature range to avoid the dangerous formation of creosote on the inside of his chimney caused by low temperature burns. Two temperature sensors, one on the stovetop and the other on the stove pipe, monitor the stove exhaust temperature. They feed data to a Node-RED system running on a Raspberry Pi which automatically notifies the user by text message when certain stove temperatures are reached.

For anyone heating with wood, tools like this are indispensable to help avoid spending an otherwise unnecessary amount of time getting a fire up to temperature quickly without over-firing the stove. Modern pellet stoves have some more modern conveniences like this built in, but many of the perks of using cord wood are lost with these devices. There are plenty of other ways to heat with wood too; take a look at this custom wood boiler which serves as a hot water heater.

35 thoughts on “Automating The Most Analog Of HVAC Equipment

          1. As a firefighter I have to say that isn’t totally true. The creosote in the chimney can burn and it can ignite the insulation around it. But the roof depends on the screen status and material and etc.

        1. War with China will mean “No more chinese products for you”, so USA will have to make it themselves again. Looking at current way things go, it will be more like “USA no longer wants to manufacture in China and deal with them -> Chinese industry endangered with collapse -> China starts war (USA to blame)”.

        2. see military industrial complex. if were at war or if there is someone to sell weapons to, or if the military just wants to play with their toys, it will be more than happy to sink billions of dollars.

          also see 34th rule of acquisition.

  1. Efficient wood burning is a field that’s ripe for high tech and scientific hacking. Between the bad efficiency, bad air quality and bad blisters, there’s plenty of room for improvement. It’s a pretty low barrier to entry to make a metal box with a door and legs, so there’s lots of garbage out there. Sure, there are a few good stoves, but not enough.

    1. Problem with wood is dosing fuel. You need to make a stove which burns efficiently in wide range of burn rates. I have pellet furnace, it still burns wood but can dose it accurately to within 2% while generating 20kW heat (there are such furnaces from 5 to 200kW). Has yearly checkups with special meter for adjusting level of generated CO and NOx, so that it still maintains highest burning efficiency and lowest pollution, but it’s pretty complicated to achieve all that efficiency. And almost impossible when burning wood. I have also normal wood stove (it feels nice, I just burn some wood from time to time just for the fire effect in room), when it comes to cleaning chimneys, wood stove makes half a bucket of tar per season, furnace chimney is always clean.

  2. It’s easy to get stuff to burn at optimal temperatures for this or that. The trick is doing that while generating the right amount of heat for a given amount of space at a given time.

    1. I used to have several “servos” I removed from houses when removing massive old coal furnaces in the late 70’s (most had been retrofitted with “modern” oil or gas burners in the 50’s or 60’s but a few were surprisingly still coal). These worked on 24V AC supplied by a transformer and raising the thermostat opened the intake air by a chain connected to various positions on the servo arm for adjustment, with a giant mercury switch in the furnace above the heat exchange to limit the temp to 250 F.
      I remember one ingenious mechanical thermostat that used a rod rotated by a bimetallic strip to tighten or release a chain thet went down through the floor to a lever arm which controlled the draft.
      Don’t know how well any of these worked, or how much of a pain to initially adjust as still variables like how much coal to shovel and how often. I guess that was left to the fireman’s art.

      1. I had a positivity beastly 500,000 BTU wood fired boiler that had a wax motor style of damper that would in theory open and close a damper based on water temperature. But it was in fact a tar and ash machine that I used one year. Couldn’t get the house over 66°F all winter.

        400,000 BTU to the room it was in, which was the attached garage, 100,000 to the heating loop. Reverse of what it should have been. But here I was wanting to keep all the filth out of the house.

        Gasification, intake air preheating, secondary air injection, and ultra high temp refractory insulation are probably good strategies to keep combustion hot, small and complete.

  3. “Other than that it drafts well considering how well insulated the house is (no fresh air intake).” (From the discussion of the link)

    Well, there is your problem: use a stove to suck your house empty of fresh air. Always include a exterior pipe for fresh air close to your stove or you will be using your just warmed up interior air for that, negating your efford to heat the space.

  4. I also had the same idea if using thermocouples to check the exhaust temperature, but found simpler and safer to use a IR temperature sensor. I pointed it at the stovepipe about 50cm away and it’s pretty responsive of, although not accurate at all.
    I’m using a mlx90614, IIRC.

    1. Wood burning is harmful everywhere. The author has a bias otherwise, and Bryan is using this as an activist platform.

      Arguably most implementations of fossil wood stoves burn LESS cleanly than typical fossil fuel heat. Wood stoves aren’t generally saddled with filters and pollution scrubbers. Wood stoves don’t actively adjust air fuel mixture. As a regular or complimentary heat source, burning wood is uncivilized.

      1. Wood burning is carbon neutral, and reducing CO2 is what the environmentalist experts are focused on these days.
        It can produce higher levels of particulate matter than other sources, especially if the type of wood is not optimal and combustion is not efficient, but there are easy fixes for that. “Clean” is not a simple definition for an energy source.

        Furthermore, in areas where forests are growing naturally, burning wood allows to keep them clean and healthy while helping the local economy: call that “uncivilized”!

        1. “Wood burning is carbon neutral”

          There’s zero science to support your claim. At best this is a result of not using scientific guidance to calculate emissions and the carbon cycle. At worst, the motivations Scott Pruitt had when he claimed this, are your motivations also.

          “but there are easy fixes for that.”

          MORE than one? Please, share just one of these easy fixes.

        2. For those interested, the origin of “burning wood is carbon neutral” is comes from Pruitt’s appointment to the EPA in 2017, where he and proclaimed, without proof, that CO2 is not a primary contributor to climate change. None of the co-signers included anyone with scientific background.

          Mr. Pruitt later resigned for accepting bribes from the methane industry.

          There are worse things to burn than wood, of course, such as peat. Thankfully peat advocates do not have the audacity to call it carbon neutral (which, according to the standard given above, peat would be)

          1. “There’s zero science to support your claim”
            There isn’t a scientific consensus wether to label wood burning “carbon neutral”, that’s true. But every single paper you can find will tell that the net contribution of carbon dioxide is zero or close to zero under certain circumstances.
            I, for instance, happen to live in a country with rapidly expanding forests, and sustainable wood is easily found. I personally cut my own: this is carbon neutral, isn’t it?

            “MORE than one? Please, share just one of these easy fixes.” …like the very article we are commenting on? Or use a decent, recent wood stove or, better, a pellet stove. Industrial plants are, obviously, better at efficiency and cleaning fumes.

            Peat is carbon neutral over some hudreds/thousands years, wood is carbon neutral if you can manage its procurement

          2. The origin of “burning wood is (approximately) carbon neutral” is not that someone well known said it, it’s the conclusion of a simple logical thought about the impact of traditional use of wood.

            Did you have the same mass of wood in your forest this year as you did last year, even though you took wood from the forest to burn in the winter? Then the trees must have grown. In order for the trees to grow, they must take in the mass of elements needed to create that mass of wood. If we didn’t know much about plants or soil and how plants get mass from air and water, we could think that maybe it was from the soil. But soil doesn’t contain enough carbon for that, and places where trees have been grown and cut down for hundreds of years do not lack carbon or soil. So it must be that the carbon was from the air. So, we know that if we conserve the forest and store a sustainable amount of wood, we get a net increase of the amount of wood in existence.

            (Pretending that rotting is much less complex than it is,) If the wood neither rots in place nor is burned, that’s a net storage of carbon. If it rots or is burned, it’s neutral, unless you released carbon in acquiring the wood, but people tend to harvest their own or buy locally, so maybe there was a few minutes with a chainsaw per tree if they didn’t use an axe and a percentage drop of efficiency in carrying the extra weight of wood home with the groceries if it was purchased instead.

            The arguments for and against neutrality which apply to burning wood as an industry do not all apply to burning wood traditionally on a farm in a woodstove.

  5. It’s only situationally good or bad to burn wood. I believe your use of the word civilized is revealing. Perhaps I might say you want an industrialized solution for the (relative to global and historic standards) wealthy urbanized American, but the truth is that there are still those who you may not consider civilized, who have plenty of wood available but not enough money to keep warm in other ways. It’s fairly easy to make a net negative of carbon if you sometimes burn wood in ways which produce charcoal which you sequester. (Carbon sequestration using fast growing sea plants is a corresponding option which is not available in a forest) It’s also generally the case that the dirtier wood stoves could burn cleaner with minor changes to user habits, though it may increase wood consumption. Better stoves and pellet based heating maintain a cleaner burn more easily, and there’s catalytic converters and other gadgets that do various things.

    That being said, so long as the carbon added by burning natural gas or lpg is offset elsewhere, I agree that those two are clean and efficient compared to other fuels and when they are affordable I support their use instead of other fossil fuels. Especially if you’re in an area where there’s not a lot of energy and industry tied up in moving the fuels to your home, but there’s a lot of fossil fuels in your electric grid mix, you may end up cleaner and greener that way than using electricity.

    Electric heat pumps work great when practical and I would love to see them used more, as long as used with reliable energy of a clean enough mix that the COP of the pump is high enough to represent a net reduction in carbon released. But they’re also not nearly so affordable, and it would pay greater dividends to improve insulation and reduce drafts first in many cases, and get a heat pump afterwards when possible.

    1. Thank you for your comment. Yes, 100%, “civilized is an ugly, archaic term but its use here served purpose.

      You point out, access to cleaner energies is largely a function of wealth. I agree with everything you said, 100%.

      Burning fuels like wood and peat are symptoms of inequality which have to be addressed to get out of this spiral we’re in. You can improve how these things burn, but only from the sense that they were the worst (and will continue to be so after improvement). Somehow we have to make wood burning and clear cutting unacceptable, without condemning people to harm.

      Once temperature increases release the methane currently trapped under Siberia (and the Pacific floor) are released, there’s probably nothing we can do to stop things even if we adopted greater will. It won’t matter which side of the boat caused it to sink.

      1. I’m not very familiar with peat, but with the minimal replacement rate and other properties, I don’t know if it’s ever really good to use, just possible. But wood is also a material of many uses, and so even if we never harvested wood for fuel alone, it’d still be a convenient thing to do with leftover wood. And there’s a more reasonable replacement rate on wood than peat; if you want to push past the traditional level of usage you can repeatedly grow young trees and still be fairly sustainable. It would be necessary to require a policy of carbon sequestration, which again is easy with wood as you can even make charcoal with tech as primitive as a dirt mound.
        Of course, there’s more advanced and faster ways to convert biomass to something more stable for sequestration, but we do plan to keep our forests around and should really consider expanding them to older levels. As such there’s a certain level of harvesting that could even be beneficial from a conservation and sequestration perspective. We already quite reasonably intend to imbalance things, such as by stopping forest fires even if they are natural for some forests, but in that case we should also intervene in other ways that make sense.

  6. The thing to do would be to add an oxygen sensor to the flue and add a small blower to the intake. Most of the time you could run it on unpowered intake air, but when starting and under some conditions, you’d want to run the blower to force intake air. The best use for the connected thermocouple in the exhaust gas would be to warn you of overheating. That’s the one case you’re not likely to not already know what’s going on. You could have it reduce the intake air when you’re running too hot, but I usually find it better to push the logs together in that situation, since decreasing the air makes a rich burn, but pushing the logs together reduces the fuel instead (reducing the burn rate without affecting the air/fuel mix).

    On the up-thread flame wars, wood stoves always emit PAH, and often (not if you properly season the wood and burn well) also PM. You can minimize the PAH formation by running around 800-900F and keeping an oxygen-rich burn. You can pretty much eliminate PM by keeping a strong flame-front in a newer stove, and getting up to operating temperature quickly. Wood heat is renewable, and is sustainable if you have more wood growing than you harvest. If you understand the carbon cycle, you know that sustainably harvested wood heating is CO2 neutral. If you use your stove to make biochar, it can be carbon negative. If you do it by deforestation, it’s arguably increasing CO2 in the air.

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