Improved my burn control

[brant2000]

So, as usual with most things that I do, this has been an ongoing work in progress for a while. I have been trying to figure out the best way to try to automate control of my intake air damper to increase the overall burn efficiency. I figured I could use a PID controller and proportional damper actuator to try to maintain a constant flue temp. I tried doing this at first with a thermocouple installed in the stove pipe, which improved things a bit but still wasn't providing adequate control. I then installed a thermocouple directly behind the cat's and have found this to provide a lot better control. Now, once I'm certain the cat's (there are two of them in my boiler) have lit off I no longer have to make any additional damper adjustments and have found that I'm burning much cleaner and generally heating the house much easier. I call it my full time fire tender.

As you can see in the pictures, I have a tendency to leave things in a state of disorder. I always hook things up temporarily to try to figure out how it works and then fail to go back and clean things up like I had planned.

 

[ewdudley]

Outstanding! What controllers are those, and what are the interface signals?

 

[brant2000]

The one that reads 567.5 (celsius) is what's controlling the damper. It's a Sestos D1S-CR-220. It was the cheapest controller I could find that provided a current (4-20 mA) output.

The other controllers are both dry contact signals. The one monitors the water temperature to kick my furnace blower on if the water reaches 200 F. The other one senses the flue temp and sounds a piezo buzzer to make sure I (or my wife) don't forget to close the bypass.

 

[ewdudley]

The one that reads 567.5 (celsius) is what's controlling the damper. It's a Sestos D1S-CR-220. It was the cheapest controller I could find that provided a current (4-20 mA) output.

The other controllers are both dry contact signals. The one monitors the water temperature to kick my furnace blower on if the water reaches 200 F. The other one senses the flue temp and sounds a piezo buzzer to make sure I (or my wife) don't forget to close the bypass.

Nice. I hadn't seen other than relay and/or SSR outputs on those types of PID controllers before, 4-20 mA opens up a lot more possibilities.

Google turned up this Hungarian version (looks like could use some tuning):

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Here's my SSR PID driven wax-cylinder heat-motor draft control, now in its fourth season:

 

[jebatty]

... and have found that I'm burning much cleaner and generally heating the house much easier.

Let's see the before and after numbers: CO, residual O2, etc.; input and output btu's; burn rate and wood MC; stack temps; and ideally particulates.

...try to automate control of my intake air damper to increase the overall burn efficiency.

I do this roughly by on-off on my draft fan. Some high end boilers (e.g. Froling) control 1) draft fan total air input; 2) portion of air going to primary burn; and 3) portion of air going to secondary burn. Are you only seeking to control total air input? My 2007 Tarm has an adjustable (but then fixed) intake air damper, and then a lever to manually adjust primary/secondary air, which I don't change often or much once it is at a setting that seems to fit my wood. I think I have found a DC blower motor that would fit the Tarm and be speed controllable to control total air input, and I don't think it would be overly difficult with a solenoid type device to control the primary/secondary air lever -- but at this time I do not have the ability to monitor and control all the air controls based on CO, O2, etc. to achieve efficiency supported by data as opposed to perceived efficiency.

Anecdotal: I sense I can burn cleaner at a cost of reduced output, as very roughly measured by stack temp and rate of rise in storage tank water. I do not seek highest output, but what seems to be a burn rate at which the Tarm "purrs."

 

[91LMS]

that b100 is a cool looking unit brant. i had never seen one before.

 

[brant2000]

Nice. I hadn't seen other than relay and/or SSR outputs on those types of PID controllers before, 4-20 mA opens up a lot more possibilities.

Here's my SSR PID driven wax-cylinder heat-motor draft control, now in its fourth season:

View attachment 126765 View attachment 126766

Very ingenious, I love the counterweight. Even if I had additional resources (which I don't), I always love trying to figure out how to make things work well with inexpensive and available materials.

 

[brant2000]

Let's see the before and after numbers: CO, residual O2, etc.; input and output btu's; burn rate and wood MC; stack temps; and ideally particulates.

I don't have the equipment that would be required to test CO or O2. You're correct that this is merely perceived efficiency. If I had more time and resources, I would love to be able to test to support this; but then if I had the means to easily and accurately test O2, I would probably be better off keying on that to control my combustion air.

Are you only seeking to control total air input?

Well, there is one damper assembly on the back of this provides restriction to multiple intake ports simulataneously. To be able to even provide this control would require substantial modification.

 

[brant2000]

that b100 is a cool looking unit brant. i had never seen one before.

Thanks, I agree. It would be much better suited (cleaned up and with a fresh paint job, of course) in a living space than in my basement. It provides a lot of radiant heat.

 

[TCaldwell]

residual o2 in the fluestack is typically controlled in a batch burn by manipulating a static mass airflow with primary and secondary damper manipulation. total mass air changes, ie variable speed motor will change btu output. European testing is concluding that co control is just as important as o2 for the health of a wood fire, it is a precursor to a o2 disturbance. I have seen data combining combustion temp and o2 and co for the not too distant next generation of small biomass combustion controllers. The problem in the past has been inexpensive robust co sensors with a high ppm limit. These controllers will use the above inputs and vary the total air mass to maintain combustion temp and co within a o2 or lambda range. Unlike most variable speed control used to reduce boiler output when approaching max water temp.

 

[jebatty]

Is it that wood combustion is "dirty" that causes much of the problem in achieving higher efficiencies? An auto engine is constantly making adjustment based on amount of fuel being combusted and load on the engine, and I assume other variables. It would seem that the wheel has been invented. What is it about wood combustion that is making it difficult to attain high efficiency?

 

[brant2000]

Is it that wood combustion is "dirty" that causes much of the problem in achieving higher efficiencies?.... What is it about wood combustion that is making it difficult to attain high efficiency?

The loss of efficiency that I was experiencing was mainly due to the fact that once I set my damper to a position, it was fixed for the entire burn cycle. This obviously isn't going to provide an optimal burn throughout the entire cycle. I'm not saying that this is even close to some of the sophisticated controls that other boilers may have, but it has significantly improved how mine operates.

The biggest benefit is that once the burn gets into full swing, it cuts the airflow to the minimum setting to lengthen the burn and minimize stack loss. Then as the temperatures come back to earth, it opens up the airflow to maintain good heat input and minimize coal buildup.

 

[jebatty]

I think your approach makes a lot of sense, not perfect, but likely a material improvement. I believe there is manufacturer of a wood burning appliance that has a microprocessor controlled air input which does this and has achieved very high efficiency results. I'm going to think more about this.

 

[TCaldwell]

Jim, the technology is out there but general motors isn't in the boiler business $$. There are inherent differences batch control vs metered fuel as a controller input variable, alone the differences in each batch, even though they look and weigh the same. This is where pellet heating shines, a consistent fuel, metered fuel rate, primary/secondary air staging, and monitoring of o2, flue temp, calculated co2 and effiency. Unlike batch burns the results are more consistent allowing for more precise honing of control algorithims and combustor designs. I think batch designs have to be more forgiving in general, as it is all feedback control not allowing for precision at all times, but working well most of the time. This area of acceptable control for a batch burn is what causes difficulties with particulate/ emissions. You have to control the combustion to tight parameters to identify the emissions and seek to control those. Because this is complex and a moving target, and expensive companies like clearstack are/have designed catalytic converters and controllers to cleanup the emissions. Not addressing the real problem but a start. As stated above the importance of carbon monoxide along with o2 and combustion temp are being tested, but are as slow to evolve as o2 control was. I guess if everybody had a wood boiler as they do a car, this wouldn't be a issue. your thoughts

 

[brant2000]

I guess if everybody had a wood boiler as they do a car, this wouldn't be a issue.

I couldn't agree more with your thoughts and sentiment. There are indeed significant differences and challenges in most solid fuel combustion appliances, and the benefits and availability of natural gas and other fuel sources has pushed most of the industry and market to those fuels. I guess it's better for us in a way, because if everybody wanted to heat with wood/biomass it would be a much different (more expensive) market.

 

[jebatty]

I'm aware of two name brand wood heating appliances that have no O2, CO or CO2 control, and on which Intertek has done efficiency and emission tests, both with very good results. One has no operator control of the burn process, only a fixed speed draft fan, and the other has some operator control but also a microprocessor which controls the air volume input during the burn cycle. I don't think the Intertek tests are necessarily what an owner will experience because an owner's wood will have more variability, I assume, than was the wood on the Intertek tests. Also, the burn methods of these two appliances are not identical to the burn process in other heating appliances, so it is not literally possible to infer similar results.

Yet, something less than complete control can achieve very good results, and this can be accomplished with design and/or relatively inexpensive air control. As I mentioned above, air volume control would be adaptable for my Tarm, probably other gasification boilers as well, and it merits further investigation.