Wood Boiler Installation Tweaks

The following is copied from a private conversation I have been having with a forum member. Might be useful for others. The question asked of me was whether or not I had a build thread. My answer, with some minor edits:

I do not have a build thread, but I have had numerous posts about my system. The basic Tarm Solo Plus 40 (140,000 btuh) and the enhancements:
1) Single speed draft fan with a manual damper to adjust airflow. Early on experienced excessively high stack temps, into the 900F range. Discovered that the draft had a damper, which I then used to limit air flow. Temps reduced to 500F range maximum. Still high. See (7) below.
2) Manual lever to adjust portion of airflow to primary and to secondary. I have used this at a "set it and forget" setting. My wood is pretty uniform in MC and size of splits.
3) Draft fan is turned on manually. Aquastat that turns off the draft fan and boiler idles until temp drops a few degrees, which I have set at 190F boiler hot water temp. Actual fan off occurs at about 195F, back on at 190F.
4) High limit aquastat that triggers the gravity dump zone at an adjustable boiler hot water temp (210F is my setting).
5) Internal adjustable control with a sensor in the smoke box to turn off the draft fan when the burn is over and boiler is "cool." I have this set at 100C.
6) As supplied, no control over any circulators, either at start-up temperature or shut-down temperature. The boiler circ needed to be turned on and off manually. I changed the wiring so that the boiler circ would turn off when the draft fan turned off on cool down.
6a) Termovar boiler return water protection valve with fixed setting at 140F.
7) Not supplied with any turbulators in the firetubes. I made up and added chain turbulators. Effect was to reduce stack temp by about 100F from pre-turbulator burn conditions.
8) Added: digital temp controller that turns on the boiler circ at adustable boiler hot water supply temp. I have this set at 140F.
9) Added: digital temp controller that turns off the draft fan at high stack temp and then back on when stack temp drops. I have this set at 250C. Stack temp drops rapidly when the draft fan is turned off. I added this as a safety feature to help prevent a run-away burn. Glad I did, because twice I inadvertently failed to shut the bypass damper after loading wood, and this controller prevented dangerously high stack temp.
10) Added: linear actuator to open a window 6" when the boiler draft fan is turned on and shuts the window when the boiler is cool and shuts down.
11) Added: digital panel meters showing boiler supply/return temp, stack temp, storage top/middle/bottom temp, system supply/return temp.
12) Added: digital temp sensors at numerous locations to log data; used these to analyze issues that arose and satisfy my curiosity as to how the boiler and system actually were performing. I rarely log data any more. Last winter (2016) I bought a Raspberry Pi computer and now use that to log data if and when desired. Previously I had to use my laptop computer. Learned some Python programming to run on the Pi to do this.

My boiler and 1000 gal storage is in my shop, very short distance 1-1/4" copper piping between the boiler and storage and between storage and system. The boiler operates solely to charge storage. System draws and returns to storage as needed to maintain shop temperature. System heat is pex in-floor set to maintain a constant floor temp of 61F. The boiler circ is a Grundfos 15-58 set normally at M. Separate circs via an hx supply hot water to the in-floor. The hx is used because the boiler/storage is water and the in-floor has an antifreeze mix. In-floor supply temp via a mixing valve is set at 100F.

Originally I had an issue many have had: boiler over-heating and repeated idling; not enough hot water available to meet demand. My initial piping was 3/4" steel, about 70 feet round trip, which was wholly inadequate to handle boiler output of 140,000 btuh with a Taco 007. I then re-did with 1" steel, which was better but still inadequate. That's when I really started to learn hydronics. Then I built a new shop, moved the boiler and storage tank, and over the last 7 years everything has operated near perfect. I have been on a long learning curve to understand hydronics, especially btus, gpm flow rate, pump head, circulators and heat exchangers.

Happy Holiday season to all, and don't shy away from keeping your feet in hot water.

Woodfarmer -- since the Garn essentially is a wood boiler with a fire tube snaking through a storage tank, Is there any reason to run the Garn circ at times other than system demand? Is it necessary to run the circ when the Garn is firing because the Garn heats storage unevenly and storage btu capacity is underused if the circ is not operating, in other words does running the circ and mixing improve the Garn performance? Otherwise, in the Garn I'm not understanding why the Garn circ necessarily should operate any differently from a circ on any other wood boiler. Sratification occurs because hotter water is less dense than cooler water, so hotter water always should rise to the top unless something is causing it to mix.

I am aware of a Garn install with a plate heat exchanger to tie the open storage Garn to a pressurized system. The facility also has another pressurized wood boiler. This facility runs the Garn circ pump through the heat exchanger even when the Garn is not firing but the pressurized wood boiler is firing. The system design then also permits the pressurized wood boiler to also use the Garn storage, and in effect the hx runs backward to move heat from the system into Garn storage.

Potsdam said:

I am interested to see your pictures. Where can I find them?

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I have lots of pictures and trying to post them all isn't very practical. Are there specific things in which you are particularly interested?

Bob Rohr said:

Nice overview Jim, thanks.

#10, what did you use for an actuator?

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Bob: a description on how the actuator works from a prior post of mine:
Relays are super cool, and they can enable so many cool things. I like your descriptions and prefer the schematic/theory approach because it lets a user be creative in putting relays to work. I think the coolest thing I have done, and an observer doesn't know a relay is involved, is the relay-controlled linear actuator on my slider shop window. When the boiler is switched "on," a DPDT relay energizes the 12-24vdc actuator +/- in one direction and it opens the window 6" to provide combustion air. When the boiler controller shuts the boiler down at end of burn, the DPDT relay energizes the actuator -/+ in the other direction and it closes the window. The movement of the window really grabs the attention of people who view my system.

And a link to more info and pictures:
https://www.hearth.com/talk/threads/combustion-make-up-air.84976/#post-1092663

dogwood said:

Jim, what device(s) are you using for this? That's an excellent idea. My Solo Innova's draft fan seems to run much longer than need be after the fire has burned down. Your tying it in to the boiler circ makes your idea that much better. That circ seems to run excessively too.

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I looked at the Solo Innova manual on-line, and it appears that when the boiler wood load is burned out, the Innova has a control which shuts off the boiler circ and the draft fan at the same time. Pg 31 of the manual at 3.4.14 and Pg 37 of the manual at (P) Lo-Limit address this. If the draft fan and boiler circ are running too long, then the Lo-Limit thermostat should be set higher than 90C. I have this set at 100C on my Tarm, but with the Tarm the Lo-Limit thermostat only turned off the fan, not the boiler circ. I added a separate temp controller to operate the boiler circ.

dogwood said:

I'd really like to adjust the high limit upwards so I could get storage temps ten degrees higher (than 180F) but their tech advised against doing boiler surgery to accomplish this.

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Is your storage pressurized, steel tank? ... or open storage with an EPDM-type liner? ... or something else?

dogwood said:

They recommended turning the Lo-Limit setting higher. I just went out to the boiler room and checked the setting, which I had reset at the 120C mark. That improved the situation, but it still seems to run longer than it should. Maybe I should adjust the Lo-Limit a bit higher.

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With the Lo-Limit set at 120C, what remains in the firebox unburned: all ash, a few chunks of coals, or larger, multiple pieces of unburned wood? If the wood load comes close to all ash with a few chunks of unburned coals, I would say that was a good burn and 120C is OK. If there remains quite a bit of wood not fully burned, then I think the Lo-Limit should be set lower until you reach a point of mostly ash with a few chunks of unburned coals. As mentioned above, for my Tarm the setting I have is 100C, and what remains is mostly ash with a few chunks of unburned coals. Those coals, even when cold, make an easy start for the next fire.

Another guide to setting the Lo-Limit would be the T between the boiler supply temp and the temp of return from storage. If the boiler is still raising the temp of return water at least a few degrees, then it is still putting useful btus into storage, and an early shut down might be similar to an unwanted idle situation rather than the time for fire out.

dogwood said:

I'd really like to adjust the high limit upwards so I could get storage temps ten degrees higher (than 180F) but their tech advised against doing boiler surgery to accomplish this.

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If Hi-Limit is 180F, you should be able to operate the boiler and heat storage to 180F or very close to that, if you use care in loading the boiler so that as storage rises close to 180, the boiler wood load is burning out and the boiler coasts to fire out condition.

I think the recommended Hi-Limit setting of 180F assumes an EPDM open storage system, as that is about as high a temp as should be used with EPDM. With a steel pressurized tank, a higher Hi-Limit should be OK, as in my Tarm the operating Hi-Limit maximum is 194F. With that setting and careful wood loading I can bring the entire 1000 gal tank up to 190-194F, although I don't usually do that. I don't know whether there is a "stop" on the Innova Hi-Limit thermostat that can be adjusted for you to achieve a Hi-Limit of greater than 180F. Be aware that as water temp increases, water expansion also increases, and your expansion capacity needs to be sufficient to accept the additional expansion if you raise the operating Hi-Limit above what you have now.

A few tweaks to add:
13) Not sure about this one, so should a pressure relief valve be periodically tested? What's the risk of damaging the gasket and the valve leaking after pulling the lever to test it? That happened with mine, and although I was able to isolate the valve for removal, it was a real pain. Thought it might have been better to leave it alone.
14) Ditto for a wye-strainer, that is, periodically open and clean it? I've got one right now that I'm pretty certain is impeding flow, but both the bottom nut and the opening nut are frozen tight. Never been opened for cleaning since installed several years ago. But, fortunate to have isolation valves around the strainer.