I have a Tarmsolo40. It doesn't have a variable speed motor for its fan. I understand that some other boilers do. Is it an advantage to be able to control the fan speed? Does it make the boiler more efficient?
Variable speed fan motors
- Thread starter chuck172
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The Eko has variable speed fan settings on the newer models (mine WOULD be the older model) and the major consensus is they help a lot. I have to cut my blower opening output way down to even come close to the efficient tune that can be achieved with the reduced blower speed settings. Some are using ceiling fan control switches to "convert" their older models to variable speed. But there are limitations for the controllers so it should only be approached with informed caution.
Seems to me , if someone is running without storage, and the boiler tends to idle too frequently, reducing the fan speed might be a benefit.
Interesting question, but not exactly an easy answer. Early on I had over-draft issues, that is, flue temps 700-900+ on occasion. So I added a motor speed control to the draft fan in an attempt to reduce the draft and flue temp. I finally substantially solved the problem by closing the draft fan damper a lot and adding the chain turbulators. It seems the problem is more related to my over-dry pine and birch wood, both of which burn very hot, than to actual over-draft.
Now back a couple of steps before I solved the draft problem and my experience with the fan speed control. It both works to slow the burn down and it doesn't work because it slows the burn down. And it works some to decrease draft in very cold weather and to allow full draft during warmer weather when more draft is needed.
If the wood load is close to perfect, small splits, and burns close to perfect in that the wood load falls pretty evenly as the burn progresses, no hang-ups or bridges, then slowing the draft fan down helps to slow the burn to drop the flue temp. But if those are not perfect, then the reduced draft ends up not allowing the burn to actually progress with overall efficiency. That extra (normal) draft is needed to quickly burn through minor hang-ups.
The long and short of it is that I still have the speed control wired with a control knob on the front panel, but I do not use it very often to reduce the draft. Overall I have tried to burn and forget it, not fussing with the controls, and just let the boiler do its work. I'm pretty sure that a modulated fan control would be the best for efficiency, but that taking the time to adjust the draft fan speed based on weather or wood conditions ends up being more trial and error, without a consistent result, rather than trial and error ending up with some real fixed idea of where to set the speed.
All that said, put one on, try it, and see what you experience. I guess if I thought it was worthless, I would have disconnected the motor speed control. Yet I use it very infrequently.
chuck172 said:
I have a RK-2001U controller, the same one that is on the EKO. Stack temperature is not connected to the controller, the fans are regulated by water temperature. They are adjustable from 50 to 100% and will throttle down when desired temperature is near.
Why are stack temps so critical on a Tarm?
So you're saying that the fan speed is regulated by the boiler water temp? I assume that the lower the water temp, more heat is needed and faster, so fan speed is high, as the water temp gets closer to the aquastat set point high limit , fan speed is automatically lowered.
Does that improve efficiency?
I do see where that might benefit those with no storage, less idling.
Does that improve efficiency?
I do see where that might benefit those with no storage, less idling.
chuck172,
I have an older controller on my EKO40 with no storage and it does slow down when the temp nears the maximum but people with storage like the lower output as well because the closer you get to maximum temperature the less efficient the boiler is at full throttle. In the case of no storage having the fan slow down also helps prevent coasting into and overheating situation with a full throttle/sudden shut down scenario.
I have an older controller on my EKO40 with no storage and it does slow down when the temp nears the maximum but people with storage like the lower output as well because the closer you get to maximum temperature the less efficient the boiler is at full throttle. In the case of no storage having the fan slow down also helps prevent coasting into and overheating situation with a full throttle/sudden shut down scenario.
Stack temps are not critical, unless for some unlikely reason dangerously high. Stack temp is related to overall efficiency, as heat up the chimney is heat not transferred to the water. From what I have read on this forum is that generally stack temp < 300F starts to get into the range where condensation in the stack may occur. Tarm advised me last year most Tarm users experience a stack temp of about 600F. My stack temp ranges between about 400-600, with 600 maybe being reached during the first 1/3 of a burn. Damping down the draft reduces combustion air, which slow combustion, which results in a lower stack temp.
Expanding on this, Damping down the draft reduces combustion air, which slow combustion, which produces less wood gas and produces a lower rate of gasification, which results in a lower stack temp.
I have been designing a "semi-automatic" control scheme as well, a kind of hybrid between Nofossil and Woodnotoil's systems. I am going to put in a stack temp sensor, with the goal of keeping the stack temp above 300*F to prevent condensation, but low enough to maixmize heat transfer to the water.
The difficulty arises in keeping the stack temp up as the boiler approaches its high temp limit. If the burn is in later stages, this is not an issue since most of the condensing substances are already burned. But what about the situation I am often in, where I tend to the coal bed with water temps around 170*, then load the boiler? In twenty minutes, the water is at temp, the draft fan is off, and stack temps are less than 200*. I find this is often the case during the overnight burn.
Perhaps building in a burn-off sequence every 24-48 hours would help to rectify this, in case of any build-up. However, with the wood I am burning I have yet to find any buildup other than a small amount of flyash in the chimney.
Of course, most of this would be moot if/when I get the tanks installed.
The difficulty arises in keeping the stack temp up as the boiler approaches its high temp limit. If the burn is in later stages, this is not an issue since most of the condensing substances are already burned. But what about the situation I am often in, where I tend to the coal bed with water temps around 170*, then load the boiler? In twenty minutes, the water is at temp, the draft fan is off, and stack temps are less than 200*. I find this is often the case during the overnight burn.
Perhaps building in a burn-off sequence every 24-48 hours would help to rectify this, in case of any build-up. However, with the wood I am burning I have yet to find any buildup other than a small amount of flyash in the chimney.
Of course, most of this would be moot if/when I get the tanks installed.
I'm just fooling around with a motor speed controller on my tarm blower. When the zones are calling for heat the boiler water temp. rises. When it gets near 190*, I throttle down the fan speed. I still have gasification, but the boiler doesn't idle and the temp remains in the 190's.
Now I do have storage so it's really not that critical but for others running without storage and idling allot, this might be worth tinkering with.
Now I do have storage so it's really not that critical but for others running without storage and idling allot, this might be worth tinkering with.
As you find this works, let us know your components and circuitry. For those with storage and still getting idling (like me), the issue also may be greatly related to gpm rate and hx effectiveness.
I have been working on gpm/hx issues, as it initially appears that for my plate hx, ideal flow rates are around 14-15 gpm's both sides. For a 5 x 12 x 30 that is a lot of pump head, which argues for a 50-70 plate hx to start with. Add to that the additional plumbing/system head. Right now I am limited on the boiler side to about 8 gpm with the Taco 009, but I will switch it out this summer. On the tank side I have a 3-speed Grundfos UPS 15-58FRC, which on HI has estimated flow of about 10 gpm. I feel confident that I could transfer more heat if I increased the flow on the boiler side, and I will be working on boiler flow rate before I spend too much more time throttling down the boiler by adjusting draft.
I have been working on gpm/hx issues, as it initially appears that for my plate hx, ideal flow rates are around 14-15 gpm's both sides. For a 5 x 12 x 30 that is a lot of pump head, which argues for a 50-70 plate hx to start with. Add to that the additional plumbing/system head. Right now I am limited on the boiler side to about 8 gpm with the Taco 009, but I will switch it out this summer. On the tank side I have a 3-speed Grundfos UPS 15-58FRC, which on HI has estimated flow of about 10 gpm. I feel confident that I could transfer more heat if I increased the flow on the boiler side, and I will be working on boiler flow rate before I spend too much more time throttling down the boiler by adjusting draft.
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