More Wood Boiler Options

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better explains the wod burning challanges. For some reason the drawings do not appear. Here is the piping suggestions from that article. It shows a plate HX for interfacing an open system type of outdoor wood burner, which you do not need, of course.

The tekmar drawing I posted above IS an actual system I installed at my neighbors.

I think, in an earlier post, tekmar offered to help you with control selection and drawings. Really all you need area solar (differential) controls. They sense when either the boiler is hotter than the buffer and start charging it. Or when the buffer is hot enough to dump into the primary loop, without calling on the boiler. A simple aquastat set at 190, or so, could also fire the primary and buffer tank to prevent over heat protection.

With a primary loop it is very easy to pipe in a back up boiler of electric, lp, oil, whatever. Even solar panels could be fed into that primary loop! that's the beauty of piping with PS. It's like a PTO on a tractor, it can drive many options.

The circle primary loop is the system in my own shop's wood boiler system. Boiler injects into and a VS pump pulls away for radiant floors.

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,4498,00.html

The other picture is a more involved (higher budget)system Siggy designed that uses two oil fired back up boiler and an Ergomax. It has a VS boiler/ buffer interface for return protection to the Tarm. I like it much better than a 3 way thermostatic. I believe Greg, at tekmar did the control package for this with a couple 155 and a 254 tekmar.

I think Siggy will revisit wood fired appliances again in an article as they are getting a lot more attention with fuel prices going crazy.

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Nick_16

More Wood Boiler Options

Hi everyone again. I think that this is my final piping setup. It provides low temp return protection for the boiler and puts the buffer tank in the boiler's primary loop so it can do it's job by adding "mass". The pannel rads will be on TRV's with constant circ and a PAB which I forgot in the drawing. This is a Wood gasification boiler which requires a fan to aid combustion, so the heat loss thru the flue shouldn't be too great. The customer wants the greatest efficiency possible but, of course, doesn't want to spend much money on controls. You can't have the best of both worlds and the wood is free. Please let me know what you think.

Nick_16

Woops...forgot the pic.

Here it is.

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Since you asked

I don't like it

Having the buffer in series with the boiler will keep the boiler in condensing mode even longer! Now the boiler has to heat itself and the quanity of water in the buffer.

You have no way to disconnect the buffer load should you want quick response to the heat distribution system.

You have no over heat dump zone for the wood boiler should the loads all be satisified and the wood burner loaded with a full charge of wood.

If the buffer and boiler come up to temperature and a load or loads are still calling, now you are taking your heated water in the buffer and running it through an un fired boier, AKA a cooling tower. So some of the water you just heated will be cooled by the drafting in the boiler.

You could do away with all these problems, and more, by taking the buffer tank off another pair of closely spaced tees on the primary loop. Or not

You could add a simple thermal clutch to the system by using a variable speed pump on the boiler interface to the primary loop. piped with full size piping the sensor would slow the pump RPM (gpm) and assure the return temperature to the boiler stays above 140°. A very simple and safe way to assure boiler return protection.

Here is a sample of some simple drawings, tekmar designed controls for a simple wood buffer. Trust me these systems will do, safely, what you are trying to make happen.



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Steve Ebels_3

Also

The way you have the flow going in your primary loop causes the heated water exiting the buffer tank to be recirculated back into the wood boiler. You should have the flow direction reversed for the boiler/buffer takeoffs and the buffer on the inlet side of the boiler.

Nick_16

I don't think

that the buffer would keep the boiler in condensing mode longer because he plans on only letting the tank get to about 140-145 minimum temp, before more wood is fired and the tank heats up. He lives in Northeast Ohio so, for the most part, when it gets cold, it stays cold. As I said before, this job is going to be done for my cousin. There is a tight budget for controls. I personaly feel that controls are a huge important part of a hydronic system, but trying to keep him happy. I know running the hot water thru the unfired boiler doesn't make a lot of sense but, as far as I know, since the boiler requires a fan for combustion, the stand-by loss as a "cooling-tower" would be very small. Maybe this isn't true. I like your piping diagram hotrod, but what tekmar control can I use to make sure that the buffer is charged when there is excess heat that the loads do need to shed? I know before you talked about a tekmar 150 or 155. In other words the boiler is 80,000 BTU at maximum firing, the total load without DHW is about 65,000 BTU. This is about the least oversizing I can do. Here in Ohio, we figure a design day temp of about -5 F. So in the fall and spring, when it is 40F outside, first, you can help by firing with less wood but, let's say that all of the loads are satisified. The control kicks in the buffer tank pump and puts the excess heat into the buffer tank, so now when the fire dies out in the boiler, and there is a buffer tank full of hot water, how can this be used in place of the boiler to heat the primary loop? I understand the system perfectly, just confused on the controls for it. Fosil fuels are so much easier because they can start-stop. Thank you for all of your help so far.

Nick_16

Hotrod,

Thanks for the help again. I have been looking deeper into the tekmar controls. From what I see, I think I would be best to use the two-stage Tekmar 152. I thought my best bet would be this: Use one sensor on the wood boiler (for protection more or less) when it gets to 190, relay 1 will kick in the wood boiler's pump and the buffer tank's pump, when temp drops to 180, both pump's stop. Sensor 2 will be on the wood boiler as well. When the temp in the boiler drops to maybe 140-150, relay 2 will kick off boiler pump and kick in buffer tank pump until wood boiler temp comes up, (aka. more wood is fired.) How does this sound?

Nick_16

Hi Steve,

Yes, I made a mistake in my drawing. Thanks for reminding me.

hr

Close, but

you really don't want to always kick on the boiler pump, necessarily. What if the buffer is fully charged to 190- 200 or more? You would want to draw from this tank ONLY, until it reached a temperature too low to do any heating. Then, and only then, the boiler would kick back on to either catch up with an ongoing demand, or recharge the buffer if no load is present.

This is also the reason I would not plumb the boiler in series, as it now has to catch up a buffer, possible load calling, and itself.

If your loads can be satisified with low temperatures you could run a real wiiiiide delta t on that buffer and store a lot more useable BTUs. Suppose it got charged to 200 and you could draw it down to 130 or so. Run those numbers on the HDS software, or the formula in that article. That is a great way to leverage delta T.

I know it sounds complicated, but once you draw it and start building it will click in you head. Best to do it right the first time.

You really want to run those gasification units hot, hot, hot! I wouldn't look at a 140 starting point as ideal. I'd rather see them run 170- 190 to keep them in their most efficient gasification mode.

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Nick_16

Yes, I see what you mean

I was also looking at the tekmar 155 Differential Set Point. This will do a good job charging the buffer tank, but it will not know when to call on the buffer to add heat to the primary loop or the boiler. How about mixing the 152 to do what I said above and the 155 to conrol the buffer tank charging.

hr

Correct

one control, only, would not be able to do both functions. I suggested tekmar make a dual differential control

Yes, any simple setpoint could be used in conjunction to trigger the buffer on when the primary loop needs a shot of BTUs.

It may not be readable in my above post, but that drawing shows both the 155 and 152 for this purpose.

I really like the tekmar differential control. Two complaints, like most tekmar controls the wiring is a challange with tiny terminals, miniature print, and very little wiring room. It also requires a seperate 24 volt power source. I do like the digital display, and data record feature so it balances out my whine

Goldline discontinued their fine line of diff control, too bad, a great product for the $$s. Heliotrope still makes a reasonably priced, basic delta t control without any bells or whistles.

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steve pajek

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