# Efficiency misconceptions........



## heaterman (Feb 1, 2012)

I bring this up because of correspondence with a Hearth member here who recently purchased a Lambda controlled gasser and is anticipating the addition of 2000 gallons of storage. Let me say at the outset that I do not disparage his choice in any way. I questioned why not just go with a Garn and he cited the "technology" of the boiler he purchased. While I don't disagree that the boiler he chose is a very good product, I think there is a fundamental disconnect in the thinking that high tech controls and O2 sensors are required to obtain hydronic nirvana.  

 I would humbly submit for discussion here, the premise that storage and dumping all the heat from a wood load into such, is a much more hassle free method of obtaining superior efficiency and reduced emission levels. Recent tests have shown that even with very high quality, O2 controlled units emission levels rise dramatically and efficiency drops when these units are subjected to low load situations. As any astute person here is aware, full boiler output is needed less than 5% of the heating season. That being the case, our heating systems are subjected to operation at less than full load for the majority of the winter.  The person I referenced above is doing it right by adding significant storage that will allow flat out burns until all the fuel is consumed under most circumstances. He will likely not have any issues other than the routine maintenance/replacement required with any lambda (O2 controlled) system. 

Using numbers [shown below] from a test on a production Garn 2000 using cordwood (not the faulty EPA test), you can see that efficiency and emissions from a good basic unit that burns the entire load of wood and _does not idle _are such that there is virtually no room for realistic improvement. 

For those who are unfamiliar with it, the Garn is a 30 year old design that was done right in the first place. It uses no controls other than operator input and a button to start the combustion fan when fueled.

 The test was conducted by Intek in accordance with the Thermal Storage Appendix XI of ASTM Document E 2618 â€“ 09, using oak cordwood just like you and I burn rather than the kiln dried cribwood in the EPA protocol.
  It was done at the Garn facility using a standard dilution tunnel sampling method and it gave the following results. 


 88.4% delivered efficiency and more tellingly, only .088 lbs of particulate/million BTUâ€™s delivered output.  


This emission result is 72% less than the current EPA Phase II Limit of .32 lbs of particulate per million BTUâ€™s delivered.
For the sake of clarity, it should be noted that wood heating efficiency is currently based upon the lower heating value of fuel industry wide.
The efficiency achieved simply physically cannot be any better or a person would encounter issues with condensation of flue gas and the resulting disaster in your heat exchanger.

So I would ask the following question; is _"the answer"_ simply storage and good design, or are high tech controls going to be the best long term choice? I tend to fall into the KISS category but I am willing to learn if I'm missing something here.

Let's hear what you think.


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## Singed Eyebrows (Feb 1, 2012)

heaterman said:
			
		

> I bring this up because of correspondence with a Hearth member here who recently purchased a Lambda controlled gasser and is anticipating the addition of 2000 gallons of storage. Let me say at the outset that I do not disparage his choice in any way. I questioned why not just go with a Garn and he cited the "technology" of the boiler he purchased. While I don't disagree that the boiler he chose is a very good product, I think there is a fundamental disconnect in the thinking that high tech controls and O2 sensors are required to obtain hydronic nirvana.
> 
> I would humbly submit for discussion here, the premise that storage and dumping all the heat from a wood load into such, is a much more hassle free method of obtaining superior efficiency and reduced emission levels. Recent tests have shown that even with very high quality, O2 controlled units emission levels rise dramatically and efficiency drops when these units are subjected to low load situations. As any astute person here is aware, full boiler output is needed less than 5% of the heating season. That being the case, our heating systems are subjected to operation at less than full load for the majority of the winter.  The person I referenced above is doing it right by adding significant storage that will allow flat out burns until all the fuel is consumed under most circumstances. He will likely not have any issues other than the routine maintenance/replacement required with any lambda (O2 controlled) system.
> 
> ...


It would be hard to fault Garn for heat transfer capabilities when the "boiler" is in the tank & I don't think too much more could be extracted from the fuel. I think for most people the efficiency comparison wasn't to the Garn, it was to small non Lambda boilers & there would be a difference with these. Could I ask why the Garn is rated as a gasification boiler? Dectra doesn't put too much info out there. I know the fuel load is burned basically horizontally. My guess would be that the reaction chamber glows red hot & secondary air is introduced in there somewhere, correct? wrong?  Randy


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## ewdudley (Feb 1, 2012)

Speaking for myself, the unit is set up to drop the burn latch relay, shut down the exhaust fan, and seal off the draft inlet as soon as storage is maxed-out, so there's no idling or smoldering.

As far as efficiency, it would take many decades to pay for the increased efficiency of a closed-loop combustion control, even supposing the lambda units have an efficiency advantage, which I doubt. Not to mention the expense of having a full inventory of replacement parts on hand should some oddball one-year one-model Elbonian control decide to wig out.  

But I can definitely see a future for any unit that can legitimately claim to minimize emissions in urban settings, alpine valleys, or other places that may well be unable to tolerate 'a little smoke on start up'.

--ewd


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## heaterman (Feb 1, 2012)

Randy, the Garn does use gasification to sustain that level of temperature (1600*+) in the secondary chamber. (When wood gas is present of course) It is configured differently than a downdrafter in that the airflow is horizontal through the fuel and combustion chamber rather than downward, which can make it a little easier to light up. More like Viessmann's wood boiler which burns horizontally at the bottom. 
With their design, primary air enters at the bottom and impinges directly on the fire while secondary air goes across the top, gets superheated and then mixes with the smoke/gas when it enters the secondary chamber where it ignites. 
The point I am bringing up is not so much controls and high tech boilers as it is the issue of storage being a simpler path to good burn characteristics.

EW, you kind of hit the nail on the head when you mentioned smoking at startup. It's virtually impossible to do and that is the advantage, as I see it, in a batch burn/storage type system where there is only one start per load. Your other comments are dead on as usual as far as I can see.


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## benjamin (Feb 1, 2012)

I couldn't agree more. I come at this from the cobbled together end of the spectrum, so I can't imagine how there could be a critical mass of demand for high tech wood burning systems. Where I was raised, if you got $20,000 you don't buy a wood burner, you buy a double wide and retire. If you add up the materials and a qualified contractor to install some of these systems, then geothermal starts to look like a bargain IMHO.

Thermal storage is definitely the way to go, whether that's steel water tanks, masonry stoves, adobe or concrete, depending on climate, needs etc. The garn is a simple, robust and effective product that has the disadvantage of size, cost, and an open system. The typical indoor gassifiers with added storage can do the same thing, but with more complex installation, more complex operation and similar cost. I just don't think there are enough Americans willing to pay the high price for quality components and custom installation, learn to operate the systems and still have to cut or buy wood. 

I would like to build-find-copy-design a woodburner similar to a garn in simplicity, refractory, blower and controls, without the built in storage. The drawbacks would be that the simplicity would not allow it to idle, and the separate storage would lead to boilover and/or overheating the boiler if circulation and backup fire damping failed. A simpler relatively high efficiency boiler would work great in conjunction with concrete shop floors, tight homes with at least moderate mass, DHW in multiple electric water heater tanks or propane tanks and heat exchangers. When all of these loads are drawn down they could easily store the output without additional water tanks.


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## Como (Feb 1, 2012)

I am not aware of any wood boiler with lambada controls where the manufacturer does not specify storage. It is a requirement due to the nature of the beast.

Depending on your situation there is a lot to be said for sizing the boiler to meet a bit less than peak load, so you burn at 100% much more of the time and then top up with something else.

I can quite see that greater controls would improve efficiency a little and decrease emissions slightly over the course of a burn. Just look at your vehicle. The biggest gain would be to get the design right.


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## hiker88 (Feb 1, 2012)

I'm one of the people considering a lambda based unit.  However, if you and I had had the discussion, I wouldn't have mentioned efficiency as the reason to go with a lambda unit.  From my massive amount of experience related to wood boilers (all gained on this forum in the last six months or so) - once you go with a quality gassifying boiler and hook it up to storage you're pretty much there efficiency wise.  I see that the lambda units claim efficiency numbers a bit higher, but not to the point where the dollar difference makes it my reason.

For me, it's the convenience factor.  Some might scoff at that, but when you're trying to replace the convenice of oil and trying to get the family on board (who will also have to tend the boiler) this can be a factor.

PS I agree that I've not come across a lamda unit that doesn't require storage.


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## jhunter19 (Feb 1, 2012)

I like the idea of having some O2 sensors on the unit.  I have a Biomass 40 and struggle to keep the unit in gassification mode.  If I had some measurement of whether I was too rich or too lean, it might make adjusting easier.  As it stands now, I tweek a llittle here and there but have no way of knowing what effect I am having on the unit.  Very frustrating.


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## pwschiller (Feb 1, 2012)

hiker88 said:
			
		

> I'm one of the people considering a lambda based unit.  However, if you and I had had the discussion, I wouldn't have mentioned efficiency as the reason to go with a lambda unit.  From my massive amount of experience related to wood boilers (all gained on this forum in the last six months or so) - once you go with a quality gassifying boiler and hook it up to storage you're pretty much there efficiency wise.  I see that the lambda units claim efficiency numbers a bit higher, but not to the point where the dollar difference makes it my reason.
> 
> For me, it's the convenience factor.  Some might scoff at that, but when you're trying to replace the convenice of oil and trying to get the family on board (who will also have to tend the boiler) this can be a factor.


That was my thinking as well. An efficiency rating difference of 3-5% didn't matter to me so much, it came down to ease of use. Also important to me was having a negative draft boiler to minimize or eliminate smoke escaping indoors and a sensor to automatically shut down the fan near the end of the burn. The three lambda boilers that I'm familiar all have those features.


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## Como (Feb 1, 2012)

hiker88 said:
			
		

> I'm one of the people considering a lambda based unit.  However, if you and I had had the discussion, I wouldn't have mentioned efficiency as the reason to go with a lambda unit.  From my massive amount of experience related to wood boilers (all gained on this forum in the last six months or so) - once you go with a quality gassifying boiler and hook it up to storage you're pretty much there efficiency wise.  I see that the lambda units claim efficiency numbers a bit higher, but not to the point where the dollar difference makes it my reason.
> 
> For me, it's the convenience factor.  Some might scoff at that, but when you're trying to replace the convenice of oil and trying to get the family on board (who will also have to tend the boiler) this can be a factor.
> 
> PS I agree that I've not come across a lamda unit that doesn't require storage.



For convenience, then pellet would be the way to go followed by wood chip.


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## maple1 (Feb 1, 2012)

On that note, might it be beneficial for some who are having tuning issues, to just install a simple a/f (lambda) meter in the exhaust outlet and use that to tune in their operating procedures?

I am quite new to this stuff as well, but from all I have read on here, it does seem that the lambda aspect is more of an ease of use thing than an efficiency gain of any significance.

EDIT: I typed too slow again, that was in response to jhunter.


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## hobbyheater (Feb 1, 2012)

heaterman said:
			
		

> Let's hear what you think.



I"m a complete believer in heat storage. My association with heat storage predates the Jetstream and the Garn. Our first wood boiler was a round barrel type with a water jacket around the fire box. Burned 22 cords in the first year of operation. The second was a Tasso cast iron down drafter, the smallest unit they made.  It burned 16 cords in a year.  Both of these boiler were creosote dragons.  A 1000 gallon storage tank was added with the hopes of eliminating the creosote problem. HA! On the storage tank, the creosote only got worse, not the boilers fault.  I knew nothing about keeping the water in the boiler above 140 F plus. The  upside of this is that the Tasso's wood consumption dropped to under 10 cords. The Jestream, in the same system, burns around 5 cords.
There is also one more step in this.  I had seen the improvement in the Tasso's efficiency when connected to storage, so I did some tests to determine just how much the oil boiler burned.  A  Hobbs meter was hooked up to the burner of the oil boiler to determine its fuel usage in heating and stand by mode. In the next step the oil boiler was connected to the storage tank and it cut the oil boiler's consumption of oil by 60% - yes, really 60%. 
Storage eliminates stand by and stand by loses can be huge.


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## jhunter19 (Feb 1, 2012)

I have 500 gal storage on my Biomass 40, but my unit has never gone into stand by mode that I can tell.  I wish is would.  About as hot as I can get my storage is 150 deg F.


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## heaterman (Feb 1, 2012)

Como said:
			
		

> hiker88 said:
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True. Automated feed of wood chips or pellets is as near to oil/gas burning as you can get.

 As far as cordwood goes, there is nothing else as convenient as filling, pushing the start button and not thinking about it again until the storage temperature gets low. With an integrated storage unit like Garn there are no pumps, no piping, no controls, no wiring and no assembly required.  And that I guess is the point of my initial question.  

Let me rephrase it.

Does anyone have documentation that high tech controls add any significant benefit to a storage based system in terms of emissions and efficiency? 

 I'm mentally comparing a "normal" gasser with storage or something like a Garn to a gasser with computer controlled combustion process.  From the numbers I'm seeing for Garn and for normal gassers with decent (four figure) storage, the issue is storage and batch burning more than anything else.


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## bpirger (Feb 1, 2012)

I'd say one of the things I like the most about the Garn is there is nothing to adjust.  I don't have to tweak or twiddle to keep the gasification going.  No vents to open/close, no smoke in the "house", no worries of boil over (unless you put on too much wood).

Now, that said, I sometimes wonder how do I know if it is working....and the answer to that is look at the exhaust.  No smoke?  Gasification.  Smoke?  Something is not ideal.  As I write this, I can look out the window and see no smoke coming from the 80+ pounds of wood burning in the Garn.  Good!  I will say that placing a small piece of wood in front of the "pile" to burn will deflect some of the primary air (entering the burn chamber at the bottom) upward.  Sometimes without doing this, I might see a bit of smoke for a bit longer.  Next year I will intentionally cut a bunch of cookies to use for exactly this purpose...about 2" thick, from maybe a 12-15 log, and half of it should be perfect.  One could very legitmately argue this is required twiddling and tinkering.

It would be interesting, and heaterman has this been done, to run a Garn without the refractory lining in the chambers and see/measure the output.  Even with a full out burn, there should be a significant increase in the emissions.  Has this been done by Dectra?


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## heaterman (Feb 1, 2012)

bpirger said:
			
		

> I'd say one of the things I like the most about the Garn is there is nothing to adjust.  I don't have to tweak or twiddle to keep the gasification going.  No vents to open/close, no smoke in the "house", no worries of boil over (unless you put on too much wood).
> 
> Now, that said, I sometimes wonder how do I know if it is working....and the answer to that is look at the exhaust.  No smoke?  Gasification.  Smoke?  Something is not ideal.  As I write this, I can look out the window and see no smoke coming from the 80+ pounds of wood burning in the Garn.  Good!  I will say that placing a small piece of wood in front of the "pile" to burn will deflect some of the primary air (entering the burn chamber at the bottom) upward.  Sometimes without doing this, I might see a bit of smoke for a bit longer.  Next year I will intentionally cut a bunch of cookies to use for exactly this purpose...about 2" thick, from maybe a 12-15 log, and half of it should be perfect.  One could very legitmately argue this is required twiddling and tinkering.
> 
> It would be interesting, and heaterman has this been done, to run a Garn without the refractory lining in the chambers and see/measure the output.  Even with a full out burn, there should be a significant increase in the emissions.  Has this been done by Dectra?



I've seen it done inadvertently when people destroy the front half of the refractory. Put mildly, it definitely effects both emissions and efficiency. That refractory is in there to prevent any heat transfer in that area and create maximum temperature possible.


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## bpirger (Feb 1, 2012)

But no actual measurements?  I'd think it would be similar to a typical OWB burning full tilt....  Obviously one wouldn't want to DO this, other than just to measure the impact of the hot refractory chamber.


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## heaterman (Feb 1, 2012)

bpirger said:
			
		

> But no actual measurements?  I'd think it would be similar to a typical OWB burning full tilt....  Obviously one wouldn't want to DO this, other than just to measure the impact of the hot refractory chamber.



I doubt it's ever been tested or tried that way purposely.


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## Singed Eyebrows (Feb 1, 2012)

I've talked up Lambda boilers as much as anybody on the forum because of the need to babysit my Atmos untill the Samson flap is down etc. For me, this would be a huge improvement in convenience. I see next to no advantage of a Lambda boiler over a Garn, I would expect the reaction chamber to heat about as fast as a coal bed is established on a downdrafter, so I doubt even a startup emissions advantage. Heaterman, I can understand you losing sales to someone needing to take a boiler down the basement steps. The others is kind of difficult, although I think thats being remedied fast here. Simple is good, & no computor no servos would be a plus for me as having the boiler right in the storage tank. Randy


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## hobbyheater (Feb 1, 2012)

heaterman said:
			
		

> So I would ask the following question; is _"the answer"_ simply storage and good design, or are high tech controls going to be the best long term choice? I tend to fall into the KISS category but I am willing to learn if I'm missing something here.
> 
> Let's hear what you think.



I like simple. Our system is simple.  Boiler and storage tank share the same water with an opened expansion tank on the next floor, internal heat exchanger in the storage tank, one for domestic supply and the other for house heat. One circulator between the boiler and tank and another for the zones.  The bottom of the storage tank is above the top of the boiler's heat exchanger so no need for any valving to prevent stack lost.
Operation of the boiler is simple - scoop the ash out of the burn chamber before lighting the fire.  Wood sizing is important with a 12" round split into three to five pieces being ideal.
This system has had six operators, two of which could not operate it safely. (We had the house rented out.)
My thought is this; if the systems get too complicated, the first generation operator is going to have no problem as he has likely has done the install and understands every thing. What about the second generation operator?


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## Adios Pantalones (Feb 1, 2012)

I like these discussions.

Mother Earth News had all sorts of plans for barrel-based rocket stoves that burned fast and hard, the exhaust going through a mass for storage much like a masonry heater.

Simple, cheap, DIY, efficient- potentially dangerous but the short burn time meant that you could monitor it the whole time.


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## Pat53 (Feb 1, 2012)

jhunter19 said:
			
		

> I have 500 gal storage on my Biomass 40, but my unit has never gone into stand by mode that I can tell.  I wish is would.  About as hot as I can get my storage is 150 deg F.



I would say that either your plumbing isn't right or perhaps your boiler is undersized or you're losing a lot of heat somewhere. With just about any boiler you should be able to get your tank up to at least 180F


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## maple1 (Feb 1, 2012)

Pat53 said:
			
		

> jhunter19 said:
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I was just about to post something similar - something seems not quite right there. Another possibility is wet wood? We might be able to help with more info posted - but likely would be better off in its own separate thread though.


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## maple1 (Feb 1, 2012)

hobbyheater said:
			
		

> heaterman said:
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I also like simple, which is why my planning has me with a natural draft boiler as first choice, and good convection heat load flows for overheat & power outage conditions.


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## Jim K in PA (Feb 1, 2012)

Pete Schiller said:
			
		

> An efficiency rating difference of 3-5% didn't matter to me so much, it came down to ease of use. Also important to me was having a negative draft boiler to minimize or eliminate smoke escaping indoors and a sensor to automatically shut down the fan near the end of the burn. The three lambda boilers that I'm familiar all have those features.



The GARN has all those features, without O2 sensors that will require replacement, air flow controls that will require maintenance, or a sophisticated control schema.  There is nothing simpler than loading, lighting, and walking away, which is what I have been doing for three seasons with my GARN.  And mine doesnt even have the new-fangled controller!


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## Jim K in PA (Feb 1, 2012)

heaterman said:
			
		

> So I would ask the following question; is _"the answer"_ simply storage and good design, or are high tech controls going to be the best long term choice? I tend to fall into the KISS category but I am willing to learn if I'm missing something here.
> 
> Let's hear what you think.



Steve - The answer I think is "both".

I think it comes down to a couple of factors, neither of which have anything to do with efficiency.  The customer that does not have a convenient way to house the GARN and does not want to build a shed will opt for the solution that "fits" their physical parameters.  The other issue is that for some, the PERCEPTION that a more "technically sophisticated" solution will provide better results rules the day, irrespective of data.  I am also a follower of Occam's Razor, so I always look for the simplest solution first.  However, a smaller unit that can fit within the desired space, plumbed with divorced storage, with cost and complexity equal to or greater than a GARN, is still a better solution than an old smoke dragon in the backyard or a hungry oil burner in the basement.  

I also lost a sale of a GARN due to nothing more than the physical constraints of the customer's situation.  The customer WANTED the GARN, but the consequential costs of accomodating its size put it out of his budget.  For those of us lucky enough to have the room to install one, well we just have to count our blessings . . .


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## goosegunner (Feb 1, 2012)

I am quite amazed and very happy running with 1000 gallons of storage. Lambda users posting the load it, light, walk away method makes me think I should have maybe went that way. Though a recent post seems as that is not quite always the case. The expensive controls kept me from buying a Lambda boiler.

I originally steered away from the Garn because of my Forced air requirement of hotter water. I was told that the Garn might not be the best choice with a Forced air and heat exchanger in the plenum.

After running with 1000 gallons storage this winter and running down to 140 on the tank my system is fine. Most days I can go 24 hours. Cold days I do 2 smaller fires.  If I had the Garn with 1500 I think it would only be better.

If I would have known last year what I do now, I would most likely have a Garn....

gg


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## mikefrommaine (Feb 1, 2012)

I avoided the lambda boilers because it seemed like the small increase in efficency was not worth the increased complexity. The associated repair costs and longer wait times for parts didn't seem worth it to me. I Remember someone on here said the froling computer was over a grand to replace. I can cut a lot of wood for that price.

Would have gone with a garn if I could have put it in my daylight basement. Just didn't have the room for another outbuilding close enough to the house with zoning setbacks and existing infrastructure.

Seems to me that making sure you have well seasoned properly prepared wood is the biggest variable that can be controlled when it comes to getting the most out of a gasser.


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## jebatty (Feb 2, 2012)

> I would humbly submit for discussion here, the premise that storage and dumping all the heat from a wood load into such, is a much more hassle free method of obtaining superior efficiency and reduced emission levels.



Heaterman, this statement is difficult to address because it subsumes one method of burning which by definition may (but I'm not sure) allow only the conclusion which you suggest. Obviously I agree that burning well-seasoned (20% MC) wood in a well-designed gasification boiler with storage sufficient to absorb the full btu output is very efficient, whether in a Garn, Tarm, Wood Gun, Froling, etc. etc. I think, however, that this statement blurs what people face in operating a gasification boiler in a real world operating environment. The fact is that many people do not have space for "sufficient" storage, even if they have space for some storage. And, not everyone loads and burns loads of wood in a manner which permits even, fast and complete burning. And, not everyone has ideal MC wood, of a size and dimension best suited for even, fast and complete burning. And there are other real world factors that enter the equation.

Given the great many variables in real world operation by real people, superior efficiency, reduced emission levels, and hassle free operation leaves plenty of room for a variety of boiler styles, capacities, control systems, and storage capacities, such that it is not reasonable to assert one method only, except in the laboratory.

That said, I return to my statement above, "Obviously I agree that burning well-seasoned  wood in a well-designed gasification boiler with storage sufficient to absorb the full btu output is very efficient, whether in a Garn, Tarm, Wood Gun, Froling, etc. etc."


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## Como (Feb 2, 2012)

mikefrommaine said:
			
		

> I avoided the lambda boilers because it seemed like the small increase in efficency was not worth the increased complexity. The associated repair costs and longer wait times for parts didn't seem worth it to me. I Remember someone on here said the froling computer was over a grand to replace. I can cut a lot of wood for that price.



That was my reasoning, but not everybody has room for a Garn.


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## SmokeEater (Feb 2, 2012)

heaterman said:
			
		

> So I would ask the following question; is _"the answer"_ simply storage and good design, or are high tech controls going to be the best long term choice? I tend to fall into the KISS category but I am willing to learn if I'm missing something here.
> 
> Let's hear what you think.



My father would look at a new car and decide whether or not to buy based on his idea of "if it's too complicated, it'll spend too much time in the repair shop".  These beliefs were used by his choice of buying any "machine", and that would include wood boilers.  I don't really know how the lambda equipped boilers work, but have an idea.  Another way of looking at the wood boiler is to view it as a reactant vessel within which a chemical reaction occurs.  If reactants are combining chemically there needs to be sufficient quantities of each to complete the reaction with each reactant being "consumed" completely in the reaction.  In the boiler one of the reactants is the wood fuel that we all spend considerable time and money to acquire.  The other is oxygen, present in the air, easy to obtain, and not too expensive(yet!).  I think a lambda wood boiler has complex (ie. expensive) controls that try to determine the quantity of oxygen to supply to the fixed quantity and kind of wood fuel need to complete the reaction with no fuel reactants and no oxygen remaining after the last of the reactants (limiting reactant) is consumed.  Not usually necessary.  Many reactions use a specific quantity of reactant(wood fuel load) and supply an excess of the easy-to-obtain and inexpensive reactant, oxygen and the wood fuel reactant is completely  consumed, whereas the excess oxygen simply leaves with the combustion products, as in the case of the Garn.  No Lambda necessary.  Maybe I've gotten it wrong, but that's how I see it.  Keep it simple and it won't break as often and often times works almost as well as the complicated version.


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## TCaldwell (Feb 2, 2012)

There really are few arguements, even from me.
I agree that the largest effiency contributors are thermal storage and dry wood to any and all batch fired cordwood systems. Also a efficient combustion hx design, that reduces flue temps to 400deg or lower, this becomes a challenge when limiting boiler return temps required on downdrafters, actually the garn benefits from this, because if you have a system requirement of 110deg supply water and wait to fire at 110, your flue temp will be low helping the efficiency to be high, rather than refiring at 140 as a example. fluestack effiency calculation [you can google the formula] is used in fluegas analysers to calculate effiency, if you do the math a very low o2 number if the fluegas temp is low will still yield a high efficiency, the garn is good at this as half its burn is below the stiometeric setpoint of 7% for wood, wich is the optimum situation because it maintains a low flue temp from firing in a large low temp body of water. Effiency decreases as the water temp increases, and that takes about a load of wood in the garn. The downside to the garn equation is the last 1/3 of the burn is overaired o2 is up, flue temp is influenced to some degree by water temp, excess air is up and effiency is low. As a example o2=15%, co2=5% flue temp 280  ambient air temp 70 nets a effiency of 58%, as the o2 rises the effiency decreases. This to some degree holds true at start of burn also, no matter what the control strategy some of this is unavoidable. It is my beliefe that o2 control is of benefit, anytime you can sustain the optimum burn parameters for 85% or more for the length of a burn you are MAINTAINING a high average effiency, not just occasional spot checks during high burn. I think downdrafters, due to the lower water mass and challenging flue temps benefit more than the garn style boiler to o2 control. O2 control may be picking hairs effiency wise vs dollars but will end up on most all boilers as is storage mandatory throughout most of europe. I still believe until shown otherwise that my boiler is maybee just a little more efficient than stock, not withstanding cost.


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## heaterman (Feb 2, 2012)

I wouldn't quibble with any of that Tom.


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## leaddog (Feb 2, 2012)

First of let it be known that I think the garn is a great boiler. I looked at them when I was going to buy. In my case I have the time to do the work, I have the time to scrounge up parts so cost became the deciding factor. I put the 2000 gal of storage against the house so any heat loss is going partly into the house. I only have less than $9000 total in my system including all the mistakes I've made along the way. I almost bought a wood gun but because of price difference during the time of looking and then dealers coming into the picture they got to high. At the time the eko was the best buy for ME. If I was to change now I probably would check out one of the newer efficient models because I have my storage and every thing in place. I do think they would be esier to run. 
With that all being said if I hadn't been able to install every thing cheaper I love the garn. If the price is the same and I have the room etc the garn wins every time.
leaddog


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## thecontrolguy (Feb 2, 2012)

If I might add to the mix, after a LOT of reading, industrial bio-mass experience, and an old farm-house heated with (a lot of) wood in a modified RSF100 wood furnace, I feel that the cleanest most efficient burns come from full-tilt batch burns from devices built like the old "Jetstream" or anything else emulating its burn characteristics.  Perhaps a further squeeze of efficiency into the Jetstream would be a Lambda sensor controlling the amount of air injection into the burn, but the high-temps and no creosote problems reported consistently from users in its 30 years of history can't be wrong.  Also, simple to operate, re-buildable, and long-lasting.  Lets see where these fancy all-electronic multi-damper lambda controlled variable-fan speed boilers will be in 25 years?  I would really be pleased to see someone offer a kit form of the Jetstream, with the user pouring his/her own vermiculite and the inner refractory liner poured by the user with good instructions to follow.  This would lead the user to trust their skills and be able to use the boiler long into the future, and the factory keep the shipping costs down to a minimum.  However, I also feel strongly that NO wood boiler should be installed without some type of accumulator installed to prevent the boiler from short-cycling or otherwise going into a turn-down or idle mode.  Creosote, condensation, corrosion. Not good for a boiler ..


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## bioman (Feb 2, 2012)

Heaterman
 Saving the world, one wood boiler at a time. Once again Heaterman tells it like it is. I like simple, Garn is simple, built like a tank. don't need no 02 sensor to burn out if you don't see no smoke then something is going right. just my 02.


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## jebatty (Feb 2, 2012)

Maybe it's important to keep this discussion focused on the premise, which is burn efficiency. We all pretty much agree that a full tilt batch burn at gasification temperature results in very high burn efficiency. TCaldwell has accurately pointed out that 





> The downside to the garn equation is the last 1/3 of the burn


 when water temps get above 140F. And with regard to the Garn WHS3200, that is exactly what Dectra has advised, that efficiency drops off with water temps above 140F.

If we all want the discussion to move from burn efficiency to boiler - system interface efficiency and usefulness/practicality, then I think the discussion may start to change considerably. And if we want to look at other design constraints of the Garn which reduce its efficiency in delivering btu's to the system, then the discussion also may start to change considerably. A number of points in these regards already have been made. Based on things stated in this thread and things not stated, there are many reasons to choose a boiler of one brand over another, and they are not all based on ignorance. There are good and valid reasons why everyone has not purchased a Garn. 

Brand hyperbole and brand bashing both need to be avoided.


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## woodsmaster (Feb 2, 2012)

Garn was on my short list when looking at boilers. Came down that to that is was simply out of my budget. Also size was
big and that translated to more money for a building to put it in. I'm happy with my decision and think I would have been
just as happy with a garn. Especially the first few weeks when I was adjusting air for the optimal burn. I was originally
going to get a conventional OWB until I found this sight and became more educated. I'm happy with the efficiency
of the biomass. I heat my house shop and DHW with only about 20 - 25% more wood than it took me to just heat
most of the house with my old wood stove and I have some heat lost to the outdoors by having it in
a shed, But that's one trade off I was willing to make for thr sake of the mess.


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## jebatty (Feb 2, 2012)

> heaterman: The test was [on a Garn 2000] conducted by Intek in accordance with the Thermal Storage Appendix XI of ASTM Document E 2618 â€“ 09, using oak cordwood just like you and I burn rather than the kiln dried cribwood in the EPA protocol.
> 
> It was done at the Garn facility using a standard dilution tunnel sampling method and it gave the following results.
> 
> 88.4% delivered efficiency and more tellingly, only .088 lbs of particulate/million BTUâ€™s delivered output.



I have reported high efficiency numbers for the Garn WHS3200 in prior posts, although not quite this high. It would be very helpful as an aid in improving the 3200 performance to get more information on the Garn 2000 tests, such as:

1) what was the exact MC of the wood, and was it uniform for all wood burned;
2) what were the dimensions of the wood burned, how much difference between splits;
3) what was the weight and volume of the ash and coals remaining in the firebox at the end of the burn;
4) what was the condition of the firebox and the hx tubes, that is, well cleaned such as a user might have after cleaning the Garn before starting a new burn season, or in the condition that might exist after a half season of substantial use;
5) was the Garn 2000 in factory delivered condition, other than installation of sensors;
6) what was the chimney configuration and dimensions used during the test;
7) what was the weight of the wood burned; was it more than one single load; how much by weight loaded and at what times during the burn;
8) what was the low heat value used for the wood:
9) what was the starting temperature of the water in the Garn and was it uniform in temperature;
10) what was the ending temperature of the water in the Garn and was it uniform in temperature;
11) what flue temperatures were measured during the burn and at what location and times were the measurements taken;
12) was the standard, one speed blower used during the entire burn, what CFM; and if not, what was used and what was the CFM;
13) what was the length in time of the burn; was it measured from first lighting until the end; was it measured during some mid-point period of the burn;
14) at what point and why was it determined that the burn was completed;
15) was the water mixed during the burn or after the burn; what method was used to mix the water during or after the burn, what circulator, what gpm, etc.;
16) what was the air temperature in the structure housing the Garn during the test;
17) what was the outside air temperature during the test;
18) what and how much insulation was placed around the Garn for the test;
19) did the efficiency calculations account for heat loss into the structure during the test;
20) did the test measure O2 or other components of the combustion process, other than particulates, and if so what were the components and the measurements.

I think this will help all of us in using our gasification boilers to achieve higher efficiency and greater satisfaction in our gasification boiler experience.


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## jebatty (Feb 2, 2012)

I was able to locate the test report on the Garn WHS1500, but not the WHS2000. Will need more time to review the report.

Test Garn WHS1500


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## MarcM (Feb 2, 2012)

jebatty said:
			
		

> I was able to locate the test report on the Garn WHS1500, but not the WHS2000. Will need more time to review the report.
> 
> Test Garn WHS1500



I don't know if it's just my crap browser, but the link didn't work for me.

For anyone else with the same issue, here's the full URL:

"http://garn.com/wp-content/themes/Chameleon/forms/G100248857MID-006R Test Report signed(3).pdf"

Do a copy/paste


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## Tennman (Feb 2, 2012)

Great discussion, I'm learning a lot. Hopefully won't be in the market for a new boiler for a while but can't help collecting data and Garn was way up on my list. I'm surprised to learn a Garn is less than idea for a forced air HX system. So as the Garn's stored temp gets higher it's efficiency drops off... because the water to exhaust gas temp differential gets less?? I guess that would be true for all boilers. I'm getting this from TC's comments regarding increase in flue temps which I'm taking that as the water to exhaust gas differential decreases the gas transfer rate decreases. Makes sense. But for my forced air system I routinely see 185F for the majority of the burn. Garns never get their water this hot? It's just interesting to me that some boilers may be more suitable for forced air. I'm stuck forever with forced air. Is that what ya'll saying here?


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## Frozen Canuck (Feb 2, 2012)

Tennman said:
			
		

> Great discussion, I'm learning a lot. Hopefully won't be in the market for a new boiler for a while but can't help collecting data and Garn was way up on my list. I'm surprised to learn a Garn is less than idea for a forced air HX system. So as the Garn's stored temp gets higher it's efficiency drops off... because the water to exhaust gas temp differential gets less?? I guess that would be true for all boilers. I'm getting this from TC's comments regarding increase in flue temps which I'm taking that as the water to exhaust gas differential decreases the gas transfer rate decreases. Makes sense. But for my forced air system I routinely see 185F for the majority of the burn. Garns never get their water this hot? It's just interesting to me that some boilers may be more suitable for forced air. I'm stuck forever with forced air. Is that what ya'll saying here?



I think the discussion is mixing a few variables here. 
Namely the physics of heating water at different temps. 
It takes more energy to heat water from 150 -190 than it does to heat it from 110 - 150. Same 40 delta, so what's up with this? 
We all think it should be a straight line right? Nope like most things it's a curve. 
Once one reads up on this one begins to understand why a country like Germany has rules in place that lower the max temp of fossil fired boilers into the high eff range 150"s as opposed to the 190"s & above that you will see on this side of the pond. 
Tennman you are right these variables will apply to all boilers as they all heat the same medium - water. 
No boiler is better or worse suited to delivering any type of water based heat, as the medium (water) is the constant. 
What is often misinterpreted as boiler trouble is in fact the poor matching of boiler to load requirement, lousy plumbing, worse pump & component selection & no thought as to what the whole system should look like/function as before someone starts cobbling parts together & calling it a system.
Just my $.02. For me I look at it the same way I do a structure. 
A structure is the assembly of thousands of components, that when assembled correctly work very well with minimal maintenance. 
When assembled incorrectly...well it's just a pile of badly assembled parts that isn't working like it should. 
99/100 it's operator/assembly error. 
Just the way it is as we (humans) are the largest most uncontrollable variable in the equation.


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## heaterman (Feb 2, 2012)

For clarification:

The Intertek testing was done in accordance with the ASTM protocol for thermal storage units that I mentioned above. Efficiency is measured not at a single point in the burn or even multiple points.

 The numbers generated for efficiency in that regimen are the average over a given period of time which include everything from lighting the match to total exhaustion of the wood supply + standby losses encountered over the entire length of the test. With a thermal storage system like the WHS2000 used in the test this could be from as little as 6-8 hours under maximum btu draw to as long as 24-26 hours when measuring efficiency at 15% of output. It is not designed to be a snapshot of a single point in the burn cycle. Measurements of that type will in all cases tend to give a false picture of what is really going on. They are just a single point "snapshot" and don't do anything but indicate what is going on right at that moment. 

Water temp is measured at the beginning and at the end to determine total btu's going into the storage as I understand it. For the testing done on the Garn beginning water temp was 120-125* and ended at 170-180*. The wood load was split red oak with a moisture content in the 23-25% range.

I wish I could publish all the entire report but it is copyrighted and considered intellectual property so I best not go there.


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## heaterman (Feb 2, 2012)

DP'd


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## heaterman (Feb 2, 2012)

Someone is watching..........I just got this in an e-mail from Garn. It may help to answer some of the questions posed about the test method and the unit itself.



Â·         The efficiency is based upon the total burn (strike of match to no remaining fuel, thus no fire). Standard GARN digital control used to turn off blower at end of burn.

Â·         8 hours of stand-by losses were deducted from the total energy stored to arrive at the overall efficiency of 88.4% (not just â€œcombustionâ€ or heat exchange efficiency).

Â·         Standby losses were measured at 170F. Unit insulated with 8â€ batt fiberglass.

Â·         Tank was thoroughly mixed pre and post burn to obtain a non stratified average temperature. Temperature determined via multiple thermocouples located within the tank.

Â·         De-stratification pump was not run during the test.

Â·         Test storage temps began at approximately 124F and ended at approx 179F.

Â·         Stock WHS 2000 unit installed per manual with about 4 months of use on the unit prior to the test.

Â·         6â€ Class A vertical flue. Flue gases collected by dilution tunnel per ASTM E2515-09. Dual vacuum sample trains used to collect particulates.

Â·         Standard GARN WHS single speed blower.

Â·         Approx 160 lbs of red oak at 23 to 24 % MC, dry weight basis per ASTM Spec was used for each test. MC was determined at 6 locations for each piece of cordwood.

Â·         Cordwood size was 3â€ to 10â€ across and 24â€ in length. Some split some not split. Purchase from the â€œopen marketâ€ of MN and WI.

Â·         Three (3) tests conducted over a one week period in October.



The tests were set up and executed in full compliance with ASTM Document E2618-09, Appendix XI for Thermal Storage Equipment and conducted by Intertek Testing of Madison , WI. The full details of how the test was set up and conducted can be found in the two ASTM Documents referenced. The two documents describe the standard method for testing cordwood fired equipment that incorporates full thermal storage (not partial thermal storage).


Gotta run. Just got a call from someone who ran into their wood boiler with their truck. Never know what a day will bring................


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## jebatty (Feb 2, 2012)

Garn deserves credit for posting the test report on the 1500; hopefully it will do the same for the 2000. And I hope other boiler mfrs post similar information, in detail. This kind of information will help shed light on many of the things that we discuss on the forum.


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## jebatty (Feb 3, 2012)

I reviewed the efficiency calculation on the WHS1500 as contained in the test report and compared it to other information to roughly test the outcome. Does the following make sense?

The report uses HHV of 8550 btu/lb, which is wood at 0% MC, and calculates the weight of the wood in the test burns as if at 0% MC. Total btu input then is 8550 x dry weight. Without quibbling over any rounding, btu input = dry weight x 8550. Using Run 4 as an example, dry fuel weight of 55 kq x 2.205 = 121.28 lbs x 8550 = 1,036,012 btu input (vs 1,029,557 in test report, and I have no issue with this variation).

The efficiency calculation is (heat stored) / (input) = 744,056 / 1,029,557 = 72.2% (vs 71.6% in test report, again I have no issue, the small variation may relate to standby loss and heat stored in the steel mass of the Garn).

For a comparison, based on 20% MC and 400F stack temp, wood has 6050 btu/lb. Energy in Wood This means that (fuel load weight) x 6050 = (143.75 + 2.2) x 6050 = 882,998 btu input. And efficiency then is 744,056 / 882,998 = 84.3%. I didn't see a flue temperature number in the test report, so it is not possible, except by speculating, to adjust this based on a lower or higher flue temperature. 

*Question: I need to think this through more, but what might be the reasons for the variation in efficiency calculation? Shouldn't the 6050 btu/lb account for the difference between a dry weight calculation and a 20% MC calculation?*

The 84% efficiency number for the 1500 compares to 80% efficiency I calculated for the 3200. Garn 3200 - Part 6 But my calculation was based on btu's supplied to the system, and my calculation did not account for standby losses or heat stored in the steel mass of the Garn. Regardless, it would not be reasonable to assume that efficiency of the 1500 and the 3200 are necessarily the same.

I think two other things would be reasonable:

1) if I could account for standby losses and heat store in the steel mass of the 3200, the efficiency calculation would be closer to the method used in the test report and efficiency would increase above 80%, and

2) my method of measuring efficiency by btu's supplied to the system is closer to what a user might expect in actual performance in use of a Garn (or any other boiler), because standby loss and heat stored in the Garn likely is not usable heat for a structure (unless the Garn is in the heated structure). I measured btu's supplied to the system by delta-T temperature measuring: (supply temp - return temp) x 500 x gpm.

I wish every boiler mfr had this kind of data available for review and scrutiny. While efficiency is not the end all in selection of a boiler, it is one important consideration.


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## PassionForFire&Water (Feb 3, 2012)

Hi Jim,
You can find the calculations in this link: http://www.epa.gov/burnwise/pdf/owhh.pdf
This is the revised EPA phase2 partnership program. Date 10/12/2011. The Test done was much earlier in 2011. So probably not 100% in line with the newer calculations.
Also this new revision allows for overall efficiency calculation according CSA B415, known as Stack Loss Efficiencies.
Calculations start on page 30.
MC is used in these calculations and then the BTU value for wood will come close to your value.
I do have an Excel spread sheet based on the older phase2 program.
PM me if you are interested.


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## jebatty (Feb 4, 2012)

The link to the EPA site produces an EPA page saying File Not Found. Maybe EPA no longer has this on its website, or EPA moved it without a cross-link.


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## PassionForFire&Water (Feb 4, 2012)

Try this link: http://www.epa.gov/burnwise/pdfs/owhhphase2agreement.pdf


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## jebatty (Feb 4, 2012)

That link works, but it looks like the crib method is covered by this procedure. I'm not an engineer, and I might be able to get my head around all of this, but not sure I want or need to get that far. If my question has an answer which I can understand, that would be great. Otherwise, without new information it may be time to move on. Thank you for the link.



> Question: I need to think this through more, but what might be the reasons for the variation in efficiency calculation? Shouldnâ€™t the 6050 btu/lb account for the difference between a dry weight calculation and a 20% MC calculation?


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## Gasifier (Feb 5, 2012)

Speaking of efficiency in any of these boilers I would say this. Boiler cleanliness is next to boiler godliness.


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## jebatty (Feb 6, 2012)

> Frozen Canuck: It takes more energy to heat water from 150 -190 than it does to heat it from 110 - 150. Same 40 delta, so whatâ€™s up with this?



I need help with this one. If 1 btu will raise 1 lb of water 1F, then the same btu's are required to raise a set volume of water from 110-150 as 150-190. So why more energy? You must have something else in mind in addition to energy required to raise the temperature of the water.


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## PassionForFire&Water (Feb 6, 2012)

Delta T from firebox temperature or flue gas temperature to water temp is smaller
Heat exchange is direct related to dT


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## DaveBP (Feb 6, 2012)

> Frozen Canuck: It takes more energy to heat water from 150 -190 than it does to heat it from 110 - 150. Same 40 delta, so whatâ€™s up with this?
> 
> I need help with this one. If 1 btu will raise 1 lb of water 1F, then the same btuâ€™s are required to raise a set volume of water from 110-150 as 150-190. So why more energy? You must have something else in mind in addition to energy required to raise the temperature of the water.



It's not that it takes more BTUs to heat the water at the higher temp range but it's harder to get the water to absorb the heat since the deltaT , as Marc says, is lower between the flue gases and the water. It takes more heat to raise the temperature of the water but some of that extra energy is going up the flue, not into the water.

The amount of heat it takes to raise the temperature of water does vary with the temperature of the water, but I believe it's less that 1% over the range that wood boilers intentionally use.


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## heaterman (Feb 6, 2012)

jebatty said:
			
		

> Garn deserves credit for posting the test report on the 1500; hopefully it will do the same for the 2000. And I hope other boiler mfrs post similar information, in detail. This kind of information will help shed light on many of the things that we discuss on the forum.



From what I understand the first place the report on the 2000 will be published is on the Garn newsletter that goes out to subscribers via the www.  A person can sign up for it on their website.


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## heaterman (Feb 6, 2012)

DaveBP said:
			
		

> > Frozen Canuck: It takes more energy to heat water from 150 -190 than it does to heat it from 110 - 150. Same 40 delta, so whatâ€™s up with this?
> >
> > I need help with this one. If 1 btu will raise 1 lb of water 1F, then the same btuâ€™s are required to raise a set volume of water from 110-150 as 150-190. So why more energy? You must have something else in mind in addition to energy required to raise the temperature of the water.
> 
> ...



Viessmann told us at a training school that the real benefit comes when the water temp is low enough to get the flue gas into condensing territory which is generally below 140*. As such, there is not a lot of benefit unless you have a boiler that will tolerate water temps that low. I'm not aware of any standard gassers that are recommended to operate at <150*.  I have seen many Garns however that are routinely operated down to the 110-120* range before firing. The Testo will tickle 90% at those temps. Once water temp gets up to 150+ the same unit will read 80-85%.


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## goosegunner (Feb 6, 2012)

heaterman said:
			
		

> DaveBP said:
> 
> 
> 
> ...





Heaterman,

With your experience with the Garn how does it perform when pushing it to higher temps for high temp emitters?

Many people here are under the impression that the Garn is not the best if using with forced air coil. Does that hold true in real world installs?

I am comfortably running my Econoburn with 1000 gallons of pressurized storage from 185 down to 140. My guess would be that the Garn with 1500 gallons would be even better if it would charge to 185 easily and say stratified.

One thing I don't understand is when the Garn users talk about the mixing pump, what is its purpose? Would that effect stratification for forced air system?

gg


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## heaterman (Feb 6, 2012)

goosegunner said:
			
		

> heaterman said:
> 
> 
> 
> ...



The limiting factor is not the Garn but rather the hot water coil  used in the furnace plenum. This is true regardless of the brand or type of boiler used. A person should always install the largest heating coil possible in order to gain good response time (furnace blower not running endlessly) and maximum use of the water available before having to refire or reburn.
 Maximum flexibility in your required water temperature is the goal because that is what allows long and sustained burns, which more than any other factor, make for clean and efficient combustion. Storage doesn't do any good if your system demands 180* water under all circumstances.

As for a mix pump on a Garn, that's entirely unnecessary. A Garn will effectively mix the whole tank within 15 minutes when fired. (the advantage of having the "boiler" inside the storage)  After that you want it to stratify so mixing is most definitely not desired.


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## bpirger (Feb 6, 2012)

I have to get my temp sensors all up and running, to provide some actual data for this next statement, but it seems to me my Garn would have a hard time delivering high temp water for very long.  It does seem to drop down from say 190-195 pretty quickly to 160.  Actual supplied water out the back, not what the sensors says on the front of the Garn.  With a couple of hours after firing and with some amount of load, the water out the back seems to be 10 degrees cooler than the sensor in the front....and then that differential just continues to grow until down to 120's....where things seem to get closer to agreement.

There's been many threads about this "sensor differential", front and actual supply water, and it seems to be somewhat consistent.

My only theory would be that the heating to 190 say isn't very uniform in the tank, i.e. the bottom stays cooler.  It's almost like there is stratifcation between the front and back....which I wouldn't think could easily happen.  I'd have to think the mixing would be good with the fire inside the water.

But like I say, this is anecdotal (though consistent) at this point....need to get that one-wire sensor controller and software written!

The picture below is the data I did acquire.   I started running the sensors just after the fire was done....only for about 2.5 hours total.  Note the Garn front well sensor said 189-185 during this time, whereas the water out the back went from 185 down to 163.  I have an 00R pump in the Garn to flat plate HX loop, all 2" IPS, 1.5" IPS, or 1.25" copper and a total length of about 20'.  If you figure the flow is 5 gpm and take a 40 degree delta T, that's 100k BTU/hr.  BUT, the pumps is actually running only a small part of this time, the rising edge of the curves....which is more like 25% of the plot....or call it 1 hour even.  So that's 50,000 BTU out of the Garn.  Which should be about 5 degrees on a 1500.  Yet the supply temp out of the back of the Garn has dropped considerably more than that....from 185 to call it maybe 165.  The other complication here is the system is cycling the demand (call for heat), so it could be that the temp would reach a higher level if it ran continuously....I guess I can't really tell from the plots if the temp would keep rising higher or not.  The radiant load will have a lower boiler setpoint than the DHW load.  Notice at 11PM the DHW came on and ran through 3 cycles of call for heat.

So, like I say, I need better data to really know.  But I consistently get the feeling that the higher temps diminish quite fast.  I do have some non-ideal piping at the moment still, so I'm going to lose more at higher temps becuase of larger delta T, but I wouldn't think I'd lose THAT much more.


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## jebatty (Feb 6, 2012)

> heaterman: Iâ€™m not aware of any standard gassers that are recommended to operate at <150*.  I have seen many Garns however that are routinely operated down to the 110-120* range before firing.



Once again, I'm missing something. With the Garn hx tube snaking through the water, it seems to me that if [flue gas] is down to the 110-120F range, it will cool any water in the Garn that is higher than that temperature. Isn't that one of the chief reasons Garn is marketing a control that shuts the draft blower down as the fire burns down? And in the Garn 1500 test report, it is carefully mentioned that the fire is considered "out" when it no longer is raising the temperature of the water. That makes sense, otherwise the flue is cooling the water down. I will need it explained to me how flue gas lower than the temperature of the surrounding water works in the Garn to extract more heat from the near dead to dead fire.


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## heaterman (Feb 7, 2012)

jebatty said:
			
		

> > heaterman: Iâ€™m not aware of any standard gassers that are recommended to operate at <150*.  I have seen many Garns however that are routinely operated down to the 110-120* range before firing.
> 
> 
> 
> Once again, I'm missing something. With the Garn hx tube snaking through the water, it seems to me that if [flue gas] is down to the 110-120F range, it will cool any water in the Garn that is higher than that temperature. Isn't that one of the chief reasons Garn is marketing a control that shuts the draft blower down as the fire burns down? And in the Garn 1500 test report, it is carefully mentioned that the fire is considered "out" when it no longer is raising the temperature of the water. That makes sense, otherwise the flue is cooling the water down. I will need it explained to me how flue gas lower than the temperature of the surrounding water works in the Garn to extract more heat from the near dead to dead fire.



Well let's see if I can elucidate, pontificate and further emote on the question.......  

Flue gas temp on a Garn is monitored at the beginning of the last pass (5th) of the HX tube.
 Consider first that a Garn uses outside air for combustion which enters the boiler at whatever the OD ambient is at the moment. Could be 35*, could be -20*. Whatever it is, no air is exhausted from the building the unit is located in. 
Now consider that the Garn control shuts down the combustion fan not based on time but rather looks for a 5* temperature differential between the water at the tank sensor and the thermocouple in the previously mentioned location. The factory says that incoming air will be raised approximately 75* before hitting the firebox. So let's assume a 10* ambient and add 75* for an actual air temp of 85* incoming. Now assume that the storage is at the temp you mentioned of 120*. If there is no fire, or even any appreciable number of coals in the firebox, the flue gas temp would be hard pressed to reach the actual tank temperature. In fact it would be impossible unless heat were being added. Therefore the combustion fan shuts down at the end of the cycle.

At the opposite end of the cycle, firing up, the control holds the combustion fan contact in for 5 minutes before it looks for the flue gas temp. That allows time for the temp to come up after loading and starting the fan. Once it "sees the flue gas temp come up above the water temp, which can only happen if a fire is present, it then allows the combustion fan to run until that "stasis point" of 5* differential is hit again and it shuts down. 

On the previous manual control, the user had a maximum time of 6 hours available and it was strictly up to him/her to observe whether the wood had kindled after loading. 

That help or did I miss your question entirely?


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## jebatty (Feb 7, 2012)

It helps a lot, but I still need some clarity. First, I think I misunderstood your statement 



> I have seen many Garns however that are routinely operated down to the 110-120* range before firing.



I mistakenly took that to mean that Garns regularly operated with flue gas in the 110-120* range, and now I see that you meant that Garn water storage is regularly drawn down to this range before the Garn is refired. We all know that flue gas must be considerably above 212F to prevent condensation, and the Garn is no different in this regard than other gasification boilers. 

I also now understand the new controller better. If on firing Garn water storage temp is brought up to 180F, for example, and as the fire burns down flue gas and air being drawn through the extraction tube drops to below 185F, the draft blower shuts down. Obviously there is no fire and no heat to be extracted to the water if flue gas is below 185F. This is a welcome addition to the Garn and would be very useful to all of the Garn owners who still rely on a timer that on occasion they may have set too long and the blower kept moving cold air through the Garn and cooling it down after the fire has burned out. The Tarm which I bought in 2007 was equipped with this kind of control and it too shuts the draft fan down when the flue gas has insufficient temp to add heat to the water.

Here is where I need more clarity because I think this statement is very misleading:



> heaterman: Iâ€™m not aware of any standard gassers that are recommended to operate at <150*.



On a personal level I *always* operate my Tarm when storage temperature is less than 150*, and frequently down to 100*, as my radiant is supplied at 100* with a mixing valve. The Garn has integral storage, I have added storage with a 1000 gal tank I bought for $900. It is misleading to compare a gasification boiler without storage to a gasification boiler with storage, be that a Tarm with storage or a Garn with storage. You, me and others have consistently recommended storage for gasification boilers, as have manufacturers. I think on reflection you would agree that you are aware of a great many standard gassers with storage, and perhaps every gasser with storage that you are aware of, that are perfectly suited to operate when storage is < 150*.


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## heaterman (Feb 7, 2012)

jebatty said:
			
		

> It helps a lot, but I still need some clarity. First, I think I misunderstood your statement
> 
> 
> 
> ...



No it is not misleading and my apologies if the statement appears so. It is a fact and one of the true beauties of the Garn design as I see it. Let me explain as best I can.

On any downdraft gasser *connected to storage*, be it Tarm, EKO, Econoburn, Effecta, Wood Gun, or whatever, it is imperative to protect the  boiler _ from low storage temperatures_ during  firing by raising the boiler water temperature to around 150*. Typically this is accomplished through the use of some type of mixing device such as a Termovar thermostatically controlled valve and is near universally recommended by all manufacturers.
 If the boiler is allowed to "deal with" the full load of the storage under situations where it is much below the 140-150* level, a sticky mess will soon develop in the heat exchanger tubes. This occurs due to flue gas condensation at water temps below the 140 mark. At least that has been my experience and observation.......

On any Garn I have seen which is allowed to hit water temperatures of <140*, all the way down to levels near 110-120, this condensation just simply does not happen. Let me be the first to say that I am not an uber guru when it comes to combustion technology but I have an inkling that this is so because of the design of the Garn which is different than any other gasification boiler. 
There are two major factors in the Garn HX design which differentiate it from any other gasser I am aware of. The first is that all the combustion air/flue gas goes through a single pass, or HX tube if you will. Other gassers use many tubes or a variation of that design where the flue gas is "divided" in several smaller tubes, or something similar, coming from a main chamber. The second is the flue gas velocity which exists in a Garn. As far as I know there is no other wood burner that operates with the "force" existing in a Garn flue tube. 

The benefit of a long single tube heat exchanger is pretty obvious when you consider it. If one would measure temperatures at the beginning of each of the five sections, you would find that only in the last 10 feet of the Garn heat exchanger do flue gasses drop into the range where condensation is possible. On a multiple tube design or some variation thereof, the entire heat exchanger can be exposed to lower than desired flue gas temperatures, the results of which are less than satisfactory. 
The second thing that is different on a Garn is flue gas velocity which is much higher than any other unit I have seen. My gut feeling is that this high velocity serves to keep moisture that may be occurring in that last pass, in suspension so to speak and not allow it to puddle in the tube itself. This is evidenced by the cloud of steam which is commonly observed coming from a Garn exhaust. (When you get down to 100* water temp one will see liquid condensation dripping from the exhaust and that is to be avoided)

All of that is just my "hunch" and is based on nothing more than what my Testo tells me and simple observation. I could be way off base on this but I have to say that after seeing many of them consistently fired into low water temperatures with no ill effect.......there has to be something going on that is different. 

Hope that clarifies things. It's as good as I can do with my limited knowledge.


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## jebatty (Feb 7, 2012)

All you're saying is that the Garn as supplied has integral storage and is of a design that does not require return water protection for operation at storage temp < 150*. No dispute. 

All that I'm saying is that a standard gasser properly installed with sufficient added storage and return water protection, which I assumed was obvious but now state for clarity, operates perfectly satisfactorily at storage temps <150*. No dispute. That is something I have done now into my 5th heating system without a drop of "sticky mess." It is something which I would venture to say 100's of standard gasser users also have enjoyed.

Perhaps standard gasser mfrs may be faulted for not marketing a combined gasser, storage, and return water protection in one package price. So be it. They have left options and choices for consumers to size according to their needs. Yet all so far as I know, except Wood Gun, recommend or require storage; and all, even Wood Gun, require return water protection. Wood Gun also clearly benefits from added storage. And if this does not appear obvious from their manuals, it is obvious from the great many posts on Hearth.com. Conscientious buyers are well advised of these requirements


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## woodsmaster (Feb 7, 2012)

I could be wrong, but what I think in short is what heaterman is saying is the the garn is more efficient due to it not needing the
mixing valve. Easier to heat the colder water than the warmer water.


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## jebatty (Feb 7, 2012)

Very true from 120* to 150*. Good observation.


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## jebatty (Feb 7, 2012)

> goosegunner: Heaterman, With your experience with the Garn how does it perform when pushing it to higher temps for high temp emitters?
> 
> Many people here are under the impression that the Garn is not the best if using with forced air coil. Does that hold true in real world installs?
> 
> I am comfortably running my Econoburn with 1000 gallons of pressurized storage from 185 down to 140. My guess would be that the Garn with 1500 gallons would be even better if it would charge to 185 easily and say stratified.





> Heaterman: The limiting factor is not the Garn but rather the hot water coil used in the furnace plenum....  A person should always install the largest heating coil possible in order to gain good response time (furnace blower not running endlessly) and maximum use of the water available before having to refire or reburn.
> 
> Maximum flexibility in your required water temperature is the goal because that is what allows long and sustained burns, which more than any other factor, make for clean and efficient combustion. Storage doesnâ€™t do any good if your system demands 180* water under all circumstances.



This is partially true. Given that a system has installed the largest heating coil possible, then an ability to supply hotter rather than cooler water adds "Maximum flexibility in your required water temperature." For example, if a system requires 140* water and storage of a set volume can only deliver 175* water, that system will have less flexibility than if storage can deliver 185* water. In goosegunner's case, he has pressurized storage. A Garn has open storage, and if used in a pressurized system must employ a heat exchanger. Most heat exchangers are spec'd with a 10* approach temperature, meaning that if the open storage is at 185*, pressurized supply through the heat exchanger will be 175*. That is a loss of 10F in flexibility, or a loss of nearly 30% of usable storage capacity in this example.

Heat exchangers can be spec'd with closer approach temperatures, but the cost also rises dramatically. There is no feasible heat exchanger which can operate at 0F approach temperature to match the pressurized storage temperature. I work with a Garn system with a substantially oversized heat exchanger which achieves an approach temperature of 5* at 69 gpm, very good. But still, there is a loss of 5* in flexibility. For a 1500 gallon system, which is the smallest Garn that I know of, as compared to 1500 gallons of pressurized storage, that equates to a loss of 62,475 btu's at 5* approach and 124,950 btu's at 10* approach. Depending on heat demand, that can make a substantial difference. In my shop, with typical demand of 12,000 btuh, that is 5-10 hours of extra heat from pressurized storage as opposed to open storage and a heat exchanger.


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## DaBackBurner (Feb 7, 2012)

jebatty said:
			
		

> > goosegunner: Heaterman, With your experience with the Garn how does it perform when pushing it to higher temps for high temp emitters?
> >
> > Many people here are under the impression that the Garn is not the best if using with forced air coil. Does that hold true in real world installs?
> >
> ...



This is precisely why I didn't add 'another' heat exchanger (flat plate or other) between the Garn and my workshop loops nor between the Garn and the water-air exchanger in the plenum for one of the homes I am heating. I don't have another 'loss'. Careful consideration for "Net Positive Suction Head" for the pumps has to be considered though. This has worked out nicely for me so far. I'm not a professional and I guess time will tell if running these systems non-pressurized vs pressurized will have any adverse effects.


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## hobbyheater (Feb 7, 2012)

heaterman said:
			
		

> If the boiler is allowed to "deal with" the full load of the storage under situations where it is much below the 140-150* level, a sticky mess will soon develop in the heat exchanger tubes.
> 
> The second thing that is different on a Garn is flue gas velocity which is much higher than any other unit I have seen.
> 
> Hope that clarifies things. It's as good as I can do with my limited knowledge.




A bit of history here. :bug: 
The Jetstream regularly sees return water of 110F and I have never seen a sticky mess in the heat exchanger tubes. The cooler water inhibits the burning of wood in the loading tube.
Flue gas velocity is 1/3 the speed of sound through the refractory tunnel (nozzle).
Had the Garn been around in 1981, there would have likely been a Garn in our boiler room :exclaim:


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## heaterman (Feb 7, 2012)

A couple clarifications:

Number 1. I just want to make clear that the velocity of the flue gas in the Garn is the primary difference between it and other boilers. It is high enough to achieve turbulent rather than laminar air flow and that is how they are able to fire directly into low water temps. I don't think there is anything else on the market that reaches that kind of velocity and that is the reason for the Garn not requiring boiler water temperature protection at any levels normally encountered.

Number 2. The Garn control in its current form does not look for a fixed water temperature or time. It looks for the *differential between the water temp and the flue gas*. If for instance you had a situation where the tank was at 140 at the end of the burn, the blower would shut down at approximately 145* flue gas temp. If you were at 170* in the tank the control would look for 175* and so on. 
When it see's that differential, at whatever actual temperatures happen to be present, it then starts a 10 minute countdown as it looks for any increase in flue temps, such as if a person would reload. If no increase occurs, it will shut off the blower at the end of the 10 minute countdown cycle.


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## goosegunner (Feb 7, 2012)

My system is pressurized because of the Econoburn with storage. I originally had a OWB with my forced air coil, it was not pressurized. If I had the Garn i would not have a heat exchanger between my load and the Garn water. I think that would allow the maximum use of the Garn storage.

The big question is how well does the Garn function when pushing the water to 185-190?

gg


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## heaterman (Feb 7, 2012)

hobbyheater said:
			
		

> heaterman said:
> 
> 
> 
> ...



Turbulent air flow "scrubs" the heat exchanger walls every time the boiler runs. Interesting that the Jetstream. And Garn were designed about the same time.


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## DaBackBurner (Feb 7, 2012)

goosegunner said:
			
		

> My system is pressurized because of the Econoburn with storage. I originally had a OWB with my forced air coil, it was not pressurized. If I had the Garn i would not have a heat exchanger between my load and the Garn water. I think that would allow the maximum use of the Garn storage.
> 
> The big question is how well does the Garn function when pushing the water to 185-190?
> 
> gg



I usually don't run the Garn up to those storage temperatures as I don't have the need for such high water temperatures for my heat emitters, but I do encounter these temps. from time to time because I have overestimated my wood load. For those occasions it is too efficient. %-P


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## hobbyheater (Feb 7, 2012)

heaterman said:
			
		

> Turbulent air flow "scrubs" the heat exchanger walls every time the boiler runs. Interesting that the Jetstream. And Garn were designed about the same time.



History. In the mid 70's, there was an article in Harrowsmith about a large sand filled bunker that had stainless steel tubing going through the sand to exchange the heat. It featured a fire box design much similar to that of the Garn.
The Jetstream is fading into history but the Garn is still here :exclaim:


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## woodsmaster (Feb 7, 2012)

Speaking of efficiency how much power does it take to operate the motor on the garn ?


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## heaterman (Feb 7, 2012)

Approximately 700-900 watts per hour depending on the model of Garn for 2-3 hours depending on load size.
There is obviously no cost involved in moving combustion heat into storage. No pumps/piping required.


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## Floydian (Feb 7, 2012)

Lots of good stuff in this thread,thanks Hearth.com!

So a Garn 2000 uses about 2100 watts to deliver about 1,275,000 btus to storage, thats about 600btus/watt.

How about some of you folks with downdrafters+storage? It would be interesting to see some numbers on electrical consumption from boiler to storage.

Heaterman, do you see ECM fan for motors for these applications in the not so distant future? Seems to be another place shave some watts.

Noah


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## bpirger (Feb 7, 2012)

I would be interested in hearing from Garn users using high temp water (i.e. not radiant).  How low can they go on the Garn temp?  How hot do they fire to?  

With my data from my 1500 back on page 4 of this thread, I don't really understand how high temp systems would work well with a Garn....at least for extended storage purposes (i.e. one fire a day).  

We love our Garn, but I've steered a few people away from it due to their need for higher temp water.  I'd like to see/know that I'm wrong...


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## heaterman (Feb 7, 2012)

bpirger said:
			
		

> I would be interested in hearing from Garn users using high temp water (i.e. not radiant).  How low can they go on the Garn temp?  How hot do they fire to?
> 
> With my data from my 1500 back on page 4 of this thread, I don't really understand how high temp systems would work well with a Garn....at least for extended storage purposes (i.e. one fire a day).
> 
> We love our Garn, but I've steered a few people away from it due to their need for higher temp water.  I'd like to see/know that I'm wrong...



If a given heating system consistently requires 180+ water then any storage system is going to be limited in its usefulness. A far better option would be to address the heating system itself or the building envelope in order to use lower water temperatures. There is a reason that by law (or papal edict?) the maximum system temperature in Europe is 167*.  The other item of note that goes on in Europe is that they routinely design systems with delta T's of 30-40 and even 50* temp drop.  Less pumping power is required and lower temp = higher system efficiency.

I have however several Garn installations that work between 150-190 and work very well. They just fire more often.


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## SmokeEater (Feb 7, 2012)

Floydian said:
			
		

> Lots of good stuff in this thread,thanks Hearth.com!
> 
> So a Garn 2000 uses about 2100 watts to deliver about 1,275,000 btus to storage, thats about 600btus/watt.
> 
> ...



I sure have a lot to learn about wood boilers and all their needs and specs to operate efficiently, but I do know a few things about energy, especially electric energy because I've been connected with producing it for over 30 yrs.  A watt is a unit of power or energy use per unit of time.  If the Garn 2000 has a total need of 700 watts to operate and it operates for 3 hours on a single "burn", then the Garn will use 700 watts x 3 hours or 2100 watt-hrs of electric energy.  Power companies charge by the amount of energy used or "consumed" and a watt-hr is that, though usually to a kilowatt-hr by dividing the use in watt-hrs by 1000 and expressed as the unit kWh.  So the Garn would use 2.1 kWh per burn to generate the 600 btu/Wh.  If the power company charges $0.10/kWh, then the energy purchased would be 2.1 kWh x $0.10/kWh or $0.21.  Just contributing my small share of knowledge with all.


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## ewdudley (Feb 7, 2012)

Floydian said:
			
		

> Lots of good stuff in this thread,thanks Hearth.com!
> 
> So a Garn 2000 uses about 2100 watts to deliver about 1,275,000 btus to storage, thats about 600btus/watt.
> 
> How about some of you folks with downdrafters+storage? It would be interesting to see some numbers on electrical consumption from boiler to storage.


Not sure about your units, it should be reducible to a dimensionless number, e.g., power divided by power or energy divided by energy.  At any rate my little boiler delivers 70000 btu per hour while consuming 165 W (fan plus circ), which is about (425 btu / hr) / watt, or a COP of 124 if you prefer.  In my case heat production is intentionally limited to get better heat transfer, so I suspect other downdraft units with better heat transfer could do better.

--ewd


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## Kemer (Feb 7, 2012)

I have a hot air system and  run between 150 -190 I can go 24 hours in this kind of weather but I like to build a fire in am & pm.By doing it am & pm all I have to do is adjust my load with the weather conditions and how much wash and showers  were done.Also I keep a higher temp and keep it in the "zone" for faster recovery.


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## bpirger (Feb 7, 2012)

Thanks Harry and Steve.  I guess two smaller burns a day would make this work.  Agreed, if you need 180, any storage is going to be hard to supply for long.  Harry, how often does your HX water pump run when it is cold outside?  Obviously this is load/house dependent.  When I think of hot air systems, I think of them cycling every 20 minutes or so....but I also lived in old, drafty houses.  Do you run the water pump to the HX independently from the blower in the plenum?

I know with those data curves, my output supply had dropped down considerably in just a couple of hours....and the pumps were on maybe 30 minutes during this time.  Obviously there's a differnce between dumping in 200,000 pounds of concrete and using the water to air HX....so perhaps your cycle times are much more infrequent, and shorter, than I'm thinking...


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## DaBackBurner (Feb 7, 2012)

bpirger said:
			
		

> Thanks Harry and Steve.  I guess two smaller burns a day would make this work.  Agreed, if you need 180, any storage is going to be hard to supply for long.  Harry, how often does your HX water pump run when it is cold outside?  Obviously this is load/house dependent.  When I think of hot air systems, I think of them cycling every 20 minutes or so....but I also lived in old, drafty houses.  Do you run the water pump to the HX independently from the blower in the plenum?
> 
> I know with those data curves, my output supply had dropped down considerably in just a couple of hours....and the pumps were on maybe 30 minutes during this time.  Obviously there's a differnce between dumping in 200,000 pounds of concrete and using the water to air HX....so perhaps your cycle times are much more infrequent, and shorter, than I'm thinking...



Bruce are you mixing or doing a variable speed prior to your flat plate? I know I brought this up once before but it seems if it was mixed prior to the flat plate it would allow better/longer stratification. I'm hoping it will as I plan to do something this spring. Definately going to do an ODR for sure and I may bypass my FP and run my house as un-pressurized like my parents house and my workshop. In the meantime I've been making two smaller fires as opposed to one bigger one and limiting my max storage temperature. It seems it has made an improvement with wood consumption because it can heat that cooler water pretty darn fast. Time will tell I guess.


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## jebatty (Feb 7, 2012)

> goosegunner: If I had the Garn i would not have a heat exchanger between my load and the Garn water. I think that would allow the maximum use of the Garn storage.



This may or may not work. Notice the comment of DaBackBurner above related to Net Positive Suction Head. If there is enough head supplied by the Garn to the circulator to prevent cavitation, and if the circulator still can still move the hot water through the system, then it may work to skip the heat exchanger. I previously used an OWB for heat to a rental house, single floor, with the OWB at the same elevation as the first level of the house, plus a weighted vent tube that maintained about 2 psi pressure in the OWB. This worked fine to heat the house without a heat exchanger. The house also had an LP boiler in the basement, and that needed a pressurized system to work. Consequently, when using the OWB I had to valve off the LP boiler, and when using the LP boiler, I had to valve off the OWB -- thus keeping both systems independent. A bit of a hassle, but it worked for 7 years.


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## goosegunner (Feb 7, 2012)

Kemer said:
			
		

> I have a hot air system and  run between 150 -190 I can go 24 hours in this kind of weather but I like to build a fire in am & pm.By doing it am & pm all I have to do is adjust my load with the weather conditions and how much wash and showers  were done.Also I keep a higher temp and keep it in the "zone" for faster recovery.



What does that do to tank stratification?

I have found if I run my econoburn pump at a low gpm I can top off the tank with hot water. If I run it at 18gpm med speed or 22gpm high speed it will mix the tank to about 160 degrees and then bring it all up from there.

For twice a day burns I like to use the lower speed and keep the hot water on the top of the tank.

gg


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## Kemer (Feb 7, 2012)

Before Heaterman educated me on Garn stratification I had my plumber put a relay on my Garn so if the fan is running my pump on the garn side is also running.


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## bpirger (Feb 8, 2012)

Back burner....On the Garn side of the HX, I just have an 00R pump which is turned on/off with the call for heat.  So when the Garn is hot, a call for heat (for radiant for example) will run the pump for about a minute or so...every few minutes.  On the other side of the HX, the hot water is dumped into my primary loop.  


My mixing for the radiant is done with variable speed injection pumps....but inside the house at the floor manifolds.

Some kind of mixing out of the Garn itself presumably would limit the temp of the water pumped out of the Garn.  Now I essentially do that by limiting the time the pump runs.  (Tekmar 363 controller is running the show...call for heat from it runs the Garn pump and the Garn secondary loop injection pump)


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## woodsmaster (Feb 8, 2012)

Floydian said:
			
		

> Lots of good stuff in this thread,thanks Hearth.com!
> 
> So a Garn 2000 uses about 2100 watts to deliver about 1,275,000 btus to storage, thats about 600btus/watt.
> 
> ...



 My boiler has two fans. On high they use 160 watts the circulator on high uses 60 watts If I remember right. so 220 watts on high
and it takes around 4 houres to burn a full load 60KW boiler.


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## DaBackBurner (Feb 8, 2012)

bpirger-

Thanks again for the explanation (forgot you are injecting) on the house side of the HX.
Daaaanggg! Just looked up the price of the 363. That's more than I expected. Oh well, guess you can't take it with you.


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## bpirger (Feb 8, 2012)

Yeah, when I built the house and designed the system, the 363 sounded like an outstanding controller so I bought it.  At the time, 2001, I wasn't very aware of everything else that was available....somehow I got turned onto Tekmar.  But it controls the mixing in the house floor, the DHW, boiler demand, boiler protection, primary pump, etc.  I think it can do more as well....when I get everything hooked up in the addition, I'll have to sit down.  I tried to set the boiler limit to 150, thinking it would shut off the garn and secondary pump (with the call for heat) keeping the water no higher than 150, no lower than what it needed....but it seems to NOT allow short cycling of the oil boiler.  SO when the floor wants 120, the primary loop will cool down to 110 or below and it won't kick it back on.  Likely I can read how to prevent this.  But it didn't seem to work as I wanted a couple of weeks ago and without all my temp sensors up and running, I can't really tell what's going on.

Sure is a fun hobby!


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