EFFICIENCY ON A FEW OWB

[eco-one]

SOME ARE GOOD SOME ARE BAD.

http://www.state.me.us/dep/air/woodsmoke/woodcombustion3.htm

 

[in hot water]

I wonder how they define efficiency, how and who did the testing"?

That 60% number seems to jive with NoFo actual test result numbers, from a previous post..

hr

 

[Nofossil]

I expect that they're looking at combustion efficiency, not system efficiency. Combustion efficiency for gasifiers ranges from 85% to over 90%, and I expect that mine is in that range. The numbers that I've reported are my measured system efficiency, which subtracts loss from the boiler itself, storage, and plumbing from the boiler's output.

I don't have the instrumentation to measure raw boiler output, but that's the only thing that makes sense if you're comparing boilers.

 

[DoubleNickel]

http://www.state.me.us/dep/air/woodsmoke/woodcombustion3.htm



Sequoyah Paradise E3400--101,020 BTU/hr--0.488 lbs/million BTU heat input--Efficiency27.0% :ahhh:


Can this be true :question: 27% :exclaim: That's worse than the non-gasification ones!! This can't be right?


It says on Sequoyah's main page it's 73-83% efficent.


I was ready to put a deposit on one. Really I was. Now I'm really confused! :bug:

Please help me with this :roll:

Thank You

 

[Nofossil]

I'll echo IHW as well as Eric from another thread - it's hard to tell what the numbers mean without a description of the test. There are a number of things that could affect the tested efficiency values:

1) Type of fuel (wood species)
2) Moisture content
3) Size / uniformity of fuel
4) Bark content
5) Inlet water temperature
6) Flow rate
7) Flue draft
8) Ambient temperature
9) Ambient humidity
10) Wind speed
11) Settings of any boiler controls, dampers, etc.
12) Test procedure (warm-up time allowed, starting technique, duration, refueling interval, etc.

Unless all of these things (and others I've not thought of) are specified and controlled, the tests are pretty meaningless. In the referenced web page, it's not even clear who performed the tests or whether the tests were all performed by the same entity.

It would be a great and helpful service if such data were available, but that doesn't appear to be the case for these. As it is, I'd be hesitant to base major decisions on these data.

By the way, there's another way to double check system efficiency: If you have a good history of fossil fuel consumption, you can calculate seasonal heat loss from that and compare to the amount of wood that you burn. Here's mine:

Historical oil consumption during heating season: 660 gallons
Oil heat BTU per gallon: 143,000
Available heat from oil: 94,380,000 BTU
Assumed oil boiler efficiency: 85%
Heat usage during heating season: 80,223,000 BTU

Wood usage during equivalent season: 4.25 cords
Heat value for wood species mix: 21,000,00 BTU/cord
Available heat from wood: 89,250,000 BTU
Wood heat seasonal efficiency: 89.8%

That number is quite a bit higher than what I get measuring heat delivered per baseboard. Part of the reason is that my boiler is indoors so unmeasurable heat losses from the boiler and plumbing end up in the living space and are not truly losses. The number is also heavily influenced by assumptions about the heating value of your firewood. I have a mix of many species in different levels of punkiness, so a real measurement is pretty hard to determine.

Still, I'd be willing to bet that my actual output into the living space is something over 80% of the theoretical maximum.

 

[DoubleNickel]

nofossil: Here's the test results on the 3400. I don't understand it. To technical for me :exclaim:



http://www.wdheat.com/pdf/Sequoyah Paradise EPA report (2).pdf

I guess you have to copy and paste it. Won't copy the whole link.

I can see you gots lots of knowledge!!


Thank you

 

[eco-one]

all epa tested owb are tested with 4+4 oak timbers. no bark and are spaced 3/4" apart vetically and horizontal, and a crib style setup and filled too
the %of the cubic feet inside thhe firebox per lb. @18-25% moisture you know how fast a 4+4 burns open too almost all sides i could try too find the process of testing these owb but it will take me time

 

[Nofossil]

Seems like a good test, though it's focused on emissions rather than efficiency.

Looking at the report, it appears that the Sequoyah has a unit efficiency of 17% at near idle, and 32% at full throttle. I ran the numbers for oak using the quantities that they had and I ended up with the same numbers.

System efficiency in actual use would likely be less due to losses in underground piping and increased losses at lower outdoor temperatures - these tests were done in August and September. Most people probably aren't burning fuel that's as good as what was used in this test, either.

 

[heaterman]

I think that we will find many of the new gasification units being brought to market by the OWB manufacturers will be marginal in overall efficiency. From what I have seen of them they aren't doing to badly in the combustion/emissions part of the equation. The rub is that they haven't figured out how to incorporate enough heat exchanger area to get the thermal efficiency up where it needs to be without two things occurring. Those would be 1: a wholesale change in the size and design of the unit and 2: developing good thermal efficiency without excessive creosote due to lowered exhaust gas temps. Time will tell.