Corn Burner w/ radiant heat BTU useage?

Andy Nesbitt

I installed a corn burning boiler and an under florr radiant heat in my 2 story victorian home. I am interested in checking the efficiency of the corn burner. I have a thermostat on the supply side and a thermostat on the return side of the radiant lines. I also have site guage flow indicators on the manifold for all of the loops. In theory I thought if I added the flow of all the loops together to get a total gpm and took the delta of the supply and return temps to get btu's used. When I do this I get an efficiency percent of about 50% on my boiler. I am wondering if my calculations are correct. So for a system using 5 gpm and a temp delta of 6 my btu's consumed are 15,022. Is this somewhat correct? Or am I missing something?

If not what can I do to increase efficency. Temp settings ect.

Thanks in advance for your replies.

Andy

Mark Eatherton1

I get about the same

The simple formula is gallons times pounds times delta T times time.

In your case, 5 X 8.33 X 6 X 60,

5 = GPM

8.33 = Lbs/Gal

3 = Delta T

60 = minutes per hour

The result is 14,994 btu's per HOUR.

As for efficiency, the corn boiler has a blower in it that is not modulated with the burn rate. If your corn input drops as the water temperature approaches set point, the dilution air that goes through the combustion chamber is whats causing the inefficiency. Solid fuel appliances are most efficient at full burn. If you added a large buffer tank to your system, and allowed the burner to run wide open to charge the tank, your net efficiency for the combuster (or would that be cornbuster) would go up. I'm not sure what the peak would be, but I'd guess somewhere around 70%. This should result in a direct reduction in fuel consumption (or would that be fuel cornsumption).

Any time a combuster lowers its fuel input but does not vary its combustion air input, poor efficiency is the result. And it's not just with solid fuel appliances. This is the reason that we see 30 to 50% reductions on fuel consumption when displacing atmospheric cast iron dinosaurs with high efficiency modulating boilers.

Now, if there were some way you could control the speed of the blower in direct relation to the corn input, your numbers would go up drasticly, but I do not endorse modifications of appliances like yours in the field. It too produces carbon monoxide..

ME

Andy Nesbitt

Very disappointing

That's a very disappointing efficency of about 50%. Anyone have ideas on how to raise this?

It is a tarm boiler which I retrofitted a corn burning pot in. I chose the Tarm because I had heard the were somewhat efficent. The corn pot has an air induction to burn the corn, real nice burn very little ash. I installed a barometric damper which I have adjusted all the way down to .02. The stack temp I have not put a thermometer in but you can hold your hand on the chimney pipe.

I just don't understand.

Thanks for your help

Andy

Lloyd Nichols

Corn boilers

Sorry that your retrofit boiler doesn't give you the high efficiency that you had hoped for. We do have corn and wood pellet fired boilers that give 85%+ efficiencies. These are automatic modulating output boilers that vary both the fuel feed rate and the combustion air to optimise performance.
Our website www.pelletboiler.com has extentive info and pictures of a number of installations. Given the price of fossil fuels and the increasing awareness that we need to use alternative energy fuels, we are very happy to be able to be part of "the solution". I'll stop now before I get my biomass heating passion too charged up!!!

Andy Nesbitt

combustion air input

The way this system works is that it is on full burn when there is corn being added to the burn pot.

The way I have it set up is as follows:
Tarm multi-fuel boiler (nice unit by the way).
The total system has approx 80 gal charge capacity.
I set the open on rise aquastat to keep at a constant temp of 160.
The boiler loop circulator is always on.
I have a variable speed injection pump for the radiant loop with an outdoor reset(continuous flow).
When the aguastat is calling for heat the corn unit augers in corn and the air blower turns on, both at a preset rate (1 speed 12# per hour). If there is no call for heat, the corn unit goes into standby and both the corn auger and the blower cycle on and off from a timer, just enough to keep the fire going. (x minutes on y minute off) I don't have the exact amount of time on and off infront of me.
I did purchase a 325 gallon storage tank but haven't installed it as I wasn't sure I woould need it with the timer setup and the large water capacity of the boiler.

Mark,

I believe you were one of the authors of articles about installing a wood stove with a storage tank that I read.

Would this setup also be inefficiant because of the modulating effect you mentioned, or if because it is full throttle when it turns on the best solution I can hope for.

Thanks for your input.

Andy

John Shea

corn burner

Lloyd,
I am a dealer for an outdoor wood boiler manufacturer. We have a corn burner unit in the final stages of development to hit the market mid-year. We are really excited about the implications of burning this fuel source. I can't tell you how many farmer's are very interested in this option. The pure economics of using this renewable resource far outweigh the cost of heating huge farmhouses with oil,gas, etc... Believe me, at the end of the day, I think biomass fuel sources will end up taking some more of the petro market share.

Andy Nesbitt

Matt

What do you believe your efficiency on this unit will be? Do you see a need to adjust the blower speed drive speed ratio based on the quality (test weight) and/or dryness of the corn?

Andy

John Shea

I'm not sure of the efficiency of the unit yet and don't want to make any guesses. For sure though, I,m told that you want to have your corn no more than 15% moisture and 1 pound of corn at 15% = 7000 btuh after derating for the moisture content. 1 bushel at 15% = 56 pounds and corn averages 2.40 a bushel. It makes sense. In regards to your air needs I think Mark is right on. Keep us posted on your findings. Not have too much experiance with these yet, I would think you would want your feed auger to modulate according to water temp and have your draft follow accordingly. This would be done with a thermistor signalling a drive for each motor.

Mark Eatherton1

Actually...

I have yet to write on the subject. I'm thinking you're thinking of my friend/associate John Siegenthaler. Here's a link to his wood burning article.

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

Not sure why the graphics don't come up, but the article is still a good one as usual.

ME

Andy Nesbitt

Exhaust tests for efficiency

Does anyone have the numbers for a biomass fuel that could be used to test the exhaust emisions for efficiency?