Efficiency of a 520 ?'

What is the efficiency of a EFM 520 ? 65% ? Would this increase as run times are longer?

The listed efficiency is 80%. That is with coal as a fuel

I suspect the efm efficiency it is lower than that between stack loss, and unburnt coal .The economic benefit of coal is the costs of the BTU you purchase. I am of course very fond of the efm especially living not far from the anthracite fields of Pa. They btus are cheaper than most other fuels so waste becomes cost effective. This is talking out my a@$ as I have not done any experiments I also have a condensing propane boiler propane and when I use it in condensing mode(I have a radiant heat system where the max water temp is less than 130F) it efficiency is 91%. Hardly anything comes out of the flue pipe and that is why the flue pipe can be pvc. Of course the btus cost more.

franpipeman wrote:I suspect the efm efficiency it is lower than that between stack loss, and unburnt coal .

I believe the "old school" specs for a 520 were 124,800 btu/hr net and 166,400 gross (reflecting a pickup factor of 1.3333) output from a recommended max feed rate of 20 lb/hr. At 12,250 btu/lb as received, 20 lb/hr potentially could produce 245k btu/hr gross input. In practice, about 10% goes unburned, so the actual gross input would be about 220,500. The efficiency would be 166,400/220,500= 75.5%, assuming it is computed on the basis of actual boiler output/input at the max feed rate. It is plausible that at lower feed rates higher efficiency might be achieved.

Mike

So which way is it the most efficient ? Low feed rates & long run times or higher feed rates with shorter run times ?

For a hydronic system I would vote for the lowest feed rate (w/properly adjusted air) that is needed to carry the load. But if the hydronic pros say otherwise I'd probably defer to them.

Mike

I would say they run most efficient at the lowest setting where the temperature of the fire is the hottest and the coal is completely burned. I know the fire is quite a bit hotter at a correctly adjusted 5 teeth than at a correctly adjusted 2 teeth. I know that at 7 or 8 teeth, coal doesn't get burned comepletely and the fire isn't much more hotter than at 5 teeth.

The most likely efficient manner is to run a device at the same rate or slightly higher then the heat loss of what you are trying to heat. In large institutional applications that is the target with incremental modulation of the energy input as/if the technology permits.

If the highest level of efficiency attained in a sophisticated multi-million dollar pulverized coal boiler is on the order of 86% to 88%, then logic alone would imply that by comparison a simple firebox burning chunks of black rocks would come in at something below this level. Else why bother with multi-million dollar technology?

http://www.brighthubengineering.com/power-plants/ ... fficiency/

What I glean from the downloadable EFM DF520 brochure is that for 10 lbs of input feed rate per hour the DFM520 yields a net energy of 74,670 BTUH's in a hot water system configuration.

If the "as received" energy potential of anthracite is 12,250 BTU's per pound (allowing for ~5-6% water content in the real world), then the total energy potential of 10 lbs. is nominally 122,500 BTU's.

74,670 / 122,500 = 0.61 (or 61% efficiency)

http://c326988.r88.cf1.rackcdn.com/DF520.pdf

I think lsayre has the calculation correct. I remember someone a while back posted a comment about an extensive analysis where they claim that they are able to get 67% ish overall out of their efm. There are also "real world" considerations as well. For example having a boiler installed in the basement without a jacket will heat your floors, and the flue pipe will radiate heat into the basement. I would assume under these conditions the overall # of BTUs entering you house would be higher, and overall efficiency would be marginally higher??? I could be wrong...not a boiler professional.

The EFM brochure states10lbs per hour will produce 85,870 BTU gross output. Where does this number come from ?? Shouldn't this be closer to 122,500 BTUs.

coldinmaine wrote:For example having a boiler installed in the basement without a jacket will heat your floors, and the flue pipe will radiate heat into the basement. I would assume under these conditions the overall # of BTUs entering you house would be higher,

I agree. If a boiler is 61 percent efficient, the question is where is the other 39 percent going.

I can only see three places.
Up the chimney as heat.
Unburned gasses and coal.
Loss as radiant heat from boiler and smoke pipe.

AS coldinmaine points out some of these losses still put heat in the house and if the chimney is interior even more heat will be retained. So what the boiler delivers to the water is not the full story.

Thanks to lsayre for that link, but I don't think the calculation is correct. The 74,670 figure is a net output figure, which assumes application of a pickup factor. The gross output available from the boiler is the 85,870 figure, which leads to an "overall" efficiency of 70.1%. The efficiency of the boiler vessel in converting heat actually released into boiler output is (85870/(122,500 x 0.9)=) 77.9%.

Mike

Penn507 wrote:The EFM brochure states10lbs per hour will produce 85,870 BTU gross output. Where does this number come from ?? Shouldn't this be closer to 122,500 BTUs.

122,500 BTUH is the input for 10 lbs. per hour of feed. The EFM brochure never mentions input BTU's. All of its various BTU references are listed as outputs. Pacowy may be correct in choosing the output that yields 70.1% for overall efficiency, but I really don't know which output figure should properly be applied here.

My Coal Gun (per my own best measurements) is similarly around 70-71% "overall" efficient. Around 67% if one insists upon using around 13,000 BTU's per pound (the lab dried figure) for anthracite.

All these numbers One minute I think I love my Efm , the next minute Im thinkin " why this thing aint so great" maybe I should try something else. I guess Ill check with Heloise ...... seriously though , you guys are awesome

waldo