This is an offshoot from the Sweet Spot discussion and something I've been wanting to do for quite a while. I would like to get a handle on just what kind of real world efficiency people are seeing with their boilers. I know the manufacturers publish all kinds of stuff...…… but I always take that kind of thing with a grain of salt and would like to see some real world numbers by real world people on the various units out there. My goal is to compile a list of the ability of various boilers to heat water...….. that IS what it's all about.
In the race car world the best test of your labor was to park the completed vehicle on a dyno and after all the bragging and bs'n was done...…… see what kind of power you put out to the tires. If you have storage on your system we can perform the same test by measuring the amount of energy we create from how much wood we burn. I would therefore like to throw down the furnace mitt and challenge all to bare their souls and divulge their numbers.
Ground rules are as follows:
Measure the weight in pounds of the wood you burn to raise your storage a given amount. I've got an old farm scale I picked up for about 50$ and have it by the boiler door for use when I load.
Be cautious about how you measure your storage temps as in my system I see 40+ degrees of stratification in my tank during draw down. You either need to mix completely - or have multiple temp sensors to get a real number on the amount of energy in the tank. I use 3 in-tank sensors hanging at the vertical quarter points and double count the middle one as it represents twice as much water volume as the other two. My experience with the Garn says that the only thing the single point temp reading from the factory sensor is good for - is an after burn value as that's is the only time there is minimal stratification.. Their readings during draw down are pretty much worthless - and I assume this to be true for most other storage situations.
For this venture we will ignore outdoor (combustion air) temps and I understand that will impact the accuracy. I assume none of us are burning in FL and we should all be looking at some similar conditions.
For this venture we will ignore wood MC as we're all big kids and none of us would be throwing 4' long sticks of green poplar in our units.
I don't think anyone with less than a couple hundred gallons of storage will be able to come up with relevant data as dynamic heat losses start to become become too large.
You need to shut down any emitters when you do this test as we can't measure any energy lost to your emitters during the test cycle. Something like the Garns kick out a couple hundred thou btu during a burn and minor losses to emitters would be much less significant than a smaller output boiler producing a fraction of that burn rate. Either way...…… try to minimize any emitter or other system heat losses during the burn as the goal is to measure the amount of energy we get to the storage tank.
For this venture we'll assume a storage temp rise from something in the range of 120 - 140 to about 180. If you cherry pick your range to the low side you should be able to improve your efficiency number - but that's not what this is about.
My Numbers:
I use 2.4 lb of wood to raise my 1500 gal of storage one degree or .0016 lb to raise one gallon a single degree. That 2.4 value is based on measuring most loads over the 4+ years of my system being in service. Using rough numbers for the btu per lb of wood I estimate that gets me somewhere about 80% efficient - but maybe somebody with a sharper pencil would like to put together a spread sheet after we get a few numbers so we could compare numbers that way. TCaldwell threw out a 3 lb number for his 2000 gal Garn in the Sweet Spot discussion and after adjusting for the difference in tank volume I was feeling inadequate as I was about 6% lower in my ability to convert lbs of wood to hot water. I then looked at the Garn specs and note that the 1500 is a couple feet shorter and each of the 5 - boiler tube passes thru the tank are shorter. Bottom line is there is less contact between the water and the exhaust tubes. Garn says the 2000 is supposed to be about 7% more efficient than my 1500 and my manhood was restored!
Should be fun. Might be neat to see pellet numbers also? Appreciate your inputs Dan
In the race car world the best test of your labor was to park the completed vehicle on a dyno and after all the bragging and bs'n was done...…… see what kind of power you put out to the tires. If you have storage on your system we can perform the same test by measuring the amount of energy we create from how much wood we burn. I would therefore like to throw down the furnace mitt and challenge all to bare their souls and divulge their numbers.
Ground rules are as follows:
Measure the weight in pounds of the wood you burn to raise your storage a given amount. I've got an old farm scale I picked up for about 50$ and have it by the boiler door for use when I load.
Be cautious about how you measure your storage temps as in my system I see 40+ degrees of stratification in my tank during draw down. You either need to mix completely - or have multiple temp sensors to get a real number on the amount of energy in the tank. I use 3 in-tank sensors hanging at the vertical quarter points and double count the middle one as it represents twice as much water volume as the other two. My experience with the Garn says that the only thing the single point temp reading from the factory sensor is good for - is an after burn value as that's is the only time there is minimal stratification.. Their readings during draw down are pretty much worthless - and I assume this to be true for most other storage situations.
For this venture we will ignore outdoor (combustion air) temps and I understand that will impact the accuracy. I assume none of us are burning in FL and we should all be looking at some similar conditions.
For this venture we will ignore wood MC as we're all big kids and none of us would be throwing 4' long sticks of green poplar in our units.
I don't think anyone with less than a couple hundred gallons of storage will be able to come up with relevant data as dynamic heat losses start to become become too large.
You need to shut down any emitters when you do this test as we can't measure any energy lost to your emitters during the test cycle. Something like the Garns kick out a couple hundred thou btu during a burn and minor losses to emitters would be much less significant than a smaller output boiler producing a fraction of that burn rate. Either way...…… try to minimize any emitter or other system heat losses during the burn as the goal is to measure the amount of energy we get to the storage tank.
For this venture we'll assume a storage temp rise from something in the range of 120 - 140 to about 180. If you cherry pick your range to the low side you should be able to improve your efficiency number - but that's not what this is about.
My Numbers:
I use 2.4 lb of wood to raise my 1500 gal of storage one degree or .0016 lb to raise one gallon a single degree. That 2.4 value is based on measuring most loads over the 4+ years of my system being in service. Using rough numbers for the btu per lb of wood I estimate that gets me somewhere about 80% efficient - but maybe somebody with a sharper pencil would like to put together a spread sheet after we get a few numbers so we could compare numbers that way. TCaldwell threw out a 3 lb number for his 2000 gal Garn in the Sweet Spot discussion and after adjusting for the difference in tank volume I was feeling inadequate as I was about 6% lower in my ability to convert lbs of wood to hot water. I then looked at the Garn specs and note that the 1500 is a couple feet shorter and each of the 5 - boiler tube passes thru the tank are shorter. Bottom line is there is less contact between the water and the exhaust tubes. Garn says the 2000 is supposed to be about 7% more efficient than my 1500 and my manhood was restored!
Should be fun. Might be neat to see pellet numbers also? Appreciate your inputs Dan
