FYI, I played with an Econoburn 100 for about 3 hours this afternoon to see what kind of numbers I could get on the combustion analyzer. I was very pleasantly surprised.
First off, a wood burner is a different beast because the fuel supply is always changing. You can set the air shutter for best performance and 15 minutes later the combustion numbers are all out of whack as your fuel changes state. So you pick an average setting and run with it. I wound up with a tad more air than the factory setting.
That being said, I'm pretty impressed with what I observed in the roughly 3 hours that I played with this boiler. I asked the owner if he would give me a ring when he had a fire in it that was about 2 hours into a burn so I had an average starting point. When I got there the boiler had a good bed of coals underneath 3 chunks of logs that were fully carbonized. I stirred the fuel a bit to settle the chunks and stuck the Testo in the flue to see what was going on. The burner was in full gasification mode with nearly the entire lower chamber filled with bluish yellow flame.
These are the numbers:
Flue gas temp 368*
CO 2630 PPM
CO2 11.2%
O2 5.1%
Efficiency 87.6%
Flue draft -0.04 wc"
Sounds like a good running oil burner except for the CO.
The next step was to load it with wood and see what happened to the numbers leaving the air gate setting as it was. I added approximately 25-30 pounds of wood and opened the flue gate to let the new wood get going. During this stage the excess air went way up and correspondingly the CO2 fell into the 5% range. I figured this was normal as the combustion air was blowing pretty much straight through the firebox. At this point the numbers looked like this.
CO 1618 PPM
CO2 5.4%
O2 11.5%
Efficiency 76.4% (that was as low as I saw it through the whole cycle)
After about 15 minutes I closed the flue gate to put it in gasification mode and monitored the analyzer. The unit started gasifying but the excess air remained high, like over 90%. It took me a minute to tumble to what was going on. The unit was in gasification mode, the wood seemed to be fully involved flame wise so why was the excess air so high? Although the unit was gasifying, the wood had not reached the temperature where it is carbonized. As this began to happen the excess air dropped, the CO2 went back up and the efficiency climbed back over 80%. After another 45-50 minutes the numbers reached nearly the same point as the initial test. After another 15 minutes or so the unit reached what I would guess to be peak burn as flue gas was reaching 450*. The gasification chamber was filled with flame and the flue gas numbers actually looked as though it could use more air as the CO2 was over 13%. CO went ballistic, reading 4500PPM before I pulled the analyzer. I'd guess that during this brief period of 10-15 minute the efficiency was crowding 90%. Very soon after that the fire passed its peak and the numbers began to look more normal..... as if 80% from a wood burner is normal.
Conclusions:
You have to give a gasifying wood burner plenty of air in order to ensure that you can sustain gasification all the way through the burn cycle. If you set it to low you can lose a lot during the peak burn time period.
Econoburn has done their homework on boiler design. The boiler cranks out efficiency and burns clean. Although the wood being used by this homeowner is not quite what it should be (24-35% moisture on the logs I tested) the boiler handles it well with little sign of creosote buildup in the heat exchanger area. There is a pretty good coating inside the fire box. I'm sure it would be less with the moisture content recommended by Econoburn (<25%)
In this day of $3.00 fuel oil, soon to be crowding $4 unless I miss my guess, we in the heating profession are going to be seeing a lot more alternative type systems going in. It's our responsibility to acquaint ourselves with what's good and what's not. The Econoburn boiler is a good place to start. It's a pressurized sealed unit so it eliminates a lot of the inherent problems of open systems. As I understand it, they have the folks from ASME in the factory as of right now reviewing their manufacturing processes and will soon have the {H} rating making it acceptable for installation everywhere. They also have the same unit available soon in an outdoor model.
Home owners considering burning wood will do themselves a favor by using a unit like this as opposed to a typical outdoor wood burner with their sub 40% efficiency and horrible particulate emissions.
First off, a wood burner is a different beast because the fuel supply is always changing. You can set the air shutter for best performance and 15 minutes later the combustion numbers are all out of whack as your fuel changes state. So you pick an average setting and run with it. I wound up with a tad more air than the factory setting.
That being said, I'm pretty impressed with what I observed in the roughly 3 hours that I played with this boiler. I asked the owner if he would give me a ring when he had a fire in it that was about 2 hours into a burn so I had an average starting point. When I got there the boiler had a good bed of coals underneath 3 chunks of logs that were fully carbonized. I stirred the fuel a bit to settle the chunks and stuck the Testo in the flue to see what was going on. The burner was in full gasification mode with nearly the entire lower chamber filled with bluish yellow flame.
These are the numbers:
Flue gas temp 368*
CO 2630 PPM
CO2 11.2%
O2 5.1%
Efficiency 87.6%
Flue draft -0.04 wc"
Sounds like a good running oil burner except for the CO.
The next step was to load it with wood and see what happened to the numbers leaving the air gate setting as it was. I added approximately 25-30 pounds of wood and opened the flue gate to let the new wood get going. During this stage the excess air went way up and correspondingly the CO2 fell into the 5% range. I figured this was normal as the combustion air was blowing pretty much straight through the firebox. At this point the numbers looked like this.
CO 1618 PPM
CO2 5.4%
O2 11.5%
Efficiency 76.4% (that was as low as I saw it through the whole cycle)
After about 15 minutes I closed the flue gate to put it in gasification mode and monitored the analyzer. The unit started gasifying but the excess air remained high, like over 90%. It took me a minute to tumble to what was going on. The unit was in gasification mode, the wood seemed to be fully involved flame wise so why was the excess air so high? Although the unit was gasifying, the wood had not reached the temperature where it is carbonized. As this began to happen the excess air dropped, the CO2 went back up and the efficiency climbed back over 80%. After another 45-50 minutes the numbers reached nearly the same point as the initial test. After another 15 minutes or so the unit reached what I would guess to be peak burn as flue gas was reaching 450*. The gasification chamber was filled with flame and the flue gas numbers actually looked as though it could use more air as the CO2 was over 13%. CO went ballistic, reading 4500PPM before I pulled the analyzer. I'd guess that during this brief period of 10-15 minute the efficiency was crowding 90%. Very soon after that the fire passed its peak and the numbers began to look more normal..... as if 80% from a wood burner is normal.
Conclusions:
You have to give a gasifying wood burner plenty of air in order to ensure that you can sustain gasification all the way through the burn cycle. If you set it to low you can lose a lot during the peak burn time period.
Econoburn has done their homework on boiler design. The boiler cranks out efficiency and burns clean. Although the wood being used by this homeowner is not quite what it should be (24-35% moisture on the logs I tested) the boiler handles it well with little sign of creosote buildup in the heat exchanger area. There is a pretty good coating inside the fire box. I'm sure it would be less with the moisture content recommended by Econoburn (<25%)
In this day of $3.00 fuel oil, soon to be crowding $4 unless I miss my guess, we in the heating profession are going to be seeing a lot more alternative type systems going in. It's our responsibility to acquaint ourselves with what's good and what's not. The Econoburn boiler is a good place to start. It's a pressurized sealed unit so it eliminates a lot of the inherent problems of open systems. As I understand it, they have the folks from ASME in the factory as of right now reviewing their manufacturing processes and will soon have the {H} rating making it acceptable for installation everywhere. They also have the same unit available soon in an outdoor model.
Home owners considering burning wood will do themselves a favor by using a unit like this as opposed to a typical outdoor wood burner with their sub 40% efficiency and horrible particulate emissions.
