deerefanatic said:The heatloss from a DD sitting outside under a roof can be staggering too!![]()
Indeed!
cheers
deerefanatic said:The heatloss from a DD sitting outside under a roof can be staggering too!![]()
Piker said:Heaterman,
Is the DD in an indoor environment? The air going into a downdraft gasser really needs to be tempered before it goes into the unit. If the secondary air is 0* it can cool the refractory down significantly to the point where gasification efficiency is effected dramatically. For instance, a DD in a three sided shed is a no-no for sure. It's best to enclose the unit inside an insulated room where the heat loss from the boiler itself can temper the air a bit before it enters the combustion path. The difference in fuel usage between a unit inside and one setting outside under a roof can be staggering.
cheers
Garnification said:Piker said:Heaterman,
Is the DD in an indoor environment? The air going into a downdraft gasser really needs to be tempered before it goes into the unit. If the secondary air is 0* it can cool the refractory down significantly to the point where gasification efficiency is effected dramatically. For instance, a DD in a three sided shed is a no-no for sure. It's best to enclose the unit inside an insulated room where the heat loss from the boiler itself can temper the air a bit before it enters the combustion path. The difference in fuel usage between a unit inside and one setting outside under a roof can be staggering.
cheers
Piker,
I have often though about this with my garn style unit. Garns pull combustion air from directly out side a most ingenious design and when temps are cold out I kinda though that the cold air was slowing combustion too but only for a little while. I was going to build an exchanger to capture exhaust heat but any colder I get my exhaust and I will be in condensing range. Running @ 240*F right now and that is the temp gauge right at the back of the boiler. The combustion air does get somewhat preheated as the intake passes through the water volume and around the air collar another ingenious design.
But my point is garns move alot of air. And moving all that air leads to great combustion with wood from 15-40% MC. Garns, in my opinion are not as finikey, shall we say as DDs but they do consume alot more electricity that DDs, but thats a price I'm willing to pay for the ease of operation and simplistic design.( simple refractory and electrics)
Piker said:Garnification said:Piker said:Heaterman,
Is the DD in an indoor environment? The air going into a downdraft gasser really needs to be tempered before it goes into the unit. If the secondary air is 0* it can cool the refractory down significantly to the point where gasification efficiency is effected dramatically. For instance, a DD in a three sided shed is a no-no for sure. It's best to enclose the unit inside an insulated room where the heat loss from the boiler itself can temper the air a bit before it enters the combustion path. The difference in fuel usage between a unit inside and one setting outside under a roof can be staggering.
cheers
Piker,
I have often though about this with my garn style unit. Garns pull combustion air from directly out side a most ingenious design and when temps are cold out I kinda though that the cold air was slowing combustion too but only for a little while. I was going to build an exchanger to capture exhaust heat but any colder I get my exhaust and I will be in condensing range. Running @ 240*F right now and that is the temp gauge right at the back of the boiler. The combustion air does get somewhat preheated as the intake passes through the water volume and around the air collar another ingenious design.
But my point is garns move alot of air. And moving all that air leads to great combustion with wood from 15-40% MC. Garns, in my opinion are not as finikey, shall we say as DDs but they do consume alot more electricity that DDs, but thats a price I'm willing to pay for the ease of operation and simplistic design.( simple refractory and electrics)
I think cold combustion air is a factor in any wood boiler... in order to burn the woodgas efficiently, it has to be raised to some pretty high temps... the higher the temps, the easier it will burn regardless of whether it's a DD, and OWB, or a garn type unit. On an OWB, I don't know that it makes as noticeable of a difference, since the efficiency is already extremely poor, but on a DD it makes a huge difference compared to how the unit operates with tempered air. If you insulate the shed or room that your DD is in, you will more than make up for the heat lost from the boiler itself by increasing the combustion efficiency with tempered air inside the room.
I have often thought of using a double wall type chimney in outdoor installations where you can draw combustion air into the shed through the space between the walls of the chimney pipe. This would utilise a great deal of the heat that gets wasted up the stack, but would also probably condense quite a bit, and produce a poor draft situation... If you could capture that condensate before it runs into the boiler you could at least protect the boiler, but the stack itself would be subject to additional acids.
cheers
We use essential cookies to make this site work, and optional cookies to enhance your experience.