Electronics > Power/Renewable Energy/EV's

wood burners

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Simon:
I know this is not strictly electrical (until someone raises the control system ;)) but. As I cut down and shred a large tree I wonder about the practicalities of having a woodburner that feeds in pellets or shavings to burn. What really turns me off wood burners is that usually they are just furnace boxes that burn wood and like a regular fireplace still send most of the heat out of the flu. What I would propose is a burner that can feed in at the correct rate for the energy demand and be fanned by an electric fan that will push the exhaust through a heat exchanger that exchanges with air or water. Does such a device already exist ? are they stupid money or something worth considering.

I grew up in italy where people used olive pip burning furnaces to heat their homes much like i am hoping to do although I have no idea how they did the heat exchanging and they were big units.

dr.diesel:
Those things are all over the place in rural US, commercial units run about $5k, but doesn't include the plumbing and installation costs.  Most of the units here are an outdoor unit with a glycol system to carry the heat inside.

Simon:
Ah right, so they are quite efficient ?

dr.diesel:
Not at all, for the most part.  I've not read anything recently, but a typical non catalytic burner was somewhere in the 50% range, but varies depending on load.  But also spews tons of particulate matter into the air, smoke like crazy.

These things are regulated by the air inlet, when the inside gets warm and the burner gets choked off, they smoke/smolder even more, at a super low combustion efficiency point.

They do make some fancier units, that once up to temp can burn the particulate/smoke in a catalytic chamber in the upper exhaust, but I've never seen one of those in action.  Probably 3x the cost as well.

mib:
A typical wood burning stove should be roughly 75% efficient. 75% of the potential heat from the wood should end up heating your home.
That sort of efficiency does require it to be installed and used correctly, something that many people fail to do.

You can also get very efficient pellet boilers here in the UK that will burn any biomass that is cut into small enough pieces and appropriately dried. They are 2-3 times the price of an equivalent gas boiler - mostly due to the much smaller market. They are a little less efficient than a condensing gas boiler due extra losses in the fuel loading and ash removal systems. But they can be 85-90% efficient.

The biggest problem with pellet burners is the physical size of the unit plus space for the fuel, which rules out their use in most homes here.

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