Monday, February 11, 2013
Technology can turn plain old wood stoves into a high-tech heating option
The Union Hybrid stove being tested, with standard combustion in the bottom portion and the "gasification" combustion happening above.
If there’s any technology that is old hat, it’s got to be the log-burning wood stove.Left behind by its sexier cousin, the pellet stove, it has been reduced to living-room decoration and grubby basement backup, something that would be right at home in Teddy Roosevelt’s hunting cabin. Right?
Wrong! It turns out that wood stoves are the subject of considerable tinkering and R&D, like so much of the technology around us.
“When we started, stoves were basically six-sided boxes, and you put a fire in it. Now we’re making equipment, with a lot of moving parts. The technology is much better and increasing rapidly,” said Tom Morrissey, owner of Woodstock Soapstone Co. in West Lebanon, which has been building cordwood-burning stoves for 35 years.
I talked to Morrissey because his company is one of 14 finalists in the Wood Stove Design Challenge, a national contest by an industry group called Alliance for Green Heat. They’re the only New Hampshire finalist amid of host of other wood stove companies, as well as some independent inventors and university engineering students.
“We are essentially making a gasification stove,” he said, referring to a form of combustion that doesn’t really use combustion. “If you look at this thing when it’s burning, the fire does not look like what you would think of as a wood fire. The whole top of firebox is like an inverted gas burner; there are 120 holes with a tube of flame coming out of each one.”
The challenge will end in a Wood Stove Decathlon on the National Mall in Washington, D.C., in November. Winners will be judged not just on efficiency – how many British thermal units do they produce from a set amount of wood – but also on the cleanliness of their emissions.
That point is important because old-timey wood stoves (like the one in my basement, I admit) are pretty dirty. Their smoke is full of soot or particulate matter – tiny bits of unburned or semi-burned wood, sometimes called “black carbon” – that is unhealthy when inhaled and has an outsized effect on global warming.
Airborne soot from wood stoves is a big reason why the Keene area has relatively unhealthy air in the winter, and why the American Lung Associations’ buy-back program, which offers money if you swap your old wood stove for a new, cleaner one, concentrates on Cheshire County.
Pollution, rather than efficiency, is also the driver for all this technology. The federal Environmental Protection Agency has new rules that reduce the amount of allowable airborne fine-particle matter from 15 micrograms to 12 micrograms per cubic meter of air.
This means just sticking a catalytic converter into the stovepipe isn’t going to be good enough any more.
“That’s kind of the stick,” said Morrissey. “There has been a lot of time and effort and money put into R&D in the last five years.”
Woodstock Soapstone Co., so named because it uses soapstone as a design element in stoves, has 30 employees and annual sales in the $4 million to $6 million range, so it’s a niche player but not a minor one.
Its contest entry, the Union Hybrid, uses both secondary combustion – a second burn of the “gasification” type that happens when the firebox is hot, which consumes more of the pollution – and a catalytic converter when on “low burn.”
The devil’s in the details of coordinating these two; Morrissey says the company uses oxygen sensors developed for the automotive industry and is developing thermocouples, which use heat to generate electricity from two different metals in close contact, to move air.
Combine that with software to give customers more control, and you can have a big boost in efficiency and reduction in pollution.
“Ten years ago, you could never imagine having a little computer on the stove. If you were in a small industry like ours, you couldn’t dream of having a graphic-user- interface, but now it’s available and affordable,” Morrissey said.
Affordable is key: Woodstock Soapstone is looking at keeping prices below $2,000, which gives them an advantage over similar-output pellet stoves.
Pellet stoves, of course, have a huge advantage over firewood stoves: The uniform size and shape of their fuel means they can be automatically fed by thermostat-controlled augers, making them a viable replacement for oil- and gas-fired furnaces. This has made biomass heat – e.g., burning wood – rebound as a minor but important energy option in the Northeast.
But cordwood stoves have advantages of their own: They work even when the power is out, and if a tree falls in your yard, you can turn it into free fuel. Try doing that with pellets!
If cordwood stoves can be made more efficient and cleaner, then we’ve got ourselves a technology race.
Tablets vs. smartphones – ho-hum! It’s cordwood stoves vs. pellet stoves, and may the best technology win.
Granite Geek appears Mondays in the Telegraph, and online at www.granitegeek.org. David Brooks can be reached at 594-6531 or firstname.lastname@example.org.