Pros & cons of wood burning

[Anonymous]

I thought I'd start this thread in response to recent posts from Chris Herring and David Olivier, specifically David's underlining of the negative side of woodburners. I've always thought of woodburners as a Good Thing, but this is making me wonder…

It certainly seems that in a newbuild situation, minimal gas backup is a better option. How about retrofit? And what difference does urban/rural setting make?

It also makes me wonder if this isn't partly an issue of different visions of the future. If we believe that fossil fuel supplies are inherently unstable and undesirable, then wood is a good option as it's renewable and local despite being polluting. If we believe that gas will continue to be available and affordable, if more expensive, then it makes much more sense to use it, it being a much more responsive and adjustable fuel, and the infrastructure already being in place.

Is anyone armed with facts and figures to make the case for the future of woodburners?

[Anonymous]

Everywhere you look another can of worms…

[David Olivier]

Although I'm building far from the nearest gas main I'll use a tiny amount of LPG rather than wood and plant a tree or two to sequester this very small amount of CO2.

The UK attitude to (coal) power station emissions used to be “let's just rely on the windy English climate to disperse them and reduce the concentration of particulates etc to low levels – tall stacks will do that”. Pressure from Norway and Sweden who received very diluted but still damaging pollutants including SO2 finally put a stop to this. I think it's a matter of time how long it takes for an equal awareness of what's in wood combustion products to become widespread.

[Anonymous]

I think it's a matter of time how long it takes for an equal awareness of what's in wood combustion products to become widespread.

So are you anti wood or would you say that there needs to be more money pumped into greening of wood combustion? There goes me coppiced wood plan…. 🙂

[David Olivier]

It could be burned fairly cleanly today in a large CHP plant but small-scale wood-burning plant isn't so well-equipped to clean up its flue gases.

[Anonymous]

Hey! Mr Olivier!

Just thought I'd try and re-awaken this debate. I'd be very interested if you have more facts and figures to address these questions. I think this is really important, as a lot of people I know within eco-building circles see maximal use of coppiced wood as the way forward, and everyone seems to be content with the reasoning that it's a carbon neutral cycle therefore good. I've never heard any concerns about local air quality. Do you think small scale wood burning should be banned?

[David Olivier]

You might like to read http://www.burningissues.org. If you do a Google with logical keywords, including “PAHs”, you'll also find a lot of other information on the web.

The attitude to emissions that if they're too dilute to smell, they're tolerable, may be understandable but it's regrettable. Paradoxically, while the UK has a policy that heating with wood = good, New Zealand is trying to persuade people to change to gas or to electric heat pumps in order to reduce air pollution. A higher proportion of NZ's population heat with wood than ours, but its population density is of course much lower.

I'm writing a technical paper for AECB on the subject over the next 6 months to one year. I'll go into more details there.

HTH

David.

[Anonymous]

I’ve has a good scan of http://www.burningissues and I am disappointed at its exclusive use of stove and fireplace statistics to ‘tar’ all types of wood burning whereas gasification of dry wood via boilers into thermal stores under lambda control is strangely omitted. Perhaps their stated honourable mission in life would not be as clear cut if they accepted that wood can be burnt much cleaner.

If you do read deeper, there are indications that after 100 metres, the smoke dispersal is such that the measurable pollutants disappear to zero, confirming my proposition that wood heat is really just for rural areas.

Handbuch Bioenergie-Kleinanlagen indicates average 44% reduction in dust emission for sub 50 kW pellet boilers compared to pellet stoves. More to the point, the range varies greatly about this average point indicating the sensitivity of wood combustion.

As the third world charities start handing out LPG and petrol stoves to reduce lung disease mortality from smoke-ridden kitchens, we should consider how the increase use of such finite reserve fuels will affect us in the long term. Once the fossils are gone, are we not back in a big circle to the fact that wood is indeed a very useful stored form of solar energy that has a high chance of burning anyway from natural forest fires. Super insulated houses don’t heat our DHW in winter nor heat our cooking, so alone can’t be the final answer. Hence I wonder what an AECB house of the future will really contain…..

[David Olivier]

There are other sources of renewable energy than wood. One alternative to solid biofuels is … liquid and gaseous fuels, which for small-scale use would be superior to wood or straw, rather as propane or methane are superior to coal.

IPCC has pointed out that there are adequate carbon sinks to absorb 5-10% of current world CO2 emissions. The biggest challenge is getting down from current CO2 emissions to 5-10%. Much of that can be accomplished via energy efficiency and by less cleaner renewable energy technologies.

I'm aware of the effects of dilution and sceptical that it's a valid approach to the emissions from wood combustion. After all, it wasn't and isn't a valid approach to SO2 from coal burning or to exposure to ionising radiation

David.

David.

[David Olivier]

Correction

In last message, for “.. less cleaner …” read “cleaner …”

D.

[Anonymous]

Exactly. I think that's why estate agents are selling land on the moon. I'm thinking of moving there myself. Seems like the whole 'civilisation on Earth' bubble is about to burst….

[David Olivier]

The subject under discussion wasn't concentrated wood smoke in developing countries, including the larger particulates; it was dilute smoke in developed countries. Since larger particles get removed with an increasing distance from the source, the problems are the smaller particles (PM2.5s), carcinogens, radioactive elements et al.

The price of oil and gas afer peak oil (and gas) isn't near-infinite; it's set by the cost of replacements (energy efficiency – cheap – and renewables). Although biomass couldn't meet all the world's energy needs after oil and gas, it's the only renewable energy source which is un-capital-intensive and can be stored as fuel rather than as heat or elecricity. Given its unique nature and the potential demand for biofuels for multiple different uses (steelmaking is just one), its price will rocket and one anticipates it will be traded like fossil fuels are today (it already is).

D.

[David Olivier]

There are a few interesting developments with pellet boilers from the manufacturer Okofen. The first link is http://www.aebiom.org/IMG/pdf/Ordner.pdf .

First development is a condensing boiler. There are hints that Okofen have developed condensing versions of each of their models up to 20 kW – their smallest model, more suited to energy-efficient buildings, is 9 kW. However, as this site indicates they have so far launched only a condensing version of the 20 kW boiler. No other company is even offering any kind of condensing wood boiler.

The smallest Okofen, the 8 kW, has lab. efficiencies of 92.2% at 9.3 kW (full load), and 93.4% at 2.3 kW (part load). These efficiencies are on the Lower Heating Value. For pellets, the Higher Heating Value is about 8.5% above the LHV, so the HHV efficiencies (as quoted in the UK) are about 85% and 86%.

The particulate emissions aren't yet quite level with oil, let alone LPG, but they may be slowly getting down towards this level. According to their website
http://www.pelletsheizung.at/sitex/index.php/page.57/action.view/entity.detail/key.31/
the non-condensing pellet boiler emits c3X more particles than an oil boiler of the same capacity and the condensing boiler c.2X as many. (I suspect they overstate the emissions of an oil boiler but it's a vast improvement on other wood-burning appliances. There's nothing on PAH emissions).

Thanks to Gordon Taylor for some help with translation.

Despite this apparent superiority over all else, the graphs suggest that so far the UK sales are negligible compared to Germany, Austria, Italy, Switzerland, France etc.

David.

[Mark Siddall]

It would seem that UK company Organic Energy have an interest in Okofen wood burning heating systems. Perhaps they will be able to offer a more thorough translation system (given that they may want to shift a few units.)
http://www.organicenergy.co.uk/content/index.php
and klick on the Okofen image.

For a review of the Okofen range that Organic Energy stock see http://www.housebuildersupdate.co.uk/2006/12/pellet-boilers-okefen-examined.html

Mark

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