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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthortony
    • CommentTimeAug 20th 2012
     
    In my view they are when locally sourced and used in a boiler or furnace designed to burn at high temperatures, they are similar to oil in performance and emissions.

    So yes.
    •  
      CommentAuthornigel
    • CommentTimeAug 20th 2012
     
    I would add that they should be in a well insulated house and not used as a way of reducing co2 emissions in lieu of high quality building.
    • CommentAuthorGBP-Keith
    • CommentTimeAug 20th 2012 edited
     
    I agree, certainly if pellets were being made within a few miles of where I live i would have installed a pellet boiler or heater by now. The concept of a pellet making machine that would be affordable to co-ops, transition groups or just local forestry companies sounds great but they do need to be made to rather exacting standards due to the sophisticated technology incorporated in the boilers.

    So for now it is just logs for me. Don't get me wrong though, logs need to be dried to high standards too. But here's a question:

    Can wood be too dry to burn? I think that I have over-dried wood before but I know that sounds silly (I have a sort of drying kiln/log conservatory ).
    What do others think about that point - can firewood become too dry?
    • CommentAuthorHairlocks
    • CommentTimeAug 20th 2012
     
    Better than oil and electric, worse than gas.

    I personally would prefer a log gasifcation boiler over a pellet boiler, but requires a larger thermal store as cannot be automated to the same level, but for a new build this should be overkill.
  1.  
    I looked at pellets before I had a decision on my heating system. I spoke to CAT and the pellet suppliers in my area seem to struggle with moisture content. As I would then need to buy from further away I went against it. The other slight problem would have been the pellet store size. I should have designed it in from an early stage. I eventually went for a GSHP. I am off gas supply,
    Gusty.
    • CommentAuthortony
    • CommentTimeAug 20th 2012
     
    Keith asks, "Can timber be too dry?" ODT, oven dry timber is often quoted in wood burning but once you get below 10% moisture content storage becomes a problem because of water ingress (wood absorbing moisture from the air). This can be a problem with storing pellets too. The dryer the fuel , the greater the efficiency because energy is not wasted in evaporating the water.
    • CommentAuthorfinny
    • CommentTimeAug 20th 2012
     
    Folk round these parts deliberately choose a couple of large wetter hardwood logs to keep the fire in all night:shocked:
    It would seem that dryer wood burns faster, so as long as you can make the most of the heat as it is released..or store it for later use..ie.. thermal stores or accumulators.. then the drier the better..
    And yes, dry wood makes for cleaner combustion. Something we should all be trying to achieve
    Oh and dry pellets stay drier in bags than blown delivery to hoppers, although some pellets appear to have a surface coating.. hopefully just lignin?!
    • CommentAuthorcrusoe
    • CommentTimeAug 20th 2012 edited
     
    Pretty well agree with most of the sentiments here if locally sourced. Scandinavian pellets? Diesel to transport etc.

    Atmos, AKA Cankar & Son, originators of European-style gasification as we know it, state that wood UNDER 12% should not be burnt. I guess gasification requires volatiles to be present. Below a reasonable level, you are at a kind-of halfway-house to charcoal burning. And as most of us know, above 20% and you are using the chemical energy to drive off the moisture, so at about 20%, with odd exceptions like Ash, you are doing OK.

    nigel: Your comments are spot-on IMO with new build or easily-upgradeable housing, insulation-wise. Spot the recent threads on listed building though - with older/non-changeable buildings would you still not fit pellets because you were not allowed to insulate to any appreciable degree?? :confused:
    • CommentAuthormike7
    • CommentTimeAug 20th 2012
     
    Posted By: GBP-Keith- can firewood become too dry?


    Can't find any iindication of a downside other than burning faster. This could also mean higher exhaust temperature than normal which could just concievably result in damage to the stove, but seems to me unlikely.
    • CommentAuthorcrusoe
    • CommentTimeAug 20th 2012
     
    mike7 - there must be some downside or they wouldn't recommend 'around' 20% as optimum. That figure has been a constant since I started fitting woodstoves (first wave) in 1978. Caveats as above.
  2.  
    If you take a look on youtube you will find quite a lot about making your own pellets from grass and dry leaves with small scale pellet mills.

    Not sure how practical it is but if you have a low heating demand, a ready supply of raw materials on site and the time and inclination to do it, then it must surely be a very low impact source of fuel?

    I've also heard of boilers which can burn certain products which would otherwise be waste such as hazelnut husks and the by-product left over after the extraction of the oil from rapeseed, what about that?
    • CommentAuthorjamesingram
    • CommentTimeAug 20th 2012 edited
     
    Would one trouble with pellets be price installability as they require more processing than logs, and will therefore change in price more relative to demand ?

    A Company i know just fitted a pellet boiler to heat thier offices/store , they did it purely for the financial benefits it will bring via the RHI, previously they used gas for space heating and HW
    • CommentAuthorGBP-Keith
    • CommentTimeAug 20th 2012 edited
     
    Continuing the dryness question (related to logs), I'm sure I read somewhere that the sugars in the cell walls begin to disintegrate and the combustible value drops away when the wood gets too dry but I might be dreaming that bit. certainly i stopped transferring wood from my outdoor shelter to my drying house early in the spring. We now transfer it an July-time to help avoid it getting too dry. I think my boiler instructions suggest 20-25% I must look it up.

    I have a habit of burning quite small stuff which will be much sappier than mature logs and it could well be that stuff that is getting too dry. As tony says, it would be nigh-on impossible to get most decent heartwood below 10% anyhow, certainly here in west Wales.
    • CommentAuthorBeau
    • CommentTimeAug 20th 2012 edited
     
    I have never heard of a log being too dry in fact the chance would be a fine thing. I have burnt off-cuts from my furniture business that were down to 8% and they burned great. I think 20-25% is a good target for anyone drying logs in the west of Britain, I know we can't get our logs bellow 20% however many years we dry them but we do live on the west side of Dartmoor. Out of interest what is the current price for wood pellets? as the last time I did some sums pellets were cheaper by the tonne than the firewood we sell :shocked:
  3.  
    <blockquote><cite>Posted By: crusoe</cite>mike7 - there must be some downside or they wouldn't recommend 'around' 20% as optimum. That figure has been a constant since I started fitting woodstoves (first wave) in 1978. Caveats as above.</blockquote>

    Is it to keep the fire temp down so that the flue doesnt risk overheating/catching fire?

    The more the humidity content of the wood, the lower the temp of the fire and more the pollution for your neighbours.
    • CommentAuthorjamesingram
    • CommentTimeAug 20th 2012 edited
     
    Beau , local supplier (SE) to me £215/tonne + delivery ( local £30 ish ) + Vat for pallet of 12.5kg bags
    , this is 2011/2012 price list not current spot price.
  4.  
    Im suprised there isnt more talk on this forum about Finnish mass ovens.
    Personally, as long as we are talking burning wood for heating and hot water, the MINIMUM spec that should be aimed for is a stove as efficient as a finnish stove. In the same way that Passive House shoudl be the min spec for new build.
    Anything else is wasting wood, inefficient and polluting.

    http://www.energyhack.com/building-an-effective-finish-mass-oven/
    Here is an article about them, mentions a humidity content of 10% being required to really get the most efficient burn.
    • CommentAuthormike7
    • CommentTimeAug 20th 2012
     
    Posted By: crusoemike7 - there must be some downside or they wouldn't recommend 'around' 20% as optimum. That figure has been a constant since I started fitting woodstoves (first wave) in 1978. Caveats as above.


    It may be that 20% became the recommended figure because it was achievable in most circumstances without undue extra effort, and any gains from going drier were subject to a law of diminishing returns.

    Not a pop at you Crusoe, but it does generally seem to be the case that there is a lot of traditional custom and practice, old saws, 'kerbside' wisdom etc about not all of which is necessarily sound, or which should be regarded with a little suspicion as we are now trying to achieve much higher standards of efficiency and pollution limitation than were acceptable in 'the good old days'.

    Personally I try to have extra dry wood for lighting and the first load of the day as I think this gets to a clean burning stage as quickly as possible.
    •  
      CommentAuthornigel
    • CommentTimeAug 21st 2012 edited
     
    Posted By: crusoe

    nigel: Your comments are spot-on IMO with new build or easily-upgradeable housing, insulation-wise. Spot the recent threads on listed building though - with older/non-changeable buildings would you still not fit pellets because you were not allowed to insulate to any appreciable degree??http:///forum114/extensions/Vanillacons/smilies/standard/confused.gif" alt=":confused:" title=":confused:" >


    I know what you mean if we all first of all reduced heat requirement and then find the best way to produce heat it would be better. Clearly listed buildings are an issue but still there are things that can be done.
    What I am against is seeing biomass as a way of achieving a SAP requirement by specifying biomass rather than specifying a high level of insulation in the design.

    Therefore through good thermal design and improving the technology of burning wood we can massively reduce particulate emissions as well as co2.
    I see biomass as primarily a fuel for areas off the gas grid which are largely rural areas.
    • CommentAuthorcrusoe
    • CommentTimeAug 21st 2012 edited
     
    I'm with you there nigel. Like landowners' mass-install of PV for grant purposes, not the intended purpose of the grant.

    mike7 - pop away - why should you be the exception :wink: And hey, I'm not that old...(he says). Still play the occasional vet's game you know. Haven't you heard that with experience comes wisdom :smile: And progress, if 'tis such, has it's price - like I can't service my own car any more...


    Hi bot...where you been hiding? So are these more efficient than kachelofen/thermal mass stoves? If so, why, pray?
  5.  
    Hi bot...where you been hiding? So are these more efficient than kachelofen/thermal mass stoves? If so, why, pray?

    Hi Crusoe, they are one and the same things
    • CommentAuthorJeff B
    • CommentTimeAug 21st 2012
     
    Posted By: BeauI have never heard of a log being to dry in fact the chance would be a fine thing. I have burnt off-cuts from my furniture business that were down to 8% and they burned great. I think 20-25% is a good target for anyone drying logs in the west of Britain, I know we can't get our logs bellow 20% however many years we dry them but we do live on the west side of Dartmoor. Out of interest what is the current price for wood pellets? as the last time I did some sums pellets were cheaper by the tonne than the firewood we sell:shocked:" alt=":shocked:" src="http:///newforum/extensions/Vanillacons/smilies/standard/shocked.gif" >


    I pay £210 per tonne inc delivery (min quantity in theory 3 tonnes, but I usually get 2 - 2.5 tonnes). BTW this is in bulk, blown directly into hopper, not bags.
    • CommentAuthorBeau
    • CommentTimeAug 21st 2012
     
    Thanks for the prices on wood pellets, yep pellets are still cheaper than our logs :shamed:
    • CommentAuthorJeff B
    • CommentTimeAug 21st 2012 edited
     
    Posted By: BeauThanks for the prices on wood pellets, yep pellets are still cheaper than our logs:shamed:" alt=":shamed:" src="http:///newforum/extensions/Vanillacons/smilies/standard/shamed.gif" >


    That is surprising as obviously pellets are sawdust that has undergone considerable processing.
    • CommentAuthorHairlocks
    • CommentTimeAug 21st 2012
     
    Beau, you probably need to change you supplier if you are pay more than £210 a tonne. A tree surgeon offered me a van load of dried logs at £60 inc delivery, which I think he claims would be a tonne.
    • CommentAuthorBeau
    • CommentTimeAug 21st 2012 edited
     
    <blockquote><cite>Posted By: Hairlocks</cite>Beau, you probably need to change you supplier if you are pay more than £210 a tonne. A tree surgeon offered me a van load of dried logs at £60 inc delivery, which I think he claims would be a tonne.</blockquote>

    No we are selling them and we are not the most expensive around here. They are very carefully dried and delivered but it is still surprising that wood pellets can be made so cheaply considering what must be involved in processing them.
    • CommentAuthorJonti
    • CommentTimeAug 22nd 2012
     
    You need to be careful of the quality of the pellets and where they are stored. There was a case last year in Switzerland where a lady went to do some work in the room being used to store wood pellets and was overcome by fumes from the pellets (bonding agent used I believe) and died. Maybe an example of the double dangers of pellets combined with airtight rooms???

    Jonti
    • CommentAuthorfinny
    • CommentTimeAug 22nd 2012
     
    Have heard of dust from poor pellets combusting in a well sealed room when a door was opened! Can't tell you where and when..maybe myth:shamed:
    I have seen a very big pellet production plant in North Wales and am convinced they are cheap because of vast subsidies to set the place up..The bags were palletised by a robot! Upfront costs astronomical.. but then hey it's like printing banknotes now!
    • CommentAuthorJonti
    • CommentTimeAug 22nd 2012
     
    Finny,

    maybe if George O did quantitative easing on a large enough scale the produced notes could be burned to produce cheap energy:bigsmile:

    but seriously, my comment about the pellets was just to illustrate hat as with most things there are some drawbacks.

    Jonti
    • CommentAuthorcrusoe
    • CommentTimeAug 22nd 2012 edited
     
    No you are right finny, 'combustible' dust is an issue, tis why the once-popular sawdust-burners bit the, errm, dust, cos they were prone to a bit of whoof now and then. More now than then, some said... :shocked:

    bot - thanks for clarification. Do the Finnish ones have any special features us woodies should be aware of? You sound very enthusiastic. Unusual for you :devil:

    Beau: Forgetting price-per-therm for a moment, I recently mentioned the three 'T's of effective combustion which we learned as sprogs. Time (of flame in firebox - in other words, flame path), Temperature - self explanatory, even in gasification where inducted air is superheated, and Turbulence (agitated/turbulated movement of flame against hot (reflective) or quenched (absorptive) or combo surface). My understanding is that when wood is too dry, it will burn at its hottest, (think charcoal) but lacks the volatiles to achieve the best effect aka secondary/tertiary combustion.
   
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