What does a cube of dry logs weigh? Test

[Woodworks]

Looking at the link in Lucan's last post does show surprising similarity in wieghts.

[Mark Bolam]

The correlation between buying in timber green in the round and selling by loose-stacked sub 20% mc is what killed Archimedes, Aristotle, Pluto and Stephen Hawking is still working on it.

It's a Unicorn.

 

 

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[Woodworks]

The correlation between buying in timber green in the round and selling by loose-stacked sub 20% mc is what killed Archimedes, Aristotle, Pluto and Stephen Hawking is still working on it.

It's a Unicorn.

 

 

Sent from my iPhone using Arbtalk

 

Your wrong there Mark. You should know it's a tonne

[Mark Bolam]

Your wrong there Mark. You should know it's a tonne

 

Sense of humour is discouraged on this topic please.

 

 

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[Woodworks]

Sense of humour is discouraged on this topic please.

 

 

Sent from my iPhone using Arbtalk

 

Sorry Mark I was forgetting that weights and measures is a serious business

[openspaceman]

Solid Hardwood 1m3 green = average 1000kg (ref blue book)

 

Solid Hardwood 1m3 at 20% MC = 750kg (ref blue book)

 

Fine and easilly checked by chucking a log into a water butt. Are we assuming this solid m3 does not then shrink as it dries to 20%? Blue book give the basic density of beech and oak at .55 and .56 and defines the basic density as oven dry weight divided by green solid volume. so the green solid m3 has about 550kg of oven dry wood in it.

 

 

Conversion of Solid to stacked = 0.7 (ref blue book again)

 

OK that allows 30% air spaces, seems reasonable

 

 

=> Stacked Hardwood 20% = 525kg

 

 

The weight of the solid m3 of hardwood is now 550kg plus the 20%moisture, so total weight is 687.5kg, i.e. it has lost 312.5kg water whilst seasoning. It now occupies a space of 1.429m3 stacked. So a 1m3 stack of 20% mc wood will weigh 481.25kg

[luke_mclachlan]

Im going to have to source this blue bible, you guys are great !

Ive just landed and im going to have to take note of everything tomorrow. Especially the talk about density-weight-volume, and of course the impact moisture has upon swelling and hence volume (and if it is at all significant when referring to seasoned wood)!! So that a conversion factor relative to all the variables can be calculated.

Some of you may wonder why this is important for me. Well, ive decided to create a simple to use kWh calculator.

[openspaceman]

Im going to have to source this blue bible, you guys are great !

Ive just landed and im going to have to take note of everything tomorrow. Especially the talk about density-weight-volume, and of course the impact moisture has upon swelling and hence volume (and if it is at all significant when referring to seasoned wood)!! So that a conversion factor relative to all the variables can be calculated.

Some of you may wonder why this is important for me. Well, ive decided to create a simple to use kWh calculator.

 

If you allow 50% air spaces the volume of loosely jumbled logs in the above example would weigh 343.75kg which fits reasonably with the original poster's experimental value of 366kg for slightly higher mc logs.

 

Of course there are lots of other unknowns, for instance if the crate were larger there would be proportionally more weight in it. Most of this is explained in the forestry mensuration handbook (Forestry Commission 39 "blue book").

 

One could do the same for other hard and softwoods.

 

Then you would have to consider differences in calorific value and this varies between species and parts of the tree (smaller branches have proportionately more bark and this has higher ash content). Perceived wisdom is that oven dry hardwood has about 18.6MJ/kg (5.166667kWh/kg) whilst the wood of a douglas fir has more lignin and resin and will be about 20MJ/kg (5.555556kWh/kg).

 

After that you need to account for stack losses and these will be mostly interrelated and due to moisture content and excess air (higher mc wood needs more primary air and hence leads to higher excess air values).

[luke_mclachlan]

Of course there are lots of other unknowns, for instance if the crate were larger there would be proportionally more weight in it. Most of this is explained in the forestry mensuration handbook (Forestry Commission 39 "blue book").

 

that's very kind of you, many thanks ! Copy ordered, will be an interesting read.

[luke_mclachlan]

Solid Hardwood 1m3 green = average 1000kg (ref blue book)

 

Solid Hardwood 1m3 at 20% MC = 750kg (ref blue book)

 

Conversion of Solid to stacked = 0.7 (ref blue book again)

 

=> Stacked Hardwood 20% = 525kg

 

Conversion from stacked to loose = 2/3 (ref previous threads)

 

=> 1m3 of loose hardwood 20% = 350kg

 

Do I get extra marks for showing my working?

 

Thanks Lucan. I have a stacked to loose factor of 0.64. I've ordered the blue book and I'll find out their methodology.