Help- working out calorific values

[StephF]

I think I have just encountered a complete nutter on phone/email, so not sure why I'm bothering but... he wants to know what is the calorific value of my 3 metre load?

I feel challanged to have a go and tell him the answer, but not a clue how to find this out. I asked him if he had a gasifying boiler and thought maybe he needed to know for the FIT etc. But no, he just wants to know. He is also presuming the 3 metres comes in 'A bag'. I suspect he will be moisture testing each log, they average between 15-20%.

[LewisB]

This will probably be a good place to start:

 

http://www.forestry.gov.uk/pdf/eng-woodfuel-woodasfuelguide.pdf/$FILE/eng-woodfuel-woodasfuelguide.pdf

 

and,

 

http://www.forestry.gov.uk/pdf/FC-BEC-InfoSheet-Wood-as-Fuel-TechSupp.pdf/$FILE/FC-BEC-InfoSheet-Wood-as-Fuel-TechSupp.pdf

 

Good luck!

Edited March 20, 2014 by LewisB

[Adam M]

This will probably be a good place to start:

 

http://www.forestry.gov.uk/pdf/eng-woodfuel-woodasfuelguide.pdf//eng-woodfuel-woodasfuelguide.pdf

 

and,

 

http://www.forestry.gov.uk/pdf/FC-BEC-InfoSheet-Wood-as-Fuel-TechSupp.pdf//FC-BEC-InfoSheet-Wood-as-Fuel-TechSupp.pdf

 

Good luck!

 

I would give the caller those links and leave him to draw his own conclusions otherwise he'll be on your case once you've dropped the load off. Sell your logs to the next person.

[matthew65]

I had a customer today who wanted to know if I sold Ash. He has a pizza oven and was told that this is the only wood he can burn. He lived over an hour away, I explained that I did have some ash and that I also sold pizza ovens. I explained that as long as the wood is dry and not softwood (due to flavour and the fact that it pops) any dry wood was suitable !.

[SamWhiting12]

To work out the energy you need to know the weight of either the bag of wood or the weight of the whole load. Then using the tables in the link above you can work out the energy per load.

 

I did so calcs for 0.75cbm bags for softwood and hardwood and they came out as 760kWh and 1200kWh respectively at and average MC of 20%. The only problem I had was getting the weight of the bags of wood (they were educated guesses from previous threads about the weight of a cbm).

 

And before Mark Bolam says anything, No they weren't a ton :001_tt2:

 

Hope this helps Steph.

[peatff]

I think I have just encountered a complete nutter on phone/email, so not sure why I'm bothering but... he wants to know what is the calorific value of my 3 metre load?

 

Why, is he going to eat it ?

[daltontrees]

I think it's reasonable to want to know.

 

Calorific value can be expessed in kWh or in Joules. As the FC documents linked by someone earlier show, a typical oven dried wood will have a total energy of about 5MWh per oven dry tonne. That's equivalent to 5,000,000J x 60 seconds x 60 minutes = 18GJ (GigaJoules). If a tonne of oven dried (or very dry anyway) logs will cost £250, then the cost of wood energy is £250/18GJ = £13.88 per GigaJoule.

 

Gas is about £0.05 per kWh which is £0.05 per 3.6MJ which is equal to £72 per GigaJoule.

 

Electricity is about £180 per GigaJoule.

 

If you're selling logs that are less than dry, the FC leaflet gives a rough way of adjusting the calorific value.

 

Bottom line is that you can point out to customer that logs are a substantially cheaper way of heating space than gas or electricity. Remember though that stoves are only about 70% efficient. So it costs more like £20/GJ.

 

This approach only applies to price poer weight. Densitied of dried woods vary considerably and the equivalent calculation for £ per cube is difficult. But since only comparison of £ per calorific values allows a customer to see the sense of buying logs, £ per cube is meaningless.

[StephF]

To work out the energy you need to know the weight of either the bag of wood or the weight of the whole load. Then using the tables in the link above you can work out the energy per load.

 

I did so calcs for 0.75cbm bags for softwood and hardwood and they came out as 760kWh and 1200kWh respectively at and average MC of 20%. The only problem I had was getting the weight of the bags of wood (they were educated guesses from previous threads about the weight of a cbm).

 

And before Mark Bolam says anything, No they weren't a ton :001_tt2:

 

Hope this helps Steph.

 

This is helpful, you have done all the hardwork for me, although I have to trust your guess on the weight of 0.75 cbm!

Logically then if I sell a 1.5cbm loose load it is double the bag (roughly)?

I may take a previous replys advice and give this customer a miss.

It sounds as if he could a lot of hassle think he has been reading too much info on the internet about log burners.

[mendiplogs]

This is helpful, you have done all the hardwork for me, although I have to trust your guess on the weight of 0.75 cbm!

Logically then if I sell a 1.5cbm loose load it is double the bag (roughly)?

I may take a previous replys advice and give this customer a miss.

It sounds as if he could a lot of hassle think he has been reading too much info on the internet about log burners.

 

HI STEPH theres all ways one try to tell you how to do your JOB MATE it all so down to how good how STOVE IS ALL THE BEST STEPH:thumbup1: jon

[SamWhiting12]

This is helpful, you have done all the hardwork for me, although I have to trust your guess on the weight of 0.75 cbm!

Logically then if I sell a 1.5cbm loose load it is double the bag (roughly)?

I may take a previous replys advice and give this customer a miss.

It sounds as if he could a lot of hassle think he has been reading too much info on the internet about log burners.

 

Yer I found weights for seasoned 1cbm bags and then scaled it down to a 0.75cbm bag.

 

He does seem like the awkward customer that will question everything you say.