Help- working out calorific values

[Woodworks]

From the previous link and here Typical calorific values of fuels a kg of wood is 4kWh of energy. The last time I weighed a load of approximately 2m3 of ash (about 20%) it weighed 640 kg. So 320 kg X 4 kWh comes out at 1280 kWh per cube.

[Alycidon]

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.

 

Exactly what I would do. Advise him of the MC of the product you currently have in stock and the usual MC in Sept when its nice and low.

 

A

[Alycidon]

Jukes

 

Are you absolutely sure your figures are right? I've never seen wood look so cheap in comparison to gas

 

Cheers

D

 

 

I thought that as well, would be pleased if its right.

 

I usually use the Nottingham Energy Partnership site to compare between fuels, they usually rate gas and logs pretty close.

 

A

[Woodworks]

I thought that as well, would be pleased if its right.

 

I usually use the Nottingham Energy Partnership site to compare between fuels, they usually rate gas and logs pretty close.

 

A

 

I can see why you use their figures

 

For those figures to be accurate you must be charging around £60 per cube or sell the most generous load ever. From what you have said in the past you charge about twice that.

 

Steph

 

I may have some time today so will try and weigh a dry cube again to check my previous figure of 320 kg for a cube of hardwood.

Edited March 21, 2014 by Woodworks

[daltontrees]

I'll have a look just now...

 

Meantime does anyone want to suggest what a going rate for a tonne of 20% moisture would be, split and delivered?

 

OK, no-one's suggesting a rate. I have checked the arithmetic for logs at £250/T three times and the rate of c.£14/GJ is right.

 

But I had made a mistake in the gas comparison. Here is the corect figure at current supplier prices of c.£0.05/kWh

 

Gas comparison £0.05/3.6MJ = £0.05/0.0036GJ

 

= £13.88/GJ (weird and coincidentally same as wood price).

 

Sorry for any confusion.

[daltontrees]

From the previous link and here Typical calorific values of fuels a kg of wood is 4kWh of energy. The last time I weighed a load of approximately 2m3 of ash (about 20%) it weighed 640 kg. So 320 kg X 4 kWh comes out at 1280 kWh per cube.

 

Equivalent calorific value in GigaJoules is 4.6 per cube then.

 

It's interesting to think of logs in kWh though. I have a 7kW stove, which is quite terrifying when it is going full blast. A cube of ash is going to give me 1280/7 = 183 burning hours. Which is a month at 6 hours a day. That about fits in with what I have been getting through recently, although I haven't quite been using a cube a month because a rarely have the stove on full tilt.

[Woodworks]

Just weighed out a carefully measured cube of logs from an IBC. The logs where 80% beech with a bit of oak, ash and hazel. Average moisture content when split was 23% and it weighed 366 kg. Looking at the forestry commision graph 23% looks like 3.8 kWh per kg so 1390 kWh for that cube.

[StephF]

Not being picky, but that would be 3 kilowatt hours

 

Steph, this might be the best customer you ever get, tell him earnestly how much heat you believe you logs would give, what good value they are, compared with oil or electricity and you will have a customer for life (possibly )

 

With logs, the most valuable part of the equation is the customer

 

I have sent him a very nice email explaining the calorific values of the logs, waiting for a response... just dont seem to have the patience I used to have with the more awkward ones, I am trying to be nice and not the 'grumpy old woman'! he is very local so could be a good customer as you say.

[Lucan]

The individual might well have a multifuel stove and therefore wanting to calculate whether it is cheaper to heat their house with firewood or coal. Based on calculations on this thread and of my own, I would say that it is significantly cheaper to heat your house with coal at the moment

[StephF]

I have had this conversation with a lass who was working with me today, and her coke aga is cheaper than a wood cooker, or around the same, but that did not take into account the time/fuel and equipment needed to process 20-25 tonnes of cordwood!

plus her stove can run all day & night with minimal input from her.

I can understand the logic of someone wanting to know how many Kwh of heat he is buying, but I have had no replies yet to my very nice email with all the information he requested!