Dry Fuel Equivalent Calculator

Dry Fuel Equivalent Calculator
Crispin and Nigel Pemberton-Pigott, October 2007

Dear Stoves Testers

See the attached Dry Fuel Equivalent Calculator drawn up for evaluation by our list readers.

There are 4 pages to the spreadsheet. The first is where a test result can be entered. If you only know the mass of damp fuel burned, the amount of charcoal remaining and the moisture content of the fuel, it should be sufficient.

Select a suitable dry fuel heat content from the chart on the right if you don’t know the figure exactly.

The first set of numbers is the actual heat value of the fuel that was offered to the pot. The second sheet is the heat value as calculated by the UCB-WBT method. The Dry Wood Equivalent figure in the UCB-WBT is not used (as previously discussed), but a different formula which can be seen in their spreadsheet by clicking on the cell.

The difference between the two output figures is calculated on the third page.

The fourth page is the two methods plotted in two different manners, the actual value of dry fuel equivalent against the UCB-WTB for a range of moisture and charcoal remaining, both as a % of wet fuel burned, then the relative value of the outputs.

You will notice, playing with the numbers, that when the heat value of the fuel is more than about 20 MJ/Kg the dry fuel equivalent has been under-reported by the UCB-WBT. Conversely, when the actual heat in the fuel is less than 20, that method over-reports the heat yielded giving the impression that the stove has not performed as well as it actually did. In the case of a fuel like rice hulls, the difference is significant. Note that the charcoal heat content should be changed for the rice hulls – see the small chart on the right of page 1.

As always, please look for errors in the calculations. Sorry about the formatting of the graphs – the cells with no or very high plus or minus values get plotted as zero, mostly in order to make the lower moisture calculations more readable.

Best regards
Crispin and Nigel Pemberton-Pigott