[Stoves] Updating your WBT and PEMS/LEMS Spreadsheet

Thu Feb 26 12:00:10 CST 2015

Dear Testers

Here is an update for your WBT v4.2.3 spreadsheet if you are using it and if
you are one of those who makes corrections to it. 

WBT v.4.2.3 Cell WBT!W32 (Effective mass of water boiled) currently
contains:

=((AA12-$N15)*(AA8-W8)/($N$20-W8)+(AA13-$N16)*(AA9-W9)/($N$20-W9)+(AA14-$N17
)*(AA10-W10)/($N$20-W10)+(AA15-$N18)*(AA11-W11)/($N$20-W11))

One part of each section of this formula [*(AA8-W8)/($N$20-W8) etc] creates
a variation in the calculated results that is not present in the raw data if
the boiling point on the day of the test is not the same as the 'official'
value.  It should be edited to 

=(W12-$N15)+(W13-$N16)+(W14-$N17)+(W15-$N18)

Note the shift from Col AA to Col W.  This removes an incorrect 'correction'
of the water mass for the temperature reached when boiling.  It is an error
that dates back decades.  Another correction (normalisation) is applied
further down in Cell W38.  The abbreviated formula will also correctly
report the mass of water boiled.

Note for PEMS/LEMS Hood users, some labs are using spreadsheet v4.2.1 "for
all Sensor Boxes":

If so, the correction from Col AA to Col W has already been implemented. You
should check your spreadsheet cell contents, however.  The current version
date in Cell DATA IMPORT!A5 is 3/21/2013 (21 March 2013) but the change
seems to have been made after that date.

The current content of WBT!W26 (Effective mass of water boiled) is

=((W12-$N17)*(AA8-W8)/($N$22-W8)+(W13-$N18)*(AA9-W9)/($N$22-W9)+(W14-$N19)*(
AA10-W10)/($N$22-W10)+(W15-$N20)*(AA11-W11)/($N$22-W11))

Note the use of Column W, not AA, which is correct.

To remove the unnecessary correction for the difference between the local
'official' boiling point and the boiling temperature achieved, it should be
changed to

=(W12-$N17)+(W13-$N18)+(W14-$N19)+(W15-$N20)

Charcoal:

If you are testing a stove that produces charcoal that the stove cannot
burn, or if it is local custom to discard all remaining char and little bits
of burned wood, enter the mass of the char container (only) in Cells
WBT!N21, AA17 and AO17 or leave all three blank.

For stoves that produce a lot of charcoal, it will give a large difference
in the performance rating for 'fuel consumption', something much closer to
its actual consumption.

In general be cautions what is put into that cell (AA17).  Ash is considered
by the calculation to be unburned char which is in turn considered to be
unburned fuel.  Penn Taylor proposed a correction for this but it is safer
to have a manually calculated set of numbers. Enter a "Weight of container"
of Zero in WBT!N21 and enter actual, reusable charcoal mass in cells AA17
and AO17. If you make the claim that it is reusable, reuse it on the next
test as part of the fuel consumed, if that is what people actually do.

Specific Fuel Consumption:

There is an incorrect, persistent belief that the heat transfer efficiency
in a biomass stove is analogous to the fuel consumption. That belief is why
a converted 'energy consumption of burned fuel' is reported as "Specific
fuel consumption" in Cell WBT!W30.  

Making the above changes (and leaving the unburnable char remaining out of
the two cells) and using the corrected water mass formula, the "Thermal
Efficiency" becomes the "System Efficiency" which is analogous to the fuel
consumption. As a result, the Specific Fuel consumption is automatically
corrected for consumed 'dry fuel' mass.

For TLUD pyrolysers that SFC number will increase more than 200%. Don't be
shocked. It is now reporting "Fuel Consumed", not "Energy Theoretically
Released turned into a dry fuel mass equivalent".

You lab test result will now be much closer to your field observation
numbers.  Please don't use the CCT 2.0 spreadsheet without making a similar
set of corrections or they still won't agree.

Regards

Crispin

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