[Stoves] Back into action

Thu Sep 7 14:46:21 CDT 2017

Dear Frank, all,

"The WBT was a successful program to compare stoves and allow the stoves
with the best potential to be picked for further consideration in the real
World."
No, it wasn't. The WBT was not successful, it was popular. Very popular.
Successful and popular are not the same.
Stakeholders who used the WBT thought it allowed them to compare and pick
the stoves with the best potential for the real world.
Since the metrics were invalid and the results absolutely unreliable,
comparing them meant nothing.

But sure, the WBT is incredibly simple to use, and makes one think it can do
something it cannot: no wonder it's been popular.

Now, I think for those who do not want to consider other protocols because
the WBT is easy and practical to use, I can suggest another testing
protocol.
It is actually way easier in its use than the WBT, so then it is way better.

It is called the Dice Roll Test (DRT).
Some say that the WBT is legitimate because it's been used for decades. Well
the Dice Roll Test has been used by various human civilizations for
thousands of years. You cannot beat such legitimacy.

The DRT is simple, you roll the dice to determine the fuel savings and
emissions (CO, PM, PM 2.5) of the stove. Then you record the results on a
sheet of paper. That’s it.
This allows comparability, and placing stoves into Tiers as well.
That's what makes it so great, and you can generate a lot of data in no
time.

Like the WBT, the more tests you do with the DRT, the more probabilities you
have that one test will represent accurately the performance. I am sure
mathematicians could argue the approach of the protocol has some perfectly
defendable merits.

So, based on the above compelling arguments, I recommend that the DRT
replaces the WBT starting from now.

More seriously: testing protocols have to be more than just easy to use.
They are testing protocols to produce and disseminate millions of stoves,
for christ sakes, it has to be really serious.
It is ok if I need to be in a fully equipped lab rather than in my backyard,
and if I need few days rather than one afternoon to do my testing. This is
an important matter, it is normal engineers and researchers have to be
mobilized for that. It is way too important.

When did easy became more important than scientifically valid?

"Lets correct these problems and get the WBT back to central to our many
faceted program."
Do you think these problems can be corrected Frank?
What would be your approach, for each issue described below this email, to
correct them for sure and once and for all?

Best,

Xavier

« Some of WBT critical issues remain unsolved. In particular, the main
weakness of the WBT concerns its real-life relevance. As a matter of fact,
the protocol prescribes to test the stove for a fixed combination of burn
sequence (high-power and low-power) and pot dimensions. This limits the test
relevance to just that particular setting: when any variation of these
parameters e which deeply affect the system performance e is introduced,
results may significantly differ. Criticism about WBT concerns also the
repeatability of the protocol, with a number of researchers claiming that it
would need to be reviewed in terms of accuracy. The WBT is a controlled
laboratory test, thus supposed to be characterized by good repeatability and
to be effective in comparing different stove designs. Nevertheless, the
choice to bring the water to the boil preventing the use of the lid e that
is made in order to better approximate a typical cooking task e is not
functional to this purpose. As a matter of fact, uncertainties related to
temperature reading and vaporisation in the boiling region lead to high
variability between test replicates. In order to improve the reliability and
replicability of the tests, the latest version of the protocol includes the
section “Changes to Testing Conditions to Improve Repeatability”, which
refers to different fuels and pot characteristics. However, eventual changes
involving other parameters (pot insulation and maximum water temperature),
which deeply affect test variability, are not mentioned. Such problems give
evidence of an unsolved conflict between the declared purpose of the WBT
(viz. to be a design-phase test, not intended to be representative of
real-use performance), and a general tendency to use the results form WBT as
a significant means to select the most appropriate cooking stove for a given
context. A lot of debate has been made around formulation of metrics,
primarily on thermal efficiency (Table C3), which is often interpreted as
the most immediate and distinctive stove performance parameter. Studies from
Bailis et al. highlighted how relying on WBT thermal efficiency outputs,
regardless of the relative importance of high and low power cooking tasks
among the target population, can lead to misleading interpretations.
Furthermore, Zhang et al. and Jetter et al. questioned the scientific
meaningfulness of thermal efficiency at simmering. Indeed, this phase is
characterised by highly variable steam production, which represents a heat
loss in the energy balance but positively contributes to the efficiency
value in the actual formulation of thermal efficiency. Finally, some
unsolved issues concerning statistical significance of data are worth
mentioning. WBT 4.2.3 includes “Statistic Lessons for Performance Testing”.
The appendix specifies that the minimum number of test replicates for each
model of stove should be three, although it is reported that this number of
replicates is not necessarily sufficient to determine a stove performance
within a certain confidence interval. Nevertheless, Wang et al. noticed how
a great majority of published studies are performed using a number of
replicates that is equal or less than three, perhaps due to a
misinterpretation of the Appendix message as “only three tests are needed”,
regardless of variability and confidence interval. Wang et al. investigated
this topic using a simplified version of the WBT 3.0 and demonstrated that
more than 5 replicates are likely to be required to avoid impractically
large 95% confidence intervals and that even more replicates may be required
to demonstrate a statistically significant difference in performance between
two or more stoves. »

-----Message d'origine-----
De : Stoves [mailto:stoves-bounces at lists.bioenergylists.org] De la part de
Frank Shields
Envoyé : mercredi 6 septembre 2017 17:03
À : Discussion of biomass cooking stoves
Objet : [Stoves] Back into action

Stovers,

The WBT was a successful program to compare stoves and allow the stoves with
the best potential to be picked for further consideration in the real World.
It was only flawed in the test method used. Lets correct these problems and
get the WBT back to central to our many faceted program.  

1) It needs to relate to the fuel planned to be used. I suggest the energy
in the Volatile Fraction to be the total energy released to the secondary.
The Fixed energy to be the maximum  char making capability of the fuel.
Results of percent energy used (if that is at all important?) is based on
the volatile energy fraction and the Percent char produced a percent of the
maximum for that biomass. That will please all three groups; TLUD, Rocket
and Ron : ).

2) We need to have it measured for the many different tasks that the stove
might be used. I suggest developing a Task Cube. This a solid metal
(platinum, aluminum, steel, titanium) of something that will last. Cubed to
exact measurements, Drilled and taped to fit a thermistor to record the
increase in temperature. Place this block in with different foods being
cooked and record the temperature profile. Develop the profile that needs be
obtained for each task. Sell the Task Cubes to labs where they can place
them in boiling water or sit on a hot surface then follow the temperature
profile to determine if the stove will work for that task and when the task
is completed.  

So we go from the actual fuel (well sort of) to the actual task (well sort
of). The program is (or was) already set up and used so should be quick to
get it running again. Purpose it to provide Cecil Cook (and others) with a
list of stoves from an unbiased source and with best chance for success into
the field so they can do the things they do. And provide the opportunity for
every stove designer to get their stove  compared with others.  

Thanks

Frank
Frank Shields
Gabilan Laboratory
Keith Day Company, Inc.
1091 Madison Lane
Salinas, CA  93907
(831) 246-0417 cell
(831) 771-0126 office

franke at cruzio.com

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