Re: LETS ADOPT A UNIVERSAL POT (and water weight and other topics)

["Ron Larson" <ronallarson@qwest.net>]

Dean (and others)

On January 5,  you sent a message, mostly directed to Lanny on his wok
design, following up on some earlier message on measuring efficiencies.
This standard pot topic is a subject we have raised many times, but I agree
this is well worth trying again.

1.  You  said on this subject:

> Could I then take this opportunity to forward a suggestion which Ron and I
> tossed about on a train heading from Rugby to London? Let's form one
center
> of sanity in the bigger stove world here on the CREST list and all agree
on
> a pot size/amount of water that we all use in our tests! Then we can
compare
> results of tests. Until we do so, this factor will confound comparisons.
> > At Aprovecho we now use a nine inch in diameter steel pot that is five
> inches high. We use five pounds of water in it. But I'm perfectly happy to
> switch to liters!!
>
(RWL1a):   Glad to hear we can agree on the kgs system.  As I was trying out
some conversions here, I was surprised by what I didn't know - especially
about the British system.  Before proceeding to the pot issue, let me give a
brief aside on what I learned:
    Many US citizens know that a British gallon is bigger than a US gallon
and most of these (and me) know the ratio is 1.2.  We also know that a US
pound is a pint, and maybe that there are 8 pints in a gallon  and that
there are 16 ounces (both a weight and a volume) in a US pound or a pint.
The question is - what is the ratio of a US ounce to a British volume ounce?
(Answer below - if readers don't know, then we can take this as a reason to
move to the kgs system - a much easier and more logical approach than this
above digression. will hopefully prove about alternatives to mks.)

(RWL1b)    It appears from my calculations that your steel pot is about half
full - and you could report the five pounds as about 2.27 liters or kg
(limiting ourselves to three significant figures - although normally I would
prefer two in our business.  If Dean had told us about doing 5 pints (and
not 5) pounds, I calculate that he should report 2.37 liters - a 4.4 %
difference [only 4.3% if I had carried more significant figures].    For
reasons given below, I prefer (as Dean has) that we use weight not volume.

2.  You then said:
> If we establish the UNIVERSAL POT SIZE FOR TESTING/AMOUNT OF WATER we will
> have done something that the befuddled stove world has not accomplished in
> decades! Let's do it and maybe we'll force the rest of the stove world to
> follow...
>

    (RWL2):    I guess I want to be a devil's advocate here.  One liter
would be a nice number to work with - but not for  a stove and pot designed
for 100 liters and maybe not even for one designed for 10 liters.  Most
interesting to me is the weight of fuel needed to boil away a realistic
amount of water.  The ratio (water boiled away to fuel consumed) we have
been calling the Figure of Merit.  There is a direct one-to-one relationship
between FOM and efficiency, although we may not all agree on that
relationship and how it should be obtained.  (Some prefer changing out water
when boiling point is reached while others prefer to boil the water away.)

    The right amount of water or fuel and the right pot to consider seems to
me to be what people will "normally" be using with a particular stove.  Each
stove designer or manufacturer can likely come pretty close to the average
pot size that will be employed.  We might use water that is close to
half-filling the "average" pot (which I think Dean has done).  I would also
be interested in the best FOM value that can obtained for each stove -
presumably with gentle boiling on a larger than average pot.  If we can all
agree on a series of standard pots, I would be pleased - but don't think we
should worry too much about standardizing at this time.  If one can't buy
the standard pot locally, I'd rather see the time, efficiency, and emissions
values published for that stove-pot combination as a footnote.  I believe if
we know FOMs and emission ratios (gm/kg or similar?), then I will feel we
can adequately compare stoves.  Time to reach a boil will say something
about applying maximum power - but this should not be our main criterion.

    Stated differently - if two stoves have certain reportable FOM
characteristics with the same pot, but each stove can achieve better FOMs
with different but still locally average pot and water-loading
configurations - then I am more interested in the latter information.

    I also urge that we talk about how many measurements should be performed
by how many operators.  Getting a single number may not be as important as
having a range of numbers even for one pot-stove combination.  How about 2
loadings (maybe call the 50% average the average of what happens with  the
same pot filled to the 25% and 75% fill levels?), and at least two fuel
loading rates (maybe giving power  or fuel consumption levels that are at
least a factor of 2 apart?).  I'd rather have two completely different
people do each level - so (for the examples given so far) one could give a
single FOM (or efficiency) number which is the average of 8 readings.  The
standard deviation may be as important as the average.  (and the same for
emissions, and perhaps time to boil).

    Then, we need to also talk about both fuel type (hard vs soft?) and fuel
moisture content.  At a minimum, they should be reported - but I can also
imagine a clever statistician telling us how to get a meaningful
understanding of their effects without going from 8 to 32 measurements.  I
do not believe we want to only report results for bone dry fuel  (or even
20% moisture) when these cannot be achieved in practice in a particular
area.

    I won't bring up doing three such measurements of each type - but I know
we would get added value from that.

    What do others think is the maximum number of measurements that is
realistic to compare one stove to another?  I am afraid I would like at
least 10 such tests - most  of which are realistic" - and then give the
average - even if we try to have the same or similar pots.  Obviously each
operator could not do the same test with a 10-test limit, but I believe
operator differences could be perceived if they exist..  As a point of
reference, I believe Khan did much more - when only varying two variables -
chimney height and fuel loading - and there were major changes in emissions
over his range of realistic variables - his standard deviations might have
even been larger than the best or the means.

    Eventually we will also have to do all this with emissions measurements
as well - and we are no where near standardizing on emissions measurement
techniques

    Lastly, for some stoves, we ideally will need some data on the weight
(and I guess the quality) of  any charcoal produced.  Not pertinent to
discuss at this time, but I am not happy with the way charcoal is handled in
some efficiency or FOM formulations.

.So, in summary, working on pot standardization is worth beginning, but I
think we have many other important variables to consider as well.

Answer to question - one US ounce is approximately (not exactly)  1.04
British ounce  (close to but not exactly the ratio of 25/24 - because there
are 20 (NOT 16!!) British ounces in the British pint - which is the key
conversion I don't ever remember learning.  Don't use a pound as a pint,
incidentally - that is only approximate even if we stick to just the US.
Although we are safer mixing volume and weight units in the mks system, I
conclude that we better stick with weights alone - in the mks system

Ron






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