[Stoves] The need to continue the discussion: simmer efficiency

Paul Anderson psanders at ilstu.edu
Thu Feb 19 18:30:39 CST 2015


Dean,

Although you point out that the WBT was designed as a lab tool, it has 
been converted into a system of evaluating cookstoves.   It has become 
the basis of the Tier structure.   Even if not yet "enforced" as a Tier 
structure for granting funds or for purchasing stoves, the mere 
suggestion that the results of a well conducted WBT (as currently 
configured) should be the basis for any, ever, future, possible judgment 
of stove qualities is becoming (in my opinion) totally unacceptable.

Also, the "lab tool" is really not the WBT.   The tools are the 
equipment for making measurements.   And I sincerely LIKE the 
capabilities of the LEMS for measurements.   But when the data are 
processed in questionable ways, or the results are combined in ways that 
give a false sense of accuracy as is implied in the WBT procedures, that 
is not appropriate and needs to be changed significantly.

Personally, I like the concept of a set of tests that can be done with 
simple water in a pot.  And we need all of the data to be available.   
Otherwise, the "gaming" of the methods is facilitated.   For example, 
the "time to boil" is certainly clocked during the testing, but is not 
reported.   Therefore, a small stove that is operated at a low power 
during the initial phase (to bring to boil) can get some better scores 
on CO and PM and efficiency of fuel consumption.   But if it is reported 
that the time to boil is 2 or 3 times longer than (for example) for a 
larger version of the same stove, it can be clear that the cooks in the 
households will NOT want such as slow stove.

I look forward to the analyzes of "gaming" (I do not want to call it 
cheating) that you and Sam are preparing.   I suspect that the list will 
be sooooo long and soooo important that there will be a outcry for 
"truth in testing."

Furthermore, there is evidence (at least very strong hearsay) of the 
LACK of correlation between WBT results and stove performance in the 
field (at least for many stoves).   This makes the WBT unacceptable as 
the basis for the Tier system of evaluations.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

On 2/19/2015 3:31 PM, Dean Still wrote:
> Dear Paul,
>
> I'll try once again.
>
> The WBT was designed to be a lab tool.
>
> The CCT and KPT are used to make stoves that please cooks, meet 
> requirements in use.
>
> The instructions in the WBT, CCT, KPT plainly state the intentions.
>
> Aprovecho uses the CCT when we want to design a stove with the local 
> cooks using their foods, pots. They operate the stoves. The cooks 
> should design the stove.
>
> The WBT teaches how to improve stove technology. Two very different uses.
>
> All Best,
>
> Dean
>
> On Thu, Feb 19, 2015 at 1:06 PM, Paul Anderson <psanders at ilstu.edu 
> <mailto:psanders at ilstu.edu>> wrote:
>
>     Dear Jiddu, and to all who share the concerns about errors in
>     testing of stoves.
>
>     Your comments are greatly appreciated.   Well said.   As we make
>     progress on these topics, the comments will be continually refined
>     for clarity of expression, and will be the composite work of too
>     many people to be individually named.   Thank you.
>
>     To know of your credentials as a theoretical physicist is
>     appreciated.   There could be people with credentials on both or
>     all sides of the discussion.   But you can talk to other
>     physicists much better than I can.   In debates (and courtrooms)
>     both sides like to have their expert witnesses.   Thanks for
>     stepping forward.
>
>     I especially like your comment that shows your convictions:
>>     I find myself in the position where I have to tell my company to
>>     produce stoves with lower rating because it will be better for
>>     women that we build them for.
>     That is worth re-reading and repeating!!!
>
>     As I get further into this topic, I am realizing that invalid
>     metrics must be STOPPED.  I do not yet know how much they have
>     hurt various stove designs, but I can see no way that such metrics
>     have been of any positive value.  ------
>
>     -----   Oh, and if some stoves are benefited by such inaccurate
>     metrics, and if the manufacturers know that they have made claims
>     based on faulty testing, THAT would be truly reprehensible.
>
>     It is fast becoming (in my opinion) the time when the defenders of
>     the status quo about the three Low Power measurements in the WBT
>     will need to speak up with some quite convincing arguments.
>
>     Paul
>
>     Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
>     Email:psanders at ilstu.edu  <mailto:psanders at ilstu.edu>    
>     Skype: paultlud      Phone:+1-309-452-7072  <tel:%2B1-309-452-7072>
>     Website:www.drtlud.com  <http://www.drtlud.com>
>
>     On 2/19/2015 1:56 AM, Jiddu Broersma wrote:
>>     Dear All,
>>
>>     First,
>>     Paul, thank you for keeping the conversation going with great
>>     intentions. Much appreciated.
>>
>>     I have been a quiet follower of the stovelist and I just caught
>>     up on the simmering discussion. I believe it is a necessary
>>     discussion.
>>
>>     I would like to share my opinion. It is one from the perspective
>>     of a stove manufacturer and a theoretical physicist.
>>     I do this purely to contribute to the discussion. Although I will
>>     formulate my opinion direct with strong language, I want to
>>     assure you all that I value everyone's opinion equally.
>>     Now, I will jump straight into the low power metrics.
>>
>>     *Simmering*
>>     As has been explained, simmering is a 'zero work' task, it does
>>     not have an efficiency. Evaporating water and overcoming heat
>>     losses require work, they can have an efficiency. However, is
>>     anyone interested in knowing the efficiency of evaporating water?
>>     Or is anyone calculating how much energy is lost from the pot?
>>
>>     Either way, simmering is only a term that we will hopefully agree
>>     on. Most important is to understand the meaning of the metrics
>>     that are calculated: Low power specific fuel consumption, Low
>>     power CO and Low power PM.
>>
>>     *Low Power Specific Fuel Consumption*
>>     From the WBT sheet I find that (equation)
>>     Low power specific fuel consumption = (weight fuel consumed *
>>     calorific value of fuel ) / (weight of water remaining * minutes
>>     of simmering * 1000)
>>     To explain in steps:
>>
>>      1. Weight of fuel consumed divided by minutes simmering is the
>>         burn rate.
>>      2. If we multiply this by calorific value we get the energy
>>         released by the combustion per minute. Let's call this the
>>         'energy rate'.
>>      3. If we divide this weight of water remaining we just divide it
>>         by a random number that has no meaning. Keeping more
>>         food/water hot does not require more energy. (I believe it
>>         does the contrary, because volume grows faster than surface
>>         when you increase quantities)
>>
>>     -> We have the energy released by the combustion divided by a
>>     random number.
>>
>>     If we wish to calculate some kind of efficiency number we require
>>     useful energy (into pot) divided by used energy (from
>>     combustion). What we have calculated is nothing close to this.
>>
>>     We could possibly calculate the energy into evaporation and heat
>>     loss from the pot, but we have no interest in this.
>>     Hence, a simmering task can't give us a useful efficiency type of
>>     number!
>>
>>     That was me as a physicist, as a employee of a manufacturer I am
>>     concerned that stoves are unfairly compared. Because the system
>>     can be manipulated to gain better results by using a pot with
>>     larger volume capacity and higher insulating properties.
>>     Also another big issue is that more efficient stoves can have
>>     lower rating at the same power output. I'll explain by example
>>     (as others have done before me):
>>     /Two stoves are equal except that one has better heat transfer
>>     efficiency. When they both run at the lowest power possible
>>     (which is the same power for both), the one with the better heat
>>     transfer efficiency will have likely evaporated more water
>>     because more energy went into the pot. Do to more evaporation it
>>     will end up with a rating that is worse!/
>>
>>     *Low power Emissions*
>>     Both PM and CO are given in
>>     weight  / (minute * liters of water)
>>
>>     Similar breakdown:
>>     Weight of emissions per minute is straightforward.
>>     Dividing this by number of liters in the pot is simply dividing
>>     the emissions by a number of your choice (the liters you fill in
>>     the pot). It has no value to stove rating.
>>
>>     Generally I think that weight of emissions per minute is not a
>>     bad metric. However, simmering is not a task that can be compared
>>     fairly between two stoves because it is not a specific task! If
>>     we can't compare the way two stoves simmer because we know
>>     nothing about the useful energy that went into the pot we are not
>>     allowed to compare the results because it means nothing without
>>     enough information.
>>
>>     *Wrap-up*
>>     The list of complications that result from these invalid
>>     simmering metrics goes on. Please read again Crispin's and Philip
>>     Lloyd's comments for a more comprehensive list.
>>
>>     Worst is that many manufacturers are optimizing their products
>>     using the WBT and that stoves are not actually improving in the
>>     field. The WBT can result into the production of bad stoves for
>>     millions of already suffering women!
>>     I find myself in the position where I have to tell my company to
>>     produce stoves with lower rating because it will be better for
>>     women that we build them for.
>>
>>     It is not a matter of right or wrong, it is a matter of how we
>>     stimulate the production of stoves that are really improving lives.
>>     My opinion is that we need to review the meaning of metrics at
>>     fundamental level. (Ie. Boiling and simmering are not scientific
>>     ways of describing a state of cooking for stoves).
>>
>>     Due to the differences in opinion in the stove world, I believe
>>     an external review (scientific: engineers, physicists,
>>     mathematicians) would be the most suitable option. The review
>>     could simply explain the physical meaning of all calculated results.
>>
>>     Best regards,
>>     Jiddu
>>
>>     *Jiddu Broersma*
>>     *Technology and Organization Officer*
>>
>>
>>     www.praktidesign.com <http://www.praktidesign.com/>
>>
>>     Spirit Sense, Old Auroville Road
>>     Bommiyarpalayam
>>     605104 Tamil Nadu
>>     INDIA
>>     stoves at lists.bioenergylists.org
>>     <mailto:stoves at lists.bioenergylists.org>
>>
>>
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