[Stoves] Examples of results of simmer efficiency Re: [Ethos] Additional presentations at ETHOS 2015

Crispin Pemberton-Pigott crispinpigott at outlook.com
Mon Feb 16 00:06:19 CST 2015


Dear Kirk

 

You cannot make a determination of the heat transfer efficiency to a hot pot
at low power using evaporated water and fire heat only. 

 

Any twiddling of the numbers will not make it possible. A determination of
the heat transfer efficiency at low power, yes you make it, but not if the
pot is already boiling hot.

 

Here is why:

 

A cold pot on a fire absorbs heat and the losses from the sides are minimal
and have a very small influence on the actual result. The actual result is
the heat available to the pot divided by the heat received by the pot. The
heat getting into the pot includes heat lost from the sides and the heat
that changes the temperature of the water and pot material, and the heat
used to evaporate water. 

 

If the pot is cold, the temperature rise is a very accurate measure of heat
gained. The loss from evaporation (which starts at about 70 C) can be added,
but the losses from the side start to rise in proportion to the temperature
of the pot. 

 

The WBT's approach is a problem:

When the pot is already boiling, the losses from the sides are at maximum.

The loss from temperature change is nil.

The loss to evaporation is measured by determining a change in mass and
calculating the number of Joules needed to evaporate the water.  The change
in temperature is considered, but the side losses are not.  

 

When the stove is simmering, especially when it is simmering at just the
right energy level to offset the losses from the sides of the pot, the size
of the side losses are the majority of all heat gained by the pot, and the
evaporative losses are minimal. The unmeasured component greatly exceeds the
measured component. That is BAD.

 

You have described the stove with a better turn-down ability as a 'better
stove' operating at a lower power level.

 

But calculating the 'efficiency' or 'heat transfer efficiency' using the
missing water and the fire heat gives a completely misleading result. The
better the turn-down and the more closely the fire matches the losses from
the sides of the pot, in other words what you described as a 'better stove',
the worse the reported efficiency.  That is REALLY BAD.

 

The less the stove can be turned down, the higher the fuel consumption. If
the heat transfer efficiency is actually the same, the WBT will report an
increase over the efficiency that is reported for lower power. That is ALSO
BAD. The fact is we don't know what the heat transfer efficiency is because
we are not measuring it - only the heat lost to evaporation divided by fire
heat. 

 

Thermal efficiency can be determined with reasonable precision for a hot
fire and a cold pot. Measuring it with a hot pot at low power gives very
misleading results.

 

Combining the two, reporting the overall thermal efficiency for boiling and
simmering a hot pot is also misleading because of the influence of the
invalid simmering number on the valid boiling number. It is easy to
determine the heat transfer rate to a pot at high and low power, but not
while simmering a hot pot. Just use a cold pot and low power, or any power
for that matter. That is what the CSI-WHT does. It does not (yet) use the
losses from the sides of the pot but that is coming too. Then the heat
transfer efficiency number you like so much will be reported accurately.

 

The variable 'heat transfer efficiency' is valid, but how it is calculated -
not so much these days.

 

Just because one method miscalculates something does not mean everyone
should. And it does not mean it cannot be determined correctly. It just
needs a conceptual re-think.

 

Thanks for raising the questions. More are welcome. We should all understand
this.

 

Regards
Crispin

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
kgharris
Sent: Monday, February 16, 2015 12:24
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Examples of results of simmer efficiency Re: [Ethos]
Additional presentations at ETHOS 2015

 

Paul,

 

I respectfully disagree.  Two stoves are burning at the same fire power and
one has better heat transfer to the pot.  The water in the better heat
transfer stove will be hotter because less heat is lost, producing more
steam and lower scores.  The better heat transfer stove will have to be
turned down to a lower power level to keep the pot the same temperature as
the worse heat transfer stove.  That is the whole reason for improving heat
transfer into the pot, to allow a lower power level for the same cooking
ability.  

 

The thing which has been shown about the WB simmering test is that it does
not work if each stove has it's own seperate simmering temperature and steam
production.  It will work if all stoves are adjusted to a fire power that
produces the same simmering temperature and steam production for all tests.
Then the lower a stoves fire power and fuel use the better the score, and no
punishment for a more efficient stove.  Keeping the simmering temperature
and steam production the same for all stove tests allows meaningful
comparisons between stoves and good protocol for tier ratings.  The results
of keeping the temperature the same will help the stove designer because
different designs can then be compared with each other on equal basis, and
the more efficient design, balanced with cost, can be chosen.

 

I must agree with Dean Still on this.

 

Kirk Harris

 

----- Original Message ----- 

From: Paul Anderson <mailto:psanders at ilstu.edu>  

To: Discussion of biomass cooking stoves
<mailto:stoves at lists.bioenergylists.org>  

Sent: Sunday, February 15, 2015 7:30 PM

Subject: Re: [Stoves] Examples of results of simmer efficiency Re: [Ethos]
Additional presentations at ETHOS 2015

 

Kirk,

Your comment contains one incorrect statement: 

The stove which gets more transfer of the heat into the pot may cause more
steam if it cannot turn down to a lower power level than the lesser stove,
but that means that the two simmering temperatures are different.

Essentially there is only one simmering temperature that is allowed, which
is to be never more than 6 deg C lower than the boiling point.   If local
boiling point is 100 C, then never less than 94 C, and probably best to keep
the temperature of the water at about 97 C.   

But even a roaring fire cannot raise the temperature above the boiling
point.   So the difference in the TEMPERATURE OF THE WATER is of little
consequence, being about 3 deg C.   And remember that the purpose or
objective of simmering is to maintain the temperature.   The purpose is NOT
to minimize the amount of evaporated water, which is only a poor reflection
of how much fuel is used.   

Please also see my next message, that is addressed to Phillip and Dean who
have exchanged messages recently.

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
Website:  www.drtlud.com <http://www.drtlud.com> 

On 2/15/2015 6:41 PM, kgharris wrote:

All,

 

I am not understanding why the WBT is invalid if the simmer temperature is
held the same for all stoves.  The stove which gets more transfer of the
heat into the pot may cause more steam if it cannot turn down to a lower
power level than the lesser stove, but that means that the two simmering
temperatures are different.  Dean is talking about the test simmering
temperature being the same for all stoves.  The stove that gets more heat
transfer into the pot will need more turn-down than the lesser stove in
order to simmer at the pre-choosen test temperature.  That is the whole
reason for improving the heat transfer into the food.  To be able to use
lower power levels, less fuel, and fewer emmissions to cook with.  The two
capabilities need to evolve together, and both are improvements which can
enhance a good field usable stove.  Also simplicity of construction and ease
of use are important qualities which need consideration and perhaps some
kind of metrics for measurements.

 

Kirk Harris

Santa Rosa, CA. USA

 

 

----- Original Message ----- 

From: Dean Still <mailto:deankstill at gmail.com>  

To: Discussion of biomass cooking stoves
<mailto:stoves at lists.bioenergylists.org>  

Sent: Sunday, February 15, 2015 1:35 PM

Subject: Re: [Stoves] Examples of results of simmer efficiency Re: [Ethos]
Additional presentations at ETHOS 2015

 

Dear Philip, 

 

The Low Power test works well when the fuel use is normalized using a set
simmering temperature. 

 

Sam and I are writing up some characteristics of the WBT and I'll post the
paper here. Lots of work to do and I look forward to our continued
collaboration.

 

Best,

 

Dean

 

On Sun, Feb 15, 2015 at 11:43 AM, Philip Lloyd <plloyd at mweb.co.za
<mailto:plloyd at mweb.co.za> > wrote:

Dear Dean

 

Crispin said it well:
"The three low power metrics are invalid. The variables selected are
inappropriately chosen. The calculated results are misleading and contrary
to any claim [that] they provide guidance for product development or
selection. We have to move on." 

 

I have looked at the simmering metrics in WBT 4.3.2 and can only concur.
That is why I do not think we should waste much more time arguing about them
- they are fundamentally wrong. Yes, stove designers need to be concerned
with simmering and turndown; no, the WBT simmering metrics do not provide
them with guidance, and can be positively misleading, which is worse.

 

Kind regards

 

Philip Lloyd

 

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org
<mailto:stoves-bounces at lists.bioenergylists.org> ] On Behalf Of Dean Still
Sent: 15 February 2015 06:38
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Examples of results of simmer efficiency Re: [Ethos]
Additional presentations at ETHOS 2015

 

Dear Prof Loyd,

 

As I pointed out, when the stoves do the same work (hold the water at 97 C,
for example) the stove with greater heat transfer efficiency scores better.
Simmering tests are important and simmering is an important part of cooking.

 

The ISO process is creating new history and approaches to old problems.
Whatever emerges will certainly be defensible as the new approaches are
forged by consensus.

 

Best,

 

Dean

 

On Sun, Feb 15, 2015 at 12:58 AM, Philip Lloyd <plloyd at mweb.co.za
<mailto:plloyd at mweb.co.za> > wrote:

I am concerned that this is turning into a very fruitless discussion.

 

On fundamental grounds the simmering test does not provide anything
meaningful.  Crispin has demonstrated that rigorously, and others have
pointed out that the test can score an efficient stove poorly and an
inefficient stove well, so it does not provide any useful measure.  To go on
defending the indefensible does not make sense, even if it did accentuate
the need for turndown - but that need was always there, it was not the
product of the WBT.

 

We need defensible measures of stove performance.  Can we please turn our
attention to developing those, and leave the indefensible to history?

 

Prof Philip Lloyd

Energy Institute

Cape Peninsula University of Technology

PO Box 652, Cape Town 8000

Tel:021 460 4216

Fax:021 460 3828

Cell: 083 441 5247

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org
<mailto:stoves-bounces at lists.bioenergylists.org> ] On Behalf Of Paul
Anderson
Sent: 15 February 2015 02:26
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Examples of results of simmer efficiency Re: [Ethos]
Additional presentations at ETHOS 2015

 

Dear Dean,    my reply is below:

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 2/14/2015 1:06 PM, Dean Still wrote:

Dear Paul, 

 

To do well on the Low Power Specific Consumption metrics the stove has to
have a good Turn Down Ratio. In other words, the stove has to have high
power and low power.

I totally agree with this.   But it is not the whole story of LPSC.   Other
factors influence LPSC, especially concerning the measurement of the
variables that are used to make the calculation.   These can include the
insulation of the pot (incl. skirts), lid on pot, pot characteristics such
as size, quantity of water in the pot at the start, and at the finish.

 

Specific Consumption is based on how much energy was used to create simmered
water. 

Simmered water is not created.   It was already hot at the start of the
simmer phase of testing.   We are interested in how much energy is used to
MAINTAIN the required temperature near boiling, but preferable about 3
degrees C lower than that boiling temperature.   In fact, a super-insulative
pot could need barely a flicker of a flame, and therefore even a well
turned-down stove could cause the water to boil and evaporate.   

If the stove only operates at high power there is more steam made and [at
the end of testing] less simmered water remains....

that is true.   but continue.

..... so energy was used to create less product.

Stove simmering is not creating a product.   It is maintaining a
temperature.   The steam that is driven off does not represent loss of
"product" which should be understood to be "cooked food" (and not meaning
water that can be added to the pot by any attentive cook in a household.)

 

I like Specific Consumption because it forces stove designers to make stoves
that simmer successfully, not just boil water. 

I agree.   But the measurement procedures need to accurately document the
ability to have that strong turn-down ratio, without calculations that can
yield ambiguous or mis-leading results.

For example, new TLUDs are better stoves because they have both high power
and low power. In my opinion, the WBT 4.2.3 helped to create these more
successful TLUDs.

The cause-and-effect relationship is not totally clear.   We have wanted
turn-down capabilities in TLUDs for many years.   

 

As Sam says, we are working on a paper showing characteristics of the WBT
4.2.3 for the ISO work. Knowing the characteristics lets folks evolve a
perfect test. 

I question the above wording to "evolve a perfect test" (which is a test
run, not the test procedures.)   Maybe the statement should be that "knowing
the characteristics let's folks operate their stoves in special ways to
obtain superior results that are not realistic for average users."  OR "...
let's folks 'game the metrics' to present 'perfected' test-results BASED ON
OPERATIONAL PROCEDURES AND NOT ON IMPROVEMENTS TO THE STOVES THEMSELVES." 

OR it could be that flawed protocols /procedures (such as dividing by the
volume of remaining water after simmering) can yield numerical results that
are questionable and perhaps disadvantageous to the development of clean
cookstoves. 

 

Sam is doing great work as he crunches all the data....

absolutely.   But we are questioning if the numbers are as valid and useful
as claimed.

 and gives ISO real numbers to work with in their discussions.


Concluding statement:   The topic of Low Power Specific Consumption is too
important to just brush aside the stated issues.   More "expert testimony"
would be useful, including a mathematical analysis of the impact of the
parts of the calculations.   

Paul



 

Best,

 

Dean

 

On Sat, Feb 14, 2015 at 8:18 AM, Paul Anderson <psanders at ilstu.edu
<mailto:psanders at ilstu.edu> > wrote:

Dear Tom H.,         and to all who are interested in proper testing of
stoves.

Your reply about your experiences is helpful.   Sounds like you had
qualified testing center do the testing, in accordance with the procedures
that Crispin is questioning.   Please send to me the full details.   Could
be off-list, but this is sufficiently important that we will want the full
results known.

I have a specific case of official testing of one of my stoves with
unfavorable results for Low-Heat Efficiency (simmering).   I will add that
into the list of examples and provide the details very soon.

I invite anyone else who has something to report about simmering efficiency
to also send details of their experiences, either favorable or unfavorable
or neutral.  

The examination of the questionable methods about simmer efficiency might
take some days, maybe weeks.   But not the months or years that this debate
has been "simmering".   

Remember:  A testing center that properly conducts testing using an endorsed
but possibly flawed procedure is NOT a culprit.  The culprit is the testing
protocols, IF found to be faulty.   And we hope that the testing center
people (employees and leaders) who understand the technical aspects of the
calculations will be among those who can help resolve these serious issues.

Even those who developed protocols that are eventually shown to be faulty
are not culprits.   Mistakes can be made.    However, the culprits can
include those who advocate a protocol that he or she knows (or reasonably
suspects) to be faulty.

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> 

 

 


_______________________________________________
Stoves mailing list

to Send a Message to the list, use the email address
stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org> 

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists
.org

for more Biomass Cooking Stoves,  News and Information see our web site:
http://stoves.bioenergylists.org/

 


_______________________________________________
Stoves mailing list

to Send a Message to the list, use the email address
stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org> 

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists
.org

for more Biomass Cooking Stoves,  News and Information see our web site:
http://stoves.bioenergylists.org/



 

  _____  

_______________________________________________
Stoves mailing list

to Send a Message to the list, use the email address
stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org> 

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists
.org

for more Biomass Cooking Stoves,  News and Information see our web site:
http://stoves.bioenergylists.org/

  _____  

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com> 
Version: 2015.0.5577 / Virus Database: 4284/9121 - Release Date: 02/15/15






_______________________________________________
Stoves mailing list
 
to Send a Message to the list, use the email address
stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org> 
 
to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists
.org
 
for more Biomass Cooking Stoves,  News and Information see our web site:
http://stoves.bioenergylists.org/
 

 

  _____  

_______________________________________________
Stoves mailing list

to Send a Message to the list, use the email address
stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org> 

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists
.org

for more Biomass Cooking Stoves,  News and Information see our web site:
http://stoves.bioenergylists.org/

  _____  

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com> 
Version: 2015.0.5577 / Virus Database: 4284/9121 - Release Date: 02/15/15

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20150216/3e5cd2b4/attachment.html>


More information about the Stoves mailing list