[Stoves] Truth in stove reports Re: FW: REQUESTfor complete sets of raw data of cookstove tests.
Otto Formo
terra-matricula at hotmail.com
Thu May 2 09:52:29 CDT 2013
Dear stovers, Iam a bit surprised to see time and efforts spend on this issue. My mother toungue is not english, but in Norway we use the terms of fuels related to a stove:Wood stove, gas stove, kerosine etc, mainly for heating. A traditional wood stove ment for both heating and cooking is called a "komfyr".They also have an oven for frying and grilling. A stove for mainly cooking with an oven for frying/grilling, we still call a "komfyr", wether it is run on gas, electricity etc. A STOVE should be very much linked to the fuels used, how its operate and named accordingly, whats the big deal?The name does not harm or shame, anyone. I feel one of the most important issues is to know what type of fuel to be used in a stove, when you want to purchase one.AND a Multi Use Stove will be the best option for "everybody", I belive.If you have access to pellets, you want a stove burning pellets, if I have access to etanol youI would like to have a stove burning ethanol, if you have charcoal you want...............:) In a stove using woody biomass you end up with char or biochar, if you like, anyhow.Most devices utelizes the char for both heating and/or cooking and the outcome of energy content spend, should be very much the "same". I hope GACC have a more broader veiw and do not loose the focus on Clean Cooking DEVICES and do not impose rigorous standards of performence, based on stringent fuel efficiency. What about emissions.................................?? Otto
From: kchisholm at ca.inter.net
To: stoves at lists.bioenergylists.org; crispinpigott at gmail.com
Date: Thu, 2 May 2013 09:15:14 -0300
CC: jetter.jim at epa.gov; rchiang at cleancookstoves.org
Subject: Re: [Stoves] Truth in stove reports Re: FW: REQUESTfor complete sets of raw data of cookstove tests.
Dear Ron
There are a relatively few distinct "Stove Categories", in
the sense of "stoves designed to accomplish stated tasks." For
example:
1: Heating stoves
2: Cooking Stoves
3: Stoves designed for both Heating and
Cooking.
Some stove systems produce char. Examples of such "char
producing stove categories" could include:
4: Stove systems intended to produce char, with no
inherent cooking or heating function
5: Stove systems intended for both char production
and heating
6: Stove systems intended for both char production
and cooking
7: Stove systems intended for char production,
cooking, and heating.
Could you please elaborate on what you would consider
"testing procedures that treat char making stoves fairly"?
What would you consider to be "testing procedures that
treat char making stoves unfairly"?
Kevin
----- Original Message -----
From:
rongretlarson at comcast.net
To: Crispin Pemberton-Pigott ; Discussion of biomass
Cc: jetter jim ; Ranyee Chiang
Sent: Thursday, May 02, 2013 2:06
AM
Subject: Re: [Stoves] Truth in stove
reports Re: FW: REQUESTfor complete sets of raw data of cookstove tests.
Crispin and
list, Ranyee, Jim
This should be viewed as part of my
campaign to be sure that IWA and WBT testing treat char-making stoves fairly.
Maybe there are ongoing discussions within GACC on that topic, but if
not maybe this will be of some help. This is not complete.
See below,
skipping my short message from last nght, and starting with Crispin's reply to
me, with new responses identified as [RWL3]
From: rongretlarson at comcast.net
To:
"Crispin Pemberton-Pigott" <crispinpigott at gmail.com>,
"Discussion of biomass" <stoves at lists.bioenergylists.org>
Sent:
Tuesday, April 30, 2013 10:58:06 PM
Subject: Re: [Stoves] Truth
in stove reports Re: FW: REQUEST
for complete sets
of raw data of cookstove
tests.
Crispin and
list.
Thanks
I see now I have
not been paying enough attention to the IWA methodology. For others, you
also may want to look at a report out of Berkeley, discussing the new IWA
ranking/comparison rules, which include a WBT (probably 4.2.1??) found
at:
http://www.docstoc.com/docs/154033344/Stove-Performance-Inventory-Report---Global-Alliance-for-Clean
I want to make sure that the IWA rules (5 % is an important
efficiency difference number!) are handlng char production in a manner fair to
char-producing stoves. I'm not yet sure of anything. More
tomorrow.
Ron
From: "Crispin Pemberton-Pigott"
<crispinpigott at gmail.com>
To:
rongretlarson at comcast.net
Sent: Tuesday, April 30, 2013 6:45:39
PM
Subject: RE: [Stoves] Truth in stove reports Re: FW: REQUEST
for complete sets
of raw data of cookstove
tests.
Dear Ron
I can
add:
>RWL1b: Is the current
WBT4.2.1 a "regular"? "blunt"? I would have guessed (not
looked) that 5% difference resolution is being claimed.
WBT 4.2.1 has a
resolution that is dependent on several things. Because it uses the final mass
of water in the pot for boiling and simmering, and these are quite variable
from one test to the next, then you cannot expect the resolution even for very
simple direct measurements to be very precise. If you look at three
replications of a test and see what the variation is, you can get a feeling
for the precision. None of that determines the accuracy which is another
matter altogether. Yes it is a blunt instrument and cannot provide, for
example, the heat transfer efficiency with a resolution of 5%. To determine
the heat transfer efficiency with good precision you have to avoid crossing
the boiling point. This is easily demonstrated by calculating the efficiency
between 40-85 degrees (remember to account for evaporation) and then between
55-100. The 40-85 degree range will consistently give the same result but the
55-100 will differ from test to test, and will differ from the 40-85 degree
figure even though the stove is operating in pretty much the same conditions
all the time.
Changing the pot
also gives a different answer because the heat transfer efficiency is a matter
of the relationship between the stove and the pot, not what is in
it.
[RWL3-1: I hope we
can hear from others on how repeatable the tests are. I have not seen
test results and would like to.
I
wonder if anyone has proposed a test trying to maximize the amount of water
boiled away for a batch (char-making presumably) stove? I think
this would be of interest to many stove purchasers and should be quite
repeatable (not "crude"). The amount of energy required for vaporization
seems to be relatively independent of pressure (altitude) and not very
dependent on the boiling point temperature. I hope others can check
those statements. I found (after quite a search) this at a New York
School system website (and couldn't find a way to give you a
cite):
"
The heat of vaporization of water at 70°C is 2.33 x 103
joules per gram, whereas at 100°C it is 2.26 x 103 joules per
gram.
This says
that Denver area at 3-4 degrees lower boiling point, assuming linearity, would
have a heat of vaporization of
about 2.27x10^3 joules per gram - a
difference of less than 1/2 %.. I had assumed until I
went looking that there would be much greater variation. Of course there
will be variation with different pot shapes and materials, but that s true for
any WBT. If need be, it seems that even this 1/2% difference can
be modified - as is the case for fuel moisture.
So
knowing weights lost should give an accurate measure of energy input - much
closer than the differences you (Crispin) describe above. Or what am I
missing?
Different energy inputs will certainly give
different speeds of vaporization, but that could be part of the testing
procedure. It is not clear that the energy inputs per kg water
evaporated will be wildly different. Has anyone experience on
this? It doesn't matter too much if the procedures are the same for all
stoves of a similar type.
Wind should make a difference by
removing water molecules above the surface, but these tests will mostly be in
a lab. Also a wind/breeze will also cool the pot and probably reduce the
flame efficiency, so a fan is not necesarily going to show better energy
transfer. But will tests in the same lab space give repeatability?
Can stoves be equitably compared? And can the placement of stoves into
the IWA categories of 1-4 be done in a fair manner with this
system? I see no reason why not.
For those who haven't read in this area, all stovers will be striving to
achieve >45% efficiency (category 4). Gas and liquid fossil
fuel stoves are reported in these sort of tests (p 18, Figure 7 of above
Berkeley report) to achieve 50%. According to that same figure,
char-making and fan stoves have a chance. End
RWL3-1
[RWL 1
or 2?]
I
think that Jim is (using WBT4.2.1) testing for and reporting on heat
transfer efficiency. Not true?
Jim and I both
report the heat transfer efficiency and the fuel efficiency.
[RWL3-2: Crispin may also
be saying he trusts his, but not those from the current WBT4.2.1 (not
saying anything about Jim Jetter's skills). So I have to ask Crispin if
that can be true? Reporting yes for both, believability no for Jim, yes
for you? ]
>>>[RWL2a In next to last sentence,
you say (emphasis added):
<< "There
are particular metrics which provide valuable information about
performance."
>[RWL2b. Are there some particular metrics
that could be, should be, and are not now supplied through the WBT 4.2.1
procedures?
There are 9 metrics
in the IWA. Only one is provided by the WBT 4.1.2 which is referenced in the
document (a proxy for heat transfer efficiency). In order to overcome that
shortfall a small team is working on updating the calculated outputs from WBT
tests. Version 4.2.1 has a new section added to each of the Test1-3 tabs which
calculates some of the metrics needed for the IWA. There may be problems with
some of those calculations. If so, they will come out in an independent
review. If there is no review, we are at risk, as before, of adopting a method
that has defects that matter.
[RWL3-3: The other "8" metrics are not clear to me. Certainly
there is a safety category, but here is a list of 13 "metrics" from the above
Berkeley report:
Output
metrics
Row
1 Fuel
use(4)
Emissions(7)
Time (2)
Row 2 Thermal
efficiency; Species: CO2, CO, CH4, NMHC, PM, BC, OC; Time per test phase
Row 3:
Specific energy consumption; Emissions per MJ
delivered; Time per task
Row 4:
Specific energy consumption rate;
Emissions per kg and MJ fuel
Row 5
Fuel use per capita; Emissions per
minute
Row
6:
Emissions per task
Row
7
Modified combustion efficiency
Row
8
Combustion efficiency
I note that there is nothing in this list about the efficiency of making char
(which is why I am writing this, but that is a different story. As long as E!,
E2, and E3 are reported, per Jim Jetter's note of a week ago. But this
list can be for various tasks and I am suggesting that one that is fair to
char-making stoves is the one above - boil away until the maximum amount of
char has been produced . This is to ask if others think this might be a
reasonable task to compare char-making stoves? If not, why
not?
The
metrics that would be added to the above list or do this as one of the tasks
(none removed) could be:
Measured:
weight of water(kg) evaporated, fuel, and char
times to complete and operator time
Calculated: E2 and E3
(percent energy in the boil-away and in the char)
ratios of water weight evaporated to input fuel and
char weights (and/or inverses - dimensionless figures of merit)
Above for minimum time (max
power) and maximum efficiency (minimum fuel use); these might require
three- four tests ranging from barely bubbling to rolling boil.
This may be excessive - maybe doing just twice near the extremes of the
turn-down ratio is enough. Mostly this test can be done unattended - for
maybe an hour. End RWL3-3]
CPP:
There are still
remaining problems which is that three of the metrics in the IWA are not
really valid. All relate to the low power phase. This has been brought to the
attention of the relevant parties. The root problem is that the heat transfer
efficiency during low power and the fuel consumed to run a ‘simmering test now
called a low power test’ is not related to the mass of water inside the pot.
As has been point out many times here in the past, the WBT rewards, with a
higher performance rating, the evaporation of water during simmering. Anytime
the mass of water in the simmered pot is divided into something, an invalid
number results.
[RWL3-4: I don't see that my above suggestion falls into
this "invalid" category. Everything is defined and repeatable in
different countries, altitudes, etc. The assumption is a normal full
load of fuel and a normal (uncapped) pot of water - something many people do
every day. How little fuel and emissions and how much char for this
task? ]
Simmering (which is
not a scientifically defined term) was discussed at the IWA meeting and it was
agreed to dispense with all references to simmering (which were duly removed).
However the metrics requested still require simmering to be obtained which is
a contradiction. You cannot, for the reason mentioned in the preceding
paragraph, have a ‘specific’ performance number from a simmering phase (which
is why it was dropped). The meaning is that you might divide the fuel, or
emissions, by the mass of water in the pot at the time. Well, the mass of
water in the pot is not related to either the fuel consumed nor the emissions
from the fire so we still have a conceptual problem. If you double the amount
of water in a pot, it does not use more fuel to simmer it. The YDD Lab has
been conducting accurate experiments showing this.
[RWL3-5: I concur that simmering is difficult. I am
proposing something much easier to do (for char-making stoves only, probably,
assuming they have primary air control). More specifically, your
sentence above which reads
"... mass of water in
the pot is not related to either the fuel consumed nor the
emissions"
can be changed to
read:
"
...
mass of water
evaporated in the pot is directly related to
both the fuel consumed and the
emissions"]
We are not
discussing conceptual problems as a group and I have raised that omissions
with the relevant parties. No doubt the WBT (which is one of several tests
that can be done) will be further refined and we will eventually agree on what
valid measurements are for it. There are still problems with definitions so I
have recently made some suggestions in that regard. I posted some definitions
of efficiencies here a few days ago.
[RW3-6: It is too late for me and this already too long.
Maybe tomorrow. But as long as char is included in the E2, E3
manner (char weight and energy related to inputs), probably other
definitions are OK as well.]
In many cases there
is no need to invent new terms or definitions. Engineers have been measuring
and describing heat transfer for many years and there are many books on the
subject but they are not the Book of the Month Club list. I try to make noise
about the most important ones and in each case provide alternative
calculations, definitions or alternative metrics which may be
valid.
As you know there
are several versions of WBT spreadsheets still in use:
UCB-WBT
3.0
CCT 2.0
UCB-WBT 3.1
(actually there are 3 or 3 versions of this one)
PEMS Hood v 7.1.2
which appears to be based on UCB-WBT 3.1
ETHOS WBT 4.1.2
(there are 2 or 3 versions of this one)
GACC 4.2.1 (current
version Feb 2013)
PEMS Hood v 4.1.2
which appears to be based on UCB-WBT 3.1 but it has elements of the last
version of 3.1 and also elements of the first (see calculation of the Dry Fuel
Equivalent)
There is another
version of the PEMS Hood spreadsheet (or program) but I have not seen it yet.
As far as I know it is the same spreadsheet as the 7.1.2 version. It is being
updated by Ryan.
If you enter the
same test data in each sheet, you will get a different answer from each for
the thermal efficiency.
[RWL3-7: I concur this array of tests is horrible. As
near as I can tell, the only test being considered by the GACC is the WBT4.21
- and it is NOT (or has not been) designed at all with char production in
mind. I think the above is a fair way to compare char-making
stoves. Other stove types can or need not do the same.
Anyone agree? End. Ron]
Regards
Crispin
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