[Stoves] Small clean burning TLUD

Mon Nov 30 20:49:25 CST 2015

Dear Paul

Sorry if anything was confusing.

>1.  This is an extremely slow burning stove.   Consistent, yes.   But it
lacks fire power.   

Hang on, there are many such small applications which require that amount of
firepower, max. See below.

>And it should therefore be compared with other small stoves.

Absolutely agree. The smallest stove I ever saw (apart from heating
vegetables at the Holiday Inn) was in Senegal. It is a tea making stove for
night guards. It looks like a tiny ceramic lined Jiko. I thought it was an
advertisement, a model, when I first saw it!

2.  I am concerned about the comment

ignoring the first 16 minutes during which the fire was getting established.

I am referring to the average thermal efficiency. It was 29% over the first
16 minutes and completely consistent after that (well over 50%). So I used
for the cooking power plot the average of the latter 7/8 of the test,
ignoring the 29% average for the first 16 minutes. I didn't tweak the time
selection to see when the high average efficiency number kicked in.

So.if I ignore the first 9 minutes, the average in that time is 10.2% and
the average for the rest is 57.8%. So, I can use the figure 57.8 instead of
59.6 (the original number). There is no visual difference on the chart. 

>That delay alone could mean rejection of the stove by users or in testing
situations.

That is a misunderstanding. There is no delay in lighting, I was talking
about where I got the average efficiency number. As you can see from the
chart, the full power level was achieved after about 7 minutes from
ignition.

3.  More details are requested:   
Size of pot (especially the diameter of the bottom), 

There was no pot involved. I used a pseudo pot to prevent outside air diving
into the combustion zone. The cooking power is calculated, not measured.

>Small stoves are not designed to boil 5 liters, so 5 L is unfair to such
stoves with low power.

Obviously. This stove would be suited to cooking 1.5 litres - a single
person's food. In fact it is likely to be used for applications such as
making batiks (turned well down to less than half power).

4.   57% cooking efficiency (capture of the heat) is wonderful.   But IF it
is only able to keep a baby's bottle of milk warm for over 80 minutes, the
usefulness needs clear statements when describing the stove.   

450-500 watts of cooking power is far more than is needed to keep something
warm. Slamm kerosene stoves have a firepower of about 1.1 kW and a thermal
efficiency of about 40% which is only 450 watts and they are bought in
hundreds of millions.

>On this Stoves Listserv we are accustomed to "standard size stoves for a
typical meal" and the use of 5 liters of water in the pot, so we run the
risk of equating stoves that are really in very different categories by
size.   .

Well, the talk is like that but the situation in the field is different -
certainly in urban areas where a majority of stove buyers live.

>5.  On the same note, but at the other extreme, the institutional stove by
InStove (60 liter capacity pot, I believe) was proclaimed several times at
the Ghana GACC Forum about its attainment of Tier 4 status.   

I am unimpressed by such claims, to be frank. First, three of the metrics
have no physical basis so achieving 'Tier 4' status on those means nothing
real. To get a useful number you have to have the raw data from the
spreadsheet and remove the division by the water mass remaining to get the
'total' number.

Next, as shown in the discussion of the Two-stove performance calculation,
the thermal efficiency does not tell you what the fuel consumption is, so
what is the Tier 4 fuel consumption per task completed? No one knows. It
could be 25% of 50%.

>That is great!!!  

Sure, we can conclude that it is 'better' but not much beyond that.

>But all should know that using larger pots and more water do greatly impact
the results of stove testing.   As Dean Still said in his Saturday night
keynote presentation at ETHOS 2015, he accomplished some Tier 4 ratings by
shifting to a pot with 9 liters instead of 5 L.   

Otherwise known as 'gaming the testing system'. It is damning evidence that
the WBT is not useful for comparing stove performance ratings.

>He did acknowledge that he had gamed the system but was within the rules,
so it was not cheating.  

Volkswagen was also working within the rules. Every car with that type of
engine passed the test. If owners never put their foot to the floor, their
car never emitted 'too much' NO. Yet people are upset!

>After ETHOS while at Aprovecho's Open House, Sam Bentson (co-author with
Dean) and I and others discussed several ways of how to game (distort) the
testing system.  But the promised summary of such methods was not prepared
(or at least not released).  Maybe it will eventually be presented.   

When writing national standard test methods, we spend a lot of time thinking
of ways to cheat the test, or evade it 'legally' and then write the text to
close every loophole we can think of.

This is done by keeping an eye on what the test is supposed to be
demonstrating, which for wood stoves in developing countries is emissions
and fuel consumption per year (etc). By having a correct concept of the
purpose of the test, one arrives at a method of testing all stoves as fairly
as possible. The big difference between small solid fuel burning stoves and
power stations is the fact they are started and stopped so frequently. This
requires a new approach.

At the moment we are discussing in China when to end the test and what rules
could be used to include the burn-out emissions (which are real and in the
home or neighbourhood) and which continue long after the cooking (or test)
sequence has ended. How long should we measure PM emissions after the formal
test has ended? Eight hours? Twelve? Until it 'stops'?

Not so simple.

Regards

Crispin

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