[Stoves] Effect of ambient temperature on stove testing at low power

Tue May 31 02:59:26 CDT 2016

Dear Kirk

I have lurked during this discussion - forgive me for entering it now.

You believed "the increase in ambient room temperature had changed the
turn-down performance of the stove." 

You may have been mistaken. I think what happened was that the ambient room
temperature changed the measurement you were attempting to make.  At the
higher ambient temperature there was less rate of heat loss from the cooking
pot, so it took less fuel to keep it hot and the turndown ratio - as you
define it - changed. So the problem may lie with your definition of the
turndown ratio.  I use the minimal sustainable firepower, determined from
the rate of fuel feed which just keeps the fire going, as my lower measure,
and the maximum firepower I can achieve without significant oxygen
starvation as the upper one, and have yet to see the sort of effect of
ambient temperature on the ratio of the upper to the lower that you report
with your definition of the ratio.

In a word, you may be picking up a change in the heat transfer from the pot
as the ambient temperature changes, rather than anything fundamental about
the stove performance.

I hope that suggestion assists.

Kind regards

Prof Philip Lloyd

Energy Institute, CPUT

SARETEC, Sachs Circle

Bellville

Tel 021 959 4323

Cell 083 441 5247

PA Nadia 021 959 4330

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
kgharris
Sent: Tuesday, May 31, 2016 8:08 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] stove test

Crispin,

My original statement was to point out how the increase in ambient room
temperature had changed the turn-down performance of the stove.  This is an
important topic if the stove principles are going to have any effect in hot
tropical countries.  If you can comment on this I would be happy to learn
from your experience, but please stop hijacking my posts and misdirecting
attention to cater to your agenda against the current test methods.  Start
your own thread if that is what you want to talk about.

All,

I will be happy to answer questions about the burning abilities and
tecniques of our stove and combustor.

Kirk

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

From: Crispin Pemberton-Pigott <mailto:crispinpigott at outlook.com>  

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

Sent: Monday, May 30, 2016 9:40 PM

Subject: Re: [Stoves] stove test

Dear Kirk

> With the support of Aprovecho Research Center, I (actually we) have
developed a very good, clean burning TLUD-ND. 

I think you have done exactly that. Good on you.

There is no misdirection at all here. You are past the verge of changing the
stove's superior performance in order to get a better rating on an invalid
metric. It is that simple. Don't get sucked into that trap. When you are
getting results as good as you are, there are new opportunities to go wrong.

The only 'misdirection' has been supplied for years by test methods that
guided people to edit their stoves to meet spurious requirements that did
not bear directly on performance, or worse, actually penalised stoves for
their superior performance.  A good example is attached.

This is not something new in the stove community. Here is a quote from the
attached Aprovecho document from 2003:

"Why was the good advice, by established experts in the field, represented
in the VITA International Standard test, the result of several well funded
international conferences, obscure in 2003? Both the Indian and Chinese
governments developed tests of their own widening the scope of PHU to
include power, rate of evaporation, time. Visser (2003) published a version
of a water boiling test based on efficiency and appropriate power for
boiling and simmering. What motivated this parallel activity? Why isn't the
VITA test in more general use?"

One reason the VITA test was not more popular was it had several conceptual
errors and a few really poor metrics that gave mis-directing outputs. One is
the efficiency of simmering, another is the concept of specific fuel
consumption for simmering.  Another was the idea of an 'average efficiency'
meaning an 'average thermal efficiency'. I believe from my research that the
specific fuel consumption for simmering and the average efficiency were both
introduced by Baldwin in 1986 or so, before his book came out. Neither are
acceptable metrics.

The document refers to the VITA test the 'international standard' which is
not supported by the evidence. Three or four minor parties agreed to it and
it was never used by the major markets in India and China. Even Eindhoven
University didn't use it and they were a party to drafting it. India pretty
much adopted the minority position taken by KK Prasad from Eindhoven and
built that into their 1991 test. The Chinese test from that era was very
similar. India, interestingly, produced a list of 28 standard sizes of
cooking pot which is a record, I believe!

The long-forgotten organisation Bois de Feu had a clear understanding of
these issues and had a test method in 1982 that didn't have these problems.
They treated the simmering phase very carefully (and differently). Prasad
(and Visser who was his student) developed multiple test methods over the
years. Piet Visser and I created one in Malawi in about 2007 which later
evolved into the ProBEC Test for heat transfer efficiency which is now a
SeTAR SOP, currently v1.05 (SeTAR is an independently managed continuation
of the 13 year long GIZ/ProBEC project). It doesn't really predict
performance, it gives a real-time heat transfer efficiency report under
varying conditions. It is very easy to perform and it supports pot-swapping,
similar to the Indian protocol.

So, ladies and gentlemen, there are no Tier 4 stoves. That achievement will
have to wait for the development of appropriate, valid low power metrics and
one will need an equipment set capable of quantifying the result.

Kirk: don't be bamboozled. You are doing good work.  Nothing is perfectly
correct. Independent investigation of truth is still required.

Best wishes

Crispin

All,

With the support of Aprovecho Research Center, I (actually we) have
developed a very good, clean burning TLUD-ND.  This is real and proven and
no amount of misdirection can change that.  It will be at Aprovecho for
stove camp for all to examine, and I will be giving a presentation on how it
burns so clean.

Respectfully,

Kirk

Santa Rosa, CA. USA

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