[Stoves] Effect of ambient temperature on stove testing at lowpower

Tue May 31 03:34:26 CDT 2016

Prof Lloyd,

This is great!  The heat loss from the pot is less because the room temperature is higher.  Thus I can't keep the water temperature down.  I will definately think this one through and try some experiments. 

Dieter has brought up the concept of retained heat cooking in an insulated container.  Would anybody even need turn-down in a cook stove?  Is retained heat cooking the better solution, or is it good to have both?

Thank You,

Kirk
  ----- Original Message ----- 
  From: Philip Lloyd 
  To: 'Discussion of biomass cooking stoves' 
  Sent: Tuesday, May 31, 2016 12:59 AM
  Subject: Re: [Stoves] Effect of ambient temperature on stove testing at lowpower

  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 

    To: 'Discussion of biomass cooking stoves' 

    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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