[Stoves] Water heating fuel efficiency formula

Jonathan P Gill jg45 at icloud.com
Fri Oct 4 16:12:25 MDT 2013


In my case, I would not measure thermal efficiency as a first order concern. That is your choice, not mine.

Nor would I use any charcoal co-product as a fuel.  There are other more valuable uses for the charcoal.

My values and goals will be made clearer when I distribute my next PDF.

As for fuel, I prefer feed stocks that do not work well, or at all, in conventional combustion devices. I am as much concern about deforestation as you. 

I am also concerned with creating a healthy diet as well as healthy air. Of course it is also desirable if you can at the same time improve the economic situation of the cook. All of this needs to confirmed by multi year field tests.  Note: I have made no mention of the value of sequestering carbon. This will only be an economic reality when we have  serious carbon taxes. I am not holding my breath.

It appears to me that I can meet more of my goals with pyrolysis.

Regards,

Jock

Extract CO2 from the atmosphere!

> On Oct 3, 2013, at 1:20 PM, Crispin Pemberton-Pigott <crispinpigott at gmail.com> wrote:
> 
> Dear Jock
> 
>> How would we measure the efficiency of such a system, an iCan TLUD, that
> provides useful heat for about 70 minutes from about 3 pounds of wood
> pellets and also harvests almost 20% of the weight of the feed stock as
> charcoal?
> 
> The system efficiency (which is the work energy divided by the available
> fuel energy) is well known for good reasons. It predicts fuel consumption in
> future for a similar task, and is a way to rate different technologies with
> access to the same amount of the same fuel.
> 
> The rating of the energy performance has to consider whether or not the fuel
> left over is useable tomorrow. A good example is an open fire burning
> sticks. Each morning the fire is lighted using the wood left over from
> yesterday. Maybe the charcoal is left to burn out each night. That has to be
> considered as well - if it is burned it is not available tomorrow so it is
> consumed even if it did no work. Local behaviour matters when considering
> what stove to promote.
> 
> The actual heat available (the effective heating value) is the potential a
> stove could get from a given mass of wood with a given moisture content and
> elemental analysis.
> 
> The stove may not yield that heat for a variety of reasons which I should
> not need to enumerate. If it does not, it is not rewarded with a 'better'
> number. If the work done, say, boiling water, remains the same, then it is
> not reasonable to reduce the amount of heat available and then say the stove
> did a better job because the ratio of the work done to heat yielded is
> better. Doing a lousier job of burning the fuel, or making use tomorrow of
> what remains today, cannot give a stove a 'better' rating.
> 
> For all these reasons, the fact that there is char remaining at the end of a
> cooking cycle is not a bonus for the thermal performance of a cooking
> system. 
> 
> When using a fuel that is a non-woody biomass, there are good arguments for,
> not special consideration, but for a reduction in the requirement for
> efficiency. This is reasonable if there is a surplus of an unused resource
> and a scarcity of a used one. So the argument that there should be a
> 'special' way to calculate the efficiency will not fly. But there is a
> chance that pleading a special case based on fuel availability could in
> principle succeed.
> 
> In the negotiations on this matter, it is not possible to sell the idea that
> a stove that uses more wood than the baseline should be promoted,
> particularly on a subsidised basis. It is a much easier sell to show that
> there is an unused resource that can 'inefficiently' be used but that will
> provide some additional benefits (real, not potential).
> 
> As for emissions into the home the usual standard would apply of course. It
> has to be clean burning.
> 
> Regards
> Crispin
> 
> 
> 
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