[Stoves] Water heating fuel efficiency formula

[Jonathan P Gill]

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
> 
> 
> 
> _______________________________________________
> Stoves mailing list
> 
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
> 
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>