[Stoves] Differences in stove testing

Wed Feb 15 20:11:30 CST 2017

Dear Tami

I think it is worth my pointing out that when the WBT 'thermal efficiency' metric was created by VITA it was not called 'thermal efficiency'. The most obvious reason for not giving it that label is that it doesn't calculate the thermal efficiency.

It was called the 'Percentage Heat Utilized'. PHU was in common use until the 2000's and I used the term myself in discussions on this list.

Two mistakes were made following the change in the name: one was changing the name to a standard term without changing the formula‎ to match, and the second was to apply it to the calculation of relative fuel consumption. Because it is not the energy or thermal efficiency, it gives the wrong answer in the relative fuel consumption calculation.

The term 'thermal efficiency' has numerous definitions but tends towards the heat transfer efficiency compensated for losses‎. That makes it harder to use because it has to be accompanied by a carefully worded definition. 'energy efficiency' is widely used to mean the system efficiency or overall efficiency. Good examples are solar cookers and vehicles with regenerative brakes.

The problem arguing for the WBT 'thermal efficiency' metric is the deduction of only part of the residual char ‎instead of all of it. The 'recoverable' portion in not the whole of the mechanical loss and the result is a non-standard term with no standard name. It is certainly not 'thermal efficiency' which is common parlance would require deducting all energy in the solid residue. The 'recoverable' portion of it is arbitrary and subject to interpretation.

We have been discussing this in a sort of 'purist' form. The actual formula used in the WBT considers the mass of char to include the mass of ash accumulated to that point and treats it as if it has char with an energy value of 29 MJ/kg. ‎The WBT protocol does not require separation of the char as proposed by Ron, but makes the error of considering ash to be char. Separating char is creates a separate error.

It seems the advocates have not examined how these formulae work. The original claim is that the metric represents the cooking efficiency‎. As Prof Lloyd has pointed out, that is determined by work done divided by energy fed into the system.

Regards
Crispin

‎
Dr.  Bond,  cc List and Dr. Chiang

1.   Because I know you are looking for engineering precedence on the main equation in our dialog,  I should have provided the cites for the two books I mentioned in last night’s response, when I said:

 ‘As I searched (more coming on the search) I found two (Google- free)  boiler books from around 1910 that have this equation. "

My search was for “subtract efficiency efficiencies denominator"

They are:
a.   On 3 pages as a part of a USGS annual document from 1907.  One can move around beyond the 3 pages that show up, without downloading the whole several hundred pages.  My search was for “denominator”;  one seems to be able to search for other terms:
 https://books.google.com/books?id=tTRGAQAAMAAJ&pg=RA1-PA137&lpg=RA1-PA137&dq=subtract+efficiency+efficiencies+denominator&source=bl&ots=5C3AgUSOP-&sig=440wVsdeLXYIxMvjrMRPHBSnklw&hl=en&sa=X&ved=0ahUKEwisqa3At4_SAhVolFQKHeapC5Y4ChDoAQghMAI#v=onepage&q=%20denominator&f=false

b.  A book from 1915  Engineering Thermodynamics   By James Ambrose Moyer, James Park Calderwood    Again a page with the idea of subtraction shows up
   https://books.google.com/books?id=fElDAAAAIAAJ&pg=PA144&lpg=PA144&dq=subtract+efficiency+efficiencies+denominator&source=bl&ots=A-tYLgv0zK&sig=ue-L88klNbAhsYOk4bqaJELW0IA&hl=en&sa=X&ved=0ahUKEwisqa3At4_SAhVolFQKHeapC5Y4ChDoAQg1MAk#v=onepage&q=subtract%20efficiency%20efficiencies%20denominator&f=false

My problem with these two is that I think you are looking for examples from other fields.  I have no doubt there are dozens of other books using this equation in the succeeding century.

2.    Not mentioned last night, but I also found these:

a.  https://www.ncbi.nlm.nih.gov/pubmed/15109753  on wheel chair efficiencies (2004), where the title says:
Mechanical efficiency during hand–rim wheelchair propulsion: effects of base-line subtraction and power output
     I didn’t choose to pay to buy this one, but there is a (small?) chance it might have what we are looking for, given the word “subtraction”..

b). Again, not willing to buy a book,  but the idea of subtraction in the denominator seems to be present in the signal processing world
https://books.google.com/books?id=6invBwAAQBAJ&pg=PA224&lpg=PA224&dq=subtract+efficiency+efficiencies+denominator&source=bl&ots=HYgiFLLTi6&sig=uJxsCjDgj21PNaHdwfG45HRlKZc&hl=en&sa=X&ved=0ahUKEwisqa3At4_SAhVolFQKHeapC5Y4ChDoAQgfMAE#v=onepage&q=subtract%20efficiency%20efficiencies%20denominator&f=false

c.  Also an expensive text (Exergy: Energy, Environment and Sustainable Development;   By Ibrahim Dincer, Marc A. Rosen)
where there is a subtraction in the denominator (p 253);  the University of Illinois may still be a main resource on Exergy (with an x - not Energy)
  https://books.google.com/books?id=FrUolHxhGVYC&pg=PA253&lpg=PA253&dq=subtract+efficiency+efficiencies+denominator&source=bl&ots=9Iml913d48&sig=vYovGRUnGhhhl1HrmwqR15xKghc&hl=en&sa=X&ved=0ahUKEwisqa3At4_SAhVolFQKHeapC5Y4ChDoAQgxMAg#v=onepage&q=subtract%20efficiency%20efficiencies%20denominator&f=false

3.   I also found some possible benefit on talk on the differences between “efficiency” and “effectiveness” - with at least one author claiming the latter is to be preferred.  Maybe the “denominator equation” is effectiveness.   I do support the concept that it is accurately saying what the efficiency would have been without char.  I believe the actual inefficiency giving what I have called e1 and e2 is NOT as bad as this equation implies for the no-char case.  Stated alternatively, a char-making stove is inherently less wasteful than the no-char case.

So,  Tami,  I am not yet happy with any of these.   I am looking to justify the use of the “denominator equation” in a slightly different manner (still using the “denominator equation”  - but maybe this above will help a tad).  And possibly the above will bring others into this WBA search/justification topic for Tier allocation.

Again thanks for putting so much time into this.

Ron

On Feb 14, 2017, at 11:52 PM, Ronal W. Larson <rongretlarson at comcast.net<mailto:rongretlarson at comcast.net>> wrote:

Drs. Chiang and Bond, cc List

I have had a lousy day ridding my computer of a virus  Among other things, I could not download this until a few hours ago:  http://www.pciaonline.org/files/ISO-IWA-Cookstoves.pdf.

<snip the rest to save bandwidth>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20170216/e40e5451/attachment.html>