[Stoves] Recorded EPA webinar and files posted

[Jetter, James]

Ron,

Thank you for your comments.  In reply to your questions:

3. For the example on Slide #46, I think we can say the "lost" energy is 50%, but we must also say that the potential energy in the unburned char is 20%.  If the char is discarded or used for some purpose other than for fuel, such as for biochar, then the "lost" energy is 70%.

4. I believe that we cannot add the "apples" and the "oranges."

5. The best thermal efficiency we have found for a char-producing TLUD stove with low-moisture wood pellet fuel and with a pot skirt was 53% (average of cold-start and hot-start) with the WBT credit for remaining char.  Results were published and are available at this link:
http://ehs.sph.berkeley.edu/krsmith/?p=1387
The ratio of energy in remaining char to energy in fuel was approximately 40%. If the char is "excluded" (discarded or used for a purpose other than for fuel), then thermal efficiency is 32%. We can say the "lost" energy is 28% if the remaining char is used for fuel, or the "lost" energy is 68% if the remaining char is not used for fuel.

Hope this is helpful.

Regards,
Jim

From: Ronal W. Larson [mailto:rongretlarson at comcast.net] 
Sent: Sunday, September 22, 2013 5:27 PM
To: Discussion of biomass cooking stoves; Jetter, James
Subject: Re: [Stoves] Recorded EPA webinar and files posted

Jim and "stoves":

   1.  Thanks for the link (below) to the PPt.  Very complete added notes - I guess transcribed.

   2.  My first question relates to the "apples and oranges" discussion on slide #46, where you give the helpful example of energy into the pot (apples) of 30% and in char (oranges) of 20%, showing a calculated efficiency of .3/(1-.2) = .375  (37.5%).  Then warnings about not being legitimate to add the 30 and 20%.  I am in support of what you have written.

   3.  I want to ask on the reverse side of this:   What is the inefficiency (lost, useless energy) number?  The obvious choices are the reciprocals of the above:  62.5%, 70%, and 50%. I can only justify 50% in my mind. Your choice?   I ask to see if char-making stove salespersons would be justified in talking of this (lowest) 50%. 

  4.   A corollary question is  -  if we don't believe that 62.5% or 70% are justified inefficiency numbers, then what do we call the sum of "apples" and "oranges"?

   5.  Some char-making stoves are seeing more than 20% char by weight  - so maybe "oranges" could be 40%.  If 30% still made it to the pot, this would lead to the "main" reported stove efficiency of .3/(1-.4)=.5 (50%) and the choices for inefficiency become 50% (100 minus number to left), 70%  (no change, by assumption on apples), and (100-30-40)=30%.  This done only to show that the "sales pitch" differences can be larger than in your example.  The question is what is the smallest inefficiency numbers you have measured yet for char-making stoves (along with the number of "apples" and "oranges" to come up with that number)

   Again - thanks for all you are doing.  

Ron


On Sep 21, 2013, at 3:35 PM, "Jetter, James" <Jetter.Jim at epa.gov> wrote:


To All,

Thanks to those who joined us for the webinar on August 29, and thanks to the Global Alliance for Clean Cookstoves for hosting.

The recorded webinar, presentation slides with notes, and draft spreadsheet have been posted for your information, review, and comments:
http://community.cleancookstoves.org/communities/forums/viewtopic/22/33/207?post_id=357#p357

The purpose of the webinar was to:
  Provide an update on the EPA cookstove testing project
  Present a format (EPA spreadsheet) for sharing data
  Discuss test methods
  Focus on example testing results for a batch-fueled pyrolytic TLUD (top-lit up-draft) stove
  Solicit further comments on methods, spreadsheet, and data sharing

Please let me know if you have any further comments by Oct. 11.  My email address is: jetter.jim at epa.gov

Regards,
Jim Jetter