[Stoves] FW: REQUEST for complete sets of raw data of cookstove tests.

[Jetter, James]

Ron,

It was great talking with you in Phnom Penh.

Let’s discuss a hypothetical example.  We start with a batch of biomass fuel that contains 10 MJ of (potentially available) energy.  After burning the batch of fuel in a certain stove, 2 MJ remains in unburned char, 3 MJ went into the cooking process (pot), and 5 MJ was “lost.”

Thermal efficiency is calculated per the WBT protocol as: 3 / (10 – 2) = 0.375

If the char is “discarded,” then thermal efficiency can be calculated as: 3 / 10 = 0.3

The thermal efficiency for char production can be calculated as: 2 / 10 = 0.2

I think you are proposing to add the thermal efficiencies for cooking and char production: ( 3 / 10 ) + ( 2 / 10 ) = 0.5
I’m not in favor of doing this, because, while there is a common denominator, I think the numerators are like apples and oranges – cooking (useful) energy and fuel (stored) energy.

Now let’s say the remaining char is burned in a charcoal stove with 50% efficiency, then 1 MJ goes into the cooking process and 1 MJ is “lost.”  Then we could calculate a cooking process efficiency for the system (including the char-producing stove and char-burning stove): ( 3 + 1 ) / 10 = 0.4

For char-producing stoves, we plan to report:
- Thermal efficiency per the WBT (remaining char gets full credit as unused potentially available energy)
- Thermal efficiency for the “discarded” char scenario
- Thermal efficiency for char production
I think reporting these results will provide complete information, and how others value the different efficiencies will depend on objectives (saving fuel, producing char, or a combination of both).

Best regards,
Jim
_____________

From: rongretlarson at comcast.net [mailto:rongretlarson at comcast.net] 
Sent: Monday, April 22, 2013 2:57 PM
To: Discussion of biomass cooking stoves; Jetter, James
Subject: Re: [Stoves] FW: REQUEST for complete sets of raw data of cookstove tests.

Jim and stove list:

   1.  I like all parts of your message below, but want to comment on this sentence:

  "  Meanwhile, we (EPA) will report future results per the current WBT protocol (energy in remaining char gets full credit in energy calculations), and we will also report results for the discarded-char scenario (energy in remaining char gets no credit)."

     I cannot concur that the "energy in remaining char" is currently getting "full credit" (as you and I discussed in Phnom Penh).  An efficiency number emerges when the energy in the char is subtracted in the denominator - but a much larger efficency number emerges when the simple ratio of char energy over input energy is added to the cookpot energy over input.   I ask that the separate char/input and pot/input energy numbers be added to the WBT data output.   
      I also hope someone can explain what the present efficiency computation actually means - as it is so different from the simple sum of the carbon neutral and carbon negative stove efficiencies


   2.  I also feel that the testing for air-controlled batch stoves needs be different from those only controlling fuel supply.   I am appending here a draft "memo" that follows one I found for charcoal-using stoves.  I think this (39 kB)  fits within the attachment rules given to us recently by list-master Andrew Heggie, but if it fails,  I will re-send through Erin.


   3.  I will also respond to another message today from Crispin that suggests all char produced should be later consumed.  This may be helpful addtionally  - but the results for char only being intended for placement in soil (as above in (1)) should still be highlighted (and is not now).

Ron