Dear Paal
Simmering is not a scientifically defined term. That is why the term was
deleted from the IWA last year after a discussion. I understood the intention
to be to remove the simmering portion of the WBT but that did not happen as
expected. ‘Simmering’ might be used colloquially but that has no standing in a
technical document.
The continued use of a ‘low power phase’ in the WBT is merely retaining the
simmering phase with another name despite the objections by delegates.
As a result of choosing this path, there are several metrics still calculated
by the WBT spreadsheets (the WBT 4.2.2 and the new 4.2.2 PEMS Hood spreadsheet)
that are not valid.
While low power operation of a stove is valid (anything might be operated at
low power) there are some calculations that are not valid when determining
performance.
Two invalid metrics are the ‘efficiency’ of simmering (operating a stove at low
power while trying to maintain the pot contents at a particular constant
temperature) and the specific fuel consumption (SCF) while doing so.
The first is invalid because the more fuel-wasteful the operator is, the higher
the rated ‘efficiency’. The less wasteful the operator is, the lower the rated
efficiency. This is a contradiction.
The second is invalid because the heat required (and therefore the fuel needed)
to keep a pot of water hot is not directly related to the mass of water in it.
Simmered mass of water is an independent variable. Dividing by an independent
variable does not give a ‘specific’ number. That is the point of the term
‘specific’ – it is a restatement of the original number with reference to a
standardised dependent variable. Like miles per hour or miles per day – there
is a time relationship that is linear.
Doubling a mass of water (that is already hot) in a pot does not (at all)
double the fuel needed to keep it hot. This is a physical fact. Thus the fuel
mass used during a low power phase cannot legitimately be divided by the volume
or mass of water to give a meaningful number. You can divide it, but you might
as well divide it by Tuesday or the colour ‘green’.
The valid numbers you can get from a stove operating at low power are:
Turn down ratio
CO and PM emitted per MJ of applied heat
Fuel burn rate
Other challengeable metrics include:
effective mass of water simmered
specific energy consumption
equivalent dry fuel consumed (should be energy, not mass of fuel)
specific CO emission, low power
specific PM emission, low power
EF-CO (g/MJ) based on Energy at low power
EF-CO2 (g/MJ) based on Energy at low power
EF-PM (mg/MJ) based on energy at low power
and a whole lot of others I don’t time to copy in.
The ‘based on energy’ above is the energy thought to have been delivered to the
pot at low power, but the method of measuring it (evaporated mass of water) is
pretty much useless for making this determination.
And so on. You can see we still have a long way to go.
Regards
Crispin
From: Stoves [mailto:[email protected]] On Behalf Of Paal
Wendelbo
Sent: Wednesday, July 24, 2013 5:42 PM
To: Inversiones Falcon; Discussion of biomass cooking stoves
Subject: Re: [Stoves] Aprovecho Stove Camp
Stove camp
Will it be possible for the camp to define the term “simmering”? From 100 C˚
down to what temperature will be classified as simmering? It is important for
the valuation of the use of bio char.
Regards Paal W
From: Inversiones Falcon
Sent: Tuesday, July 23, 2013 6:56 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Aprovecho Stove Camp
Ron Thanks for keeping us informed, I am personally very grateful, I wonder if
you can take some pictures especially the Guatemala plancha.
Thanks againg
Gus
From: "[email protected]" <[email protected]>
To: Discussion of biomass <[email protected]>
Cc: Art Donnelly <[email protected]>
Sent: Tuesday, July 23, 2013 8:14 AM
Subject: [Stoves] Aprovecho Stove Camp
List:
This just a short summary of yesterday's first of five days at the
Aprovecho Stove Camp. This year, they are focusing on TLUDs. About 50 people
were at the opening session, with about 20 - 25 from the different parts of
Aprovecho, and maybe 10 staying of those on as part of the camp.
The old timers here included
a Dean Still, who was the key organizer. I was most amazed of everything
here about how much Aprovecho has grown and changed over the 15 or so years I
have known Dean (who says he will retire in a year).
1. We go maybe today to a new factory for an off-shot firm called
InStove (Only institutional stoves (like one 100 liters). Damon Ogle is with
them now. A first overseas factory coming soon. Only Rocket principles here.
2. We will visit the factory where they are making the US StoveTec
3. We will visit a new 5 acre campus about 6 miles away - a former high
school where they will be moving to this year.
4. I heard a little about a new large research grant from DoE - one of
four nationally,
5. There were staff people all over the place - maybe more than ten
(?) not part of the camp.
6. A key organizer who introduced Dean was Mark Hatfield.
7. Owner of the Apro property was Fred Colgan - alo head of InStove
8. Larry Winiarski is a leader of one on 4-5 subgroups that formed.
Interestng oven design with a Rocket, built by a couple named Anderson. Also
a ceramic Rocket from Philippines.
9. Dean is leading one of the 4-5 subgroups - which is mostly on TLUDs,
but one large plancha design (18 by 24 inch - $22) plancha from Guatemala.
Much of yesterday learning how to use test equipment
b. Paul Anderson, who brought 10 flat packs of a nice looking new TLUD
design from Uganda, for on-site assembly.
Maybe 8-10 people in his subgoup. Mostly will be doing testing here on (like
all)
Paul gave a nice one hour intro to TLUDS. Both a son and grandson are here.
c. Art Donnelly at last minute decided to assemble one of his very large
TLUD stoves from Costa Rica. His primary air control from slight tilt using a
wedge at the bottom.
Of course many new-comers. I ended up speaking most to three school teachers
from D.C., hoping to establish a stove design challenge for 7th and 8th graders
More coming. Questions? Ron
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