[Stoves] Skirt on institutional stoves
Todd Albi
todd.r.albi at gmail.com
Mon Dec 25 22:56:06 CST 2017
Paul:
Skirts:
The Aprovecho Institutional stove created by Damon Ogle used a 60
liter pot *partially
imbedded* into the institutional stove, as you are aware. The original SSM
institutional produced stove used clay for insulation and Damon appeared to
question some of the precision of the gaps, as I recall. The stove was
around $250 USD in 2008. The stove body is an exterior 55 gallon from with
insulation between the inner wall with a 1 cm gap between inter stove wall
and pot, which you know. I consider it formulation only a single skirt that
you are describing as a double skirt. Perhaps an insulated skirt, but not
a double skirt. The early Aprovecho household stove pot skirts Damon and
Nordica designed, that were compatible on the SSM (StoveTec, EcoZoom &
EnviroFit) household stoves were problematic on several levels.
1. They did not hold their shape and easily distorted.
2. They fit only a small range of pot diameters.
3. They slipped when heated.
4. They only covered a small percentage of most typical cook pots
vertically.
5. They were sharp and cooks cut their hands.
6. The soot was difficult to remove and almost impossible for clean.
7. End users were not receptive to utilizing.
During this era, Nordica was hung up on fins and finned pots to increase
heat transfer. I pushed instead for creating a skirted pot design. Dean
was interested in both concepts at the time, but I continued to point out
the disadvantages of Nordica's design. It had no common sense
application. The design was user unfriendly, the fins ran across the
bottom and side walls and were difficult to clean and the cook could cut
their hands. The design was precarious on the stove top too. You'd smart
have to insure your last tetanus shot was up to date, as well. I arranged
to have the first full skirted pot fabricated at Roy Elliot's sheet metal
shop in 2008. Dean insisted on producing Nordica's finned wall pot,
despite lack of application for any sensible end user. We commissioned
both designs. Nordica's design was a waste of fabrication funds for
reasons stated above. Dean and I had SSM produce an additional skirted pot
off Roy Elliott's design later that Fall in China. We worked with several
gaps. The more efficient gaps to shoot for is 7 - 10 mm. Manufacturing to
1 - 2mm tolerances with pot skirts can be problematic, why the advised
range.
Pots with skirts are not a new concept, nor did they originate from
Aprovecho. I have a cast iron cookware with skirts dating back to 1873.
Griswold and other cookware manufactures had multiple designs. I think one
of the most popular was a skillet with a cast skirt with vents, and had an
additional trough to catch grease. It was marketed as a greaseless
skillet, or skillet that made less of a mess. It also had side channels
vents to insure that flames on wood stoves did not impede velocity and
lick walls of skillet un-impeded. To not impede velocity of course, was
also one of Dr. Larry Wininarski's rocket stove design principles, that we
adapted this principle to our household cook pot.
Advantages:
1. Increase heat transfer to cookware.
2. Reduce emissions, by reducing cooking time.
3. Reduce fuel use , by reducing cooking time.
4. Increase cookware surface area by 30 - 60% (extend to top rim of pot ),
the Aprovecho skirt only partially covered bottom portion of 30% most pots.
5. Improve safety, by extending pot skirt below cooktop, pot is not
dislodged when stirred.
6. Serve as an additional wind skirt, when cooking in windy conditions.
The full skirted pot was a great design, however Dean would not approve
production and Nordica continued to dink around with her finned pot in
2008. I left Aprovecho the following year. StoveTec next was run by Ben
West, Daniel Wald, and Adam Crawford. I was called back in 2011 after Ben
West tried to buy StoveTec for $30K, which Dean and the ARC board
recognized they did not want to sell at that price. Ben, unable to take
control of StoveTec left and made his own deal with SSM and formed EcoZoom
with Daniel Wald and Adam Crawford. When I re-assumed management of
StoveTec, one of my requirements was to place the skirted pot into
production. The first skirted pot I christened the *StoveTec Super Pot*.
The 201 ss pot skirt material had to be changed however, due to the skirt
splitting due to the machinery that expanded skirt when crimping to pot
during production.
Full pot skirt production is more difficult then it appears. An insulated
skirt stove body is likely a given with an institutional sunken pot rocket
stove or TLUD design (eliminates skirt expansion and direct to pot crimp
process required with household skirted pot production). It likely does not
make sense with a stove top piece of cookware. Washing the pot, additional
weight, and ergonomics likely all undesirable and problematic design
attributes when cooking with open flame. Simply incorporating a haybox post
cooking makes more sense to insulate meal for later use, rather than
expense of the addition an insulated skirt on household stove I would guess.
We improved this design with SilverFire and it is offered as the SilverFire
Dragon Pot. It is shown on the ground in front of our TLUD chimney stove
donation in Puerto Rico last week. The women below lost her house in
Maria, she rode out the Hurricane in the bathroom below. Unfortunately her
house was a total loss. FEMA has still not appeared with her approved blue
tarp they promised to place over her missing roof a month ago. She's
thrilled though with our TLUD chimney stove.
Todd Albi, SilverFire.
On Sun, Dec 24, 2017 at 1:38 PM, Paul Anderson <psanders at ilstu.edu> wrote:
> Crispin,
>
> You made some excellent points about pot skirts (that also can apply to
> chimneys). Too much increase in draft can be negative..
>
> Thanks,
>
> Paul
>
> Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
> Email: psanders at ilstu.edu
> Skype: paultlud Phone: +1-309-452-7072
> Website: www.drtlud.com
>
> On 12/24/2017 10:56 AM, Crispin Pemberton-Pigott wrote:
>
>> Dear Paul and All
>>
>> This investigation by Dale Andreatta was quite valuable in once respect
>> that is not normally mentioned when discussion Rocket Stoves: excess air.
>>
>> Rocket stoves, if made in the 'usual manner' to 'usual dimension ratios'
>> have very high excess air. This cools the fire and produces excess CO. It
>> also lowers the heat transfer efficiency.
>>
>> " Dale has done work on skirts on regular-size pots, with (I believe)
>> results showing some but not so much impact as we would like."
>>
>> What he showed was that while the skirt does not itself produce a big
>> advantage, it does two other things that were not the 'intended effect'.
>> One is that it increases the draft on the fire which can be a big negative.
>> Two, Dale showed that when the skirt was tight enough, it reduced the free
>> flow of air and decreased the excess air ratio.
>>
>> There are multiple advantages to this. Reducing the unneeded air flowing
>> into the stove raises the combustion temperature, increases the heat
>> transfer efficiency, reduced CO and PM, and makes the fire power more
>> controllable.
>>
>> If you can re-read his presentation to ETHOS on the testing he mentions
>> this effect. Extensive testing by Aprovecho showed them that there was a
>> particular pot-skirt gap that seemed to optimise the heat transfer
>> efficiency. It is quite a small gap. It is not the gap that is 'magic', it
>> is that for any given architecture, there is a way to use the skirt as a
>> choke on the total gas flow that increase the performance on all metrics.
>>
>> This concept was put to use in the development in 2012 of the SAE stove
>> in Java, and the Keren Super Nova, both of which have a greatly reduced
>> pot-stove body gap. It was traditionally 25 mm. We found the best
>> performance was achieved by reducing it to 7mm. The experiment was
>> conducted using 1m steps from 3 to 20mm. It only took a few hours. The
>> Keren stove, the traditional clay product very much like a thin Mandaleo
>> stove, is widely used and employs something like 300,000 people in the
>> production and distribution chain (Ref Cecil Cook).
>>
>> The advantages of a skirt are optimised when checking the O2 content of
>> the exhaust stream to see that it is in the range of 90-120% EA (about 11%
>> O2 concentration). Even a primitive stove will give reasonable results of
>> that target can be achieved.
>>
>> If the skirt mates to the stove (seals pretty well all round) the heat
>> transfer efficiency is best and it is resistant to the negative influence
>> of cross-drafts. N small stoves the skirt can double the draft so be
>> careful that make the skirt does not make the efficiency or combustion of
>> heating speed worse.
>>
>> Regards
>> Crispin
>>
>>
>> Stovers, especially Fred, Damon, Adam, Dale, Sam and Dean, and Jim Jetter.
>>
>> First, Merry Christmas to all of you, everywhere!!
>>
>> Now my stove topic: What is known about using a skirt or double skirt
>> with institutional size stoves. The heat source is not the issue (Rocket,
>> TLUD, LPG, other). The issue is heat transfer and reduction of fuel used,
>> and not about emissions.
>>
>> Dale has done work on skirts on regular-size pots, with (I believe)
>> results showing some but not so much impact as we would like.
>>
>> The InStove folks (Fred, Damon and Adam) are (I believe) the front
>> runners on putting skirts onto large pots. And they do it with a DOUBLE
>> skirt (heat up one side of the skirt next to the pot, then downward on the
>> other side of that skirt, withing an outer barrier
>> (cylinder) that even has some insulation.
>>
>> Certainly Rocket and probably other institutional stoves with "imbedded
>> pots" or "sunken pots" are made and used. I believe that they have been
>> measured by Aprovecho and EPA and testing centers, but maybe not with
>> comparative data without the skirts / brick surrounds.
>>
>> So, the questions are: are there results (we hope for numeric, carefully
>> collected data) that compares with some "baseline" or "un-skirted" pot,
>> about
>>
>> 1. the impact of a single skirt.
>>
>> 2. Impact of the double skirt
>>
>> 3. with and without insulation.
>>
>> I hope some data already exist and can be shared.
>>
>> Objective: is the extra expense of the skiirt (whatever configuration,
>> even the brick enclosure structure) suficiently offset by the improved
>> heat capture?
>>
>> Thanks in advance!! And Season's Greetings to all!!!!!!!!!!!!!!!!
>>
>> Paul
>>
>> --
>> Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
>> Email: psanders at ilstu.edu
>> Skype: paultlud Phone: +1-309-452-7072
>> Website: https://eur01.safelinks.protection.outlook.com/?url=www.
>> drtlud.com&data=02%7C01
>>
>
>
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