Once a month we’re turning our newsletter over to Sam Bentson, to tell you more about their activities:
Hello to everyone at the Regional Knowledge and Testing Centers (RTKCs), and to our newsletter readers, from Sam Bentson, General Manager at Aprovecho!
Sam was recently in Ghana and Senegal and then visited
the Instituto de Investigación y Desarrollo de Procesos Químicos (CPC) in La
Paz, Bolivia helping with stove testing and their LEMS emission hood. La Paz has the highest elevation of any
government city in the world at an altitude of 3,650m!
The atmospheric pressure at CPC in La Paz is 20Hg. Our
lab in Oregon is 241 meters above sea level where the atmospheric pressure is 30Hg.
Sam and the CPC staff determined that at their high elevation, and with the
voltage applied to the Jet-Flame motor increased to 8V, the mass flow in the
Jet-Flame was 82% of the mass flow measured at the ARC lab.
Altitude had a big effect on boiling water and on the Jet-Flame!
When Sam returned home, he started thinking about keeping in touch with all
of his friends at the RTKCs and to share reports of activities. We are starting
with CPC and highly recommend that anyone interested in doing research or a
stove project make use of this wonderful resource in Bolivia!
ARC engineers rely on feedback from field testing to improve the real-world function of biomass cooking systems. Sometimes the news is challenging, but in this instance the news was very encouraging!
In 2014 the UNHCR (The UN’s Refugee Agency) conducted pilot testing of the SSM SuperPot in seven refugee camps in four countries in East Africa: Kenya (Kakuma, Dadaab), South Sudan (Yida, Maban), East Sudan (Kilo 26), and Ethiopia (Dollo Ado; Bambasi).
Kakuma: “Tests conducted in Kakuma overall yielded very positive results. The participants confirmed that cooking time is faster, fuel is saved, and water is conserved even if only by a scant amount. Participants agreed that SuperPot is a much better option than the regular cooking pots not only because of the efficiency but they are apparently also easier to clean, saving more energy and water.”
Dadaab: “Smoke expelled from the sides of the pan and does not enter the pot thus no change in the smell and taste of food. SuperPot cooks food faster and thus less firewood used. Less usage of firewood and faster cooking would mean less protection incidents, more time for infant/child care. With the SuperPot there was less heat loss and firewood consumption by wind as most of the surface was covered with the pan unlike the traditional pot.”
Batil: “Significant differences in cooking time were noted: for CSB++ (corn-soy blend flour) the Stovetec SuperPot cooked 8 minutes faster than the local pot; for cereal, there was a difference of 4 minutes. With pulses, super pot cooked faster by 5 minutes. Overall, Stovetec is time efficient. The fuel savings are particularly impressive.”
Yida: “Together, both tests saved women 20 minutes in overall cooking time. According to the participants, this time saved ‘can be used for other productive household economic activities or be dedicated to childcare which will effectively improve the nutrition and health status of the children and the entire household members.'”
East Sudan: “Testing was conducted at hospital kitchen inside Kilo 26 hospital complex by four people including two cooks and the HAI nutrition coordinator. 500g of lentils were cooked in 750ml of water in both pots on improved stoves. The super pot cooked the lentils in 27 minutes, as opposed to aluminum pot, which took 34 minutes, for a difference of 7 minutes.”
Assossa: “Results indicate that community perspectives are positive for the StoveTec super pot. The water boiled faster in the super pot by 3 minutes and the lentils were cooked 15 minutes earlier on kerosene stove, while also being 9% more fuel efficient than the regular pot. When testing CSB on kerosene stove, super pot was 4% more fuel efficient and saved 7 minutes of cooking time.”
Hilaweyn: “Tests were ran in Buramino Block 13 and Buramino Block 24 Line A with woman groups. In Block 13, the women tested cooking time for 500g of rice over an improved stove (with windshield). The Stove Tec pot cooked the rice faster by 8 minutes. In Block 24, women cooked 500g of lentils over firewood. Stove Tec pot out performed local pot only by 2 minutes. Neither water used nor fuel consumption were measured.”
“Results indicate that the super pot is fuel efficient, effective in saving time, safe and well accepted by the community.”
In their summary report, the UNHCR Food Security and Nutrition Unit advised “Procurement and distribution of SuperPot in select humanitarian contexts within priority countries according to needs of the most vulnerable households.”
http://aprovecho.org/wp-content/uploads/2022/07/7.11.22-Batil-Camp-SuperPot.jpg591725Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-07-11 15:37:572022-07-11 15:37:59Learning From The Field, Part 3
In Part 1, we gave examples of how field studies can provide unpleasantly surprising results. Rocket stoves were designed to make a little less smoke and use substantially less fuel. So when the rocket stove was field tested by USAID the inventor, Dr. Larry Winiarski, was not surprised that the stove still made smoke. But the ARC team was surprised that it was not a real improvement over the open fire.
In 2011 the goals for cookstoves published by the Department of Energy asked that a stove use 50% less fuel and make 90% less PM2.5 to protect health when used indoors. Now in 2022 stoves are also supposed to address climate change, which means emitting less PM2.5 and hopefully making less than 8% black carbon. Field tests show that we need to make more improvements to meet these specific goals.
are these reductions achieved in the lab?
Use a chimney to reduce in-home concentrations of CO and PM2.5.
In lab tests, approximately 850°C gases need to flow in tight channel gaps around the pot(s) to reduce the fuel used to cook by about 50%.
Molecular mixing at 850°C (0.2 second residence time) can achieve something like a 90% reduction of PM2.5 (requires forced draft in a Rocket stove).
This mixing reduces greenhouse gas emissions by about the same amount.
Natural-draft and forced-draft TLUD stoves burning pellets and forced draft Jet-Flame stoves burning dry sticks without bark get close to these reductions in the lab. Unfortunately, they frequently do not yet meet these goals in the field.
The lab has to move into the field to learn if current technology can accomplish modern goals. Let’s go!
Next week in Part 3: sometimes field tests show success.
http://aprovecho.org/wp-content/uploads/2022/05/threestonepreference.jpg11211200Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-07-01 15:57:102022-07-01 16:07:42Learning From The Field, Part 2
ARC has been unpleasantly surprised on several occasions by the results of USAID field studies. For example:
When a popular high mass Rocket stove (6-brick stove) used about as much wood to cook compared to open fires. In fact, the open fire outperformed or equaled the performance of all the high mass stoves!
http://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-06-23 17:44:352022-06-23 18:16:10Learning From The Field, Part 1
The air in a kitchen has to be very clean to protect women and children from multiple diseases. Unfortunately, moderate amounts of smoke seem to damage health almost as much as higher concentrations.
As exposure rises from zero, the chance that a child will get pneumonia increases sharply and then levels off so that indoor air with 200μg/m3 PM2.5 is almost as dangerous as air at 400μg/m3 (Burnett et al., 2014). The World Health Organization Intermediate Guideline for PM2.5 is 35μg/m3.
In order of effectiveness, when cooking in a kitchen, health interventions seem to be:
Venting smoke up a functional chimney.
Increasing the fresh air entering the kitchen to dilute smoke and gases. (When the outdoor air is clean and the air exchange rate is doubled, the indoor air pollution is reduced by half.)
Burning up almost all of the smoke in the stove.
Unvented Rocket stoves, and other ‘moderately clean burning’ stoves (such as a carefully tended open fire with pot skirt), emit much too much smoke and gas to protect health in houses.
Cooking outside, especially upwind of the fire in a bit of breeze, is highly effective in lowering harmful concentrations of PM2.5.
Cooking outside seems to be a first choice intervention, when applicable. Even ‘moderately clean burning biomass stoves’ can be used when the cook is upwind of the fire in a bit of a breeze, meeting the WHO Intermediate Guideline for PM2.5.
Of course, cooking with a low emission stove is preferable, when possible!
http://aprovecho.org/wp-content/uploads/2021/05/ghana-practical-stove.jpg500375Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-06-10 17:57:592022-06-10 17:58:01Cooking Outdoors as a Health Intervention
In 2018, the World Health Organization concluded, “Every day around the world, billions of children are exposed to unsafe levels of air pollution. The result is a global public health emergency.”
The WHO recommends that a combination of actions may be most effective. Aprovecho has used Retained Heat Cookers (Hayboxes) for decades and we recommend them, especially where beans make up a part of the diet.
Retained Heat Cookers simmer food to completion reducing CO emissions by 56%, PM emissions by 37% and saving 50% of the fuel and time spent cooking. (Test Results of Cook Stove Performance, 2011). When food is simmering, the fire is constantly replacing the heat lost from the pot. If the heat is captured instead, the retained heat in the boiling pot finishes cooking the food.
In the same way, a drafty and uninsulated house has to have a big fire going all the time to keep the house warm. The super-insulated, almost airtight house can stay warm for a long time after the fire is extinguished. In Oregon, Haybox homes are called “Super Good Cents” homes.
Once the boiling pot is in the box, food cooks without further attention. Even pinto beans will finish softening if the box, with waterproof R-7 insulation, is almost airtight. Makes cooking a lot easier, too!
When Dean Still came to Aprovecho in 1989, Dr. Larry Winiarski asked him to compare the thermal efficiency of the Lorena stove and the Three Stone Fire. The testing revealed a problem for the ARC staff when our Lorena used three times more fuel than a carefully operated open fire!
Half of the staff, who had written books about the Lorena and taught thousands of people about their invention, were never convinced that a problem existed. The other half were embarrassed and became fervent believers in Dr. Kirk Smith’s famous saying that “You get what you inspect, not what you expect.”
Making a public mistake pushed a reconstituted ARC to proceed more slowly, to challenge speculation, and to try to generate reliable data. We learned that a lot of local knowledge is required to take successful products to market. Evidence can help to overcome inventors’ pride, cognitive dissonance, and the financial cost of changing directions. At the same time, inventor’s pride, cognitive dissonance, and the cost of changing direction also influence decision making.
Smaller fires are often cleaner burning compared to larger fires, and higher heat transfer efficiencies allow the use of smaller fires while the time to boil stays acceptable. A pot skirt which creates a narrow channel gap reduces fuel use and time to boil.
Dr. Sam Baldwin recommended 10mm to 11mm channel gaps for household cook stoves at normal high firepowers (4kW to 5kW).
ARC uses tighter channel gaps at 5kW and we do not seem to experience problems. ARC recommends 6mm channel gaps in pot skirts for 20cm in diameter (or larger) pots.
It is interesting to note that Dr. Baldwin decreased the channel gap to 8mm with bigger institutional sized pots. We just tested a 6mm gap in a skirt surrounding a 40cm in diameter (60 liter) pot. The result, with a small open fire, was around 48% thermal efficiency.
We recommend a 6mm channel gap to achieve close to 50% thermal efficiency with a large range of pots..
The tight channel gap seems to be OK, so far. It would be great to model velocity, temperature drop, etc. as the channel gap changes! We will do it one of these days…
http://aprovecho.org/wp-content/uploads/2021/01/baldwin-institutional-graph.png15362090Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-05-13 15:15:182022-05-13 15:36:566mm Gaps Recommended for Pot Skirts
As with any tool, the skill of the operator determines how well the work is accomplished. It takes years to learn how to use a hammer or shovel. The Three Stone Fire can be effective and clean or it can be very dirty and wasteful. In some kitchens, large fires use a lot of wood and make a great deal of smoke. Small fires are also made that cook food relatively cleanly.
Watching indigenous experts cook with fire has led to a better understanding of improved biomass fuel use. Cooks who are trying to conserve wood tend to burn the wood at the tip of the stick making flames. Knowledgeable cooks only need a small, hot fire close to the pot to boil water.
Improving upon a well-made Three Stone Fire has been more difficult than expected. Learning from expert users helped teach engineers how to make better stoves. Well-constructed Three Stone Fires protected from the wind and tended with care, score between 20% and 30% thermal efficiency. Open fires made with moister wood and operated with less attention can score as low as 5%.
When Tami Bond achieved 33% thermal efficiency with a Three Stone Fire, ARC started to depend on the pot skirt with a 6mm channel gap to help folks use less fuel to cook food. Expertise with the Three Stone Fire is an important skill that empowers the cook and has to be respected.
http://aprovecho.org/wp-content/uploads/2021/12/12-8-fire-with-pot.jpg236316Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-05-06 18:07:152022-05-06 18:26:21Learning from the Three Stone Fire
The ARC/EPA 2011 book “Test Results of Cook Stove Performance” compares performance and emissions, including turn down ratio and firepower, from survey of 18 stoves. Firepower is a measure of how much energy is released per unit of time. More energy is required to quickly boil water. Less energy is needed to simmer food.
The most effective cooking stove should be fuel efficient at both high and low power. The ratio between high and low firepower is called the turn-down ratio (TDR). It is a measure of how well the stove can be “turned down” from high to low power.
A TDR of 2 means that half as much fuel was consumed while maintaining a simmer, compared to bringing water to boiling. Cooks usually appreciate a stove that is capable of both high-and low-power operation. Many foods will burn if the heat can’t be reduced enough.
It is interesting that the liquid-fueled stoves were generally low powered, at less than 2kW. Most of the wood burning stoves ranged from 8kW to around 6kW. In Mexico, gas stoves can have a hard time cooking tortillas.
The Mud/ Sawdust (TDR 3.9) and VITA (TDR 3.8) stoves had the highest Turn Down Ratio. The average for the other wood-burning stoves without chimneys was 2.4. The average for stoves with chimneys was 2.2. The Gyapa charcoal stove (TDR 2.8) scored slightly higher.
The chart shows the average high firepower and the low firepower for each stove. It should be noted that in these tests the pot was uncovered, which increases the energy input needed to maintain the water at simmering temperatures.
http://aprovecho.org/wp-content/uploads/2022/04/Screen-Shot-2022-04-28-at-3.40.57-PM.png8941708Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-04-28 14:57:452022-04-28 14:57:46Turn Down Ratio and Firepower in 18 Stoves
Aprovecho Research Center
PO Box 1175
Cottage Grove, OR 97424, USA