Appreciating Local Expertise

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Cooking over an open fire in Ghana. (Photo: Global Alliance for Clean Cookstoves)

Cooks are experts!

Community organizers often say that to be successful the solution has to come from the folks with the problem. Another important factor is to appreciate the culture and long evolved expertise in their technical and social solutions. The women at Rancho San Nicolas, where I lived for eight years, were incredibly skillful at cooking on an open fire and were understandably proud of their abilities when cooking perfect tortillas, fish, beans, soup, etc. At a fish camp, guys who were not cooking every day, had a lot of trouble making anything close to a succulent home cooked meal.

Along with the hundreds of technical skills that made ranching fun, culture made life easier and more beautiful. Ranch culture was at least half of competency and expertise. Laughing at life’s problems made overcoming them much more likely. Religion, nature, the beauty of living outdoors and liking the slow pace were strengths in my friends that I grew to envy and attempted to emulate.

Bringing innovations started with lots of failure. The first Rocket stoves became flowerpots. The first solar cookers became toilet seats and windows. Eventually, ARC appropriate technologists made prototypes that were simply put on public display. Of our many attempts to introduce ‘helpful’ technology, cement rat proof boxes were the biggest success.

We learned a lot more than we taught, starting with listening to our expert hosts. The shorter and higher firepower Rocket stove that has gone viral was created by women in 18 villages in Southern India. Dr. Winiarski had the idea and the cooks made it practical.

Deforestation, Health, Climate

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Catching up to changing stove expectations reminds me of human maturation. Babies may only need to laugh to keep parents happy, but as kids grow up the stages of development result in further complications. Happily, meeting the expanding goals of protecting deforestation, health and climate can make stoves increase their abilities without changing an essential character that continues to please the cook.

Designed to protect forests, the initial stove featured increased thermal efficiency.

The health-protecting stove added burning up carbon monoxide (CO) and particulate matter (smoke, especially PM2.5).

Protecting climate matures the same stove as harmful climate forcers are combusted as well (NOx, Black Carbon, VOCs, Methane, etc.). Importantly, attempting to burn 100% renewable biomass can zero out the warming effect of Carbon dioxide (CO2).

In simple terms, a stove loved by cooks can be changed to cook using as little wood as possible, then CO and PM2.5 are combusted and then the previously uncounted gasses and black component in smoke are burned up, too.  The biomass fuel should be as renewable as possible to decrease adding CO2 to climate.

The same stove does better and better making stakeholders proud.

Fir trees and blue sky

Black and White Smoke

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Fir trees and blue sky

Biomass: Captured sunlight

Wood burning cookstoves make smoke and many different gases that change climate. Carbon dioxide (CO2) is absorbed when the plant grows and the same amount of carbon dioxide can be released when that biomass is burned. So emissions of CO2 can be zero with no effect on global warming (carbon neutral) if the burned biomass is used at the same rate as it grows.

But other emissions from combustion are also bad for climate change. Generally, wood burning cookstoves do not make a lot of methane and carbon monoxide so these gases do not add a lot to their effect on climate change. 

On the other hand, biomass cookstoves without engineered forced draft can make a lot Black Carbon (the soot in smoke) and BC is very bad for climate change. For this reason, when protecting climate, cookstoves should make as little black smoke as possible. 

White smoke can have a cooling effect on climate. ARC has been learning how to make combustion chambers that emit as little smoke as possible and make 95% white smoke and 5% black smoke. We are working with manufacturers to make stoves with health/climate combustion chambers.

Short-lived Climate Forcers and Climate Change

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It is not difficult to estimate the emissions of Black Carbon from cook stoves.

The emissions that change climate include various gases and the colors of smoke. If the wood used for cooking is 100% renewably harvested, the emissions of CO2 can be carbon neutral. Why? CO2 is absorbed when the plant grows and the same amount of CO2 can be released when biomass is burned. 

100% renewability can help CO2 to become climate neutral. However, the fraction of non-renewability (fNRB) does not change the amounts of other climate forcing emissions. Smoke is smoke. Etc.

What are the most powerful cook stove emissions affecting climate?

In general, adding methane and carbon monoxide to Carbon dioxide (CO2) adds a bit to the total warming influences (CO2e). 

However, adding short-lived climate forcers such as NOx, SOx and Black Carbon to the above has been estimated to more than double the warming potential. 

For this reason, it seems to be important to add the short-lived climate forcers when calculating how to address climate change with cook stoves. 

Lab Tests: Cooking and Heating Stoves

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Unfortunately, although introductions to lab tests warn that results do not predict actual performance, the recent use of lab data to earn carbon credits has made an unfortunate error more commonplace. For decades, introductions to lab tests have warned that only field-testing can determine actual efficiency, emissions, effectiveness, market validity, etc. The World Health Organization based their stove standards aimed at protecting health on field-testing for this reason. 

Lab tests are helpful when comparing performance to understand how fire might be more useful. Starting with the 1985 International Standards, test users were advised not to use lab data to predict actual performance. While improving other carbon methodologies, using field-testing to estimate reductions would dramatically improve the accuracy of offsets.  

Carefully performed lab tests tend to overestimate fuel efficiency and underestimate emissions. This has landed cook stoves and heating stoves in serious controversy. A lab tested Tier 4 cookstove can be Tier 2 in real life – or mistaken for a flowerpot. My first Rocket stoves were often used for this important function in Mexico. 

A lab tested 2 g/hr PM heating stove often emits a lot more smoke when the harmful pollutant is measured from chimneys in houses. In an effort to reduce confounding variables, lab tests show closer to optimal performance. Real life human beings tend to operate stoves with less care, wood is wet, life deserves attention, too.

Maybe the test warnings should have been highlighted in green?

International Standards, 1985

“This is a laboratory test…while it does not necessarily correlate to actual stove performance, when cooking food, it facilitates the comparison of stoves under controlled conditions with relatively few cultural variations.” (Testing the Efficiency of Wood Burning Cookstoves, International Standards 1985).

(ISO 19867-1)

“This document provides a standard test sequence that can be used to compare the performance of various cookstove types, cookstove fuels, and cooking practices under controlled laboratory test conditions, as specified in this document. For evaluation of the performance and predicted outcomes of a cooking system in the field [comprising cookstove(s), fuel(s), cooking vessel(s), kitchen, ventilation, and user(s)], ISO 198691 applies.”

https://www.iso.org/obp/ui/#iso:std:iso:19867:-1:ed-1:v1:en

Over the Moon

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A couple of weeks ago, Claudia Truesdell and Shane Washburn from Google’s X – The Moonshot Factory visited us for the day. We made lunch on an earthen Rocket stove and on a metal pot skirt stove with Jet-Flame while doing a field test that generated some numbers. Google’s X was interested in what we have learned since 1976. 

Our staff had various things to share. I found myself explaining how to improve fuel efficiency in high mass stoves. Maybe ~95% of biomass stoves in use are high mass (?), made from earthen mixtures. 40% clay and 60% sand works well, especially when a relatively dry mix is pounded into a form. Metal is hard to find, expensive when purchased, and even stainless steel doesn’t last for a very long time near the fire. Improving earthen stoves might help lots of people.

When we did seminars with the Partnership for Clean Indoor Air, we showed that fuel use could be reduced by a minimum of 30% by:

  • Moving the flame further away from the mass walls.
  • Lowering the pot closer (but not too close) to the fire to increase the temperature of gases contacting the pot .
  • Using a constant cross sectional pot support to increase heat transfer efficiency to the bottom of the pot.
  • Adding an adjustable pot skirt that, especially when tight, forces the hot gasses closer to the sides of the pot.
  • Nowadays, we suggest adding a Jet-Flame to improve both heat transfer and combustion efficiency.
  • Most importantly, as recommended by Mahatma Gandhi, adding a functional chimney!

A chef cooks at a stove with a flaming wok

Turn Down Ratio: Cooking and Heating Stoves

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The successful stove delivers the needed amount of heat to perform a task. In Haiti, our little charcoal stove could not bring the big pots of rice and beans to boil although the thermal efficiency at low power (simmering) was above 40%.

In the same way, a tight, well-insulated house requires a low amount of heat to stay warm. A “leaky” house needs higher firepowers to replace the constant flow of hot air lost through cracks under doors, etc.

Generally, a good stove has a minimum three to one turn down ratio. Heating stove experts have suggested a high power of 5 pounds burned per hour and a low power of 1.5 pounds. If a heating stove cannot turn down sufficiently, the tight, well-insulated house gets too warm. On the other hand, a “leaky’ house needs a big fire.  To save fuel, a tight house is more important than a new stove.

To boil 5 liters of water in less than 25 minutes in an uncovered pot, low mass cook stoves with tight pot skirts typically need a high power between 3kW and 2.5kW. However, firepower is often a lot higher when cooks are trying to get food on the table. In our experience, many cooks prefer ~ 5kW. 

Experiments at ARC have shown that with a low mass stove, lid, tight skirt on a 5 liter pot, it takes only ~0.4 kW to maintain a 97°C simmering temperature. But, cooking requirements vary a lot from country to country. Chinese cookstoves tend to use 10-15kW and may not need low power. 

Village cooks in Southern India cooked with many small pots and often did not bring the water to a full boil. For India, Dr. K. K. Prasad proposed, “…an ideal burner design with the power output ranging from 2.64 kW to 0.44 kW… (Prasad and Sangen, 1983, pp. 108-109). Dr. Baldwin adds, “One of the most important factors determining field performance of a stove is the firepower it is run at during the simmering phase. Because simmering times tend to be long, quite modest increases in firepower above the minimum needed can greatly increase fuel consumption.” (Baldwin, 1987)

With careful operation, the heat exchanger efficiency of houses and pots combined with delivering the appropriate firepower largely determines the fuel used per task. 

Dr. Tom Reed: “Smoking Backwards”

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Dr. Tom Reed: “Smoking Backwards”

Our beautiful friend Tom Reed (1926-2018) at a Winter Stove Camp

ONE: Starting in 1985, Tom invented the natural and forced draft Top Lit Up Draft stoves (TLUD). He would demonstrate one of the clean burning principles at Stove Camps by lighting the tip of a cigarette and then sucking on the burning end in his mouth. With practice, he did not burn his tongue.  Remarkable!

Sucking the woodgas through the burning end of the cigarette cleaned up a lot of the harmful gases and protected him from most of the smoke. Similarly, lighting the top of the fuel bed in a vertical cylinder pulled the made woodgas up through the charcoal bed and flame in a TLUD. (UP DRAFT)

TWO: In the same way, sticks of wood can be placed in a horizontal cylinder, lit under the short chimney of a Rocket stove, where the made woodgas is pulled through the burning combustion zone resulting in cleaner combustion. (HORIZONTAL DRAFT)

THREE: We tune stoves under the emissions hood to reduce emissions by combining the proper 1.) amount of metered fuel turned into woodgas, 2.) temperature, 3.) air/fuel ratio, 4.) mixing, 5.) 100% of woodgas pulled into the flame, and 6.) long enough residence time of woodgas in the combustion zone.

FOUR: Before iterating changes in the stove to reduce emissions, we try to optimize heat transfer efficiency so the least amount of biomass completes the task.

FIVE: Tom, we remember you so fondly! Thanks for the help!

Rocket Bread Ovens

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I ran across this old video when exploring Rocket stoves on YouTube. It is great to have both peer reviewed journal articles and places like YouTube. I hope that our publications library at aprovecho.org includes, perhaps even combines, helpful information from both academia and the field.

We baked with a high mass bread oven for years at the Aprovecho campus. We bragged about it. It was only when Dr. Winiarski built a Rocket bread oven next to the old stove that we experienced the differences. Then, it took less than a week for baking to switch to the Rocket oven. No more throwing logs into a mud/sand cave for hours to try to get up to temperature! Why try to heat up a thousand pounds of mud when you want to make 20 pounds of bread?

Larry’s Rocket oven got to 400°F in about 30 minutes and used hand fulls of twigs to bake enough bread for the hungry eco-scientists. I loved the Rocket bread ovens and helped Larry to build them in Mexico. We learned a lot from Larry including that using a new stove was a lot more convincing that talking about it. Why not let the new oven or stove speak for itself.  Then stand aside and watch when folks like it enough to improve the prototype? 

So nice to let the experts (the cooks) tune the cooking functions of a stove! So nice to empower their hard won expertise! So appropriate to sit back and learn.

red sign with white letters reading Wood Burning Prohibited

Clean Burning of Biomass

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red sign with white letters saying Wood Burning Prohibited

Scotland has banned the use of climate polluting home heating systems such as oil and gas boilers, and wood burning stoves (except in cases of need) in new construction. Heating homes creates one fifth of Scotland’s CO2e. The plan is to switch to electric heat pumps, hydrogen and tighter, better-insulated homes in an effort to achieve carbon neutrality by 2045. https://www.bbc.com/news/uk-scotland-68778757

Oil and gas (fossil fuel) burners create too much CO2. Burning renewably harvested biomass can emit close to zero CO2, but old stoves make too much black smoke which is ~2000 times worse for climate change compared to CO2 by weight.

Heating stoves that burn sustainable biomass cleanly enough to protect health and climate are starting to become available. Testing the new generation of stoves in use will show whether biomass can join solar, wind, and hydro as a useful renewable energy resource in the post fossil fuel era.

Maybe those red signs will become green?

Green sign saying Sure, Light Up