Dr. Larry Winiarski
Dr. Larry Winiarski
Dr. Larry Winiarski, 1940-2021

Dr. Larry Winiarski, the Technical Director of Aprovecho Research Center (ARC), died this past week at the age of 81. In the 1980’s and 90’s, Dr. Sam Baldwin defined how to improve heat transfer efficiency in biomass cook stoves (pot skirts, etc.), Dr. Tom Reed created the TLUD, and Dr. Winiarski invented the Rocket stove. The saying “We stand on the shoulders of giants” certainly applies to the stove community.

Larry led teams from ARC around the world starting in Central America, where the plancha stove was evolved, after he found that a floor tile called a baldosa made a long lasting and relatively low mass combustion chamber that was surrounded by wood ash, a great natural source of refractory insulation. Larry discovered that Rocket type stoves, like plancha stoves, can be described by ten design principles and that these simple engineering principles could be taught to indigenous people, mostly women, who were the experts in using the stoves. My memories of Dr. Winiarski, who was born in Nicaragua, are often about him having a wonderful time speaking Spanish as stoves were constructed and flavorful food prepared.

It is not an exaggeration to say that Larry had a heart of gold. He picked up sick kids and walked from the city dump in Managua to a distant hospital. He slept on cement floors for months at a time in Haiti. Larry lived as others lived in Africa for years and because of his character was loved and respected in villages worldwide. His Rocket stove found a place in people’s homes in the same way that Larry was cared for, accepted, and loved by strangers. Larry is missed by thousands of friends and he was blessed with a life well lived.

There will be a Celebration of Larry’s Life on Saturday, August 28, 2021 at 1:30 PM, at Colgan’s Island, 79099 Hwy 99 N in Cottage Grove, Oregon.

It can be challenging to find the time to read a book so here’s a ten-minute video introduction to “Clean Burning Biomass Cookstoves” (2020), our recent updating of the 2015 edition. Download the book for free on the publications page. We spent a significant part of last year rewriting most of the book trying to put in one place pretty much everything that ARC has learned in the last five years. The plan is to do the same in 2025.

The summary includes:

  • The energy ladder and renewable biomass
  • Fire is investigated in the lab
  • Stoves are designed by cooks in the field
  • Factories tell us how to help them
  • Chimneys and air exchange rates protect health
  • A new outside air model helps to predict PM2.5
  • Increasing heat transfer efficiency! No problem
  • Residence time is shorter than previously imagined
  • Metering and mixing get us most of the way to cleaner combustion
  • There are great new stoves!
  • Let’s move faster

Aprovecho Research Center is pleased to announce that it has just been awarded a $50,000 grant from The Osprey Foundation in support of expanding research into the connection between biomass combustion and climate change.

To date, a handful of lab and field studies have resulted in relatively little information on how stove/fuel interventions could impact emissions. The Gates funded GH Labs has partnered with us in this project because information is vitally needed to make sure that stove interventions are most productive.

Research has identified renewable biomass as carbon neutral but only when burned without making climate forcing emissions.  Aprovecho manufactures and sells the Laboratory Emissions Monitoring System (LEMS) as a tool to characterize cook stove performance. The LEMS enables ARC to develop stoves addressing climate, health, and effectiveness. It has become the centerpiece of more than 60 cookstove laboratories worldwide.

The LEMS measures thermal efficiency and the emissions rates of PM2.5, CO, CO2, and Black Carbon. Minimizing those emissions is important for addressing climate change and protecting human health. The effectiveness of the stoves is assured when cooks are deeply involved in designing them.

Non-methane hydrocarbons (NMHC) and methane contribute to a significant fraction of the global warming potential, especially from charcoal burning stoves, but to date have not been measurable with the LEMS.

The Osprey Foundation sponsored project goals are:

  • Adding the measurement of methane and NMHC to the LEMS.
  • Surveying the global warming potential of wood burning stoves and charcoal stoves and creating market driven designs that address climate/health/effectiveness.
  • Widely distributing open source information (including CAD drawings) describing how to minimize climate forcers in biomass stoves.

At the Leaders Summit on Climate hosted by President Biden, the U.S. government pledged to help countries achieve their climate ambitions through expanding access to clean cooking. We feel very lucky to be investigating how to manufacture improved biomass stoves that cook well, are affordable, and protect personal and planetary health. Thank you, Osprey Foundation!

Prices of carbon credits used by companies to offset their emissions are currently low, due to an excess of supply built up over several years.

According to recent research at the University of London, without the excess supply, prices would be around $15/tCO2e higher, compared to $3-5/tCO2e today. (tCO2e means tonnes of carbon dioxide equivalent, “carbon dioxide equivalent” being a standard unit for counting greenhouse gas (GHG) emissions.)

The paper predicts that the surplus will not last forever, with demand for carbon credits expected to increase five to ten-fold over the next decade as more companies adopt Net Zero climate commitments. This growth in demand should see carbon credit prices rise to $20-50/tCO2e by 2030, as more investment is required in projects that take carbon out of the atmosphere in the long-term. With a further increase in demand expected by 2040, carbon credit prices could rise in excess of $50/tCO2e.

Guy Turner, CEO of Trove Research and lead author of the study said “It is encouraging to see so many companies setting Net Zero and Carbon Neutral climate targets. What this new analysis shows is that these companies need to plan for substantially higher carbon credit prices and make informed trade-offs between reducing emissions internally and buying credits from outside the company’s value chain.”

Imagine the stoves that could be supported by a $20 price for an avoided tonne of carbon dioxide. Stoves with good thermal efficiency can save three tonnes or more per year making long lasting, super clean stoves with chimneys a great deal for carbon developers and investors.

And a great deal for consumers.

Report: https://trove-research.com/wp-content/uploads/2021/06/Trove-Research-Carbon-Credit-Demand-Supply-and-Prices-1-June-2021.pdf

When this sort of fire is maintained, a high mass Rocket stove can get close to Tier 3 for CO (less than 7.2g/MJd) and PM2.5 (less than 218mg/MJd).

Testing stoves means that many, many hours are spent watching the flames and pushing sticks of wood into the fire. We watch the real time emissions, water temperature, excess air, and temperatures in the combustion chamber on a computer screen as the testing continues. After hundreds of hours it becomes obvious that clean combustion has a certain “look.” For instance, when there is a lot of flame above the sticks the real time CO goes down on the computer screen. Without flame above the fuel, the gas rises up and is not combusted. That’s why charcoal can be dangerous, because burning charcoal does not create a lot of flame above the fuel.

When the wood sticks are changed into charcoal, the PM2.5 is dramatically reduced, as well. Pushing the unburned sticks into the fire creates smoke. Pushing the sticks in quickly makes a lot of smoke and pushing the sticks in slowly makes less smoke. Charcoal does not make much smoke and that’s one of the reasons that people like cooking with it. Feeding a fire is a compromise, as firepower and PM2.5 tend to rise together. A rocket stove can look OK as long as the sticks are fed slowly into the fire at less than about 2.5 kW. But at high power, Rockets start to smoke like crazy.

How can these two experiences be factored into a mathematical model of combustion? By using a video camera hooked up to a computer program? Residence time and temperature are easily measured, but the extent that turbulence occurs is not easily quantified. Engineers get past these sorts of problems by figuring out how to optimize mixing (using jets of air, for example), but a mathematical model is more easily filled in with numbers for other sorts of phenomena, such as the excess air ratio.

Both experiments and mathematical modeling shed light on how to make better stoves and hopefully complement each other. Arguments have been known to happen. I have been trying to figure out how to make clean burning biomass fires since 1989, and one thing has not changed since Dr. Winiarski started me on this path. I continue to be happier trying to answer questions that begin with the word “What” instead of “Why.”

Selling LPG in Rwanda

LPG (liquefied petroleum gas) is among the most important fuels for achieving clean cooking. Many countries are actively developing intervention programs. In a five year project starting in 2007, an Indonesian program converted over 50 million households cooking with kerosene to LPG. In 2016, India intensified their campaign providing free connections to LPG cylinders to “Below Poverty Line” homes. In China, gas and biomass fuels, the dominant energy fuels for cooking, are used by 44.8% and 32.1% of households, respectively. In 2014, 47.6% of rural cooks used biomass, whereas urban households were more likely to cook with gas (65.8%) (Applied Energy 2014, 136:692-703 Duan, et al.).

Even older LPG stoves burn cleanly. Five different LPG stoves were tested 89 times and described in a 2018 article. Two stoves were manufactured in China and obtained in a local market near Beijing. One was manufactured in Japan and purchased in Kampala, Uganda. Solgas Repsol Downstream Peru (an international LPG distributor) disseminated another stove. A worn-out appliance was obtained from a rural household in Cameroon  (Environ. Sci. Technol. 2018, 52, 904−915 Guofeng Shen, et al.).

  • The average thermal efficiency for the LPG cook stoves was 51 ± 6%.
  • Approximately 90% of the PM2.5 data was below the level of detection.
  • The other 10% of the stoves had an average PM2.5 score of 0.20 ± 0.16 mg/minute. (The WHO Emission Rate target is 0.23mg/minute).

However, in a country like Rwanda the switch from wood and charcoal to LPG is slow. In 2019, only 2% of cooks were using LPG in the cities. 64% used a charcoal or wood stove and in rural areas “the use of clean fuels is negligible” (The World Bank, 2019). 93% of rural households use wood, 6% of charcoal, and 0.2% of gas (National Institute of Statistics Rwanda, 2019).

The cost of LPG is a big factor. “Prices are much higher in rural areas and upcountry towns as retail traders factor in transport logistics. Rising prices for cooking gas in the country have sparked concerns of likely reversing gains made in the push for a clean cooking solution as more households turn to wood and charcoal.”  

Marie-Jeanne Uwanyiringira, a businesswoman who sells LPG, says that the fluctuation in prices has caused frustration among consumers. “When someone buys gas from me at RWF 3,500 and the next month I tell them that it is RWF 5,500, ($5 USD) they don’t seem to understand that it is not the seller’s fault.” (Rwanda Today, April 9, 2021).

WASHINGTON, DC, April 22, 2021 — At the Leaders Summit on Climate hosted by President Biden, the U.S. government pledged to help countries achieve their climate ambitions through expanding access to clean cooking.

“Providing clean energy to households is critical to achieving global climate and sustainable development goals,” said Helena Molin Valdés, Head of the Climate and Clean Air Coalition Secretariat. “Smoke from fireplaces, cook stoves, and lighting is responsible for more than half of human-made black carbon emissions and millions of premature deaths from household air pollution. The Climate and Clean Air Coalition partners welcome the U.S. government’s re-engagement in the issue and look forward to cooperating to put in place solutions that improve lives and protect the planet.” 

The United Nations Foundation’s Clean Cooking Alliance

Would it be helpful to add climate metrics to the health-based ISO 19867? Currently, Scoring Tier 5 for emissions of PM2.5 and CO means that safety is assured in average households. As the score decreases from Tier 5 to Tier 0 the estimated amounts of ill health from breathing smoke and gas increase.

During ISO 19867 testing under an emissions hood, the fuel use, thermal efficiency and emissions of CO2, CO, and PM2.5 are measured and the data is used to determine a ranking on the voluntary tiers of performance. ARC multiplies lab data by a factor of three to estimate in field emissions. Usually in cook stoves, the CO2 has by far the largest effect on climate change. However, PM (black to white in color), CO, methane (CH4), non-methane hydrocarbons (NMHC), and nitrous oxide (N2O) also have varying amounts of climate forcing potentials. Currently, CO2, PM2.5, and CO are measured as a part of ISO 19867. ARC also determines the amount of black carbon in every test (using a filter) of PM2.5. Adding methane and non-methane hydrocarbons to the measured gases is not difficult. In fact, Sam is working on adding them to the LEMS right now.

The effects of inhaling particulate matter have been widely studied in humans and animals. They include asthma, cardiovascular disease, and premature death. Particles can also have an extremely strong effect on the atmosphere by absorbing and/or scattering the sun’s incoming radiation, depending on their color. The black particles have an approximate warming potential by weight of 680 times that of CO2 (Roden and Bond, 2006; Bond and Sun, 2005).

Total global warming impact, grams CO2 equivalent on a 100-year time-frame, per liter of water boiled and simmered for 30 minutes, normalized for starting temperature and fuel moisture content. Inclusive of CO2 and all PICs.

When we studied the global warming impact of five cook stoves burning biomass, CO2 was shown to be the major component, as seen above. At the time (2008), estimates of the various warming potentials were:

CO2….1  (IPCC, 2007)
CO….1.9  (IPCC, 2007)
CH4….25  (IPCC, 2007)
NMHC….12  (Edwards and Smith, 2002)
N2O….298  (IPCC, 2007)
PM – Black….680  (Roden and Bond, 2006; Bond and Sun, 2005)
PM – White….-50 (Estimate – Bond, 2007)

Warming potential, 100-year, CO2 equivalents

  • When biomass is harvested sustainably, the CO2 emissions from biomass-burning are considered to be greenhouse-neutral.
  • Although N2O is a strong climate-forcing constituent, emissions from the wood- and charcoal-burning stoves were very low, contributing less than 1% to the overall warming potentials.
  • The data suggests that there are biomass stoves that can be designed to (1) reduce the fuel used to cook, (2) reduce health-damaging emissions and (3) address climate change. The considerable differences in climate-changing emissions from the stoves in this study should be noted. Large-scale use of cleaner burning stoves might well reduce global warming effects, especially when the biomass is harvested in a “carbon neutral” manner. (N. MacCarty, D. Ogle, D. Still, T. Bond, C. Roden, Energy for Sustainable Development, 2008)

When I went to UC Berkeley, studying psychology as an undergrad, lots of people made fun of Freud, Jung, and Adler who wrote (a lot) about divergent theories of what makes people tick. UCB liked to think of itself as a scientific institution, and facts are proven by statistical validity. Why should we believe speculation from the dear departed? I eventually agreed and I was intrigued by the big question: How do we know the truth?

The paradigm that captured my thinking was the BLACK BOX. In black box theory facts are like an elephant in a box. Scientists poke sticks into small holes in the box and one stick hits a toenail. A scientist exclaims, “Why, what is in the box is hard and slippery!” Other sticks hit the softer belly or the trunk, resulting in very different observations. Hopefully, after many experiments an accurate description of the elephant can emerge. (Although, what the elephant is thinking may well remain private.)

I was really excited by statistics!

If you’re trying to know the effectiveness of something, calculating the statistical significance can help. It gives you a measured amount of confidence in the hypothetical conclusion. At UCB we did experiments and 95% confidence was the minimum that students had to achieve to get an “A.” To achieve 95%, the sample size and the size of the effect had to be big enough.

Here’s the application to stoves

When we try to use found wood sticks from the forest in our experiments, one stick, for example, has two inches of bark on it. Another stick has three inches of bark and the two sticks make very different amounts of smoke. So, the variable of using sticks that emit different amounts of smoke makes it more difficult to know the truth: Did changing the air/fuel ratio, for example, result in the stove making less smoke? Using wood with no bark, we can achieve confidence in five to seven tests. We have to do a lot more tests when the fuel has added variables.

When trying to understand heat transfer or combustion efficiency in the lab (not what happens in the field) limiting variables has a great appeal to lazy researchers like me at ARC. So, we do not design stoves in the lab!

We realized quite a long time ago that we could only investigate heat transfer and combustion efficiency in the lab, and then with great relief go to an amazing place, work with wonderful people in a new culture, eat incredible meals, etc. in order to help a local team evolve a stove using found everything (and testing/statistics).