thermal image of house juxtaposed with daylight image of same house

COP 28: Near-zero emissions in global building sectors

thermal image of a house juxtaposed with daylight image of same house
Heat can constantly leak out of older homes. Photo: Gina Sanders

Aprovecho is investigating how to design and manufacture biomass-heating stoves that protect health and climate when burning renewably harvested biomass. Of course, staying warm depends on many factors including how much energy is being leaked from the building.

Net-zero buildings are usually tight and well insulated. A net-zero home can have a heating load of 10,000 to 15,000 Btuh (or ~3 to 4 kW) in a cold, northern climate. At COP 28, a minority of nations agreed to move towards net zero homes to reduce climate change by heating the better buildings with renewables. Green Building Advisor: 28 Countries Sign Buildings Breakthrough Agreement at COP28

Since the 1970’s, architects and engineers have learned how to dramatically reduce energy losses in buildings. Many net-zero homes take advantage of solar power to assist heating and create electricity. Solar gain helps a tight, well-insulated home to stay warm.

The United Nations found that buildings and construction account for 39% of total carbon emissions annually. Net Zero Homes: Your Guide to the Greenest Housing Option  If a new generation of very clean burning biomass heating stoves can protect health and climate, might they assist COP* countries to move towards near-zero emissions in global building sectors? *COP is the decision-making body of the UN Framework Convention on Climate Change.

From: EPA’s Lab Test Results for Household Cookstoves, Jim Jetter, 2012 

Since 2012, optimized biomass cook stoves have been tested at ~50% thermal efficiency

The temperature of the hot gases flowing past the surface of the pot is increased by

  1. Creating as much flame (1,100C) as possible in a low mass, insulated combustion chamber.
  2. Decreasing the distance between the fire and the pot without making excess smoke.
  3. Not allowing external air to cool the combustion gasses.

In convective heat transfer, the primary resistance is the surface boundary layer of still air immediately adjacent to a wall. 

Increasing Temperatures, increasing exposed Area, increasing Radiation, increasing Velocity in a 6mm to 7mm channel gap (10cm or higher) pot skirt has been shown (up to 5kW firepower) in a 24cm or larger diameter pot to result in ~50% thermal efficiency. Reducing losses from the exterior of the pot skirt with refractory ceramic fiber insulation also increases thermal efficiency. 

60% thermal efficiency has been demonstrated in the lab.

Helpful links:

Cleaner Burning Biomass Stoves: In Homes!

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The British Petroleum clean burning Oorja FD-TLUD stove from India

If protecting health and climate are important in stove projects, why not monetize the reductions of health/climate pollutants in carbon-offset projects?

Only the reduction in fuel use earns carbon income now!

With equal heat transfer efficiency, dirty burning stoves earn as much as clean burning stoves.

Dirty burning stoves are less expensive. “Market demand” reinforces the use of biomass stoves with low combustion efficiency.

Why not add income from reductions in CO, PM2.5 and Black Carbon, etc. to carbon projects to get cleaner burning stoves into use?

The approved 2017 Gold Standard Methodology already exists to do this! See: www.goldstandard.org/articles/black-carbon-and-other-short-lived-climate-pollutants

Moving Forward: Thanks to Jim Jetter’s EPA Lab!

Champion (2021) average energy emission factors (g/MJ) from ISO high, medium, and low tests. 

Champion, Wyatt M., et al. “Cookstove Emissions and Performance Evaluation Using a New ISO Protocol and Comparison of Results with Previous Test Protocols.” Environmental Science & Technology, 2021, 55, (22), 15333-15342.
DOI: 10.1021/acs.est.1c03390

Lab testing can quickly compare emissions from stoves. The EPA and ARC labs now measure the climate emission factors, not just PM2.5 and CO. It has been proven that only field tests show real world performance. Together, lab and field tests help to move stoves forward as we get closer to market driven stoves that please cooks, successfully cook food, use a lot less fuel, and protect health/climate.

The above chart contains a lot of information. Some takeaways are:

  1. Wow! The Three Stone Fire (TSF) was pretty bad! 943g/MJ for PM2.5, 15.5 g/MJ for CO.
  2. Charcoal made ~90% less PM2.5.
  3. The Carbon Monoxide (CO) from charcoal was only a bit higher than the Three Stone Fire (19.2g/MJ).
  4. LPG did so well! (Too bad that we are entering the end of the fossil fuel era).
  5. The forced draft pellet stove looked great, as well. (PM2.5: 30g/MJ, 2.2g/MJ CO)
  6. Black Carbon (EC) is much worse than CO2 for climate change. Many of the stoves, except the Rocket stove, successfully reduced Black Carbon. 
  7.  In this recent lab test, as in the previous MacCarthy study (2008), the Rocket stove emitted a lot of Black Carbon.  www.sciencedirect.com/science/article/abs/pii/S0973082608604299
  8. R&D has shown that the Rocket stove requires successful forced draft mixing at high temperatures to decrease emissions of Black Carbon and potentially address climate. 

When the emissions factors are summed and converted to global warming potential the forced draft stoves have the potential to generate large amounts of carbon offsets. 

Happy Holidays, 2023!

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That the days are shorter is easy to attest to here at Blue Mountain. Our campus is wedged between parallel rows of 100-foot tall Fir trees. Yesterday, the rare sun fell down below the celestial horizon at 2PM.  We envy the valley farmers whose day lasts until around five. On the other hand, being surrounded by the forest up here makes the air sweet and clean. But only when the wood burning heating and cooking stoves that we are developing and testing are protecting health and climate.

It can be so terrible when traditional stoves are belching smoke! I have had pneumonia three times and get nervous when my throat gets sore. Clean burning makes me a lot happier. 

HEALTH: Can biomass be burned cleanly enough to protect air quality when warming houses and cooking food? 

CLIMATE: Can the Global Warming Potential of burned biomass meet the Paris Agreements and join solar, hydro and wind as a renewable energy source? 

Sure, we do both every day.  

Celebrating life and scientific endeavor in the forest becomes pleasant and comforting when we are toasty warm, and the smoke disappears. 

Feels downright civilized.

Iterative Development of Stoves and Black Box Theory

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“The concept of black boxes has been around since the early days of systems theory though some attribute the first use to the field of electrical engineering.

It is a simple concept and has a straightforward definition: we know the inputs and subsequent outputs to a system but the internal workings of the system are not visible to us.

Black boxes approaches focus on input and output rather than the details of how inputs are transformed into outputs”.

-John M. Green, The Application of Black Box Theory to System Development

Data Driven Hypothesis Generation

The results of experiments guide the subsequent experiments. For instance, adding secondary air jets into flame is shown to decrease PM2.5. Guided by the result, further investigation in a prototype under the emission hood determines the most successful application by varying parameters.

Random Experimental Design

In a Black Box (where the situation is complex and not understood) randomized approaches to experimental design can be effective and efficient.

H.R.6316 – Clean Cooking Support Act

Following the COP26 international climate conference, Senator Susan Collins (R-ME) and Senator Dick Durbin (D-IL), have introduced a bill to accelerate access to clean cooking. Here is the opening text of the section defining the activities directed in the bill. H.R.6316 has been referred to the Subcommittee on Energy:

SEC. 5. CLEAN COOKING PROGRAM.

(a) Department Of State; United States Agency For International Development.—The Secretary of State and the Administrator of the United States Agency for International Development shall work with the Clean Cooking Alliance, founded in 2010—

(1) to engage in a wide range of diplomatic activities, including with countries across the globe and with United States embassies abroad, to support activities of the Clean Cooking Alliance and the clean cookstoves and fuels sector;

(2) to continue the clean cooking initiatives supported by the Climate and Clean Air Coalition, an intergovernmental organization formed in 2012, to reduce emissions of climate pollutants;

(3) to advance programs that support the adoption of affordable cookstoves that require less fuel to meet household energy needs and release fewer pollutants, as a means to improve health, reduce environmental degradation, mitigate climate change, foster economic growth, and empower women; and

(4) to carry out other activities authorized under this Act.

(b) Department Of Energy.—The Secretary of Energy shall work with the Clean Cooking Alliance—

(1) to conduct research to spur development of low-cost, low-emission, high-efficiency cookstoves through research in areas such as combustion, heat transfer, and materials development;

(2) to conduct research to spur development of low-emission, high-efficiency energy sources;

(3) to support innovative small businesses in the United States that are developing advanced cookstoves and improved cookstove assessment devices; and

(4) to carry out other activities authorized under this Act.

The bill continues on in sections (c) through (f) to direct the National Institutes of Health, Centers for Disease Control and Prevention, Environmental Protection Agency and other federal agencies to engage in supportive activities. You can read the full text of the bill at https://www.congress.gov/bill/117th-congress/house-bill/6316/text

A Short History of Cookstove Durability

Tin can stove by Katska on Flickr

The Problem with Metal

It’s great to start making stoves and testing ideas with tincanium (cut up tin cans). Making new prototypes from tin cans is a quick, inexpensive way to start the design process but tin cans only last for a limited amount of time, depending on the temperature of the combustion chamber. At 1000C in fire, a tin can burns out in an hour or so!

One of the most challenging components in a cookstove is the combustion chamber, which can operate at high temperatures (often ≥600 °C) in wet and salty conditions. Wood can be salty and water vapor is produced when wood is burned.

In 2017, M.P. Brady and T.J. Theiss shocked the stove world by showing that in their tests even expensive metals could not be estimated to be long lasting. (Energy for Sustainable Development 37 (2017) 20–32, Alloy Corrosion Considerations in Low-Cost, Clean Biomass Cookstoves for the Developing World Michael P. Brady, et al.).

“Corrosion evaluation under cookstove-relevant conditions was studied by two methods: 1) lab furnace testing and 2) in-situ exposure in an operating cookstove. The lab furnace testing was conducted in air with 10 volume percent of H2O to simulate water vapor release from burning biomass, and direct deposition of salt onto the test samples to simulate the burning of highly corrosive biomass feedstocks. In particular, relatively high levels of salt species are encountered in many types of biomass and can lead to significantly accelerated alloy corrosion rates (Antunes and de Oliveira, 2013; Baxter et al., 1998; Saidur et al., 2011; Okoro et al., 2015). The in-situ cookstove testing was conducted using wood fuel that was pre-soaked in a salt water solution to yield accelerated, highly corrosive conditions.”

“Each day of testing, cookstoves were burned continuously for an average of ~6 h. The average fuel consumption rate was 570 g/h. To determine the range of temperatures that the alloy test samples would experience, a thermocouple was placed inside the chimney of each stove at the same height as the coupon fixture. Typical combustion chamber temperature profiles for the cookstoves, where test coupons were placed, are shown in Fig. 2. The average gas temperature range during steady state in-situ testing was 663 °C ± 85 °C”

“Much faster corrosion rates were observed in the 800 °C lab furnace testing where evaluation of most alloys stopped after 500 h of exposure due to excessive corrosion. Of the alloys tested to 1000 h, only the FeCrSi and pure Ni samples exhibited good corrosion resistance. The FeCrAlY and 310S alloy samples were consumed through-thickness in some crosssection locations.”

“Type 201 stainless steel, type 316 L stainless steel, and the 12 and 20Ni AFA alloys all exhibited relatively poor corrosion resistance in the in-situ cookstove testing, with metal losses in excess of −200 μm after only 500 h of exposure, consistent with the lab furnace trends. The types 310S and 446 stainless steels exhibited moderately worse corrosion resistance, with metal loss values of −190 μm and -230 μm after 1000 h. Despite exhibiting the best corrosion resistance in the lab furnace testing, the pure Ni suffered from −300 μm metal loss after only 500 h in the in-situ cookstove testing.”

What could stove companies do? Attempts were made to reduce temperatures in combustion chambers. Insulation was removed and external air was directed to cool the external surfaces of the metal.

Refractory Ceramic, A Viable Alternative

When Dr. Winiarski insulated the combustion chamber in his Rocket stoves, it became all too obvious that available metals were short lived. Unfortunately the alternative – heavy ceramic materials that were free and available – absorbed heat which lowers temperatures, resulting in reduced thermal efficiency and higher emissions. 

More than 20 years ago, the quest began for an inexpensive, refractory metal and/or a durable, low mass, abrasion resistant refractory ceramic material. In Central America, Don O’Neal and Dr. Winiarski found a locally manufactured, inexpensive, thin walled refractory tile called a baldosa that can last for about seven years in a plancha stove and is now in use in hundreds of thousands of stoves.

The wisdom of using refractory ceramic was confirmed in 2011. Metallurgy experts at a DOE Biomass Cookstoves Technical Meeting pointed out that only refractory ceramic seemed to meet the requirements of being affordable with a prolonged longevity. Unfortunately, making lightweight, abrasion resistant refractory ceramic has proven to be difficult.

Shengzhou Stove Manufacturer has for years manufactured low mass, abrasion resistant refractory ceramic combustion materials in China. Since 1407AD, potters in eastern China have used rare local clays to make and sell these combustion chambers to East Africa. In 2023, SSM sells ceramic combustion chambers in Rocket stoves globally.

Though not necessarily refractory, simple earthen ceramic stoves continue to to be the most popular models in many countries. These stoves are locally produced, inexpensive and are replaced relatively frequently as needed. These heavy bucket shaped stoves can save fuel when used with a pot skirt.

The Importance of Durability

Durability has became more important as carbon credits, which currently support most large-scale stove projects, are generated only when the stove is in use. Carbon credits are based on improvements in fuel use while emissions of CO and PM2.5 are not counted. The ‘perfect’ carbon credit stove is least cost, long lived, and as fuel efficient as possible. When ARC is asked to develop a cookstove for a carbon project we usually aim for cost under $20, over 40% thermal efficiency, with a minimum 5 year durability.

The ARC carbon credit stove is dependent on a tight fitting pot skirt (close to optimal heat transfer efficiency) coupled with as cool as possible temperatures in metal parts, resulting in improved lifespan. Shengzhou Stove Manufacturer sells millions of carbon credit stoves with their light weight, abrasion resistant combustion chambers. 

ARC tries to add mixing in the combustion chamber and a chimney whenever possible. Cooking outside/increasing the air exchange rate in houses is also effective in reducing exposure. The Jet-Flame is moving into greater use and has been field tested in Africa. Carbon revenue is moving better stoves into homes as humanitarian oriented partners like C-Quest Capital replace older stoves with better stoves. Progress has picked up in the last five years.

Electricity: Planning for Net Zero by 2040

www.weforum.org/agenda/2023/04/electricity-generation-solar-wind-renewables-ember/
  • Transitioning to carbon neutral electric generation would replace a big climate problem in the U.S., since about 60% of its electricity comes from burning natural gas. 
  • The World Energy Forum forecasts that around 40% of electricity could be from wind and solar doing most of the heavy lifting by 2040, enabling a net zero global future. 
  • Today hydropower provides about 16% of the world’s electricity, generating power in all but two U.S. states. 80% to 90% of our electricity at the lab comes from the wonderful Columbia River.
  • ARC is working to clean up combustion so renewable biomass (domestic switch grass, for example) could cook food and heat homes when fossil fuels are no longer available.
  • Reading a book at night in a warm house is a wonderful thing. Somebody is playing the piano… Dinner was great.

Earth Day 2023: The Future Can Be Fun!

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(R. Crumb)

If renewable switch grass, for example, was burned cleanly enough biomass could join solar, wind, hydro, and thermal energy as sustainable energy replacements in the post fossil fuel era. ARC estimates that an emissions rate of 0.3 grams/hour of PM2.5 would protect air quality in cities and meet the Paris Agreements when replacing natural gas.

Not all that hard to do…

 “Earth is likely to cross a critical threshold for global warming within the next decade, and nations will need to make an immediate and drastic shift away from fossil fuels to prevent the planet from overheating dangerously beyond that level, according to a recent report from the Intergovernmental Panel on Climate Change.

… It says that global average temperatures are estimated to rise 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels sometime around ‘the first half of the 2030s,’ as humans continue to burn coal, oil and natural gas.

…Under the 2015 Paris climate agreement, virtually every nation agreed to ‘pursue efforts’ to hold global warming to 1.5 degrees Celsius. Beyond that point, scientists say, the impacts of catastrophic heat waves, flooding, drought, crop failures and species extinction become significantly harder for humanity to handle.” Brad Plumer reporting in the New York Times, 4/21/23

On the other hand, transitioning to renewability accomplishes an almost universal dream of humanity.