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Appropriate Technology, Development
Appropriate Technology, Development
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Appropriate Tech Classes
- Decision Matrix -
- Design -
To build an effective mud stove that can be made with local resources while maintaining affordability. In order to do this we will define the best mix of natural materials.
Different combinations of natural materials will be tested for compression and heat resistance. The most durable design will then be utilized to build our stove.
To start, we tested the following material combinations:
2. Clay and sand
3. Clay and dirt
4. Clay and straw
5. Clay and walnut shells
6. Cobb (Clay, straw and sand)
We made four blocks for each combination, allowed two bricks to dry naturally and two to dry with heat, and then tested compressive strength and heat of each individual brick. After this first round of testing, we refined the materials to find the best for a mud rocket stove.
Bricks to be tested
Video of Compression Tests
In this video, we are testing cob (clay, sand, straw).
Graph of Compressive Strength Testing
1: Somewhat significant. Worth considering but not a major impact to the creation or development of a project
2: Significant. A major impact is considered with a multiplier of 2. This multiplier can effect the project negatively, but will not necessary stall the project.
3: Very Significant. A category that must absolutely be considered and will have a major impact on the development of a project. This multiplier can make a project unfeasible if it isn't seriously considered.
Foreign Access to Materials
People in developing nations do not always have access to construction materials as found in developed nations. Materials such as steel and concrete may not be readily available in small towns. Further, heavy concrete and steel may be difficult to transport without access to trucks. Natural materials however, may be available within a short distance of small communities. Since some materials may not be readily available in developing countries, this category gets a multiplier of 3.
Cost of Materials
For most people in developing countries, costs are a prohibitive part of life. When many people live day to day, buying materials such as steel and concrete may be too expensive. A multiplier of 3 is necessary to ensure that a stove project in developing countries is not stalled by high costs.
Ease of Construction
People with specialized skills for building things may not be common in developing countries. Thus, people need to be able to build stoves by themselves, with little outside input. A multiplier of 2 ensures that people are capable of producing the stoves they need, mostly on their own.
The stoves will be subjected to compressive strengths from cooking pots full of food and water. Using materials which are capable of handling the required loads makes this category have a multiplier of two.
Emissions from the building materials themselves. It was assumed that the stoves would produced approximately the same emissions from the fuels they burn, even if they are made of different materials. Some materials such as concrete and steel require large amounts of energy to produce. Steel must be mined, refined, and transported and thus has high carbon dioxide emissions over its total lifecycle. Local materials such as clay, straw and sand are naturally produced, require nearly no energy to extract, and will likely be transported individually, thus emitting no delivery emissions. Lifecycle emissions contribute to global warming and should be considered with a multiplier of one.
We chose to use unbaked cob to build our stove after examining the data from the strength compression test and weighing the pros and cons of all the materials. While baked cob was the strongest, we feel that unbaked materials may be more appropriate and available in developing countries. unbaked cob was the strongest of the unbaked materials.
Making Cob: Cob Dance!
We read up on how to make cob (clay, sand, straw) and found that walking in the mixture helped to mix everything thoroughly.
Building the mud stove:
We started by putting pieces of wood and built around them using mud. This way, we could create a passage for the heat/flame without using only our cob mixture.
Once we built the stove up big enough to hold a pot, we added a coffee can to serve as a pipe between the two pots. This way, the heat would be funneled through efficiently and we were able to use recycled metal (see images above and below).
Piping from other side of stove. Hole in the bottom is the combustion chamber.
We added the beginning of a chimney to one side of the stove. We originally planned to make the chimney out of recycled coffee cans, but ended up purchasing tubing instead. That way, we were able to build a taller chimney.
Final project: We decided to purchase a chimney tube to provide a longer chimney than we could have built with coffee cans. We also added PVC piping to create a stand to hold up the chimney. After adding the chimney to the stove, we noticed that most of the smoke created was pulled through the chimney and no longer seeped through the cracks of the stove. Our group was very happy about this!
During the presentation, we boiled water and cooked macaroni and cheese using the mud stove and shared it with the class. We were happy to be able to cook something and have most of the smoke escaping from the chimney.
Future classes: We hope that future classes can use our stove and continue to improve its design. Perhaps they will also be able to include our hybrid idea, which will include agricultural waste as fuel (sketch of design included below).
Literature Review (1/21/2012)
This literature review is a compilation of reseach done in regards to the construction of a mud stove
our own building and shaping of the project. The insights and suggestions below are based on mudstoves successfully created before. The links to see and view them are included in the review, as well. Our group, while modeling the basic structure of the stove, made a few changes and modifications in order to address our initial posed problem: which material (made from natual resources) would be the most effective, cost-efficient, and most durable?
Rocket Stove Research and Review
The incorporation of the heat rocket stove is a movement promoted by the sustainable energy world in our society today. The ultimate aim of those creating them is to create efficient combustion of fuels at high temperatures. Under the correct construction methods, the heat rocket stove results in: good air draft, controlled fuel usage, complete combustion of volatiles, and again, the efficient use of resulting heat. The four main components of the stove are: the fuel magazine, the combustion chamber, the chimney, and the heat exchanger. The fuel magazine is the first part which connects to the fuel chamber where unburned heat is placed. Next is the combustion chamber which is where the wood is stored. The chimney follows, which is designed in a vertical method such to allow for updraft and maintain the fire. Last is the heat exchanger whose job is to transfer the heat to where it is needed. The heat exchanger is the part that needs the most attention in terms of sustainability. The design is effective in the sense that it can function on half of the fuel as a traditional fire and can perform the same tasks given smaller pieces of wood. The exhaust leaving the stove is usually warm and damp, which is indicative of efficient heat extraction. Additional benefits have shown that the thermal mass can absorb daytime heat from the room and later on, release it at night. In this way, a cooling and heating system can be implemented in the house. In terms of the thermal mass, a mixture of clay, sad, and straw is normally given moisture and then allowed to dry and harden. The advantage to this construction is “that the final shape can assume curved and artistic forms not possible in other thermal mass stoves and can be constructed into whatever form is most appropriate for your living space.” While it seems as though there may be no problems with the implementation of these stoves, three main concerns have arisen in testing their capabilities. First, many people are already comfortable with what is provided to them and are not willing to change what they’re familiar with. Next, the construction and incorporation of the stoves in a new house requires a strong building foundation. Lastly, in terms of the cost-efficiency of the mudstove, studies have shown that the different parts of the stove may need additional assistance or revamping at a later date. In terms of needing to fix and revisit different parts, this may become costly over time. All things being considered, the green concept is definitely a step in the right direction for energy efficiency and with additional attention has the potential to be a very influential innovation.
Rocket Stove Profile
"Rocket Stove." Wikipedia, the Free Encyclopedia. Web. 23 Jan. 2012. <
"Rocket Stoves - a Hot Name for a Fantastic Stove." Wood Stove Wizard - Everything You Need to Know about Wood Burning Stoves. 2011. Web. 23 Jan. 2012.
In the end, our construction of the stove differed from the picture above in a few different aspects. First and foremost, we created a stove which heats two pots instead of only one. In this way, the different structures listed above have been manipulated, more or less. In looking at our stove straight on, there is a small opening to the combustion chamber. We placed the wood in here and light it, which when ignited, maintains the fire and boils the water in the first stove sitting directly above it. The escaping heat then travels through the combustion chamber, created by a coffee can, to transfer and provide heat to the area reserved for the second pot. We've included three rocks to direct air flow here, as well. The air, from this point, travels to the chimney upward and out as heat, which would ideally serve to warm a house. Again, our design differs from the original plans we had first observed, but worked well in the end and to, indeed, bring our water to a boil. Our decision to work with a cobb material (clay+sand+straw) is not only cost-effective, but also serves as the best option because of its capacity to withstand the most compression.
Unfired Bricks Compression Strength
Air drying can put our group at an advantage because this process helps the bricks “reduce shrinkage and improve strength” (Heath). Choosing to make clay bricks is also a relatively environmentally-friendly way to build. Traditionally, these types of bricks are made from materials such as cob, mud and adobe, and were used in the past to create very thick (thus strong) walls.
According to Heath, unfired clay bricks have “14% of the embodied energy of fired bricks and 25% of the embodied energy of concrete blocks.”
Heath states that unfired clay/mudbricks tend to deal with changes in humidity better than fired bricks. This is because the bricks absorb the excess moisture at high humidity and release it at low humidity (Heath). Heath provides data demonstrating that unfired natural bricks absorb moisture much more effectively than fired or concrete bricks. This has been shown in areas with medium humidity (40-60% relative humidity).
It is sometimes difficult to determine strength of unfired bricks because their composition and water content may vary from brick to brick. According to Heath, clay content is one of the most important factors when determining the strength of unfired bricks. It appears that low clay content tends to have a slight advantage in compression strength; it also has a larger advantage in higher humidity. However, there is still only a small difference between the two.
Overall, unfired bricks tend to be weaker than fired bricks or concrete blocks.
Heath notes that using a sand mixture as a material for an unfired brick helps to increase its strength.
Interesting points straight from Heath’s page:
Bricks, blockwork or unfired clay bricks - which is best?
There is no simple answer to which is best, as the different materials are suited to different applications. Some points to consider are:
Unfired brickwork generally has lower embodied energy and is easier to recycle and dispose of at end of use than blockwork or fired clay masonry.
Unfired brickwork has the ability to absorb more moisture from the air than blockwork or fired brick masonry, and therefore provides better passive humidity control.
Unfired brickwork does not have the same moisture resistance as blockwork or fired clay masonry, and detailing should ensure it is kept dry during and after construction.
Unfired brickwork generally has a lower strength than blockwork or fired clay masonry, and it is currently not recommended to use thin-walled earth masonry in high-load structural applications. It will also not support as high a load from fixings as fired clay bricks and concrete blockwork.
Heath, Andrew. “Unfired clay bricks.” Copyright Greenspec 2010. Web. January 22, 2012.
Turbo Stove Research and Review
The Turbo Stove
The turbo stove, also known as the Mayon Turbo Stove and
Lò Trấu (Meaning rice husk stove in Vietnamese) is a cheap, portable cooking stove designed to efficiently utilize agricultural waste residues in developing countries. These stoves provide adequate, concentrated heat for cooking and boiling and are much more efficient than simple wood burning fires. The fuel from agricultural residues is typically much cheaper than wood or coal and is also more readily available (REAP 2012).
Design and Materials
The stove is shaped like a circular cone up side down. Within the circular cone are two smaller steel pipes, one inside the other. Looking from the top, the stove resembles a target shape. Agricultural residues used as fuel are placed in a donut shape between the inside of the circular cone and the outward steel pipe. Holes on the outside of the cone allow air to react with the fuel. As the fuel burns and gasifies, emissions and heat travel upward to be utilized for cooking and boiling (Nunez 2010).
Welded Steel Turbo Stove
Most designs appear to be made of welded steel, allowing for a rigidity and heat tolerance. See above picture. The empty stoves weigh about 4 kg (REAP 2012). Although many other types of stoves are made from mud, bricks, clay and other materials, the turbo stove appears to be only made of welded steel. This may allow for investigation on uses of other materials in the creation of a Mayon Turbo Stove (HEDON).
A steel Mayon Turbo Stove (stove) was used to conduct several performance and emissions related tests. These included fuel use, carbon monoxide and particulate matter emissions. The fuel requirements using rice hulls were approximately 85.2 g/L to boil 1 L of water (ARC 2005).
Approximately 25 kg of rice hulls are required to support one family for a week (REAP 2012).
The performance of the Mayon Turbo Stove was also compared to an open fire. Many experiments proved that the stove was more efficient than an open fire. Improvements in efficiency by using the stove resulted in a 31.1% reduction in fuel use for boiling 1 L of water and a 16.1% reduction in time to boil 5 L of water (ARC 2005). Comparatively, one liter of water can be boiled in about 6-7 minutes (REAP 2012).
The emissions related tests for boiling 1 L of water resulted in 3.0 g of carbon monoxide (CO) and 28 mg of particulate matter (PM). As a reference, 5 L of water took 25.1 minutes to boil (ARC 2005). Compared to an open fire, emissions of CO stayed relatively similar and actually increased by 0.08% when boiling 1 L of water. Particulate matter emissions however were significantly reduced by 69.9% when boiling 1 L of water (ARC 2005).
The stove is typically made out of welded steel and has a lifetime of 2-3 years (REAP 2012). The design and construction are relatively simple if materials and tools are available. However, the circular cone may be rather difficult to construct in many developing nations. For fixing a stove, the availability of welding services in many countries may either be very limited or expensive. Thus, the use of other, nature or less expensive materials may be desired.
The steel welded stove has been produced within the Phillipines for about 800 Phillipine Pesos ($18.43 USD as of 1/19/12) each. In the Phillipines, 10 kg sacks of rice hulls are free, and cost only 5 Pesos ($0.12 USD) to transport (Miles ND). In other areas, fuel from agricultural waste may cost up to $20 annually, however which is still 10 times cheaper than the average annual firewood and charcoal costs of up to $200 (REAP 2012).
Bryden, Dr. Mark, Dr. Tami Bond, Dean Still, Damon Ogle, and Nordica Hudelson. "Stove Performance Report: Mayon Rice Hull Stove." Aprovecho Research Center (ARC), 18 July 2005. Web. 19 Jan. 2012.
HEDON Household Energy Network. "Unbaked Clay Stoves." HEDON Household Energy Network. Web. 23 Jan. 2012. <
Miles, Tom. "LoTrau Stove, Mayon Turbo, IRRI." Improved Biomass Cooking Stoves. No Date. Web. 19 Jan. 2012. <
Nunez, Austin, Kelly Hanson, Sean Basalyga, and Leyla Naimi. "Biofuel Stove." The Mayon Turbo Stove. Appropriate Technologies Cal Poly 2010, 2010. Web. 2012. <
Resource Efficient Agricultural Production (REAP). "Mayon Turbo Stove: Introduction." Welcome to Resource Efficient Agricultural Production - REAP - Canada. 2012. Web. 19 Jan. 2012. <
Interesting links for later use.
Ceramic Jiko stove:
Maputo Ceramic Stove
Malawi Mud stove
unbaked mud/clay stoves!
Appropriate Mud Stoves in East Africa
Building with Cob
Cob is an environmentally friendly style of building. Cob is a material comprised of clay rich soil, sand, and straw that is mixed together in different proportions with the addition of water. Cob houses date back over 500 years ago and are still in good condition. This material got its name from the palm sized loaves that were made in order to be stacked for the structure.
The maleable material is made by adding buckets of wet clay and sand added together and stomped by people walking on top of it. After mixing the sand and clay throughly , the straw is added and then mixed again to form the final material. When the material dries it is compared to concrete in its strength. Cob is a material known as monolithic, meaning that it is worked together to form one large structure, rather than using bricks that are stacked.
Cob is becoming a more popular building material due to its low environmental energy output. Very little energy is used in producing cob and the products of it are all organic. The sand, clay,
and straw are all products that come from the ground beneath us. This environmentally friendly building technique hosts itself to many great projects.
Comments. "Natural Building 101: Building a Cob House." Reporting on Sustainably Built Environments from Bricks to Cities. Web. 22 Jan. 2012. <
"What Is Cob." Cob Projects - Cob Houses and Timeless Art of Cob Building. Web. 22 Jan. 2012. <
here is a great video on someone making cob using limited tools..... only human power with some dirty boots.
Another great video on building with Cob.. So inspiring
Decision Matrix-Turbo Stove Design.
On the left, we will decide which material is best based on the five column categories of
Access to Materials, Cost of Materials, Ease of Construction, Durability and Emissions.
Multipliers have not been determined at this time.
Access to Materials:
How available are the various stove making materials to people in developing nations? Steel and concrete may difficult (and heavy) to obtain in small villages. Steel also requires welding and plasma cutting, which may be a difficult service to find. Other materials such as clay, straw, sand, etc. may be much more available locally.
Cost of Materials:
Costs for a stove are very important as people in developing nations are often financially insecure. Materials such as steels and concrete may be to expensive. Natural, clay based materials may be nearly free.
Ease of Construction:
How easy is the stove to build? Can someone with limited construction skill build the stove in a reasonable amount of time? How will they build it? Does it require extra help from welding and plasma cutting staff? Ultimately, something which could be built within a week by someone with low construction skills is ideal.
How long will the stove last? A metal turbo stove is said to last about 2-3 years. Clay and concrete mixtures must be on par then. Steel and Concrete, if built correctly should be rather durable. Currently in lab the Mud Stove group is determining the durability of the bottom 5 materials on the decision matrix.
It is likely that most stoves, if built similarily will have little differences in local emissions of particulate matter and carbon monoxide. However, steel and concrete products require enormous energy inputs. The life cycle assessment and emissions of all materials from production of that material, to their role within the stove will be evaluated to improve not only local health, but national as well.
* End of Literature Review
Click here to see the data collected from various tests.
Cover Image Credit:
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