A Major Qualifying Project - Worcester Polytechnic Institute

A Major Qualifying Project - Worcester Polytechnic Institute
MQP-MQF 3102
A Major Qualifying Project
Submitted to the faculty
of the
WORCESTER POLYTECHNIC INSTITUTE
In partial fulfillment of the requirements for the
Renewable Energy Burning Cookstove and Surface Environment
By
Matthew Goon
Brian Grabowski
Nicholas Knight
Michael Jenkins
June 4, 2012
Approved
Prof. M.S. Fofana, Advisor
Mechanical Engineering Department
Justin Mathews
Abstract
The purpose of this major qualifying project is to design and implement an electrical
control system into a wood burning stove to increase its safety and efficiency.
Measures
implemented to increase safety include extra thermal insulation in key areas to prevent contact
burns, and an embedded system designed to monitor the stove and its surroundings.
The
embedded system utilizes gas and temperature sensors that can notify its user of hazardous
conditions via alarms and flashing lights. It is within the scope of this project to design an electromechanical system capable of automatically regulating the burner’s heat energy output. The
design calls for a processor that is programmed to control the combustion box’s air intake through
a series of feedback loop of temperature sensors, mechanical linkages, and DC motors. Overall
efficiency of the stove is improved through the implementation of non-catalytic combustors to
reduce emissions and increase fuel efficiency by inducing a more complete combustion cycle.
Other features include an automated emergency shut-off mechanism to reduce the risk of kitchen
fires and dangerous levels of toxic fumes. Mechanical features include a modular design allowing
for interchangeability between various types of heating elements, including electric coils and oil
burners. Adaptability is quantified by the stove’s ability to combust various fuels including wood,
coal, biomass, and kerosene while providing the additional option of utilizing electricity from a
grid. Furthermore, the batteries that power the embedded system are designed with an automatic
recharging circuit. Voltage can be generated from the combustion process by creating temperature
differences across the plates of a Peltier junction. Proper implementation of the features from
these designs will increase functionality while dramatically improving on the safety and efficiency
of antique cooking stoves. The versatility and modularity of these concepts can influence the
future of cookstove design and design considerations.
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Table of Contents
Abstract ............................................................................................................................................... i
Table of Contents............................................................................................................................... ii
List of Figures .................................................................................................................................... v
List of Tables .................................................................................................................................... vi
Acknowledgements ......................................................................................................................... vii
Chapter 1: Development of a Renewable Energy Cookstove ............................... 2
1. Introduction ................................................................................................................................ 2
Chapter 2: Evolution of Cookstove Design and Environmental Effects .............. 4
2.1 Introduction .............................................................................................................................. 4
2.2 Evolution of Stoves .................................................................................................................. 7
2.2.1 Three Stone Fire ................................................................................................................ 7
2.2.2 Lorena Adobe Stove .......................................................................................................... 9
2.2.3 Rocket Stove ................................................................................................................... 11
2.3: Safety of the Stove ................................................................................................................ 13
2.3.1: Wood Stove Fire Risks................................................................................................... 13
2.3.2 Causes of Cooking Fires ................................................................................................. 14
2.3.3 Costs of Cooking Fires .................................................................................................... 15
2.3.4 Cooking Fire Prevention ................................................................................................. 16
2.4: Global Warming ................................................................................................................... 18
2.4.1 Wood Stove Environmental Risks .................................................................................. 21
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2.4.2 Catalytic Converters and Non-Catalytic Combustors ..................................................... 22
2.5 Wood Stove Health Risks ...................................................................................................... 23
2.6: Consumer Demographic ....................................................................................................... 25
2.7 Examples of Stoves ................................................................................................................ 29
2.7.1 Antique Stoves ................................................................................................................ 30
2.7.2 Hybrid Stoves .................................................................................................................. 32
2.8: Electrical Controls ................................................................................................................ 33
Chapter 3: Renewable Energy Cookstove Design ................................................ 38
3.1 Design Specifications............................................................................................................. 38
3.2 Hybrid Stove Test .................................................................................................................. 39
3.3 Stove Design .......................................................................................................................... 44
3.4 Final Design Drawings .......................................................................................................... 47
3.5 Electrical Design Overview ................................................................................................... 50
3.6 Implementation ...................................................................................................................... 51
3.6.1Processor .......................................................................................................................... 51
3.6.2 Power System .................................................................................................................. 52
3.6.3 Sensor Inputs ................................................................................................................... 54
3.6.4 Outputs ............................................................................................................................ 55
3.7 Design Analysis ..................................................................................................................... 57
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Chapter 4: Concluding Remarks ........................................................................... 60
4.1 Mechanical Design................................................................................................................. 60
4.2 Electrical System Design ....................................................................................................... 61
References ................................................................................................................ 64
Appendices ............................................................................................................... 67
Appendix A: Code for the Stove Controls ................................................................................... 67
Appendix B: Burn Test #1 3lbs Dura Flame Log ........................................................................ 72
Appendix C: Burn Test #2 9 lbs. Dry Logs ................................................................................. 73
Appendix D: How to Build the Improved Household Stove ....................................................... 74
Appendix E: Authorship .............................................................................................................. 92
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List of Figures
Figure 1: Modern Wood Stove [18] .................................................................................................. 4
Figure 2: Older Design [2]................................................................................................................. 5
Figure 3: Safe Stove [3] ..................................................................................................................... 6
Figure 4: Three Stone Fire [13] ......................................................................................................... 7
Figure 5: Energy Output of Three-Stone-Fire [13] ........................................................................... 8
Figure 6: Lorena Adobe Stove [5] ..................................................................................................... 9
Figure 7: How a Rocket Stove Works [8] ....................................................................................... 11
Figure 8: Standalone Rocket Stove [15] .......................................................................................... 12
Figure 9: A fire caused by a wood stove [23].................................................................................. 13
Figure 10: Fires caused by cooking over past 30 years [1] ............................................................. 14
Figure 11: Source of fire ignition [1]............................................................................................... 15
Figure 12: Flowchart of Device Logic System [6] .......................................................................... 17
Figure 13: Ash Pan Assembly [11].................................................................................................. 18
Figure 14: Change in Gases Levels over Time [18] ........................................................................ 20
Figure 15: Change in Average Global Temperature [18] ................................................................ 21
Figure 16: Relative Emissions of Fine Particles [21] ...................................................................... 22
Figure 17: A common catalytic converter [20] ............................................................................... 23
Figure 18: Non-Catalytic Wood stove (right), Catalytic Wood Stove (left) [20]............................ 23
Figure 19: Effect of Smoke on lungs [22] ....................................................................................... 24
Figure 20: The Patsari Cookstove ................................................................................................... 26
Figure 21: The Big Bear Sheepherder ............................................................................................. 30
Figure 22: The Sheepherder ............................................................................................................ 31
Figure 23: Combination wood, coal, electric stove ......................................................................... 33
Figure 24: Thermometer, pot, and lid arrangement for experiment on range top ........................... 41
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Figure 25: Hybrid Stove Design Top View ..................................................................................... 44
Figure 26: Isometric view of hybrid cookstove design with front and side panels removed .......... 45
Figure 27: View of Non - Catalytic Combustor Tubing in the Top of the Burn Box ..................... 46
Figure 28: Isometric view of stove with drawers pulled out ........................................................... 47
Figure 29: Final Design Drawing .................................................................................................... 48
Figure 30: Exploded View of Final Design ..................................................................................... 49
Figure 31: Circuit Design Block Diagram ..................................................................................... 51
Figure 32: Olimex 40 Pin Development Board and USB Pocket Programmer .......................... 52
Figure 33: MQP Goal Block Diagram ............................................................................................ 62
Figure 34: Parts List for MQP parts .............................................................................................. 63
List of Tables
Table 1: Major Greenhouse Gases [17] ........................................................................................... 19
Table 2: Catalytic Converters vs. Non-Catalytic Combustors ........................................................ 23
Table 3: Water boiling test results of improved wood cookstove (Patsari) and open-fires............. 27
Table 4: Fuel wood and energy consumed for a standard cooking task .......................................... 28
Table 5: Kitchen Performance Tests ............................................................................................... 29
Table 6: The Big Bear Sheepherder Dimensions ............................................................................ 31
Table 7: The Sheepherder Dimensions ............................................................................................ 32
Table8: Part Numbers of Design Components ................................................................................ 49
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Acknowledgements
Thank you Professor Mustapha Fofana, without whom, this project would not have existed.
Special thanks to Professor Robert C. Labontѐ, your guidance and advice was invaluable
throughout the execution of this project. Ramsey Abouzahra, thank you for your assistance with
troubleshooting our processor during the programing phase of the embedded system. Finally, we
would also like to acknowledge the members of Worcester Polytechnic Institute’s staff in both the
Mechanical Engineering and Electrical & Computer Engineering Departments who made this
project possible.
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Chapter 1: Development of a Renewable Energy Cookstove
1. Introduction
Throughout the world, approximately two million annual deaths are attributed to smoke
inhalation due to poorly ventilated or unventilated combustion used for cooking. These deaths are
most heavily concentrated in third world nations as well as impoverished regions. However, they
are all completely avoidable and preventable. Cooking conditions for these areas usually involves
dwellings completely filled with smoke from an open fire. These unhealthy conditions endanger
the family still inside. Current cookstove technology ranges from three stones placed around an
open fire to hold a pot, to homemade wood stoves, which are usually unsafe due to poor
ventilation and thermal insulation. The inefficiency of these systems along with improper fuel
selection results in incomplete combustion, which generates millions of tons of carbon emissions
each year. Carbon emissions produced by people cooking with solid fuels is still a large
contributor to the increasing amounts of greenhouse gasses in our atmosphere. Overall, a large
portion of the world still does not have the safe, clean, and energy efficient standards of cooking
as more developed nations are accustomed to. This brings about a negative impact on general
health, as well as the environment.
The goal of this project was to develop an affordable cook-stove that is safe, reliable,
energy efficient, and adaptable to various renewable and conventional fuel sources. The end user
of this product could only afford to pay a few hundred dollars on a commercial wood burning
cookstove; therefore the product was to be designed for a cost of under $500. The product needed
to be resilient and maintainable, utilizing intuitive design and standard components; because the
end user could not afford to buy a new stove should the cook-stove fail. The product needed to
monitor levels of harmful emissions in the dwelling and alert the user of hazardous conditions.
The cook-stove was also properly thermally insulated, with the exception of the heating element,
2
so the user or a child would not be severely burned upon making contact with the outer surfaces of
the stove. The cookstove needed to be well ventilated to prevent harmful emissions from entering
the dwelling. The product needed to induce more complete combustion than current stoves to
reduce harmful emissions and increase efficiency. Because electricity is an energy source limited
to developed nations, and consumer batteries are an expensive and inefficient, the cook-stove
needed to be capable of powering its system without a readily available electrical source. Oils and
natural gas are expensive fuel sources with limited availability to the targeted end user. Therefore,
the cook-stove needed to be capable of combusting the various fuel sources available to a region,
including bio-mass, wood, wood pellets, and fire logs. Overall, this product will save the end user
money by reducing fuel usage and increasing energy efficiency. Affordability was achieved by
proper selection of materials and components, as well as developing methods for reducing
operating costs for the user.
Safety was be achieved by reducing fire and injury hazards,
monitoring harmful gas levels, and implementing an effective ventilation design. Fire and injury
hazards were reduced by proper insulation of the cook-stove. Hazardous emissions will be
monitored through an embedded computer system. Effective ventilation was achieved by proper
design of the cook-stove flue. Energy efficiency was achieved by increasing complete combustion
in the firebox, which will also reduce harmful emissions. Reliability was achieved with a sturdy
structural design that included resilient materials, and reliable electrical components.
In chapter 2, we discuss current cook-stove designs, emissions data of various fuel sources,
as well as the electrical components of the embedded safety and control system. In chapter 3, we
discuss the final design, implementation strategy, design analysis, and results of various
components of the cook-stove. Finally, chapter 4 discusses our conclusions, along with our
recommendations for improvement and future work.
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Chapter 2: Evolution of Cookstove Design and Environmental Effects
2.1 Introduction
The main requirements for our stove are that it is a wood or oil burning stove, that it is
safe, affordable, environmentally friendly, and comparable in efficiency to modern stoves. The
most innovative feature of this stove will be that people will not be exposed to an open flame at
all. This will drastically cut down on the number of house fires and the deaths related to those
fires. A few possible designs can be seen in this chapter.
Figure 1: Modern Wood Stove [18]
This modern word stove in Figure 1 is similar to the configuration and size of the stove
that the MQP group intends to build. The main advantage of a side-by-side combustion chamber
and oven like the one in Figure 1 is that it heats the oven fully, while not taking up too much
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vertical space in the kitchen. It also heats one side of the stovetop to a very high temperature while
the far side will be a lower temperature for controlled cooking without the use of electric controls.
There is also a heat exhaust vent on the front of the stove that can be used to heat the house.
Figure 2: Older Design [2]
The Bake’s Oven Stove from Antiquestoves.com shown in Figure 2 is an older version of a
cook stove. The combustion chamber is between the cook top and the oven. This stove has an
alternative location for the burn box that saves horizontal space. Key features are firebricks that
increase thermal mass to stabilize the temperature and protect the firebox and an ash lip that
prevents hot coals from dropping on to the floor. Important dimensions of the Baker’s Oven Stove
from Antiquestoves.com are of the firebox and oven 13”w x 11”d x 14”h and 14”w x 13”d x 11”h
5
respectively [2]. The Baker’s Oven Stove puts out 30,000 BTUs and can proved heat for 700-900
sq. ft. of living space.
Figure 3: Safe Stove [3]
This stove seen in Figure 3 is from Sideros S.p.a and has safety features that can be
implemented in the design for this project. One feature is a cover that goes over the hot cooking
surface of the stove. This protects the user from accidentally burning themselves on the hot
surface. There is also a tray at the bottom of the stove that allows the user to easily remove the ash
and debris that did not burn [3].
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2.2 Evolution of Stoves
The evolution of stoves goes over the increasing complexity and sophistication of stoves
and cooking environments of stoves in developing nations. The purpose of learning this is to
explore the different types of cooking methods used around the world. This relates to the purpose
of the MQP because part of the project is to learn about the cooking conditions in developing
nations. Knowing the cooking conditions in these countries will also give a good background to
know why indoor air pollution and global warming are a growing problem due to cooking.
2.2.1 Three Stone Fire
The three-stone-fire is the most primitive version of a cooking fire that still resembles a
stove seen in Figure 4.
Figure 4: Three Stone Fire [13]
The concept behind the stove in Figure 4 is that three stones of equal height can be used to balance
a pot or pan over a fire. This method is dangerous because people using these cooking fires are
7
directly exposed to open flames. Another dangerous aspect of this method of cooking is that the
stones used as support for the pot aren’t always stable resulting in the pot falling off the stones
potentially injuring people. Air toxicity can be very dangerous when people use these stoves
inside. This method also has potential to start house fires because of the open nature of the
cooking flame [13].
Aspects of the three-stone-fire that make it inferior to most other methods that are not
related to safety are that it wastes a lot of fuel and it generally cannot cook for a lot of people. The
fuel is wasted due to incomplete combustion of open flames. Most of the energy is lost to the
surroundings. A diagram depicting the energy output of a three stone fire can be seen in Figure 5
Figure 5: Energy Output of Three-Stone-Fire [13]
When a fire is open like it is in a three-stone-fire the fuel isn’t under enough pressure to
completely combust. Wasting fuel makes using this method more costly and wastes the time of the
person using the fire. The reason why a three-stone-fire is ineffective for large groups of people is
8
inherent in its design. The setup is intended to cook one pot over a fire. Unless the pot is extremely
large, this method makes it a lot more time consuming to cook for a large family [13].
2.2.2 Lorena Adobe Stove
The next development to improve stoves is the Lorena adobe stove that is widely used in
Central America. It is a stove made of mud and sand packed together to create the stove seen in
Figure 6.
Figure 6: Lorena Adobe Stove [5]
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Improvements over the three-stone-fire technique are that this stove has a chimney, which
prevents most of the indoor air pollution. This stove design also contains the heat of the fire much
better than the previously described stoves because it isn’t a completely open fire design.
Although there are improvements in safety, the Lorena adobe stove is less efficient than the threestone-fire. This is because the amount of material that is used for insulation acts as a heat absorber
sometimes called thermal mass. The stove uses more fuel than the three-stone-fire in order to cook
the same amount of food. Even though this stove is less efficient, it is still safer than having an
open flame [15]. Figure 6 is of a well-designed and built Lorena cook stove.
The stove in Figure 6 has metal burners and a metal chimney. Figure 6 also shows the
stove’s smooth sides and clean cut edges. Many lower cost versions of this stove are very crude,
and the material is composed of any dirt and sand that can be found in the area. Also, the burners
are sometimes made to fit exactly one pot, or be covered by a single pan that is always used on
that burner.
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2.2.3 Rocket Stove
The rocket stove is a much cleaner stove than both the Lorena adobe stove method and the
three-stone-fire. The rocket stove has higher ventilation and more insulation than both the
previous methods. The wood in the fire burns hotter, which causes the smoke leaving the chimney
to be cleaner with fewer unburned particles. A study of a program in Southern Africa that sold
rocket stoves to residents of the Malawi had great results. The conclusion was the most
encouraging part of the program, “Given that wood savings are measured at 70% per stove there is
no doubt of the financial benefit to the users. Nor is there any doubt that immediate pollution is
reduced” [12]. Figure 7 shows the components and operation of a rocket stove.
Figure 7: How a Rocket Stove Works [8]
The air is vented in through the opening that allows wood to be loaded. Fuel options are
generally any biomass that is available in the area, but preferable dry sticks or wood chips. After
being loaded, the wood will either slowly move down a chute, or need to be manually pushed into
the combustion chamber. Once in the combustion chamber the wood is fanned by the primary
vent. The smoke then rises up the chimney and new air is introduced into the system creating a
11
secondary combustion point. This secondary combustion decreases the amount of pollutants in the
exhaust [15].
Figure 8 is a stand-alone rocket stove called “Darius”.
Figure 8: Standalone Rocket Stove [15]
An interesting feature of the rocket stove is that it can be used in conjunction with the
Lorena adobe stove. This improves the efficiency of the stove. When the Lorena adobe stove is
designed with a rocket stove combustion chamber it can become a lot more efficient, and have
much cleaner emissions, while still having the extra safety effects. Currently, a modified Lorena
stove seems to be the best solution for people living in developing nations.
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2.3: Safety of the Stove
Safety is a major concern when it comes to wood burning stoves. Fire, health, and
environmental risks all have to be taken into consideration when designing a stove. This section
will discuss the risks and hazards of operating a wood-burning stove.
2.3.1: Wood Stove Fire Risks
Wood is a highly flammable material. When burned, there is always the opportunity for
accidental fires to happen. These fires can result in loss of property, injury, or life. Preventing
accidental fires is a matter of safety oriented design and user responsibility. Figure 9 shows the
results of a fire caused by a wood burning stove.
Figure 9: A fire caused by a wood stove [23]
Approximately 36% of structure fires reported in the US originate in the kitchen.
According to the National Fire Protection Association, from 2004 to 2008 there were on average
154,700 fires a year involving cooking equipment. These fires are responsible for property
13
damage, injury, and even death. Common causes of kitchen fires include unattended cooking
equipment, misuse of cooking appliances, combustible material placed close to heating appliances,
and the ignition of food products used in cooking. The number of reported structure fires caused
by cooking from 1980-2009 is shown below in Figure 10 [1].
Figure 10: Fires caused by cooking over past 30 years [1]
From the data in Figure 10 it can be seen that over the last thirty years structure fires have
remained consistently over 100,000 a year and in some years up 160,000. This is an amazing
statistic to look at when people assume that homes have been getting safer over the years. Looking
at this chart this assumption is clearly not true and home structure fires from cooking equipment
are still problem.
2.3.2 Causes of Cooking Fires
Ignition of grease, oil, and fat are a common cause of cooking fires. These materials have
a natural tendency to ignite when exposed to high heat for an extended period of time. The most
common heating element involved in cooking fires is the range or cooktop. This is mainly due to
use of open flame burners and the lack of containment mechanism if a fire were to ignite. Fires
originating from a cooktop are responsible for 58% of all cooking fires. These fires are also
statistically the most dangerous. 77% of injuries and 84% of deaths resulting from kitchen fires
14
originated on a cooktop. The second most common origin of cooking fires is the oven. Oven fires
cause 16% of all cooking fires, but are only responsible for 4% of deaths [1]. Ignition sources for
kitchen fires in shown in Figure 11.
Figure 11: Source of fire ignition [1]
2.3.3 Costs of Cooking Fires
Fires caused by cooking are usually small and confined to the kitchen. Therefore they
generally do not cause as much damage to a home or business when compared to fires that
originated in other locations. Kitchen fires cause on average $4,736 in property damage. This can
be compared to the average cost off all structure fires, which is about $14,252. One reason for this
is that almost all kitchen fires are confined to the room of origin [1].
Injuries associated with cooking fires occur at about the same rate as all structure fires.
Cooking fires result in approximately 32 injuries per 1,000 fires. Death occurs in approximately
15
half as many cooking fires when compared with all structure fires. The rate of death caused by
cooking fires is 2 per 1,000 fires. Structure fires in general result in a fatality in 5.1 per 1,000
cases [1].
2.3.4 Cooking Fire Prevention
In a commercial setting such as a restaurant, fire suppression systems are required to
preventing the spread of fires caused by cooking. However, these systems are very expensive and
not commonly found in residential kitchens. The following are patents for devices designed for
fire prevention in residential cooking appliances.
Fire safety device for stove-top burner
Stovetop burners are responsible for almost 60% of fires caused by cooking equipment [1].
Many of these fires were caused by leaving the stove unattended. A patent was filed in 1997 that
aimed to prevent these fires from starting. It is called “Fire Safety Device For Stove-Top Burner.
The device relies on electronic sensors to determine if power should be cut off to stove for safety
reasons. One of the main features of the device is its ability to determine the temperature of the
cooking surface. If the device detects a temperature at an unsafe level, the burners on the stove
are automatically shut off. This only happens if the user is not present. A motion detector
deactivates the sensor if when a person is interacting with the stove. The flowchart in Figure 12
displays the devices logic system.
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Figure 12: Flowchart of Device Logic System [6]
Ash Storage Safety
A common cause of house fires due to wood stoves is improper ash removal and storage.
Approximately 9,070 fires are caused each year by improperly discarded ashes. Coals can stay hot
for up to four days after use. Simply emptying hot coals into a plastic bag is a common way to
start am accidental fire. Hot ash must be kept in a secure metal container away from flammable
materials in order to be safe.
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Figure 13: Ash Pan Assembly [11]
The invention shown in Figure 13 allows the user to safely remove hot ash from a wood
stove without having to directly handle the hot ash. The ash is securely confined within a portable
container that can be removed from the stove. This container can be stored in a safe place until
the ash has cooled. The ash is then safely removed. This invention both prevents injury from
handling hot ash and accidental fires started by improper storage of hot ash [11].
2.4: Global Warming
Global warming is sometimes called the “greenhouse effect” because pollutant gases that
trap heat in the atmosphere. These gases that are the biggest contributors to the “greenhouse
effect” are carbon dioxide, water vapor, methane, nitrous oxide, chlorofluorocarbons. Excluding
Chlorofluorocarbons, these gases occur naturally and are necessary for Earth to stay warm, but
they need to be kept within a certain range in order to support life. If these gas levels dropped, the
earth would be too cold, and if they get too high too much heat will stay trapped.
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The way that greenhouse gases trap heat is through reflecting heat from the sun. Of the
light coming to earth, about 26% is reflected back to space by the atmosphere, 19% is absorbed in
atmospheric gases, 4% is reflected from earth’s surface, and about 51% of the energy from the sun
makes it all the way to the surface of the earth. Once heated, the earth’s surface radiates energy by
heating air. Some of this radiation makes it to space, but with an increase of greenhouse gases, a
lot of it to get reflected back to the surface. A chart of the major greenhouse gases and their
increase over the years is shown below in Table 1[17].
Table 1: Major Greenhouse Gases [17]
Climate models suggest that between the years 2030 and 2060 greenhouse gas levels will
have doubled pre-industrial levels. The same models also suggest that if current annual emission
levels remain constant the greenhouse gas levels will double pre-industrial levels by 2100. The
result of the greenhouse gas levels rising will increase the temperature of the planet anywhere
from 2-5° Celsius in the next fifty years and 3-10° Celsius. This type of temperature change can be
compared to the difference in temperature between the last ice age and today [18].
When temperatures are higher, plant absorbs less carbon dioxide. When regions have
longer warm seasons, permafrost can melt, and in some cases release methane pockets. The result
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of these types of reactions to global warming could increase the global temperature by an
additional 1-2° Celsius [17].
One result of the impending massive climate changes is a redistribution of global heat that
will change regional weather patterns and climates. Another result will be that the water cycle will
intensify. This means that regions that have droughts will have worse droughts, and regions
experiencing drought conditions will increase between 1 and 30 % [18].
Figure 14: Change in Gases Levels over Time [18]
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Figure 15: Change in Average Global Temperature [18]
Figure 14 and Figure 15 show the correlation between greenhouse gases and the global
average near-surface temperature. The two figures follow a very similar curve trending upward.
This trend seems to prove that there is a direct relationship to the concentration of greenhouse
gases and the average global temperature. If this data is accurate there is a serious need to reduce
emissions, or the world may be permanently affected by humans.
2.4.1 Wood Stove Environmental Risks
Wood stoves release a considerable amount of pollutants into the environment. Pollutants
released by wood stoves include fine particulates, nitrogen oxides, sulfur oxides, carbon
monoxide, volatile organic compounds, dioxins, and furans. Compared to stoves that use other
types of fuel sources, wood stoves release a lot more pollution. The figure below shows this.
Emissions of fine particles are measured in lbs./MMBtus of heat output [20]. Figure 16 shows that
EPA certified woodstoves release about three times fewer emissions than uncertified woodstoves.
Pellet stoves release even less emissions than EPA certified stoves (0.49 vs. 1.4). However, all of
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these options are not nearly as clean burning as oil or gas. Oil only releases 0.013 lbs./MMBtus of
fine particles. Gas is the cleanest burning fuel shown at 0.0083 lbs./MMBtus.
Figure 16: Relative Emissions of Fine Particles [21]
2.4.2 Catalytic Converters and Non-Catalytic Combustors
A catalytic converter is a standard future on all modern automobiles. Catalytic converters
are a major factor in reducing toxic exhaust emissions. Catalytic converters are also commonly
found on generator sets, forklifts, mining equipment, trucks, buses, trains, airplanes and other
engine-equipped machines. Widespread use of converters first started in 1975 automobiles. The
most modern catalytic converter is a three way converter [20]. A catalytic converter is shown
below in Figure 17. Figure 18 shows a side-by-side comparison of wood stoves, one with a
catalytic converter (left) and one with a non-catalytic combustor (right).
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Figure 17: A Common Catalytic Converter [20]
A comparison of catalytic and non-catalytic combustors is shown in Table 2 below.
Table 2: Catalytic Converters vs. Non-Catalytic Combustors
Catalytic Combustor
Higher efficiency than non-catalytic
Catalytic converter must be replaced as often as
every 2 years
Longer burn times
Enables the use of features such as top-loading
Non-Catalytic Combustor
Lower cost
No catalytic converter to replace
Add to firebox insulation
Requires less maintenance than catalytic stoves
Figure 18: Non-Catalytic Wood stove (right), Catalytic Wood Stove (left) [20]
2.5 Wood Stove Health Risks
People with chronic lung diseases are at increased risk of negative health effects from
wood burning stoves. This includes conditions such as COPD, emphysema, or asthma. Particulate
matter, small particles released from the burning wood, can be inhaled into the lungs and cause
problems. Particulate matter, when inhaled, can lead the development of health problems such as
23
cancer. Some studies show that inhale smoke from as wood stove is just as bad as smoking
cigarettes [24].
Children are especially vulnerable to the toxic emissions of wood stoves. There is an
increase in cases of ear infection in children who live in areas with wood stoves. Children also
breathe in more air than adults in proportion to their weight. This causes air pollution from wood
stoves to have a greater effect on them. The Figure 19 shows difference between a healthy lung
and one that is inflamed [22].
Figure 1917: Effect of Smoke on lungs [22]
Although children breathe in more air than adults the extent of exposure is a major factor.
Women are exposed to the indoor air pollution for a much longer time than children because they
are generally in charge of taking care of the household in developing nations. This extended
exposure to indoor air pollution has a dramatic effect on women in developing nations.
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2.6: Consumer Demographic
The consumer demographic of the cookstove is geared toward developing nations. Mexico
has made long strides in improving the well-being of rural housewives and their children by
investing into the development of Patsari stoves. Professors from the National Autonomous
University of Mexico (UNAM) and University of California at Irvine (UC Irvine) created an
energy evaluation of the Patsari stove using three different efficiency tests.
Mexico has made advances in cookstove technology for the improvement to the thermal
efficiency of cooking and the respiratory health of the user and family. Professors from UNAM
and UC Irvine have compared three different types of cookstoves: a traditional and simple three
stone fire, a clay U-type cookstove, and the Patsari cookstove. The Patsari cookstove is an
efficient wood-burning stove developed by the Interdisciplinary Group on Appropriate Rural
Technology and the Center for Ecosystems Research in UNAM. The name of the Patsari stove
comes from the Purhepecha language meaning “the one that keeps” for its intent to tend to the
salutary, environmental, and economic future of the users. A sample size consisting of rural
households in the state of Michoacán, Mexico was selected to replace traditional stoves with a
Patsari cookstove. The three different tests performed to evaluate the efficiency of the cookstoves
are the water boiling test (WBT), controlled cooking test (CCT), and the kitchen performance test
(KPT). Below are pictures of the Patsari cookstove inside of a rural household and a crosssectional view of the cookstove.
25
Figure20: The Patsari Cookstove
The water-boiling test is a three part evaluation to determine the time and fuel needed to
boil three liters of water. The first evaluation of the WBT is the high-power boiling test with a set
amount of fuel and the starting conditions at room temperature. The second evaluation is a similar
process, but the starting conditions occur right after the cold start test when the stove is still warm.
The third evaluation is a low-power simmering phase performed after the high-power tests to heat
water to 3°C under the boiling point for 45 minutes. The WBT determines thermal efficiency (H),
firepower (P), and specific fuel consumption (SC) mathematically derived from three equations
derived below.
𝐻=
𝐶 × 𝑊𝑤 �𝑇𝑓 − 𝑇𝑖 � + ∆𝐻𝑣𝑎𝑝 × 𝑊𝑣𝑎𝑝
𝑓𝑑 × 𝐿𝐻𝑉
𝑃=
𝑓𝑑 × 𝐿𝐻𝑉
60�𝑡𝑓 − 𝑡𝑖 �
𝑆𝐶 =
𝑓𝑑
𝑊𝑤𝑓
In the thermal efficiency (H) equation; C is the specific heat of water, Ww is the mass of
the water in the pot, (Tf – Ti) is the change in water temperature, ΔHvap is the latent heat of
vaporization of water, Wvap is the amount of evaporated water, ƒd is set amount of fuelwood and
26
LHV is the lower heating value. Regarding the firepower (P) equation, (tf – ti) is the time elapsed
for the duration of the water boiling test. Wwf is the mass of the boiled water in the specific fuel
consumption (SC) equation. Table 3 displayed below, correlates the results from the WBT of three
different cookstoves in three separate starting conditions.
Table 3: Water boiling test results of improved wood cookstove (Patsari) and open-fires
The controlled cooking test is a stove performance evaluation of cooking handmade corn
tortillas. Measured factors of the CCT include the moisture levels of the fuel wood, ambient
temperature, elapsed cooking time and the time required to light the firewood. The CCT equation
for the specific fuel consumption (SC) is different from the WBT equation and derived below.
𝑆𝐶 =
𝑓𝑑 − �𝐶ℎ �
𝐻𝑜𝑓𝑤
𝐻𝑜𝑐ℎ
��
1 𝑘𝑔 𝑜𝑓 𝑡𝑜𝑟𝑡𝑖𝑙𝑙𝑎𝑠
27
In the CCT, specific fuel consumption equation; Ch is the amount of remaining charcoal, Hofw is
the enthalpy of the fuel wood and Hoch is the enthalpy of the charcoal. Table 4 compare the energy
and mass of fuel wood required to cook tortillas.
Table 4: Fuel wood and energy consumed for a standard cooking task
The third evaluation performed is called the kitchen performance test (KPT) designed to
test the stove’s performance under the conditions of the local communities. During the KPT study,
600 Michoacán households were selected for the assessment of the Patsari stove’s effect on
respiratory health. The KPT was a field test spanning over a year of observations throughout
three-phase test cycle. Phase 1 consisted of evaluating a base of 43 households using just fuel
wood (23 households) or a mix of fuel wood and liquid propane gas (20 households) in a
traditional U-type stove. Phase 2 consisted of evaluating 32 households (21 households using just
fuel wood and 11 using a mix of fuels) with a Patsari stove installed six months after phase 1.
Phase 3, occurring a year after the beginning of phase 2, evaluates 14 households (8 households
using just fuel wood and 6 using the mixed fuels) on the average fuel and energy consumed
between the different types of stoves. Table 4 above displays the KPT data before and after the
28
implementation of the Patsari stove into Michoacán households. Table 5 is a kitchen performance
test evaluating the difference of fuel wood consumption between households just using fuel wood
and households that use a mix of fuel wood and LPG.
Table 5: Kitchen Performance Tests
The kitchen performance test compares the energy consumption between using only fuel
wood and using a mix of fuel wood and liquid propane gas. The traditional U-shaped stove
requires more fuel wood and consumes more energy to perform the same cooking task as the
energy-efficient Patsari cook stove. Users of the Patsari cook stove, adopting a mix of fuel wood
and liquid propane gas, required less weight in fuel wood and reduced the overall energy
consumed compared to a Patsari stove solely burning fuel wood. The U-shaped, open fire stoves
were proven to be detrimental to respiratory health and required the per capita energy
consumption of over 67% more than the energy used by the Patsari cook stove. The per capita
energy consumption of the hybrid Patsari stove decreased to almost 74% in households that had a
supplementary used of liquid propane gas.
2.7 Examples of Stoves
The examples of stoves in this section is intended to represent the different ways a stove
can be modified in order to make it safer and burn cleaner. It will also help to visualize the variety
of stoves that are available and how they can be specialized for particular functions. The stoves are
29
also similar to the type of stove that is being designed to this project because the safety features
and dimensions.
2.7.1 Antique Stoves
Figure 21: The Big Bear Sheepherder
The Big Bear Sheepherder ® household cook stove by Transocean Ltd, seen in Figure 21,
is an example of a simply designed stove that is incredibly functional. The oven is large enough to
cook a meal large enough for an average family without the use of any electricity. The fire box can
burn both coal and wood and can heat a space 1850- 2100 square feet. The stovetop is made of
5/16 inch plate steel and the walls are ¼ inch plate steel. The glass for the doors is made of
pyroceram glass. There is a 4.2 gallon water reservoir on the side so that hot water is always
available. The total weight for this stove is 370 lbs. which is rather heavy, but is expected when
30
using plate steel for the construction of the whole stove. The dimensions of the Big Bear
Sheepherder ® are in Table 6.
Table 6: The Big Bear Sheepherder Dimensions
Parameter
Cooking
Surface
Fire Box
Oven Size
Wall
Thickness
Top
Thickness
Vent
Depth
Width
Height Diameter
(Inches) (Inches) (Inches) (Inches)
34
34
12
18
0.25
12
14
18
14
0.3125
6
Figure 22: The Sheepherder
31
Table 7: The Sheepherder Dimensions
Parameter
Total
Cooking
Surface
Fire Box
Oven
Size
Wall
Thickness
Top
Thickness
Vent
Depth
Width
Height Diameter
(Inches) (Inches) (Inches) (Inches)
25
16
19
28
14
20
12
13
16
12
9
0.25
0.3125
6
Another oven by Transocean Ltd. is the Sheepherder®, seen in Figure 22. This oven is
essentially the original version of the Big Bear Sheepherder ®. The oven will heat over 800 square
feet and is a size that is manageable enough to just be used as a heating oven on a regular basis
and only used for cooking in the event of extend power outages. The dimensions for The
Sheepherder stove can be seen in Table 7. The fuel that can be used in this oven is generally wood
or coal. The size of this oven is more similar to the size of the oven that is being designed in this
project and will be a good comparison during the design process.
2.7.2 Hybrid Stoves
Hybrid stoves are stoves that can cook food through the use of multiple energy sources.
These can include any combination of wood, gas, electric, coal, bio-fuel, etc… Hybrid stoves
have many advantages over single energy source stove. For example, a wood/electric stove would
still be operational if electrical power was lost. The ability to have a wood back up option is very
useful in areas subject to frequent power disruptions.
The stove shown in the Figure 23 can burn coal and wood. It can also run on electricity.
32
Figure 23: Combination wood, coal, electric stove
The stove in Figure 23 is the most similar to the stove used in the tests for this project because it is
a woodstove electric stove. This is an intermediate development in stoves when electricity wasn’t
the most reliable source of energy. The ability for people to decide whether or not to use
electricity made this stove a popular choice in the 50’s.
2.8: Electrical Controls
The electrical portion of this project will ultimately function as a monitoring, warning, and
control system. This portion of the project is necessary to improve the fuel efficiency as well as
the safety of the cook-stove. The system will achieve its goal of regulating burning temperatures
by monitoring temperatures of the inside and outside of the stove. By keeping track of the
temperatures the system will be able to regulate them by controlling a flue vent with a stepper
motor. The system will also be able to run off an outlet and use electric heating coils for stovetop
and oven cooking. The system will have LEDs as well as a buzzer to provide the user with
warnings about unsafe levels of harmful gasses around the stove. The system will also have an
LED to indicate there is combustion happening in the stove. The user will be able to adjust the
33
temperature of the stove with up and down arrow buttons. Finally the electrical system will have
an LCD screen to provide the user with some basic information such as temperature of the
cooktop, cooking timer and burning and igniter fuel indicators. Overall all of these features will be
necessary in order to make the stove as easy to operate as pushing a button and will ultimately
make the stove much safer and fuel-efficient.
The stove will be capable of working off of both burning materials as well as electricity. If
the consumer has access to electricity they can use the stove with the electrical coils for cooking
instead of burning materials. This will not only increase the output of more harmful gasses but
also decrease the time it takes to cook a meal since electrical coils are a lot faster than having to
wait for the heat of the burning chamber to heat the entire stove. These electrical coils will be
removable from the top of the stove and have metal heating plates underneath them that will be
heated by the burning of materials in the combustion chamber. By having electrical coils as well
as a combustion chamber increases the market for the stove to anybody who wants one since it
allows them to have the option to burn to heat the stove when electricity goes out. Overall having
a stove capable of working with both electricity and burning materials is a big part of what will
make a market for it.
The electrical system will have to be capable of running off a small amount of electricity
generated either by a small solar panel or the heat of the stove. The heat of the stove can be
converted into electricity in many different ways however; two ways have proven to be the most
feasible for this project. The first of the ways of converting the heat of the stove into electricity is
to use a Sterling engine that would push a magnetic piston through coils of wire in a linear motion.
This idea came from the hand-powered flashlights that you shake to power. The second way of
converting the heat to electricity is to use an electrical device called a TEG (Thermoelectric
Generator) module, which is done by a process called the Seebeck effect that converts temperature
differences between two thermal plates directly into electricity. Solar panels are also a
considerable power option however solar energy is inconsistent and would therefore require some
34
battery storage that increases the overall price of the project. Finally we considered wind power
however this is both inconsistent and considerably more expensive than the other options
considered due to the high precision and tolerances in the manufacturing of the moving parts.
Overall The TEG module or solar panel would be preferable since they are solid-state devices.
Using a Sterling engine requires moving parts, which can mean breakdown of the stove and this is
not acceptable.
The system will use feedback loops in order to regulate temperatures inside the stove better
and better over time. This temperature control will be achieved by monitoring the differences
between the desired and actual temperatures as well as movement of the flue vent. As the system
runs for more uses and even as humidity changes it will be able to adapt by constant monitoring
and adjusting. The ventilation fan will also play a role in this by being adjustable in speed and thus
increasing the amount of air flowing out from the stove’s burning chamber.
In order to achieve all of the functionality described the system will need a microprocessor
both low power enough to be feasible for use with the small amounts of electricity that will be
generated by the stove. It will also have to be fast enough to achieve all the monitoring,
controlling and reporting in a timely fashion. Finally the microprocessor must be an affordable
model as the overall stove design cannot cost much more than $100 USD to the consumer. For
design purposes the an Atmel processor from the AT91 series will be used for building and testing
and can be switched out with a cheaper more energy efficient microprocessor when in a
manufacturing stage.
A few TEG modules have been looked into for powering the electrical system. The first of
the modules is the TEP1-1264-1.5. This module generates 8.6VOC (Volts Open Circuit) with a hot
side temperature of 230°C and cold side temperature of 50°C. This output voltage and an output
wattage of about 5.4W this should be plenty of power for the electrical system. The second
module that was looked into was the TEP1-12656-0.8 and the 0.6. These two modules produce
open circuit voltages of 8.7V and output wattages of 10.5 and 14.7 respectively. Overall the TEP135
1264-1.5 is the most cost effective for the application and thus should be the one that will be used.
This module costs around $60 for 1-10 units and around $14 for 1000+ units. This means that for
2 of these modules per stove, if needed, would be around $28 at production cost and translates to
about a $2.60 cost/watt minus the cost of burning fuel.
During the research into designing the electrical control and safety system turned up one
project that is similar and could be considered competition for our cook-stove design. The stove
found in researching was designed by a team of engineers in Nepal and is called the Batho Chulho
[2], which means smart cook-stove in Napalese. This stove uses a microcontroller control system
to control a flue vent in order to regulate airflow and control the burning temperature. The Batho
Chulho also has an LCD display with indicators to the cooking mode that consists of multiple
temperature ranges for the stove to be operating at and a knob to increase or decrease the heat of
the stove. The LCD panel also gives indications to cooking timer controlled by a cooking time
knob, igniter and burning fuels, as well as battery power level. Finally the system includes a power
LED that tells the user there is combustion inside the stove. The Batho Chulho stove is estimated
to cost around $37.50 and has an operating cost of around $0.15 per briquette which is estimated
to last for two cooking sessions for a family of 5 people plus another $1.50 and $1.00 every 2
months for a battery, and igniter fuel and lighter respectively [2].
Although the Batho Chulho is much less expensive than we are aiming to make our stove
for it does not include all of the added functionality and safety measures that our cook-stove will
have. The Batho Chulho lacks a harmful gas monitoring and reporting system, which is a very
important part of this project since one of the biggest concerns is to keep the user safe while they
are using the stove. The Batho Chulho also lacks exhaust the smoke from the stove any faster than
air wants to flow through it, whereas the stove that is being designed in this project will have a
small inline vent fan that will allow for quick exhausting of potentially harmful gasses when
needed. Also the Batho Chulho does not have an auto burning fuel feeder, which the project
group’s prototype will have, hopefully further increase the burning efficiency of the stove. Finally
36
the Batho Chulho is a much smaller stove than the prototype and is only a single burner with no
oven and can really only cook for a few people at a time. Overall, the prototype should have an
advantage over the Batho Chulho since it has some added safety features, more ways of increasing
the burning efficiency, and can cook for a large family whereas the Batho Chulho cannot.
37
Chapter 3: Renewable Energy Cookstove Design
3.1 Design Specifications
The following are design specifications that we intend to accomplish in this MQP.
1. The usable power output must be greater than 1.86 KW.
2. The device must cost under $500.
3. The device must be intuitive to operate.
4. The device must release fewer toxic emissions than comparable cookstoves used in thirdworld countries.
5. There must be no surfaces on the exterior of the stove that our capable of burning the user
with the exception of the cook top.
6. The device must alert the user of toxic conditions in the operating environment.
7. The device must have a system for monitoring toxic emissions.
8. A ventilation system that will prevent harmful gases from entering the living quarter of the
user must be developed.
9. The device must induce a more complete combustion than current similar cookstoves.
10. The device must run on multiple fuel sources including wood, gas, oil, coal, wood pellets,
and bio-fuel.
11. The device must be more energy efficient than current similar cookstoves.
12. The device must weigh less than 600lbs
13. The device must be capable of being transported by 3 or fewer adults using standard
moving equipment.
14. The user must not be exposed to any source of open flame.
15. The internal components of the device must only be assessable to a qualified technician.
16. The device must feature an intuitive control system.
17. The device must be able to be operated by an untrained adult.
38
18. The device must have a method for controlling oven temperature.
19. The burn box should be inaccessible to the user.
In the next section we will describe a test conducted by the group that is used to define design
specification #1.
3.2 Hybrid Stove Test
The usable power output of a stove is the amount of thermal energy that is able to be
applied towards heating or cooking over time. This attribute can be correlated to the idealized
verses actual energy output of a thermodynamic system. There are many factors that affect the
energy efficiency of a stove. This includes fuel selection, material selection in the stove as well as
the cookware, condition of the stove in terms of maintenance, overall design.
In the field of thermodynamics and heat transfer, a British Temperature Unit (BTU), is the
amount of energy required to raise 1 pound of water 1 degree Fahrenheit. A US pint is the volume
of water that has a mass of approximately 1 pound at room temperature. The following procedure
and materials were utilized to obtain baseline measurements for the actual usable power outputs
from an 8 inch (nominal) electric coil burner on a consumer electric range top into an aluminum
cooking pot.
Materials:
- 1 Aluminum cooking pot with glass lid
- Measuring Cup
- Scale
- Tap Water
- Cooking Thermometer
- Electric Range Top
- Clock
Procedure:
39
1.) Measure 4 US Pints (8 US Cups) of room temperature tap water to equate to 4 pounds and pour
them into the cooking pot, weigh and record mass of water.
2.) Turn on the electric range top to desired setting (Low, Medium, Med-Hi, or High)
3.) Allow for the electric coil burner to properly heat up.
4.) Place the thermometer into the water so its probe does not directly contact the bottom surface
of the pot, while allowing the gage to stick out of the pot. Place the lid on top of the pot to hold the
thermometer in place as seen in Figure 24.
5.) Record the Temperature reading on the thermometer as Tinitial.
6.) Immediately after recording Tinitial, Carefully place the pot onto the electric coil burner and
Record Time as t initial.
7.) Observe the temperature change of the water over time.
8.) When the water boils its temperature will reach approximately 212° Fahrenheit, record the
final time in minutes and seconds as t final.
- If the temperature of the water ceases to rise before boiling, record the final temperature as Tfinal
and the final time as t final.
9.) Turn off burner and allow pot to cool before removing.
10.) Repeat steps 1-9 for other available settings (Low, Medium, Med-Hi, or High)
11.) Analyze Results.
40
Figure 24: Thermometer, pot, and lid arrangement for experiment on range top
The difference between recorded temperatures in a predetermined mass of water can be
utilized to calculate the usable energy output of the heating element from the electric range top
into the aluminum cooking pot. In the case of this experiment, 4 US pounds was determined to be
an appropriate mass. In the equation below m is specific heat, ∆𝑇 is the change in temperature of
the water, and E is energy.
𝑚 ∗ ∆𝑇 = E
The difference between recorded temperatures in a predetermined mass of water over time
can be utilized to calculate the usable power output of the heating element from the electric range
top into the aluminum pot. The reasoning behind using a mass of 4 lbs. of water was to reduce the
magnitude of error that could be potentially induced into our analysis and calculations by
imprecise recording of times throughout the experiment. The new variables in the equation below
are ∆𝑡 the change in time and P which is power.
E
𝑚 ∗ ∆𝑇
=
= P
∆𝑡
∆𝑡
41
Throughout the experiment, the water mass is assumed to be constant and the system
pressure is assumed to be atmospheric. These assumptions are included due to the gaps between
the pot and lid where the thermometer is inserted as well as the small vent hole in the glass lid to
the left of the lid’s handle, as shown in Figure 24. Although water vapor will escape the system
through both of these gaps, the mass of the water that is lost due to vaporization is assumed to be
minimal; due to the small area of the gaps coupled with the short timeframe where significant
amounts of water vapor are produced throughout each trial. Conversely, the area of the vent hole
alone is significant enough to prevent the system of heating water from building up any notable
pressure.
At the start of the first trial, the 4 lbs. of tap water was measured to have a temperature of
60 °F. Utilizing the "High" setting on the burner, the water was brought to a constant full boil, 212
°F, in 6:00 minutes. Remembering that 1 BTU is approximately the amount of energy to raise one
pound of water 1 °F:
𝑇𝑖𝑛𝑖𝑡𝑖𝑎𝑙 = 60 ℉
V = 8 𝑈𝑆 𝐶𝑢𝑝𝑠 = 0.0668402778 ft 3
𝑣𝑓,water 60 ℉ = 0.01604
ft3
𝑙𝑏𝑚
𝑚 = V ∗ 𝑣𝑓,water 60 ℉ = 4.16709961 𝑙𝑏𝑚
𝑚 = 4.167 𝑙𝑏𝑚
𝑇𝑓𝑖𝑛𝑎𝑙 = 212 ℉
∆𝑇 = 𝑇𝑓𝑖𝑛𝑎𝑙 – 𝑇𝑖𝑛𝑖𝑡𝑖𝑎𝑙 = (212 ℉) − (60 ℉)
∆𝑇 = 152 ℉
E = 𝑚 ∗ ∆𝑇
𝐄 = 𝟔𝟑𝟑. 𝟑𝟗𝟗𝟏 𝑩𝑻𝑼
E = (4.17 𝑙𝑏𝑚 ) ∗ (152 ℉) = 633.399141 BTU
42
The electric coil was able to create a 152 degree F change in temperature in 4 lbs. of water
in 6 minutes. By dividing the energy output by the time, we can calculate the power output and
convert it to several different sets of units.
E = 633.3991 𝐵𝑇𝑈
∆𝑡 = 6 𝑚𝑖𝑛𝑢𝑡𝑒𝑠 ∶ 0 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 = 360 𝑠𝑒𝑐𝑜𝑛𝑑𝑠
P =
P =
E
∆𝑡
=
𝑚 ∗ ∆𝑇
∆𝑡
633.3991 𝐵𝑇𝑈
𝐵𝑇𝑈
360 𝑠
1 𝑠𝑒𝑐𝑜𝑛𝑑 X
= 1.759442059
3600 𝑠𝑒𝑐𝑜𝑛𝑑𝑠
1 ℎ𝑜𝑢𝑟
P = 6333.991412469
𝐵𝑇𝑈
1 𝑠𝑒𝑐𝑜𝑛𝑑 X
1 kJ
𝐵𝑇𝑈
0.94781712 𝐵𝑇𝑈
P = 1.856309642 kW
𝐵𝑇𝑈
=
𝐵𝑇𝑈
s
hr
hr
=
kJ
s
= kW
𝐏 = 𝟔𝟑𝟑𝟒
𝑩𝑻𝑼
𝐡𝐫
𝐏 = 𝟏. 𝟖𝟓𝟔 𝐤𝐖
43
3.3 Stove Design
Figure 25 seen below is the 3-D top view of the hybrid stove. Descriptions of parts A1to
A5 are below the figure.
Figure25: Hybrid Stove Design Top View
A1 – Conduction plates for combustion heated range top. Both plates are 8” in diameter, and
made from ¼” plate steel. Both also feature a square notch that a hook can be placed into to pull
out the burner plate when hot.
A2 – This is a ¾ “lip on the top surface of the cook stove that covers the entire perimeter of the
range top. The lip can catch and contain a large volume of spilled liquids on range top, creating a
buffer between the user and a cascade of boiling liquid in event that a pot of hot liquid is
accidently knocked over.
A3 – The exhaust flue for was positioned on the rear of the range top to allow the cookstove body
to fit into a standard sized countertop opening for an oven, the average dimensions being 30” W x
26” D, without overtly protruding beyond the front plane of standard sized kitchen countertops.
44
By placing the duct on top of the oven and properly insulating the back panel of the cookstove, the
oven can be flush-mounted to the wall if it is accordance with the guidelines, laws, codes, and
standards of the NFPA and AHJ.
A4 – 6” (Nominal) Nichrome coil electrical heating element. This burner assembly v=can be
interchanged with a kerosene burner.
A5 – 8” (Nominal) Nichrome coil electrical heating element. This burner assembly can be
interchanged with a kerosene burner.
Figure 27 is a much more detailed 3-D assembly view of the stove where the interior is
visible. The description of each component can be seen below the figure.
Figure 26: Isometric View of Hybrid Cookstove Design with Front and Side Panels Removed
B1 – Air intake for Non-catalytic combustors.
B2 – Sidewall of burn box.
B3 – Exhaust ducting, comprised of 4-layered thin gauge sheet steel.
B4 – Oven compartment, made of thin gauge stainless steel.
45
B5 – Storage drawer for pots pans and trays.
B6 – Ceramic brick insulation used to line interior wall of burn box
B7 – Ash pan
Figure 27 is a detailed view of the non-catalytic converter.
Figure 27: View of Non - Catalytic Combustor Tubing in the Top of the Burn Box
C1 – Non-catalytic combustor, made from 3/4 “ stainless steel tubing with holes drilled along the
length allowing airflow into the burn box. As the hot exhaust gases from combustion rises from
the burn box, remnants of the fuel that did not combust leave with it. This means that the fuel did
not undergo complete combustion, resulted in less fuel efficiency, less usable energy output, and
an increase in emissions. Adding a secondary air intake, more oxygen is allowed to react with the
non-combusted fuel particulate in the exhaust gases, creating a secondary phase of combustion.
This increases the stove’s fuel efficiency, increases the usable energy output, and decreases
emissions.
Figure 28 is a 3-D model showing the drawers working.
46
Figure 28: Isometric view of stove with drawers pulled out
D1 – Ash pan slides out so the ashes can be safely emptied and disposed of after the embers have
been properly extinguished and cooled.
D2 – The sliding storage drawer is protected from exhaust gases by insulation and plate steel
Nominal) Nichrome coil electrical heating element. This burner assembly v=can be interchanged
with a kerosene burner.
3.4 Final Design Drawings
The drawing seen in Figure 29 is the completely assembled drawing with dimensions of
the height width and depth. This drawing gives a good idea of how large the whole stove is and
47
how it will fit into a kitchen.
Figure 29: Final Design Drawing
Figure 30 is an exploded view drawing of the overall view of the cookstove final design.
Each part is labeled as an item number that can be referenced in Table 8.
48
Figure 30: Exploded View of Final Design
This list of materials that corresponds to the numbers in Figure 30 can be seen below.
Table8: Part Numbers of Design Components
ITEM NO.
1
2
3
PART NUMBER
Frame
Burn Box
Non-Catalytic
Combustor
QTY.
1
1
1
4
5
6
7
8
9
10
Burn Box Loft
Range Top
Exterior Side Wall
Exterior Back Wall
Ash Box Holster
Ash Box
Oven Compartment
1
1
2
1
1
1
1
49
11
12
13
14
15
16
17
18
19
20
21
22
Exhaust
Burner Drip Pan
6in Nichrome Coil
8in Nichrome Coil
Storage Drawer
Burner Contact Plate
Oven Front Skirt
Brick Insulation
Left Door
Right Door
Ash Box Door
Burn Box Door
1
1
1
1
1
2
1
1
1
1
1
1
In the next section we will describe the electrical components of our cookstove. The
integration and implementation of these components will be discussed as well.
3.5 Electrical Design Overview
The design of this system has been mapped out into an easy to understand block
diagram, which can be seen in Figure 32. You can see in the diagram that the center of the
system is the microprocessor. To the left of the microprocessor is the power system
including wall power and the TEG modules along with the battery charging circuit. To the
top of the microprocessor are all of the various sensor inputs including gas sensors, thermal
resistive sensors, and potentiometers. Finally all of the outputs of the system are shown
below the microprocessor and they include the LCD screen, LEDs, DC motors, and a buzzer.
All of these pieces of the system are described in more detail in the implementation section
below.
50
Figure 181: Circuit Design Block Diagram
3.6 Implementation
3.6.1Processor
The processor that is being used to implement this design is the ATmega32-16PU.
This is an 8-bit AVR processor manufactured by Atmel. The processor is set onto an Olimex
development board that has voltage regulation onboard. The development board also has an
LED, a single button, RS232 port, and JTAG connector. The JTAG connector is connected
through USB via a programmer that goes from USB-JTAG. The code involved with this project
will involve interfacing with various I/O devices as well as feedback loops between the
temperature sensors and the vent controller motors. For programming software we are
using IAR kickstart for AVR processors as well as another freeware program called
AVRstudio 5.0. IAR kickstart can program the board directly while AVRstudio 5.0 needs a
secondary program to download the compiled code called WinAVR. Both programs work for
programming the ATmega32 AVR processor, however IAR kickstart does not come with the
library of header files for the processor. Both programming software are capable of
programming the AVR processor through the USB programmer. The development board and
USB programmer can be seen in the Figure 33.
51
Figure 192: Olimex 40 Pin Development Board and USB Pocket Programmer
For design purposes and due to some time constraints an MSP430 was used to design
and test the functionality of the electrical control system. These processors are designed for
very low power consumption and are readily available for use in the ECE labs. The code for
these tests can be seen in the appendix. The functionality of the code is to read a
potentiometer and thermistor value. It also controls a DC motor accordingly to represent
the opening and closing of an air intake valve in the stove.
3.6.2 Power System
The power system will be comprised of several components. These components
include AC/DC converter for DC power from a wall outlet, AC and DC voltage regulators,
Thermo-Electric Generator Modules, and Battery Storage.
Wall Power
In order to utilize 120V, 60Hz wall power an AC/DC converter circuit will be designed
to regulate the wall power down to 9VDC. This AC/DC converter circuit will not be
implemented in this MQP, however if needed an AC/DC converter by ROHM part number
BP503405 will be used to convert the wall power down to 5VDC. The 5VDC is enough
voltage to power the processor and all of the I/O devices, however for the final design
52
implementation a circuit will need to be designed as this converter only provides
100mAmax and this is not enough to run all the I/O devices at the same time.
Thermo-Electric Generation
In researching renewable energy sources devices called TEG modules were
discovered. These modules utilize a process called the “Seebeck Effect”, a process which
turns a temperature differential across two ceramic plates into electricity through NPN
junctions. The modules were tested on top of an electric range sandwiched between two
heat sinks. The two modules tested were wired in series and produced a maximum of about
4.2VDC. The setup of this experiment can be seen in the image below. The heat differential
across the two plates of both modules has yet to be measured as a thermometer capable of
reading temperatures over 600°F. Five of these modules will be placed on a wall of the
stoves burn chamber and will have heat sinks on the other side to keep the temperature
differential as high as possible. With the five modules purchased for this project there should
be plenty of output to power the processor along with all of the I/O devices. Because the
voltage output of these modules can vary and is not always producing current we need both
battery storage as well as voltage regulation to charge the battery storage cells at a constant
voltage. In some cases a battery charging circuit will also be required but can easily be
purchased as an IC along with some battery cells.
Voltage Regulation
As mentioned above the output voltage of the TEG modules is not always consistent
as it is a function of the temperature differential between the two ceramic plates. In order to
regulate this voltage to a constant supply to charge a battery or provide voltage to a charging
circuit a DC voltage regulator will be utilized in a regulator circuit. This will most likely be
done with a small voltage regulator IC.
53
Battery Storage
When wall power is not available battery backup that is charged by both the TEG
modules as well as the wall power. This will allow the circuit to be functional even when wall
or heat power is not available, until the stove heats up again. In order to allow the batteries
to charge and be used as supply for the circuit charging will have to switch between two
battery backup cells.
3.6.3 Sensor Inputs
The system will include multiple sensor inputs that will be described further below.
The sensors that will be used in this system include various gas sensors, thermal resistive
sensors, and potentiometers.
Gas Sensors
This project will include various gas sensors including carbon monoxide (CO), carbon
dioxide (CO2), methane (CH4), nitric oxide (NO), and nitrogen oxide (NO2). All of these gas
sensors will be connected to and monitored by the ADC of the microprocessor. There will be
interrupts which will trigger if any of the levels on any of the sensors reach a certain
threshold. This threshold will be determined from researching the dangerous levels of each
of the various gasses. All the gas sensors will be places around where the user will be
cooking, as that is the area we want to ensure has good air quality. If all the sensors are in
the safe levels then the area is safe for cooking. Upon reaching any unsafe levels the
microprocessor will sound a loud buzzer alerting the user to evacuate the area and ventilate.
The microprocessor will also shut off airflow to the stove causing the fire inside the burn box
to extinguish. Overall the gas sensors will ensure the user is not breathing any harmful
gasses while cooking.
54
Thermal Resistive Sensors
This design is going to include various temperature sensors that will be read by the
microprocessors ADC as well. These values, once calibrated will allow the microprocessor to
determine how much to open or close the air intake and flue vent valve in order to reach the
right temperatures on the stovetop and inside the oven. These sensors are going to be placed
at various points around the stove as determined by the ME group designing the actual stove
and will also be shielded with some type of metal in order to ensure they do not directly
contact any open flame.
Potentiometers
The system will include various potentiometers, ultimately two to control the
stovetop heating coils, and one for the oven temperature control. These controls will work
by being calibrated with the ADC of the microprocessor and the lowest and highest settings
of each potentiometer will correspond to completely off all the way up to full heat.
3.6.4 Outputs
The system will include various outputs in order to communicate certain things to the
user. These outputs will be explained further below and will include and LCD screen,
Feedback LEDs, DC motors, and a buzzer.
LCD
The LCD screen in this project will be used to display the oven temp as well as time
and cooking timers. The LCD screen being used for this project is a small black and white 8-
bit LCD screen. The LCD screen has internal memory to store 8-bits of the display at a time.
The screen is communicated to by 8 parallel bus lines, which will be cycled with a sequence
of 8-bit pages. The LCD screen then prints page by page to the 127x32 pixel screen starting
in the top left and moving to the right and down just like we read a book. The LCD screen
55
also includes a backlight so it can be seen at night and will be kept on while the stove is off in
order to display a clock at night.
LEDs
This system will include multiple LEDs for various functions. First there will be bright
white LEDs mounted above the cooking surface in order to allow for nighttime cooking.
There will also be a red LED indicating that the stove is hot and warns the user not to touch
it. Finally there will be a couple LEDs in order to notify the user if the gas sensors go off as to
which one exceeded its safety threshold.
DC Motors
DC motors will be included in this project in order to demonstrate a way of opening
and closing an air intake or flue valve. The DC motors will have a gear ration such that the
spinning of the arm will have a good amount of torque and slow RPMs to ensure accurate
amounts of opening or closing of the valves. The motors are hooked into an H-Bridge in
order to allow switching of voltage across the DC motor reversing the polarity and allowing
the motor to spin one way or the other.
Buzzer
As mentioned above in the gas sensor section, a buzzer will be implemented in order
to notify the user of any unsafe conditions that may arise with the stove indicating to the
user that they should evacuate the area around the stove. In order to ensure that the buzzer
is loud and piercing enough to notify the user properly a buzzer was chosen with a dB rating
of over 80dB @ 1m and a frequency of over 2,000Hz. The buzzer chosen has an internal
crystal oscillator and therefore just needs to be provided with a DC voltage to be operated. In
order to make the buzzer even more noticeable the buzzer will beep rather than just staying
on constantly and will go off when the gas levels are back within a safe range. In the next
56
section we will discuss the results of our project by analyzing our results vs. the original
design specifications.
3.7 Design Analysis
The following section analyzes to what level we have reached our design goals set forth in chapter
3.1.
1. The usable power output must be greater than 1.86 KW.
This goal will be accomplished in the future if the cookstove is constructed and tested.
2. The device must cost under $500.
Component costs for the developed design are under $500. This does not include
manufacturing cost.
3. The device must be intuitive to operate.
The operation concept in the design is similar to that of a regular consumer
household stove.
4. The device must release fewer toxic emissions than comparable cookstoves used in thirdworld countries.
A non-catalytic combustor was implemented in the design to reduce emissions.
5. There must be no surfaces on the exterior of the stove that our capable of burning the user
with the exception of the cook top.
The amount of insulation used in the design is sufficient to reduce the temperature off
exterior surfaces to not burn the user.
6. The device must alert the user of toxic conditions in the operating environment.
A control system was developed to alert the user of toxic conditions
7. The device must have a system for monitoring toxic emissions.
An electronic system was developed to monitor toxic emissions.
57
8. A ventilation system that will prevent harmful gases from entering the living quarter of the
user must be developed.
The final design includes a ventilation system that releases all emissions outside of the
living quarters.
9. The device must induce a more complete combustion than current similar cookstoves.
The design features a non-catalytic converter that allows for more complete
combustion.
10. The device must run on multiple fuel sources including wood, gas, oil, coal, wood pellets,
and bio-fuel.
The prototype design is capable of running on primarily wood, and can be modified
to run off of other fuels.
11. The device must be more energy efficient than current similar cookstoves.
There are many features including a non-catalytic combustor that increase the energy
efficiency of the designed cookstove.
12. The device must weigh less than 600lbs
The designed cookstove weighs less than 600lbs.
13. The device must be capable of being transported by 3 or fewer adults using standard
moving equipment.
This design specification has not been tested.
14. The user must not be exposed to any source of open flame.
The design of the cookstove prevents the user from coming into contact with any
sources of open flames.
15. The internal components of the device must only be assessable to a qualified technician.
This feature will be implemented in future revisions of the design.
16. The device must feature an intuitive control system.
58
The device features a comparable control system to that found in modern consumer
stoves.
17. The device must be able to be operated by an untrained adult.
The device can be operated by anyone capable of operating a modern stove.
18. The device must have a method for controlling oven temperature.
The device features a control system for monitoring and controlling oven
temperature.
19. The burn box should be inaccessible to the user.
Future revisions of the design will feature a mechanism for preventing access to the
burn box.
59
Chapter 4: Concluding Remarks
4.1 Mechanical Design
The design outlines in Chapter 3 of this report is a design of a stove geared towards safety
and efficiency. Even though we feel that this stove was design to the best of our understanding of
the problem statement and our objects we also feel like there are alternative solution to our
problem that do not involve the design of a prefabricated stove made of steel or cast iron. The
initial problem presented for this project was to design a stove that is efficient, clean and
inexpensive. The purpose of this was to provide a way for developing nations to cook safely and
save money on fuel. Through research it was determined that there are many programs already in
place to help people with this problem. As seen in the appendix there is a lot of information
available on how to build an efficient stove on the internet and being spread person to person in
developing nations. The idea that is being spread worldwide is the idea of the combination of a
rocket stove and a Lorena Adobe stove. The appendix shows a complete guide on how to build
one of these fuel efficient and significantly safer stoves.
Moving on from the original problem that was presented in this project, we began
designing a stove that could be using in America and in developing nations. The aspect that
allowed it to be used in both extremely different demographics was that it was a hybrid stove. The
stove was designed to be both a biomass burning stove, and also run off of electricity or gas. This
idea is very good because it will allow people in developing nations to use it when they can only
use biomass fuels. On top of this, the electrical implements allow the stove to be incredibly safe
even when they are not connected to the grid. The major setback was the price of the stove. The
stove would be too expensive for anyone in a developing nation to buy with their yearly income.
In America the stove could still sell well because it applies to a niche group of people who would
like to have a wood burning stove. However, for the general public a wood burning stove cooks
60
too slow or causes too much of a hassle compared to other conventional methods as confirmed by
the water boiling test described in the previous chapter.
The solution to the problem of the general public not wanting to use a wood burning stove
and the stove being too expensive to people in developing nations is simple. People who want to
buy the stove for themselves in America can still buy the stove for themselves. The stove will be
marketed to wealthier people who would like to donate the stove to people in developing nations.
This will advertise the stove promoting more people to buy the stove because it supports a good
cause and give the stove to people who need it. This marketing strategy will be effective if we can
find a philanthropist willing to buy a lot of the stoves for the less fortunate and this is well
publicized. After this it will be easy to continue selling the stoves we designed. Through this
method the project will have successfully accomplished the goal it set to design a safe and
efficient stove for people in developing nations.
4.2 Electrical System Design
For this project, all of the functionality described in the design and implementation
sections above were not completely achieved due to time constraint; however, the project
could be continued and the full functionality of the design could be achieved. The
continuation of the project will include working with the processor to achieve a small proof
of concept circuit. This circuit will include interfacing with the DC motors; also the
potentiometers will be monitored in order to decide how to control the motors. Also the
relationship between the values of the potentiometer and the value of the thermal resistive
sensors will designate how long and in which directions to move the DC motors. The
diagram below shows which parts of the system will be implemented for this MQP, which
parts might be implemented shall time allow, and which components will not be
implemented for this MQP. In the block diagram shown in Figure 34 each square is color
coded. The green squares are the components that will be implemented for this MQP, the
61
orange squares are the ones that may be implemented if time permits, and the red squares
are the components are that will not be implemented for this MQP. The block diagram in
Figure 34 is the same as the one in the previous section except that it has color coded
squares to indicate what the goals of this MQP are.
Figure 203: MQP Goal Block Diagram
An overall parts list for all the components used for this MQP can be seen in the excel
spreadsheet below. The cost of all the parts is just around $150.00 and is under $100.00 at
the bulk prices.
62
Figure 34: Parts List for MQP parts
63
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66
Appendices
Appendix A: Code for the Stove Controls
67
68
69
70
71
Appendix B: Burn Test #1 3lbs Dura Flame Log
H2O Front Ashbox Triangle Burnbox Sidewall S1 S2
Mid L Mid M Mid R Back A Back B Back C Exhaust
4:14:00 AM
62
62
62
62
62
62 62
62
62
62
62
62
62
62
62
4:55:00 AM
85
244
59
73.5
106
67.5
84
73
138 96.5 73.5
150
5:01:00 AM
95
5:03:00 AM
99
5:04:00 AM 100
230
70
5:05:00 AM
57
74
113
131
98 76.5
5:07:00 AM
188
185
5:08:00 AM
130
5:10:00 AM
75
65
5:11:00 AM 109
5:14:00 AM 111
225
73
72
67
5:16:00 AM
185
190
5:17:00 AM
124
97
75
142
5:18:00 AM
61
71
114
5:19:30 AM 114
5:23:00 AM 115
228
78
68.5
5:24:00 AM
57
77
117
5:26:00 AM
120.5
92 73.5
5:27:00 AM
186
175
5:28:00 AM 119
139
5:36:00 AM 122
218
5:37:00 AM
186
140
76
71
5:40:00 AM
110 90.5 72.5
5:42:00 AM
130
5:43:00 AM 72.5
5:45:00 AM
57
76.5
115
5:46:00 AM 125
5:50:00 AM 125
6:00:00 AM 126 172.5
79
200 70.5
6:02:00 AM
140 156.5
6:05:00 AM
100 81.5 61.5
6:06:30 AM 125
6:07:00 AM
106
6:09:00 AM
56
64
107.5
6:10:45 AM 124
6:18:00 AM 125
6:23:00 AM 124
72
Appendix C: Burn Test #2 9 lbs. Dry Logs
7:02:00 AM
7:03:00 AM
7:04:00 AM
7:04:30 AM
7:05:00 AM
7:06:00 AM
7:07:00 AM
7:08:00 AM
7:09:00 AM
7:09:30 AM
7:10:00 AM
7:12:00 AM
7:13:00 AM
7:13:30 AM
7:14:00 AM
7:14:45 AM
7:15:30 AM
7:17:00 AM
7:18:00 AM
7:18:30 AM
7:20:00 AM
7:21:00 AM
7:21:30 AM
7:22:00 AM
7:23:00 AM
7:24:00 AM
7:25:00 AM
7:26:00 AM
7:27:00 AM
7:28:00 AM
369
508
535
502
460
450
81
135
70
199
128
109
4:50
550
620
H2O Front Ashbox Triangle Burnbox Sidewall S1
55
65
100
120
150
180
172
181
195
198
200
S2
530
502
385
552
635
545
83
140
130
345
470
240
360
270
140
208
180
500
690
Mid L Mid M Mid R Back A Back B Back C Exhaust
110
135
175
318
340
73
Appendix D: How to Build the Improved Household Stove
THE REPUBLIC OF UGANDA
MINISTRY OF ENERGY AND MINERAL DEVELOPMENT
Energy Advisory Project
HOW TO BUILD THE
IMPROVED HOUSEHOLD STOVES
A CONSTRUCTION MANUAL FOR THE ROCKET – LORENA AND SHIELDED FIRE
STOVES
With the Support of the German Technical Cooperation
74
Editor:
Rosette K. Kabuleta
(GTZ – EAP Consultant)
Text, technical diagrams and photography by:
Leonard Mugerwa (GTZ
– EAP Consultant)
Photos were taken during stove construction workshops for artisans held at Kabale and
Ruharo – Bushenyi in October 2003.
Pictures by:
Haruna Lubwama
Advisory:
Philippe Simonis (GTZ - EAP)
John Kuteesakwe (GTZ - EAP)
Godfrey Ndawula (MEMD)
Published by:
Ministry of Energy and Mineral Development (MEMD)
Energy Advisory Project (EAP)
Supported by the German Technical Cooperation (GTZ)
Cover page:
Prossy Bidda
(Cooking with Rocket - Lorena stove)
Christine Nakalema
(Cooking with Shielded fire stove)
Date:
October 2004
© 2004 MEMD / EAP
First Edition November 2003
Revised Edition November 2004
75
Table of Contents
Topic
Page
Acknowledgement .......................................................................................................... ii
Introduction ....................................................................................................................iii
The improved firewood stoves .................................................................................. iv
Things to consider when preparing to build the improved stoves............................. 1
1.0
Shelter ................................................................................................................ 1
2.0
Tools ................................................................................................................... 1
3.0
Stove construction materials ......................................................................... 2
4.0
Purchase and delivery of materials .............................................................. 2
5.0
Mapping out the stove position ..................................................................... 2
6.0
Materials preparation .......................................................................................... 3
Part 1 .................................................................................................................................... 7
How to build the improved rocket - lorena stove ........................................................ 7
Part 2 ..................................................................................................................................17
How to build the shielded fire stove ........................................................................17
9.0
Fitting the firewood shelf……...……………………………………………23
10.0
Using the stoves..……...…………………………………………………..24
10.1
Efficient cooking practices...........................................................................25
10.2
Cleaning the stove........................................................................................25
10.3
Stove maintenance and repair ...................................................................26
Appendix 1
Calculation to determine the diameter of a circular
combustion chamber ………………………………………………………...27
Appendix 2
Relationship between pot / saucepans diameter and
combustion chamber sizes……………………………………….…….……28
76
Acknowledgement
This publication is attributed to the work done by several players. Appreciation goes to:
The Ministry of Energy and Mineral Development Energy Advisory Project
(MEMD / EAP) for perceiving the idea of presenting and preserving the
improved firewood stove technology in a stepwise teach-it-yourself
booklet, which is an effective channel in creation of awareness.
GTZ – Energy Advisory Project for funding this publication.
Peter Scott of Aprovecho Research Centre, Oregon, USA, for cooperating with
GTZ – EAP during the research work on the rocket – elbow combustion
chamber in Uganda.
The Uganda Industrial Research Institute (UIRI), Nakawa-Kampala, for the
cooperation with MEMD / EAP that enabled the research work to be performed
at UIRI premises, during the biomass energy efficient technology development
and testing.
77
Introduction
Uganda faces a biomass energy crisis marked by an increasing imbalance
between the supply and the demand of the firewood by households,
institutions and industries.
One of the most effective strategies to sustainably contribute towards the
reduction of this problem is through an extensive dissemination of
biomass energy efficient technologies.
The purpose of this manual is to provide to all interested parties a practical tool to
use in the construction of improved firewood stoves i.e the rocket – lorena and
the shielded fire.
The improved biomass energy efficient technologies have been developed to
improve energy efficiency for household, institutional and industrial practices.
They include the domestic and institutional firewood stoves and the firewood
baking oven.
These improved household stoves have efficiencies of 30 % (average)
compared to the traditional (open) 3-stone fire stove at 15.6 %, in a high power
water-boiling test∗.
The main objective in developing the improved firewood stoves is to achieve
relatively efficient firewood combustion and maximising heat transfer to the food
being cooked.
These improved stoves help the users to have firewood savings of 50 – 60 %
when compared to the traditional (open) 3 stone stove. Yet another strength of
these stoves is that they are built using local materials including clay, anthill soil
and sand for the body whereas insulating materials include sawdust, pumice
and vermiculite.
∗
Data source: GTZ – EAP / MEMD records. “Firewood Cook stoves Development and Testing”
by Leonard Mugerwa, September 2003.
78
THE IMPROVED FIREWOOD STOVES
The improved stoves are able to achieve maximum transfer of heat to the food because they
heat at least 90 % of the saucepan’s surface area and have insulation around the
combustion chamber and the fire passages.
Advantages
Firewood Fuel Savings
The stoves have been tested and proven to be economical in firewood consumption, with an
efficiency averaging 30% compared to the traditional (open) 3-stone fireplace at 15.6%. This
means that by using the improved stove, you double the amount of energy is transferred from
the wood to the food being cooked.
2
Almost Smokeless Operation
1
The stoves hardly produce smoke during their operation. A bit of smoke is produced
only when lighting the fire.
3
Easy to Operate
Once lit, the stove fire does not stop unless firewood feed into the stove is stopped. There
is no need of straining one’s lungs to blow air into the stove to fan the flame as it is with the
Traditional (open) 3-stone fire. This is done by the air chamber below the feeding shelf.
4
Affordable
The stoves are constructed using local materials including anthill soil and sand for the
body whereas vermiculite, sawdust, pumice, etc are used for thermal insulation.
5
Safe to Use
The stoves are safe-to-use domestic appliances. Firewood is neither toxic nor highly
inflammable. The shielded fire is screened (out of reach) and therefore less likely to
cause burns to children and the user.
6
Environmentally Friendly
The stoves use less firewood leading to reduction of the deforestation rate. The stoves are
less pollutant because of their nearly smokeless operation, attributed to the shelf-fitted rocket
elbow combustion chamber, which improves the air : fuel ratio.
79
THINGS TO CONSIDER WHEN PREPARING TO BUILD THE IMPROVED STOVES
1.0
SHELTER
Ensure that there is a kitchen in place to house and protect the stove to be built from
intrusion and unfavourable weather conditions e.g. rain.
2.0
TOOLS
The tools required when building the improved firewood stoves include:
Tool
1
2
3
4
5
6
7
8
9
10
11
Purpose
Hoe
Digging foundation base and mixing ingredients
Shovel or Spade
Mixing ingredients
Jerry can
Fetching water
Sieve (4 mm)
Sifting ingredients
Trough (karaayi)
Measuring materials by volume and carrying mixtures
Trowel / blunt machete Smoothing plaster / stove finish
Measuring Tape / ruler Taking measurements
Bow saw
Cutting pumice blocks into insulation slabs
Spirit level (optional) Inspecting horizontal level for laid bricks / stove finish
Plumb line (optional) Inspecting vertical alignment for laid bricks / structure
Try Square (optional) Inspecting right angled corners
Safety Gear
1
2
3
1
2
1
Device
Nose Mask
Overalls / work clothes
2
First Aid Kit
Purpose
Protection against inhaling dust during sifting
Protection of clothes during work
Treatment for injuries
Recommended for use where available.
Professional workshop practice recommends that a First Aid kit should be in place.
80
3.0
STOVE CONSTRUCTION MATERIALS
Quantity
Materials
Options
1 Clay
2
Anthill soil
Dry chopped grass, dry
chopped banana leaves,
Sawdust vermiculite or pumice
3 Mud bricks
4 Clay tile
5
Water
6 Sand
-
4.0
Rocket - Lorena
Shielded Fire
8 – 12 wheel barrows
4 – 6 wheel barrows
8 – 12 wheel barrows
60 – 80 bricks
1 pc (25 x 13 x 1 cm)
7 – 10 jerry cans
(20 litres each)
8 – 12 wheel barrows
4 – 6 wheel barrows
10 bricks
1 pc (25 x 13 x 1 cm)
4 jerry cans
(20 litres each)
4 – 6 wheel barrows
PURCHASE AND DELIVERY OF MATERIALS
Purchase the construction materials and deliver them outside the kitchen where the stove
is to be built.
5.0
MAPPING OUT THE STOVE POSITION
Choose a corner in the kitchen to be occupied by the stove. This will save it from accidental
damage and it will also be useful in preventing the stove from direct intake of cold air.
Recommended
stove position
Stove
KITCHEN
Door
Do not position the stove firebox along the
axis of the doorway to avoid direct intake of
cold air
Kitchen plan
81
NOTE:
It is advisable that one week prior to
stove construction, a 200 X 200 X
30cm high platform be built in the
kitchen corner that has been marked
above. On this platform, the stove
will be constructed. This will help to
keep the stove out of reach for very
young children.
6.0
82
MATERIALS PREPARATION
The Stove
30 cm
200 cm
Stove platform
Kitchen floor
200 cm
Prepare the construction materials, at least two days before the time for stove
construction. The preparation procedure will depend on the materials combination
chosen as described below:
6.1
Sawdust and clay (or anthill soil option)
6.1.1 Crash the clay (or
anthill soil) into
smaller granules,
which can be sieved
through the 4 mm
sieve.
6.1.2 Using the sieve, sift the clay
(or anthill soil) to
obtain fine granules.
In the same way sift
an equal amount of
sawdust to obtain fine
particles.
6.1.4 Slowly add water to the mixture
to make it mouldable.
83
6.1.5 Blend the mixture using the feet
similar to the way it is locally
done when preparing mud for
brick making.
In the event that sawdust is not available in your place, you may use any of the
following stove construction materials combination depending on availability:
6.2
Grass and clay (or anthill soil option)
6.2.1 Use the machete (panga) to chop dry grass into small pieces of approximate
length 1 cm.
6.2.2 Using the sieve, sift the clay (or anthill soil) to obtain fine ingredients.
6.2.3 Mix the chopped dry grass and clay (or anthill soil option) volumetric ratio 1:1.
6.2.4 Slowly add water to the mixture just to make it mouldable.
6.2.5 Blend the mixture using feet similar to the way it is locally done when preparing
mud for brick making.
6.3
Dry banana leaves and clay (or anthill soil option)
6.3.1 Separate the stalk and mid-rib from the lamina. Use the dry lamina of the
dry banana leaves.
6.3.2 Use the machete (panga) to chop the dry lamina into small pieces of approximate
length 1 cm.
6.3.4 Using the sieve, sift the clay (or anthill soil) to obtain fine ingredients.
84
6.3.5 Mix the chopped lamina and clay (or anthill soil option) volumetric ratio 1:1.
6.3.6 Slowly add water to the mixture just to make it mouldable.
6.3.7 Blend the mixture using feet similar to the way it is locally done when preparing
mud for brick making.
6.4
Pumice, anthill soil and sand.
6.4.1 Using the sieve, sift the sand and clay (or anthill soil) separately to obtain
fine ingredients.
6.4.2 Mix the clay (or anthill soil) and sand (ratio 1:1).
6.4.3 Slowly add water to the mixture just to make it mouldable.
85
Blend the mixture using feet similar to the way it is locally done when preparing mud
for brick making.
6.4.5 Cut / shape the pumice into
slabs of 5cm thickness.
Note: The slabs will later be used in
providing thermal insulation
around the combustion
chamber and the fire (hot flue
gases) passage. They will be
fastened together using the
anthill soil – sand mixture.
86
PART 1
HOW TO BUILD THE IMPROVED ROCKET - LORENA STOVE
Chimney
Saucepan seats
Shelf
Firebox
87
HOW THE ROCKET LORENA STOVE WORKS
Below is the sectioned front view of the stove, showing how it is intended to
function. Note that the saucepan seats are deep enough to have the saucepans
submerged into the stove’s hot gases’ passage. This increases the surface
area of the saucepan being exposed to the fire (hot flue gases), which results
into increased heat transfer into the saucepan.
Saucepans
(Covered with lids)
Chimney
Fire
(Hot flue gases)
Saucepan
supports
Thermal Insulation
(5 cm minimum
thickness)
Shelf
If available,
bricks are laid
here
Air passage
Thermal Insulation
(5 cm minimum thickness)
7.0
Building the Rocket - Lorena Stove
The size of the stove will depend on the size of the saucepans that will be used
when cooking with it.
Example:
For a home that frequently uses two saucepans with diameter 26 cm and 23 cm, the bigger
saucepan should be positioned directly above the combustion chamber while the smaller
one takes the other position. The size of the combustion chamber will be 12 X 12 cm (or
circular option diameter = 13.5 cm). This will be the inner diameter of the chimney.
The stove designed for 26 cm bigger diameter and 23 cm smaller diameter
saucepans will have the resulting outer dimensions = 107 X 56 cm.
88
Length of the stove body
s
saucepan
(diameter
2 6
=
Chimney
diameter =
13.5 cm
=
cm
26
cm)
d
h resulti
e ng
stove bod y
c
m
BBigger
1
5
Smaller
saucepan
(diameter
= 23 cm)
1 c
0 m
10 cm
dt
h
of
15 cm
15 cm
Position of the 12 X 12 cm
combustion chamber
Sketch of the stove plan
Draw the outline of the stove foundation on the platform as illustrated above. The bigger
saucepan should be positioned directly above the combustion chamber while the
smaller one takes the other position. In the event that a measuring tape is not available,
use the palm width. The width of your palm approximates 10 cm. For the 15 cm
measurement use 1½ palm widths.
7.1
Wet the position to be occupied by the
stove. Using the mixture in 6.1.5
above, lay down a 2 cm high base for
the stove, bordered by the marked out
line.
7.2
Lay the foundation bricks on the
2 cm high mixture. If bricks are
not available, use the sawdustclay mixture.
7.3
While setting the foundation the
combustion chamber base should
be catered for as shown. For
example if the bigger saucepan
diameter is 26 cm, build a 12 cm
wide combustion chamber (refer to
the tables in appendix).
89
7.4
Clay - sawdust
insulation mixture
Set the combustion position at the base as shown below
6
6
6
PLAN
VIEW
Centre position for
combustion chamber
½d
Bricks
12 cm gap for the
combustion chamber
4 cm
FRONT
VIEW
90
2 cm
2 cm high mixture for
the foundation base
7.5
6 cm
Clay - sawdust
insulation mixture
Building the combustion chamber
You will need some material to mould the combustion chamber shape during stove
construction.
In order to build a square cross section combustion chamber of 12 X 12 cm for support
use square cross section bricks of same size (12 X 12 cm) covered in polythene
material.
For the option of a circular combustion chamber use diameter = 13.5 cm.
(For details of the calculation, refer to appendix 1)
91
Appendix E: Authorship
Chapter 1: Development of a Renewable Energy Cookstove
1. Introduction
Brian Grabowski
Chapter 2: Evolution of Cookstove Design and Environmental Effects
2.1 Introduction
Michael Jenkins
2.2 Evolution of Stoves
Michael Jenkins
2.2.1 Three Stone Fire
Michael Jenkins
2.2.2 Lorena Adobe Stove
Michael Jenkins
2.2.3 Rocket Stove
Michael Jenkins
2.3: Safety of the Stove
Justin Mathews
2.3.1: Wood Stove Fire Risks
Justin Mathews
2.3.2 Causes of Cooking Fires
Justin Mathews
2.3.3 Costs of Cooking Fires
Justin Mathews
2.3.4 Cooking Fire Prevention
Justin Mathews
2.4: Global Warming
Michael Jenkins
2.4.1 Wood Stove Environmental Risks
Justin Mathews
2.4.2 Catalytic Converters and Non-Catalytic Combustors Justin Mathews
2.5 Wood Stove Health Risks
Justin Mathews
2.6: Consumer Demographic
Matthew Goon
2.7 Examples of Stoves
Michael Jenkins
2.7.1 Antique Stoves
Michael Jenkins
2.7.2 Hybrid Stoves
Michael Jenkins
2.8: Electrical Controls
Nicholas Knight
92
Chapter 3: Renewable Energy Cookstove Design
3.1 Design Specifications
Justin Mathews
3.2 Hybrid Stove Test
Brian Graboski
3.3 Stove Design
All
3.4 Final Design Drawings
All
3.5 Electrical Design Overview
Nicholas Knight
3.6 Implementation
Nicholas Knight
3.6.1Processor
Nicholas Knight
3.6.2 Power System
Nicholas Knight
3.6.3 Sensor Inputs
Nicholas Knight
3.6.4 Outputs
Nicholas Knight
3.7 Design Analysis
Justin Mathews
Chapter 4: Concluding Remarks
4.1 Mechanical Design
Michael Jenkins
4.2 Electrical System Design
Nicholas Knight
References
Michael Jenkins, Justin Mathews
Appendices
Appendix A: Code for the Stove Controls
Nicholas Knight
Appendix B: Burn Test #1 3lbs Dura Flame Log
Brian Grabowski
Appendix C: Burn Test #2 9 lbs. Dry Logs
Brian Grabowski
Appendix D: How to Build the Improved Household Stove Michael Jenkins
Appendix E: Authorship
Revised and Edited:
Justin Mathews, Michael Jenkins
93
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