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The bean test: Student stove goes head-to-head against Tanzanian three-stone stove to test efficiency

The views expressed are those of the author and are not necessarily those of Scientific American.


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Dartmouth,Tanzania, energyEditor’s Note: Students from Dartmouth’s Thayer School of Engineering are working in Tanzania to help improve sanitation and energy technologies in local villages. This series chronicles work being done by the student-led group, known as Humanitarian Engineering Leadership Projects (HELP), to design "rocket stoves" in the village of Mwamgongo and top-light updraft design (TLUD) gasification stoves in the village of Kalinzi. The goal is to create a healthier, more energy-efficient cooking apparatus that these villagers will accept and use. HELP students are filing these dispatches from the field during their trip. This is their 10th blog post for Scientific American.

When we arrived, Jirani (Swahili for neighbor and the name we were told to call her) brought out a bench and smiled, "Karibuni (Welcome)!" As you may have noticed from our other posts, Tanzanians have a strong tradition of welcoming visitors into their homes. Once we sat down, Kevin explained the plan for the day: to cook beans. By measuring the amount of wood consumed during the two-to-three hour cooking process of a staple food, we are able to gauge the relative efficiencies of different stove designs.

As Kevin began to explain the process, Jirani sat down and started to breastfeed her baby, a common occurrence in a country where 44 percent of the population is under 14 years old. As Americans, a stranger breastfeeding their child in the middle of a conversation was new for us, but Kevin kept his composure while talking to her by looking in her direction to show respect, but not in a way that would make her feel uncomfortable. He continued to explain how we would be measuring the levels of "bad pollution" from each stove. Ryan demonstrated the combustion analyzer, a device that plugs into the laptop and measures the parts per million (ppm) of carbon monoxide levels in the air. Jirani nodded, "Sawa (Okay)."

I turned my head to the right, and I saw another neighbor entering the household.

"Hodi, (May I enter)?"

"Karibu, (Welcome)!" said Jirani. As the only local Wazungu (white people) in the village, we were used to often drawing crowds wherever we went.

Kevin began setting up the bean test, which would pit the traditional three-stone stove against our TLUD (top-lit up-draft) gasification stove in an efficiency battle. We started off by creating two piles of wood: one for the three-stone stove and one for our stove. Ryan calibrated our electronic scale with the fuel box (a small container that kept the wood steady as it was measured), and then added around 2.5 kilograms of wood to one pile. Jirani, who was very interested in the testing process, looked at the scale inquisitively. Dartmouth, Tanzania, energy

Since we didn’t have enough firewood cut up for the second pile, I started chopping wood behind the house. A little girl, who seemed to appear from out of nowhere, watched me intently. A piece of timber flew off into the distance and she soundlessly ran over to grab it for me. When I thought I had chopped enough wood, we measured out a second pile of similar weight.

Another neighbor, also breastfeeding her child, and an older woman wearing a bright dress covered with sun patterns arrived to observe the process.

We added a liter of water and half a kilogram of beans into two pots of similar size, and Jirani started both fires at the same time. Our stove started off with a roaring flame, but then started smoking much more smoke than we would have liked.

Another woman with a full black headdress and an older man followed by an assembly of children entered the household. Our crowd was growing larger.

Ryan sat inside the cooking hut with Jirani holding the combustion analyzer while the three-stone stove spewed smoke into the air. Ryan desperately tried to fend off the acrid smoke by holding his shirt over his face, but even this had little effect.

"Time 12:36, CO 366 ppm," Ryan yelled to me, as I recorded the carbon monoxide data.

Jirani entered the hut and fed the fire, carrying her sleeping baby boy strapped on her back.  She didn’t seem to be bothered by the smoke and the harsh particulates of the three-stone stove that engulfed her and her child. Judging by how well-behaved and polite Jirani’s children act, we knew Jirani was a responsible parent; sadly, she was unknowingly exposing her child to indoor air pollution. One of the fundamental goals of our project is to help educate people about the connection between indoor air pollution and health problems. Hopefully in the future Jirani will make an effort to minimize her family’s exposure to wood smoke.

Constantly breathing smoke from indoor stoves has been shown to be associated with increased risk for developing acute respiratory infections (ARIs) in children and chronic lung disease and lung cancer in adulthood. It was estimated in the year 2000 that indoor air pollution was responsible for 1.5-to-2 million deaths or 4-to-5 percent mortality worldwide.* Almost half of these deaths were in children suffering from acute lower respiratory tract infections such as pneumonia. Prevalence of ARI is high in the Kigoma region of Tanzania, particularly for children. In the most recent National Demographic and Health Survey of Tanzania conducted in 2004-05, 23 percent of children under the age of five in Kigoma had symptoms of an ARI within two weeks before the survey, compared with the national average of 8 percent.** The use of open fire, three-stone stoves in poorly ventilated areas is certainly affecting increases in these statistics.

I tried to remove these disturbing facts from my mind as a woman arrived with a hefty bundle of firewood on her head. We paid for the wood in order to reimburse Jirani for the sticks we burned during the test. A "bundle" of firewood cost the equivalent of around 75 cents. Although this doesn’t seem like a lot, it is a significant expense for people in the Kigoma region, many of whom live on less than $2 a day.

Once Jirani declared that each pot of beans was cooked (the most arbitrary component of the test), we measured the amount of remaining wood for each stove. The test showed that our stove used around 40 percent less wood. This was a great result considering our average was around 33 percent for bean tests and our stoves were made of scrap metal, but it was still less than the 50 percent reduction benchmark we were aiming to reach. While considering potential design changes to the current wood burning gasification stove, we also discussed changing our attention back to using only coffee husks as a fuel source in order to have a 100 percent reduction of wood fuel—this would surely have the greatest impact in terms of deforestation—but we would need to invent a new stove design and to determine issues of coffee husk supply.  We certainly have more work ahead.



Photos courtesy of Wendy Hado

* Ezzati M, Kammen DM. The health impacts of exposure to indoor air pollution from solid fuels in developing countries: knowledge, gaps, and data needs. Environ Health Perspect. 2002 Nov;110(11):1057-68

** National Bureau of Statistics (NBS) [Tanzania] and ORC Macro. 2005. Tanzania Demographic and Health Survey 2004-05. Dar es Salaam, Tanzania: National Bureau of Statistics and ORC Macro

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  1. 1. tjj300 2:24 pm 09/15/2010

    Interesting series, but I would be just as interested in what Jirani thought of the new stove, compared to her traditional one.

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  2. 2. idzikows 2:25 pm 09/15/2010

    Editors – I expect science in these articles not judgement.

    "As Americans, a stranger breastfeeding their child in the middle of a conversation was new for us, but Kevin kept his composure while talking to her by looking in her direction to show respect, but not in a way that would make her feel uncomfortable."

    Writers – I applaud your efforts as a group to directly reduce the resource consumption and the effects of pollution these people experience. I could do without a description of the ‘moral rectitude’ you display at their ability to feed their children without shame (see above quote). Please don’t group all Americans in with your attitude, maybe you’ve never heard of La Leche League?

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  3. 3. throw.snow 3:04 pm 09/15/2010

    This comment serves as evidence that no matter what you write, someone somewhere will find something to whine about.

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  4. 4. David Fredericks 3:41 pm 09/15/2010

    I think the nonreligious and open minded need to learn about such selfless gestures to keep things in perspective. It’s wonderful what science can bring — in a small way — to the world’s poorest and most disadvantaged.

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  5. 5. Plaisham 4:52 pm 09/15/2010

    I, too, would like to have had a report of the woman’s reaction or even the audiences’.

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  6. 6. Wayne Williamson 7:05 pm 09/15/2010

    nice article…it would have been nice to have seen the difference in smoke produced, since it sounds like they were measuring it….

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  7. 7. S. Iqbal 11:01 pm 09/15/2010

    Eighteen years ago I had an opportunity to visit Tanzania while I spent three nights in a hotel, Jumbo Inn, in Dar-es-salam. Yes, the views of Tanzania is seen by the HELP enthusiasts are very akin to that of that days. By and large, the Tanzanians are simple by nature with fewer exceptions in the public sector. However, smoke produced by the stoves depends on many factors (parameters); but here I found none of them discussed. Needs attention in this matter……….

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  8. 8. jeanlan02 11:16 pm 09/15/2010

    It sounds very interesting… but please send some pics/drawings of the prototype. THX

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  9. 9. jeanlan02 11:19 pm 09/15/2010

    A laudable effort. Please send some pics/drawings of the prototype. THX

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  10. 10. Alan Buckle 10:27 am 09/16/2010

    S. Iqbal’s comment – that attention be paid to certain aspects is to the point. For example: how dry is the wood? Much energy is consumed to dry out the wood when burning it; an extreme case is when the energy of combustion is almost completely used to dry very humid wood, leaving little heat for ‘work’. Sadly, in some regions wood must be stacked for up to two years, under cover to allow the reduction of humidity to a reasonable level.

    What is the design of the stove? What are the insulating propertiesof the stove walls? Is there control of the air flow into the combusion zone? What design efforts have been made to maximize energy conservation and efficiency?

    If we could be given some details then I am sure that the readers will be able to provide some useful suggestions.

    And who are the people involved in this programme – experience, education etc.? I managed projects in developing countries for some 15 years as an s/m of a UN organization and prior to this I lived for 19 years in South America. I am an informed skeptic!

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  11. 11. Rohbiwan 6:40 pm 09/16/2010

    I think it is fairly simple, our experimenters are not parents. You are right, there is nothing wrong, embarrassing, etc… about breastfeeding a child – even here in America. Nothing funnier than smart people acting really childish.

    Still a great goal for them, and I am sure that while the breastfeeding was no big deal to most of us, perhaps we should go easy on those who are afflicted with shame for no good reason. They meant well.

    I would like some more design specifics, but I am assuming (a risk I know) that these guys did control for the level of humidity in the wood etc to a reasonable point. The number I care about, regardless of design is: 40% less wood used to achieve the same thing – not perfect, but a vast improvement for anyone, from a high school student to a PhD.

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  12. 12. focalist 7:15 am 09/17/2010

    Guys, this is an entry from a running blog. Previous posts include photos of the stove, etc- much of what you are looking for. Great read. Think there’s links to the details. Remember these are blog posts by students.. not the writing and editorial staff.. gven that, I think it’s not bad at all..

    As for the breastfeeding, I’ve got two kids.. but I still somewhat avert my gaze if someone begins breastfeeding. If you want to be offended because I’m trying to be courteous- you are looking for a reason to be offended, and that’s plain unacceptable. You are actually complaining about someone being nice to you!

    Please do not say "act like nothing is happening". That’s unreasonable. Anybody doing something that is different from the group is at least noticed, and you modify behaviour accordingly. If I know the guy behind me is in a wheelchair, I may just hold the door for him, same logic applies.

    When people breastfeed, they must realize that they are the elephant in the room- so if people try to be courteous, get over it..

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  13. 13. S. Iqbal 6:24 am 09/19/2010

    Hello Mr. Buckle! Thank you for your attention. I appreciate your discussion on the stove-issue that included more than expected topic of "smoke". Surely wood-smoke is a gaseous flow contains more co2 and co than the normal breathing air. When the theoretical air (exact amount of air containing oxygen required to combust the carbon and hydrogen of the fuel) supply is less into the system boundary (the wood burning zone within the stove), the hydrocarbon remains partially unburned that produces black smoke. However, in the wood buring we watch curled trails of white smoke which really contains an extra amount of water (in this case vapor). Same is the case, when we crank our automobiles during the winter morning. Thus, the moisture content in the wood matters in producing smoke. Sequentially, while drying wood before combustion (burning) takes place, stove will be producing only white smoke and will turn into black as soon it evaporates the contained moisture in full.

    Most probably, HELP researchers are mostly concerned with the black smoke which leads to idea of developing a fuel efficient stove.

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  14. 14. shylohjacobs 11:47 am 04/5/2011

    Thank you for sharing this! It sounds like a lot of <a href="http://tm.org/westchestercounty">stress</a&gt; is on these kids but, I’m sure the results are satisfying!

    Link to this

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