Chapters 8.15
8.15 - High efficiency cook stoves and pot skirts
Gryphon Theriault-Loubier, University of Guelph, Canada
Suggested citation for this chapter.
Theriault-Loubier,G (2022) High efficiency cook stoves and pot skirts. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
Introduction
Humans have been cooking food for at least 250,000 years, with some anthropological evidence dating the use of fire in cooking to 1.2 million years ago (Wrangham, 2003). Historically, cooking food has been a laborious endeavor, requiring the gathering of fuel in the form of wood and maintenance of equipment (Wrangham, 2003). Globally, a continued reliance on fuel woods is thought to be associated with deforestation, or at least forest degradation (Adeoye, 2011; Htun, 2013). As fuel wood becomes unavailable, some common substitutions for cooking fuel are crop residues and animal dung, which are crucial agricultural inputs for a subsistence farmer.
Most often, wood gathering has been relegated to children and women in particular, taking up a large proportion of their time (FAO, n.d.). Sexual assault often occurs as females collect fuelwood so minimizing the number of trips improves security (FAO, n.d.)
In many cultures, cooking indoors is a matter of practicality due to weather. Indoor cooking results in measurable impacts on the short term and long term health of women caused by the normal products of combustion including particulate matter (smoke) and noxious by-products such as benzene (C6H6) and carbon monoxide (CO). Naehler (2007) found that smoke from burnt wood suppresses the immune system. Some of the most commonly implicated illnesses are eye and lung irritations and associated pneumonias (Ochieng, 2013). Person (2012) estimates that globally, women and children are exposed to an average daily median of five hours of indoor air pollution where indoor cooking fires are commonplace. This exposure has been associated with approximately 1.5 million deaths in children <5 years of age, caused by acute respiratory infections related to indoor smoke, ostensibly from “inefficient” cooking stoves (Person 2012). This does not take into qualitative discomfort of coughing or runny nose or associated exposure to heightened room temperatures (Person, 2012).
Increasing the efficiency of cooking - thereby reducing pollution, fuel use, and time spent cooking is critical to improving social and economic outcomes. Recognizing this, many small-scale projects have emerged in various countries with products to meet this challenge. There are important misconceptions, however, about which cooking stove models improve either fuel efficiency or negative health effects (see below). Table 1 below evaluates a few promising cook stoves. One widely used stove is the ‘upesi jiko’ (Swahili for “quick stove”), which has been described by the United Nations as a “local solution to a global problem” (UNEP, n.d.) The distribution of this stove had a measurable effect in reducing fuel use and cook time, as well as visible smoke in the homes and associated eye irritation (Foote, 2013). The cost is approximately $2 USD for a single unit stove, and an additional $3 USD for a more permanent installation (Foote, 2013), though it should be noted that research indicated a high variability in stove design, price, efficiency, and health effects.
Table 1. Summary of selected improved cook stoves.
Understanding Engineering Principles of Healthy, High-Efficiency Stoves (Adapted from Aprovecho Technical Manual)
Though there is a wide variance in available products, many of the general engineering principles are similar. The information provided below is intended to inform the reader of the characteristics and misconceptions of what defines a high-quality stove, which need not be expensive.
Efficiency
There is an apparent misconception about what makes a cook stove efficient: cook stove efficiency is not only about converting fuel into heat but also about transferring the heat to the pot. For example, a three-stone fire is considered quite effective at turning wood into heat, known as combustion (70-90% efficient), but its inefficiency comes from only 10-40% of the released heat reaching the pot. Improving the efficiency of heat transfer is now thought to be more critical for human health by reducing emissions.
Insulation
around the fire itself should ideally be made of lightweight, semi-porous, heat resistant materials. Insulation with a porous material helps to maintain airflow and temperature, encouraging a more complete combustion that reduces smoke and other toxic byproducts. Many commercial Jiko stoves use a ceramic liner for this purpose – some models have an insulative brick chimney.Airflow
is critically important to ensure efficient combustion. For this reason, a grate is often used under the space where combustion (fire) occurs to allow airflow to the fuel from all sides. A draft is important as well; closed box type stoves should have an access door and chimney that are roughly the same size to help maintain a steady draft. Insufficient airflow will result in more smoke and charcoal, but an excess of air will keep fire temperature low. A method of controlling airflow would be helpful, to adjust as necessary according to task.Venting
is the use of a chimney to evacuate smoke to the outdoors. Venting has been shown to have superior health benefits, but is usually costly than a simple intervention as it requires installation.Critical Analysis
Wood reduction:
Barnes (1993) estimated that approximately 300-600 kg of wood per family per year was saved, at a value of $15-84 (1993 USD) with the use of more efficient cook stoves, depending on location and materials used. For families that survive on $1-2 per day, these savings are substantial.Human health:
Research is ongoing to determine the health effects of using an improved cook stove. The issue is complex, not least because so many different models exist. Generally, it seems logical that most stoves, when used properly and maintained, will emit less carbon monoxide and other toxic gases. However, in 2010, the University of California-Berkeley evaluated 50 different models of improved cooking stoves in laboratory tests. The Berkeley study found that even poorly designed stoves can reduce fuel use compared to a three-stone fire, but may increase emissions of carbon monoxide perhaps because the improved stoves use charcoal (MacCarty, 2010). Ochieng (2013) found that a homemade rocket mud stove does produce less carbon monoxide than a three-stone fire, but still emits above World Health Organization guidelines, which is “unlikely to lead to appreciable health benefits.” While Harris (2011) found a 26% decrease in reported lower respiratory tract clinic visits in Santa Avelina, Guatemala, after the implementation of ONIL brand efficient stoves in 90% of households, Foote (2013) found that Jiko stoves are not effective in preventing respiratory diseases in children. Foote cited one of the main reasons for this observation was that combined use of Jiko with more traditional methods continues to prevail in households. The reasons for this are not explicitly stated, however Barnes (1993) attributes the prevailing use of traditional stoves over efficient stoves to a number of reasons, including perceived protection from insects provided by smoke, better and more efficient accommodation of pan sizes, waste heat as heating the home, and in some cases the wider variance of acceptable fuels in traditional stoves. Barnes also notes that cash expenditures are often non-existent in construction of traditional stoves, As a result, it is suggested that deployment of this technology would need to be highly region specific, taking into account the reasons traditional stoves are used. Interestingly, Barnes (1993) believes that the best market for new stove technology deployment will be urban and peri-urban, where fuel woods are already scarce and people alreadypurchase both fuel and stoves.
Improved stoves for profit and jobs:
More cost-effective cook stoves can enable post harvest processing and value addition of goods such as converting grains into flat bread or dry, roasted snacks. Stove building can also create a source of local employment (Ingwe, 2008). However, Wawire (2010) noted mixed results in Jiko stove making as an enterprise. While economically successful and sustainable, individuals cited relatively heavy time commitments needed to make the stoves and the tedious nature of the work as being among the factors influencing negative perception of the industry.Constraints to adoption
In addition to the above discussion, there are several constraints to adoption of improved cook stoves. For example, Foote (2013) found that despite market subsidization and market promotion in the region studied, less than 20% of households owned a stove. Some high-efficiency stoves, such as the ONIL brand, are in the price range of $150 each and are therefore most likely out of reach for many families (http://www.helpsintl.org/programs/stove.php). Of interest is the effect of the local perception of fuel shortages as compared to scientifically predicted shortages. For example, if a local population does not perceive an imminent wood shortage, Barnes (1993) showed it might not adopt jiko stoves as easily. The reader is encouraged to read a more recent article which has integrated potential constraints to adoption of improved cook stoves into a cost-benefit analysis for different stove types, including capital costs, costs of
repair and fuel, time savings, health and environmental benefits (Jeuland and Pattanayak, 2012).
One critical issue is that improved stoves typically only accommodate one pot, whereas a three-stone fire can accommodate several pans at once while also keeping other food warm through proximity.There are cultural reasons why an improved cooking stove may not be adopted. For example, a traditional Punjab dish in India is Kadhi, which uses chickpea flour and buttermilk or yoghurt to produce a creamy dish eaten with pakoras, roti or boiled rice. Rocket stoves are most often designed with the fastest water boiling time as benchmark. Yet in this instance, the boiling of a liquid is not desired because the milky stew would scald (Barnes, 1993) -- few stoves have an option to “turn down the heat” once the fuel has been inserted aside from removing some of the fuel. Other cuisines seek to ‘slow cook’ food to increase flavor. In addition, some cultures use clay pots with rounded bottoms to cook food – a stove with a flat heating surface would be inefficient and possibly unsafe for heating this kind of pot. Many stove models can be adjusted to have ‘open’ access points that allow a rounded pot to sit comfortably – a skirt around the pot or a chimney would be necessary to ensure adequate airflow.
Therefore, adjustments to an introduced stove, or additional technology may be needed according to cooking preferences. Ultimately, field-testing the stoves in situ will be of critical importance in determining efficacy prior to large-scale projects.
Pot Skirts
An appropriate technology would in this case be one that is adaptable and expandable to a given situation. To this end, one of the most inexpensive and simple interventions in cooking in the developing world may be the pot skirt. A pot skirt wraps around a pot to seal any gaps around the pot relative to the fuel source below, thus improving heat transfer. In fact, pot skirts have been found to increase fuel efficiency of rocket stoves by 20% (MacCarty, 2010). A pot skirt can also be used in conjunction with a jiko stove or traditional three-stone fire. An advantage of an effective pot skirt is that it can be adapted to a variety of sizes of pan or pot.
Currently, affordable pot skirts are not for sale, however the Haiti rocket stove project has full instructions on how to construct a relatively efficient stove and accompanying pot skirt.
Picture Based Lesson to Train Farmers
Source: MN Raizada and L Smith (2016) A Picture Book of Best Practices for Subsistence Farmers. eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada.
Further Information
The Gaia Movement has insturctions on How to Build a Jiko Stove. Also see How to build a rocket stove . Aprovecho, an NGO based out of Oregon, has high quality, open access information on the design and improvement of cook stoves, with information in Spanish and Italian in addition to English. Visit the website or contact info@aprovecho.org 541-767-0287
Purchasing information
In Kenya, through mPesa, which delivers to 20+ locations around East Africa http://kenyacharcoal.blogspot.ca/2009/12/buy-energy-saving-jiko-and-plant-52.html) Contact Teddy via email at teddykinyanjui@hotmail.com
A highly polished line of advanced products is available through Colorado State university (http://www.envirofit.org/products/?pid=4) For ONIL stoves http://www.helpsintl.org/programs/stove.php
Further Sites of Interest:
http://www.cleancookstoves.org/
http://www.povertyactionlab.org/
(http://www.solutions-site.org/kids/stories/KScat2_sol60.htm)
References
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