Fuel types
A methane rich gas produced through the anaerobic (without air) digestion of organic wastes. It can be generated from animal and kitchen wastes, as well as some crop residues.
Biomass refers to all organic matter derived from living or recently living organisms, plant or animal-based. Processing the biomass into compact, evenly sized pieces, such as pellets or briquettes, allows the biomass to burn more efficiently and evenly, increasing energy density and transportability.
Briquettes are molds of compressed biomass and can be made into a variety of shapes and sizes depending on the feedstock, the level of compactness and mold used and are usually no smaller than 2cm. Carbonized fuel briquettes are made from waste materials that have undergone carbonization (the conversion of organic substances into carbon in the absence of oxygen) and act as a replacement for charcoal. Non-carbonized briquettes are produced from waste materials that are partially decomposed and then dried and often serve as a replacement for firewood and raw biomass fuel.
A wood fuel made from burning wood in a low-oxygen environment. The dense black substance that results is made up mostly of carbon and produces more heat and energy per kilogram than wood.
A black, solid, carbon-rich material found underground and is among the most prevalent fossil fuels.
Crop residues
Non-edible plant parts that are left in the field after harvest. Crop residues can include straws, stems, stalks, leaves, husks, shells, peels, etc.
A clean liquid biofuel that can be made from a variety of feedstocks including sugary materials such as sugar cane, molasses, sugar beet, or sweet sorghum; starchy materials such as cassava (manioc), potatoes, or maize; or cellulosic materials such as wood, grasses, corn stover and other agricultural residues.
Ethanol Gel
Produced by denaturing ethanol from sugar or starch crops and mixing it with a thickening agent (cellulose) and water through a very simple technical process, resulting in a combustible gel.
A liquid product of crude oil that is widely used in urban households for cooking, heating, and lighting. Also called paraffin in some countries.
Liquefied Petroleum Gas (LPG)
A co-product of natural gas and crude oil production and usually consists of a mixture of propane and butane for standard heating and cooking purposes.
Smaller and denser, short roundish sticks of 6-12 mm diameter and are shaped by pressing dry biomass through a die with many holes. They are made through a process called densification, by applying intense pressure to loose biomass residues.
Direct sunlight is used to heat and cook by directing the sun’s thermal energy to power solar cook stoves.
A type of biomass that is a porous and fibrous tissue found in the stems and roots of trees and other woody plants. In the context of cooking, ‘wood fuel’ refers to any energy source that comes from woody biomass. These cover a range of fuels, including fuelwood (sometimes termed firewood), charcoal, wood pellets, biogas, cellulosic ethanol, and other advanced forms of bioenergy. Fuelwood, or firewood, consists of any unprocessed woody biomass used to fuel a small fire, most often for cooking or warmth.
IWA metric for efficiency, high power
Thermal Efficiency
Fraction of heat produced by the fuel that made it directly to the water in the pot. The remaining energy is lost to the environment. So a higher thermal efficiency indicates a greater ability to transfer the heat produced into the pot. This metric is more appropriate than specific consumption for the high power phases of testing.
IWA metric for efficiency, low power
Specific consumption
Amount of fuel required to boil (or simmer) 1 liter of water for one minute. This metric is more appropriate than thermal efficiency for the lower power (simmer) phase of testing.
IWA metric for indoor emissions, CO and PM
Emissions rate, CO or PM
Mass of CO or PM emitted per time
IWA metric for total emissions, high power, CO and PM
Emissions per energy delivered to pot, CO or PM
Mass of CO or PM per cooking energy delivered to the pot. Preferable for high-power phases because emissions is reported in terms of the desired output, cooking energy and enables comparisons between stoves and fuels
IWA metric for total emissions, low power, CO and PM
Specific emissions rate, CO or PM
Mass of emissions of CO or PM per time per liter of water. This metric is preferable for the low-power phase because the difficulty in calculating the cooking energy delivered to pot due to relatively constant water temperatures) and variation in steam production.
IWA Tiers of Performance
Efficiency/Fuel Use IWA Tier Value
Based on specific consumption (low power) and thermal efficiency (high power)
Indoor Emissions IWA Tier Value
Based on emissions rate
IWA Tiers of Performance
The International Organization for Standardization (ISO) International Workshop Agreeement (IWA) outlines four indicators for rating performance, each along five tiers. Tier 4 is the highest performing and Tier 0 is the lowest performing. The IWA also specifies minimum requirements for methodology. Tiers of Performance for efficiency, total emissions, and indoor emissions are determined by taking the minimum of the low power and high power metrics. This definition of Tiers may change with future updates to the ISO IWA in the ongoing standards development process. For stoves that are designed to operate at one power level, please refer to the sub-tiers to evaluate the performance for the intended power level.
Safety IWA Tier Value
Based on the result from the Biomass Stove Safety Protocol
Total Emissions IWA Tier Value
Based on specific emissions rate (low power) and emissions per energy delivered to the pot (high power)
Emissions per mass of fuel, CH4, CO, PM2.5
Mass of emissions of methane, CO, or PM2.5 per mass of fuel used
How quickly fuel was burning, reported in Watts (Joules per second). It is affected by both the stove (size of fuel entrance/combustion chamber) and user operation (rate of fuel feeding). A higher or lower value is not necessarily preferable, but rather is an indicator of the size of the stove.
Fuel consumed
Mass of fuel consumed per task
Mean time to boil
Time needed for the water to reach boiling temperature from the starting temperature, averaged between the cold and hot start phases.
Biomass Stove Safety Protocol
This protocol includes set of guidelines and safety evaluation procedures using simple equipment to evaluate sharp edges, tipping, fuel containment, and surface temperature. The protocol also includes guidelines for use by designers to create safer stoves. An overall safety rating can be calculated through a combination of individual test results.
Controlled Cooking Test
The Controlled Cooking Test (CCT) is a field test that measures stove performance in comparison to traditional cooking methods when a cook prepares a pre-determined local meal. The CCT is designed to assess stove performance in a controlled setting using local fuels, pots, and practice. It reveals what is possible in households under controlled conditions but not necessarily what is actually achieved by households during daily use.
Field Testing
Field-based tests demonstrate how stoves perform with local cooks, foods, practices, and fuels.
Heterogeneous Testing Procedure
This standard operating laboratory procedure, developed for use at the SeTAR Centre at the University of Johannesburg, is intended to describe routine operation of stove emissions performance and stove efficiency performance with detailed quality control procedures for the reproduction of results. This procedure uses mass loss and temperature gain for the determination of thermal efficiency.
Kitchen Performance Test
The Kitchen Performance Test (KPT) is a field test used to evaluate stove performance in real-world settings. It is designed to assess actual impacts on household fuel consumption. KPTs are typically conducted in the course of an actual dissemination effort with real populations cooking normally, and give the best indication of real world performance.
Laboratory Testing
Laboratory-based tests evaluate stove performance and quality in a controlled settings with repeatability, allowing for differentiation between stoves, selecting the most promising products for field trials, and ensuring that manufactured stoves meet intended performance based on designs.
Uncontrolled Cooking Test
The University of Johannesburg SeTAR Centre has developed this method that is similar to the CCT, but meal is not constrained and the cook is free to prepare what they want, how they want, with the only measurements being that of the firewood used and the final mass of food cooked as part of an actual household meal. Compared to the KPT, the UCT has the potential to offer a more rapid and lower cost way of assessing the energy savings delivered by a new technology.
Water Boiling Test
The Water Boiling Test (WBT) is a laboratory-based test that can be used to measure how efficiently a stove uses fuel to heat water in a cooking pot and the quantity of emissions produced while cooking. This test can be used to evaluate stove changes during development, compare the effectiveness of different designs, select the most promising products for field trials, and ensure that manufactured stoves meet intended performance.
Stove characteristics
Batch loaded
A stove in which fuel is loaded one time for each use
Stoves which produce charcoal through the process of pyrolysis of biomass
Built in place
A stove that is built in place in a home and cannot be moved
Stoves with insulation to keep heat inside
A structure which provides ventilation of gas and smoke from the stove to the outdoors
Stoves with a fan to improve combustion
Gasifier (TLUD)
Stoves in which the pyrolysis and combustion phases of burning fuel are separated
A stove with a griddle surface
A stove used for cooking that is also designed to provide heat
Heat-trap box
A type of solar cooker
Stoves appropriate for use in a domestic/home/family setting
Cooking by electromagnetic induction through heating a conducting material
Stoves appropriate for large scale cooking, used in public settings such as businesses, schools, etc.
Multiple burners
A stove that accommodates the use of more than one pot at a time
Natural draft/Rocket
A type of stove also known as side-feed
Newer stove technology designed to improve efficiency, cleanliness, and/or safety
Other open fire
A cooking structure without a sealed combustion chamber or ventilation system
A type of solar cooker
A type of solar cooker
A lightweight, smaller stove designed for mobility or easy transport
Pot skirt
A tube, usually made of sheet steel, that surrounds a pot creating a narrow space so that more of the heat in the flue gases enter the pot
A type of alcohol stove with pressurized burners
A stove model still under development
Stoves with a door or opening on the side which allows for side-loading of fuel
Sunken pot
Type of stove in which the pot is sunken into the stove to improve heat transfer
Thermoeletric generator (TEG)
An added device to convert excess heat to electricity that can be used to power a fan, power a light or charge a phone
Three stone fire
Traditional method of cooking where a pot is balanced on three stones over an open fire
Local methods of cooking using cultural practices and methods
A dried mud or brick stove enclosure with the opening in the front for fuel and a smaller hole at the rear for ventilation
Used to draw fuel from a tank or reservoir to a burner
Test phases
High power, cold start phase of WBT
Begins with the stove at room temperature and the stove is operated on high power
High power, hot start phase of WBT
Conducted after the cold start phase while the stove is still hot and the stove is operated on high power
Low power phase of WBT
The stove is operated on low power, enough to simmer water just below boiling point for 45 minutes
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