Purpose:
In this workshop you will get to see four or five different cook stoves in operation. You will measure the energy used by each stove to cook a meal of rice and beans and compare these to the other stoves or electrical burners. Using authentic set ups for cooking means that the pot size, flame control and many other factors may not be the same. You will extrapolate to the amount of fuel that it would take for a year of cooking and how much that would cost or the environmental impact.
Why this is an environmental problem:
Many people in the world cook their food on indoor or outdoor cook stoves that are run on wood, propane or kerosene. These stoves range from two adobe walls with sticks burning to more sophisticated stove design. Cooking is required to provide the full nutrition from staples such as beans and rice as well as for preparation of meats. In addition, many times water needs to be boiled for drinking or cooking.
Wood, fibrous plants and dung are a common source of cooking fuel. Traditional cooking stoves can be very inefficient which leads to several types of impacts:
- higher fuel requirement leads to deforestation near population centers
- turning wood into charcoal so that it can be shipped to urban areas is a dangerous and polluting process on it's own
- cooking indoors creates particulate and gas pollutants that are hazardous to the health of the, mostly, women and children who are inside
- creation of soot and wasted carbon dioxide contributes to climate change
This is a case of examining the I=P*A*T equation and looking for ways to reduce the impact by employing better (more efficient) technologies.
Facts for context
There is reported to be a fuelwood crisis in the third world. Demand is outstripping the availability of wood for cooking, leading to deforestation and soil degradation because no new organic input to the soil.
80% of energy in Sub-Saharan Africa is biomass.
In India, indoor air pollution is estimated to cause 400,000 to 500,000 premature deaths per year.
Energy input, loss and use:
A crude estimate of the minimum amount of energy it takes to cook a meal would be to calculate how much fuel would have to be burned to heat 1 liter of water to boiling. After the water is boiling or if the food preparation calls for simmering, the subsequent energy use (after getting it to boiling) would be less per minute, but might require a long cook time.
Estimating the energy required:
- to raise the temperature of 1 liter of water from 25 C to 100 C requires 75 deg * 1000 cal/deg = 75 kcal of energy at 100% efficiency
- of 300 kcal of energy at 25% efficiency
- A 25% total efficiency is a guess but includes all the heat escaping from the stove, the heat to warm up the stove itself, etc.
Wood as fuel to get 300 kCal:
- wood contains about 4 kcal/gram of wood
- (300 kcal) / (4 kcal/gram) = 75 grams of wood or about 2.5 ounces of wood
Propane as fuel to get 300 kCal:
- propane contains about 12 kCal / g of fuel
- 300 kCal/(12 kCal/gram) = 25 grams of fuel (less than an ounce)
Using an electric burner to get 300 kCal:
- 1 kW-hr is equal to 860.5 kCal
- 300/860.5 = 0.35 kW-hrs
- which is the same as the energy put out by a 1000 watt burner for 21 minutes.
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