Increasing rates of deforestation have resulted in demand exceeding supply and thus large increases in the price of wood. In Kenya, many schools with 400 pupils now, on average, spend $3000 per year on fuel for cooking.
In some areas, as wood becomes scarce, schools resort to burning residues. This leads to an increase of toxic emissions. Health authorities are concerned about the decrease in hygiene and safety in the kitchen and are looking for solutions to the problem.
Over the past 4 years, Biomass Energy Services and Technology (BEST) has worked with researchers, entrepreneurs and extension of ficers in developing and developed countries to meet the needs of such institutions.
In the Pacific island nations of Vanuatu and the Solomon Islands, architects at Gazzard Sheldon have been designing schools to be as energy-efficient as possible. The criteria for their stoves included the following:
- long life and low maintenance requirement
- should be able to be repaired locally
- easy to light and quick to heat, will stay hot over night
- can boil 180 litres of water in under 60 minutes
- smokeless in the kitchen
- use a pot with a 200 litre capacity, easy to stir and remove
- cost less than US$3.000 delivered to the school.
During the design phase, materials were selected, design calculations were carried out and a prototype built and tested. Modifications were made and a production model was built. After further tests, another 11 stoves were built for tests in the field.
The inner walls are lined with insulating refractory material to ensure heat retention and quick heating to operating temperature. The firebox is lined with tough firebrick to withstand abrasion from the wood and the grate is made of 6mm mild steel angle. This steel is available in the Pacific Islands and can be easily obtained when the grate wears out (after about 5-10 years). The doors are made of mild steel plate and lined on the inside with stainless steel. The handles for the door and air controls are made from stainless rod.
Design work was carried out on a range of pot sizes, resulting in a pot size of 750mm die with a depth of 500mm. A bronze tap is fitted to the bottom to allow hot water to be easily removed and for the pot to be cleaned.
The use of secondary air and a properly sized grate ensures that, once the stove is operating, it is nearly smokeless. Time for boiling 150 litres of wateris approximately 35 minutes with a thermal efficiency of about 45% (5-10 times more than an open fire).
If the unique air control system is used properly, the cook needs only to stoke the fire 2-3 times. At the end of each day the air holes are closed and the stove will remain hot, producing 40°C hot water overnight. This can be used to make the morning tea or for bathing.
Table 1: Stove Specifications
|Pot capacity||200 litres|
|Pot diameter||750 mm|
|Grate area||23 m2|
|Approximate weight||100 kg|
|Chimney diameter||20 cm|
It can be seen that the performance of this stove is dependent on the heat output. If the fire is carefully controlled, then an efficiency of 47.7% can be achieved. If the cooks are in a hurry to bring the water to boil, the efficiency can be as low as 35.6%. Under all operating conditions, water will boil in less than 60 minutes. The stove needs to be stoked 3 to 4 times to bring the water to boil, after which there is sufficient retained heat in the walls and charcoal to keep the food simmering for another hour.
Table 2: Summary of Test Results
|Stove||Output Boil Simmer Efficiency|