The Comparative Water Boiling Test for Charcoal
The Comparative Water Boiling Test (CWBT) is an adaptation by Jean-François Rozis of the test method and procedure of the international standard Water Boiling Test (WBT), modified to account for the real customs and habits of cooking in Cambodia. CWBT is only for comparing stoves’ Potential Fuel Savings under similar conditions of use, which eliminates error sources from fuel heat value calculations.
The CWBT is designed to duplicate as closely as possible real cooking conditions. As well, the CWBT is designed to be simple – it requires minimum equipment easily available in Cambodia and is easy to conduct in the field. The CWBT also simplifies the calculation at the end of the test.
The CWBT is designed for Cambodia, but its general procedure could be adapted for use in other countries.
Procedures presented here are for testing of charcoal. The following two sets of procedures are also available:
Minimum Recommended Equipment: The best way to process this test is on a minimum of two stoves at the same time to obtain exactly the same external conditions (it depends on thermocouple probes availability).
- A digital watch with second precision
- An accurate platform scale (ratio between precision of the measure and maximum weight should be lower than or equal at 1%), a simple balance almost available in all villages (like Tanita 2 kg balance made in Vietnam and accurate within 10 grams)
- Digital thermometer with thermocouple K type probes if possible or other type of thermometer able to indicate temperature in water until 100 °C (accuracy of 1 °C)
- A form for recording data
- Cylindrical aluminum pots/pans with flat bottom and with lids: diameter of the pot rim and bottom should be 23,8 cm, the height should be 11 cm, and the thickness of the pan should be 2 mm. Two pan lids should allow for the thermocouple probes to be fixed through the insulated cap in the center of lids and 1 cm above the internal bottom of the pot to permit measurement of the water temperature. Cylindrical aluminum pots with flat bottom with lids; diameter of the pot rim and bottom part 23,8 cm, height: 11 cm and thickness of pan: 2 mm
- 25 grams of local resin (from dipterocarpus alatus) used traditionally as fire starter
- 400 gram of charcoal for 3 liters of water (to be adapted following fuel consumption of your stove, to obtain reasonable TTB –around 20 minutes-and TTT – around 60 minutes)
Moisture range of wood: Charcoal has to be stored in a dry location for ensuring moisture content between 3,5 to 5 %.
Test principle for a one-pot hole like Lao Bucket Stove: - Weigh the recommended amount of charcoal (400 gr).
- For comparative information, register the room temperature.
- The stove should be cold and clean, installed in a room protected from the wind in the direction to the fire door.
- Ignite the charcoal by burning the resin and placing it in the stove grate, followed by a few pieces of charcoal, then add all remaining pieces of charcoal.
- Wait 5 minutes after ignition.
- Place the pot with the instrumented pot lid 1 cm above the internal bottom of the pan on the stove.
- The fuel is managed in such a manner as to obtain the maximal output power possible during the high power phase, so as to reach as quickly as possible the boiling point in the first pot. The boiling point is reached when the temperature is stabilized, around 99 °C, after 10 seconds.
- Time To Boil (TTT) is recorded.
- As the habit when cooking with charcoal is to maintain the high power phase, allow the combustion process to continue without intervention. This permits a kind of regulation to operate, as each charcoal stove has its specific operating power, and thus accounts for the fact that the individual cooking prefers the stove which can ensure the higher operating power; also accounted for is the fact that the cook prefers the stove which consumes less charcoal (or a longer Total Time Test in our case).
- Check the fire to obtain total charcoal combustion without any temperature drop under Boiling Temperature minus 2 °C.
- Total Test Time is recorded.
- The maximum remaining charcoal weight must be 20 grams to accept the test.
- Weigh the remaining water in the pot.
NB: If this is the first time the cookstove to be tested has been used, make two to three cooking processes before initiating any comparative test to take out any moisture content in the stove body.
Analysis of the test measurements The test should be conducted at least three times (CWBT 1, CWBT 2, CWBT 3); be aware of the similar initial conditions (e.g., cold at ambient temperature, clean stove, no wind, water, pot). If the test is conducted with two stoves at the same time, then change the instrumented pots between the two stoves to reduce the experimental error.
Calculate the average (sum of the three tests divided by 3)
- Calculation of Useful Energy (UE)
Useful energy depends on the quantity of water, the starting water temperature and the amount of water evaporated water:
For example, UE [in KJ]= 1068 + 2257* (3-remaining water [in Kg])
- Potential Charcoal Savings (PCS) Compared With Old Design
Percentage of Charcoal Savings is the difference between Useful Energy of the New Stove Design and Useful Energy of the Old Stove Design, divided by Useful Energy of the Old Stove. If negative, then the new design is consuming more fuel for the same purpose than is the old design.
So, PCS [in %]= 100*(UE new stove – UE old stove)/UE old stove
Related topics - The Water Boiling Test based on VITA 1985 - the 'International Standards'.
- The Indian standard WBT procedures developed by the Bureau of Indian Standards, for measuring the efficiency of the cookstoves.
- The Chinese standard WBT procedures developed by the State Standards Organization of the People's Republic of China - "Testing Method for the Heat Properties of Civil Firewood Stoves".
Contributors User:Erin Boyd 27 March 2006
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