1. The Water Boiling Test (WBT)
Jackson Mutegeki
Bio-energy Lab technician
CREEC-
Makerere University

2. The Water Boiling Test (WBT)
The WBT is intended to measure stove performance under standardized laboratory conditions:
High (boiling) and Low (simmering) power
Stove body starting Cold and Hot
Standard amount of water in standard testing pot: 5 litres or 2.5 liters
Quantities of time, fuel use, and water evaporated are measured
Every stove is carefully tended to ensure it is operating at its best – all stoves given equal chance to do well.
Each stove is tested at least 3 times
The goal is to compare stoves performing a standard task, to see which can most effectively combust the fuel and transfer the heat into the cooking vessel.

3. Purpose of WBT
WBT is not intended to predict field performance. It is a measure of the capability of the stove design to complete a standard task. Field performance will always depend on the local cooking practice, which cannot be standardized.
The WBT does help make sure that the physical design of the stove is the best it can be.

4. Advantages to the WBT Stoves from around the world can be compared
A target performance level (benchmark) can be set based on comparisons
Effects of changes to a stove’s design can be observed quite clearly

5. Disadvantages to the WBT
Fuel of differing composition/moisture content may behave differently
User operation has a large effect
Difficult to calculate for multi-task stoves
griddle stove for frying, heating stoves
New stoves may perform differently than stoves in use for some time
chimney cleaned or not, parts burning out, etc.

6. WBT Supplies Supplies Needed Standard Testing Pot holding 5L of water
2.5 L can be used for low-powered stoves
Electronic Scale (10-15 kg capacity, 1-2 gram resolution) with Heat-Resistant Pad
Thermometer/Thermocouple (with fast response)
At least 3 kilos of testing wood per test
10L or more of room-temperature water
Metal Tray for Weighing Charcoal
Tools for removing charcoal (tongs, spatula)
Heat resistant gloves

7. WBT Procedure Bring 5L to boil with stove body starting cold
Bring 5L to boil with stove body starting hot
Continue into simmer for 45 minutes at about 3 degrees below boiling
Between each phase, we measure and record:
Time
Mass of fuel
Mass of water in pot
Mass of charcoal remaining

8. WBT Procedure  45 min. SIMMER  COLD START HOT START Tboil
Tboil-6degC
Water
Temperature
Fresh Water
Troom
Time

9. WBT Procedure Phase COLD START HOT START SIMMER Task
Bring to Boil 5L in first pot
Bring to Boil fresh 5L in first pot
Simmer remaining 5L for 45 minutes
Record
Time
Fuel
Water Charcoal
Water
*Assume Same Charcoal as Cold Start*
Charcoal

10. WBT Procedure Need to determine Local boiling point
Temperature as measured when a rolling boil with bubbles breaking the surface is observed
Temperature stops rising
Wood Species and their Calorific value:.
Moisture content of wood

11. WBT Data Analysis
Upon completion of the test, simply enter the data into the WBT Data-Calculation Spreadsheet (available online):

12. WBT Data Analysis Automatic Data Calculation Sheet Provides:
Results are corrected for
starting temperature of water
moisture content of fuel
Energy remaining in charcoal not provided to the pot
Time to boil, firepower, and thermal efficiency are calculated.
Results can best be presented in the form of temperature-corrected specific fuel consumption and specific emissions, g/L, representing the fuel and emissions per task completed.
This is preferable to Thermal Efficiency

13. WBT Data Analysis Mass of Water Boiled Specific Fuel Consumption = X [
Starting Temperature
Correction
Moisture Content
Correction
Charcoal
Correction 75
(Tboil-Tstart)
X [
MassWood-MassMoisture-Mass *Char]
Wood Used to Evaporate Moisture
Mass of Water Boiled
Specific (per Liter)
Correction

14. WBT Data Analysis
The overall number we most look investigate is:
FUEL USE TO COMPLETE the 5L WBT =
Average of Cold and Hot start Specific Consumption
Specific Consumption to Simmer
5 x +

15. WBT Data Analysis
In case you want to compare the Fuel use of stoves burning different energy content fuels, you can calculate energy consumption by:
Energy Use (kJ) = Fuel Use (kg) *
Calorific Value (kJ/kg)

16. WBT Sample Size
At least three full tests per stove design are recommended
Then variation can be analyzed and used to determine if more tests are needed

17. WBT Emissions
“Collection Hood” -- The best way to measure emissions during the WBT is to collect them and analyze the total mass emitted during each test phase. This is done by knowing both the concentration and flow rate exiting the collection hood.
“Test Kitchen” -- If all WBTs are conducted in one room with stable ventilation, then levels of IAP can be measured and compared. This is a reasonable option if a hood is not available, but will not give as precise information. It also subjects the tester to breathing smoke, and additional smoke is created between test phases.

18. WBT - PEMS
The Portable Emissions Monitoring System (PEMS) collects all of the emissions and measures:
CO Concentration
CO2 Concentration
PM Concentration
Flow through the hood
Temperature of flow
Then mass of each pollutant is calculated in an automatic spreadsheet when data from the WBT is provided, giving:
Total Emissions
Pollutant/CO2 ratios
Emissions to complete the WBT used for benchmarking