Wood-fired Water Heater Test Results: Woodstove vs Rocket Stove
WOODSTOVE
The wood stove system had an efficiency of about 33% and a power of 4.1kW
For the wood stove test I loaded the stove with 8lbs/3.63kg of very dry Larch firewood which lasted through the entire test of heat 106 liters of water from 45F/7.2C to 140F/60C and took 95 minutes. After the water reached 140F/60C I removed all the remaining wood in the wood stove and let it go out. There was about 1.25lbs/0.57kg of fuel left so I used 8lbs/3.6kg for my efficiency calculations which go as follows.
8lbs/3.6kg of dry Larch
106 liters of water
45F/7.2C to 140F/60C
95 minutes/5700 seconds
Gasoline used cutting firewood - 0.0065 liters
Energy content of larch wood - 19.5 MJ/kg
Energy content of gasoline - 34.2 MJ/L
Calculations:
Heat transferred to water - Q=m⋅cp⋅ΔT
m=106kg
cp=4.18 kJ/kg°C
ΔT=60°C - 7.22°C = 52.78°C
Q=106×4.18×52.78=23362.31 kJ
Energy inputs
E=kJ
Larch=70760.35 kJ
gasoline=222.3 kJ
total=70982.65 kJ
Efficiency
Q/E
23362.31/70982.65=0.329127
32.9% efficiency
Power=Q/t
23362.31/5700=4.1kW
ROCKET STOVE
The rocket stove system had an efficiency of about 30% and a power of 7.3kW
For the rocket stove test I used 9lbs/4.08kg of dry Larch firewood for the entire test to heat 106 liters of water from 43.2F/6.22C to 141F/60.56C and took 55 minutes.
9lbs/4.08kg of dry Larch
106 liters of water
43.2F/6.22C to 141F/60.56C
55 minutes/3300 seconds
Gasoline used cutting firewood - 0.0065 liters
Energy content of larch wood - 19.5 MJ/kg
Energy content of gasoline - 34.2 MJ/L
Calculations:
Heat transferred to water - Q=m⋅cp⋅ΔT
m=106kg
cp=4.18 kJ/kg°C
ΔT=60.56°C - 6.22°C = 54.34°C
Q=106×4.18×54.34=24064.87 kJ
Energy inputs
E=kJ
Larch=79605.39 kJ
gasoline=222.3 kJ
total=79827.69 kJ
Efficiency
Q/E
24064.87/79827.69=0.329127
30.15% efficiency
Power=Q/t
24064.87/3300=7.29kW
