The gross (high) and net (low) heating values.
The heat value is
- the amount of heat produced by combustion a unit quantity of a fuel
We differentiate between gross and net heating values:
Gross (or high, upper) Heating Value
The gross or high heating value is the amount of heat produced by the complete combustion of a unit quantity of fuel.
The gross heating value is obtained when
- all products of the combustion are cooled down to the temperature before the combustion
- the water vapor formed during combustion is condensed
In thermodynamics, the term standard heat of combustion corresponds to Gross heating value. See Heat of combustion for examples of calculation of gross heating values from standard heat of formation of substances.
Net (or lower) Heating Value
The net or lower heating value is obtained by
- subtracting the latent heat of vaporization of the water vapor formed by the combustion
from the gross or higher heating value.
Common units for heating value:
- 1 Btu/lb = 2326.1 J/kg = 0.55556 kcal/kg
- 1 J/kg = 0.00043 Btu/lb = 2.39x10-4 kcal/kg
- 1 kcal/kg = 1.80 Btu/lb = 4187 J/kg