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what is calorific value?

The calorific value (or energy value or heating value) of a substance, usually a fuel or food, is the amount of heat released during the combustion of a specified amount of it. The energy value is a characteristic for each substance. It is measured in units of energy per unit of the substance, usually mass, such as: kJ/kg, kJ/mol,kcal/k,Btu/lb.Heating value is commonly determined by use of a bomb calorimeter.

The heat of combustion for fuels is expressed as the HHV, LHV, or GHV.

Higher Calorific Value (or Gross Calorific Value - GCV, or Higher Heating Value - HHV) - the water of combustion is entirely condensed and that the heat contained in the water vapor is recovered.

Lower Calorific Value (or Net Calorific Value - NCV, or Lower Heating Value - LHV) - the products of combustion contains the water vapor and that the heat in the water vapor is not recovered

Gross heating value-Gross heating value accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal, which will usually contain some amount of water prior to burning.