Higher heating value

The higher heating value (HHV;also known gross calorific value or gross energy) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25°C) once it is combusted and the products have returned to a temperature of 25°C. The higher heating value takes into account the latent heat of vaporization of water in the combustion products, and is useful in calculating heating values for fuels where condensation of the reaction products is practical (e.g., in a gas-fired boiler used for space heat).The higher heating value is experimentally determined by concealing a stoichiometric mixture of fuel and oxidizer (e.g., two moles of hydrogen and one mole of oxygen) in a steel container at 25°C. Then the exothermic reaction is initiated by an ignition device and the chemical reaction of the components is completed. This test device is known as a bomb calorimeter. If hydrogen and oxygen are combined, water vapor emerges at high temperatures. Subsequently, the vessel and its content are cooled down to the original 25°C and the “Heat of Formation” (or the "Higher Heating Value" HHV) is determined by measuring the heat released between identical initial and final temperatures.
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Quantity of heat liberated by the complete combustion of a unit volume or weight of a fuel assuming that the produced water vapor is completely condensed and the heat is recovered; also known as gross calorific value. See lower heating value.