Higher heating value

Higher heating value

The higher heating value (HHV;also known as the 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).

Measuring heating values

The higher heating value is experimentally determined in a bomb calorimeter 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 combustion reactions completed. When hydrogen and oxygen react during combustion, water vapor emerges. Subsequently, the vessel and its content are cooled down to the original 25 °C and the higher heating value is determined as the heat released between identical initial and final temperatures.

When the lower heating value (LHV) is determined, cooling is stopped at 150 °C and the reaction heat is only partially recovered. The limit of 150 °C is an arbitrary choice.

Relation to lower heating value

The difference between the two heating values depends on the chemical composition of the fuel. In the case of pure carbon or carbon dioxide, both heating values are almost identical, the difference being the sensible heat content of carbon dioxide between 150°C and 25°C (sensible heat exchange causes a change of temperature. In contrast, latent heat is added or subtracted for phase changes at constant temperature. Examples: heat of vaporization or heat of fusion). For hydrogen the difference is much more significant as it includes the sensible heat of water vapor between 150°C and 100°C, the latent heat of condensation at 100°C and the sensible heat of the condensed water between 100°C and 25°C. All in all, the higher heating value of hydrogen is 18.2% above its lower heating value (142 MJ/kg vs. 120 MJ/kg). For hydrocarbons the difference depends on the hydrogen content of the fuel. For gasoline and diesel the higher heating value exceeds the lower heating value by about 10% and 7%, respectively, for natural gas about 11%.

Higher (HHV) and lower (LHV) heating values for some fuels are shown in the following table.

Table A. Heating values for selected fuels [Ulf Bossel: [http://www.efcf.com/reports/E10.pdf Well-to-Wheel Studies, Heating Values, and the Energy Conservation Principle] , Proceedings of Fuel Cell Forum 2003] ---- Fuel HHV(MJ/kg) LHV(MJ/kg) HHV/LHV LHV/HHV Coal 1) 34.1 33.3 1.024 0.977 CO 10.9 10.9 1.000 1.000 Methane 55.5 50.1 1.108 0.903 Natural gas 2) 42.5 38.1 1.115 0.896 Propane 48.9 45.8 1.068 0.937 Gasoline 3) 46.7 42.5 1.099 0.910 Diesel 3) 45.9 43.0 1.067 0.937 Hydrogen 141.9 120.1 1.182 0.846 ----1) Anthracite, average
2) Groningen (The Netherlands)
3) Average gas station fuels


ee also

*Energy conversion efficiency
*Thermal efficiency
*Lower heating value

Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Higher Heating Value — (HHV)   The maximum heating value of a fuel sample, which includes the calorific value of the fuel (bone dry) and the latent heat of vaporization of the water in the fuel. (See moisture content and net (lower) heating value, below.) …   Energy terms

  • Lower heating value — The lower heating value (also known as net calorific value , net CV , or LHV ) of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25 °C or another reference state) and returning the temperature of …   Wikipedia

  • Heating Value —   The amount of heat produced from the complete combustion of a unit of fuel. The higher (or gross) heating value is that when all products of combustion are cooled to the pre combustion temperature, water vapor formed during combustion is… …   Energy terms

  • Net (Lower) Heating Value — (NHV)   The potential energy available in a fuel as received, taking into account the energy loss in evaporating and superheating the water in the fuel. Equal to the higher heating value minus 1050W where W is the weight of the water formed from… …   Energy terms

  • Value added tax — Taxation An aspect of fiscal policy …   Wikipedia

  • Underfloor heating — Heat can be provided by circulating heated water or by electric cable, mesh, or film heaters.Underfloor heating can be used with concrete and wooden floors, with all types of floor covering (e.g., stone, tile, wood, vinyl, and carpet), and at… …   Wikipedia

  • R-Value —   A measure of the capacity of a material to resist heat transfer. The R Value is the reciprocal of the conductivity of a material (U Value). The larger the R Value of a material, the greater its insulating properties.   ***   A measure of a… …   Energy terms

  • Geothermal heating — has been used since the time of the Roman Empire as a way of heating buildings and spas by utilizing sources of hot water and steam that exist near the Earth s surface. [Climate.Org Renewable Energy: Geothermal,… …   Wikipedia

  • Minimum efficiency reporting value — Minimum efficiency reporting value, commonly known as MERV rating is a measurement scale designed in 1987 by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) to rate the effectiveness of air filters. The… …   Wikipedia

  • Minimum Efficiency Reporting Value — Minimum Efficiency Reporting Value, commonly known as MERV Rating is a measurement scale designed in 1987 by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) to rate the effectiveness of air filters.The scale …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”