Lower heating value
The lower heating value (also known as "net calorific value", "net CV", or "LHV") of a
fuelis defined as the amount of heatreleased by combusting a specified quantity (initially at 25 °C or another reference state) and returning the temperature of the combustionproducts to 150 °C. [http://www.efcf.com/reports/E10.pdf Ulf Bossel, Well-to-Wheel Studies, Heating Values, and the Energy Conservation Principle]
The LHV assumes that the
latent heat of vaporizationof waterin the fuel and the reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below 150 °C cannot be put to use.
By contrast, the
higher heating value(HHV) (a.k.a. "gross calorific value" or "gross CV") includes the heat of condensation of water in the combustion products.
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
Coal1) 34.1 33.3 1.024 0.977 CO 10.9 10.9 1.000 1.000 Methane55.5 50.1 1.108 0.903 Natural gas2) 55.0 49.7 1.111 0.900 Propane48.9 45.8 1.068 0.937 Gasoline3) 46.7 42.5 1.099 0.910 Diesel3) 45.9 43.0 1.067 0.937 Hydrogen141.9 120.1 1.182 0.846 ----1) Anthracite, average
2) Groningen (
3) Average gas station fuels
For historical reasons, the efficiency of power plants and
combined heat and powerplants in Europe is calculated based on the LHV, while in e.g. the US, it is generally based on the HHV. This has the peculiar result that contemporary combined heat and power plants, where flue gascondensation is implemented, may report efficiencies exceeding 100 % in Europe.
Many engine manufacturers rate their engine fuel consumption by the lower heating values. American consumers should be aware that the corresponding fuel consumption figure based on the higher heating value would be somewhat higher.
The above is but one definition of Lower heating value adopted by the
American Petroleum Institute(API) and they used a reference temperature of 60 °F (15.56 °C).
Another definition [used by GPSA - Gas Processors Suppliers Association and originally used by API (data collected for API research project 44)] is that the lower heating value is the
enthalpyof all combustion products, minus the enthalpy of the fuel at the reference temperature [API research project 44 used 25 °C. GPSA currently uses 60 °F] , minus the enthalpy of the stoichiometric oxygen(O2) at the reference temperature, minus the heat of vaporizationof the vapor content of the combustion products.
The distinction between the two is that this second definition assumes that the combustion products are all returned back down to the reference temperature but then the heat content from the condensing vapor is considered to be not useful.This is more easily calculated from the higher heating value than when using the previous definition and will in fact give a slightly different answer.
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