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» Economics » Heat energy technology » Topics begins with C » Calorific value

Page modified: Wednesday, July 13, 2011 12:22:13

The calorific value Hs (in former times also upper heat value Ho called) of a fuel indicates the amount of heat, which is produced during burn and following cooling of the incineration gases on 25 "°C. It considers both the necessary energy for heating the combustion air and the exhaust gases, and, in particular Wasser.Im contrast to it (lower) the heat value the usable amount of heat designates the evaporation and/or condensation warmth of liquids during release of hot exhaust gases. The heat value is therefore clearly smaller. The calorific value in Kilo joules per kilogram (kJ/kg) is indicated, per litre (kJ/l) or also per cubic meter (kJ/m

In former times was called the symbol for the calorific value Ho, which reads current symbols Hs or B. the "s" stands for the English word "superior", which here is called as many as "higher".


With each burn process water vapour results from the connection of oxygen from the combustion air and hydrogen from the fuel. In the water vapour and thus in the exhaust gas contained energy is lost with conventional technology over the hot exhaust gases through the fire-place. Modern calorific value technology condenses the water vapour contained in the exhaust gas over a heat exchanger. Thus the condensation warmth contained in the exhaust gas is recovered as far as possible. The calorific value is considered also during the account of heating energy (see gas energy).

The calorific value use is with gaseous fuels, contrary to fuel oil or even wood (only 4%), the hydrogen content most effectively there here is very high.

DIN regulations about calorific value

DIN 51900 determination of the calorific value with the Bombenkalorimeter and computation of the heat value

Part 1 general instructions, basic equipments, basic procedures (April 2000)

Part 2 procedures with isoperibolem or calorimeter static jacket (May 2003)

Part 3 procedure with adiabatic coat (July 2004)

DIN of 1340 gaseous fuels and other gases, kinds, components, use (December 1990)

DIN of 1871 gaseous fuels and other gases - density and other volumetric sizes (May 1999)

DIN of 51857 gaseous fuels and other gases - computation of calorific value, heat value, density, relative density and Wobbeindex of gases and gas mixtures (March 1997)

DIN 51612 examination of liquid gas; Computation of the heat value (June 1980)

DIN 51854 examination of gaseous fuels and other gases; Determination of the ammonia content (September 1993)

DIN 1343 reference condition, standard temperature and pressure, standard volume; Terms and values (January 1990)

DIN 5499 calorific value and heat value, terms (January 1972)

Physiological calorific value

The physiological calorific value of food corresponds to their energy content with burn. The warmth freed thereby becomes in Kilo joules (kJ) (in former times: Kilocalories (kcal)) measured. With the many food it is prescribed by the feeding value marking regulation to indicate on the packing the appropriate calorific value in a feeding value table.

Conversion: 1 kcal = 4.1868 kJ 1 kJ = 0.2388 kcal 1 kcal = 1.163 Wh 

A indicates the power requirement of an adult according to its body weight in kilograms:

Power requirement (kJ) = body weight (kg) x 24 (hours) x 4.2 (kJ) 

Therefore a 70 kg of heavy adults per day needs somewhat more than 7000 kJ. During physical load by sport or manual labor this value can almost double itself.

The calorific value of protein and coal hydrates amounts to approx. in each case 17.16 kJ per gram, that by fat approx. 38.9 kJ per gram.

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