The calorific value is the amount of energy that the unit mass of matter can give off a chemical reaction upon oxidation (excluding nuclear reactions, not chemical, nuclear fission or fusion, since this will use the formula E mca ).
The calorific value is the maximum energy which can release a chemical bonding between fuel and oxidizer and is equal to the energy that kept together the atoms in the molecules of fuel, less energy used in the formation of new molecules in the materials ( generally gases) formed in the combustion. Energy is expensive and can be even more expensive The magnitude of the calorific value may vary depending on how it is measured. Depending on the form is used to measure the calorific value higher expression (for short, PCS) and lower heating value (for short, PCI).
Most of the usual fuels are compounds of carbon and hydrogen, burn it to combine with oxygen to form carbon dioxide (CO2) and water (H2O) respectively. When the research scientist of the combustion process, it is considered that for the proper functioning of the boilers which produced that was burnt gases out of the flue pipe at a certain temperature to generate the minimum necessary to draft a good thermal operation. This temperature is above 100 C, which produced no water condenses and loses heat exchange status, which in water is estimated at 2261 kJ (540 kcal) per kilogram of water, so that there was need to define the lower heating value, so that the boilers had apparently yields more encouraging.
Therefore, we used the description for the lower heating value untapped heat energy from the condensation of water, and higher calorific value, which takes into account the heat of condensation.
Most of the boilers and engines tend to expel the water in vapor form. However, there are now condensing boilers that take advantage of this heat of condensation, with much higher yields than traditional, higher than 100 of PCI, but, of course, always below 100 of PCS. However, they must produce hot water at about 70 C, which limits its uses and furthermore, can only be used with sulfur-free fuels (like natural gas) to avoid acid condensation, for lack of sufficient temperature and for So for lack of stone heat boilers in the evacuation of these gases should be done by a fan.