Calorific Value (CV)
The calorific value (CV) of a fuel is the heat available from that fuel when it is completely burned, expressed as heat units per unit of fuel weight or volume.
The gross, or higher, value is determined in the laboratory using a calorimeter. It can be defined as the total heat liberated by the complete combustion of the fuel. It is determined by measuring the heat removed when cooling the products of combustion to a standard reference temperature, and it includes latent heat recovered from condensation of the water vapour component. This water vapour forms as a result of the combustion of any hydrogen molecules contained within the fuel, and the vaporisation of any moisture present.
The net, or lower, value is determined by calculation and equals the gross calorific value minus the latent heat of the water vapour formed from the combustion of hydrogen and from any moisture present in the fuel.
The net value is more representative of the heat available in practice when fuels are burned in equipment such as furnaces and boilers. The latent heat of the water vapour contained in exhaust gases is not normally recoverable, except where low-temperature heat recovery involving condensation is used.
Listed to the left are the calorific values (Gross CV) of some common materials. A material can burn without supporting fuel when it has a calorific value of minimum 14400 KJ/Kg which is approximately dry wood. To know the overall calorific value of waste you need to measure the calorific value or estimate by analyzing the composition. If there is no chemical reaction by mixing different materials together, a weighted average of the different calorific values is a good approximate value for the CV of the waste mix.