Heating & calorific value

Heating value and calorific value describe the heat released during the complete combustion of a fuel. The heating value only calculates the usable heat without the condensation heat of the water, while the calorific value also takes this into account.

Definition
The calorific value (Hi) is the amount of energy released during the combustion of a fuel without taking into account the condensation heat of the water vapor contained in the exhaust gases. The calorific value (Hs) includes both the calorific value and the amount of energy contained in the exhaust gases and the water vapor.

Background / origin
Heating value and calorific value are decisive parameters for assessing the efficiency of fuels. The calorific value is traditionally used to indicate how much energy can be generated from a fuel if the water remains unused as water vapor. In contrast, the calorific value is determined when the exhaust gas is cooled below the condensation point, allowing the heat of condensation to be utilized. The calorific value is therefore always greater than or equal to the heating value.

The relevant terms have developed historically over the years, whereby the calorific value was previously also referred to as the upper heating value (Ho). The calorific value, known as the lower calorific value (Hu), has also become established as the standard. In practice, heating value and calorific value are often given in kilojoules per kilogram (kJ/kg) or kilowatt hours per kilogram (kWh/kg); for gases, however, they are measured in kilojoules per cubic meter (kJ/m³).

In addition, condensing boilers have become popular since the efficiency requirements for heating systems were tightened. These boilers use the condensation heat of the water, which leads to higher efficiency levels than with conventional boilers. This can be seen, for example, in oil condensing boilers with an efficiency of 106% and gas condensing boilers of up to 111%.

Properties
Heating value and calorific value refer to the specific heat energy of fuels and are made up of various components:

- The heating value (Hi) and calorific value (Hs) are given in specific energy units.
- The calorific value does not take into account the condensation heat contained in the water vapor.
- The calorific value is determined when the exhaust gases are cooled below the condensation point, whereby additional energy is recovered.

The use of the two terms varies depending on the type of fuel - solid, liquid or gaseous. For solid fuels (e.g. hard coal, wood), calorific values and heating values can be given specifically in megajoules per kilogram (MJ/kg). This is also the case for liquid fuels (e.g. petrol, heating oil) and gaseous fuels (e.g. natural gas), although the energy density is usually variable and can fluctuate depending on the type of fuel.

Application and significance in the market
Heating value and calorific value are of central importance for the selection and use of fuels in heating technology. The efficiency of heating systems, especially when using condensing boilers, can be significantly increased by using the different values. In industry, calorific values play an important role in calculating the energy yield that can be obtained from different fuels.

In addition, the specified values are relevant in the development and marketing of new fuels. The differences between heating value and calorific value can have an influence on the cost and benefit factor for consumers and on the design of energy strategies at international level.

Differentiation from similar terms
The main difference between heating value and calorific value lies in the consideration of the condensation heat of the water vapor. While the heating value only measures the directly usable heat, the calorific value also includes the energy contained in the water vapor of the exhaust gases. Condensing boilers use this additional energy, whereas conventional boilers only take the calorific value into account.

Summary
Heating value and calorific value are key parameters when evaluating the energy yield of fuels. The heating value measures the directly usable heat without condensation heat, while the calorific value also includes this energy. The application of the two values is of significant importance for the efficiency of heating systems, especially for condensing boilers. This has savings potential as well as an influence on the valuation and marketing of fuels on the energy market.