The basic principles of heat transfer help us best understand how insulation works. The three ways of transfer are the following: heat conduction, heat transfer /convection/ and emission /radiation/.
Thermal conductivity
Thermal conductivity is the property of materials to transfer heat. The transfer of heat from warmer to cooler parts of a body is called thermal conduction. Heat transfer occurs from the region of higher to the region of lower temperature through the kinetic energy of the atoms. The ability of materials to conduct heat is characterized by the so-called coefficient of thermal conductivity. The lower the value of this coefficient, the better the material is a heat insulator, and vice versa. The thermal conductivity of cotton wool depends on its density and changes depending on the temperature at which it is used.
Convection
Convection is the transfer of heat through liquids and gases. For example, in natural (free) convection, the volumes of fluid that are near the surface of the heated body are heated, expanded, lightened and moved, and their place is taken by colder layers. Mineral wool prevents convection by trapping air in its structure. Air is a good insulator.
Radiation
Radiation is the transmission of energy through space by electromagnetic waves. The radiated heat moves at the speed of light through the air without heating the space between them, just as it feels the heat of the sun on the face. The heat emanating from the sun warms the earth without heating the space between them.
What do the indicators of insulation materials show?
One of the main indicators that we can see in the technical maps of the insulation materials are the following:
Coefficient of thermal conductivity λ
Different insulation materials prevent the transfer of thermal energy to the external environment to one degree or another. The indicator that characterizes materials in this regard is the coefficient of thermal conductivity λ, measured in W/(m.K). It expresses the amount of heat passing in 1 second through 1 m2 of material 1 meter thick, at a temperature difference between the two surfaces of 1 K (Kelvin). The smaller the value of lambda λ for a given material, the better its insulating properties. The coefficient of thermal conductivity depends on: the volume density of the wool, the humidity of the material and the application temperature.
The thermal resistance R
The property of insulating materials to prevent the transfer of heat is called thermal resistance. The thermal resistance of the material R is measured in m2.K/W. It is different depending on the thickness of the material. With the same coefficient of thermal conductivity of the material, the greater its thickness – the better the thermal resistance value.
Heat transfer coefficient U [W/m2K] measures the heat flow. The lower this coefficient, the slower the insulation material transfers heat from your home to the outside and back again.
There are European standards that define these and other characteristics of insulation materials. These include the procedures for testing, conformity assessment, marking and labeling of these materials. For mineral wool products, the main standards are BDS EN 13162 or BDS EN 14303. The first refers to thermal insulation products for buildings – mineral wool (MW) products produced in factory conditions. The second is for thermal insulation products for construction facilities and industrial installations – mineral wool (MW) products produced in factory conditions.
The values of the tested characteristics that are required for a given application are given in the normative acts and regulations. The requirements of these regulations apply to the design and implementation of residential and public buildings, as well as to the reconstruction, renovation and major repair and remodeling of existing buildings.
