Heat

Thermal conductivity coefficients of building materials: features and tables of values

January 12, 2020

Today the issue of rational use of energy resources is very acute. Ways to save heat and energy are being worked out continuously in order to ensure energy security of economic development as a country., and each individual family.

Creation of efficient power plants and thermal insulation systems (equipment, which provides the greatest heat transfer (example, steam boilers) and, vice versa, from which it is undesirable (melting furnaces)) impossible without knowledge of the principles of heat transfer.

Approaches to thermal protection of buildings have changed, increased requirements for building materials. Every house needs insulation and heating systems. Therefore, the calculation of thermal conductivity is important in the thermal calculation of enclosing structures.

The concept of thermal conductivity

Thermal conductivity - this is such a physical property of the material, in which the thermal energy inside the body passes from the hottest part of it to the colder. The value of thermal conductivity shows the degree of heat loss in residential areas. Depends on the following factors:

  • the density of the subject: increases with its increase;
  • structures: for example, wood with transverse fibers has high thermal resistance, than with longitudinal;
  • porosity the higher the value, the lower the average density;
  • the nature of the voids still: materials with connected pores have high thermal conductivity, with closed fine-grained pores - smaller;
  • humidity: dry items are less conductive;
  • temperature - heat transfer decreases with increasing;
  • pressure - the rate increases with increasing pressure.

You can quantify the property of objects to transmit thermal energy using the coefficient of thermal conductivity. It is very important to make the right choice of building materials, insulation to achieve maximum heat transfer resistance. Miscalculations or unwise savings in the future can lead to a deterioration of the indoor microclimate, humidity in the house, wet walls, stuffy rooms. And most importantly - to the high cost of heating.

For comparison, the table below shows the thermal conductivity of materials and substances.

Table 1

Materials and substances aluminum steel stainless steel concrete air water Particleboard roofing material cardboard rubber polyethylene glass
Thermal conductivity coefficient Two hundred and twenty-one Fifty-eight 17,5 1,5 0,02 0,6 0,15 0,17 0,18 0,04 0,3 0,7

Metals have the highest values, low - heat-insulating objects.

Classification of building materials and their thermal conductivity

Thermal conductivity of reinforced concrete, brickwork, expanded clay concrete blocks, commonly used for the construction of enclosing structures, differs in the highest normative indicators. In the construction industry, wooden structures are used much less often.

Depending on the value of thermal conductivity, building materials are divided into classes:

  • structural and heat-insulating (from 0,210);
  • heat-insulating (to 0,082 - A, from 0,082 to 0,116 - B, etc.).

Efficiency of multilayer constructions

Density and thermal conductivity

Currently there is no such building material, high bearing capacity which would be combined with low thermal conductivity. Construction of houses on the principle of multilayer structures allows:

  • meet the design standards for construction and energy saving;
  • leave the dimensions of the enclosing structures within reasonable limits;
  • reduce material costs for the construction and maintenance of the facility;
  • achieve durability and maintainability (example, when replacing one sheet of mineral wool).

Combination structural material and thermal insulation allows to provide durability and to reduce losses of thermal energy to optimum level. Therefore at design of walls at calculations each layer of a future protecting design is considered.

It is also important to consider the density in the construction of the house and its insulation.

Density of matter is a factor, which affects its thermal conductivity, the ability to retain the main insulator - air.