Today the question is very acute rational use TER. Ways to save heat and energy are continuously being developed in order to ensure energy security for the development of the economy of both the country and each individual family.
Creation of efficient power plants and thermal insulation systems (equipment that provides the greatest heat transfer (for example, steam boilers) and, conversely, from which it is undesirable ( melting furnaces)) is impossible without knowledge of the principles of heat transfer.
Approaches to thermal protection of buildings have changed, and requirements for building materials have increased. Any home needs insulation and a heating system. Therefore, when performing thermal engineering calculations of enclosing structures, it is important to calculate the thermal conductivity index.
The concept of thermal conductivity
Thermal conductivity - this is a physical property of a material in which thermal energy inside a body moves from its hottest part to the colder one. The value of the thermal conductivity indicator shows the degree of heat loss in residential premises. Depends on the following factors:
Quantify the ability of objects to pass thermal energy possible through the thermal conductivity coefficient. It is very important to make the right choice building materials, insulation to achieve the greatest heat transfer resistance. Miscalculations or unreasonable savings in the future can lead to deterioration of the indoor microclimate, dampness in the building, wet walls, and stuffy rooms. And most importantly - high heating costs.
For comparison, below is a table of thermal conductivities of materials and substances.
Table 1
Metals have the highest values, heat-insulating items have the lowest values.
Classification of building materials and their thermal conductivity
Thermal conductivity of reinforced concrete, brickwork, expanded clay concrete blocks, usually used for the construction of enclosing structures, are distinguished by the highest standard indicators. In the construction industry wooden structures are used much less frequently.
Depending on the thermal conductivity values, building materials are divided into classes:
- structural and thermal insulation (from 0.210);
- thermal insulation (up to 0.082 - A, from 0.082 to 0.116 - B, etc.).
Efficiency of multilayer structures
Density and thermal conductivity
Currently, there is no building material whose high load-bearing capacity would be combined with low thermal conductivity. The construction of buildings based on the principle of multilayer structures allows:
Combination structural material and thermal insulation allows you to ensure strength and reduce the loss of thermal energy to optimal level. Therefore, when designing walls, calculations take into account each layer of the future enclosing structure.
It is also important to take into account the density when building a house and when insulating it.
The density of a substance is a factor that affects its thermal conductivity and ability to retain the main heat insulator - air.
Calculation of wall thickness and insulation
Calculation of wall thickness depends on the following indicators:
- density;
- calculated thermal conductivity;
- heat transfer resistance coefficient.
According to established standards, the value of the heat transfer resistance of external walls must be at least 3.2λ W/m °C.
Calculation thickness of walls made of reinforced concrete and other structural materials presented in Table 2. Such building materials are characterized by high load-bearing characteristics, they are durable, but they are ineffective as thermal protection and require an irrational wall thickness.
table 2
Structural thermal insulation materials are capable of being subjected to fairly high loads, while significantly increasing the thermal and acoustic properties of buildings in wall enclosing structures (Table 3.1, 3.2).
Table 3.1
Table 3.2
Thermal insulation building materials can significantly increase the thermal protection of buildings and structures. The data in Table 4 shows that lowest values of thermal conductivity coefficient have polymers, mineral wool, slabs made of natural organic and inorganic materials.
Table 4
The values of the tables of thermal conductivity of building materials are used in calculations:
Choice problem optimal materials for construction, of course, implies more A complex approach. However, even such simple calculations already at the first stages of design they allow us to determine the most suitable materials and their number.
What is thermal conductivity? Not only professional builders need to know about this value, but also ordinary people who decide to build a house on their own.
Each material used in construction has its own indicator of this value. Its lowest value is for insulation materials, the highest for metals. Therefore, you need to know the formula that will help calculate the thickness of both the walls being built and the thermal insulation in order to ultimately get a cozy home.
Comparison of heat conductivity of the most common insulation materials
To have an idea of heat conductivity different materials intended for insulation, you need to compare their coefficients (W/m*K) given in the following table:
As can be seen from the above data, the thermal conductivity index of building materials such as thermal insulation varies from minimum (0.019) to maximum (0.5). All thermal insulation materials have a certain range of readings. SNiPs describe each of them in several forms - dry, normal and wet. The minimum thermal conductivity coefficient corresponds to a dry state, the maximum to a wet state.
If individual construction is planned
When building a house, it is important to consider specifications all components (wall material, masonry mortar, future insulation, waterproofing and steam-removing films, finishing).
To understand which walls will best retain heat, you need to analyze the thermal conductivity coefficient of not only the wall material, but also mortar, as can be seen from the table below:
| Order number | Wall material, mortar | Thermal conductivity coefficient according to SNiP |
| 1. | Brick | 0,35 – 0,87 |
| 2. | Adobe blocks | 0,1 – 0,44 |
| 3. | Concrete | 1,51 – 1,86 |
| 4. | Foam concrete and cement-based aerated concrete | 0,11 – 0,43 |
| 5. | Foam concrete and lime-based aerated concrete | 0,13 – 0,55 |
| 6. | Cellular concrete | 0,08 – 0,26 |
| 7. | Ceramic blocks | 0,14 – 0,18 |
| 8. | Cement-sand mortar | 0,58 – 0,93 |
| 9. | Mortar with added lime | 0,47 – 0,81 |
Important . From the data given in the table it can be seen that each building material has a fairly large spread in the thermal conductivity coefficient.
This is due to several reasons:
- Density. All insulation materials are produced or laid (penoizol, ecowool) of varying densities. The lower the density (more air is present in the insulating structure), the lower the heat conductivity. And, conversely, for very dense insulation materials this coefficient is higher.
- The substance from which it is produced (base). For example, brick can be silicate, ceramic, or clay. The thermal conductivity coefficient also depends on this.
- Number of voids. This applies to bricks (hollow and solid) and thermal insulation. Air is the worst conductor of heat. Its thermal conductivity coefficient is 0.026. The more voids, the lower this figure.
Mortar conducts heat well, so it is recommended to insulate any walls.
If you explain it on your fingers
For clarity and understanding of what thermal conductivity is, you can compare a brick wall, 2 m 10 cm thick, with other materials. Thus, 2.1 meters of brick stacked into a wall on an ordinary cement-sand mortar are equal:
- a 0.9 m thick wall made of expanded clay concrete;
- timber, diameter 0.53 m;
- wall, 0.44 m thick, made of aerated concrete.
If we are talking about such common insulation materials as mineral wool and expanded polystyrene, then only 0.18 m of the first thermal insulation or 0.12 m of the second is required for the thermal conductivity values to be enormous brick wall turned out to be equal to a thin layer of thermal insulation.
Comparative characteristics of thermal conductivity of insulation, construction and finishing materials, which can be done by studying SNiPs, allows you to analyze and correctly compose an insulating pie (base, insulation, finishing). The lower the thermal conductivity, the higher the price. A striking example is the walls of a house made of ceramic blocks or ordinary high-quality bricks. The former have a thermal conductivity of only 0.14 - 0.18 and are much more expensive than any of the best bricks.
It is better to start the construction of each facility with project planning and careful calculation of thermal parameters. Accurate data will be obtained from a table of thermal conductivity of building materials. Proper construction of buildings contributes to optimal indoor climate parameters. And the table will help you choose the right raw materials to be used for construction.
Thermal conductivity of materials affects the thickness of walls
Thermal conductivity is a measure of the transfer of thermal energy from heated objects in a room to objects at a lower temperature. The heat exchange process is carried out until the temperature indicators are equalized. To indicate thermal energy, a special thermal conductivity coefficient of building materials is used. The table will help you see all the required values. The parameter indicates how much thermal energy is passed through a unit area per unit time. The larger this designation, the better the heat exchange will be. When constructing buildings, it is necessary to use a material with a minimum thermal conductivity value.
The thermal conductivity coefficient is a value that is equal to the amount of heat passing through a meter of material thickness per hour. The use of such a characteristic is mandatory to create better thermal insulation. Thermal conductivity should be taken into account when selecting additional insulating structures.
What influences the thermal conductivity index?
Thermal conductivity is determined by the following factors:
- porosity determines the heterogeneity of the structure. When heat is passed through such materials, the cooling process is insignificant;
- an increased density value affects close contact of particles, which contributes to faster heat transfer;
- High humidity increases this indicator.
Using thermal conductivity values in practice
The materials are presented in structural and thermal insulation varieties. The first type has high thermal conductivity. They are used for the construction of floors, fences and walls.
Using the table, the possibilities of their heat transfer are determined. In order for this indicator to be low enough for a normal indoor microclimate, walls made of some materials must be especially thick. To avoid this, it is recommended to use additional thermal insulating components.
Thermal conductivity indicators for finished buildings. Types of insulation
When creating a project, you need to consider all ways of heat leakage. It can come out through walls and roofs, as well as through floors and doors. If you do the design calculations incorrectly, you will have to be content only with the thermal energy received from heating devices. Buildings built from standard raw materials: stone, brick or concrete need to be additionally insulated.
Additional thermal insulation is carried out in frame buildings. Wherein wooden frame imparts rigidity to the structure, and insulating material is laid in the space between the posts. In buildings made of brick and cinder blocks, insulation is done from the outside of the structure.
When choosing insulation materials, you need to pay attention to factors such as humidity levels, the influence of elevated temperatures and the type of structure. Consider certain parameters of insulating structures:
- the thermal conductivity indicator affects the quality of the heat-insulating process;
- moisture absorption has great importance when insulating external elements;
- thickness affects the reliability of insulation. Thin insulation helps maintain usable area premises;
- Flammability is important. High-quality raw materials have the ability to self-extinguish;
- thermal stability reflects the ability to withstand temperature changes;
- environmental friendliness and safety;
- Sound insulation protects against noise.
The following types of insulation are used:
- mineral wool is fire resistant and environmentally friendly. TO important characteristics low thermal conductivity;
- polystyrene foam is lightweight material with good insulation properties. It is easy to install and is moisture resistant. Recommended for use in non-residential buildings;
- basalt wool differs from mineral wool best performance resistance to moisture;
- Penoplex is resistant to humidity, elevated temperatures and fire. It has excellent thermal conductivity, is easy to install and durable;
- polyurethane foam is known for such qualities as non-flammability, good water repellent properties and high fire resistance;
- Extruded polystyrene foam undergoes additional processing during production. Has a uniform structure;
- penofol is a multi-layer insulating layer. The composition contains foamed polyethylene. The surface of the plate is covered with foil to provide reflection.
Bulk types of raw materials can be used for thermal insulation. These are paper granules or perlite. They are resistant to moisture and fire. And from organic varieties you can consider wood fiber, flax or cork covering. When choosing, Special attention pay attention to such indicators as environmental friendliness and fire safety.
Note! When designing thermal insulation, it is important to consider the installation of a waterproofing layer. This will avoid high humidity and will increase resistance to heat transfer.
Table of thermal conductivity of building materials: features of indicators
The table of thermal conductivity of building materials contains indicators various types raw materials used in construction. Using this information, you can easily calculate the thickness of the walls and the amount of insulation.
How to use the table of thermal conductivity of materials and insulation?
The table of heat transfer resistance of materials presents the most popular materials. When choosing a specific thermal insulation option, it is important to consider not only physical properties, but also such characteristics as durability, price and ease of installation.
Did you know that the easiest way to install penoizol and polyurethane foam. They are distributed over the surface in the form of foam. Such materials easily fill the cavities of structures. When comparing solid and foam options, it should be emphasized that foam does not form joints.
Values of heat transfer coefficients of materials in the table
When making calculations, you should know the heat transfer resistance coefficient. This value is the ratio of the temperatures on both sides to the amount of heat flow. In order to find the thermal resistance of certain walls, a thermal conductivity table is used.
You can do all the calculations yourself. To do this, the thickness of the heat insulator layer is divided by the thermal conductivity coefficient. This value is often indicated on the packaging if it is insulation. Home materials are measured independently. This applies to thickness, and the coefficients can be found in special tables.
The resistance coefficient helps to select a specific type of thermal insulation and the thickness of the material layer. Information on vapor permeability and density can be found in the table.
At correct use tabular data you can choose quality material to create a favorable indoor microclimate.
Thermal conductivity of building materials (video)
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Construction of a private house is a very difficult process from start to finish. One of the main issues this process is the choice of construction raw materials. This choice must be very competent and thoughtful, because most of the life in the new home depends on it. What stands apart in this choice is the concept of thermal conductivity of materials. It will determine how warm and comfortable the house will be.
Thermal conductivity is an ability physical bodies(and the substances from which they are made) transfer thermal energy. Explaining more in simple language, this is the transfer of energy from a warm place to a cold one. For some substances, such transfer will occur quickly (for example, most metals), and for some, on the contrary, very slowly (rubber).
To put it even more clearly, in some cases, materials with a thickness of several meters will conduct heat much better than other materials with a thickness of several tens of centimeters. For example, a few centimeters of drywall can replace an impressive brick wall.
Based on this knowledge, it can be assumed that the most correct choice of materials will be with low values of this quantity so that the house does not cool down quickly. For clarity, let us denote percentage heat loss in different areas Houses:
What does thermal conductivity depend on?
Values of this quantity may depend on several factors. For example, the thermal conductivity coefficient, which we will talk about separately, the humidity of building materials, density, and so on.
- Materials with high densities have, in turn, a high ability to transfer heat due to the dense accumulation of molecules inside the substance. Porous materials, on the contrary, will heat up and cool down more slowly.
- Heat transfer is also affected by the humidity of materials. If the materials get wet, their heat transfer will increase.
- Also, the structure of the material greatly influences this indicator. For example, a tree with transverse and longitudinal grains will have different meanings thermal conductivity.
- The indicator also changes with changes in parameters such as pressure and temperature. With increasing temperature it increases, and with increasing pressure, on the contrary, it decreases.
Coefficient of thermal conductivity
For quantification such a parameter are used special thermal conductivity coefficients, strictly declared in SNIP. For example, the thermal conductivity coefficient of concrete is 0.15-1.75 W/(m*C) depending on the type of concrete. Where C is degrees Celsius. On this moment there are coefficient calculations for almost everyone existing types construction raw materials used in construction. Thermal conductivity coefficients of building materials are very important in any architectural and construction work.
For convenient selection of materials and their comparison, special tables of thermal conductivity coefficients are used, developed in accordance with SNIP standards (building codes and regulations). Thermal conductivity of building materials, the table of which will be given below, is very important in the construction of any objects.
- Wood materials. For some materials, the parameters will be given both along the fibers (Index 1, and across – index 2)
- Various types of concrete.
- Various types of construction and decorative bricks.
Calculation of insulation thickness
From the above tables we see how different the heat conductivity coefficients of different materials can be. To calculate the thermal resistance of the future wall, there is a simple formula, which connects the thickness of the insulation and its thermal conductivity coefficient.
R = p / k, where R is the thermal resistance index, p is the layer thickness, k is the coefficient.
From this formula it is easy to extract the formula for calculating the thickness of the insulation layer for the required thermal resistance. P = R * k. Thermal resistance value is different for each region. There is also a special table for these values, where they can be viewed when calculating the thickness of the insulation.
Now let's give some examples the most popular insulation materials and their technical characteristics.
Whatever the scale of construction, the first step is to develop a project. The drawings reflect not only the geometry of the structure, but also the calculation of the main thermal characteristics. To do this, you need to know the thermal conductivity of building materials. the main objective construction is the construction of durable structures, durable structures that are comfortable without excessive heating costs. In this regard, knowledge of the thermal conductivity coefficients of materials is extremely important.
Brick has better thermal conductivity
Characteristics of the indicator
The term thermal conductivity refers to the transfer of thermal energy from more heated objects to less heated ones. The exchange continues until temperature equilibrium occurs.
Heat transfer is determined by the length of time during which the temperature in the rooms is in accordance with the ambient temperature. The smaller this interval, the greater the heat conductivity of the building material.
To characterize the conductivity of heat, the concept of thermal conductivity coefficient is used, which shows how much heat passes through such and such a surface area in such and such a time. The higher this indicator, the greater the heat exchange, and the building cools down much faster. Thus, when constructing structures, it is recommended to use building materials with minimal heat conductivity.
In this video you will learn about the thermal conductivity of building materials:
How to determine heat loss
The main elements of the building through which heat escapes:
- doors (5-20%);
- gender (10-20%);
- roof (15-25%);
- walls (15-35%);
- windows (5-15%).
The level of heat loss is determined using a thermal imager. Red indicates the most difficult areas, yellow and green indicate less heat loss. Areas with the least losses are highlighted in blue. The thermal conductivity value is determined in laboratory conditions, and a quality certificate is issued to the material.
The value of thermal conductivity depends on the following parameters:
- Porosity. Pores indicate heterogeneity of the structure. When heat passes through them, cooling will be minimal.
- Humidity. High level humidity provokes the displacement of dry air by droplets of liquid from the pores, which is why the value increases many times over.
- Density. Higher density promotes more active interaction between particles. As a result, heat exchange and temperature balancing proceed faster.
Coefficient of thermal conductivity
Heat loss in a house is inevitable, and it occurs when the temperature outside is lower than inside. The intensity is variable and depends on many factors, the main ones being the following:
- The area of surfaces involved in heat exchange.
- Thermal conductivity indicator of building materials and building elements.
- Temperature difference.
The Greek letter λ is used to denote the thermal conductivity of building materials. Unit of measurement – W/(m×°C). The calculation is made for 1 m² of a meter thick wall. Here a temperature difference of 1°C is assumed.
Case Study
Conventionally, materials are divided into thermal insulation and structural. The latter have the highest thermal conductivity; they are used to build walls, ceilings, and other fences. According to the table of materials, when constructing walls made of reinforced concrete to ensure low heat exchange with environment their thickness should be approximately 6 m. But then the structure will be bulky and expensive.
If the thermal conductivity is incorrectly calculated during design, the residents of the future home will be content with only 10% of the heat from energy sources. Therefore, it is recommended to additionally insulate houses made from standard building materials.
By doing proper waterproofing insulation, high humidity does not affect the quality of thermal insulation, and the resistance of the structure to heat transfer will become much higher.
Most best option– use insulation
The most common option is a combination load-bearing structure made of high-strength materials with additional thermal insulation. For example:
- Frame house. The insulation is placed between the studs. Sometimes, with a slight decrease in heat transfer, additional insulation is required on the outside of the main frame.
- Construction from standard materials. When the walls are brick or cinder block, insulation is done from the outside.
Building materials for external walls
Walls today are built from different materials, but the most popular remain: wood, brick and building blocks. The main differences are in the density and thermal conductivity of building materials. Comparative analysis allows you to find the golden mean in the relationship between these parameters. The greater the density, the greater the load-bearing capacity of the material, and therefore of the entire structure. But thermal resistance becomes less, that is, energy costs increase. Usually at lower densities there is porosity.
Thermal conductivity coefficient and its density.
Insulation for walls
Insulation materials are used when the thermal resistance of external walls is not enough. Typically, a thickness of 5-10 cm is sufficient to create a comfortable indoor microclimate.
The value of the coefficient λ is given in the following table.
Thermal conductivity measures the ability of a material to transmit heat through itself. It greatly depends on the composition and structure. Dense materials such as metals and stone are good conductors of heat, while low-density substances such as gas and porous insulation are poor conductors.