Calculation of heat losses. How thick should the insulation be, comparison of the thermal conductivity of materials Thermal insulation properties of building materials table

In order to properly organize, and premises, you need to know certain features and properties of materials. The thermal stability of your house directly depends on the qualitative selection of the required values, because if you make a mistake in the initial calculations, you risk making the building inferior. A detailed table of thermal conductivity of building materials, described in this article, is provided to help you.

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What is thermal conductivity and how important is it?

Thermal conductivity is the quantitative property of substances to transmit heat, which is determined by the coefficient. This indicator is equal to the total amount of heat that passes through a homogeneous material having a unit of length, area and time with a single temperature difference. The SI system converts this value into a thermal conductivity coefficient, which in letter designation looks like this - W / (m * K). Thermal energy is propagated through the material by means of rapidly moving heated particles, which, when colliding with slow and cold particles, transfer some of the heat to them. The better the heated particles are protected from the cold ones, the better the accumulated heat will be retained in the material.

Detailed table of thermal conductivity of building materials

The main feature of heat-insulating materials and building parts is the internal structure and compression ratio of the molecular basis of the raw materials from which the materials are composed. The values ​​of thermal conductivity coefficients for building materials are tabulated below.

Important! To achieve more effective insulation, you need to combine different materials. Compatibility of surfaces with each other is indicated in the instructions from the manufacturer.

Explanation of indicators in the table of thermal conductivity of materials and insulation: their classification

Depending on the design features of the structure to be insulated, the type of insulation is selected. So, for example, if the wall is built in two rows, then 5 cm thick foam is suitable for full insulation.

Due to the wide range of densities of foam sheets, they can perfectly insulate walls from OSB and plaster from above, which will also increase the efficiency of the insulation.

You can see the level of thermal conductivity, tabulated in the photo below.

Thermal insulation classification

According to the method of heat transfer, heat-insulating materials are divided into two types:

• Insulation that absorbs any effect of cold, heat, chemical attack, etc.;
• Insulation that can reflect all types of impact on it;

According to the value of the thermal conductivity coefficients of the material from which the insulation is made, it is distinguished by classes:

• A class. Such a heater has the lowest thermal conductivity, the maximum value of which is 0.06 W (m * C);
• B class. It has an average SI parameter and reaches 0.115 W (m*S);
• To class. It is endowed with high thermal conductivity and shows an indicator of 0.175 W (m * C);

Note! Not all heaters are resistant to high temperatures. For example, ecowool, straw, chipboard, fiberboard and peat need reliable protection from external conditions.

The main types of heat transfer coefficients of the material. Table + examples

The calculation of the necessary, if it concerns the external walls of the house, comes from the regional location of the building. To explain clearly how it happens, in the table below, the figures given will relate to the Krasnoyarsk Territory.

Material type	Heat transfer, W/(m*°С)	Wall thickness, mm	Illustration
3D		5500
Hardwood trees from 15%	0,15	1230
Expanded clay concrete	0,2	1630
Foam block with a density of 1 thousand kg / m³	0,3	2450
Coniferous trees along the fibers	0,35	2860
Oak lining	0,41	3350
on a mortar of cement and sand	0,87	7110
Reinforced concrete

Each building has different heat transfer resistance materials. The table below, which is an excerpt from the SNiP, clearly demonstrates this.

Examples of building insulation depending on thermal conductivity

In modern construction, walls consisting of two or even three layers of material have become the norm. One layer consists of, which is selected after certain calculations. Additionally, you need to find out where the dew point is.

To organize, it is necessary to comprehensively use several SNiPs, GOSTs, manuals and joint ventures:

• SNiP 23-02-2003 (SP 50.13330.2012). "Thermal protection of buildings". Edition from 2012;
• SNiP 23-01-99 (SP 131.13330.2012). "Construction climatology". Edition from 2012;
• SP 23-101-2004. "Design of thermal protection of buildings";
• Benefit. E.G. Malyavin “Heat loss of the building. Reference book";
• GOST 30494-96 (replaced by GOST 30494-2011 since 2011). Buildings are residential and public. Indoor microclimate parameters”;

Making calculations on these documents, determine the thermal features of the building material enclosing the structure, the resistance to thermal transfer and the degree of coincidence with regulatory documents. The calculation parameters based on the thermal conductivity table of the building material are shown in the photo below.

1. Do not be lazy to spend time studying the technical literature on the thermal conductivity properties of materials. This step will minimize financial and thermal losses.
2. Do not ignore the climate in your area. Information about GOSTs on this matter can be easily found on the Internet.

   
   Climate feature Mold on the walls Tightening the foam with waterproofing

The process of transferring energy from a hotter part of the body to a less heated one is called thermal conduction. The numerical value of such a process reflects the thermal conductivity of the material. This concept is very important in the construction and repair of buildings. Properly selected materials allow you to create a favorable microclimate in the room and save a significant amount on heating.

The concept of thermal conductivity

Thermal conductivity is the process of thermal energy exchange, which occurs due to the collision of the smallest particles of the body. Moreover, this process will not stop until the moment of temperature equilibrium comes. This takes a certain amount of time. The more time spent on heat exchange, the lower the thermal conductivity.

This indicator is expressed as the coefficient of thermal conductivity of materials. The table contains already measured values ​​for most materials. The calculation is made according to the amount of thermal energy that has passed through a given surface area of ​​the material. The larger the calculated value, the faster the object will give up all its heat.

Factors affecting thermal conductivity

The thermal conductivity of a material depends on several factors:

• With an increase in this indicator, the interaction of material particles becomes stronger. Accordingly, they will transfer the temperature faster. This means that with an increase in the density of the material, heat transfer improves.

• The porosity of a substance. Porous materials are heterogeneous in their structure. There is a lot of air inside them. And this means that it will be difficult for molecules and other particles to move thermal energy. Accordingly, the coefficient of thermal conductivity increases.

• Humidity also has an effect on thermal conductivity. Wet material surfaces allow more heat to pass through. Some tables even indicate the calculated thermal conductivity of the material in three states: dry, medium (normal) and wet.

When choosing a material for room insulation, it is also important to consider the conditions in which it will be used.

The concept of thermal conductivity in practice

Thermal conductivity is taken into account at the design stage of a building. This takes into account the ability of materials to retain heat. Thanks to their correct selection, residents inside the premises will always be comfortable. During operation, money for heating will be significantly saved.

Insulation at the design stage is optimal, but not the only solution. It is not difficult to insulate an already finished building by carrying out internal or external work. The thickness of the insulation layer will depend on the materials chosen. Some of them (for example, wood, foam concrete) can in some cases be used without an additional layer of thermal insulation. The main thing is that their thickness exceeds 50 centimeters.

Particular attention should be paid to the insulation of the roof, window and door openings, and the floor. Most of the heat escapes through these elements. Visually, this can be seen in the photo at the beginning of the article.

Structural materials and their indicators

For the construction of buildings, materials with a low coefficient of thermal conductivity are used. The most popular are:

• Reinforced concrete, the thermal conductivity value of which is 1.68 W / m * K. The density of the material reaches 2400-2500 kg/m 3 .

• Wood has been used as a building material since ancient times. Its density and thermal conductivity, depending on the rock, are 150-2100 kg / m 3 and 0.2-0.23 W / m * K, respectively.

Another popular building material is brick. Depending on the composition, it has the following indicators:

• adobe (made from clay): 0.1-0.4 W / m * K;

• ceramic (made by firing): 0.35-0.81 W / m * K;

• silicate (from sand with the addition of lime): 0.82-0.88 W / m * K.

Concrete materials with the addition of porous aggregates

The coefficient of thermal conductivity of the material allows you to use the latter for the construction of garages, sheds, summer houses, baths and other structures. This group includes:

• Expanded clay concrete, the performance of which depends on its type. Solid blocks do not have voids and holes. With voids inside, they are made which are less durable than the first option. In the second case, the thermal conductivity will be lower. If we consider the general figures, then it is 500-1800kg / m3. Its indicator is in the range of 0.14-0.65 W / m * K.

• Aerated concrete, inside which pores 1-3 mm in size are formed. This structure determines the density of the material (300-800kg/m3). Due to this, the coefficient reaches 0.1-0.3 W / m * K.

Indicators of thermal insulation materials

The coefficient of thermal conductivity of thermal insulation materials, the most popular in our time:

• expanded polystyrene, the density of which is the same as that of the previous material. But at the same time, the heat transfer coefficient is at the level of 0.029-0.036 W / m * K;

• glass wool. It is characterized by a coefficient equal to 0.038-0.045 W / m * K;

• with an indicator of 0.035-0.042 W / m * K.

Table of indicators

For convenience, the coefficient of thermal conductivity of the material is usually entered in the table. In addition to the coefficient itself, such indicators as the degree of humidity, density, and others can be reflected in it. Materials with a high coefficient of thermal conductivity are combined in the table with indicators of low thermal conductivity. An example of this table is shown below:

Using the coefficient of thermal conductivity of the material will allow you to build the desired building. The main thing: to choose a product that meets all the necessary requirements. Then the building will be comfortable for living; it will maintain a favorable microclimate.

Properly selected will reduce due to which it will no longer be necessary to “heat the street”. Thanks to this, financial costs for heating will be significantly reduced. Such savings will soon return all the money that will be spent on the purchase of a heat insulator.

Building a private house is a very difficult process from start to finish. One of the main issues of this process is the choice of building materials. This choice should be very competent and deliberate, because most of life in a new house depends on it. Standing apart in this choice is such a thing as the thermal conductivity of materials. It will depend on how warm and comfortable the house will be.

Thermal conductivity- this is the ability of physical bodies (and the substances from which they are made) to transfer thermal energy. In simpler terms, this is the transfer of energy from a warm place to a cold one. For some substances, such a transfer will occur quickly (for example, for most metals), and for some, on the contrary, very slowly (rubber).

Speaking 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 choice of materials will be the most correct. with low values ​​of this quantity so that the house does not cool down quickly. For clarity, we denote the percentage of heat loss in different parts of the house:

What does thermal conductivity depend on?

Values ​​of this quantity may depend on several factors. For example, the coefficient of thermal conductivity, which we will talk about separately, the humidity of building materials, density, and so on.

• Materials with high density indicators, in turn, have 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 moisture content of materials. If the materials get wet, their heat transfer will increase.
• Also, the structure of the material strongly affects this indicator. For example, wood with transverse and longitudinal fibers will have different thermal conductivity values.
• 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

To quantify this parameter, we use 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. At the moment, there is a calculation of coefficients for almost all existing types of building materials used in construction. The 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 according to the norms of SNIP (building codes and rules). Thermal conductivity of building materials, the table on 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 building and decorative bricks.

Calculation of the thickness of the insulation

From the tables above, we can see how different heat conduction coefficients can differ for different materials. To calculate the thermal resistance of the future wall, there is a simple formula, which relates the thickness of the insulation and the coefficient of its thermal conductivity.

R \u003d p / k, where R is the heat resistance index, p is the layer thickness, k is the coefficient.

From this formula, it is easy to single out the formula for calculating the thickness of the insulation layer for the required heat resistance. P = R*k. The value of heat resistance is different for each region. For these values, there is also a special table, where they can be viewed when calculating the thickness of the insulation.

Now let's give some examples the most popular heaters and their technical specifications.

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

The creation of efficient power plants and thermal insulation systems (equipment that provides the greatest heat exchange (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 the thermal protection of buildings have changed, the requirements for building materials have increased. Every house needs insulation and heating system.. Therefore, in the heat engineering calculation of enclosing structures, it is important to calculate the thermal conductivity index.

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 its hottest part to the colder one. The value of the thermal conductivity index shows the degree of heat loss by residential premises. Depends on the following factors:

It is possible to quantify the property of objects to pass thermal energy through the coefficient of thermal conductivity. It is very important to make a competent choice of building materials, insulation to achieve the greatest resistance to heat transfer. Miscalculations or unreasonable savings in the future can lead to a deterioration in the indoor climate, dampness in the building, wet walls, stuffy rooms. And most importantly - to high heating costs.

For comparison, below is a table of thermal conductivity of materials and substances.

Table 1

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

Classification of building materials and their thermal conductivity

The thermal conductivity of reinforced concrete, brickwork, expanded clay concrete blocks, commonly used for the construction of enclosing structures, is characterized by the highest standard values. 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 heat-insulating (from 0.210);
• heat-insulating (up to 0.082 - A, from 0.082 to 0.116 - B, etc.).

Efficiency of sandwich structures

Density and thermal conductivity

Currently, there is no such building material, the high bearing capacity of which 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 to ensure strength and reduce the loss of thermal energy to an optimal level. Therefore, when designing walls, each layer of the future enclosing structure is taken into account in the calculations.

It is also important to take into account the density when building a house and when it is insulated.

The density of a substance is a factor that affects its thermal conductivity, the ability to retain the main heat insulator - air.

Calculation of wall thickness and insulation

The calculation of the wall thickness depends on the following indicators:

• density;
• calculated thermal conductivity;
• heat transfer resistance coefficient.

According to the established norms, the value of the heat transfer resistance index of the outer walls must be at least 3.2λ W/m °C.

Calculation thickness of walls made of reinforced concrete and other structural materials is 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 irrational wall thickness.

table 2

Structural and heat-insulating materials are capable of being subjected to sufficiently high loads, while significantly increasing the thermal and acoustic properties of buildings in wall enclosing structures (tables 3.1, 3.2).

Table 3.1

Table 3.2

Heat-insulating building materials can significantly increase the thermal protection of buildings and structures. Table 4 shows that the lowest values ​​of the thermal conductivity coefficient have polymers, mineral wool, plates from natural organic and inorganic materials.

Table 4

The values ​​​​of the tables of thermal conductivity of building materials are used in the calculations:

The task of choosing the optimal materials for construction, of course, implies a more integrated approach. However, even such simple calculations already at the first stages of design make it possible to determine the most suitable materials and their quantity.

The issue of insulation of apartments and houses is very important - the ever-increasing cost of energy carriers obliges you to take good care of the heat in the room. But how to choose the right insulation material and calculate its optimal thickness? To do this, you need to know the indicators of thermal conductivity.

What is thermal conductivity

This value characterizes the ability to conduct heat inside the material. Those. determines the ratio of the amount of energy passing through a body with an area of ​​1 m² and a thickness of 1 m per unit of time - λ (W / m * K). Simply put, how much heat will be transferred from one surface of the material to another.

As an example, consider an ordinary brick wall.

As you can see in the figure, the temperature in the room is 20°C, and outside - 10°C. To comply with such a regime in the room, it is necessary that the material from which the wall is made be with a minimum coefficient of thermal conductivity. It is under this condition that we can talk about effective energy saving.

Each material has its own specific indicator of this value.

During construction, the following division of materials that perform a specific function is accepted:

• Construction of the main frame of buildings - walls, partitions, etc. For this, concrete, brick, aerated concrete, etc. are used.

Their thermal conductivity values ​​are quite high, which means that in order to achieve good energy savings, it is necessary to increase the thickness of the outer walls. But this is not practical, as it requires additional costs and an increase in the weight of the entire building. Therefore, it is customary to use special additional insulating materials.

• Heaters. These include polystyrene, polystyrene foam and any other material with a low thermal conductivity.

They provide proper protection of the house from the rapid loss of thermal energy.

In construction, the requirements for basic materials are - mechanical strength, reduced hygroscopicity (moisture resistance), and least of all - their energy characteristics. Therefore, special attention is paid to heat-insulating materials, which should compensate for this "shortcoming".

However, the practical application of the thermal conductivity is difficult, since it does not take into account the thickness of the material. Therefore, the opposite concept is used - the heat transfer resistance coefficient.

This value is the ratio of the thickness of the material to its coefficient of thermal conductivity.

The value of this parameter for residential buildings is prescribed in SNiP II-3-79 and SNiP 23-02-2003. According to these regulatory documents, the heat transfer resistance coefficient in different regions of Russia should not be less than the values ​​\u200b\u200bspecified in the table.

SNiP.

This calculation procedure is mandatory not only when planning the construction of a new building, but also for the competent and efficient insulation of the walls of an already erected house.