Comparison of the thermal conductivity of building materials - we study important indicators. Thermal conductivity of building materials Comparison of materials by thermal conductivity

When building private and multi-apartment buildings, many factors must be taken into account and a large number of norms and standards must be observed. In addition, before construction, a house plan is created, calculations are made for the load on the supporting structures (foundation, walls, ceilings), communications and heat resistance. The calculation of heat transfer resistance is no less important than the others. It not only determines how warm the house will be, and, as a result, energy savings, but also the strength and reliability of the structure. After all, walls and other elements of it can freeze through. The cycles of freezing and thawing destroy the building material and lead to dilapidated and accident-prone buildings.

Thermal conductivity

Any material can conduct heat. This process is carried out due to the movement of particles, which transmit the change in temperature. The closer they are to each other, the faster the heat transfer process. Thus, denser materials and substances cool or heat up much faster. The intensity of heat transfer primarily depends on the density. It is expressed numerically in terms of the thermal conductivity coefficient. It is denoted by the symbol λ and is measured in W/(m*°C). The higher this coefficient, the higher the thermal conductivity of the material. The reciprocal of the thermal conductivity is the thermal resistance. It is measured in (m2*°C)/W and is denoted by the letter R.

Application of concepts in construction

In order to determine the thermal insulation properties of a building material, the heat transfer resistance coefficient is used. Its value for various materials is given in almost all building guides.

Since most modern buildings have a multilayer wall structure, consisting of several layers of different materials (external plaster, insulation, wall, internal plaster), the concept of reduced heat transfer resistance is introduced. It is calculated in the same way, but in the calculations a homogeneous analogue of a multilayer wall is taken, passing the same amount of heat over a certain time and with the same temperature difference inside and outside.

The reduced resistance is calculated not for 1 square meter, but for the entire structure or some part of it. It summarizes the thermal conductivity of all wall materials.

Thermal resistance of structures

All external walls, doors, windows, roof are enclosing structures. And since they protect the house from the cold in different ways (they have a different coefficient of thermal conductivity), the heat transfer resistance of the building envelope is individually calculated for them. Such structures include internal walls, partitions and ceilings, if there is a temperature difference in the premises. This refers to rooms in which the temperature difference is significant. These include the following unheated parts of the house:

• Garage (if it is directly adjacent to the house).
• Hallway.
• Veranda.
• Pantry.
• Attic.
• Basement.

If these rooms are not heated, then the wall between them and the living quarters must also be insulated, like the outer walls.

Thermal resistance of windows

In the air, the particles that participate in heat exchange are located at a considerable distance from each other, and therefore, air isolated in a sealed space is the best insulator. Therefore, all wooden windows used to be made with two rows of sashes. Due to the air gap between the frames, the heat transfer resistance of the windows increases. The same principle applies to front doors in a private house. To create such an air gap, two doors are placed at some distance from each other or a dressing room is made.

This principle has remained in modern plastic windows. The only difference is that the high heat transfer resistance of double-glazed windows is achieved not due to the air gap, but due to hermetic glass chambers, from which air is pumped out. In such chambers, the air is discharged and there are practically no particles, which means that there is nothing to transfer the temperature to. Therefore, the thermal insulation properties of modern double-glazed windows are much higher than those of old wooden windows. The thermal resistance of such a double-glazed window is 0.4 (m2*°C)/W.

Modern front doors for private houses have a multilayer structure with one or more layers of insulation. In addition, additional heat resistance is provided by the installation of rubber or silicone seals. Thanks to this, the door becomes practically airtight and the installation of a second one is not required.

Calculation of thermal resistance

The calculation of the heat transfer resistance allows you to estimate the heat loss in W and calculate the necessary additional insulation and heat loss. Thanks to this, you can correctly select the required power of heating equipment and avoid unnecessary spending on more powerful equipment or energy carriers.

For clarity, we calculate the thermal resistance of the wall of a house made of red ceramic bricks. Outside, the walls will be insulated with extruded polystyrene foam 10 cm thick. The thickness of the walls will be two bricks - 50 cm.

Heat transfer resistance is calculated using the formula R = d/λ, where d is the thickness of the material and λ is the thermal conductivity of the material. From the building guide it is known that for ceramic bricks λ = 0.56 W / (m * ° C), and for extruded polystyrene foam λ = 0.036 W / (m * ° C). Thus, R (brickwork) \u003d 0.5 / 0.56 \u003d 0.89 (m 2 * ° C) / W, and R (extruded polystyrene foam) \u003d 0.1 / 0.036 \u003d 2.8 (m 2 * °C)/W. In order to find out the total thermal resistance of the wall, you need to add these two values: R \u003d 3.59 (m 2 * ° C) / W.

Table of thermal resistance of building materials

All the necessary information for individual calculations of specific buildings is given by the heat transfer resistance table below. The example of calculations given above, in conjunction with the data in the table, can also be used to estimate the loss of thermal energy. To do this, use the formula Q \u003d S * T / R, where S is the area of ​​\u200b\u200bthe building envelope, and T is the temperature difference between the street and the room. The table shows the data for a wall with a thickness of 1 meter.

Warm designs, methods, materials

In order to increase the resistance to heat transfer of the entire structure of a private house, as a rule, building materials with a low coefficient of thermal conductivity are used. Thanks to the introduction of new technologies in the construction of such materials is becoming more and more. Among them are the most popular:

• Wood.
• Sandwich panels.
• ceramic block.
• Expanded clay block.
• Aerated concrete block.
• Foam block.
• Polystyrene concrete block, etc.

Wood is a very warm, environmentally friendly material. Therefore, many in the construction of a private house opt for it. It can be either a log house, or a rounded log or a rectangular beam. The material used is mainly pine, spruce or cedar. However, this is a rather capricious material and requires additional measures to protect against weathering and insects.

Sandwich panels are a fairly new product on the domestic building materials market. Nevertheless, its popularity in private construction has increased greatly in recent years. After all, its main advantages are a relatively low cost and good resistance to heat transfer. This is achieved through its structure. On the outside there is a rigid sheet material (OSB boards, plywood, metal profiles), and inside - foamed insulation or mineral wool.

Building blocks

The high resistance to heat transfer of all building blocks is achieved due to the presence of air chambers or a foam structure in their structure. So, for example, some ceramic and other types of blocks have special holes that, when laying the wall, run parallel to it. Thus, closed chambers with air are created, which is a fairly effective measure of preventing heat transfer.

In other building blocks, the high resistance to heat transfer lies in the porous structure. This can be achieved by various methods. In foam concrete aerated concrete blocks, a porous structure is formed due to a chemical reaction. Another way is to add a porous material to the cement mixture. It is used in the manufacture of polystyrene concrete and expanded clay concrete blocks.

The nuances of the use of heaters

If the heat transfer resistance of the wall is insufficient for the given region, then insulation can be used as an additional measure. Wall insulation, as a rule, is carried out outside, but if necessary, it can also be applied on the inside of load-bearing walls.

Today, there are many different heaters, among which the most popular are:

• Mineral wool.
• Polyurethane foam.
• Styrofoam.
• Extruded polystyrene foam.
• Foam glass, etc.

All of them have a very low coefficient of thermal conductivity, therefore, for the insulation of most walls, a thickness of 5-10 mm is usually sufficient. But at the same time, one should take into account such a factor as the vapor permeability of the insulation and wall material. According to the rules, this indicator should increase outwards. Therefore, the insulation of walls made of aerated concrete or foam concrete is possible only with the help of mineral wool. Other heaters can be used for such walls if a special ventilation gap is made between the wall and the heater.

Conclusion

The thermal resistance of materials is an important factor to be considered in construction. But, as a rule, the warmer the wall material, the lower the density and compressive strength. This should be taken into account when planning a house.

One of the most important indicators of building materials, especially in the Russian climate, is their thermal conductivity, which is generally defined as the body's ability to heat exchange (that is, the distribution of heat from a hotter environment to a colder one).

In this case, the colder environment is the street, and the hotter one is the interior space (in summer it is often the other way around). Comparative characteristics are given in the table:

The coefficient is calculated as the amount of heat that will pass through a material 1 meter thick in 1 hour with a temperature difference of 1 degree Celsius inside and outside. Accordingly, the unit of measurement for building materials is W / (m * ° C) - 1 Watt, divided by the product of a meter and a degree.

A comparison of the thermal conductivity of building materials, as well as their density and vapor permeability, is presented in the table.

The most effective materials used in the construction of houses are highlighted in bold.

Below is a visual diagram from which it is easy to see how thick a wall of different materials should be in order for it to retain the same amount of heat.

Obviously, according to this indicator, the advantage is for artificial materials (for example, polystyrene foam).

Approximately the same picture can be seen if we make a diagram of building materials that are most often used in work.

In this case, environmental conditions are of great importance. Below is a table of thermal conductivity of building materials that are operated:

• under normal conditions (A);
• in conditions of high humidity (B);
• in dry climates.

The data are taken on the basis of relevant building codes and regulations (SNiP II-3-79), as well as from open Internet sources (web pages of manufacturers of relevant materials). If there is no data on specific operating conditions, then the field in the table is not filled.

The higher the indicator, the more heat it passes, ceteris paribus. So, for some types of polystyrene foam, this indicator is 0.031, and for polyurethane foam - 0.041. On the other hand, the coefficient of concrete is an order of magnitude higher - 1.51, therefore, it transmits heat much better than artificial materials.

Comparative heat losses through different surfaces of the house can be seen in the diagram (100% - total losses).

Obviously, most of it leaves the walls, so finishing this part of the room is the most important task, especially in the northern climate.

Video for reference

The use of materials with low thermal conductivity in the insulation of houses

Basically, artificial materials are used today - polystyrene foam, mineral wool, polyurethane foam, polystyrene foam and others. They are very efficient, affordable and fairly easy to install without requiring special skills.

• when erecting walls (their thickness is less, since the main load on saving heat is taken on by heat-insulating materials);
• when servicing the house (less resources are spent on heating).

Styrofoam

This is one of the leaders in its category, which is widely used in wall insulation both outside and inside. The coefficient is approximately 0.052-0.055 W / (o C * m).

How to choose a quality insulation

When choosing a specific sample, it is important to pay attention to the marking - it contains all the basic information that affects the properties.

For example, PSB-S-15 means the following:

Mineral wool

Another fairly common insulation, which is used both in interior and exterior decoration, is mineral wool.

The material is quite durable, inexpensive and easy to install. At the same time, unlike polystyrene, it absorbs moisture well, therefore, when using it, waterproofing materials must also be used, which increases the cost of installation work.

Modern insulation materials have unique characteristics and are used to solve problems of a certain spectrum. Most of them are designed for processing the walls of the house, but there are also specific ones designed for arranging door and window openings, junctions of the roof with load-bearing supports, basements and attics. Thus, when comparing thermal insulation materials, it is necessary to take into account not only their operational properties, but also the scope of application.

Main parameters

The quality of the material can be assessed based on several fundamental characteristics. The first of these is the coefficient of thermal conductivity, which is denoted by the symbol "lambda" (ι). This coefficient shows how much heat passes through a piece of material with a thickness of 1 meter and an area of ​​1 m² in 1 hour, provided that the difference between the temperatures of the environment on both surfaces is 10 ° C.

The indicators of the thermal conductivity coefficient of any heaters depend on many factors - on humidity, vapor permeability, heat capacity, porosity and other characteristics of the material.

moisture sensitivity

Humidity is the amount of moisture contained in the insulation. Water is an excellent conductor of heat, and the surface saturated with it will contribute to the cooling of the room. Consequently, waterlogged heat-insulating material will lose its qualities and will not give the desired effect. And vice versa: the more water-repellent properties it has, the better.

Vapor permeability is a parameter close to humidity. In numerical terms, it represents the volume of water vapor passing through 1 m2 of insulation in 1 hour, subject to the condition that the difference in potential vapor pressure is 1 Pa, and the temperature of the medium is the same.

With high vapor permeability, the material can be moistened. In this regard, when insulating the walls and ceilings of the house, it is recommended to install a vapor barrier coating.

Water absorption - the ability of a product to absorb liquid when in contact with it. The water absorption coefficient is very important for materials that are used for arranging external thermal insulation. Increased air humidity, atmospheric precipitation and dew can lead to a deterioration in the characteristics of the material.

Density and heat capacity

Porosity is the number of air pores expressed as a percentage of the total volume of the product. Distinguish pores closed and open, large and small. It is important that they are evenly distributed in the structure of the material: this indicates the quality of the product. Porosity can sometimes reach 50%, in the case of some types of cellular plastics, this figure is 90-98%.

Density is one of the characteristics that affect the mass of a material. A special table will help determine both of these parameters. Knowing the density, you can calculate how much the load on the walls of the house or its floors will increase.

Heat capacity - an indicator showing how much heat is ready to accumulate thermal insulation. Biostability - the ability of a material to resist the effects of biological factors, such as pathogenic flora. Fire resistance - the resistance of insulation to fire, while this parameter should not be confused with fire safety. There are other characteristics, which include strength, bending endurance, frost resistance, wear resistance.

Also, when performing calculations, you need to know the coefficient U - the resistance of structures to heat transfer. This indicator has nothing to do with the qualities of the materials themselves, but you need to know it in order to make the right choice among a variety of heaters. The coefficient U is the ratio of the temperature difference on both sides of the insulation to the volume of heat flow passing through it. To find the thermal resistance of walls and ceilings, you need a table where the thermal conductivity of building materials is calculated.

You can do the necessary calculations yourself. To do this, the thickness of the material layer is divided by the coefficient of its thermal conductivity. The last parameter - if we are talking about insulation - must be indicated on the packaging of the material. In the case of house structural elements, everything is a little more complicated: although their thickness can be measured independently, the thermal conductivity of concrete, wood or brick will have to be sought in specialized manuals.

At the same time, materials of different types are often used to insulate walls, ceilings and floors in the same room, since the coefficient of thermal conductivity must be calculated separately for each plane.

Thermal conductivity of the main types of insulation

Based on the U coefficient, you can choose which type of thermal insulation is better to use, and what thickness the material layer should have. The table below contains information about the density, vapor permeability and thermal conductivity of popular heaters:

Advantages and disadvantages

When choosing thermal insulation, it is necessary to take into account not only its physical properties, but also parameters such as ease of installation, the need for additional maintenance, durability and cost.

Comparison of the most modern options

As practice shows, it is easiest to carry out the installation of polyurethane foam and penoizol, which are applied to the treated surface in the form of foam. These materials are plastic, they easily fill the cavities inside the walls of the building. The disadvantage of foamable substances is the need to use special equipment for spraying them.

As the table above shows, extruded polystyrene foam is a worthy competitor to polyurethane foam. This material comes in solid blocks, but can be cut into any shape with a regular carpenter's knife. Comparing the characteristics of foam and solid polymers, it is worth noting that the foam does not form seams, and this is its main advantage compared to blocks.

Comparison of cotton materials

Mineral wool is similar in properties to foam plastics and expanded polystyrene, but at the same time it “breathes” and does not burn. It also has better resistance to moisture and practically does not change its quality during operation. If there is a choice between solid polymers and mineral wool, it is better to give preference to the latter.

Stone wool has the same comparative characteristics as mineral wool, but the cost is higher. Ecowool has an affordable price and is easy to install, but it has low compressive strength and sags over time. Fiberglass also sags and, in addition, crumbles.

Bulk and organic materials

For thermal insulation of the house, bulk materials are sometimes used - perlite and paper granules. They repel water and are resistant to pathogenic factors. Perlite is environmentally friendly, it does not burn and does not settle. However, bulk materials are rarely used for wall insulation; it is better to equip floors and ceilings with their help.

From organic materials, it is necessary to distinguish flax, wood fiber and cork. They are environmentally friendly, but are prone to burning unless impregnated with special substances. In addition, wood fiber is exposed to biological factors.

In general, given the cost, practicality, thermal conductivity and durability of insulation, the best materials for finishing walls and ceilings are polyurethane foam, penoizol and mineral wool. Other types of insulation have specific properties, as they are designed for non-standard situations, and it is recommended to use such insulation only if there are no other options.

A strong and warm house is the main requirement for designers and builders. Therefore, even at the design stage of buildings, two types of building materials are laid in the structure: structural and heat-insulating. The former have increased strength, but high thermal conductivity, and it is they that are most often used for the construction of walls, ceilings, bases and foundations. The second are materials with low thermal conductivity. Their main purpose is to cover structural materials with themselves in order to lower their thermal conductivity. Therefore, to facilitate calculations and selection, a table of thermal conductivity of building materials is used.

Read in the article:

What is thermal conductivity

The laws of physics define one postulate, which states that thermal energy tends from a high temperature medium to a low temperature medium. At the same time, passing through the building material, thermal energy spends some time. The transition will not take place only if the temperature on different sides of the building material is the same.

That is, it turns out that the process of transferring thermal energy, for example, through a wall, is the time of heat penetration. And the more time it takes, the lower the thermal conductivity of the wall. Here is the ratio. For example, the thermal conductivity of various materials:

• concrete -1.51 W/m×K;
• brick - 0.56;
• wood - 0.09-0.1;
• sand - 0.35;
• expanded clay - 0.1;
• steel - 58.

To make it clear what is at stake, it must be indicated that the concrete structure will not, under any pretext, pass thermal energy through itself if its thickness is within 6 m. It is clear that this is simply impossible in housing construction. This means that it will be necessary to use other materials with a lower indicator to reduce thermal conductivity. And they veneer a concrete structure.

What is the coefficient of thermal conductivity

The coefficient of heat transfer or thermal conductivity of materials, which is also indicated in the tables, is a characteristic of thermal conductivity. It denotes the amount of thermal energy passing through the thickness of the building material for a certain period of time.

In principle, the coefficient denotes a quantitative indicator. And the smaller it is, the better the thermal conductivity of the material. From the comparison above, it can be seen that steel profiles and structures have the highest coefficient. So, they practically do not keep heat. Of the building materials that retain heat, which are used for the construction of load-bearing structures, this is wood.

But there is another point to be made. For example, all the same steel. This durable material is used for heat dissipation where there is a need to make a quick transfer. For example, radiators. That is, a high thermal conductivity is not always a bad thing.

What affects the thermal conductivity of building materials

There are several parameters that greatly affect thermal conductivity.

1. The structure of the material itself.
2. Its density and moisture

As for the structure, there is a huge variety: homogeneous, dense, fibrous, porous, conglomerate (concrete), loose-grained, and so on. So it is necessary to indicate that the more heterogeneous the structure of the material, the lower its thermal conductivity. The thing is that to pass through a substance in which a large volume is occupied by pores of different sizes, the more difficult it is for energy to move through it. But in this case, thermal energy is radiation. That is, it does not pass uniformly, but begins to change directions, losing strength inside the material.

Now about density. This parameter indicates the distance between the particles of the material inside it. Based on the previous position, we can conclude: the smaller this distance, which means the greater the density, the higher the thermal conductivity. And vice versa. The same porous material has a density less than a homogeneous one.

Humidity is water that has a dense structure. And its thermal conductivity is 0.6 W/m*K. A fairly high figure, comparable to the coefficient of thermal conductivity of a brick. Therefore, when it begins to penetrate into the structure of the material and fill the pores, this is an increase in thermal conductivity.

The coefficient of thermal conductivity of building materials: how it is applied in practice and the table

The practical value of the coefficient is the correct calculation of the thickness of the supporting structures, taking into account the insulation used. It should be noted that the building under construction consists of several enclosing structures through which heat escapes. And each of them has its own percentage of heat loss.

• up to 30% of the thermal energy of the total consumption goes through the walls.
• Through the floors - 10%.
• Through windows and doors - 20%.
• Through the roof - 30%.

That is, it turns out that if it is incorrect to calculate the thermal conductivity of all fences, then people living in such a house will have to be content with only 10% of the thermal energy that the heating system emits. 90% is, as they say, money thrown to the wind.

Expert opinion

HVAC design engineer (heating, ventilation and air conditioning) LLC "ASP North-West"

“The ideal house should be built from thermal insulation materials, in which all 100% of the heat will remain inside. But according to the table of thermal conductivity of materials and heaters, you will not find the ideal building material from which such a structure could be erected. Because the porous structure is the low bearing capacity of the structure. Wood may be an exception, but it is not ideal either.”

Therefore, in the construction of houses, they try to use different building materials that complement each other in terms of thermal conductivity. It is very important to correlate the thickness of each element in the overall building structure. In this regard, a frame house can be considered an ideal house. It has a wooden base, we can already talk about a warm house, and heaters that are laid between the elements of the frame building. Of course, taking into account the average temperature of the region, it will be necessary to accurately calculate the thickness of the walls and other enclosing elements. But, as practice shows, the changes being made are not so significant that one could talk about large capital investments.

Consider several commonly used building materials and compare their thermal conductivity through thickness.

Thermal conductivity of bricks: table by variety

Thermal conductivity of wood: table by species

The coefficient of thermal conductivity of cork wood is the lowest of all wood species. It is cork that is often used as a heat-insulating material during insulation measures.

Thermal conductivity of metals: table

This indicator for metals changes with a change in the temperature at which they are used. And here the ratio is - the higher the temperature, the lower the coefficient. The table shows the metals that are used in the construction industry.

Now, regarding the relationship with temperature.

• Aluminum at -100°C has a thermal conductivity of 245 W/m*K. And at a temperature of 0 ° С - 238. At + 100 ° С - 230, at + 700 ° С - 0.9.
• For copper: at -100°С -405, at 0°С - 385, at +100°С - 380, and at +700°С - 350.

Table of thermal conductivity of other materials

Basically, we will be interested in the table of thermal conductivity of insulating materials. It should be noted that if for metals this parameter depends on temperature, then for heaters it depends on their density. Therefore, the table will list the indicators taking into account the density of the material.

And a table of thermal insulation properties of building materials. The main ones have already been considered, let's denote those that are not included in the tables, and which belong to the category of frequently used ones.

The coefficient of thermal conductivity of the air gap

Everyone knows that air, if left inside a building material or between layers of building materials, is an excellent insulator. Why is this happening, because the air itself, as such, cannot hold back heat. For this, it is necessary to consider the air gap itself, enclosed by two layers of building materials. One of them is in contact with the zone of positive temperatures, the other with the zone of negative.

Thermal energy moves from plus to minus, and meets a layer of air on its way. What's going on inside:

1. Convection of warm air inside the interlayer.
2. Thermal radiation from a material with positive temperature.

Therefore, the heat flow itself is the sum of two factors with the addition of the thermal conductivity of the first material. It should be immediately noted that radiation occupies a large part of the heat flux. Today, all calculations of the heat resistance of walls and other load-bearing building envelopes are carried out on online calculators. As for the air gap, it is difficult to carry out such calculations, therefore, the values ​​\u200b\u200bthat were obtained by laboratory studies in the 50s of the last century are taken.

They clearly stipulate that if the temperature difference of the walls bounded by air is 5°C, then the radiation increases from 60% to 80% if the thickness of the interlayer is increased from 10 to 200 mm. That is, the total volume of the heat flux remains the same, the radiation increases, which means that the thermal conductivity of the wall decreases. And the difference is significant: from 38% to 2%. True, convection increases from 2% to 28%. But since the space is closed, the movement of air inside it has no effect on external factors.

Calculation of wall thickness by thermal conductivity manually using formulas or a calculator

Calculating wall thickness is not easy. To do this, you need to add up all the thermal conductivity coefficients of the materials that were used to build the wall. For example, brick, exterior plaster, plus exterior cladding if one is to be used. Internal leveling materials, it can be all the same plaster or gypsum boards, other slab or panel coatings. If there is an air gap, then take it into account.

There is the so-called specific thermal conductivity by region, which is taken as a basis. So the calculated value should not be more than the specific value. In the table below, the specific thermal conductivity is given by city.

That is, the further south, the less the total thermal conductivity of materials should be. Accordingly, the thickness of the wall can also be reduced. As for the online calculator, we suggest watching the video below, which explains how to use such a settlement service correctly.

If you have any questions that you thought you did not find answers to in this article, write them in the comments. Our editors will try to answer them.

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.