Thermal conductivity and thermal insulation: what you need to know

Thermal Conductivity and Its Role in Thermal Insulation

Thermal conductivity is one of the key characteristics of any material, as it determines how quickly heat spreads through that material. This indicator directly affects the quality of thermal insulation in buildings and individual structures. In this article, we will discuss what thermal conductivity is, how it is determined, what coefficients of thermal conductivity exist for materials, and why its indicators are so important when choosing thermal insulators.

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What is Thermal Insulation?

Thermal insulation is a set of measures and the use of special materials to reduce heat loss or heat gain in buildings, structures, and other systems. The task of thermal insulation is to:

1. Retain heat in the cold season and thus reduce heating costs.
2. Maintain coolness in the summer when it is hot outside, and reduce the load on air conditioners.

With properly selected thermal insulation materials, it is possible to significantly increase the energy efficiency of a building, reduce the costs of maintaining a comfortable microclimate, and extend the service life of structures.

Thermal Conductivity: Definition and Essence

Thermal conductivity is the ability of a material to transfer heat from a hotter area to a cooler one. This process occurs at the molecular level: the closer the molecules are arranged, the better they transfer thermal energy.

1. Thermal conductivity coefficient (λ):

   • Measured in W/(m·K) (watts per meter-kelvin).
   • Indicates how much heat will pass through 1 m of material thickness with a temperature difference of 1 K (kelvin).
   • The lower the thermal conductivity coefficient, the better the thermal insulation properties of the material.

2. Dependence of thermal conductivity on the structure of the material:

   • Density and porosity. The more air pockets in the material, the worse it conducts heat (i.e., the better it insulates). For example, polystyrene foam has many air bubbles inside, making it an excellent thermal insulator.
   • Moisture. Water has a higher thermal conductivity than air. If a material absorbs moisture, its thermal insulation properties decrease.
   • Composition and chemical structure. Different substances conduct heat differently. Metals have very high thermal conductivity, while organic or porous materials have much lower conductivity.

Thermal Conductivity of Materials: Examples

Below are approximate thermal conductivity coefficients of the most common materials (W/(m·K)):

• Mineral wool: 0.03 – 0.05
• Polystyrene foam (expanded polystyrene): 0.03 – 0.04
• Wood (dry): 0.12 – 0.16
• Water: ~0.58 (note that this is quite a high value compared to air)
• Air: ~0.024
• Brick: 0.3 – 0.7
• Concrete: 1.0 – 1.7
• Steel: ~50

From the examples provided, it is clear that water conducts heat significantly better than air, so the saturation of a material with moisture sharply deteriorates its thermal insulation properties. Porous materials (polystyrene foam, mineral wool) have low thermal conductivity due to a large number of air pockets.

Thermal Insulators: What They Are and Their Examples

Thermal insulators are materials with low thermal conductivity (i.e., low λ coefficient). They are used to reduce heat loss in buildings, pipelines, industrial installations, etc.

What are Thermal Insulators?

These can be both natural and synthetic substances, as long as they effectively restrain the flow of heat. The main characteristics of thermal insulators include:

• Low thermal conductivity.
• Dimensional stability.
• Moisture resistance (or the ability to dry quickly and not lose their properties).
• Mechanical strength (to withstand loads).

Examples of Thermal Insulators

1. Polystyrene foam (expanded polystyrene) — lightweight, inexpensive, and easy to install.
2. Mineral wool (glass wool, stone wool) — resistant to high temperatures, does not burn.
3. Extruded polystyrene (XPS) — has better mechanical strength than polystyrene foam.
4. Polyurethane foam (PUR/PIR) — used in the form of sandwich panels and spray insulation.
5. Ecowool (cellulose wool) — an eco-friendly and well-insulating material made from recycled paper.
6. Wood fiber boards — an organic material with a porous structure, often used in eco-friendly construction.

Each of these materials has its advantages and disadvantages. The choice of thermal insulator depends on where and how it is planned to be used, as well as the required characteristics (thermal insulation, mechanical strength, moisture resistance, fire resistance, etc.).

How Does Thermal Conductivity Affect Thermal Insulation?

1. Heat Loss: Materials with high thermal conductivity (e.g., metals or water) quickly transfer heat and lead to significant losses during the heating season.
2. Energy Efficiency: Buildings, structures, or engineering systems that contain elements with low thermal conductivity retain heat in winter and coolness in summer, reducing climate control costs.
3. Comfort: Proper thermal insulation ensures a stable temperature in rooms, freeing residents from sharp fluctuations and discomfort.

The Importance of Choosing the Right Materials

When choosing a thermal insulation material, be sure to consider:

• Thermal Conductivity Coefficient: the lower, the better.
• Moisture Resistance: water has quite high thermal conductivity (~0.58 W/(m·K)), which negatively affects the insulation when it gets wet.
• Fire Resistance: in many cases, it is important that the material does not burn and does not emit toxic substances.
• Layer Thickness: a thicker layer of insulation means lower heat losses, but at the same time increases costs and may reduce the usable area of rooms.
• Mechanical Loads: in some cases, the material must withstand pressure, for example, in floor structures.

FAQ (Frequently Asked Questions)

1. What is thermal conductivity in simple terms?
   Thermal conductivity is the ability of a material to transfer heat. The better a material conducts heat, the higher its thermal conductivity.

2. Why is it important to choose materials with low thermal conductivity for insulation?
   Materials with low thermal conductivity (thermal insulators) effectively retain heat inside the room in winter and coolness in summer, helping to save on heating and cooling.

3. What is the thermal conductivity coefficient of water and why is it important?
   The thermal conductivity coefficient of water is about 0.58 W/(m·K), which is quite high compared to most insulators. If the insulation gets wet, it starts to conduct heat much better and loses its effectiveness.

4. What are the most common examples of thermal insulators?
   The most commonly used are polystyrene foam, mineral wool, extruded polystyrene, polyurethane foam, and ecowool. The choice depends on the budget, operating conditions, and requirements for environmental friendliness and fire safety.

5. What is “thermal insulation” and why is it needed?
   Thermal insulation is a set of measures aimed at reducing heat loss in a house or other structure. It is needed to reduce heating costs, maintain optimal temperature, and ensure a comfortable microclimate.

6. How can I determine how effectively the insulation works in my house?
   You can perform a thermal imaging scan of the building to see areas with the highest heat losses. The effectiveness is also reflected in reduced heating or cooling bills and a stable temperature inside the house.

7. Does the thickness of the insulation affect its effectiveness?
   Yes, the thicker the layer of insulation (with a constant thermal conductivity coefficient), the less heat passes through the structure, thus providing better overall thermal insulation.

Conclusion

Thermal conductivity is a fundamental property of a material that determines how quickly heat moves through it. In the context of construction and renovation, it plays a crucial role in forming effective thermal insulation. Materials with low thermal conductivity allow for retaining heat in winter and coolness in summer, reducing energy costs and providing a comfortable microclimate.

When planning insulation for a home or other building, it is worth studying the characteristics of potential materials in detail, paying attention not only to the thermal conductivity coefficient but also to moisture resistance, fire safety, and durability. Properly selected thermal insulation will help optimize energy consumption costs, improve quality of life, and provide reliable protection for building structures from external influences.