What are the main evaluation indicators of thermal performance of building materials?

The thermal performance of building materials is one of the important indicators for evaluating its application effect in buildings, which is directly related to the energy consumption of buildings, indoor environmental comfort and overall thermal stability.

1. Thermal conductivity
Definition and importance: Thermal conductivity is the core indicator for measuring the thermal performance of building materials. It reflects the ability of materials to conduct heat under steady-state conditions. Specifically, thermal conductivity refers to the rate of heat transfer through unit area and unit temperature difference per unit time. The smaller the thermal conductivity, the weaker the material's ability to conduct heat, that is, the better the thermal insulation performance.

Influencing factors: Thermal conductivity is affected by many factors such as material type, density, porosity, and moisture content. For example, porous materials have a lower overall thermal conductivity because the thermal conductivity of air in the pores is much lower than that of solid materials; while the thermal conductivity of dense materials is relatively high.

Application example: In buildings, in order to maintain the stability of indoor temperature and reduce heat loss, building materials with low thermal conductivity, such as polystyrene (EPS), polyurethane and other insulation materials, are often used for enclosure structures (such as exterior walls and roofs).

2. Heat transfer coefficient
Definition and difference: The heat transfer coefficient is different from the thermal conductivity coefficient. It measures the thermal performance of the entire enclosure structure (rather than a single material). The heat transfer coefficient refers to the heat transferred through an area of ​​1 square meter in 1 hour when the air temperature difference on both sides of the enclosure structure is 1°C under steady-state conditions. The heat transfer coefficient is not only related to the thermal conductivity of the building material, but also affected by factors such as the construction, thickness, and surface condition of the enclosure structure.

Importance: The heat transfer coefficient directly determines the thermal insulation performance of the enclosure structure. In cold areas, reducing the heat transfer coefficient helps reduce indoor heat loss and improve the insulation effect of the building; in hot areas, it helps to block outdoor heat from entering the room and keep the room cool.

3. Thermal resistance
Definition: Thermal resistance is the ability of a material or enclosure structure to hinder heat transfer. The greater the thermal resistance, the more difficult it is to transfer heat, that is, the better the thermal insulation performance of the material. Thermal resistance is inversely proportional to the thermal conductivity of the material and directly proportional to the thickness of the material.

Application: In building design, by increasing the thermal resistance of the enclosure structure (such as using multi-layer composite walls, increasing the thickness of the insulation layer, etc.), the thermal insulation performance of the building can be effectively improved and energy consumption can be reduced.

4. Thermal storage coefficient
Definition: The thermal storage coefficient reflects the ability of building materials to absorb or release heat when the temperature changes. Materials with a large thermal storage coefficient can absorb or release more heat when the temperature changes, which helps to stabilize indoor temperature fluctuations.
Importance: In areas with large temperature differences between day and night, the use of materials with a large thermal storage coefficient can reduce the range of indoor temperature fluctuations and improve living comfort.