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Thermal inertia: definition and impact on insulation

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We speak of thermal inertia when the physical capacity of the material maintains its temperature. It allows the heat from the sun's rays to be stored in winter and restores it inside thanks to the walls. Where does the importance of the choice of materials come from when constructing a building for better inertia such as high-density insulation or refractory bricks. One can in particular build a wall with inertia in water. The heavier the materials, the greater the inertia. For better energy efficiency, thermal inertia must be significant.

How does thermal inertia work?

Its operation is simple, regardless of your heating method, whether electric or wood , the heat it will diffuse will be captured by the walls and keep the house at the temperature you want. There is no heat loss. Ditto during hot weather, heatwaves, the freshness will be kept inside for better comfort of the inhabitant and thus prevent overheating of the living rooms.

How is thermal inertia measured?

It can be measured with two elements which are thermal effusivity and thermal diffusivity. They determine the thermal phase shift. The thermal effusivity measures the capacity of the material to block, stop the transmission of heat. Walls with low diffusivity benefit from better inertia. Thermal diffusivity, on the other hand, indicates the rate of temperature of a material as a function of outside temperatures.
The phase shift indicates the time between 3 phases in the frame:
  • Absorption
  • Storage
  • Diffusion (hot or cold)
For a good thermal phase shift, the effusivity must be high and the diffusivity must be low.

What are the advantages of thermal inertia?

Builders are increasingly interested in it during a construction or renovation because it is very advantageous and economical. Good thermal inertia offers better comfort for the inhabitant. It helps to avoid overheating or an intense feeling of cold. It maintains a stable temperature. It also offers great energy savings, a very significant gain.
Be careful not to confuse thermal inertia and insulation , they are two different things and their principles are very different. The function of the insulators is to maintain the temperatures inside while the thermal inertia promotes storage. When building a house, it is not negligible to use materials for good thermal energy inertia, it is ecological and economical.