When summer temperatures reach high levels, thermal comfort becomes a priority. To understand how to maintain a comfortable temperature inside buildings during hot periods, it is essential to understand the concept of thermal effusivity.
Definition of thermal effusivity:
Thermal diffusivity is a measure of a wall's ability to exchange heat with its surroundings. It characterizes a wall's ability to absorb and store energy.
Calculate thermal effusivity:
Heat transfer depends on several factors, including the density, specific heat capacity, and thermal conductivity of the materials that make up the wall. It can be calculated using the following formula:
Effusivity = E = √(λρC)
Where E is the thermal diffusivity, λ is the thermal conductivity, and ρC is the specific heat capacity.
Interpretingthermal effusivity data:
Effusivity provides valuable information about the thermal properties of a wall. A wall with high effusivity will take longer to absorb heat and reach a high temperature, while a wall with low effusivity will respond quickly to temperature changes. Thus, a wall with high effusivity can help maintain a cooler, more consistent indoor temperature on hot summer days.
Role of effusivity in summer comfort:
Effusivity plays a key role in maintaining thermal comfort during the summer. Materials with high effusivity, such as stone or concrete-based materials, can help regulate temperature by absorbing excess heat during the day and slowly releasing it at night. This creates a cooler and more stable indoor environment, reducing dependence on air conditioning and electric fans.
On the other hand, materials with low effusivity, such as those used on roofs (tiles, slates), quickly absorb and release heat into their environment. This is why the temperature in attics can reach twice the outside temperature.
Furthermore, effusivity alone is not enough to guarantee summer comfort. Other factors, such as the orientation of the building and its ventilation, must also be taken into account to create a pleasant indoor environment during periods of intense heat.
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Association of Bio-based Construction Manufacturers (AICB)
Effusivity & damping:
If effusivity is the ability of a material to exchange energy with its environment (to absorb and store it), it is complementary to thermal damping. Damping (or amplitude attenuation) is the ability of a material to dissipate a thermal wave and attenuate its intensity. Thus, the more a material absorbs and stores a thermal wave (high effusivity), the more the intensity of this thermal wave will be reduced (high damping).
Effusivity is a key concept in the field of summer thermal comfort. It provides information about a material's ability to exchange heat with its environment. Materials with high effusivity can help maintain a cooler and more stable indoor temperature, while materials with low effusivity allow heat to pass through more easily. But effusivity alone is not enough to guarantee summer comfort, and other factors must be taken into account. By understanding effusivity and applying it appropriately, it is possible to create more comfortable indoor environments during periods of intense summer heat.
