Thermal Insulation

From lambda value to energy efficiency of a building : this is the scope of thermal insulation .

The same basic thermal principles are always applying to the material , product ,walls or total building.

Heat flow transmission : 3 modes

A building needs energy for heating during cold seasons in order to compensate heat losses through its various parts and keep a nice temperature inside .

To get a heat flow you need a temperature difference between inside and outside . The heat flow will depend of the nature and thermal quality of the wall .

3 heat transmission modes exist :

-conduction through solid material or gaz :the more insulant the material , the less the conduction

-convection : the heat "travels" thanks to air movements ,because of temperature and density gradient. Hot air moves up and heat dissipates.The quieter the air , the less the convection

-radiation : each material absorbs or emits thermal radiations depending on its temperature and its emissivity .Heat exchange is function of propagation media (vacuum or air )
When radiation is absorbed or reflected , there is less thermal transfer.

Thermal insulation stops conduction , convection and radiative effects : -by creating a thermal barreer against conduction
-by suppressing air movements
-by limiting radiative effects

Thermal conductivity : lambda value

A thermal insulant will play the 3 functions and is characterized by its thermal conductivity named lambda value

Thermal conductivity measures the capacity of a material to lead or to resist to heat transfer

The smallest the lambda, the best the thermal insulation .

This standard measure is made in laboratories according ISO 8301 norm and is declared at 10°C temperature and expressed in W/m.K

Here are some examples of thermal conductivity for usual building materials:

Still air 0,025

It is admitted that materials are thermal insulants if their conductivity is less than 0,065 W/m.K.

Thermal resistance : R value
This value will measure the capacity of a product to fight against heat loss . It will depend on thickness and thermal conductivity .
The highest the R , the best performing the product

R combines thermal property of the material itself and thickness of the product

Thermal performance R and U of a wall depend mainly on thermal insulation

The Heat flow , going through the wall depends on temperature difference between inside and outside and thermal resistance R of the wall.
Each element constituting the wall has thermal properties : bricks or concrete, insulation, rendering .
Wall thermal resistance is the addition of thermal resistance of each components from interior coating to exterior rendering , and superficial resistances.

These latter are due to exchanges by convection and radiation on wall surfaces in contact with internal and external climate .
With higher R , the wall will resist more to heat loss.

U value is the coefficient which characterizes the ability of the wall surface to heat transfer
U value is the inverse of R value and is expressed in W/m2.K

Thermal performance of a whole building

It takes in account heat losses , energy necessary for cooling , hot domestic water , lighting and solar gains .
Regarding heat losses , the performance will depends on :
- U values of the different building parts : walls , roof , floors, doors ,windows .
- Thermal bridges : linear losses due to links between building parts

Isover provides solutions highly and reliably performing ,allowing to reduce in a efficient and permanent way thermal losses of the building envelope