Properties of common insulating materials
Keywords: insulation, insulation, insulation, materials, property, performance, performance, lambda coefficient, calculation, losses, loss, heat balance…
All lambda are given in W / (mK)
Calculation of the thermal resistance of a wall or a wall
The thermal resistance is given by the following formula:
R = e / lambda
With e = wall thickness in m
and lambda = coefficient of heat loss of the materials used.
For walls made up of several layers of materials the thermal resistances add up, thus for a wall made up of 2 materials 1 and 2:
Total R = R1 + R1 = e1 / lambda1 + e2 / lambda2
We thus obtain R in m2.K / W which is not very significant, on the other hand its inverse: W / m2.K it is: it is the thermal transmission in Watts (in other words: the thermal losses) of the wall per degree of difference in T ° and m2 of the wall.
A thermal resistance at least equal to 2 is considered as standard insulation.
Example for an insulated wall with a resistance of 3:
- R = 3
- Outdoor temperature: 5 ° C
- Indoor temperature: 19 ° C
The losses by conduction in the wall will therefore be equal to (19-5) * 1 / 3 = 4,66 W per m2 of surface of this wall. If the wall is 40m2 the heating power to be supplied is therefore 4,66 * 50 = 233 Watts to maintain the interior temperature at 19 ° C, assuming that this is the only heat loss from this room.
This is a first simple approach to carry out the thermal balance of a house (other losses occur by convection, air renewal, thermal bridges, carpentry, etc.).