Heat transfer resistance or thermal insulation
In the new system of units, the temperature in degrees Celsius is denoted by the symbol ° C, while the temperature difference – symbol K. Hence the record – W/(m² • K) The reciprocal of the heat transfer coefficient 1 / k is called the heat transfer resistance or thermal insulation:
R = 1 / k
If we know, what materials the partition is made of, then we can calculate the k-factor using the norm – on "Thermal protection of buildings".
Average heat transfer coefficient – ksr. [W/(m² • K)] non-uniform partition (boards, air, boards), in which the ratio of the greatest to the smallest thermal resistance is not greater than 5,0 we calculate according to the formula:
where:
A1, A2, An – surfaces of partition sections obtained by conventional division of this partition with planes perpendicular to its surface into uniform sections or composed of uniform layers (m ),
A – total area of the partition (m²),
k1, k2, kn – heat transfer coefficients of individual partition sections, [W/(m² • K)].
However, the heat transfer coefficient – k[W/(m² • K)] A uniform partition or partition consisting of uniform layers is calculated using the formula:
wherein:
Ri, Re – resistance to heat transfer [m² • K/W],
ΣR – sum of thermal resistance of individual layers in the partition [m² • K/W];
Examples of heat transfer coefficient – k.
and the thermal resistance of the layer in the partition:
wherein:
d – the actual thickness of the layer or partition (m).
λ – design coefficient of thermal conductivity of the material used [W /(m · K)] taken from the table 4,
Rp – thermal resistance of the closed air layer [m · K/W] taken from the table 5.
For air layers, which are in contact with the surface covered with aluminum foil, should be used on a warmer surface.
The lower the heat transfer coefficient (k) walls, ceilings, roofs and floors, the warmer the house will be and the lower the costs of heating it. Currently built walls should have a k-factor of approx 0,5. When the coefficient is 0,5, is the heat loss on a wall with an area 1 m2 within 1 the hours are 0,5 [W/m2 • K] at a temperature difference of 1 ° C (K).
