Thermal
Curtains with certain characteristics can help keep rooms cool.
Thermal
Curtains with certain characteristics can help keep rooms cool.
To understand how sotexpro fabrics can provide a thermal solution, it is important to explain certain thermal phenomena to help you choose the right fabrics.
Thermal comfort refers to the feeling of well-being experienced in an indoor environment.
In winter, good thermal comfort must guarantee a sufficient feeling of warmth.
In summer, it must limit heat to avoid overheating.
Thermal conductivity
The thermal conductivity of a material refers to its ability to let heat through or block it (transmission of thermal energy).
The higher the conductivity of the material is, the more heat it lets through; the lower its conductivity is, the more effective it is as a thermal insulator, against both hot and cold. Thermal conductivity is a characteristic specific to each material.
Copper and aluminium, for example, are materials with very high thermal conductivity. Wood, polystyrene and air are good insulators.
To assess the thermal insulation performance of a fabric and, by extension, of a curtain, we need to know its resistance to heat transfer.
This thermal resistance depends on the thickness, density and thermal conductivity of the material or materials of which it is made.
It also depends, in particular, on the ability of its structure (weave) to trap air.
Conclusion: the greater thermal resistance is, the more the fabric insulates.
Thermal radiation
Thermal radiation is the amount of energy emitted by a heat source in the form of electromagnetic radiation. Thermal radiation is how the sun transmits heat almost instantaneously.
With a curtain, it’s the sun’s rays we are interested in, which are made up of roughly half visible light, half infrared and 1% ultraviolet rays.
When it strikes the fabric, solar radiation is partly transmitted, absorbed or reflected by said fabric. These phenomena can be measured using 3 coefficients:
These phenomena cause the temperature in a room to vary when the curtain is drawn.
To assess the thermal performance of a curtain against the sun’s rays, it is important to use two coefficients that take into account all the characteristics of the installation:
• Total solar factor, Gtot or Gt:
This indicator measures the amount of sunlight energy that enters a room through glazing and the solar protection material, in our case the curtain.
> A low percentage indicates good thermal performance against solar radiation.
Gtot calculation takes into account:
- The position of the solar protection material (inside, outside or between panes).
- The performance of the solar protection material in terms of transmission, reflection and absorption in the range of solar wavelength (300 – 2,500 nanometres) and visible light zone (380 – 780 nanometres).
- The thermal properties of a specific glazing (e.g. the standard glazings identified in ISO 52022-2 or DIN EN 14500/DIN EN 14501):
∙ A: Single glazing > Ug = 5.8 W/(m²K) – g=0.85
∙ B: Air-filled double glazing > Ug = 2.9 W/(m²K) – g=0.76
∙ C: Argon-filled double glazing with low-emissivity coating > Ug = 1.2 W/(m²K)- g=0.59
∙ D: Solar control, argon-filled double glazing with low-emissivity coating > Ug = 1.1 W/(m²K) – g=0.32
∙ E: Argon-filled triple glazing with low-emissivity coating > Ug = 0.8 W/(m²K) – g=0.55
Default glazing recommended in standard EN 14501 is C:
∙ Argon-filled double glazing with low-emissivity coating > Ug = 1.2 W/(m²K)- g=0.59A.
• Shade change factor/shade masking factor for solar protection materials: Fc (Fc=gtot/g), where g is the degree of energy permeability of the glazing) :
This indicator measures the improvement in reducing energy penetration into a room through the additional use of a solar protection material, in our case a curtain.
> A low percentage indicates good performance in reducing energy penetration into a room
Curtain parameters that influence thermal performance against solar radiation:
- The role of colour:
Dark colours reflect little or none of the sun’s rays, but absorb them, while light colours reflect them.
This is why, for the same fabric, the coefficients linked to thermal radiation will differ depending on the colour chosen (which faces the window and therefore the sun).
This parameter must be taken into account when choosing the curtain and the desired performance. That is why we tested our properties solely on light and medium colours.
- The role of aluminised surfaces:
Aluminium is highly effective against the diffusion of electromagnetic waves and therefore solar radiation.
We often use this process in curtains to guarantee protection against heat radiation regardless of the colour.
Laboratory thermal performance results on request
You can find all these values in our thermal performance data sheets, published for each reference and available on request. These are based on the results of tests conducted by an accredited laboratory. Request a test.
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