Rs: Solar reflectance , As : Solar absorptance, Ts : Solar Transmittance, Te: Dirrect Solar transmittance,
Qi: Secondary heat transfer factor , G: G-factoor = total solar energy transmittance, Te,n-dif :
Diffuse solar transmittance, Te,n-n : Normal solar transmittance. Tv" Visible light transmittance.
Ts+Rs+As = 100% of solar energy.
Influence of colours
The choice of the colour has direct influence on
the criteria which justify the use of sunscreen
Protection against visiable light, expressed by the factor Tv.
Protection against sun-energy, expressed by the G value.
Protection against secondary heat, expressed by the factor Qi
Protection aginst UV Light , expressed by the factor Tuv.
Sunscreens are always used in combination with a glazing.
These together will prevent a large quantity of energy,
sent by the sun to the earth, which is indicated by the :
Total Solar Energy Transmittance , or G-factor.
The G value is the ratio between the total solar energy transmitted
into a room through a window and the incident of glazing and
solar protection device. The Gv is the solar factor of th e glazing alone.
Then shading coefficient is defined as the ratio of the solar factor of
the combined glazing and solar protection device Gtot to that of the glazing alone Gv.
The total solar energy transmitted through a window consists of two parrts:
1) Radiation : Measured by the solar transmittance : Te ,tot.
2) Heat : Measured by the secondary heat, transfer : Qi
G= Te,tot + Qi
The factor Te,tot, is quantity of energy,
which will pass the combination solar protcton device and window.
The factor Qi is the quantity of heat, which is released by the absorption
of engery in the sunscreen proction system = combinatoin sunscreen + glazing.
The G factor is the most important factor to explain the efficiency
of a combination sunscreen + glazing, as protection against the energy of the sun.
The G-factor divided into his components explains
the difference in eficiency between exterior and interior sunscreen
G= Te, tot + Qi
The direct, solar transmittance Te,tot is the same for interior
and exterior use of sunscreens, The secondary heat factor
Qi for interior sunscreen is bigger than for exterior sunscreen.
For interior use, the heat produced by the absorption of energy,
will be tansmitted to the room inside. By exterior use,
the heat will be transmitted to the outside ,
without any inconvenience at the inside.
Also the color of the sunscreen has an inflence of the G-factor.
Da가 colors will absorb a lot of sun engergy and will tranmit this to heat,
if the screen is used for exterior, heat will have no influence inside the room,
contrary to a screen used for interior.
This is why a darker screen is ideal for exterior use and a lighter screen for interior use.